The influence of facility agriculture production on phthalate esters distribution in black soils of northeast China

Science of the Total Environment 506–507 (2015) 118–125

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The influence of facility agriculture production on phthalate esters distribution in black soils of northeast China Ying Zhang ⁎, Pengjie Wang, Lei Wang, Guoqiang Sun, Jiaying Zhao, Hui Zhang, Na Du School of Resources & Environment, Northeast Agricultural University, Harbin 150030, PR China

H I G H L I G H T S

G R A P H I C A L

A B S T R A C T

• DEHP, DBP, DEP, and DMP were the main PAE contaminants in the black soil region studied. • Facility agriculture black soils in northeast China shows higher pollution situation. • Utilization of mulching film and increase in fertilizer usage increased soil PAEs in summer. • Significant difference existed in the concentration of PAEs with different seasons.

a r t i c l e

i n f o

Article history: Received 24 June 2014 Received in revised form 21 October 2014 Accepted 21 October 2014 Available online xxxx Editor: Kevin V. Thomas Keywords: Phthalate ester Facility agriculture Black soil Agricultural production Seasons

a b s t r a c t The current study investigates the existence of 15 phthalate esters (PAEs) in surface soils (27 samples) collected from 9 different facility agriculture sites in the black soil region of northeast China, during the process of agricultural production (comprising only three seasons spring, summer and autumn). Concentrations of the 15 PAEs detected significantly varied from spring to autumn and their values ranged from 1.37 to 4.90 mg/kg-dw, with a median value of 2.83 mg/kg-dw. The highest concentration of the 15 PAEs (4.90 mg/kg-dw) was determined in summer when mulching film was used in the greenhouses. Probably an increase in environmental temperature was a major reason for PAE transfer from the mulching film into the soil and coupled with the increased usage of chemical fertilizers in greenhouses. Results showed that of the 15 PAEs, di(2-ethylhexyl) phthalate(DEHP), di-n-butyl phthalate (DBP), diethyl phthalate (DEP) and dimethyl phthalate (DMP) were in abundance with the mean value of 1.12 ± 0.22, 0.46 ± 0.05, 0.36 ± 0.04, and 0.17 ± 0.01 mg/kg-dw, respectively; and their average contributions in spring, summer, and autumn ranged between 64.08 and 90.51% among the 15 PAEs. The results of Principal Component Analysis (PCA) indicated the concentration of these four main PAEs significantly differed among the facility agricultures investigated, during the process of agricultural production. In comparison with foreign and domestic results of previous researches, it is proved that the black soils of facility agriculture in northeast China show higher pollution situation comparing with nonfacility agriculture soils. © 2014 Elsevier B.V. All rights reserved.

⁎ Corresponding author. Tel.: +86 451 5519 0993; fax: +86 451 5519 1170. E-mail address: [email protected] (Y. Zhang).

http://dx.doi.org/10.1016/j.scitotenv.2014.10.075 0048-9697/© 2014 Elsevier B.V. All rights reserved.

Y. Zhang et al. / Science of the Total Environment 506–507 (2015) 118–125

1. Introduction Phthalate esters (PAEs) are the main components of plastic products which are being used as plasticizers and to improve the softness and flexibility of poly vinyl chloride (PVC), rubber, cellulose and styrene materials (Wang et al., 2013; Qureshi et al., 2013). PAEs are studied as hazardous substances and their presence in soil can be of possible threat to human beings and wildlife by different paths (Guo and Kannan, 2011). The potential routes of human exposure to phthalates are inhalation, skin absorption, dietary intake and so on (Guo and Kannan, 2011; Schettler, 2006; Wormuth et al., 2006). Current study reported that PAEs have estrogenic effects on animals and human as mentioned earlier that they can interfere with the endocrine system and procreation ability (Duty et al., 2003; Moore, 2000; Higuchi et al., 2003). Rising plastic industries are producing many common agricultural plastic films to use in on-site agricultural activities; but the subsequent environmental and associated human health problems cannot be ignored. PAEs as plasticizers have good inter-miscibility in plastic products, and plastics. Chemically, they did not form a covalent bond with plastic substrates; rather they are linked together by the hydrogen bond and van der Waal force. Hence, with the passage of time these PAEs are readily migrated into the soil (Chen et al., 2011; Kong et al., 2012). Consequently, the phthalate molecules are able to drift from the soil into other spheres of the ecosystem (Kong et al., 2013; Yin et al., 2003). In China, plasticizer production level for the years 2006 and 2007 reached up to 1.25 and 1.45 million tons, respectively (Xu et al., 2008); and in 2011 it was marked up to 2.2 million tons, most of which were used in the plastic film production (CPPIU, 2011). In early 2004, the global production of PAEs reached about 6 million tons (Xu et al., 2008); hence the PAEs were enlisted as the most potential pollutants. The use of polyvinyl chloride (PVC) as greenhouse film, especially in mulching materials, is about 50 000 tons per annum in northeast China. PVC contents were about 20–30% in actual manufacturing of agricultural films, but for more flexibility of the material it is usually increased up to 60% of the final product (Chen et al., 2011; Liu et al., 2010a). As the utility of mulch material increases in per agricultural production year, there is an increase in the pollution level, which affects the quality of agricultural production (Chen et al., 2011; Fu et al., 2011). PAE pollution has become a serious issue in the field of environmental researches. Many researchers have reported the presence of PAEs in different mediums such as the atmosphere (Kong et al., 2013; Wang et al., 2012), surface water and sediments (Srivastava et al., 2010), sewage sludge (Cai et al., 2007), and in soil (Wang et al., 2013; Kong et al., 2012; Yin et al., 2003; Zeng et al., 2009). Detected PAE concentrations in these mediums were noted to be higher than those reported in the Netherlands and Denmark (Zeng et al., 2009). PAE contaminations have been reported to be higher in China than in US (Cui et al., 2010); similarly, when compared with other parts of the world, PAE pollution in China was reported to be relatively severe (Zeng et al., 2008a, 2009). Different studies investigated the soil PAE contamination in the east, south, southwest, north, northwest and northeast regions of China (Hu et al., 2003), Tianjin (Liu et al., 2010b), Guangzhou (Zeng et al., 2009), Handan (Xu et al., 2008), Hangzhou (Chen et al., 2011). According to different researches of soil PAE analysis from different regions, DEHP and DnBP detection was high; while DMP, DEP, BBP and DnOP detection was relatively low (Cui et al., 2010). Although there already exist many researches focusing on PAE concentration in the environment, yet only a few reports are available on the PAE content in facility agriculture soils (Wang et al., 2013; Chen et al., 2011), As per our knowledge and information, there has not been any study conducted on the black soils of facility agriculture in northeast China, especially during the periods of agricultural production. The aims and objectives of this study were to investigate the PAE concentration of black soils (0–20 cm) collected from different locations in northeast China, and to discuss the contamination profiles with seasonal variation characteristics. This study will provide a reliable

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data set for soil bioremediation and risk assessment of the facility agriculture soil of the northeast, and will encourage a full use and protection of the declining black soil resources, which are of great significances to agricultural production. 2. Materials and methods 2.1. Reagents and chemicals Fifteen PAE standard mixtures, containing dimethyl phthalate (DMP), diethyl phthalate (DEP), diisobutyl phthalate (DiBP), di-n-butyl phthalate (DBP), bis(2-methoxyethyl) phthalate (DMEP), bis(4-methyl-2-pentyl)phthalate (BMPP), di(2-ethoxyethyl) phthalate (DEEP), diphenyl ortho-phthalate (DPP), diheptyl phthalate (DHP), butylbenzyl phthalate (BBP), di(2-n-butoxyethyl) phthalate (DBEP), dicyclohexyl phthalate (DCHP), di(2-ethylhexyl) phthalate (DEHP), dioctyl phthalate (DOP), and di-iso-nonyl phthalate (DINP) at 1000 mg/L each were dissolved in hexane. The pure standard mixture (N 99%) was purchased from AccuStandard Inc., USA. Internal standard of di(2-ethylhexyl) phthalate-D4 (DEHP-D4) was acquired initially as a solid of 99% purity (Dr. Ehrenstorfer GmbH, Germany). The acetone and n-hexane (HPLC grade) were supplied by Tedia Inc., USA. 2.2. Description of the sampling sites The black soil zone of China cuts across the north of Nenjiang in Heilongjiang province to Changtu in the south of Liaoning province, specifically located along the Binbei-Binchang railroad area. Nine representative locations were selected from this black soil region based on change in latitude, which covers three provinces of Songnen, Liaohe and Sanjiang plain (Xu et al., 2010). All sampling points were located in the temperate zone monsoon climate, with a wide variation in winter and summer temperatures. The zones are also characterized with warm summer and low winter temperatures; the lowest temperature in winter is usually around −40 °C, and soil freezing depth was reported up to 0.5–1.3 m; thus, the winter season has not been usually suitable for agricultural production (Jing et al., 2008). The average temperatures of the three seasons across the different sampling sites varied between 21.1 and 25.8 °C. The crops cultivated at these sampling sites are cucumbers, and the average sizes of the greenhouses were all about 90 × 10 × 4.5 m (as length, width, and Empyrean). The locations of the sampling sites are given in Fig. 1 and the information of the location is given in Table 1. 2.3. Soil sample collection Soil samples at depth of 0–20 cm (surface soil) were collected from greenhouse facilities in nine cities (Jiusan, Hailun, Harbin, Shangzhi, Songyuan, Mudangjiang, Changchun, Siping and Changtu), all within the three provinces of Heilongjiang, Jilin, and Liaoning. It is necessary to report that all sampling sites used agricultural films of 0.008 mm thickness. The sampling soil was characterized as black soils of the northeast region of China. A total of 27 soil samples were taken in May, August and November of 2013, depicting each climatic season at the nine sites. At the greenhouse, surface soils were collected into pre-cleaned aluminum foil envelopes using a pre-cleaned stainless steel soil sampler. Before sample collection, particles of small vegetation or/and litters were removed where necessary (Wang et al., 2013). From each site, and each season, one soil sample (within 5 × 5 m2, 500 g each) composed of five sub-samples were collected. The soil samples were cooled in a temperature-controlled box filled with ice bags during transport to the laboratory. In the laboratory, soils were sieved to remove stones and visible roots and fauna, and divided into two parts: one part was directly

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Y. Zhang et al. / Science of the Total Environment 506–507 (2015) 118–125

Fig. 1. Schematic diagram showing the geographical location of (a) the three northeast provinces in China; (b) black soil zone in the three northeast province regions; and (c) the sampling sites within the black soil zone.

passed through the 1 mm sieve and subjected to dry conditions, later used for PAE extraction in the soil; the other part was used to determine basic soil physical and chemical properties (Teixeira et al., 2010). The basic soil properties were measured by the standard methods recommended by the Chinese Society of Soil Science.

ASE extraction conditions: furnace temperature 100 °C; 1500 ps pressure; static time: 5 min; nitrogen purging: 100 s; elution volume: 120% of the solvent extraction pool; static loop three times (Wang et al., 2013; Yang et al., 2013; Sun et al., 2013). 2.5. GC-MS analysis

2.4. Sample extraction and fractionation Ten grams of soil samples was extracted using rapid pressure solvent extraction method. Solvent extraction was done with 70 ml acetone and n-hexane (1:1, v/v), the extract was further concentrated by gentle use of nitrogen gas blowing to a volume of 1–2 ml, and 10 ml n-hexane was added to convert the solvent. The solvent was once again concentrated to 1–2 ml by gentle use of nitrogen gas blowing. To purify the liquid through the activated Florisil column, it was eluted first with 4 ml hexane, and the upper portion was leached into a mixture containing 8 ml n-hexane and diethyl ether (v/v, 9:1). The resulting solvent was concentrated by gentle use of nitrogen gas blowing to a volume of 0.8 ml, and diluted with n-hexane to 1.0 ml for GC/MS determination.

The extracted compounds were determined with a gas chromatography-mass spectrometry system (GC-MS) (Agilent Technologies) operated in electron impact and selective ion monitoring mode and with a HP-5MS (30 m × 0.25 mm × 0.25 mm) fused-silica capillary column for chromatographic separation. High purity helium (99.9999%) was used as the carrier gas and was maintained at a constant flow rate of 1.0 ml/min. The temperature program column oven was set to 60 °C for 1 min and raised to 220 °C at 20 °C/min, maintained for 1 min, then raised to 280 °C at 5 °C/min and held for 5 min. Each extract (1 μl) was injected into the GC-MS system in non-pulse and splitless mode with an injector temperature of 250 °C. The GC-MS transfer line was set at 280 °C (Wang et al., 2013; Yang et al., 2013; Sun et al., 2013).

Table 1 The information of sampling points. Station code

Province

City

Latitude Na

Longitude Ea

Elevation(m)

Greenhouse type

Average temperatures(°C)

Crop

Mulching film

ST1 ST2 ST3 ST4 ST5 ST6 ST7 ST8 ST9

HeiLongjiang HeiLongjiang HeiLongjiang HeiLongjiang HeiLongjiang JiLin JiLin JiLin LiaoNing

NenJiang HaiLun Harbin ShangZhi MuDanjiang SongYuan ChangChun SiPing ChangTu

48.8593° 47.4561° 45.6884° 45.2121° 44.581° 45.0294° 43.8086° 43.0878° 42.8311°

125.285° 126.9303° 126.8302° 127.928° 129.3931° 126.069° 125.373° 124.2083° 124.1161°

260 235.5 158.5 220.3 313.9 170 215.2 177 152.5

Arch; Plastic Arch; Plastic Arch; Plastic Arch; Plastic Arch; Plastic Arch; Plastic Arch; Plastic Arch; Plastic Arch; Plastic

24.6 23.8 23.1 21.1 23.1 24.3 24.7 25.8 24.2

Cucumber Cucumber Cucumber Cucumber Cucumber Cucumber Cucumber Cucumber Cucumber

Yes No Yes No Yes No Yes No No

a

Coordinates given in decimal degrees.

Y. Zhang et al. / Science of the Total Environment 506–507 (2015) 118–125

2.6. Quality assurance and quality control A procedural blank, a spiked blank and a sample duplicate were processed along with each batch of 10 samples. The surrogate standards were added to all the samples to monitor matrix effects and the instruments were calibrated daily with calibration standards (Wang et al., 2013; Zeng et al., 2009). The procedural blanks were controlled by a 1 μl injection of pure n-hexane solvent. The concentration of the individual PAE compounds found in the procedural blanks was less than 1 μg/kg and respectively subtracted from the sample testing results. The surrogate recoveries were 84.6–89.2% for di(2-ethylhexyl) phthalate-D4 (DEHP-D4). Recoveries of the 15 kinds of PAEs ranged from 86.3 to 109.2% in the spiked sample blanks with a relative standard deviation ranging from 3.4 to 9.8%. The method detection limit (MDL) for DMP, DEP, DiBP, DBP, DMEP, BMPP, DEEP, DPP, DHP, BBP, DBEP, DCHP, DEHP, DOP and DINP were 2.51, 3.80, 4.69, 1.87, 3.31, 4.34, 1.13, 1.43, 7.79, 3.13, 2.20, 1.90, 0.79, 1.37, and 0.50 μg/kg respectively. Hence, this indicates the method is capable of detecting PAEs at very low limits within the soil. The method therefore has advantages of simple and rapid operation, and high accuracy and precision. To avoid contamination of the laboratory equipment during handling and analysis, all glassware were washed and rinsed in anhydrous ethanol after immersing and washing by soapy water in a laboratory ultrasonic washer (Ma et al., 2013). Glassware were subsequently heated up to 400 °C for 6 h and then thoroughly rinsed with acetone: n-hexane (1:1 v/v) before use. 2.7. Analyses of soil physical and chemical properties The organic matter of the soil was measured by SU-LH high intelligent soil parameter tester. Soil pH was measured by pH meter with a soil/water ratio of 1:5. The porosity of the soil was determined according to calculations obtained from the bulk density of the soil; bulk density was measured by ring knife method. 3. Result and discussion 3.1. Description of soil properties Soils were collected from facility agricultures distributed across the black soil region of northeast china and were analyzed based on their properties, such as organic matter, pH and porosity. Soil organic matter is one of the important indicators of soil fertility (Yang et al., 2013); the average content of organic matter in the summer was 5.51%, 3.79% in spring and 4.38% in autumn. The average porosity of soil from spring

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to autumn was 51.64%, 46.42% and 41.01%, respectively, presenting a reducing trend. No matter which season, the pH in the soil varied from neutral to acidic, with a mean value of 6.46 and only a few samples were lower than 6.0. 3.2. Effects of seasonal variations on PAE concentrations in soils of facility agricultures Table 2 shows the individual concentrations of the 15 PAEs in black soils of northeast facility agriculture in the three seasons of spring, summer and autumn. The presence of PAEs was detected in all the facility agriculture soil samples analyzed, thus indicating PAEs as ubiquitous environmental contaminants. Fig. 2 shows that the average concentrations of the 15 measured PAEs (Σ15PAEs) varied significantly from spring to autumn, ranging from 1.37 to 4.90 mg/kg-dw, with a median value of 2.83 mg/kg-dw. Significantly high concentrations of 15 PAEs in black soils of facility agriculture were observed in summer due to high temperature and increased agricultural production activities in summer (such as fertilization). The highest 15 PAE concentration level (4.90 mg/kg-dw) was found at ST3 in summer where mulching film was commonly used in the greenhouses. In facility agricultures, PAEs occur in many greenhouse materials, such as greenhouse films, mulching film, and fertilizers (Liu et al., 2010b; Mo et al., 2008; Pedersen et al., 2008). The discharge of these compounds from the agricultural films is the main source of soil contamination in facility agricultures (Wang et al., 2013; Cai et al., 2008). It has been described in many studies that the PAE contents in the soil are directly proportional to the amount of agricultural films used in the soil (Chen et al., 2011; Hu et al., 2003). As high temperature is characteristic of summer season, hence this could have caused an increase in the temperature within the plastic mulching films and the reduction in bond strength of the plasticizer and PVC chain, thus resulting in increased discharge of PAEs into the surrounding soil (Chen et al., 2011). Fertilizer is an essential material in agricultural production facilities. Mo et al. have studied 22 widely used-fertilizers, and reported that the total amount of PAE compounds detected in the fertilizers ranged from 0.01 mg/kg to 2.8 mg/kg (Mo et al., 2008). The application of such fertilizers which contained PAE compounds could lead to the deposition and hence accumulation of PAEs in the soil (Fu et al., 2011; Cai et al., 2008). As summer is the most vigorous season for plant cultivation, hence application of soil nutrients in the form of fertilizers is the mostly required activity, as compared to the spring and winter seasons. Zorníková reported that the more fertilizer usage in the soil, the more PAE accumulation in that soil (Zorníková et al., 2011).

Table 2 The individual concentrations of PAEs (mg/kg-dw) in black soils of northeast facility agriculture in the spring, summer, and autumn. PAE

DMP DEP DBP DiBP DMEP BMPP DEEP DPP DHP BBP DBEP DCHP DOP DEHP DINP

Spring

Summer

Autumn

Range

Mean ± S.D.

Median

DF

Range

Mean ± S.D.

Median

DF

Range

Mean ± S.D.

Median

DF

0.121–0.378 0.063–0.472 0.276–0.676 0.0022–0.268 0.0068–0.141 0.013–0.125 0.003–0.194 0.0015–0.099 0.011–0.137 0.017–0.139 0.0024–0.392 0.0082–0.153 0.0079–0.151 0.517–1.386 0.0013–0.098

0.219 0.248 0.462 0.071 0.049 0.042 0.058 0.054 0.048 0.053 0.096 0.043 0.05 0.898 0.05

0.189 0.237 0.431 0.055 0.043 0.029 0.028 0.063 0.038 0.047 0.075 0.031 0.030 0.903 0.037

100 100 100 100 100 100 100 100 100 100 100 100 100 100 100

0.071–0.453 0.150–0.851 0.376–0.957 0.021–0.232 0.020–0.151 0.029–0.133 0.016–0.095 0.012–0.141 0.024–0.096 0.017–0.083 0.033–0.170 0.0061–0.35 0.0059–0.097 0.719–2.121 0.0043–0.074

0.156 0.556 0.655 0.076 0.072 0.060 0.038 0.049 0.053 0.059 0.067 0.090 0.047 1.471 0.05

0.133 0.561 0.693 0.136 0.075 0.055 0.034 0.033 0.051 0.069 0.123 0.064 0.034 1.345 0.061

100 100 100 100 100 100 100 100 100 100 100 100 100 100 100

0.076–0.294 0.147–0.463 0.051–0.427 0.019–0.197 0.036–0.089 0.025–0.057 0.016–0.098 0.062–0.143 0.020–0.097 0.022–0.058 0.010–0.138 0.016–0.072 0.021–0.161 0.565–1.862 0.029–0.172

0.013 0.286 0.263 0.046 0.056 0.037 0.028 0.093 0.048 0.033 0.077 0.048 0.064 0.995 0.059

0.097 0.251 0.217 0.026 0.056 0.037 0.019 0.092 0.042 0.028 0.072 0.057 0.060 0.796 0.049

100 100 100 100 100 100 100 100 100 100 100 100 100 100 100

± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.0065 0.017 0.022 0.0053 0.0016 0.001 0.0031 0.0009 0.0012 0.0006 0.0013 0.0019 0.0020 0.079 0.00077

± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.012 0.047 0.044 0.015 0.0112 0.0010 0.0005 0.0019 0.0054 0.0063 0.0029 0.0123 0.0018 0.212 0.0005

Reported concentrations were corrected by subtracting the mean blank values. DF: detection Frequency (%).

± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.0042 0.011 0.016 0.0029 0.0062 0.0027 0.0012 0.0064 0.0017 0.0002 0.011 0.0034 0.014 0.17 0.0017

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Y. Zhang et al. / Science of the Total Environment 506–507 (2015) 118–125

Fig. 2. Seasonal variations in the concentration of 15 PAEs in nine sample sites. Data are expressed as mean ± SD (N = 5, N: the number of replicated samples). Means with different small letters are significantly different from one another under the Σ15PAE concentration between three seasons in one sampling site, and different capital letters are significantly different from one another under the Σ15PAE concentration between different sampling sites in one season.

High concentrations of the Σ15 PAEs were found at ST2, ST4, ST6, ST8 and ST9 in summer, at the levels of 2.83, 2.82, 3.46, 3.03 and 2.01 mg/kg-dw, respectively, when mulching films were not used on the soils. While, at sites ST1, ST3, ST5 and ST7 where mulching films were used, higher concentrations of Σ15 PAEs were detected at the

levels of 4.83, 4.90, 4.02 and 4.24 mg/kg-dw, respectively. From spring to summer the soil PAE content was found in higher levels where mulching was used as compared to where mulching was not used. So, the current study indicated that the plastic mulching film was an important route causing the increase of PAE levels in the soil.

Fig. 3. Correlations between the Σ15PAE concentrations with soil organic matter at the nine sampling sites in spring (a), summer (b), and autumn (c).

Y. Zhang et al. / Science of the Total Environment 506–507 (2015) 118–125

In the evaluation of seven sampling sites, and in comparison with sites ST2 and ST8, the seven sites had higher levels of PAEs in spring than in autumn, because base fertilizers were applied for the growth of plants in spring; in autumn, the greenhouse crops were harvested and there was no need for fertilizer application. Whereas analysis of soil samples collected at sites ST2 and ST8 with no previous fertilizer application, at the spring season, indicated an obviously different phenomenon. It was observed that due to seasonal changes, rates of fertilizer application also changes, which resulted to a change in soil organic matter. Therefore, it was considered that soil organic matter (SOM) has great influence on distribution and concentration of hydrophobic organic contaminants (HOCs) (Xu et al., 2008; Cui et al., 2010; Xu and Li, 2008; Cousins et al., 2000). Similarly in the present study, the highest average concentration of organic matter was 5.51% in summer; consequently, the highest average concentration of PAEs was also detected in summer. Fig. 3 shows the correlation between PAE concentrations among different seasons and organic matter, correlation coefficient (R2) ranged from 0.6685 for autumn to 0.7147 for summer (p b 0.02, n = 9), which showed highly significant positive correlation between PAEs and organic matter in the investigated soils in spring, summer, and autumn.

3.3. The main PAEs in black soil of facility agricultures The presence of the fifteen PAEs was observed at all the sites and the detection frequencies were up to 100%, for the three seasons studied. However, in addition to DBP, DEP, DMP and DEHP, the average concentration of the other PAEs was lower than 0.1 mg/kg-dw. Fig. 4 indicates the relative contributions of the 15 PAEs in black soils of northeast facility agriculture in different seasons. Irrespective of the season, occurrence of DEHP was remarkably higher in the black soils of facility agricultures and its contributions ranged from 26.87 to 63.62%, while DBP, DEP and DMP, contributions ranged from 3.47 to 28.18%, 2.64 to 21.32% and 1.98 to 16.26%, respectively. DBP, DEP, DMP and DEHP were the four most dominant PAEs in spring summer and autumn, and their contributions to the overall 15 PAE concentrations ranged from 64.08 to 89.15%, 74.77 to 90.51% and 68.84 to 81.70%. DBP, DEP, DMP and DEHP are listed as priority organic pollutants by the USA Environmental Protection Agency (NYSDEC, 1994).

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DEHP has been detected in most widely used-fertilizers (Mo et al., 2008). The amount of DEHP added in flexible PVC products could reach up to 40% (Chao and Cheng, 2007) and the concentration of PAE in a finished plastic product ranged between 10 and 60% by weight of the finished material (Gomez-Hens and Aguilar-Caballos., 2003). Among other PAE compounds, DEHP was distinguished for its physicochemical properties such as a high relative molecular mass, low solubility in water, and greater octanol–water partition coefficient. Moreover, it has been reported as vulnerable to soil adsorption and has poor mobility in the soil. DEHP is not easily biodegradable; therefore, it easily accumulates in the soil at high levels (Cartwright et al., 2000; Inman et al., 1984). PAEs of lower molecular weight, such as DMP, DEP and DBP, are typically used in plastic products but in lower volume compared to DEHP (Zeng et al., 2009). PAEs of low molecular weight also have lower soil adsorption coefficient and are relatively soluble in water, and thus occurs low levels of soil residuals (Yang et al., 2013; Li et al., 2010). In comparison with results obtained from other places both within and outside the country, the PAE concentration in black soil of northeast China showed relatively high DEHP, DEP, DBP, and DMP concentrations (Table 3). Moreover, the PAE concentration of cultivated soil was higher than the urban soil in China; in all, it was higher than the foreign soils. The levels of these four kinds of PAEs in this study were quite similar to the study of Hangzhou facility agricultural soil, but higher than levels found in soils of non-facility agricultural sites. Principal component analysis (PCA) is often used to reduce the dimensions of data sets, while keeping the largest contribution to the variance of characteristics of the data set, and has been used in other studies (Kong et al., 2012, 2013; Cai et al., 2007; Zeng et al., 2009; Zhang et al., 2007). In the present study, principal component analysis was applied to analyze differences in distribution pattern of PAEs among the three seasons and in facility agricultures of the black soil regions of northeast China. Concentrations of four PAEs (DBP, DEP, DMP and DEHP) in the three seasons were used as active variables, and 27 samples were selected as subjects. Principal components (PCs) were derived from the correlation matrix. The PCA extracted four principal components with eigenvalues N1 explaining 40.54%, 21.5%, 11.34% and 9.64% of the total variation, respectively. The plot of loading factors for the first and second principal components (component 1, component 2) is shown in Fig. 5. The concentrations of four PAEs in summer were loaded mainly by principal component 1. The concentrations

Fig. 4. Relative contributions of 15 PAE in black soils of northeast facility agriculture in the spring (Sp), summer (Su), and autumn (Au).

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Table 3 Comparison of concentrations (mg/kg-dw) of major PAEs (DEHP, DBP, DEP, and DMP) in soils measured in this study with concentrations reported from other studies. Location

Facility Agricultural soil, BeiJing Facility Agricultural soil, HangZhou Agricultural soil, LeiZhou Peninsula Agricultural soil, TianJin Agricultural soil, ZhongShan Agricultural soil, NanChang Agricultural soil, DongGuan Urban soil, GuangZhou Uncultured Soil Soil Soil Facility agricultural soil, Northeast a b

Country

China China China China China China China China Danish Netherlands UK China

PAEs

Reference

DEHP

DBP

DEP

DMP

0.22–0.74 0.81–2.20 ND–1.388 0.0321–0.981 ND–0.74 ND–0.27 ND–1.47 0.107–2.74 0.016 0.0001–0.00235 0.0222–0.5499 0.517–2.121

a NA 0.14–0.35 ND–0.054 0.0004–0.189 NA ND–0.074 NA NA 0.0021 0.0004–0.00133 NA 0.051–0.950

b0.01–0.05 0.06–1.49 ND–0.0759 0.0021–0.077 ND–0.02 ND–0.047 ND–0.930 0.001–0.178 NA NA 0.0002–0.018 0.063–0.851

b0.01–0.02 b ND ND–0.07 0.0022–0.0875 ND–0.08 NA ND 0.001–0.157 NA NA 0.0001–0.026 0.071–0.453

Ma et al. (2003) Guan et al. (2007) Liu et al. (2010) Yang et al. (2007) Xiong et al. (2008) Zhang et al. (2009) Zeng et al. (2008b) Vikelsøe and Carlsen (2002) Peijnenburg and Struijs (2006) Gibson et al. (2005) This study

NA, not analyzed. ND, not detected.

of four PAEs in spring and autumn were loaded mainly by component 2; however the concentrations of four PAEs in spring were loaded in the positive quadrant of the component 1, and the concentrations of four PAEs in autumn were loaded in the negative quadrant of the component 1. Statistically significant difference was found between the concentration of PAEs and change in season.

with PAEs. PAE data originated by the current study will provide reference for soil bioremediation within the facility agriculture black soils of northeast China, as well as at the national agriculture stages. Similarly, it is also expected to provide scientific evidence about prevention and control planning for related management departments. Further studies can be conducted on the environmental behaviors of PAEs, their health risk assessment, and to protect the declining black soil resources, which are of great agricultural significance.

4. Conclusion Acknowledgments This study has provided baseline information on the levels of 15 PAEs in black soils collected from facility agricultures in northeast China, during the process of agricultural production at only three different climatic seasons: spring, summer, and autumn. PAEs were detected in all soil samples. Σ15PAE concentrations ranged from 1.37 to 4.90 mg/kg-dw from spring to autumn. PAE concentrations in all soil samples differed significantly in all seasons, but the highest concentrations of PAEs were recorded in the summer due to high temperature. The present study concluded that increasing temperature enhanced the PAE discharge from the mulching film to the surrounding soil rapidly. Fertilizer application within the facilities agricultural greenhouses in summer was also high. According to the current study, among the 15 analyzed PAEs, four (DMP, DBP, DEP and DEHP) were detected in higher concentrations. A comparison with other studies showed that the facility agriculture black soils of northeast China were contaminated

Fig. 5. Diagrams of factor loading of principal components for PAEs (DEHP, DBP, DEP, and DMP) in black soils of northeast facility agriculture in different seasons: spring (Sp), summer (Su), and autumn (Au).

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