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Occurrence, distribution and seasonal variation of five neonicotinoid insecticides in surface water and sediment of the Pearl Rivers, South China
Accepted Manuscript Occurrence, distribution and seasonal variation of five neonicotinoids insecticides in surface water and sediment of the Pearl Rivers, South China Chao Zhang, Di Tian, XiaoHui Yi, Tao Zhang, Jujun Ruan, Renren Wu, Chen Chen, Mingzhi Huang, GuangGuo Ying PII:
S0045-6535(18)32121-0
DOI:
https://doi.org/10.1016/j.chemosphere.2018.11.024
Reference:
CHEM 22508
To appear in:
ECSN
Received Date: 30 August 2018 Revised Date:
28 October 2018
Accepted Date: 2 November 2018
Please cite this article as: Zhang, C., Tian, D., Yi, X., Zhang, T., Ruan, J., Wu, R., Chen, C., Huang, M., Ying, G., Occurrence, distribution and seasonal variation of five neonicotinoids insecticides in surface water and sediment of the Pearl Rivers, South China, Chemosphere (2018), doi: https://doi.org/10.1016/ j.chemosphere.2018.11.024. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Graphical Abstract
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Occurrence, distribution and seasonal variation of five neonicotinoids insecticides in
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surface water and sediment of the Pearl Rivers, South China
3 Chao Zhang1,2#, Di Tian2, XiaoHui Yi1#, Tao Zhang3#, Jujun Ruan3#, Renren Wu4, Chen
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Chen4, Mingzhi Huang1,2*,GuangGuo Ying1
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Ministry of Education, South China Normal University, Guangzhou 510631, PR China
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Environmental Research Institute, Key Laboratory of Theoretical Chemistry of Environment
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School of Geography and Planning, Guangdong Provincial Key Laboratory of Urbanization
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and Geo-simulation, Sun Yat-sen University, Guangzhou 510275, PR China
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510275, China
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Guangzhou 51065, China
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*Corresponding author
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Mingzhi Huang, E-mail: [email protected] and [email protected];
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South China Institute of Environmental Science, Ministry of Environmental Protection,
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School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou
# These authors contributed equally to this work
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Abstract
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Occurrence and distribution of five neonicotinoids (NEOs) in surface water and sediment
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were studied in the Pearl Rivers, including three trunk streams, Dongjiang, Beijiang, Xijiang
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River (DR, BR and XR), South China. At least one neonicotinoid was detected in surface
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water and sediment of the Pearl Rivers, with imidacloprid (IMI) and thiamethoxam (THM)
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being the frequently detected NEOs. Total amount of NEOs (∑5neonics) in surface water and
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sediment ranged from 24.0 to 322 ng/L, and from 0.11 to 11.6 ng/g dw, respectively.
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Moreover, the order of contamination level of NEOs in the Pearl Rivers was as follows: XR >
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DR > BR for surface water, and BR > DR > XR for sediment. Local agricultural activities and
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effluents of local wastewater treatment plants (WWTPs) could be major sources of NEOs in
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the Pearl Rivers. Solubilization and dilution of NEOs between surface water and sediment
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during different seasons (spring and summer) could be attributed to rainfall intensities or
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climate of the Pearl River Delta. An ecological risk assessment of the exposure to current
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environmental concentration of imidacloprid and ∑5NEOs suggests a threat to sensitive
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non-target invertebrates, including aquatic invertebrates. Results would provide a better
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understanding of NEOs contamination in the Pearl Rivers, as well as being a reliable dataset
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for decision-making in contamination control and environmental protection.
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Keywords:
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neonicotinoid; imidacloprid; thiamethoxam; aquatic invertebrates; the Pearl River Delta
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1. Introduction Neonicotinoids (NEOs) have become the most widely used class of insecticides in the
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world since they were first developed in the late 1980s and early 1990s as imidacloprid (IMI)
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(Douglas and Tooker, 2015; Sparks and Nauen, 2015; Terayama et al., 2016). Application of
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NEOs is carried out by means of seed treatment, foliar sprays, soil drenches, granules, and
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injection (Stewart et al., 2014; Bonmatin et al., 2015; Simon-Delso et al., 2015). As one of the
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largest agricultural countries, kinds of neonicotinoids have been widely used for pest control
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to meet food needs for about 1.4 billion population, and China plays an essential role in the
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production, application and research of NEOs (Shao et al., 2013).
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However, heavy use of NEOs were reported to lead to a variety of potentially adverse
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effects on ecosystem and human health (Zeng et al., 2013; Sanchez-Bayo, 2014; Gibbons et
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al., 2015; Christen et al., 2016), such as decline in population of pollinators (e.g., honeybees)
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and harmful to non-target organisms, which have drawn extensive attention (Anderson et al.,
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2015; Bonmatin et al., 2015; Morrissey et al., 2015). Previously reports shows that NEOs can
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cause toxic effects to insects and vertebrates (Hallmann et al., 2014; Nicodemo et al., 2014;
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Cimino et al., 2017; Bishop et al., 2018). Signs of oxidative stress and DNA damage have
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been observed in freshwater fish, such as loach and zebrafish, exposed to IMI and
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thiamethoxam (THM) (Ge et al., 2015; Xia et al., 2016; Yan et al., 2016). What’s more,
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extensive exposure to NEOs may lead to hazardous effect on human health (Anderson et al.,
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2015). Therefore, to approach crises and challenges, various countries have issued a series of
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policies and acts for restrictions on NEOs use (Canada, 2013; Columbia, 2013; EU, 2013).
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ACCEPTED MANUSCRIPT Lots of data about residue NEOs in water and soil of the US, Canada, Europe have
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been reported. Hladik and Kolpin (2016) collected water samples from 48 streams across
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the United States and found that NEOs were detected in 63% of streams with 37% and 21%
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detection frequencies for imidacloprid (IMI) and thiamethoxam (THM), respectively. 93%
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of river water near Sydney in Australia were observed to contain two or more kinds of
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NEOs, and the maximum concentration for IMI and Thiacloprid (THA) were detected at
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4.56 and 1.37 µg/L, respectively (Sanchez-Bayo and Hyne, 2014a). Several studies report
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that clothianidin (CLO), IMI, and THM are usually the predominant NEOs detected
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(Hladik et al., 2014; Hladik and Kolpin, 2016). Kinds of NEOs have been detected at above
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35 ng/L in around 75% surface water of southern Ontario, Canada, which could be conduct
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a potential effect on aquatic invertebrate (Struger et al., 2017). Dinotefuran was the most
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frequent and highest in surface water in Osaka of Japan (Yamamoto et al., 2012). However,
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until now, there are few reports on occurrence and distribution of NEOs in surface water for
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China, and studies on NEOs residue in sediments are also limited, which could have
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potential negative effects through transportation into water and others.
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The Pearl River is the third longest river of China with a total drainage area of 0.45 ×
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106 km2 (mostly within the Guangdong Province), including the Dongjiang Xijiang,
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Beijiang Rivers and other river networks. With the rapid economic development and
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continued population growth in the Pearl River Delta, the Pearl River has suffered from
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serious environmental pollution in recent years. Since the Pearl Rivers, flowing through
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metropolitan Guangzhou, Dongguan, Shenzhen, Hong Kong and more surrounding towns, 4 / 33
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activities (forestation and cultivation of rice and kinds of vegetables and fruits, accounting
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for about 60~70% and 15~20% of total areas, respectively), so, monitoring contaminants of
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NEOs in surface water is of immense importance.
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Therefore, the main objectives of present work were: (1) to investigate occurrence and
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residue level of five NEOs (IMI, THM, CLO, ACE and THA) in surface water and sediments
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of the Pearl Rivers; (2) to explore possible sources and spatial and seasonal variation of NEOs;
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(3) to evaluate the potential environmental risks of NEOs to organisms of the Pearl Rivers.
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Results would provide a better understanding of NEOs contamination of the Pearl Rivers, as
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well as being a reliable dataset for decision-making in pollution control and conservation.
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2. Materials and Methods
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2.1. Chemicals and Reagents
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Standards for five representative NEOs, imidacloprid (IMI), thiamethoxam (THM),
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clothianidin (CLO), acetamiprid (ACE) and thiacloprid (THA) (in order of market shares),
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were purchased from the Dr. Ehrenstorfer GmbH (Augsburg, Germany). The corresponding
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isotope labeling products, IMI (IMI-d4), THM-d3, CLO (CLO-d3), ACE (ACE-d3) and
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THA-(thiazolidin ring-d4), were obtained from the Sigma-Aldrich Chemical (St Louis, MO,
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USA) and used as the internal standards (information was summarized in Table S1-S2, SI).
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Stock solutions of five individual compounds and internal standards were prepared with
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acetonitrile at a concentration of 1,000 mg/L. Acetonitrile, dichloromethane and methanol
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(UHPLC Grade) were obtained from the ANPEL Laboratory Technologies (Shanghai) Inc.
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ACCEPTED MANUSCRIPT Poly-Sery hydrophilic–lipophilic balanced (HLB) solid-phase extraction (SPE) cartridges
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(500 mg, 6 mL) were used for sample extraction and concentration. Milli-Q water (Millipore,
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Bedford, MA, USA) was utilized throughout this work.
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2.2. Study areas and sample collection
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Surface water and sediment were collected from 49 sites of the Pearl Rivers (including
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the Dongjiang (DR), Xijiang (XR), and Beijiang (BR) Rivers) and outlets of three WWTPs
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(Fig. 1). Distribution of 49 sampling sites are as follows: 9 sites (D1-D9) from the DR, 24
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sites (B1-B24) from the BR, 13 sites (X1-X13) from the XR, and 3 sites (W1-W3) from the
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WWTPs. More information about sampling sites and treatment process of three WWTPs is
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given in the SI file (Text S1-S2, SI). Sample collection was carried out during two periods:
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March and April in spring , and August and September in summer season of South China.
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Water samples were collected from a depth of 50 cm below the surface using portable water
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samplers and stored in polypropylene (PP) bottles (pre-treated with methanol and Milli-Q
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water thrice). Physical indexes (pH; ORP; turbidity; temperature and dissolved oxygen (DO))
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of water were accurately measured before storage. Stainless steel grab samplers were utilized
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for sediment collection at 10 cm upper, and polypropylene (PP) bags were used for storage.
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After collection, water and sediment samples were transferred to the laboratory as soon as
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possible and stored in 4 °C and -20 °C before analysis, respectively.
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--Fig. 1-2.3. Sample extraction and LC-MS/MS analysis Briefly, 500 mL filtered (0.45 µm) water within injection of internal standards mixture 6 / 33
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Loading rate of water samples was maintained at 3 mL/min. Subsequently, the target fraction
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was eluted with 5 mL of Milli-Q water and methanol respectively. Extracted solutions were
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concentrated under a gentle nitrogen gas flow, and then re-dissolved in 0.5 mL acetonitrile.
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5.0 g freeze-dried sediment was extracted using the dispersive liquid–liquid microextraction.
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Specifically, 20 mL mixtures of acetonitrile and dichloromethane (v/v, 2/1) were used. Extract
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was re-dissolved in 1.0 mL acetone and transferred into 10 mL Milli-Q water using a
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centrifuge tube. A 0.8 g NaCl and 2 mL dichloromethane were added into the same tube,
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followed by vortex agitation for 1 min, ultrasonic extraction for 10 min, and separation by
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centrifuging at 4000 rpm for 5 min. The lower layer of the liquid was transferred with a
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microinjector after stratification and concentrated under nitrogen, and then dissolved in 0.5
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mL acetonitrile. A 0.2 µm nylon filter was used for the purification of extract and filtrate was
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then transferred into a 2 mL autosampler vial prior to analysis (a flowchart of water and
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sediment samples extraction and pretreatment was shown in Fig. S1, SI).
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Referring to methods reported by Sanchez-Bayo and Hyne (2014b) and Watanabe et al.
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(2015), extracts of surface water and sediment were subsequently quantified using a triple
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quadruple LC-MS/MS (TSQ Quantum Ultra. Thermo Scientific, USA) equipped with an
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electrospray ionization (MRM) positive mode. Three microliters aliquot of the final extract
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were injected into a Thermo Hypersil GOLD C18 column (2.1 mm × 100 mm, 1.9 µm.
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Thermo, USA) maintained at 40
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formic acid-water solution) and 10% B (acetonitrile), followed by a linear gradient from 90 to
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. A gradient elution program was started with 90% A (0.1%
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6.0 min for an addition 1.5 min, in final reverted to 90% A at 7.5 min before analysis end at
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10 min. Mobile was kept at a flow rate of 300 µL/min. MRM transitions, collision energy and
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retention time of the five target NEOs analyzed are shown in Table S3, SI.
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Analyte quantitation was performed using external standard method, and IMI-d4,
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ACE-d3, CLO-d3, THM-d3, and THA-(thiazolidin ring-d4) were used as internal references
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for qualitative analysis. A total of 15-point calibrations were prepared in acetonitrile with a
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range from 1–1000 ng/L for each NEO. Linear 1/Y weighted regressions, not forced through
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the origin, were based on external standard calibration and have a correlation coefficient
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greater than 0.99 (shown in Table S4, SI).
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2.4. Quality assurance and quality control
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The limit of detection (LOD) and the limit of quantification (LOQ) were defined as 3
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and 10 times the noise level of the chromatogram in blank, respectively, and in this work, the
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LOQ of five NEOs ranged between 0.01 ng/L and 0.05 ng/L for water sample and between
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0.001 ng/g and 0.005 ng/g for sediments. For the calculation of ∑5NEOs, the concentrations
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below LOQ and the non-found detection results were all assigned as zero. However,
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concentrations below the LOQ were treated as half the LOQ for individual analysis. The
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recoveries ranged from 83% to 106% for water and from 81% to 112% for sediments.
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Duplicates were also analyzed, and the coefficient of variation was less than 12% (Table S4).
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3. Results and Discussion
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3.1. Occurrence and concentration detected of NEOs in surface water The detection frequency (DF), range (min-max), average and median concentration of
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IMI, THM, CLO, ACE, THA, and total amount of Σ5NEOs in surface water from the DR,
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XR, BR, and effluents of three WWTPs are summarized in Table 1. THM, CLO and ACE
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were detected from all 49 sampling sites of the Pearl Rivers and three WWTPs effluents.
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Total amount of ∑5NEOs ranged from 24.0 (site D3) to 322 ng/L (site X8), with an average
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of 91.05 ng/L from the Pearl Rivers. Taking three WWTPs effluents into consideration, the
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order of NEOs detected from surface water (based on the average concentration of ∑5NEOs)
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was: the WWTP effluents (179 ± 86.0 ng/L) > XR (102 ± 54.9 ng/L) > DR (98.7 ± 68.5
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ng/L) > BR (96.5 ± 60.7 ng/L). Concentration of ∑5NEOs detected from the WWTPs
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effluents was about 1.75~1.8 folds than the Pearl rivers, indicating that local WWTPs
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effluents could be a source of the NEOs contamination in the receiving waters (rivers).
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THM was the dominant NEO detected in the Pearl Rivers, accounting for about 11~53% of
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the amount of ∑5NEOs at different sites. Contributions of individual NEO for the ∑5NEOs
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tend to follow the descending order as: THM (34.9%) > IMI (29.2%) > ACE (19.3%) >
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CLO (16.4%) > THA (0.2%), and was consistent with order of hydrophilicity of NEOs
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(Raina-Fulton, 2016), hinting a significant relevance between the physicochemical
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characteristics of NEOs (hydrophilicity in especial) and environmental residue effect.
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Almost five NEOs were detected from the DR with 100% frequencies except for THA,
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and total amount of Σ5NEOs in surface water of the DR ranged from 24.0 to 243 ng/L. 9 / 33
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22.3, 24.9 ± 24.0 and 24.7.4 ± 18.1 ng/L, respectively. Moreover, THA was detected at 39%
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with a range from ND to 3.73 ng/L, the lowest detection frequency and concentration. A
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similar amount of Σ5NEOs was also found from the BR ranging from 28.0 to 285 ng/L,
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with IMI and THM as the dominant NEOs accounting a detection frequency of 100% and
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concentration of 33.9 ± 26.4 and 29.4 ± 22.4 ng/L in the BR, respectively. THM, CLO,
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ACE and THA were detected in most of sites of the XR, and the total amount of Σ5NEOs
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was ranged from 53.1 to 322 ng/L. THM was detected with the highest average
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concentration of 35.2 ± 15.2 ng/L in the XR, a little higher than IMI (32.5 ± 33.4 ng/L).
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only at the site X12, no IMI was detected (DF: 96%, 22/23), which might be correlated
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with junction of the WWTP effluent flow near site X12 due to dilution effect. THM and
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CLO were two dominant NEOs with a concentration of 79.5 ± 35.7 and 49.7 ± 26.2 ng/L
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from the WWTP effluents, respectively, which were much different with previous research
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(Sadaria et al., 2016) as IMI and CLO dominated in the WWTP effluents with a
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concentration of 58.5 ± 29.1 and 70.2 ± 121.8 ng/L (THM was not detected).
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Differences between occurrence and concentration of NEOs detected within the current
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work and those reported globally was investigated and shown in Table 3. occurrence and
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distribution of NEOs with surface water detected in the Pearl Rivers were different from those
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observed in other countries. The most detectable NEOs in the Pearl Rivers were IMI, THM,
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and ACE, whereas in North America are THM, IMI, and CLO. Concentration of IMI in the
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Pearl Rivers were much higher than those presented in the rivers of Osaka (Japan) 10 / 33
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Sydenham River of Canada and the streams across the United States, but lower than those
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determined from rivers around Sydney, and Dutch surface water. Concentration of THM in
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the Pearl Rivers was higher than those in rivers of Osaka City, and much lower than those in
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streams across the United States, Sydenham River (Struger et al., 2017) and rivers around
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Sydney. ACE levels, in the present study, were higher than most reported water bodies around
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the world. Levels of CLO in the Pearl Rivers were like those in streams across the United
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States (Hladik and Kolpin, 2016), which were higher than those in rivers of Osaka, Japan, and
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lower than those determined in Sydenham River and rivers around Sydney (Sanchez-Bayo
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and Hyne, 2014a). THA in the Pearl Rivers was similar to those water bodies reported around
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the world but approximately two orders of magnitude lower than that in rivers around Sydney.
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Overall, the Pearl Rivers could be confronted with a moderate level of NEOs contamination.
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--Table 1--
3.2. Occurrence and concentration detected of NEOs in the sediment
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Statistical data of ACE, THM, CLO, IMI, THA and Σ5NEOs in sediment from the DR,
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BR, XR and the effluents of three WWTPs are showed in Table 2. Total amount of the
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Σ5NEO in sediment ranged from 0.11 to 11.6 ng/g dw, with an average of 2.16 ng/g dw for 85
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sampling sites of the Pearl Rivers. The order of detection concentration of NEOs in sediment
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(based on mean value) was: the BR (4.08 ± 9.01 ng/g dw) > DR (2.83 ± 2.82 ng/g dw) > XR
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(1.30 ± 1.55 ng/g dw) > WWTP effluents (0.49 ± 0.36 ng/g dw). IMI was detected with the
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highest frequency and concentration among the NEOs in sediment of the Pearl Rivers.
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level and detection frequency of IMI. In the WWTP effluents, IMI showed a remarkably low
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concentration (0.04 ± 0.11 ng/g) and the detection frequency (17%). Detection frequencies of
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ACE were 89% in the DR, 91% in the BR, 96% in the XR, and 100% in WWTP effluents,
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with a mean of 0.53 ng/g dw in the Pearl Rivers and 0.06 ng/g dw in effluents of WWTPs.
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Concentration of THM with high hydrophilicity, was detected in a low level in sediment of
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the Pearl Rivers, with a mean of 0.26 ng/g dw. THA in sediment maintained quite low levels
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ranging from ND to 1.31 ng/g. Based on mean concentration in sediments from tributaries in
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the Pearls Rivers, contributions from various NEOs followed the order: IMI (73.3%) > ACE
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(14.8%) > CLO (6.1%) > THM (5.1%) > THA (0.7%).
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IMI was detected in all sediments of the DR. ACE and IMI, with concentrations of 1.21
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± 1.66 and 1.16 ± 1.05 ng/g dw, respectively, were relatively abundant compared to others.
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Five NEOs were also detected in most of sites in the BR, and the concentration of the
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Σ5NEOs in sediment of the BR ranged from 0.11 to 11.6 ng/g dw. Moreover, IMI was the
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most frequently detected NEO (100%) with the highest mean concentration (1.33 ± 1.71 ng/g
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dw) in the BR, followed by ACE. IMI was also detected with concentration of up to 0.62 ±
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0.71 ng/g dw and as the dominant NEO in the XR. A comparison of residual NEOs in river
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sediment between the Pearl Rivers and other countries was shown in Table 3 based on limited
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data reported. Residual NEOs in river sediment from the Pearl Rivers was lower than soil
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from wetland near agricultural lands in Canada (Main et al., 2014) and higher than others
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reported (Felsot and Ruppert, 2002).
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--Table 2--, --Table 3-3.3. Spatial distribution of NEOs in the Pearl Rivers Spatial distribution of five NEOs detected in the Pearl Rivers was shown in Fig. 2. An
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regional difference of NEOs distribution in surface water and sediments was observed.
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Concentrations of NEOs were increased from upstream to downstream of the DR, flowing
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through the cities of Heyuan, Huizhou, and Dongguan. Level of NEOs contamination at
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upstream of the DR remain relatively low, whereas site D3 remains high, which might be
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due to intensive agricultural and gardening activities, the main industries of the Heyuan,
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hinting the source of NEOs contamination at the upstream of the DR could be wastewater
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discharge from livestock waste and agricultural runoff. Moreover, the Xinfengjiang
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Reservoir (one of the major drinking water supply resources for the Guangdong province
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and Hong Kong) is located at the upstream of the DR, and an small decline of NEOs in site
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D4 and D5 could be related to dilution effect of the Xizhijiang River. Dongguan, located in
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the middle and lower reaches of the DR, is a typical industrial and immigrant city with
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more than 8 million residents by the end of year 2016. The statistics (the year 2016) also
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showed that the total amount of wastewater discharge (including industrial and domestic)
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from the Dongguan reached about 1,289 million tons, which might be accounting for NEOs
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contamination in the sites D6–D9. Furthermore, Dongguan has relatively large artificial
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greening areas and developed farming and stock breeding system. Since the ACE has been
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extensively applied to pest control of horticultural plants of the urban landscaping as a class
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of NEOs, residual levels of the ACE and Σ5NEOs along the river flow in the Dongguan part
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of the DR hold an obvious tendency of increase. In the BR, the level of NEOs from downstream and upstream of the BR was generally
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higher than that from midstream. The highest amount of Σ5NEOs was found in site B22
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with a concentration of 241 ng/L. Sites B1–B3 were located in Shaoguan city, where the
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cultivated land (average) ranked first in the Guangdong province. Moreover, the
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agricultural farming, livestock and poultry were main industries in the cities of Heyuan and
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Qingyuan, where B4–B9 are located. Therefore, the source of NEOs at upstream of the BR
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could be from the agricultural runoff. Additionally, the frequent flooding at site B6 which
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mostly lead to inundation of neighboring villages and farmlands should be noted.
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Consequent flow erosion and soil transfer could be related to the unexpected significant
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NEOs contamination at site B6, and large numbers of livestock and poultry breeding waste
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(forage) at B6 was also a probable source of high residual level of NEOs. Owing to the
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dilution of water from three tributaries of the Pajiang, Lianjiang, and Binjiang Rivers,
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levels of NEOs from B7 to B9 were relatively stable. NEOs detected from sites B10–B17
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(near Foshan city, an agricultural and industrial region) might be mainly from discharge of
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industrial and domestic wastewater and agricultural runoff. In addition, B14 was located
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downstream of the confluence of the BR and XR and significantly influenced by the high
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NEO levels during spring season in the Suijiang River. Moreover, B21 and B22 are
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adjacent to the Liuxi River, where vegetable plantations are widely distributed.
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Levels of NEOs at upstream of the XR (X1–X4) were generally higher than that
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downstream except for X6, X7, and X12. The highest concentration of Σ5NEOs was found 14 / 33
ACCEPTED MANUSCRIPT in site X4 with a value of 107 ng/L. Sites X1–X3 were in Zhaoqing, with the agricultural
291
farming and livestock and poultry as major industries. Site X4 is at the downstream of the
292
confluence of the BR and XR and significantly influenced with NEOs contamination from
293
the Gaoming River. The low concentration of these NEOs in the estuary is probably due to
294
sea water dilution. Sites X6, X7, and X12 are at the downstream of the outlets of three
295
WWTPs. Concentration of the Σ5NEOs in X6, X7, X12, and effluents of W1–W3 was
296
found to be higher than those in the XR, DR, and BR. Surface water from effluents of
297
W1–W3 with excessive THM and CLO mostly be due to the discharges from domestic
298
wastewater and pest control and cultivation of horticultural plants.
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Fluctuation of NEOs in the surface water of the Pearl Rivers tends to be relatively
300
smoother than that in sediment along the flow direction of rivers. As far NEOs, a class of
301
strong hydrophilic contaminants, occurrence and high residual concentration were mainly
302
observed in surface water than sediments, which could be accounted for physicochemical
303
characteristics of NEOs. Additionally, NEOs detected from samples of sites where farming
304
lands were frequently submerged with flood (site B6), and an exchange of NEOs from soil
305
to water could be a source. Furthermore, biodegradation of the NEOs is difficult through
306
treatment flows of traditional WWTPs (Sadaria et al., 2016). What’s more, timing of the
307
NEOs application to crops (rice) in different regions was varied, which may also contribute
308
to variations of NEOs in different tributaries and regions. Therefore, seasonal variation of
309
NEOs in the Pearl Rivers is discussed.
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3.4. Seasonal variation of five NEOs in the Pearl Rivers Seasonal variations of the five NEOs in the Pearl Rivers are showed in Fig. 3.
313
Concentrations of NEOs in surface water during the summer were higher than those in spring,
314
whereas for sediment, an opposite trend was observed. The Pearl River Delta mostly belongs
315
to the subtropical monsoon climate zones, and rainfall displays an uneven characteristic and
316
mainly occurs in summer (Text S3, SI). During the summer, NEOs could be tended to
317
dissolve form and transfer from soil and sediment to water via erosion of frequent rainfall.
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Detection level of the THM in surface water during the summer is, evidently,
319
significantly increased compared to other NEOs. Correspondingly, nearly no THM was
320
detected from sediment during summer, indicating that the solubilization effect on the
321
residue level in surface water is stronger than dilution for the highly hydrophilic NEOs.
322
As for IMI, the first NEO developed, due to its extensive application and usage, it was
323
widespread distributed in all surface water and sediments. Despite the high residue level of
324
IMI from samples in spring, a significant increase was also observed in the majority of
325
surface water samples during summer. Predictably, a dramatic decline was detected in IMI
326
concentration in sediment during summer. What’s more, residual level of ACE and CLO
327
was also remained high in surface water, and took a corresponding decrease in sediments.
328
Results indicated that solubilization and dilution might be played equivalent roles in the
329
ACE and CLO washing through rainfall runoff in summer. With the increasing in rainfall
330
activities (capacities and intensities) during the rainy season, nearly all THA in the
331
sediments were re-dissolved in surface water and diluted to an low concentration.
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ACCEPTED MANUSCRIPT Periods of NEOs application varied with the growing season of crops in various
333
farming lands due to definite characteristics of crops in different tributaries of the Pearl
334
Rivers. For example, level of NEOs at site B12 (located in Suijiang River) was abundant in
335
spring but relatively poor in summer, reflecting a rather high application for main crops in
336
spring. For site X4, residue level of NEOs in spring was higher than that in summer; which
337
might relate to considerable application of NEOs for main crops in Gaoming River during
338
spring. Similarly, a high residue level of the ACE in Dongguan (D6–D9) is perhaps due to
339
the long-term pest management and cultivation of horticultural plants.
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--Fig. 3--
3.5. Ecological risk assessment of the current discharged NEOs of the Pearl Rivers Considering the large flow volume and circulation of rivers and high detection
343
concentration of individual(s) NEOs in water and sediment of the Pearl Rivers, the entire
344
Pearl River Delta could be confronted with a significant contamination of NEOs since low
345
concentrations of the NEOs were also known to affect wide range of free-living organisms
346
(Wood and Goulson, 2017). Morrissey et al. (2015) suggested that ecological guideline for
347
surface water ∑nNEOs concentrations need to be controlled under 200 ng/L (short-term acute)
348
or 35 ng/L (long-term chronic) to avoid negative effects on sensitive aquatic invertebrates. As
349
for three tributaries of the Pearl Rivers, 87.5% (21/24) of sampling sites in the BR, 69% (9/13)
350
in the XR, and 66.7% (6/9) in the DR are exceeded the long-term guideline (35 ng/L) in
351
spring, and 100% (39/39) was ahead of this limit in summer based on Σ5NEOs concentration.
352
Similarly, 100% (6/6) of the WWTP effluents were several times higher than that of the
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ACCEPTED MANUSCRIPT guideline (Fig. 4). Additionally, a part of surface water exceeded the short-term guideline
354
(200 ng/L). Results indicated that serious risks on aquatic organisms’ biodiversity should be
355
suffered in water environments of the Pearl Rivers with NEOs contamination. A lower
356
concentration of 20 ng/L (long-term chronic) for IMI was also proposed (Van Dijk et al.,
357
2013). frequencies of IMI Detection above the limit were 78.3% (3/46) and 97.4% (38/39)
358
from the Pearl Rivers in spring and summer, respectively, additionally, 83.3% (5/6) from
359
WWTP effluents. The maximum concentration of IMI were 55.7, 180, and 89.1 ng/L for
360
water from the Pearl Rivers in spring, summer season and the WWTP effluents, respectively,
361
which are 4.3, 13.8, and 6.9 times over the guideline.
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However, little information about acute or chronic toxicity of sediment residue NEOs on
363
invertebrate species was known. Due to the high environmental risk of NEOs in water
364
environment and frequent movement of NEOs between water and sediment through
365
precipitation and runoff scouring in summer, it can be inferred that NEOs in sediment can
366
have considerable negative influences on sensitive invertebrate species (Sánchez-Bayo et al.,
367
2016). Moreover, residual NEOs in sediment of the Pearl Rivers could be shown adverse
368
effects with a concentration range from 0.11 to 11.6 ng/g dw and a mean of 2.16 ng/g dw
369
(Zhang et al., 2015; Zhang et al., 2018). Further studies are needed to clarify accurately
370
determine environmental risk of neonicotinoids over broad scales.
371 372 373
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--Fig. 4--
4. Conclusion Occurrence, distribution and seasonal variation of five neonicotinoids insecticides in 18 / 33
ACCEPTED MANUSCRIPT surface water and sediment were investigated in the Dongjiang, Beijiang and Xijiang River,
375
three trunk streams of the Pearl Rivers. At least one selected neonicotinoid was detected in
376
surface water and sediment of the Pearls Rivers. Total concentration of five NEOs
377
(∑5NEOs) ranged from 24.0 to 322 ng/L, with a mean of 91.05 ng/L in the Pearl Rivers,
378
and the total concentration of the Σ5NEO in sediments ranged from 0.11 to 11.6 ng/g dw,
379
with a mean of 2.16 ng/g dw for 85 sampling sites of the Pearl Rivers. Based on the
380
detection concentration of NEOs, the order of contamination level of NEOs is as follows:
381
the WWTP effluents > BR > DR > XR for surface water and DR > BR > XR > the WWTP
382
effluents for sediment. Spatial distribution of NEOs exhibited that the main sources of
383
pollution into the river could be local human and agricultural activities, livestock and
384
poultry farming and WWTPs effluents. Solubilization and dilution of NEOs between the
385
surface water and sediment during different seasons could be attributed to rainfall
386
intensities or climate of the Pearl River Delta. Finally, risk assessment revealed that current
387
residual NEOs in the Pearl Rivers may pose a threat to sensitive non-target invertebrates.
388
Acknowledgements
389
This research was supported by National Natural Science Foundation of China (No.
390
21677184), Natural Science Foundation of Guangdong Province (No. 2016A030306033),
391
Guangdong
392
2014A020216007), Technological Innovation Young Talents of Guangdong Special Support
393
Plan (No. 2014TQ01Z530), and Pearl River Nova Program of Guangzhou (No.
394
201506010058).
395
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Provincial
Science
and
Technology
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Plan
Project
Foundation
(No.
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Tables
100% 7.71 to 102 29.4 21.5
96% ND to 41.2 32.5 20.6
100% 13.1 to 69.2 35.2 31.9 100% 35.6 to 145 79.5 76.0
83% ND to 89.1 36.5 32.2
∑5NEOs
100% 3.13 to 60.4 24.7 16.8
39% ND to 3.73 0.67 0.03
100% 24.0 to 243 98.7 74.6
100% 3.38 to 67.6 18.4 12.4
75% ND to 9.35 0.90 0.53
100% 28.0 to 285 96.5 78.2
100% 9.38 to 48.3 23.3 15.4
100% 3.65 to 36.7 9.42 6.42
91% ND to 2.38 0.40 0.04
100% 53.1 to 322 102 78.1
100% 34.7 to 103 49.7 40.0
100% 3.65 to 67.6 12.3 7.07
67% ND to 1.35 0.59 0.56
100% 108 to 350 179 153
SC
100% 4.02 to 162 33.9 26.4
100% 0.55 to 45.7 18.1 16.3
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100% 6.21 to 77.0 30.4 23.3
100% 0.74 to 67.2 13.9 9.46
TE D
100% 0.84 to 70.9 24.9 14.9
EP
DR (Dongjiang River) (n=18) DF Range (min-max) Average (ng/L) Median (ng/L) BR (Beijiang River) (n=44) DF Range (min-max) Average (ng/L) Median (ng/L) XR (Xijiang River) (n=23) DF Range (min-max) Average (ng/L) Median (ng/L) Effluent of WWTPs (n=6) DF Range (min-max) Average (ng/L) Median (ng/L)
RI PT
Table 1. Concentrations (ng/L) of five NEOs detected from surface water in the Pearl Rivers and three WWTPs IMI THM CLO ACE THA
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Table 2. Concentrations (ng/g dw) of five NEOs detected from sediment in the Pearl Rivers and three WWTPs ∑5NEOs
89% ND to 5.33 1.21 0.39
44% ND to 1.06 0.11 0.01
100% 0.17 to 8.77 2.83 1.19
72% ND to 1.91 0.31 0.17
91% ND to 2.13 0.29 0.08
50% ND to 1.31 0.08 0.01
100% 0.11 to 11.6 4.08 1.00
96% ND to 0.42 0.08 0.08
83% ND to 0.57 0.17 0.19
96% ND to 0.77 0.14 0.13
43% ND to 0.06 0.01 0.01
100% 0.11 to 6.74 1.30 1.01
83% ND to 0.36 0.18 0.19
100% 0.07 to 0.41 0.19 0.16
100% 0.02 to 0.11 0.06 0.05
50% ND to 0.05 0.01 0.01
100% 0.12 to 1.08 0.49 0.42
100% 0.10 to 3.11 1.16 0.69
89% ND to 0.54 0.14 0.10
61% ND to 0.97 0.21 0.01
100% 0.02 to 7.16 1.33 0.54
72% ND to 2.13 0.19 0.05
91% ND to 3.20 0.62 0.47 17% ND to 0.26 0.04 ND
ACE
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DR (Dongjiang River) (n=18) DF Range (min-max) Average (ng/g dw) Median (ng/g dw) BR (Beijiang River) (n=44) DF Range (min-max) Average (ng/g dw) Median (ng/g dw) XR (Xijiang River) (n=23) DF Range (min-max) Average (ng/g dw) Median (ng/g dw) Effluent of WWTPs (n=6) DF Range (min-max) Average (ng/g dw) Median (ng/g dw)
THA
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THM
CLO
31.0 (ND to 180) 5.5 (ND-25.0) 2.0 (2.34-19.20)
30.6 (4.97 to 102) 2.6 (ND-11.0)
16.6 (0.55 to 67.2) 3.2 (ND-12.0)
-
-
ND-140
ND-190
5.49 (ND-39.1) 200 (ND-4560)
58.6 (ND-743) 100 (ND-200)
5-28000
-
ND to 7.16
Reference
17.1 (3.13 to 67.6)
1.33 (ND to 12.4)
the present study
-
-
(Yamamoto et al., 2012)
-
-
(Masia et al., 2013)
ND−66
ND-40
-
(Hladik and Kolpin, 2016)
28.7 (ND-182) 60 (ND-420)
0.26 (ND-1.52) 80 (ND-380)
-
(Struger et al., 2017)
150 (ND-1370)
-
-
-
(Sanchez-Bayo and Hyne, 2014a) (Vijver and van den Brink, 2014)
ND to 1.91
ND to 5.33
ND to 1.31
the present study
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ND to 2.13
THA
SC
IMI
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Surface water (ng/L) Pearl Rivers Guangdong, China Rivers Osaka,Japan Guadalquivir River Spain Streams across the USA Sydenham River Canada Rivers Sydney, Australia surface water Dutch Sediment (ng/g dw) Pearl River, Guangdong, China Wetlands Prairie Pothole, Canada Willapa Bay Washington state, USA
ACE
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Table 3. Comparison of NEOs detected in surface water and sediment from the Pearl Rivers and other countries.
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ND to 17.5
ND to 20.0
ND to 3.9
ND
-
(Main et al., 2014)
ND to 2.5
-
-
-
-
(Felsot and Ruppert, 2002)
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Figure captions
524
Fig. 1. Map of sampling sites in the Pearl Rivers and three WWTPs. Color circles: sites
525
from the rivers; Black squares: sites from the WWTPs.
526
Fig. 2. Spatial distribution of induvial and total concentration of NEOs in the Pearl Rivers
527
and three WWTPs.
528
Fig. 3. Seasonal variation of induvial NEOs detected from surface water and sediment in
529
the Pearl Rivers and three WWTPs.
530
Fig. 4. Boxplots for NEOs detected in the Pearl Rivers and three WWTPs based on the total
531
amount of five NEOs in spring and summer season.
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1. At least one NEO was detected in water and sediment of the Pearl Rivers
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2. Imidacloprid and thiamethoxam were the most frequently detected NEOs 3. Local agricultural runoff and wastewater discharge could be the main sources
4. Seasonal differences of NEOs contamination could be attributed to rainfall intensities
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5. Exposure to current level would pose a potential threat to sensitive non-target invertebrates
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S0045-6535(18)32121-0
DOI:
https://doi.org/10.1016/j.chemosphere.2018.11.024
Reference:
CHEM 22508
To appear in:
ECSN
Received Date: 30 August 2018 Revised Date:
28 October 2018
Accepted Date: 2 November 2018
Please cite this article as: Zhang, C., Tian, D., Yi, X., Zhang, T., Ruan, J., Wu, R., Chen, C., Huang, M., Ying, G., Occurrence, distribution and seasonal variation of five neonicotinoids insecticides in surface water and sediment of the Pearl Rivers, South China, Chemosphere (2018), doi: https://doi.org/10.1016/ j.chemosphere.2018.11.024. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Graphical Abstract
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Occurrence, distribution and seasonal variation of five neonicotinoids insecticides in
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surface water and sediment of the Pearl Rivers, South China
3 Chao Zhang1,2#, Di Tian2, XiaoHui Yi1#, Tao Zhang3#, Jujun Ruan3#, Renren Wu4, Chen
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Chen4, Mingzhi Huang1,2*,GuangGuo Ying1
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Ministry of Education, South China Normal University, Guangzhou 510631, PR China
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Environmental Research Institute, Key Laboratory of Theoretical Chemistry of Environment
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School of Geography and Planning, Guangdong Provincial Key Laboratory of Urbanization
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and Geo-simulation, Sun Yat-sen University, Guangzhou 510275, PR China
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510275, China
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Guangzhou 51065, China
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*Corresponding author
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Mingzhi Huang, E-mail: [email protected] and [email protected];
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South China Institute of Environmental Science, Ministry of Environmental Protection,
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School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou
# These authors contributed equally to this work
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Abstract
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Occurrence and distribution of five neonicotinoids (NEOs) in surface water and sediment
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were studied in the Pearl Rivers, including three trunk streams, Dongjiang, Beijiang, Xijiang
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River (DR, BR and XR), South China. At least one neonicotinoid was detected in surface
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water and sediment of the Pearl Rivers, with imidacloprid (IMI) and thiamethoxam (THM)
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being the frequently detected NEOs. Total amount of NEOs (∑5neonics) in surface water and
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sediment ranged from 24.0 to 322 ng/L, and from 0.11 to 11.6 ng/g dw, respectively.
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Moreover, the order of contamination level of NEOs in the Pearl Rivers was as follows: XR >
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DR > BR for surface water, and BR > DR > XR for sediment. Local agricultural activities and
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effluents of local wastewater treatment plants (WWTPs) could be major sources of NEOs in
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the Pearl Rivers. Solubilization and dilution of NEOs between surface water and sediment
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during different seasons (spring and summer) could be attributed to rainfall intensities or
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climate of the Pearl River Delta. An ecological risk assessment of the exposure to current
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environmental concentration of imidacloprid and ∑5NEOs suggests a threat to sensitive
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non-target invertebrates, including aquatic invertebrates. Results would provide a better
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understanding of NEOs contamination in the Pearl Rivers, as well as being a reliable dataset
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for decision-making in contamination control and environmental protection.
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Keywords:
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neonicotinoid; imidacloprid; thiamethoxam; aquatic invertebrates; the Pearl River Delta
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1. Introduction Neonicotinoids (NEOs) have become the most widely used class of insecticides in the
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world since they were first developed in the late 1980s and early 1990s as imidacloprid (IMI)
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(Douglas and Tooker, 2015; Sparks and Nauen, 2015; Terayama et al., 2016). Application of
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NEOs is carried out by means of seed treatment, foliar sprays, soil drenches, granules, and
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injection (Stewart et al., 2014; Bonmatin et al., 2015; Simon-Delso et al., 2015). As one of the
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largest agricultural countries, kinds of neonicotinoids have been widely used for pest control
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to meet food needs for about 1.4 billion population, and China plays an essential role in the
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production, application and research of NEOs (Shao et al., 2013).
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However, heavy use of NEOs were reported to lead to a variety of potentially adverse
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effects on ecosystem and human health (Zeng et al., 2013; Sanchez-Bayo, 2014; Gibbons et
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al., 2015; Christen et al., 2016), such as decline in population of pollinators (e.g., honeybees)
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and harmful to non-target organisms, which have drawn extensive attention (Anderson et al.,
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2015; Bonmatin et al., 2015; Morrissey et al., 2015). Previously reports shows that NEOs can
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cause toxic effects to insects and vertebrates (Hallmann et al., 2014; Nicodemo et al., 2014;
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Cimino et al., 2017; Bishop et al., 2018). Signs of oxidative stress and DNA damage have
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been observed in freshwater fish, such as loach and zebrafish, exposed to IMI and
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thiamethoxam (THM) (Ge et al., 2015; Xia et al., 2016; Yan et al., 2016). What’s more,
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extensive exposure to NEOs may lead to hazardous effect on human health (Anderson et al.,
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2015). Therefore, to approach crises and challenges, various countries have issued a series of
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policies and acts for restrictions on NEOs use (Canada, 2013; Columbia, 2013; EU, 2013).
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ACCEPTED MANUSCRIPT Lots of data about residue NEOs in water and soil of the US, Canada, Europe have
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been reported. Hladik and Kolpin (2016) collected water samples from 48 streams across
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the United States and found that NEOs were detected in 63% of streams with 37% and 21%
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detection frequencies for imidacloprid (IMI) and thiamethoxam (THM), respectively. 93%
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of river water near Sydney in Australia were observed to contain two or more kinds of
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NEOs, and the maximum concentration for IMI and Thiacloprid (THA) were detected at
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4.56 and 1.37 µg/L, respectively (Sanchez-Bayo and Hyne, 2014a). Several studies report
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that clothianidin (CLO), IMI, and THM are usually the predominant NEOs detected
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(Hladik et al., 2014; Hladik and Kolpin, 2016). Kinds of NEOs have been detected at above
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35 ng/L in around 75% surface water of southern Ontario, Canada, which could be conduct
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a potential effect on aquatic invertebrate (Struger et al., 2017). Dinotefuran was the most
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frequent and highest in surface water in Osaka of Japan (Yamamoto et al., 2012). However,
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until now, there are few reports on occurrence and distribution of NEOs in surface water for
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China, and studies on NEOs residue in sediments are also limited, which could have
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potential negative effects through transportation into water and others.
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The Pearl River is the third longest river of China with a total drainage area of 0.45 ×
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106 km2 (mostly within the Guangdong Province), including the Dongjiang Xijiang,
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Beijiang Rivers and other river networks. With the rapid economic development and
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continued population growth in the Pearl River Delta, the Pearl River has suffered from
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serious environmental pollution in recent years. Since the Pearl Rivers, flowing through
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metropolitan Guangzhou, Dongguan, Shenzhen, Hong Kong and more surrounding towns, 4 / 33
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activities (forestation and cultivation of rice and kinds of vegetables and fruits, accounting
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for about 60~70% and 15~20% of total areas, respectively), so, monitoring contaminants of
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NEOs in surface water is of immense importance.
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Therefore, the main objectives of present work were: (1) to investigate occurrence and
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residue level of five NEOs (IMI, THM, CLO, ACE and THA) in surface water and sediments
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of the Pearl Rivers; (2) to explore possible sources and spatial and seasonal variation of NEOs;
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(3) to evaluate the potential environmental risks of NEOs to organisms of the Pearl Rivers.
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Results would provide a better understanding of NEOs contamination of the Pearl Rivers, as
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well as being a reliable dataset for decision-making in pollution control and conservation.
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2. Materials and Methods
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2.1. Chemicals and Reagents
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Standards for five representative NEOs, imidacloprid (IMI), thiamethoxam (THM),
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clothianidin (CLO), acetamiprid (ACE) and thiacloprid (THA) (in order of market shares),
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were purchased from the Dr. Ehrenstorfer GmbH (Augsburg, Germany). The corresponding
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isotope labeling products, IMI (IMI-d4), THM-d3, CLO (CLO-d3), ACE (ACE-d3) and
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THA-(thiazolidin ring-d4), were obtained from the Sigma-Aldrich Chemical (St Louis, MO,
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USA) and used as the internal standards (information was summarized in Table S1-S2, SI).
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Stock solutions of five individual compounds and internal standards were prepared with
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acetonitrile at a concentration of 1,000 mg/L. Acetonitrile, dichloromethane and methanol
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(UHPLC Grade) were obtained from the ANPEL Laboratory Technologies (Shanghai) Inc.
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(500 mg, 6 mL) were used for sample extraction and concentration. Milli-Q water (Millipore,
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Bedford, MA, USA) was utilized throughout this work.
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2.2. Study areas and sample collection
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Surface water and sediment were collected from 49 sites of the Pearl Rivers (including
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the Dongjiang (DR), Xijiang (XR), and Beijiang (BR) Rivers) and outlets of three WWTPs
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(Fig. 1). Distribution of 49 sampling sites are as follows: 9 sites (D1-D9) from the DR, 24
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sites (B1-B24) from the BR, 13 sites (X1-X13) from the XR, and 3 sites (W1-W3) from the
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WWTPs. More information about sampling sites and treatment process of three WWTPs is
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given in the SI file (Text S1-S2, SI). Sample collection was carried out during two periods:
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March and April in spring , and August and September in summer season of South China.
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Water samples were collected from a depth of 50 cm below the surface using portable water
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samplers and stored in polypropylene (PP) bottles (pre-treated with methanol and Milli-Q
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water thrice). Physical indexes (pH; ORP; turbidity; temperature and dissolved oxygen (DO))
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of water were accurately measured before storage. Stainless steel grab samplers were utilized
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for sediment collection at 10 cm upper, and polypropylene (PP) bags were used for storage.
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After collection, water and sediment samples were transferred to the laboratory as soon as
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possible and stored in 4 °C and -20 °C before analysis, respectively.
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--Fig. 1-2.3. Sample extraction and LC-MS/MS analysis Briefly, 500 mL filtered (0.45 µm) water within injection of internal standards mixture 6 / 33
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Loading rate of water samples was maintained at 3 mL/min. Subsequently, the target fraction
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was eluted with 5 mL of Milli-Q water and methanol respectively. Extracted solutions were
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concentrated under a gentle nitrogen gas flow, and then re-dissolved in 0.5 mL acetonitrile.
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5.0 g freeze-dried sediment was extracted using the dispersive liquid–liquid microextraction.
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Specifically, 20 mL mixtures of acetonitrile and dichloromethane (v/v, 2/1) were used. Extract
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was re-dissolved in 1.0 mL acetone and transferred into 10 mL Milli-Q water using a
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centrifuge tube. A 0.8 g NaCl and 2 mL dichloromethane were added into the same tube,
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followed by vortex agitation for 1 min, ultrasonic extraction for 10 min, and separation by
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centrifuging at 4000 rpm for 5 min. The lower layer of the liquid was transferred with a
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microinjector after stratification and concentrated under nitrogen, and then dissolved in 0.5
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mL acetonitrile. A 0.2 µm nylon filter was used for the purification of extract and filtrate was
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then transferred into a 2 mL autosampler vial prior to analysis (a flowchart of water and
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sediment samples extraction and pretreatment was shown in Fig. S1, SI).
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Referring to methods reported by Sanchez-Bayo and Hyne (2014b) and Watanabe et al.
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(2015), extracts of surface water and sediment were subsequently quantified using a triple
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quadruple LC-MS/MS (TSQ Quantum Ultra. Thermo Scientific, USA) equipped with an
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electrospray ionization (MRM) positive mode. Three microliters aliquot of the final extract
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were injected into a Thermo Hypersil GOLD C18 column (2.1 mm × 100 mm, 1.9 µm.
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Thermo, USA) maintained at 40
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formic acid-water solution) and 10% B (acetonitrile), followed by a linear gradient from 90 to
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. A gradient elution program was started with 90% A (0.1%
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6.0 min for an addition 1.5 min, in final reverted to 90% A at 7.5 min before analysis end at
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10 min. Mobile was kept at a flow rate of 300 µL/min. MRM transitions, collision energy and
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retention time of the five target NEOs analyzed are shown in Table S3, SI.
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Analyte quantitation was performed using external standard method, and IMI-d4,
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ACE-d3, CLO-d3, THM-d3, and THA-(thiazolidin ring-d4) were used as internal references
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for qualitative analysis. A total of 15-point calibrations were prepared in acetonitrile with a
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range from 1–1000 ng/L for each NEO. Linear 1/Y weighted regressions, not forced through
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the origin, were based on external standard calibration and have a correlation coefficient
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greater than 0.99 (shown in Table S4, SI).
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2.4. Quality assurance and quality control
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The limit of detection (LOD) and the limit of quantification (LOQ) were defined as 3
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and 10 times the noise level of the chromatogram in blank, respectively, and in this work, the
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LOQ of five NEOs ranged between 0.01 ng/L and 0.05 ng/L for water sample and between
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0.001 ng/g and 0.005 ng/g for sediments. For the calculation of ∑5NEOs, the concentrations
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below LOQ and the non-found detection results were all assigned as zero. However,
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concentrations below the LOQ were treated as half the LOQ for individual analysis. The
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recoveries ranged from 83% to 106% for water and from 81% to 112% for sediments.
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Duplicates were also analyzed, and the coefficient of variation was less than 12% (Table S4).
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3. Results and Discussion
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3.1. Occurrence and concentration detected of NEOs in surface water The detection frequency (DF), range (min-max), average and median concentration of
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IMI, THM, CLO, ACE, THA, and total amount of Σ5NEOs in surface water from the DR,
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XR, BR, and effluents of three WWTPs are summarized in Table 1. THM, CLO and ACE
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were detected from all 49 sampling sites of the Pearl Rivers and three WWTPs effluents.
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Total amount of ∑5NEOs ranged from 24.0 (site D3) to 322 ng/L (site X8), with an average
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of 91.05 ng/L from the Pearl Rivers. Taking three WWTPs effluents into consideration, the
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order of NEOs detected from surface water (based on the average concentration of ∑5NEOs)
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was: the WWTP effluents (179 ± 86.0 ng/L) > XR (102 ± 54.9 ng/L) > DR (98.7 ± 68.5
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ng/L) > BR (96.5 ± 60.7 ng/L). Concentration of ∑5NEOs detected from the WWTPs
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effluents was about 1.75~1.8 folds than the Pearl rivers, indicating that local WWTPs
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effluents could be a source of the NEOs contamination in the receiving waters (rivers).
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THM was the dominant NEO detected in the Pearl Rivers, accounting for about 11~53% of
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the amount of ∑5NEOs at different sites. Contributions of individual NEO for the ∑5NEOs
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tend to follow the descending order as: THM (34.9%) > IMI (29.2%) > ACE (19.3%) >
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CLO (16.4%) > THA (0.2%), and was consistent with order of hydrophilicity of NEOs
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(Raina-Fulton, 2016), hinting a significant relevance between the physicochemical
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characteristics of NEOs (hydrophilicity in especial) and environmental residue effect.
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Almost five NEOs were detected from the DR with 100% frequencies except for THA,
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22.3, 24.9 ± 24.0 and 24.7.4 ± 18.1 ng/L, respectively. Moreover, THA was detected at 39%
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with a range from ND to 3.73 ng/L, the lowest detection frequency and concentration. A
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similar amount of Σ5NEOs was also found from the BR ranging from 28.0 to 285 ng/L,
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with IMI and THM as the dominant NEOs accounting a detection frequency of 100% and
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concentration of 33.9 ± 26.4 and 29.4 ± 22.4 ng/L in the BR, respectively. THM, CLO,
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ACE and THA were detected in most of sites of the XR, and the total amount of Σ5NEOs
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was ranged from 53.1 to 322 ng/L. THM was detected with the highest average
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concentration of 35.2 ± 15.2 ng/L in the XR, a little higher than IMI (32.5 ± 33.4 ng/L).
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only at the site X12, no IMI was detected (DF: 96%, 22/23), which might be correlated
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with junction of the WWTP effluent flow near site X12 due to dilution effect. THM and
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CLO were two dominant NEOs with a concentration of 79.5 ± 35.7 and 49.7 ± 26.2 ng/L
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from the WWTP effluents, respectively, which were much different with previous research
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(Sadaria et al., 2016) as IMI and CLO dominated in the WWTP effluents with a
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concentration of 58.5 ± 29.1 and 70.2 ± 121.8 ng/L (THM was not detected).
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Differences between occurrence and concentration of NEOs detected within the current
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work and those reported globally was investigated and shown in Table 3. occurrence and
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distribution of NEOs with surface water detected in the Pearl Rivers were different from those
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observed in other countries. The most detectable NEOs in the Pearl Rivers were IMI, THM,
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and ACE, whereas in North America are THM, IMI, and CLO. Concentration of IMI in the
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Pearl Rivers were much higher than those presented in the rivers of Osaka (Japan) 10 / 33
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Sydenham River of Canada and the streams across the United States, but lower than those
208
determined from rivers around Sydney, and Dutch surface water. Concentration of THM in
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the Pearl Rivers was higher than those in rivers of Osaka City, and much lower than those in
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streams across the United States, Sydenham River (Struger et al., 2017) and rivers around
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Sydney. ACE levels, in the present study, were higher than most reported water bodies around
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the world. Levels of CLO in the Pearl Rivers were like those in streams across the United
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States (Hladik and Kolpin, 2016), which were higher than those in rivers of Osaka, Japan, and
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lower than those determined in Sydenham River and rivers around Sydney (Sanchez-Bayo
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and Hyne, 2014a). THA in the Pearl Rivers was similar to those water bodies reported around
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the world but approximately two orders of magnitude lower than that in rivers around Sydney.
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Overall, the Pearl Rivers could be confronted with a moderate level of NEOs contamination.
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--Table 1--
3.2. Occurrence and concentration detected of NEOs in the sediment
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Statistical data of ACE, THM, CLO, IMI, THA and Σ5NEOs in sediment from the DR,
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BR, XR and the effluents of three WWTPs are showed in Table 2. Total amount of the
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Σ5NEO in sediment ranged from 0.11 to 11.6 ng/g dw, with an average of 2.16 ng/g dw for 85
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sampling sites of the Pearl Rivers. The order of detection concentration of NEOs in sediment
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(based on mean value) was: the BR (4.08 ± 9.01 ng/g dw) > DR (2.83 ± 2.82 ng/g dw) > XR
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(1.30 ± 1.55 ng/g dw) > WWTP effluents (0.49 ± 0.36 ng/g dw). IMI was detected with the
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highest frequency and concentration among the NEOs in sediment of the Pearl Rivers.
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level and detection frequency of IMI. In the WWTP effluents, IMI showed a remarkably low
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concentration (0.04 ± 0.11 ng/g) and the detection frequency (17%). Detection frequencies of
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ACE were 89% in the DR, 91% in the BR, 96% in the XR, and 100% in WWTP effluents,
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with a mean of 0.53 ng/g dw in the Pearl Rivers and 0.06 ng/g dw in effluents of WWTPs.
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Concentration of THM with high hydrophilicity, was detected in a low level in sediment of
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the Pearl Rivers, with a mean of 0.26 ng/g dw. THA in sediment maintained quite low levels
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ranging from ND to 1.31 ng/g. Based on mean concentration in sediments from tributaries in
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the Pearls Rivers, contributions from various NEOs followed the order: IMI (73.3%) > ACE
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(14.8%) > CLO (6.1%) > THM (5.1%) > THA (0.7%).
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IMI was detected in all sediments of the DR. ACE and IMI, with concentrations of 1.21
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± 1.66 and 1.16 ± 1.05 ng/g dw, respectively, were relatively abundant compared to others.
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Five NEOs were also detected in most of sites in the BR, and the concentration of the
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Σ5NEOs in sediment of the BR ranged from 0.11 to 11.6 ng/g dw. Moreover, IMI was the
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most frequently detected NEO (100%) with the highest mean concentration (1.33 ± 1.71 ng/g
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dw) in the BR, followed by ACE. IMI was also detected with concentration of up to 0.62 ±
243
0.71 ng/g dw and as the dominant NEO in the XR. A comparison of residual NEOs in river
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sediment between the Pearl Rivers and other countries was shown in Table 3 based on limited
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data reported. Residual NEOs in river sediment from the Pearl Rivers was lower than soil
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from wetland near agricultural lands in Canada (Main et al., 2014) and higher than others
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reported (Felsot and Ruppert, 2002).
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--Table 2--, --Table 3-3.3. Spatial distribution of NEOs in the Pearl Rivers Spatial distribution of five NEOs detected in the Pearl Rivers was shown in Fig. 2. An
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regional difference of NEOs distribution in surface water and sediments was observed.
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Concentrations of NEOs were increased from upstream to downstream of the DR, flowing
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through the cities of Heyuan, Huizhou, and Dongguan. Level of NEOs contamination at
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upstream of the DR remain relatively low, whereas site D3 remains high, which might be
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due to intensive agricultural and gardening activities, the main industries of the Heyuan,
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hinting the source of NEOs contamination at the upstream of the DR could be wastewater
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discharge from livestock waste and agricultural runoff. Moreover, the Xinfengjiang
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Reservoir (one of the major drinking water supply resources for the Guangdong province
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and Hong Kong) is located at the upstream of the DR, and an small decline of NEOs in site
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D4 and D5 could be related to dilution effect of the Xizhijiang River. Dongguan, located in
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the middle and lower reaches of the DR, is a typical industrial and immigrant city with
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more than 8 million residents by the end of year 2016. The statistics (the year 2016) also
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showed that the total amount of wastewater discharge (including industrial and domestic)
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from the Dongguan reached about 1,289 million tons, which might be accounting for NEOs
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contamination in the sites D6–D9. Furthermore, Dongguan has relatively large artificial
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greening areas and developed farming and stock breeding system. Since the ACE has been
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extensively applied to pest control of horticultural plants of the urban landscaping as a class
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of NEOs, residual levels of the ACE and Σ5NEOs along the river flow in the Dongguan part
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of the DR hold an obvious tendency of increase. In the BR, the level of NEOs from downstream and upstream of the BR was generally
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higher than that from midstream. The highest amount of Σ5NEOs was found in site B22
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with a concentration of 241 ng/L. Sites B1–B3 were located in Shaoguan city, where the
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cultivated land (average) ranked first in the Guangdong province. Moreover, the
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agricultural farming, livestock and poultry were main industries in the cities of Heyuan and
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Qingyuan, where B4–B9 are located. Therefore, the source of NEOs at upstream of the BR
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could be from the agricultural runoff. Additionally, the frequent flooding at site B6 which
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mostly lead to inundation of neighboring villages and farmlands should be noted.
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Consequent flow erosion and soil transfer could be related to the unexpected significant
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NEOs contamination at site B6, and large numbers of livestock and poultry breeding waste
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(forage) at B6 was also a probable source of high residual level of NEOs. Owing to the
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dilution of water from three tributaries of the Pajiang, Lianjiang, and Binjiang Rivers,
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levels of NEOs from B7 to B9 were relatively stable. NEOs detected from sites B10–B17
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(near Foshan city, an agricultural and industrial region) might be mainly from discharge of
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industrial and domestic wastewater and agricultural runoff. In addition, B14 was located
285
downstream of the confluence of the BR and XR and significantly influenced by the high
286
NEO levels during spring season in the Suijiang River. Moreover, B21 and B22 are
287
adjacent to the Liuxi River, where vegetable plantations are widely distributed.
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Levels of NEOs at upstream of the XR (X1–X4) were generally higher than that
289
downstream except for X6, X7, and X12. The highest concentration of Σ5NEOs was found 14 / 33
ACCEPTED MANUSCRIPT in site X4 with a value of 107 ng/L. Sites X1–X3 were in Zhaoqing, with the agricultural
291
farming and livestock and poultry as major industries. Site X4 is at the downstream of the
292
confluence of the BR and XR and significantly influenced with NEOs contamination from
293
the Gaoming River. The low concentration of these NEOs in the estuary is probably due to
294
sea water dilution. Sites X6, X7, and X12 are at the downstream of the outlets of three
295
WWTPs. Concentration of the Σ5NEOs in X6, X7, X12, and effluents of W1–W3 was
296
found to be higher than those in the XR, DR, and BR. Surface water from effluents of
297
W1–W3 with excessive THM and CLO mostly be due to the discharges from domestic
298
wastewater and pest control and cultivation of horticultural plants.
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Fluctuation of NEOs in the surface water of the Pearl Rivers tends to be relatively
300
smoother than that in sediment along the flow direction of rivers. As far NEOs, a class of
301
strong hydrophilic contaminants, occurrence and high residual concentration were mainly
302
observed in surface water than sediments, which could be accounted for physicochemical
303
characteristics of NEOs. Additionally, NEOs detected from samples of sites where farming
304
lands were frequently submerged with flood (site B6), and an exchange of NEOs from soil
305
to water could be a source. Furthermore, biodegradation of the NEOs is difficult through
306
treatment flows of traditional WWTPs (Sadaria et al., 2016). What’s more, timing of the
307
NEOs application to crops (rice) in different regions was varied, which may also contribute
308
to variations of NEOs in different tributaries and regions. Therefore, seasonal variation of
309
NEOs in the Pearl Rivers is discussed.
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3.4. Seasonal variation of five NEOs in the Pearl Rivers Seasonal variations of the five NEOs in the Pearl Rivers are showed in Fig. 3.
313
Concentrations of NEOs in surface water during the summer were higher than those in spring,
314
whereas for sediment, an opposite trend was observed. The Pearl River Delta mostly belongs
315
to the subtropical monsoon climate zones, and rainfall displays an uneven characteristic and
316
mainly occurs in summer (Text S3, SI). During the summer, NEOs could be tended to
317
dissolve form and transfer from soil and sediment to water via erosion of frequent rainfall.
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Detection level of the THM in surface water during the summer is, evidently,
319
significantly increased compared to other NEOs. Correspondingly, nearly no THM was
320
detected from sediment during summer, indicating that the solubilization effect on the
321
residue level in surface water is stronger than dilution for the highly hydrophilic NEOs.
322
As for IMI, the first NEO developed, due to its extensive application and usage, it was
323
widespread distributed in all surface water and sediments. Despite the high residue level of
324
IMI from samples in spring, a significant increase was also observed in the majority of
325
surface water samples during summer. Predictably, a dramatic decline was detected in IMI
326
concentration in sediment during summer. What’s more, residual level of ACE and CLO
327
was also remained high in surface water, and took a corresponding decrease in sediments.
328
Results indicated that solubilization and dilution might be played equivalent roles in the
329
ACE and CLO washing through rainfall runoff in summer. With the increasing in rainfall
330
activities (capacities and intensities) during the rainy season, nearly all THA in the
331
sediments were re-dissolved in surface water and diluted to an low concentration.
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ACCEPTED MANUSCRIPT Periods of NEOs application varied with the growing season of crops in various
333
farming lands due to definite characteristics of crops in different tributaries of the Pearl
334
Rivers. For example, level of NEOs at site B12 (located in Suijiang River) was abundant in
335
spring but relatively poor in summer, reflecting a rather high application for main crops in
336
spring. For site X4, residue level of NEOs in spring was higher than that in summer; which
337
might relate to considerable application of NEOs for main crops in Gaoming River during
338
spring. Similarly, a high residue level of the ACE in Dongguan (D6–D9) is perhaps due to
339
the long-term pest management and cultivation of horticultural plants.
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--Fig. 3--
3.5. Ecological risk assessment of the current discharged NEOs of the Pearl Rivers Considering the large flow volume and circulation of rivers and high detection
343
concentration of individual(s) NEOs in water and sediment of the Pearl Rivers, the entire
344
Pearl River Delta could be confronted with a significant contamination of NEOs since low
345
concentrations of the NEOs were also known to affect wide range of free-living organisms
346
(Wood and Goulson, 2017). Morrissey et al. (2015) suggested that ecological guideline for
347
surface water ∑nNEOs concentrations need to be controlled under 200 ng/L (short-term acute)
348
or 35 ng/L (long-term chronic) to avoid negative effects on sensitive aquatic invertebrates. As
349
for three tributaries of the Pearl Rivers, 87.5% (21/24) of sampling sites in the BR, 69% (9/13)
350
in the XR, and 66.7% (6/9) in the DR are exceeded the long-term guideline (35 ng/L) in
351
spring, and 100% (39/39) was ahead of this limit in summer based on Σ5NEOs concentration.
352
Similarly, 100% (6/6) of the WWTP effluents were several times higher than that of the
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ACCEPTED MANUSCRIPT guideline (Fig. 4). Additionally, a part of surface water exceeded the short-term guideline
354
(200 ng/L). Results indicated that serious risks on aquatic organisms’ biodiversity should be
355
suffered in water environments of the Pearl Rivers with NEOs contamination. A lower
356
concentration of 20 ng/L (long-term chronic) for IMI was also proposed (Van Dijk et al.,
357
2013). frequencies of IMI Detection above the limit were 78.3% (3/46) and 97.4% (38/39)
358
from the Pearl Rivers in spring and summer, respectively, additionally, 83.3% (5/6) from
359
WWTP effluents. The maximum concentration of IMI were 55.7, 180, and 89.1 ng/L for
360
water from the Pearl Rivers in spring, summer season and the WWTP effluents, respectively,
361
which are 4.3, 13.8, and 6.9 times over the guideline.
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However, little information about acute or chronic toxicity of sediment residue NEOs on
363
invertebrate species was known. Due to the high environmental risk of NEOs in water
364
environment and frequent movement of NEOs between water and sediment through
365
precipitation and runoff scouring in summer, it can be inferred that NEOs in sediment can
366
have considerable negative influences on sensitive invertebrate species (Sánchez-Bayo et al.,
367
2016). Moreover, residual NEOs in sediment of the Pearl Rivers could be shown adverse
368
effects with a concentration range from 0.11 to 11.6 ng/g dw and a mean of 2.16 ng/g dw
369
(Zhang et al., 2015; Zhang et al., 2018). Further studies are needed to clarify accurately
370
determine environmental risk of neonicotinoids over broad scales.
371 372 373
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--Fig. 4--
4. Conclusion Occurrence, distribution and seasonal variation of five neonicotinoids insecticides in 18 / 33
ACCEPTED MANUSCRIPT surface water and sediment were investigated in the Dongjiang, Beijiang and Xijiang River,
375
three trunk streams of the Pearl Rivers. At least one selected neonicotinoid was detected in
376
surface water and sediment of the Pearls Rivers. Total concentration of five NEOs
377
(∑5NEOs) ranged from 24.0 to 322 ng/L, with a mean of 91.05 ng/L in the Pearl Rivers,
378
and the total concentration of the Σ5NEO in sediments ranged from 0.11 to 11.6 ng/g dw,
379
with a mean of 2.16 ng/g dw for 85 sampling sites of the Pearl Rivers. Based on the
380
detection concentration of NEOs, the order of contamination level of NEOs is as follows:
381
the WWTP effluents > BR > DR > XR for surface water and DR > BR > XR > the WWTP
382
effluents for sediment. Spatial distribution of NEOs exhibited that the main sources of
383
pollution into the river could be local human and agricultural activities, livestock and
384
poultry farming and WWTPs effluents. Solubilization and dilution of NEOs between the
385
surface water and sediment during different seasons could be attributed to rainfall
386
intensities or climate of the Pearl River Delta. Finally, risk assessment revealed that current
387
residual NEOs in the Pearl Rivers may pose a threat to sensitive non-target invertebrates.
388
Acknowledgements
389
This research was supported by National Natural Science Foundation of China (No.
390
21677184), Natural Science Foundation of Guangdong Province (No. 2016A030306033),
391
Guangdong
392
2014A020216007), Technological Innovation Young Talents of Guangdong Special Support
393
Plan (No. 2014TQ01Z530), and Pearl River Nova Program of Guangzhou (No.
394
201506010058).
395
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Provincial
Science
and
Technology
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Plan
Project
Foundation
(No.
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Tables
100% 7.71 to 102 29.4 21.5
96% ND to 41.2 32.5 20.6
100% 13.1 to 69.2 35.2 31.9 100% 35.6 to 145 79.5 76.0
83% ND to 89.1 36.5 32.2
∑5NEOs
100% 3.13 to 60.4 24.7 16.8
39% ND to 3.73 0.67 0.03
100% 24.0 to 243 98.7 74.6
100% 3.38 to 67.6 18.4 12.4
75% ND to 9.35 0.90 0.53
100% 28.0 to 285 96.5 78.2
100% 9.38 to 48.3 23.3 15.4
100% 3.65 to 36.7 9.42 6.42
91% ND to 2.38 0.40 0.04
100% 53.1 to 322 102 78.1
100% 34.7 to 103 49.7 40.0
100% 3.65 to 67.6 12.3 7.07
67% ND to 1.35 0.59 0.56
100% 108 to 350 179 153
SC
100% 4.02 to 162 33.9 26.4
100% 0.55 to 45.7 18.1 16.3
M AN U
100% 6.21 to 77.0 30.4 23.3
100% 0.74 to 67.2 13.9 9.46
TE D
100% 0.84 to 70.9 24.9 14.9
EP
DR (Dongjiang River) (n=18) DF Range (min-max) Average (ng/L) Median (ng/L) BR (Beijiang River) (n=44) DF Range (min-max) Average (ng/L) Median (ng/L) XR (Xijiang River) (n=23) DF Range (min-max) Average (ng/L) Median (ng/L) Effluent of WWTPs (n=6) DF Range (min-max) Average (ng/L) Median (ng/L)
RI PT
Table 1. Concentrations (ng/L) of five NEOs detected from surface water in the Pearl Rivers and three WWTPs IMI THM CLO ACE THA
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Table 2. Concentrations (ng/g dw) of five NEOs detected from sediment in the Pearl Rivers and three WWTPs ∑5NEOs
89% ND to 5.33 1.21 0.39
44% ND to 1.06 0.11 0.01
100% 0.17 to 8.77 2.83 1.19
72% ND to 1.91 0.31 0.17
91% ND to 2.13 0.29 0.08
50% ND to 1.31 0.08 0.01
100% 0.11 to 11.6 4.08 1.00
96% ND to 0.42 0.08 0.08
83% ND to 0.57 0.17 0.19
96% ND to 0.77 0.14 0.13
43% ND to 0.06 0.01 0.01
100% 0.11 to 6.74 1.30 1.01
83% ND to 0.36 0.18 0.19
100% 0.07 to 0.41 0.19 0.16
100% 0.02 to 0.11 0.06 0.05
50% ND to 0.05 0.01 0.01
100% 0.12 to 1.08 0.49 0.42
100% 0.10 to 3.11 1.16 0.69
89% ND to 0.54 0.14 0.10
61% ND to 0.97 0.21 0.01
100% 0.02 to 7.16 1.33 0.54
72% ND to 2.13 0.19 0.05
91% ND to 3.20 0.62 0.47 17% ND to 0.26 0.04 ND
ACE
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CLO
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THM
EP
DR (Dongjiang River) (n=18) DF Range (min-max) Average (ng/g dw) Median (ng/g dw) BR (Beijiang River) (n=44) DF Range (min-max) Average (ng/g dw) Median (ng/g dw) XR (Xijiang River) (n=23) DF Range (min-max) Average (ng/g dw) Median (ng/g dw) Effluent of WWTPs (n=6) DF Range (min-max) Average (ng/g dw) Median (ng/g dw)
THA
IMI
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THM
CLO
31.0 (ND to 180) 5.5 (ND-25.0) 2.0 (2.34-19.20)
30.6 (4.97 to 102) 2.6 (ND-11.0)
16.6 (0.55 to 67.2) 3.2 (ND-12.0)
-
-
ND-140
ND-190
5.49 (ND-39.1) 200 (ND-4560)
58.6 (ND-743) 100 (ND-200)
5-28000
-
ND to 7.16
Reference
17.1 (3.13 to 67.6)
1.33 (ND to 12.4)
the present study
-
-
(Yamamoto et al., 2012)
-
-
(Masia et al., 2013)
ND−66
ND-40
-
(Hladik and Kolpin, 2016)
28.7 (ND-182) 60 (ND-420)
0.26 (ND-1.52) 80 (ND-380)
-
(Struger et al., 2017)
150 (ND-1370)
-
-
-
(Sanchez-Bayo and Hyne, 2014a) (Vijver and van den Brink, 2014)
ND to 1.91
ND to 5.33
ND to 1.31
the present study
M AN U
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ND to 2.13
THA
SC
IMI
EP
Surface water (ng/L) Pearl Rivers Guangdong, China Rivers Osaka,Japan Guadalquivir River Spain Streams across the USA Sydenham River Canada Rivers Sydney, Australia surface water Dutch Sediment (ng/g dw) Pearl River, Guangdong, China Wetlands Prairie Pothole, Canada Willapa Bay Washington state, USA
ACE
RI PT
Table 3. Comparison of NEOs detected in surface water and sediment from the Pearl Rivers and other countries.
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521
ND to 17.5
ND to 20.0
ND to 3.9
ND
-
(Main et al., 2014)
ND to 2.5
-
-
-
-
(Felsot and Ruppert, 2002)
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Figure captions
524
Fig. 1. Map of sampling sites in the Pearl Rivers and three WWTPs. Color circles: sites
525
from the rivers; Black squares: sites from the WWTPs.
526
Fig. 2. Spatial distribution of induvial and total concentration of NEOs in the Pearl Rivers
527
and three WWTPs.
528
Fig. 3. Seasonal variation of induvial NEOs detected from surface water and sediment in
529
the Pearl Rivers and three WWTPs.
530
Fig. 4. Boxplots for NEOs detected in the Pearl Rivers and three WWTPs based on the total
531
amount of five NEOs in spring and summer season.
M AN U
SC
RI PT
523
AC C
EP
TE D
532
29 / 33
ACCEPTED MANUSCRIPT Fig. 1
EP
535
AC C
534
TE D
M AN U
SC
RI PT
533
30 / 33
ACCEPTED MANUSCRIPT Fig. 2
EP
538
AC C
537
TE D
M AN U
SC
RI PT
536
31 / 33
ACCEPTED MANUSCRIPT Fig. 3
M AN U
SC
RI PT
539
540
AC C
EP
TE D
541
32 / 33
ACCEPTED MANUSCRIPT Fig. 4
M AN U
SC
RI PT
542
AC C
EP
TE D
543
33 / 33
ACCEPTED MANUSCRIPT Highlights
1. At least one NEO was detected in water and sediment of the Pearl Rivers
RI PT
2. Imidacloprid and thiamethoxam were the most frequently detected NEOs 3. Local agricultural runoff and wastewater discharge could be the main sources
4. Seasonal differences of NEOs contamination could be attributed to rainfall intensities
AC C
EP
TE D
M AN U
SC
5. Exposure to current level would pose a potential threat to sensitive non-target invertebrates
1/1