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Alkylphenols in surface sediments of the Yellow Sea and East China Sea inner shelf: Occurrence, distribution and fate
Chemosphere xxx (2014) xxx–xxx
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Alkylphenols in surface sediments of the Yellow Sea and East China Sea inner shelf: Occurrence, distribution and fate Xiao-yong Duan a, Yan-xia Li a,b, Xian-guo Li a,⇑, Da-hai Zhang a, Yi Gao c a
Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China Hong De School, Weifang University, Weifang 261061, China c Qingdao Municipal Drainage Monitoring Station, Qingdao 266100, China b
h i g h l i g h t s Alkylphenols in the Yellow Sea and East China Sea sediments were analyzed. Relationships between alkylphenols distributions and sources were illustrated. Environment fate of alkylphenols in the Yellow Sea and East China Sea were studied.
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Article history: Received 4 September 2013 Received in revised form 12 December 2013 Accepted 18 December 2013 Available online xxxx Keywords: Nonylphenol Octylphenol Yellow Sea East China Sea Sediment
a b s t r a c t Alkylphenols (APs) have been found as ubiquitous environmental pollutants with reproductive and developmental toxicity. In this study, APs in surface sediments of the Yellow Sea (YS) and East China Sea (ECS) inner shelf were analyzed to assess influences of riverine and atmospheric inputs of pollutants on the marine environment. NP concentrations ranged from 349.5 to 1642.8 ng/g (average 890.1 ng/g) in the YS sediments and from 31.3 to 1423.7 ng/g (average 750.1 ng/g) in the ECS inner shelf sediments. NP distribution pattern was mainly controlled by the sedimentary environment. OP concentration was 0.8– 9.3 ng/g (average 4.7 ng/g) in the YS sediments and 0.7–11.1 ng/g (average 5.1 ng/g) in the ECS sediments. Assessment of the influence of distances from land on OP concentrations provided evidence for the predominance of coastal riverine and/or atmospheric inputs rather than long-range transport. And the biological pump may play an important role for sequestration of OP in the nearshore area. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction Nonylphenol (NP) and octylphenol (OP) have been extensively used in the manufacture of nonionic surfactants (alkylphenol ethoxylates, APEOs) since 1940s (White et al., 1994). Nonylphenol polyeothoxylates (NPEOs) and octylphenol polyeothoxylates (OPEOs) respectively account for about 80% and 20% of total APEOs (Ying et al., 2002). Annual global production of APEOs was over 500,000 tons in 1997 (Ying et al., 2002), and production continues to rise in recent years. Along with a great deal of sewage and garbage being increasingly drained into the sea (Hawrelak et al., 1999; Céspedes et al., 2008), a large portion of APEOs is released into the environment and finally ends up in the aquatic environment (Renner, 1997; Solé et al., 2000). APEOs are unstable in aquatic environments with a half-life of several days and are subject to degradation to alkylphenols (APs) through bio- and photo-degradation (Li et al., 2013a). However, the degradation products, NP ⇑ Corresponding author. Tel.: +86 532 66782215. E-mail address: [email protected] (X.-g. Li).
and OP, are much more stable in the environment with a half-life of several decades in sediments (Isobe et al., 2001). Therefore, NP and OP are ubiquitous in the general environment, especially rich in the sphere around city and factory (Ying et al., 2002; Ying, 2006; Soares et al., 2008). Due to the harmful effects of NP and OP in the environment, the use and production of such compounds have been banned or strictly monitored in many countries (Soares et al., 2008). But up to now, APs are still widely used in China and the Korean peninsula. And with the development of economy, pollution caused by APs becomes clinically evident. As reported by Peng et al. (2007) and Hong et al. (2010), the levels of NP have increased sharply in recent decades in sediments of China’s Pearl River estuary (Peng et al., 2007) and Korea’s Lake Shihwa (Hong et al., 2010). A large proportion of released pollutants from man-made sources will ultimately sink to continental shelf sediments (Jönsson et al., 2003; Huang et al., 2007). And the Yellow Sea (YS) and the East China Sea (ECS) inner shelf are considered as important sinks of pollutants originated from land-based pollution sources (Duan et al., 2013a,b; Li and Dag, 2004).
0045-6535/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.chemosphere.2013.12.054
Please cite this article in press as: Duan, X.-y., et al. Alkylphenols in surface sediments of the Yellow Sea and East China Sea inner shelf: Occurrence, distribution and fate. Chemosphere (2014), http://dx.doi.org/10.1016/j.chemosphere.2013.12.054
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Thus, in order to assess the impacts of anthropogenic activities on the YS and ECS inner shelf, it is necessary to determine the levels of current sediment contaminants. Despite a few studies (Li et al., 2005; Fu et al., 2007; Hong et al., 2010; Wang et al., 2010) regarding AP levels in coast of the YS, our understanding on the occurrence and fate of AP in the YS and ECS is very limited. In this work, 66 surface sediment samples were collected from the YS and ECS inner shelf to demonstrate the spatial distribution of NP and OP and to study their fate in marine sediments in this region. 2. Materials and methods 2.1. Standards and reagents 4-Nonylphenol (NP, technical mixture) was purchased from Tokyo Chemical Industry. 4-tert-octylphenol (OP), internal standard hexa-methyl benzene (HMB) and surrogate standard 4-tertbutylphenol (BP) were purchased from Dr. Ehrenstorfer GmbH. NP consists of 11 isomer peaks due to various branched structures in the standard which was quantified by using the sum of all peak areas. 2.2. Sampling area and sample collection The YS, a typical semi-enclosed epicontinental sea, is an important storage sink of terrestrial matter from mainland China and the Korean peninsula. Many rivers (exclude the Yellow River and Yangtze River) drain directly into the YS. While most of the mud deposits in the central YS are considered to be derived primarily from the Yellow River and old Yellow River subaqueous delta based on the circulation pattern in the central YS. (Lee and Chough, 1989; Yang et al., 2003; Yang and Youn, 2007). And under the control of cyclonic circulation and cold water gyre, the sedimentary environment is relatively stable in the YS. The muddy sediments in southwestern Cheju Island were derived from diverse sources (Including the Yangtze River and Yellow River, Yang et al., 2004; Yang and Youn, 2007). The oceanographic conditions (especially oceanic circulation patterns) greatly constrain sediments distributions in this unique epicontinental sea (Hu et al., 2011). The ECS is a typical Western Pacific marginal sea, with the world’s broadest continental shelf. Most of the suspended particulate matters discharged from the Yangtze River (YR) are ultimately deposited in the YR estuary; 20–30% of them move to the south with the coastal current and are finally buried in the inner shelf of ECS, forming a ribbon of mud areas (Liu et al., 2007). Thus the YS and ECS inner shelf are considered as important sink of pollutants originated from land-based pollution sources (Duan et al., 2013a,b; Li and Dag, 2004). We collected 66 surface sediment samples (0–2 cm) from the YS and ECS inner shelf with a stainless steel box-corer during 2010 and 2011. A description of the sampling stations was shown in Fig. 1. Efforts were made to minimize disturbance of the surface sediment layers. All the samples were wrapped in aluminum foil after collection and immediately stored at 20 °C until analysis. 2.3. Sample preparation and GC/GC–MS analysis The sediments were freeze-dried and homogenized. Each sample (10.0 g) was spiked with BP as a surrogate standard. The samples were then ultrasonic extracted with n-hexane and acetone (1:1, v/v). Activated copper powder was added into the extracted samples to remove sulfur. The extract was rotary-evaporated to about 2 mL and then cleaned and fractionated on a multilayer silica alumina composite column, which consisted of 7.0 g of 5% deactivated silica gel, 7.0 g of 5% deactivated aluminum oxide,
and 2.0 g of anhydrous sodium sulfate from bottom to top. The column was pre-cleaned with 50 mL of n-hexane and the extract was eluted in sequence with 20 mL of hexane (first fraction), 40 mL of dichloromethane/hexane (3:7, v/v) (second fraction), and 50 mL n-hexane/acetone (2:8, v/v) (third fraction). The third fraction was collected and concentrated to near dryness under a gentle N2 stream and then reconstituted in 100 lL of isooctane. Prior to analysis, a certain amount of HMB was added as internal standard. NP and OP were quantified with a Shimadzu 2010 plus GC equipped with an AOC-20i auto injector, a flame ionization detector (FID) and a DB-5MS (Ultra Inert) fused silica column (30 m 0.25 mm i.d. 0.25 lm film thickness). Operating conditions of GC were as described by Li et al. (2013a). A group of the extracted samples were also detected on a HP6890 gas chromatography (GC) equipped with a HP 5973 mass selective detector and a DB-5MS fused silica capillary column (30 m 0.25 mm i.d. 0.25 lm film thickness). And there is very little interference from impurities in most of the extracted samples. Therefore, quantification of NP and OP was performed using the internal calibration method based on the data obtained by GC. The five-point calibration curves for NP and OP showed high linearity (r2 > 0.999). NP and OP concentrations were reported on a dry weight basis. 2.4. TOC and Total Nitrogen (TN) analysis As reported by Zhao et al. (2013), prior to analysis, the homogenized dry sediment samples were decalcified with 4 M HCl at room temperature for 24 h, and then rinsed with deionized water and dried in an oven at 55 °C. The TOC and TN analysis were performed using a Thermal Flash 2000 Elemental Analyzer, with standard deviations of ±0.02 wt% (n = 6) and ±0.002 wt% (n = 6), respectively. 2.5. Quality assurance/quality control Glassware and sodium sulfate were solvent-rinsed and heated 4 h at 450 °C prior to use. Reproducibility and efficiency of the analytical procedure was determined by six replicate analyses of preextracted sediments spiked with APs standards prior to ultrasonic extraction. The average recovery of NP and OP were 104.7% and 92.4%, respectively, and their RSD were 5.4% and 8.9%, respectively. For each batch of 8 samples, a procedural blank (no sediment), a spiked blank (AP directly dissolved into solvent), a matrix-spiked sample (a pre-extracted sediments spiked with AP) and a sample duplicate were processed in the same way as the sample. The surrogate recoveries for all the samples were 76.3–109.1% for BP.
3. Results 3.1. Sediments grain size and TOC 3.1.1. YS and southwestern Cheju Island TOC in surface sediments of the YS and southwestern Cheju Island mud areas ranged from 0.29% to 1.56% (dry weight) of the sediments and the mean was 0.81% (Table S1). The higher values were detected in the samples collected from the central YS mud area. The TOC distribution showed an evident increasing trend from the edge to the central zone (Fig. 2). TOC/TN ranged from 5.4 to 7.71 with a mean of 6.60 (Table S1). The sediments in the YS consisted largely of silt (4–63 lm, 27.5–78.4%) and clay (<4 lm, 11.7–33.4%). The average mud (sum of the clay and silt) content was 89.2%. There was a positive correlation between TOC and the median grain size (r2 = 0.34, p < 0.05) or mud constituents
Please cite this article in press as: Duan, X.-y., et al. Alkylphenols in surface sediments of the Yellow Sea and East China Sea inner shelf: Occurrence, distribution and fate. Chemosphere (2014), http://dx.doi.org/10.1016/j.chemosphere.2013.12.054
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Fig. 1. Location of sampling sites (dots). Circulation systems (arrows) and mud areas (in light gray) are after Liu et al. (2007) and Hu et al. (2011).
(r2 = 0.33, p < 0.05), indicating that the TOC content could be dependent on the sediment grain size.
3.1.2. ECS inner shelf TOC in surface sediments of the ECS inner shelf mud area ranged from 0.16% to 0.95% (dry weight) of the sediments and the mean was 0.62% lower than the 0.81% in central YS mud area. There was a slight increasing trend of the TOC content along the coast southward from the YR estuary (Fig. 3a). TOC/TN ranged from 5.0 to 8.0 with a mean of 6.2 which showed an decreasing trend from the north to the south (Fig. 3b). The grain size and mud content distribution showed an obvious seaward decreasing trend (Fig. 3c and d). There was a good positive correlation between TOC and the median grain size (r2 = 0.69, p < 0.05) or mud constituents (r2 = 0.65, p < 0.05).
3.2. Occurrence of NP and OP 3.2.1. YS and southwestern Cheju Island The distribution characteristic of NP and OP were shown in Fig. 4a and b, respectively. NP concentration ranged between 349.5 and 1642.8 ng/g (average 890.1 ng/g). These values were comparable to the concentrations ranged in most sediments collected within the Pearl River Delta and adjacent South China Sea (69–571 ng/g, Chen et al., 2005; 59–7808 ng/g, Chen et al., 2006), the Yellow River (38.4–863.0 ng/g, Xu et al., 2006), and in Korea’s Han River (25.4–932.0 ng/g, Li et al., 2004a), but much lower than the concentration in sediments from highly industrialized areas
such as the Korea’s Shihwa lake (0.3–31.7 lg/g; Li et al., 2004b) and rivers of Tianjin, China (4.1–9.9 lg/g, Yu et al., 2009). OP concentration ranged between 0.8 and 9.3 ng/g (average 4.7 ng/g). These values were comparable to the concentration ranged in most sediments collected within the rivers and bay of China (1–18 ng/g, Chen et al., 2005) and Korea peninsula (N.A.-11.01 ng/ g, Koh et al., 2002; 4.61 ng/g, Koh et al., 2006), and also much lower than the concentration in sediments from highly industrialized areas such as Ulsan Bay in Korea (120 ng/g, Khim et al., 2001) and Scine watershed in France (5.0–490 ng/g, Fenet et al., 2003). The ratio of w(NP)/w(OP) ranged between 56.6 and 1041.1 (average 281.7, Fig. 4c). These values were higher than the values in sediments from Pearl River estuary (18.7–138.7, Chen et al., 2005), Tokyo bay (Yamashita et al., 2000) and Ulsan bay (Khim et al., 2001). 3.2.2. ECS inner shelf The occurrence and distribution characteristic of NP and OP in the ECS inner shelf were showed in Fig. 5a and b, respectively. NP concentration ranged between 31.3 and 1423.7 ng/g (average 750.1 ng/g). These values were comparable to the concentration ranged in sediments collected in the same area as reported by Liu (116.9–559.0 ng/g; 2012). OP concentration ranged between 0.7 and 11.1 ng/g (average 5.1 ng/g). The levels of NP in the ECS inner shelf sediments were lower than in the YS sediments, while the levels of OP in the ECS inner shelf sediments were higher than in the YS sediments. The ratio of w(NP)/w(OP) ranged between 2.8 and 1001.8 (average 236.7). These values were lower than the values in sediments of the YS (average 281.7).
Please cite this article in press as: Duan, X.-y., et al. Alkylphenols in surface sediments of the Yellow Sea and East China Sea inner shelf: Occurrence, distribution and fate. Chemosphere (2014), http://dx.doi.org/10.1016/j.chemosphere.2013.12.054
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Fig. 2. Distributions of TOC content (wt%), TOC/TN, median grain size (lm) and mud proportions in the YS and southwestern Cheju Island mud areas surface sediments. The gradient distributions were calculated using Kriging by Surfer 8.0.
4. Discussion 4.1. Distribution and fate of APs in the YS and southwestern Cheju Island There was an increasing trend of NP concentration from the edge to the central areas (Fig. 4a). The highest concentration was mainly at the 35°N and 36°N sections. The NP distribution pattern was similar to that of polycyclic aromatic hydrocarbons (PAHs; Lin et al., 2011), organo-chlorine pesticides (OCPs; Hu et al., 2011) and polychlorinated biphenyls (PCBs; Duan et al., 2013a) in this area. The high NP concentration in the central YS was coupled with high TOC and mud content (Fig. 4a and Fig. 2a and d), implying that the spatial distribution of NP was constrained by the TOC and mud content of sediments. This TOC dependent post-depositional sorption environment in the YS was usually confined by the homogenous environmental conditions (Hu et al., 2011). TOC in the sediments appeared to be an important factor in controlling the fate of these compounds (Céspedes et al., 2008). Similar to other pollutants, APs can be readily adsorbed on the particulate matters due to their high hydrophobicities (Cash, 1995). As indicated by ratios of TOC/TN (<10, Fig. 2), organic matter in the YS was mainly originated from marine organism. The settling of organic carbon was the main transfer route of NP to the sediment. However, poor correlation was observed between NP concentration and TOC (R2 = 0.1266, p < 0.05).
As noted above, there is no large local coastal river that can input silt to the central mud deposits of the YS, and the YS is far from the direct sources in the Bohai Sea (Ren and Shi, 1986; Saito et al., 2001). The YS cold water mass, the YS warm current and the coastal currents dominate the regional sedimentary (Zhu and Chang, 2000; Hu et al., 2011). The hydrodynamic transportation and deposition of the fine grained sediments, as well as the potential impact of atmospheric deposition, therefore become the dominant factors in controlling the distribution and fate of NP in the YS. Large amount of nutrient elements and pollutant metals were observed to be transported into the oligotrophic central YS by atmosphere (Gao et al., 1992; Zhang and Liu, 1994; Zou et al., 2000). And it can account for a majority of the total input of inorganic elements to the YS as well as for organic pollutants (Lammel et al., 2007; Lin et al., 2011). Therefore, atmosphere deposition was probably also the most important input way for NP in the central YS. A decreasing OP concentration profile appeared following the distance from mainland increasing (Fig. 4b). And very poor correlations were observed between TOC, TOC/TN, grain size, and mud content with OP (p > 0.05) in the YS, implying that the spatial distribution of OP were not constrained by the TOC or grain size of sediments. It also demonstrated that OP is less hydrophobic than NP. Assessment of the influence of distances from land on OP concentrations provided evidence for the predominance of coastal inputs rather than long-range transport.
Please cite this article in press as: Duan, X.-y., et al. Alkylphenols in surface sediments of the Yellow Sea and East China Sea inner shelf: Occurrence, distribution and fate. Chemosphere (2014), http://dx.doi.org/10.1016/j.chemosphere.2013.12.054
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Fig. 3. Distributions of TOC content (wt%), TOC/TN, median grain size (lm) and mud proportions in the ECS inner shelf sediments. The gradient distributions were calculated using Kriging by Surfer 8.0.
The higher concentration of OP was appeared in southwestern Cheju Island mud area (Fig. 4b). In this area the sedimentary environment is mainly controlled by current, wind waves and the Yangtze diluted water (Lim et al., 2007; Youn and Kim, 2011) and the surficial sediments mainly consist of mud (Fig. 2). Unlike the central YS, this area can be significantly influenced by the Yangtze diluted water in summer (Ichikawa and Beardsley, 2002; Kim et al., 2009), and concentrations of NP and OP in river (Li et al., 2004a, 2013b; Xu et al., 2006) and municipal sewage (Li et al., 2005; Jin et al., 2008) were significantly higher in warmer seasons. As shown in Fig. 4a, there was also a decreasing trend of NP concentration with the distance from the YR Estuary increased. That would suggest that NP and OP concentrations in sediments of southwestern Cheju Island mud area were significantly influenced by Yangtze diluted water, especially for OP. And this point can be supported by the lower ratios of w(NP)/w(OP) (Fig. 4c) and the highest OP concentrations were detected in samples collected in this area (Fig. 4b). We also found that the distribution of OP in the YS has high similar characteristic to the distribution of chlorophyll concentrations and primary productivity (Son et al., 2005; Wei et al., 2008). As reported by Berrojalbiz et al. (2011a,b), marine organism played an important role for the accumulation of pollutants. The bio-concentration of phytoplankton for the less hydrophobic compounds showed maximum due to the higher freely dissolved concentration (Nizzetto et al., 2012). Dissolved OP accumulated
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by phytoplankton after discharged into ocean by river, oceanic outfalls and atmospheric deposition and then uptake by zooplankton (Dachs et al., 1999). After that, OP was settled out from the water column by adsorbed on the fecal particles and dead bodies. This means that marine organic matter (e.g. fecal pellets, dead bodies) controlled the removal of OP to coastal YS sediments. This process has also been found in Dabob Bay (Prahl and Carpenter, 1979) and Polar regions (Cropp et al., 2011). And it was powerful in accounting for the poor correlation between the contents of TOC and OP in the YS sediments. As showed in Fig. 4c, the high value of w(NP)/w(OP) was appeared at regions near the 35°N section. w(NP)/w(OP) displayed a consistent distribution trend with TOC/TN (Fig. 4c and Fig. 2b). Linear regression analyses showed that w(NP)/w(OP) in the sediments were correlated to TOC/TN with correlation coefficients of 0.3402 (p < 0.05). This indicates that the sources of the sediment organic matter (OM) plaed an important role in controlling the levels and compositions of APs in sediments. The high value of w(NP)/ w(OP) in the central YS was attributed to the different environment fate of NP and OP which were caused by the properties difference between NP and OP. OP was more readily transported by river (Johnson et al., 1998). Thus OP was enriched in the area near land (Fig. 4b) under the role of biological pump as discussed above. While a large proportion of NP were settled out from the water column to the river bed by being adsorbed on the particle surface during the transportation processes due to the higher log Kow (Cash, 1995; Bennett and Metcalfe, 1998; Ferguson et al., 2001), the concentrations of NP declined to near background levels in rivers far away cities (Bennett and Metcalfe, 2000; Gross et al., 2004). In other words, NP was hardly transported by river compared with OP. Several studies (Xie et al., 2006; Zhang et al., 2009) have demonstrated that the volatilization of NP from water surface to atmosphere played a more important role for the decline of NP concentrations in water rather than OP. This showed that NP was more readily long range transported by atmosphere and finally precipitated to the ocean by atmospheric dry and wet deposition especially during winter (Fries and Püttmann, 2004). Therefore, like other pollutants in the YS (Hu et al., 2011; Duan et al., 2013a), NP probably enters the central YS mainly by atmospheric deposition. It was difficult for OP to be transported to the areas far from land compared with NP. And this point also will be supported by the following discussion (lower ratios of w (NP)/w(OP) in ECS inner shelf sediments, Fig. 5c). 4.2. Distribution and fate of APs in the ECS inner shelf Sediments in the ECS inner shelf are strongly constrained by the YR (Yang et al., 2003; Liu et al., 2007). And then the sedimentation rate in the ECS inner shelf is much higher than in the YS (Huh and Su, 1999; Lim et al., 2007). Therefore, NP concentrations in the ECS inner shelf sediments were dragged down by large amount of suspended sediments from the YR (diluting effects). However, OP concentration was slightly higher in the ECS inner shelf sediments due to the high delivery efficiency of OP by river which caused by the higher water solubility (Johnson et al., 1998). High NP concentration was in the Coastal Mud Zone rather than in the YR estuary (Fig. 5a), which suggested the possibility of long distance transport of NP through the ECS coastal current. NP concentrations were not significantly correlated with the distance from the YR estuary and/or China mainland, indicating other factors (particle deposition rate, sediment grain size and sedimentation environment, etc.) obviously affecting the distribution pattern. Sediments particle features were showed in Fig. 3. The linearity regression analysis indicated, only TOC/TN was correlated with NP concentration (R2 = 0.1567, P < 0.05). In our previous studies, the poor correlations between sediment features and PCBs
Please cite this article in press as: Duan, X.-y., et al. Alkylphenols in surface sediments of the Yellow Sea and East China Sea inner shelf: Occurrence, distribution and fate. Chemosphere (2014), http://dx.doi.org/10.1016/j.chemosphere.2013.12.054
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Fig. 4. Distributions of NP concentration (a), OP concentration (b), the measured values were marked in the plot, ng/g dry weight) and ratio of w(NP)/w(OP) (c) in the YS and southwestern Cheju Island mud areas surface sediments. The gradient distributions were calculated using Kriging by Surfer 8.0.
Fig. 5. Distributions of NP concentration (a), OP concentration (b), the measured values were marked in the plot, ng/g dry weight) and ratio of w(NP)/w(OP) (c) in the ECS inner shelf surface sediments. The gradient distributions were calculated using Kriging by Surfer 8.0.
in sediments of the ECS inner shelf were also found because of their heterogeneous sources and sedimentary process (Duan et al., 2013b).
OP concentrations in the ECS inner shelf sediments were generally higher than in the YS sediments, and higher OP concentrations were constrained in the near-shore areas of ECS with an offshore
Please cite this article in press as: Duan, X.-y., et al. Alkylphenols in surface sediments of the Yellow Sea and East China Sea inner shelf: Occurrence, distribution and fate. Chemosphere (2014), http://dx.doi.org/10.1016/j.chemosphere.2013.12.054
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decreased trend towards the outer shelf (Fig. 5b), suggesting a direct influence of the riverine inputs and the proximity to the direct land-based sources in the coastal ECS. And a similar distribution pattern was also found in the YS, with decreasing OP levels from the edge to the central areas (Fig. 4b). Therefore, the terrestrial inputs of OP by rivers, sewage and on-water activities were appreciably greater than the other sources (such as long range atmospheric transportation). In this area, the distribution pattern of OP showed obvious source dependent characteristics. And the most interesting was that the similar distribution patterns were also presented by less hydrophobic homologues of PCBs (Duan et al., 2013b) and PAHs (Lin et al., 2013) in this area. The linearity regression analysis indicated, OP concentration was correlated with TOC (R2 = 0.2552, P < 0.05), TOC/TN (R2 = 0.2641, p < 0.05) and grain size (R2 = 0.2735, p < 0.05). And very poor correlation was found between NP concentration and TOC content or grain size. OP distribution pattern was strongly influenced by the marine organism as found in the YS and constrained by distances from land (Fig. 5). NP had stronger binding on the sediment particles than OP (Ying et al., 2003). NP was largely adsorbed by the suspended particles in the river during the transportation process (Sekela et al., 1999; Xu et al., 2006). After discharged into the ocean, NP was hardly desorption from the sediments due to the salting-out effect. And the release of NP from contaminated sediments was highly dependent on the age of sediments. Meanwhile, the aged OM has a relatively higher affinity for NP compared with freshly produced OM (Yoshida et al., 2009). Therefore, the correlation between OM and NP content was weakened by the newly joined marine OM after discharging into the ocean. However, the correlations between such less hydrophobic compound (OP) and TOC or grain size was probably caused by the rebalances under the strong disturbance condition. Another significant point to be considered was the occurrence of colloids. A large portion of those less hydrophobic components (e.g. OP) were adsorbed by colloids in river. And the adsorption of OP was enhanced in the presence of salts after discharged into ocean, due to the salting out effect (Zhou, 2006). Thus high OP level presented in the nearshore (Fig. 5b) coupled with high TOC content (Fig. 3a) and large grain size (Fig. 3c), which was attributed to the influences of riverine and coastal inputs. The ratio of w(NP)/w(OP) were lower than the values in sediments of the YS. This was probably caused by the higher water solubility of OP and shorter distances from land, and these two factors make OP easier entered the coastal region via rivers and coastal sewage discharge compared with the YS. w(NP)/w(OP) was constrained by the sources of APs. And this point was strongly supported by the significant relationship between w(NP)/w(OP) and TOC/TN (R2 = 0.5902, P < 0.05). As indicated by TOC/TN ratios (Fig. 3), OM in the ECS inner shelf was mainly originated from phytoplankton (<10, Marinari et al., 2006). Spatial distribution patterns of TOC/TN presented a decreasing trend southward along the coastline, suggesting a spreading tendency southward from the YR estuary and the north of the inner shelf. In conclusion, NP contained in the sediments of ECS inner shelf was mainly from the YR by adsorbing on the suspended particles, and the distribution pattern was dominated by the sedimentary environment. However, OP was primary discharged from coastal sources by largely adsorbed on the colloids in river, and obvious source dependent characteristic was presented.
5. Conclusions NP and OP in surface sediments of the YS and ECS inner shelf were analyzed in this paper. The main conclusions can be drawn as follows:
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In the YS surface sediments, NP concentration ranged between 349.5 and 1642.8 ng/g (average 890.1 ng/g) with an increasing trend from the edge to the central areas. The highest concentration was mainly at the 35°N and 36°N sections. OP concentration ranged between 0.8 and 9.3 ng/g (average 4.7 ng/g) with a decreasing trend from the edge to the central areas, and the highest OP levels were measured in samples collected from Cheju Island mud area. Atmospheric deposition was probably the most important route for NP in the YS, while the distance from sources was the most important factor for OP input. The Yangtze diluted water has a significant influence on NP and OP levels in Cheju Island mud area. In the ECS inner shelf surface sediments, NP concentrations ranged between 31.3 and 1423.7 ng/g (average 750.1 ng/g) and the distribution pattern was constrained by the heterogeneous sources and sedimentary process. OP concentration ranged between 0.7 and 11.1 ng/g (average 5.1 ng/g), higher levels of OP were constrained in the nearshore areas with an offshore decreased trend towards the outer shelf, suggesting a direct influence of the riverine inputs. During the transportation processes in the river, NP was largely adsorbed by the suspended particles (including colloids, but not limited to) while OP was probably mainly adsorbed by colloids in water. And marine OM played an important role for the adsorption of OP. Acknowledgments This study was supported by the National Basic Research Program of China (973 Program, Grant No. 2010CB428901). Grain size data was provided by Dr. Xiaodong Zhang (Marine Geosciences College of the Ocean University of China). We want to thank the editor and reviewers for their useful and constructive comments which significantly improved our paper. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.chemosphere. 2013.12. 054. References Bennett, E.R., Metcalfe, C.D., 1998. Distribution of alkylphenol compounds in great lakes sediments, United States and Canada. Environ. Toxicol. Chem. 17 (7), 1230–1235. Bennett, E.R., Metcalfe, C.D., 2000. Distribution of degradation products of alkylphenol ethoxylates near sewage treatment plants in the lower Great Lakes. North Am. Environ. Toxicol. Chem. 19 (4), 784–792. Berrojalbiz, N., Dachs, J., Del Vento, S., 2011a. Persistent organic pollutants in Mediterranean seawater and processes affecting their accumulation in plankton. Environ. Sci. Technol. 45, 4315–4322. Berrojalbiz, N., Dachs, J., Ojeda, M.J., Valle, M.C., 2011b. Biogeochemical and physical controls on concentrations of polycyclic aromatic hydrocarbons in water and plankton of the Mediterranean and Black Seas. Global Biogeochem. Cy. 25 (4), GB4003. http://dx.doi.org/10.1029/2010GB003775. Cash, G.G., 1995. Correlation of physicochemical properties of alkylphenols with their graph-theoretical e parameter. Chemosphere 31 (10), 4307–4315. Céspedes, R., Lacorte, S., Ginebreda, A., Barceló, D., 2008. Occurrence and fate of alkylphenols and alkylphenol ethoxylates in sewage treatment plants and impact on receiving waters along the Ter River (Catalonia, NE Spain). Environ. Pollut. 153 (2), 384–392. Chen, B., Mai, B.X., Duan, J.C., Luo, X.J., Yang, Q.S., Sheng, G.Y., Fu, J.M., 2005. Concentrations of alkylphenols in sediments from the Pearl River estuary and South China Sea, South China. Mar. Pollut. Bull. 50, 993–1018. Chen, B., Duan, J.C., Mai, B., Luo, X.J., Yang, Q.S., Sheng, G.Y., 2006. Distribution of alkylphenols in the Pearl River Delta and adjacent northern South China Sea, China. Chemosphere 63, 652–661. Cropp, R., Kerr, G., Bengtson-Nash, S., Hawker, D., 2011. A dynamic biophysical fugacity model of the movement of a persistent organic pollutant in Antarctic marine food webs. Environ. Chem. 8 (3), 263–280.. Dachs, J., Eisenreich, S.J., Baker, J.E., Ko, F.C., 1999. Coupling of phytoplankton uptake and air water exchange of persistent organic pollutants. Environ. Sci. Technol. 33 (20), 3653–3660.
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Alkylphenols in surface sediments of the Yellow Sea and East China Sea inner shelf: Occurrence, distribution and fate Xiao-yong Duan a, Yan-xia Li a,b, Xian-guo Li a,⇑, Da-hai Zhang a, Yi Gao c a
Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China Hong De School, Weifang University, Weifang 261061, China c Qingdao Municipal Drainage Monitoring Station, Qingdao 266100, China b
h i g h l i g h t s Alkylphenols in the Yellow Sea and East China Sea sediments were analyzed. Relationships between alkylphenols distributions and sources were illustrated. Environment fate of alkylphenols in the Yellow Sea and East China Sea were studied.
a r t i c l e
i n f o
Article history: Received 4 September 2013 Received in revised form 12 December 2013 Accepted 18 December 2013 Available online xxxx Keywords: Nonylphenol Octylphenol Yellow Sea East China Sea Sediment
a b s t r a c t Alkylphenols (APs) have been found as ubiquitous environmental pollutants with reproductive and developmental toxicity. In this study, APs in surface sediments of the Yellow Sea (YS) and East China Sea (ECS) inner shelf were analyzed to assess influences of riverine and atmospheric inputs of pollutants on the marine environment. NP concentrations ranged from 349.5 to 1642.8 ng/g (average 890.1 ng/g) in the YS sediments and from 31.3 to 1423.7 ng/g (average 750.1 ng/g) in the ECS inner shelf sediments. NP distribution pattern was mainly controlled by the sedimentary environment. OP concentration was 0.8– 9.3 ng/g (average 4.7 ng/g) in the YS sediments and 0.7–11.1 ng/g (average 5.1 ng/g) in the ECS sediments. Assessment of the influence of distances from land on OP concentrations provided evidence for the predominance of coastal riverine and/or atmospheric inputs rather than long-range transport. And the biological pump may play an important role for sequestration of OP in the nearshore area. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction Nonylphenol (NP) and octylphenol (OP) have been extensively used in the manufacture of nonionic surfactants (alkylphenol ethoxylates, APEOs) since 1940s (White et al., 1994). Nonylphenol polyeothoxylates (NPEOs) and octylphenol polyeothoxylates (OPEOs) respectively account for about 80% and 20% of total APEOs (Ying et al., 2002). Annual global production of APEOs was over 500,000 tons in 1997 (Ying et al., 2002), and production continues to rise in recent years. Along with a great deal of sewage and garbage being increasingly drained into the sea (Hawrelak et al., 1999; Céspedes et al., 2008), a large portion of APEOs is released into the environment and finally ends up in the aquatic environment (Renner, 1997; Solé et al., 2000). APEOs are unstable in aquatic environments with a half-life of several days and are subject to degradation to alkylphenols (APs) through bio- and photo-degradation (Li et al., 2013a). However, the degradation products, NP ⇑ Corresponding author. Tel.: +86 532 66782215. E-mail address: [email protected] (X.-g. Li).
and OP, are much more stable in the environment with a half-life of several decades in sediments (Isobe et al., 2001). Therefore, NP and OP are ubiquitous in the general environment, especially rich in the sphere around city and factory (Ying et al., 2002; Ying, 2006; Soares et al., 2008). Due to the harmful effects of NP and OP in the environment, the use and production of such compounds have been banned or strictly monitored in many countries (Soares et al., 2008). But up to now, APs are still widely used in China and the Korean peninsula. And with the development of economy, pollution caused by APs becomes clinically evident. As reported by Peng et al. (2007) and Hong et al. (2010), the levels of NP have increased sharply in recent decades in sediments of China’s Pearl River estuary (Peng et al., 2007) and Korea’s Lake Shihwa (Hong et al., 2010). A large proportion of released pollutants from man-made sources will ultimately sink to continental shelf sediments (Jönsson et al., 2003; Huang et al., 2007). And the Yellow Sea (YS) and the East China Sea (ECS) inner shelf are considered as important sinks of pollutants originated from land-based pollution sources (Duan et al., 2013a,b; Li and Dag, 2004).
0045-6535/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.chemosphere.2013.12.054
Please cite this article in press as: Duan, X.-y., et al. Alkylphenols in surface sediments of the Yellow Sea and East China Sea inner shelf: Occurrence, distribution and fate. Chemosphere (2014), http://dx.doi.org/10.1016/j.chemosphere.2013.12.054
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Thus, in order to assess the impacts of anthropogenic activities on the YS and ECS inner shelf, it is necessary to determine the levels of current sediment contaminants. Despite a few studies (Li et al., 2005; Fu et al., 2007; Hong et al., 2010; Wang et al., 2010) regarding AP levels in coast of the YS, our understanding on the occurrence and fate of AP in the YS and ECS is very limited. In this work, 66 surface sediment samples were collected from the YS and ECS inner shelf to demonstrate the spatial distribution of NP and OP and to study their fate in marine sediments in this region. 2. Materials and methods 2.1. Standards and reagents 4-Nonylphenol (NP, technical mixture) was purchased from Tokyo Chemical Industry. 4-tert-octylphenol (OP), internal standard hexa-methyl benzene (HMB) and surrogate standard 4-tertbutylphenol (BP) were purchased from Dr. Ehrenstorfer GmbH. NP consists of 11 isomer peaks due to various branched structures in the standard which was quantified by using the sum of all peak areas. 2.2. Sampling area and sample collection The YS, a typical semi-enclosed epicontinental sea, is an important storage sink of terrestrial matter from mainland China and the Korean peninsula. Many rivers (exclude the Yellow River and Yangtze River) drain directly into the YS. While most of the mud deposits in the central YS are considered to be derived primarily from the Yellow River and old Yellow River subaqueous delta based on the circulation pattern in the central YS. (Lee and Chough, 1989; Yang et al., 2003; Yang and Youn, 2007). And under the control of cyclonic circulation and cold water gyre, the sedimentary environment is relatively stable in the YS. The muddy sediments in southwestern Cheju Island were derived from diverse sources (Including the Yangtze River and Yellow River, Yang et al., 2004; Yang and Youn, 2007). The oceanographic conditions (especially oceanic circulation patterns) greatly constrain sediments distributions in this unique epicontinental sea (Hu et al., 2011). The ECS is a typical Western Pacific marginal sea, with the world’s broadest continental shelf. Most of the suspended particulate matters discharged from the Yangtze River (YR) are ultimately deposited in the YR estuary; 20–30% of them move to the south with the coastal current and are finally buried in the inner shelf of ECS, forming a ribbon of mud areas (Liu et al., 2007). Thus the YS and ECS inner shelf are considered as important sink of pollutants originated from land-based pollution sources (Duan et al., 2013a,b; Li and Dag, 2004). We collected 66 surface sediment samples (0–2 cm) from the YS and ECS inner shelf with a stainless steel box-corer during 2010 and 2011. A description of the sampling stations was shown in Fig. 1. Efforts were made to minimize disturbance of the surface sediment layers. All the samples were wrapped in aluminum foil after collection and immediately stored at 20 °C until analysis. 2.3. Sample preparation and GC/GC–MS analysis The sediments were freeze-dried and homogenized. Each sample (10.0 g) was spiked with BP as a surrogate standard. The samples were then ultrasonic extracted with n-hexane and acetone (1:1, v/v). Activated copper powder was added into the extracted samples to remove sulfur. The extract was rotary-evaporated to about 2 mL and then cleaned and fractionated on a multilayer silica alumina composite column, which consisted of 7.0 g of 5% deactivated silica gel, 7.0 g of 5% deactivated aluminum oxide,
and 2.0 g of anhydrous sodium sulfate from bottom to top. The column was pre-cleaned with 50 mL of n-hexane and the extract was eluted in sequence with 20 mL of hexane (first fraction), 40 mL of dichloromethane/hexane (3:7, v/v) (second fraction), and 50 mL n-hexane/acetone (2:8, v/v) (third fraction). The third fraction was collected and concentrated to near dryness under a gentle N2 stream and then reconstituted in 100 lL of isooctane. Prior to analysis, a certain amount of HMB was added as internal standard. NP and OP were quantified with a Shimadzu 2010 plus GC equipped with an AOC-20i auto injector, a flame ionization detector (FID) and a DB-5MS (Ultra Inert) fused silica column (30 m 0.25 mm i.d. 0.25 lm film thickness). Operating conditions of GC were as described by Li et al. (2013a). A group of the extracted samples were also detected on a HP6890 gas chromatography (GC) equipped with a HP 5973 mass selective detector and a DB-5MS fused silica capillary column (30 m 0.25 mm i.d. 0.25 lm film thickness). And there is very little interference from impurities in most of the extracted samples. Therefore, quantification of NP and OP was performed using the internal calibration method based on the data obtained by GC. The five-point calibration curves for NP and OP showed high linearity (r2 > 0.999). NP and OP concentrations were reported on a dry weight basis. 2.4. TOC and Total Nitrogen (TN) analysis As reported by Zhao et al. (2013), prior to analysis, the homogenized dry sediment samples were decalcified with 4 M HCl at room temperature for 24 h, and then rinsed with deionized water and dried in an oven at 55 °C. The TOC and TN analysis were performed using a Thermal Flash 2000 Elemental Analyzer, with standard deviations of ±0.02 wt% (n = 6) and ±0.002 wt% (n = 6), respectively. 2.5. Quality assurance/quality control Glassware and sodium sulfate were solvent-rinsed and heated 4 h at 450 °C prior to use. Reproducibility and efficiency of the analytical procedure was determined by six replicate analyses of preextracted sediments spiked with APs standards prior to ultrasonic extraction. The average recovery of NP and OP were 104.7% and 92.4%, respectively, and their RSD were 5.4% and 8.9%, respectively. For each batch of 8 samples, a procedural blank (no sediment), a spiked blank (AP directly dissolved into solvent), a matrix-spiked sample (a pre-extracted sediments spiked with AP) and a sample duplicate were processed in the same way as the sample. The surrogate recoveries for all the samples were 76.3–109.1% for BP.
3. Results 3.1. Sediments grain size and TOC 3.1.1. YS and southwestern Cheju Island TOC in surface sediments of the YS and southwestern Cheju Island mud areas ranged from 0.29% to 1.56% (dry weight) of the sediments and the mean was 0.81% (Table S1). The higher values were detected in the samples collected from the central YS mud area. The TOC distribution showed an evident increasing trend from the edge to the central zone (Fig. 2). TOC/TN ranged from 5.4 to 7.71 with a mean of 6.60 (Table S1). The sediments in the YS consisted largely of silt (4–63 lm, 27.5–78.4%) and clay (<4 lm, 11.7–33.4%). The average mud (sum of the clay and silt) content was 89.2%. There was a positive correlation between TOC and the median grain size (r2 = 0.34, p < 0.05) or mud constituents
Please cite this article in press as: Duan, X.-y., et al. Alkylphenols in surface sediments of the Yellow Sea and East China Sea inner shelf: Occurrence, distribution and fate. Chemosphere (2014), http://dx.doi.org/10.1016/j.chemosphere.2013.12.054
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Fig. 1. Location of sampling sites (dots). Circulation systems (arrows) and mud areas (in light gray) are after Liu et al. (2007) and Hu et al. (2011).
(r2 = 0.33, p < 0.05), indicating that the TOC content could be dependent on the sediment grain size.
3.1.2. ECS inner shelf TOC in surface sediments of the ECS inner shelf mud area ranged from 0.16% to 0.95% (dry weight) of the sediments and the mean was 0.62% lower than the 0.81% in central YS mud area. There was a slight increasing trend of the TOC content along the coast southward from the YR estuary (Fig. 3a). TOC/TN ranged from 5.0 to 8.0 with a mean of 6.2 which showed an decreasing trend from the north to the south (Fig. 3b). The grain size and mud content distribution showed an obvious seaward decreasing trend (Fig. 3c and d). There was a good positive correlation between TOC and the median grain size (r2 = 0.69, p < 0.05) or mud constituents (r2 = 0.65, p < 0.05).
3.2. Occurrence of NP and OP 3.2.1. YS and southwestern Cheju Island The distribution characteristic of NP and OP were shown in Fig. 4a and b, respectively. NP concentration ranged between 349.5 and 1642.8 ng/g (average 890.1 ng/g). These values were comparable to the concentrations ranged in most sediments collected within the Pearl River Delta and adjacent South China Sea (69–571 ng/g, Chen et al., 2005; 59–7808 ng/g, Chen et al., 2006), the Yellow River (38.4–863.0 ng/g, Xu et al., 2006), and in Korea’s Han River (25.4–932.0 ng/g, Li et al., 2004a), but much lower than the concentration in sediments from highly industrialized areas
such as the Korea’s Shihwa lake (0.3–31.7 lg/g; Li et al., 2004b) and rivers of Tianjin, China (4.1–9.9 lg/g, Yu et al., 2009). OP concentration ranged between 0.8 and 9.3 ng/g (average 4.7 ng/g). These values were comparable to the concentration ranged in most sediments collected within the rivers and bay of China (1–18 ng/g, Chen et al., 2005) and Korea peninsula (N.A.-11.01 ng/ g, Koh et al., 2002; 4.61 ng/g, Koh et al., 2006), and also much lower than the concentration in sediments from highly industrialized areas such as Ulsan Bay in Korea (120 ng/g, Khim et al., 2001) and Scine watershed in France (5.0–490 ng/g, Fenet et al., 2003). The ratio of w(NP)/w(OP) ranged between 56.6 and 1041.1 (average 281.7, Fig. 4c). These values were higher than the values in sediments from Pearl River estuary (18.7–138.7, Chen et al., 2005), Tokyo bay (Yamashita et al., 2000) and Ulsan bay (Khim et al., 2001). 3.2.2. ECS inner shelf The occurrence and distribution characteristic of NP and OP in the ECS inner shelf were showed in Fig. 5a and b, respectively. NP concentration ranged between 31.3 and 1423.7 ng/g (average 750.1 ng/g). These values were comparable to the concentration ranged in sediments collected in the same area as reported by Liu (116.9–559.0 ng/g; 2012). OP concentration ranged between 0.7 and 11.1 ng/g (average 5.1 ng/g). The levels of NP in the ECS inner shelf sediments were lower than in the YS sediments, while the levels of OP in the ECS inner shelf sediments were higher than in the YS sediments. The ratio of w(NP)/w(OP) ranged between 2.8 and 1001.8 (average 236.7). These values were lower than the values in sediments of the YS (average 281.7).
Please cite this article in press as: Duan, X.-y., et al. Alkylphenols in surface sediments of the Yellow Sea and East China Sea inner shelf: Occurrence, distribution and fate. Chemosphere (2014), http://dx.doi.org/10.1016/j.chemosphere.2013.12.054
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Fig. 2. Distributions of TOC content (wt%), TOC/TN, median grain size (lm) and mud proportions in the YS and southwestern Cheju Island mud areas surface sediments. The gradient distributions were calculated using Kriging by Surfer 8.0.
4. Discussion 4.1. Distribution and fate of APs in the YS and southwestern Cheju Island There was an increasing trend of NP concentration from the edge to the central areas (Fig. 4a). The highest concentration was mainly at the 35°N and 36°N sections. The NP distribution pattern was similar to that of polycyclic aromatic hydrocarbons (PAHs; Lin et al., 2011), organo-chlorine pesticides (OCPs; Hu et al., 2011) and polychlorinated biphenyls (PCBs; Duan et al., 2013a) in this area. The high NP concentration in the central YS was coupled with high TOC and mud content (Fig. 4a and Fig. 2a and d), implying that the spatial distribution of NP was constrained by the TOC and mud content of sediments. This TOC dependent post-depositional sorption environment in the YS was usually confined by the homogenous environmental conditions (Hu et al., 2011). TOC in the sediments appeared to be an important factor in controlling the fate of these compounds (Céspedes et al., 2008). Similar to other pollutants, APs can be readily adsorbed on the particulate matters due to their high hydrophobicities (Cash, 1995). As indicated by ratios of TOC/TN (<10, Fig. 2), organic matter in the YS was mainly originated from marine organism. The settling of organic carbon was the main transfer route of NP to the sediment. However, poor correlation was observed between NP concentration and TOC (R2 = 0.1266, p < 0.05).
As noted above, there is no large local coastal river that can input silt to the central mud deposits of the YS, and the YS is far from the direct sources in the Bohai Sea (Ren and Shi, 1986; Saito et al., 2001). The YS cold water mass, the YS warm current and the coastal currents dominate the regional sedimentary (Zhu and Chang, 2000; Hu et al., 2011). The hydrodynamic transportation and deposition of the fine grained sediments, as well as the potential impact of atmospheric deposition, therefore become the dominant factors in controlling the distribution and fate of NP in the YS. Large amount of nutrient elements and pollutant metals were observed to be transported into the oligotrophic central YS by atmosphere (Gao et al., 1992; Zhang and Liu, 1994; Zou et al., 2000). And it can account for a majority of the total input of inorganic elements to the YS as well as for organic pollutants (Lammel et al., 2007; Lin et al., 2011). Therefore, atmosphere deposition was probably also the most important input way for NP in the central YS. A decreasing OP concentration profile appeared following the distance from mainland increasing (Fig. 4b). And very poor correlations were observed between TOC, TOC/TN, grain size, and mud content with OP (p > 0.05) in the YS, implying that the spatial distribution of OP were not constrained by the TOC or grain size of sediments. It also demonstrated that OP is less hydrophobic than NP. Assessment of the influence of distances from land on OP concentrations provided evidence for the predominance of coastal inputs rather than long-range transport.
Please cite this article in press as: Duan, X.-y., et al. Alkylphenols in surface sediments of the Yellow Sea and East China Sea inner shelf: Occurrence, distribution and fate. Chemosphere (2014), http://dx.doi.org/10.1016/j.chemosphere.2013.12.054
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Fig. 3. Distributions of TOC content (wt%), TOC/TN, median grain size (lm) and mud proportions in the ECS inner shelf sediments. The gradient distributions were calculated using Kriging by Surfer 8.0.
The higher concentration of OP was appeared in southwestern Cheju Island mud area (Fig. 4b). In this area the sedimentary environment is mainly controlled by current, wind waves and the Yangtze diluted water (Lim et al., 2007; Youn and Kim, 2011) and the surficial sediments mainly consist of mud (Fig. 2). Unlike the central YS, this area can be significantly influenced by the Yangtze diluted water in summer (Ichikawa and Beardsley, 2002; Kim et al., 2009), and concentrations of NP and OP in river (Li et al., 2004a, 2013b; Xu et al., 2006) and municipal sewage (Li et al., 2005; Jin et al., 2008) were significantly higher in warmer seasons. As shown in Fig. 4a, there was also a decreasing trend of NP concentration with the distance from the YR Estuary increased. That would suggest that NP and OP concentrations in sediments of southwestern Cheju Island mud area were significantly influenced by Yangtze diluted water, especially for OP. And this point can be supported by the lower ratios of w(NP)/w(OP) (Fig. 4c) and the highest OP concentrations were detected in samples collected in this area (Fig. 4b). We also found that the distribution of OP in the YS has high similar characteristic to the distribution of chlorophyll concentrations and primary productivity (Son et al., 2005; Wei et al., 2008). As reported by Berrojalbiz et al. (2011a,b), marine organism played an important role for the accumulation of pollutants. The bio-concentration of phytoplankton for the less hydrophobic compounds showed maximum due to the higher freely dissolved concentration (Nizzetto et al., 2012). Dissolved OP accumulated
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by phytoplankton after discharged into ocean by river, oceanic outfalls and atmospheric deposition and then uptake by zooplankton (Dachs et al., 1999). After that, OP was settled out from the water column by adsorbed on the fecal particles and dead bodies. This means that marine organic matter (e.g. fecal pellets, dead bodies) controlled the removal of OP to coastal YS sediments. This process has also been found in Dabob Bay (Prahl and Carpenter, 1979) and Polar regions (Cropp et al., 2011). And it was powerful in accounting for the poor correlation between the contents of TOC and OP in the YS sediments. As showed in Fig. 4c, the high value of w(NP)/w(OP) was appeared at regions near the 35°N section. w(NP)/w(OP) displayed a consistent distribution trend with TOC/TN (Fig. 4c and Fig. 2b). Linear regression analyses showed that w(NP)/w(OP) in the sediments were correlated to TOC/TN with correlation coefficients of 0.3402 (p < 0.05). This indicates that the sources of the sediment organic matter (OM) plaed an important role in controlling the levels and compositions of APs in sediments. The high value of w(NP)/ w(OP) in the central YS was attributed to the different environment fate of NP and OP which were caused by the properties difference between NP and OP. OP was more readily transported by river (Johnson et al., 1998). Thus OP was enriched in the area near land (Fig. 4b) under the role of biological pump as discussed above. While a large proportion of NP were settled out from the water column to the river bed by being adsorbed on the particle surface during the transportation processes due to the higher log Kow (Cash, 1995; Bennett and Metcalfe, 1998; Ferguson et al., 2001), the concentrations of NP declined to near background levels in rivers far away cities (Bennett and Metcalfe, 2000; Gross et al., 2004). In other words, NP was hardly transported by river compared with OP. Several studies (Xie et al., 2006; Zhang et al., 2009) have demonstrated that the volatilization of NP from water surface to atmosphere played a more important role for the decline of NP concentrations in water rather than OP. This showed that NP was more readily long range transported by atmosphere and finally precipitated to the ocean by atmospheric dry and wet deposition especially during winter (Fries and Püttmann, 2004). Therefore, like other pollutants in the YS (Hu et al., 2011; Duan et al., 2013a), NP probably enters the central YS mainly by atmospheric deposition. It was difficult for OP to be transported to the areas far from land compared with NP. And this point also will be supported by the following discussion (lower ratios of w (NP)/w(OP) in ECS inner shelf sediments, Fig. 5c). 4.2. Distribution and fate of APs in the ECS inner shelf Sediments in the ECS inner shelf are strongly constrained by the YR (Yang et al., 2003; Liu et al., 2007). And then the sedimentation rate in the ECS inner shelf is much higher than in the YS (Huh and Su, 1999; Lim et al., 2007). Therefore, NP concentrations in the ECS inner shelf sediments were dragged down by large amount of suspended sediments from the YR (diluting effects). However, OP concentration was slightly higher in the ECS inner shelf sediments due to the high delivery efficiency of OP by river which caused by the higher water solubility (Johnson et al., 1998). High NP concentration was in the Coastal Mud Zone rather than in the YR estuary (Fig. 5a), which suggested the possibility of long distance transport of NP through the ECS coastal current. NP concentrations were not significantly correlated with the distance from the YR estuary and/or China mainland, indicating other factors (particle deposition rate, sediment grain size and sedimentation environment, etc.) obviously affecting the distribution pattern. Sediments particle features were showed in Fig. 3. The linearity regression analysis indicated, only TOC/TN was correlated with NP concentration (R2 = 0.1567, P < 0.05). In our previous studies, the poor correlations between sediment features and PCBs
Please cite this article in press as: Duan, X.-y., et al. Alkylphenols in surface sediments of the Yellow Sea and East China Sea inner shelf: Occurrence, distribution and fate. Chemosphere (2014), http://dx.doi.org/10.1016/j.chemosphere.2013.12.054
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Fig. 4. Distributions of NP concentration (a), OP concentration (b), the measured values were marked in the plot, ng/g dry weight) and ratio of w(NP)/w(OP) (c) in the YS and southwestern Cheju Island mud areas surface sediments. The gradient distributions were calculated using Kriging by Surfer 8.0.
Fig. 5. Distributions of NP concentration (a), OP concentration (b), the measured values were marked in the plot, ng/g dry weight) and ratio of w(NP)/w(OP) (c) in the ECS inner shelf surface sediments. The gradient distributions were calculated using Kriging by Surfer 8.0.
in sediments of the ECS inner shelf were also found because of their heterogeneous sources and sedimentary process (Duan et al., 2013b).
OP concentrations in the ECS inner shelf sediments were generally higher than in the YS sediments, and higher OP concentrations were constrained in the near-shore areas of ECS with an offshore
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decreased trend towards the outer shelf (Fig. 5b), suggesting a direct influence of the riverine inputs and the proximity to the direct land-based sources in the coastal ECS. And a similar distribution pattern was also found in the YS, with decreasing OP levels from the edge to the central areas (Fig. 4b). Therefore, the terrestrial inputs of OP by rivers, sewage and on-water activities were appreciably greater than the other sources (such as long range atmospheric transportation). In this area, the distribution pattern of OP showed obvious source dependent characteristics. And the most interesting was that the similar distribution patterns were also presented by less hydrophobic homologues of PCBs (Duan et al., 2013b) and PAHs (Lin et al., 2013) in this area. The linearity regression analysis indicated, OP concentration was correlated with TOC (R2 = 0.2552, P < 0.05), TOC/TN (R2 = 0.2641, p < 0.05) and grain size (R2 = 0.2735, p < 0.05). And very poor correlation was found between NP concentration and TOC content or grain size. OP distribution pattern was strongly influenced by the marine organism as found in the YS and constrained by distances from land (Fig. 5). NP had stronger binding on the sediment particles than OP (Ying et al., 2003). NP was largely adsorbed by the suspended particles in the river during the transportation process (Sekela et al., 1999; Xu et al., 2006). After discharged into the ocean, NP was hardly desorption from the sediments due to the salting-out effect. And the release of NP from contaminated sediments was highly dependent on the age of sediments. Meanwhile, the aged OM has a relatively higher affinity for NP compared with freshly produced OM (Yoshida et al., 2009). Therefore, the correlation between OM and NP content was weakened by the newly joined marine OM after discharging into the ocean. However, the correlations between such less hydrophobic compound (OP) and TOC or grain size was probably caused by the rebalances under the strong disturbance condition. Another significant point to be considered was the occurrence of colloids. A large portion of those less hydrophobic components (e.g. OP) were adsorbed by colloids in river. And the adsorption of OP was enhanced in the presence of salts after discharged into ocean, due to the salting out effect (Zhou, 2006). Thus high OP level presented in the nearshore (Fig. 5b) coupled with high TOC content (Fig. 3a) and large grain size (Fig. 3c), which was attributed to the influences of riverine and coastal inputs. The ratio of w(NP)/w(OP) were lower than the values in sediments of the YS. This was probably caused by the higher water solubility of OP and shorter distances from land, and these two factors make OP easier entered the coastal region via rivers and coastal sewage discharge compared with the YS. w(NP)/w(OP) was constrained by the sources of APs. And this point was strongly supported by the significant relationship between w(NP)/w(OP) and TOC/TN (R2 = 0.5902, P < 0.05). As indicated by TOC/TN ratios (Fig. 3), OM in the ECS inner shelf was mainly originated from phytoplankton (<10, Marinari et al., 2006). Spatial distribution patterns of TOC/TN presented a decreasing trend southward along the coastline, suggesting a spreading tendency southward from the YR estuary and the north of the inner shelf. In conclusion, NP contained in the sediments of ECS inner shelf was mainly from the YR by adsorbing on the suspended particles, and the distribution pattern was dominated by the sedimentary environment. However, OP was primary discharged from coastal sources by largely adsorbed on the colloids in river, and obvious source dependent characteristic was presented.
5. Conclusions NP and OP in surface sediments of the YS and ECS inner shelf were analyzed in this paper. The main conclusions can be drawn as follows:
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In the YS surface sediments, NP concentration ranged between 349.5 and 1642.8 ng/g (average 890.1 ng/g) with an increasing trend from the edge to the central areas. The highest concentration was mainly at the 35°N and 36°N sections. OP concentration ranged between 0.8 and 9.3 ng/g (average 4.7 ng/g) with a decreasing trend from the edge to the central areas, and the highest OP levels were measured in samples collected from Cheju Island mud area. Atmospheric deposition was probably the most important route for NP in the YS, while the distance from sources was the most important factor for OP input. The Yangtze diluted water has a significant influence on NP and OP levels in Cheju Island mud area. In the ECS inner shelf surface sediments, NP concentrations ranged between 31.3 and 1423.7 ng/g (average 750.1 ng/g) and the distribution pattern was constrained by the heterogeneous sources and sedimentary process. OP concentration ranged between 0.7 and 11.1 ng/g (average 5.1 ng/g), higher levels of OP were constrained in the nearshore areas with an offshore decreased trend towards the outer shelf, suggesting a direct influence of the riverine inputs. During the transportation processes in the river, NP was largely adsorbed by the suspended particles (including colloids, but not limited to) while OP was probably mainly adsorbed by colloids in water. And marine OM played an important role for the adsorption of OP. Acknowledgments This study was supported by the National Basic Research Program of China (973 Program, Grant No. 2010CB428901). Grain size data was provided by Dr. Xiaodong Zhang (Marine Geosciences College of the Ocean University of China). We want to thank the editor and reviewers for their useful and constructive comments which significantly improved our paper. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.chemosphere. 2013.12. 054. References Bennett, E.R., Metcalfe, C.D., 1998. Distribution of alkylphenol compounds in great lakes sediments, United States and Canada. Environ. Toxicol. Chem. 17 (7), 1230–1235. Bennett, E.R., Metcalfe, C.D., 2000. Distribution of degradation products of alkylphenol ethoxylates near sewage treatment plants in the lower Great Lakes. North Am. Environ. Toxicol. Chem. 19 (4), 784–792. Berrojalbiz, N., Dachs, J., Del Vento, S., 2011a. Persistent organic pollutants in Mediterranean seawater and processes affecting their accumulation in plankton. Environ. Sci. Technol. 45, 4315–4322. Berrojalbiz, N., Dachs, J., Ojeda, M.J., Valle, M.C., 2011b. Biogeochemical and physical controls on concentrations of polycyclic aromatic hydrocarbons in water and plankton of the Mediterranean and Black Seas. Global Biogeochem. Cy. 25 (4), GB4003. http://dx.doi.org/10.1029/2010GB003775. Cash, G.G., 1995. Correlation of physicochemical properties of alkylphenols with their graph-theoretical e parameter. Chemosphere 31 (10), 4307–4315. Céspedes, R., Lacorte, S., Ginebreda, A., Barceló, D., 2008. Occurrence and fate of alkylphenols and alkylphenol ethoxylates in sewage treatment plants and impact on receiving waters along the Ter River (Catalonia, NE Spain). Environ. Pollut. 153 (2), 384–392. Chen, B., Mai, B.X., Duan, J.C., Luo, X.J., Yang, Q.S., Sheng, G.Y., Fu, J.M., 2005. Concentrations of alkylphenols in sediments from the Pearl River estuary and South China Sea, South China. Mar. Pollut. Bull. 50, 993–1018. Chen, B., Duan, J.C., Mai, B., Luo, X.J., Yang, Q.S., Sheng, G.Y., 2006. Distribution of alkylphenols in the Pearl River Delta and adjacent northern South China Sea, China. Chemosphere 63, 652–661. Cropp, R., Kerr, G., Bengtson-Nash, S., Hawker, D., 2011. A dynamic biophysical fugacity model of the movement of a persistent organic pollutant in Antarctic marine food webs. Environ. Chem. 8 (3), 263–280.
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Please cite this article in press as: Duan, X.-y., et al. Alkylphenols in surface sediments of the Yellow Sea and East China Sea inner shelf: Occurrence, distribution and fate. Chemosphere (2014), http://dx.doi.org/10.1016/j.chemosphere.2013.12.054