Ecotoxicology and Environmental Safety 108 (2014) 329–334
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Distribution and accumulation of hexachlorobutadiene in soils and terrestrial organisms from an agricultural area, East China Zhenwu Tang a, Qifei Huang b,n, Jiali Cheng c, Dan Qu a, Yufei Yang b, Wei Guo a a MOE Key Laboratory of Regional Energy and Environmental Systems Optimization, Resources and Environmental Research Academy, North China Electric Power University, Beijing 102206, China b State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China c National Institute for Nutrition and Food Safety, Chinese CDC, Beijing 100021, China
art ic l e i nf o
a b s t r a c t
Article history: Received 1 April 2014 Received in revised form 23 July 2014 Accepted 24 July 2014 Available online 13 August 2014
Hexachlorobutadiene (HCBD) is a potential persistent organic pollutant that has been found in abiotic environments and organisms. However, information on HCBD in soils and its accumulation in terrestrial food chains is scarce. This study investigated the accumulation of HCBD in soils, plants, and terrestrial fauna in a typical agricultural area in Eastern China, and drew comparisons with organochlorine pesticides (OCPs). The HCBD concentrations in soils were o 0.02–3.1 ng/g dry weight, which were similar to α-endosulfan concentrations but much lower than the concentrations of some other OCPs. The HCBD soil–plant accumulation factors, 8.5–38.1, were similar to those of o,p0 -DDT and higher than those of HCHs and p,p0 -DDT, indicating that HCBD is strongly bioaccumulated by rice and vegetables. HCBD concentrations of 1.3–8.2 ng/g lipid weight were found in herbivorous insects, earthworms, and Chinese toads. The biomagnification factor, the ratio between the lipid-normalized concentrations in the predator and the prey, was found to be 0.16–0.64 for different food chains of Chinese toads, so HCBD was found not to biomagnify, which is in contrast with OCPs. Further research into whether HCBD is biomagnified in high trophic level organisms or through the entire terrestrial food web is required. & 2014 Elsevier Inc. All rights reserved.
Keywords: Hexachlorobutadiene (HCBD) Soils Terrestrial organisms Plant accumulation Biomagnification
1. Introduction Hexachlorobutadiene (HCBD), a halogenated aliphatic hydrocarbon, has been used as an intermediate in the production of a variety of chemicals and as an ingredient in transformer, hydraulic, and heat-transfer liquids (Lecloux, 2004; POPRC (Persistent Organic Pollutants Review Committee), 2013). It is also unintentionally generated during the production of chlorinated hydrocarbons, particularly perchloroethylene, trichloroethylene, and carbon tetrachloride (Brüschweiler et al., 2010). Hexachlorobutadiene is generally moderately acutely toxic and has been found to be genotoxic and carcinogenic in some laboratory animals (Rabovsky, 2000; Brüschweiler et al., 2010; POPRC (Persistent Organic Pollutants Review Committee), 2013). Adverse effects on marine and freshwater species have been observed from exposure to relatively low HCBD concentrations (POPRC (Persistent Organic Pollutants Review Committee) 2013) and HCBD has been detected in various abiotic and biotic media such as surface water,
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Corresponding author. Fax: þ 86 10 8491 3903. E-mail addresses: [email protected] (Z. Tang), [email protected] (Q. Huang), [email protected] (J. Cheng), [email protected] (D. Qu), [email protected] (Y. Yang), [email protected] (W. Guo). http://dx.doi.org/10.1016/j.ecoenv.2014.07.024 0147-6513/& 2014 Elsevier Inc. All rights reserved.
sediments, ambient air, and organisms (Lee and Fang, 1997; Vorkamp et al., 2004; Li et al., 2008; Juang et al., 2010; Miège et al., 2012). Thus, HCBD has been classed as a priority pollutant in many countries, including Canada, China, the UK, and the USA. In 2012, HCBD was listed as a candidate persistent organic pollutant by the Stockholm Convention for its toxicity, persistence, and potential for bioconcentration and long-range transport in the environment (POPRC (Persistent Organic Pollutants Review Committee), 2012). The potential for HCBD to bioconcentrate in aquatic organisms has been experimentally confirmed. For fish bioconcentration factor (BCF, which is the ratio of the chemical concentration in an organism to the concentration in water) values from 1 to 19,000 L/kg on a whole body basis are reported by Environment Canada (1999). The International Programme on Chemical Safety (IPCS (International Programme on Chemical Safety), 1994) stated that HCBD bioaccumulation factors (BAFs), calculated using wet weight concentrations, in plankton, crustaceans, molluscs, insects, and fish in surface waters were comparable to those observed in the laboratory, and were in the range of 33–11,700 L/kg. Some previous studies have showed the levels of HCBD in aquatic organisms to be relatively low perhaps owing to the mild pollution in the waters studied (Environment Canada, 1999; Miège et al., 2012; Jürgens et al., 2013). At the same time, relatively higher
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concentrations of HCBD have been reported in the aquatic species surrounding industrial areas (IKSR (Internationale Komission zum Schutz des Rheins), 2002; Environment Canada, 1999). A previous report found that the level of HCBD in the mussels that were caged in the river near to three industrial areas of the St. Clair River for three weeks was 36 ng/g wet weight (Environment Canada, 1999). However, recent HCBD monitoring data, especially for HCBD concentrations in terrestrial organisms are scarce and there is limited information available on HCBD bioaccumulation in terrestrial species. Because of its lipophilicity (log Kow ¼4.78) and ability to bioaccumulate (POPRC (Persistent Organic Pollutants Review Committee), 2013), HCBD is likely to biomagnify through food chains and food webs. Based on the BCF according to the European Commission (2003), The Netherlands (2012) estimated the HCBD biomagnification factor (BMF) as being 3 kg/kg, indicating that HCBD has the potential to be biomagnified. In contrast, Kelly et al. (2007) performed bioaccumulation modeling studies and found HCBD BMF values of o1 for all the organisms modeled, including water-respiring and air-breathing organisms. No field-based food chain studies have been performed, so the modeled BMF values (especially for terrestrial food chains) cannot be verified in natural food chains. Thus, the biomagnification potential of HCBD remains undetermined and investigations are urgently needed. Many bioconcentrative chemicals, especially organochlorine pesticides (OCPs), have been investigated in depth and shown to bioaccumulate strongly, and to biomagnify through both aquatic and terrestrial food webs (Hoekstra et al., 2003; Weber et al., 2010; Foster et al., 2011; Silva Barni et al., 2014). It is known that HCBD and OCPs have many similar chemical properties and characteristics. In this study, the occurrence of HCBD in soils and terrestrial organisms in a typical agricultural area in Eastern China was investigated and the accumulations of HCBD and some OCPs in terrestrial plants were assessed to determine whether HCBD acts in a similar way to OCPs; being efficiently transferred from the abiotic environment into plants, and then entering the terrestrial food chain. The transfer of HCBD and OCPs through terrestrial food
chains and the potential for HCBD to be biomagnified was also determined. This research will enable better understanding of the environmental behavior and fate of HCBD.
2. Materials and methods 2.1. Study area Taicang, a city in Eastern China, with a population of 470,000 and an area of 810 km2, is close to Shanghai. With the initiation of the “Reform and Open” policy in 1978, Taicang entered the fastest industrialization period ever experienced, and this has been sustained until today. Being one of the most developed industrial cities in the Yangtze River Delta, Taicang has many chemical synthesis plants and other industrial enterprises. It is possible that HCBD has been released from some local industrial sources into the surrounding farmlands. At the same time, the agriculture in this region is comparatively advanced and produces mainly vegetables and rice, because of the better weather and soil conditions. There has been intensive historic use of OCPs for supporting or improving the agricultural productivity in this area. In the Taicang area suburban farms, a variety of terrestrial plants and animals are widely distributed making it a suitable area for studying pollutant accumulation and transport in terrestrial species at different trophic levels. 2.2. Sample collection In October 2011, soil and organism samples were collected from an agricultural area in the suburbs of Taicang (Fig. 1). Soil samples (0–10 cm deep) were collected from a total of 23 sites (five replicate samples from each site), in the east and south of Xintang, a village in a suburb of Taicang, using a stainless steel shovel. Each soil sample was placed in a pre-cleaned aluminum box and freeze dried before being ground, homogenized, and stored at 20 1C until analysis. Rice (Oryza sativa) and some vegetables, including cabbage (Brassica chinensis), cowpea (Vigna unguiculata), pumpkin (Cucurbita moschata), mustard (Brassica juncea), and cauliflower (Brassica oleracea), were collected at the same time as soil sampling. The rice samples were collected from near the soil sampling sites 11–23 and the other plants were collected from vegetable plots at sites 6 and 7 (shown in Fig. 1). The rice was sampled by collecting all aboveground parts and the aboveground stems and leaves were collected for every vegetable sample. Each composite sample consisted of five subsamples. The numbers of composite samples are given in Table S1. The plant samples were washed with tap water and cut into lengths o 1 cm and mixed well. Then the samples were freeze dried and ground, homogenized, and stored at 20 1C.
N 31º32′24″
E 121º13′12″
E 121º11′24″
N 31º31′12″ Fig. 1. Map showing the soil sampling sites in suburban Taicang, East China.
Z. Tang et al. / Ecotoxicology and Environmental Safety 108 (2014) 329–334 The terrestrial animals including grasshoppers (Acrida chinensis), locusts (Oxya chinensis), cabbage worms (Pieris rapae Linne), butterflies (Eurema hecabe Linnaeus), earthworms (Eisenia foetida), and Chinese toads (Bufo gargarizans) were collected in the locations where plants were sampled within a week after the soil collecting. Several hundred grasshoppers, locusts and butterflies were sampled using funnel traps (20 cm diameter) and transferred to a precleaned glass bottle. Approximately 70 cabbage worms were collected by hands and several hundred earthworms were sampled from soils using spades. A total of 15 Chinese toads from three sites were collected from where other animals were found. All the animals were frozen and then thawed, and rinsed individually with deionized water to remove impurities. Complete organisms of the smaller biological samples were obtained after removal of the viscera. For the Chinese toads, only the muscle tissues were collected. Then all biological samples were freeze dried and then ground to a powder, divided into subsamples and stored at 20 1C until analysis. 2.3. Sample preparation The soils and plants were extracted using a procedure based on the recommendations found in the “Standard of Soil Quality Assessment for Exhibition Sites” and on procedures used in other studies (Verreault et al., 2005; SEPA (State Environment Protection Agency of China), 2007b; Tang et al., 2007). Briefly, 10 g of freeze-dried soil or freeze-dried plant material was extracted with 30 mL of a 1:1 v/v mixture of hexane and dichloromethane in an ultrasonic bath for 30 min, twice. Surrogate recovery standards of 2,4,5,6-tetra-chloro-m-xylene (100 ng) were added prior to extraction. The two extracts were combined, and activated copper was added to remove elemental sulfur. Further purification was achieved by passing the extract through a 12 mm i.d. glass column containing 5 cm of alumina and 5 cm of silica gel, which was eluted with 70 mL of a 7:3 v/v mixture of hexane and dichloromethane. The volume of the extract was then reduced to 0.2 mL under a nitrogen stream, and internal standards were added before the extract was analyzed by gas chromatography (GC). The HCBD and OCPs were extracted from the animal samples in a similar way to the procedure described above, but 4–10 g of each freeze-dried sample was extracted and the purification column contained 5 cm of neutral alumina and 8 cm of neutral silica gel. 2.4. Sample analysis The quantitative analysis of HCBD and OCPs was carried out using an Agilent gas chromatograph 7890 (USA) coupled with an HP-5 column (30 m 0.32 mm 0.25 mm film thickness, Agilent), using a modification of the procedure of Tang et al. (2013). A 63Ni-ECD detector was used for analysis. The GC system was operated in splitless mode and the injection volume was 1 mL. The oven temperature program started at 60 1C, which was held for 2 min, then increased at 20 1C/min to 160 1C, at 5 1C/min to 210 1C, then at 5 1C/min to 270 1C, which was held for 3 min. The injector and detector temperatures were 250 1C and 315 1C, respectively. The carrier gas was nitrogen, and the flow rate was 1.0 mL/min. Total organic carbon (TOC) in soil was measured on a Liqui TOC (Elementar, Germany) at a combustion temperature of 950 1C.
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3. Results and discussion 3.1. HCBD in soils HCBD was detected in 21 of the 23 soil samples, indicating that it is widely distributed in soil in the study area. Fig. 2 shows the results of the soil analyses. The HCBD concentrations were in the range of o0.02–3.1 ng/g dw, and the mean was 0.3 ng/g dw. Webber and Wang (1995) found HCBD concentrations between oMDL and 0.05 ng/g dw in Canadian soils. In China, Zhang et al. (2014) reported that the concentrations in soil around a chemical plant had a range of 0.04–3.33 ng/g dw. But the HCBD concentrations in soils in this study was three to five orders of magnitude lower than those reported in soils from plants producing perchloroethylene and trichloroethylene in the United States (USEPA (United States Environmental Protection Agency), 1976). Currently, there is limited information available on HCBD pollution in other soils (POPRC (Persistent Organic Pollutants Review Committee), 2013). No HCBD concentration limit has been set in the Chinese environmental quality evaluation standards for farmland used for growing edible agricultural products (SEPA (State Environment Protection Agency of China), 2007a), but the HCBD concentration limit is 1.0 μg/g for uncontaminated soils, and this is based on the Chinese standards for soil-quality assessment for exhibition sites (SEPA (State Environment Protection Agency of China), 2007b). HCBD concentration limits of 6.7 and 10.0 ng/g for agricultural coarse- and fine-grained soils, respectively, have been recommended in the environmental quality standard draft for Saskatchewan, Canada (Saskatchewan Ministry of Environment, 2011). Compared with these limits, it was concluded that only lowlevel HCBD contamination was present in these soils from Taicang. The OCP concentrations found in the soils are also shown in Fig. 2. There were significant differences between the HCBD and β-HCH (p ¼0.001), and p,p0 -DDT concentrations (p¼ 0.026), but the HCBD concentrations were not significantly different from the concentrations of the other OCPs (p4 0.05). The mean HCBD concentration was two orders of magnitude lower than the β-HCH and p,p0 -DDT concentrations and an order of magnitude lower than the other OCP concentrations, which reflects the extensive historical agricultural use of OCPs in this area. Correlation analyses
2.5. Quality assurance/quality control The standard solution of OCPs, pentachloronitrobenzene, 2,4,5,6-tetrachlorom-xylene and HCBD were purchased from Supelco (USA). The identities of the target compounds were determined by their match with the average retention times of individual authentic standards, and they were confirmed using an Agilent gas chromatograph/mass spectrometry (Agilent 7890 GC/5975MSD; Agilent Technologies). The 2,4,5,6-tetrachloro-m-xylene was used as a surrogate standard and pentachloronitrobenzene was used as an internal standard. The analytes were not corrected for recoveries. Procedural blanks and samples spiked with the standard mixture were used to monitor the method performance and matrix effects. All of the analyses were carried out in duplicate. The mean spiked HCBD recoveries were 91.6 percent, 78.2 percent, and 82.0 percent in the soil, plant, and animal samples, respectively. The mean spiked OCP recoveries in the soil and organism samples were 74.9–119.4 percent. The mean recoveries of 2,4,5,6-tetrachloro-m-xylene were 81.7 percent, 76.2 percent, and 69.2 percent for the soil, plant and animal samples, respectively. The method detection limits (MDLs) were defined as three times the baseline noise (i.e., a signal-to-noise ratio of three). The MDLs for HCBD and the OCPs were 0.02 ng/g and 0.01–0.07 ng/g dry weight, respectively, in each of the matrices. 2.6. Statistical analysis Analysis of variance was performed on all experimental data and means were compared using the Duncan’s Multiple Range test with SPSS version 18.0 software. The significance level was p o0.05. Correlation analyses and principal component analysis (PCA) were also tested with SPSS version 18.0 software.
Fig. 2. Box plots of hexachlorobutadiene (HCBD) and organochlorine pesticide concentrations in the soil samples from suburban Taicang, East China. The lower and upper limits of the whiskers indicate 5 percent and 95 percent values, respectively; boxes extend from 25th to 75th percentiles; horizontal lines within the boxes represent medians; circles below or above the whiskers indicate outlier values.
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were performed and no significant positive correlations between TOC contents and the concentrations of HCBD as well as the nine OCPs were found. Significant positive correlations were found between HCBD concentrations and α-chlordane (r ¼0.659, p o0.01), α-endosulfan (r ¼0.518, p o0.05), and β-endosulfan (r ¼0.757, p o0.01) concentrations. Principal component analysis was also used to examine the relationships between HCBD and OCP concentrations, and the results are shown in the supporting information (Fig. S1). HCBD, α-chlordane, γ-chlordane, α-endosulfan, and β-endosulfan showed similar loadings in both principal components and were grouped together, separate from the HCHs and DDTs. The HCBD draft risk management evaluation stated that HCBD is present in the raw hexachlorocyclopentadiene product (POPRC (Persistent Organic Pollutants Review Committee), 2013). As it is well known, hexachlorocyclopentadiene was a raw material or intermediate in the industrial synthesis of endosulfan and chlordane (Saha and Lee, 1969; Ding and An, 2001). The products of chlordane and endosulfan might contain HCBD as an impurity. In addition to industrial release, therefore, the historical or current use of pesticides in agriculture might play an important role in the HCBD pollution in soils in this area. 3.2. Accumulation of HCBD in plants The HCBD concentrations in the six plants analyzed were 0.8– 2.0 ng/g dw, and are shown in Table S1. Only small differences in HCBD concentrations were found between different plants. There is so little information available on HCBD concentrations in plants that it is difficult to compare and understand the differences in HCBD concentrations found in plants from different regions. In contrast, the OCP concentrations in different plants were distinctly different. The OCP concentrations in the cauliflower samples were lower than those in the other plant samples. The levels of OCPs found in this study were comparable with those investigated in vegetables in Nanjing (Gao and Jiang, 2005). The OCP concentrations were generally higher than the HCBD concentrations in the plants, but the chlordane and α-HCH concentrations were in the same order of magnitude as the HCBD concentrations. The HCBD and OCP BAFs in the plants were calculated to evaluate the bioaccumulative potential of these chemicals. The HCBD BAFs were 8.5–38.1, as shown in Fig. 3. Despite the low HCBD concentrations in the soils in the studied area these BAFs were, surprisingly, relatively high in all six plant species, suggesting that HCBD can easily accumulate in plants. Berry-Spark et al. (2003) investigated the uptake of HCBD by carrots and lettuces under laboratory conditions. The plants were grown in sand or clay soils containing low (artificially added) HCBD concentrations (29–87 ng/g), and the BAF values were 5.0 and 9.3 in the carrots and 1.75 and 1.90 in the lettuce in the sand and clay soils, respectively. This supports the present finding that there is a strong potential for HCBD to become more concentrated in plants than in the soil they grow in, which implies that there will be potential ecological risks even in soils containing low HCBD concentrations. The BAF values in the laboratory study mentioned above were, however, only 1.18–1.98 and 0.02–0.47 in carrots and lettuces, respectively, when the HCBD concentrations in the soils were 5000–10,000 ng/g (Berry-Spark et al., 2003). Further investigations into HCBD bioaccumulation and the risks associated with soils that are highly contaminated with HCBD are needed. The bioaccumulative capacities of the plants for HCBD and the OCPs were different, as is shown in Fig. 3. The BAF values for αendosulfan in rice and for α-endosulfan and α-chlordane in cowpea were an order of magnitude higher than the corresponding BAF values for HCBD. In contrast, cauliflower accumulated HCBD more strongly than the OCPs. The BAF values for HCBD in cauliflower were one to two orders of magnitude higher than the
Fig. 3. Bioaccumulation factors (BAFs) calculated for hexachlorobutadiene (HCBD) and (A) α-endosulfan, β-endosulfan, α-HCH, β-HCH, p,p0 -DDT and (B) γ-HCH, o,p0 DDT, α-chlordane, γ-chlordane, based on the chemical concentrations in plants and soils from the agricultural studied area in suburban Taicang, East China. The bars indicate the standard deviations of calculated BAFs.
BAFs for all of the OCPs except α-chlordane. As is shown in Fig. 3, on the whole, the soil-to-plant concentration potentials of HCBD and o,p0 -DDT were similar. Nevertheless, the BAFs for HCBD were lower than those for α-endosulfan and much higher than those for the HCHs and p,p0 -DDT. 3.3. HCBD in terrestrial animals HCBD concentrations of 1.3–8.2 ng/g lipid weight (lw) were found in the terrestrial animals, and the results are shown in Table S2. Only a few studies of HCBD residues in terrestrial animals have been published. The status of HCBD concentrations in animals in this study was compared with those in previous reports. Vorkamp et al. (2004) found HCBD concentrations of oMDL–4.9 ng/g lw in terrestrial animals from Greenland. HCBD concentrations of between 1.2 and 8.9 ng/g wet weight, with an arithmetic mean of 3.7 ng/g, have been found in plasma and fat samples from polar bears in Svalbard, Norway (Gabrielsen et al., 2004). However, relatively higher HCBD concentrations, 5.7–13.7 ng/g wet weight, have been found in human liver samples, which may be related to hepatic metabolism of HCBD and the fact that most of the absorbed HCBD had been transported to the liver (IPCS (International Programme on Chemical Safety), 1994). Research into the toxicity of HCBD has focused on aquatic organisms and
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laboratory mammals. The HCBD concentrations in the animals analyzed in this study were much lower than the concentrations given in an HCBD hazard assessment for animals (POPRC (Persistent Organic Pollutants Review Committee), 2013), but the potential effects of HCBD on organisms, especially terrestrial invertebrates, need further study. Large interspecies differences were found in the HCBD and OCP concentrations in the animals, and all of the chemicals were found at much higher concentrations in butterflies than in the other species. The HCBD concentrations in the terrestrial animals were generally lower than the OCP concentrations, and, in particular, an order of magnitude lower than the o,p0 -DDT and α-endosulfan concentrations. In the soils and plants, the HCBD concentrations were relatively low compared with the OCP concentrations in this study area. This may be an important reason for the relatively lower HCBD concentrations than OCPs in animals. Notably, the lower HCBD concentrations do not indicate a lower bioaccumulation potential of HCBD in terrestrial animals, because the levels of HCBD in air, animal foods, and other environmental media were not determined in this study. However, Environment Canada (1999) found that HCBD was eliminated with a half-life of 6.3 days from goldfish. Animal studies with radiolabelled HCBD have also shown that most of the compound is excreted within 72 h via urine and feces (IPCS (International Programme on Chemical Safety), 1994). Such a fast depuration rate might play an important role in the low levels of HCBD in animals.
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terrestrial food chains. Kelly et al. (2007) reported HCBD BMF values, calculated using a bioaccumulation model, of o1.0 for amphibians, reptiles, terrestrial herbivores, and terrestrial carnivores. This was confirmed by the IPCS (International Programme on Chemical Safety) (1994), which mentioned two fish studies in which biomagnification was not found. HCBD has a low Kow and a low Koa, so it might be efficiently eliminated from terrestrial animals through respiration and metabolism. It is particularly important to determine whether HCBD is biomagnified in hightrophic-level organisms (such as birds and wolves) or through the whole terrestrial food web (including high-trophic-level animals). The OCP BMFs were also determined for the food chains of Chinese toads (Table 1). As expected, except for the DDTs, the OCPs were all biomagnified through many of the food chains, but not through every one. The highest OCP BMFs were found for the earthworm–toad food chain. The biomagnification of OCPs through terrestrial food chains and food webs has previously been reported (Senthilkumar et al., 2001; Kelly and Gobas, 2003; Vorkamp et al., 2004). The OCP and HCBD BMFs were plotted against the log Kow and log Koa values for the chemicals, but no significant correlations were found between the BMFs and the partition coefficients (p 4 0.05). This indicates that the transfer of these chemicals through the food chains examined is probably affected by many factors.
4. Conclusions 3.4. HCBD transfer in terrestrial food chains Chinese toads (B. gargarizans) are common amphibians in farmland in Eastern China, and they mainly feed on arthropods, including insects such as coleoptera, diptera, lepidoptera, and orthoptera, some of which are pests, such as grasshoppers, locusts, cabbage worms, and butterflies (Zhou and Song, 1997; Hu et al., 2007). Grasshoppers and locusts generally form a significant proportion of the farmland arthropod biomass (Schmidt, 1986; Fu et al., 2011), and they are common herbivorous invertebrates at these sampling sites. Grasshoppers and locusts are also prey to other insectivorous vertebrates and high-trophic-level species such as birds. Toads and frogs also eat earthworms (Unrine et al., 2012). The BMF values (the ratio between the lipid-normalized concentrations in the predator and prey) for HCBD were calculated in several Chinese toad food chains (Table 1), to better understand the transfer of HCBD through terrestrial food chains. The HCBD BMF values were 0.16–0.64, indicating that HCBD did not biomagnify in any of the food chains examined. To the best of our knowledge, this is the first field study of HCBD transfer through Table 1 Biomagnification factors (BMFs) found for hexachlorobutadiene (HCBD) and organochlorine pesticides in the food chains of the common Chinese toad. Chemical
Grasshoppers/ CT a
Locust/ CT
Cabbage worm/CT
Butterfly/ CT
Earthworm/ CT
HCBD α-HCH β-HCH γ-HCH p, p0 -DDT o, p0 -DDT α-Chlordane γ-Chlordane α-Endosulfan β-Endosulfan
0.28 0.56 0.18 0.17 0.22 0.10 1.6 2.4 0.49 0.030
0.64 0.53 0.28 0.21 0.12 0.070 0.89 0.72 0.38 0.040
0.33 0.35 1.4 0.21 0.15 0.080 0.72 1.2 0.42 0.050
0.16 0.10 0.25 0.040 0.030 0.020 0.28 0.17 0.080 0.010
0.57 1.1 2.1 1.2 0.45 0.67 0.69 2.8 1.5 0.22
a
CT ¼Chinese toad.
HCBD was found to be distributed widely in farmland soils and terrestrial organisms in the study area, although the HCBD concentrations were relatively low compared with the OCP concentrations. Soil–plant accumulation factors for HCBD suggested that it could easily accumulate in plants. The plants studied had similar capacities to bioaccumulate HCBD and o,p0 -DDT, and higher capacities to bioaccumulate HCBD than HCHs or p,p0 -DDT. The occurrence of HCBD in a range of terrestrial animals and the transfer of HCBD through several typical Chinese toad food chains was also investigated. Unlike the OCPs, HCBD was not found to biomagnify in Chinese toad food chains, which is consistent with previously reported HCBD BMF values calculated using bioaccumulation models.
Acknowledgments This research was supported by the National Natural Science Foundation of China (No. 41001329), the special fund for Public Service Sector of the State Environmental Protection Agency of China (Nos. 201209020 and 201309023), the Natural Science Foundation of Hebei province (No. B2011502017), and the Fundamental Research Funds for the Central Universities (No. 12MS01).
Appendix A. Supporting information Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.ecoenv.2014.07.024. References Berry-Spark, K., Morgan, P., Sweetman, A., 2003. Assessment of HCBD Uptake by Edible Plants. Laboratory Programme to Determine Uptake of HCBD by Carrot and Lettuce and Validation of Plant Uptake Models, Reference 6285 R1. Runcorn: ICI Regional and Industrial Businesses. Brüschweiler, B., Märki, W., Wülser, R., 2010. In vitro genotoxicity of polychlorinated butadienes (Cl4–Cl6). Mutat. Res. 699, 47–54. Ding, Z., An, L., 2001. Synthesis method of endosulfan. Pesticides 40, 18–21.
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Distribution and accumulation of hexachlorobutadiene in soils and terrestrial organisms from an agricultural area, East China Zhenwu Tang a, Qifei Huang b,n, Jiali Cheng c, Dan Qu a, Yufei Yang b, Wei Guo a a MOE Key Laboratory of Regional Energy and Environmental Systems Optimization, Resources and Environmental Research Academy, North China Electric Power University, Beijing 102206, China b State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China c National Institute for Nutrition and Food Safety, Chinese CDC, Beijing 100021, China
art ic l e i nf o
a b s t r a c t
Article history: Received 1 April 2014 Received in revised form 23 July 2014 Accepted 24 July 2014 Available online 13 August 2014
Hexachlorobutadiene (HCBD) is a potential persistent organic pollutant that has been found in abiotic environments and organisms. However, information on HCBD in soils and its accumulation in terrestrial food chains is scarce. This study investigated the accumulation of HCBD in soils, plants, and terrestrial fauna in a typical agricultural area in Eastern China, and drew comparisons with organochlorine pesticides (OCPs). The HCBD concentrations in soils were o 0.02–3.1 ng/g dry weight, which were similar to α-endosulfan concentrations but much lower than the concentrations of some other OCPs. The HCBD soil–plant accumulation factors, 8.5–38.1, were similar to those of o,p0 -DDT and higher than those of HCHs and p,p0 -DDT, indicating that HCBD is strongly bioaccumulated by rice and vegetables. HCBD concentrations of 1.3–8.2 ng/g lipid weight were found in herbivorous insects, earthworms, and Chinese toads. The biomagnification factor, the ratio between the lipid-normalized concentrations in the predator and the prey, was found to be 0.16–0.64 for different food chains of Chinese toads, so HCBD was found not to biomagnify, which is in contrast with OCPs. Further research into whether HCBD is biomagnified in high trophic level organisms or through the entire terrestrial food web is required. & 2014 Elsevier Inc. All rights reserved.
Keywords: Hexachlorobutadiene (HCBD) Soils Terrestrial organisms Plant accumulation Biomagnification
1. Introduction Hexachlorobutadiene (HCBD), a halogenated aliphatic hydrocarbon, has been used as an intermediate in the production of a variety of chemicals and as an ingredient in transformer, hydraulic, and heat-transfer liquids (Lecloux, 2004; POPRC (Persistent Organic Pollutants Review Committee), 2013). It is also unintentionally generated during the production of chlorinated hydrocarbons, particularly perchloroethylene, trichloroethylene, and carbon tetrachloride (Brüschweiler et al., 2010). Hexachlorobutadiene is generally moderately acutely toxic and has been found to be genotoxic and carcinogenic in some laboratory animals (Rabovsky, 2000; Brüschweiler et al., 2010; POPRC (Persistent Organic Pollutants Review Committee), 2013). Adverse effects on marine and freshwater species have been observed from exposure to relatively low HCBD concentrations (POPRC (Persistent Organic Pollutants Review Committee) 2013) and HCBD has been detected in various abiotic and biotic media such as surface water,
n
Corresponding author. Fax: þ 86 10 8491 3903. E-mail addresses: [email protected] (Z. Tang), [email protected] (Q. Huang), [email protected] (J. Cheng), [email protected] (D. Qu), [email protected] (Y. Yang), [email protected] (W. Guo). http://dx.doi.org/10.1016/j.ecoenv.2014.07.024 0147-6513/& 2014 Elsevier Inc. All rights reserved.
sediments, ambient air, and organisms (Lee and Fang, 1997; Vorkamp et al., 2004; Li et al., 2008; Juang et al., 2010; Miège et al., 2012). Thus, HCBD has been classed as a priority pollutant in many countries, including Canada, China, the UK, and the USA. In 2012, HCBD was listed as a candidate persistent organic pollutant by the Stockholm Convention for its toxicity, persistence, and potential for bioconcentration and long-range transport in the environment (POPRC (Persistent Organic Pollutants Review Committee), 2012). The potential for HCBD to bioconcentrate in aquatic organisms has been experimentally confirmed. For fish bioconcentration factor (BCF, which is the ratio of the chemical concentration in an organism to the concentration in water) values from 1 to 19,000 L/kg on a whole body basis are reported by Environment Canada (1999). The International Programme on Chemical Safety (IPCS (International Programme on Chemical Safety), 1994) stated that HCBD bioaccumulation factors (BAFs), calculated using wet weight concentrations, in plankton, crustaceans, molluscs, insects, and fish in surface waters were comparable to those observed in the laboratory, and were in the range of 33–11,700 L/kg. Some previous studies have showed the levels of HCBD in aquatic organisms to be relatively low perhaps owing to the mild pollution in the waters studied (Environment Canada, 1999; Miège et al., 2012; Jürgens et al., 2013). At the same time, relatively higher
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concentrations of HCBD have been reported in the aquatic species surrounding industrial areas (IKSR (Internationale Komission zum Schutz des Rheins), 2002; Environment Canada, 1999). A previous report found that the level of HCBD in the mussels that were caged in the river near to three industrial areas of the St. Clair River for three weeks was 36 ng/g wet weight (Environment Canada, 1999). However, recent HCBD monitoring data, especially for HCBD concentrations in terrestrial organisms are scarce and there is limited information available on HCBD bioaccumulation in terrestrial species. Because of its lipophilicity (log Kow ¼4.78) and ability to bioaccumulate (POPRC (Persistent Organic Pollutants Review Committee), 2013), HCBD is likely to biomagnify through food chains and food webs. Based on the BCF according to the European Commission (2003), The Netherlands (2012) estimated the HCBD biomagnification factor (BMF) as being 3 kg/kg, indicating that HCBD has the potential to be biomagnified. In contrast, Kelly et al. (2007) performed bioaccumulation modeling studies and found HCBD BMF values of o1 for all the organisms modeled, including water-respiring and air-breathing organisms. No field-based food chain studies have been performed, so the modeled BMF values (especially for terrestrial food chains) cannot be verified in natural food chains. Thus, the biomagnification potential of HCBD remains undetermined and investigations are urgently needed. Many bioconcentrative chemicals, especially organochlorine pesticides (OCPs), have been investigated in depth and shown to bioaccumulate strongly, and to biomagnify through both aquatic and terrestrial food webs (Hoekstra et al., 2003; Weber et al., 2010; Foster et al., 2011; Silva Barni et al., 2014). It is known that HCBD and OCPs have many similar chemical properties and characteristics. In this study, the occurrence of HCBD in soils and terrestrial organisms in a typical agricultural area in Eastern China was investigated and the accumulations of HCBD and some OCPs in terrestrial plants were assessed to determine whether HCBD acts in a similar way to OCPs; being efficiently transferred from the abiotic environment into plants, and then entering the terrestrial food chain. The transfer of HCBD and OCPs through terrestrial food
chains and the potential for HCBD to be biomagnified was also determined. This research will enable better understanding of the environmental behavior and fate of HCBD.
2. Materials and methods 2.1. Study area Taicang, a city in Eastern China, with a population of 470,000 and an area of 810 km2, is close to Shanghai. With the initiation of the “Reform and Open” policy in 1978, Taicang entered the fastest industrialization period ever experienced, and this has been sustained until today. Being one of the most developed industrial cities in the Yangtze River Delta, Taicang has many chemical synthesis plants and other industrial enterprises. It is possible that HCBD has been released from some local industrial sources into the surrounding farmlands. At the same time, the agriculture in this region is comparatively advanced and produces mainly vegetables and rice, because of the better weather and soil conditions. There has been intensive historic use of OCPs for supporting or improving the agricultural productivity in this area. In the Taicang area suburban farms, a variety of terrestrial plants and animals are widely distributed making it a suitable area for studying pollutant accumulation and transport in terrestrial species at different trophic levels. 2.2. Sample collection In October 2011, soil and organism samples were collected from an agricultural area in the suburbs of Taicang (Fig. 1). Soil samples (0–10 cm deep) were collected from a total of 23 sites (five replicate samples from each site), in the east and south of Xintang, a village in a suburb of Taicang, using a stainless steel shovel. Each soil sample was placed in a pre-cleaned aluminum box and freeze dried before being ground, homogenized, and stored at 20 1C until analysis. Rice (Oryza sativa) and some vegetables, including cabbage (Brassica chinensis), cowpea (Vigna unguiculata), pumpkin (Cucurbita moschata), mustard (Brassica juncea), and cauliflower (Brassica oleracea), were collected at the same time as soil sampling. The rice samples were collected from near the soil sampling sites 11–23 and the other plants were collected from vegetable plots at sites 6 and 7 (shown in Fig. 1). The rice was sampled by collecting all aboveground parts and the aboveground stems and leaves were collected for every vegetable sample. Each composite sample consisted of five subsamples. The numbers of composite samples are given in Table S1. The plant samples were washed with tap water and cut into lengths o 1 cm and mixed well. Then the samples were freeze dried and ground, homogenized, and stored at 20 1C.
N 31º32′24″
E 121º13′12″
E 121º11′24″
N 31º31′12″ Fig. 1. Map showing the soil sampling sites in suburban Taicang, East China.
Z. Tang et al. / Ecotoxicology and Environmental Safety 108 (2014) 329–334 The terrestrial animals including grasshoppers (Acrida chinensis), locusts (Oxya chinensis), cabbage worms (Pieris rapae Linne), butterflies (Eurema hecabe Linnaeus), earthworms (Eisenia foetida), and Chinese toads (Bufo gargarizans) were collected in the locations where plants were sampled within a week after the soil collecting. Several hundred grasshoppers, locusts and butterflies were sampled using funnel traps (20 cm diameter) and transferred to a precleaned glass bottle. Approximately 70 cabbage worms were collected by hands and several hundred earthworms were sampled from soils using spades. A total of 15 Chinese toads from three sites were collected from where other animals were found. All the animals were frozen and then thawed, and rinsed individually with deionized water to remove impurities. Complete organisms of the smaller biological samples were obtained after removal of the viscera. For the Chinese toads, only the muscle tissues were collected. Then all biological samples were freeze dried and then ground to a powder, divided into subsamples and stored at 20 1C until analysis. 2.3. Sample preparation The soils and plants were extracted using a procedure based on the recommendations found in the “Standard of Soil Quality Assessment for Exhibition Sites” and on procedures used in other studies (Verreault et al., 2005; SEPA (State Environment Protection Agency of China), 2007b; Tang et al., 2007). Briefly, 10 g of freeze-dried soil or freeze-dried plant material was extracted with 30 mL of a 1:1 v/v mixture of hexane and dichloromethane in an ultrasonic bath for 30 min, twice. Surrogate recovery standards of 2,4,5,6-tetra-chloro-m-xylene (100 ng) were added prior to extraction. The two extracts were combined, and activated copper was added to remove elemental sulfur. Further purification was achieved by passing the extract through a 12 mm i.d. glass column containing 5 cm of alumina and 5 cm of silica gel, which was eluted with 70 mL of a 7:3 v/v mixture of hexane and dichloromethane. The volume of the extract was then reduced to 0.2 mL under a nitrogen stream, and internal standards were added before the extract was analyzed by gas chromatography (GC). The HCBD and OCPs were extracted from the animal samples in a similar way to the procedure described above, but 4–10 g of each freeze-dried sample was extracted and the purification column contained 5 cm of neutral alumina and 8 cm of neutral silica gel. 2.4. Sample analysis The quantitative analysis of HCBD and OCPs was carried out using an Agilent gas chromatograph 7890 (USA) coupled with an HP-5 column (30 m 0.32 mm 0.25 mm film thickness, Agilent), using a modification of the procedure of Tang et al. (2013). A 63Ni-ECD detector was used for analysis. The GC system was operated in splitless mode and the injection volume was 1 mL. The oven temperature program started at 60 1C, which was held for 2 min, then increased at 20 1C/min to 160 1C, at 5 1C/min to 210 1C, then at 5 1C/min to 270 1C, which was held for 3 min. The injector and detector temperatures were 250 1C and 315 1C, respectively. The carrier gas was nitrogen, and the flow rate was 1.0 mL/min. Total organic carbon (TOC) in soil was measured on a Liqui TOC (Elementar, Germany) at a combustion temperature of 950 1C.
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3. Results and discussion 3.1. HCBD in soils HCBD was detected in 21 of the 23 soil samples, indicating that it is widely distributed in soil in the study area. Fig. 2 shows the results of the soil analyses. The HCBD concentrations were in the range of o0.02–3.1 ng/g dw, and the mean was 0.3 ng/g dw. Webber and Wang (1995) found HCBD concentrations between oMDL and 0.05 ng/g dw in Canadian soils. In China, Zhang et al. (2014) reported that the concentrations in soil around a chemical plant had a range of 0.04–3.33 ng/g dw. But the HCBD concentrations in soils in this study was three to five orders of magnitude lower than those reported in soils from plants producing perchloroethylene and trichloroethylene in the United States (USEPA (United States Environmental Protection Agency), 1976). Currently, there is limited information available on HCBD pollution in other soils (POPRC (Persistent Organic Pollutants Review Committee), 2013). No HCBD concentration limit has been set in the Chinese environmental quality evaluation standards for farmland used for growing edible agricultural products (SEPA (State Environment Protection Agency of China), 2007a), but the HCBD concentration limit is 1.0 μg/g for uncontaminated soils, and this is based on the Chinese standards for soil-quality assessment for exhibition sites (SEPA (State Environment Protection Agency of China), 2007b). HCBD concentration limits of 6.7 and 10.0 ng/g for agricultural coarse- and fine-grained soils, respectively, have been recommended in the environmental quality standard draft for Saskatchewan, Canada (Saskatchewan Ministry of Environment, 2011). Compared with these limits, it was concluded that only lowlevel HCBD contamination was present in these soils from Taicang. The OCP concentrations found in the soils are also shown in Fig. 2. There were significant differences between the HCBD and β-HCH (p ¼0.001), and p,p0 -DDT concentrations (p¼ 0.026), but the HCBD concentrations were not significantly different from the concentrations of the other OCPs (p4 0.05). The mean HCBD concentration was two orders of magnitude lower than the β-HCH and p,p0 -DDT concentrations and an order of magnitude lower than the other OCP concentrations, which reflects the extensive historical agricultural use of OCPs in this area. Correlation analyses
2.5. Quality assurance/quality control The standard solution of OCPs, pentachloronitrobenzene, 2,4,5,6-tetrachlorom-xylene and HCBD were purchased from Supelco (USA). The identities of the target compounds were determined by their match with the average retention times of individual authentic standards, and they were confirmed using an Agilent gas chromatograph/mass spectrometry (Agilent 7890 GC/5975MSD; Agilent Technologies). The 2,4,5,6-tetrachloro-m-xylene was used as a surrogate standard and pentachloronitrobenzene was used as an internal standard. The analytes were not corrected for recoveries. Procedural blanks and samples spiked with the standard mixture were used to monitor the method performance and matrix effects. All of the analyses were carried out in duplicate. The mean spiked HCBD recoveries were 91.6 percent, 78.2 percent, and 82.0 percent in the soil, plant, and animal samples, respectively. The mean spiked OCP recoveries in the soil and organism samples were 74.9–119.4 percent. The mean recoveries of 2,4,5,6-tetrachloro-m-xylene were 81.7 percent, 76.2 percent, and 69.2 percent for the soil, plant and animal samples, respectively. The method detection limits (MDLs) were defined as three times the baseline noise (i.e., a signal-to-noise ratio of three). The MDLs for HCBD and the OCPs were 0.02 ng/g and 0.01–0.07 ng/g dry weight, respectively, in each of the matrices. 2.6. Statistical analysis Analysis of variance was performed on all experimental data and means were compared using the Duncan’s Multiple Range test with SPSS version 18.0 software. The significance level was p o0.05. Correlation analyses and principal component analysis (PCA) were also tested with SPSS version 18.0 software.
Fig. 2. Box plots of hexachlorobutadiene (HCBD) and organochlorine pesticide concentrations in the soil samples from suburban Taicang, East China. The lower and upper limits of the whiskers indicate 5 percent and 95 percent values, respectively; boxes extend from 25th to 75th percentiles; horizontal lines within the boxes represent medians; circles below or above the whiskers indicate outlier values.
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were performed and no significant positive correlations between TOC contents and the concentrations of HCBD as well as the nine OCPs were found. Significant positive correlations were found between HCBD concentrations and α-chlordane (r ¼0.659, p o0.01), α-endosulfan (r ¼0.518, p o0.05), and β-endosulfan (r ¼0.757, p o0.01) concentrations. Principal component analysis was also used to examine the relationships between HCBD and OCP concentrations, and the results are shown in the supporting information (Fig. S1). HCBD, α-chlordane, γ-chlordane, α-endosulfan, and β-endosulfan showed similar loadings in both principal components and were grouped together, separate from the HCHs and DDTs. The HCBD draft risk management evaluation stated that HCBD is present in the raw hexachlorocyclopentadiene product (POPRC (Persistent Organic Pollutants Review Committee), 2013). As it is well known, hexachlorocyclopentadiene was a raw material or intermediate in the industrial synthesis of endosulfan and chlordane (Saha and Lee, 1969; Ding and An, 2001). The products of chlordane and endosulfan might contain HCBD as an impurity. In addition to industrial release, therefore, the historical or current use of pesticides in agriculture might play an important role in the HCBD pollution in soils in this area. 3.2. Accumulation of HCBD in plants The HCBD concentrations in the six plants analyzed were 0.8– 2.0 ng/g dw, and are shown in Table S1. Only small differences in HCBD concentrations were found between different plants. There is so little information available on HCBD concentrations in plants that it is difficult to compare and understand the differences in HCBD concentrations found in plants from different regions. In contrast, the OCP concentrations in different plants were distinctly different. The OCP concentrations in the cauliflower samples were lower than those in the other plant samples. The levels of OCPs found in this study were comparable with those investigated in vegetables in Nanjing (Gao and Jiang, 2005). The OCP concentrations were generally higher than the HCBD concentrations in the plants, but the chlordane and α-HCH concentrations were in the same order of magnitude as the HCBD concentrations. The HCBD and OCP BAFs in the plants were calculated to evaluate the bioaccumulative potential of these chemicals. The HCBD BAFs were 8.5–38.1, as shown in Fig. 3. Despite the low HCBD concentrations in the soils in the studied area these BAFs were, surprisingly, relatively high in all six plant species, suggesting that HCBD can easily accumulate in plants. Berry-Spark et al. (2003) investigated the uptake of HCBD by carrots and lettuces under laboratory conditions. The plants were grown in sand or clay soils containing low (artificially added) HCBD concentrations (29–87 ng/g), and the BAF values were 5.0 and 9.3 in the carrots and 1.75 and 1.90 in the lettuce in the sand and clay soils, respectively. This supports the present finding that there is a strong potential for HCBD to become more concentrated in plants than in the soil they grow in, which implies that there will be potential ecological risks even in soils containing low HCBD concentrations. The BAF values in the laboratory study mentioned above were, however, only 1.18–1.98 and 0.02–0.47 in carrots and lettuces, respectively, when the HCBD concentrations in the soils were 5000–10,000 ng/g (Berry-Spark et al., 2003). Further investigations into HCBD bioaccumulation and the risks associated with soils that are highly contaminated with HCBD are needed. The bioaccumulative capacities of the plants for HCBD and the OCPs were different, as is shown in Fig. 3. The BAF values for αendosulfan in rice and for α-endosulfan and α-chlordane in cowpea were an order of magnitude higher than the corresponding BAF values for HCBD. In contrast, cauliflower accumulated HCBD more strongly than the OCPs. The BAF values for HCBD in cauliflower were one to two orders of magnitude higher than the
Fig. 3. Bioaccumulation factors (BAFs) calculated for hexachlorobutadiene (HCBD) and (A) α-endosulfan, β-endosulfan, α-HCH, β-HCH, p,p0 -DDT and (B) γ-HCH, o,p0 DDT, α-chlordane, γ-chlordane, based on the chemical concentrations in plants and soils from the agricultural studied area in suburban Taicang, East China. The bars indicate the standard deviations of calculated BAFs.
BAFs for all of the OCPs except α-chlordane. As is shown in Fig. 3, on the whole, the soil-to-plant concentration potentials of HCBD and o,p0 -DDT were similar. Nevertheless, the BAFs for HCBD were lower than those for α-endosulfan and much higher than those for the HCHs and p,p0 -DDT. 3.3. HCBD in terrestrial animals HCBD concentrations of 1.3–8.2 ng/g lipid weight (lw) were found in the terrestrial animals, and the results are shown in Table S2. Only a few studies of HCBD residues in terrestrial animals have been published. The status of HCBD concentrations in animals in this study was compared with those in previous reports. Vorkamp et al. (2004) found HCBD concentrations of oMDL–4.9 ng/g lw in terrestrial animals from Greenland. HCBD concentrations of between 1.2 and 8.9 ng/g wet weight, with an arithmetic mean of 3.7 ng/g, have been found in plasma and fat samples from polar bears in Svalbard, Norway (Gabrielsen et al., 2004). However, relatively higher HCBD concentrations, 5.7–13.7 ng/g wet weight, have been found in human liver samples, which may be related to hepatic metabolism of HCBD and the fact that most of the absorbed HCBD had been transported to the liver (IPCS (International Programme on Chemical Safety), 1994). Research into the toxicity of HCBD has focused on aquatic organisms and
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laboratory mammals. The HCBD concentrations in the animals analyzed in this study were much lower than the concentrations given in an HCBD hazard assessment for animals (POPRC (Persistent Organic Pollutants Review Committee), 2013), but the potential effects of HCBD on organisms, especially terrestrial invertebrates, need further study. Large interspecies differences were found in the HCBD and OCP concentrations in the animals, and all of the chemicals were found at much higher concentrations in butterflies than in the other species. The HCBD concentrations in the terrestrial animals were generally lower than the OCP concentrations, and, in particular, an order of magnitude lower than the o,p0 -DDT and α-endosulfan concentrations. In the soils and plants, the HCBD concentrations were relatively low compared with the OCP concentrations in this study area. This may be an important reason for the relatively lower HCBD concentrations than OCPs in animals. Notably, the lower HCBD concentrations do not indicate a lower bioaccumulation potential of HCBD in terrestrial animals, because the levels of HCBD in air, animal foods, and other environmental media were not determined in this study. However, Environment Canada (1999) found that HCBD was eliminated with a half-life of 6.3 days from goldfish. Animal studies with radiolabelled HCBD have also shown that most of the compound is excreted within 72 h via urine and feces (IPCS (International Programme on Chemical Safety), 1994). Such a fast depuration rate might play an important role in the low levels of HCBD in animals.
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terrestrial food chains. Kelly et al. (2007) reported HCBD BMF values, calculated using a bioaccumulation model, of o1.0 for amphibians, reptiles, terrestrial herbivores, and terrestrial carnivores. This was confirmed by the IPCS (International Programme on Chemical Safety) (1994), which mentioned two fish studies in which biomagnification was not found. HCBD has a low Kow and a low Koa, so it might be efficiently eliminated from terrestrial animals through respiration and metabolism. It is particularly important to determine whether HCBD is biomagnified in hightrophic-level organisms (such as birds and wolves) or through the whole terrestrial food web (including high-trophic-level animals). The OCP BMFs were also determined for the food chains of Chinese toads (Table 1). As expected, except for the DDTs, the OCPs were all biomagnified through many of the food chains, but not through every one. The highest OCP BMFs were found for the earthworm–toad food chain. The biomagnification of OCPs through terrestrial food chains and food webs has previously been reported (Senthilkumar et al., 2001; Kelly and Gobas, 2003; Vorkamp et al., 2004). The OCP and HCBD BMFs were plotted against the log Kow and log Koa values for the chemicals, but no significant correlations were found between the BMFs and the partition coefficients (p 4 0.05). This indicates that the transfer of these chemicals through the food chains examined is probably affected by many factors.
4. Conclusions 3.4. HCBD transfer in terrestrial food chains Chinese toads (B. gargarizans) are common amphibians in farmland in Eastern China, and they mainly feed on arthropods, including insects such as coleoptera, diptera, lepidoptera, and orthoptera, some of which are pests, such as grasshoppers, locusts, cabbage worms, and butterflies (Zhou and Song, 1997; Hu et al., 2007). Grasshoppers and locusts generally form a significant proportion of the farmland arthropod biomass (Schmidt, 1986; Fu et al., 2011), and they are common herbivorous invertebrates at these sampling sites. Grasshoppers and locusts are also prey to other insectivorous vertebrates and high-trophic-level species such as birds. Toads and frogs also eat earthworms (Unrine et al., 2012). The BMF values (the ratio between the lipid-normalized concentrations in the predator and prey) for HCBD were calculated in several Chinese toad food chains (Table 1), to better understand the transfer of HCBD through terrestrial food chains. The HCBD BMF values were 0.16–0.64, indicating that HCBD did not biomagnify in any of the food chains examined. To the best of our knowledge, this is the first field study of HCBD transfer through Table 1 Biomagnification factors (BMFs) found for hexachlorobutadiene (HCBD) and organochlorine pesticides in the food chains of the common Chinese toad. Chemical
Grasshoppers/ CT a
Locust/ CT
Cabbage worm/CT
Butterfly/ CT
Earthworm/ CT
HCBD α-HCH β-HCH γ-HCH p, p0 -DDT o, p0 -DDT α-Chlordane γ-Chlordane α-Endosulfan β-Endosulfan
0.28 0.56 0.18 0.17 0.22 0.10 1.6 2.4 0.49 0.030
0.64 0.53 0.28 0.21 0.12 0.070 0.89 0.72 0.38 0.040
0.33 0.35 1.4 0.21 0.15 0.080 0.72 1.2 0.42 0.050
0.16 0.10 0.25 0.040 0.030 0.020 0.28 0.17 0.080 0.010
0.57 1.1 2.1 1.2 0.45 0.67 0.69 2.8 1.5 0.22
a
CT ¼Chinese toad.
HCBD was found to be distributed widely in farmland soils and terrestrial organisms in the study area, although the HCBD concentrations were relatively low compared with the OCP concentrations. Soil–plant accumulation factors for HCBD suggested that it could easily accumulate in plants. The plants studied had similar capacities to bioaccumulate HCBD and o,p0 -DDT, and higher capacities to bioaccumulate HCBD than HCHs or p,p0 -DDT. The occurrence of HCBD in a range of terrestrial animals and the transfer of HCBD through several typical Chinese toad food chains was also investigated. Unlike the OCPs, HCBD was not found to biomagnify in Chinese toad food chains, which is consistent with previously reported HCBD BMF values calculated using bioaccumulation models.
Acknowledgments This research was supported by the National Natural Science Foundation of China (No. 41001329), the special fund for Public Service Sector of the State Environmental Protection Agency of China (Nos. 201209020 and 201309023), the Natural Science Foundation of Hebei province (No. B2011502017), and the Fundamental Research Funds for the Central Universities (No. 12MS01).
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