STOTEN-16063; No of Pages 7 Science of the Total Environment xxx (2014) xxx–xxx

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Organochlorine pesticides and polychlorinated biphenyls in grass, yak muscle, liver, and milk in Ruoergai high altitude prairie, the eastern edge of Qinghai-Tibet Plateau Jing Pan a, Nan Gai a,⁎, Hua Tang b, Shu Chen a, Dazhou Chen b, Guohui Lu a, Yongliang Yang a,⁎ a b

National Research Center for Geoanalysis, Beijing 100037, China Division of Metrology in Chemistry, National Institute of Metrology, Beijing 100013, China

H I G H L I G H T S • • • •

OCPs and PCBs in yak in Ruoergai highland at 3,500 m (a.s.l.) were measured. HCHs, DDTs, and PCBs were detected in yak muscle, liver, and milk. HCB and β-HCH were the main POPs in yak milk. The consumptions of yak muscle and milk would not pose risk to local people.

a r t i c l e

i n f o

Article history: Received 30 October 2013 Received in revised form 14 March 2014 Accepted 14 March 2014 Available online xxxx Editor: D. Barcelo Keywords: OCPs PCBs Ruoergai plateau Yak muscle Yak milk

a b s t r a c t In highland pastures, where no agricultural and industrial activities exist, organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) are believed to be mainly coming from water–soil–grass system which is subject to air–water and air–soil exchanges and atmospheric precipitation. Samples of grass and yak muscle, liver, and milk were measured for OCPs and PCBs in the summer and winter of 2011. The total concentrations of HCHs, DDTs, endosulfans, HCB, and PCBs in grass samples were in the range of 0.53–2.45, 1.6–6.0, 1.10–4.38, 0.30–1.24, 0.65–2.04 ng g−1 dw (dry weight), with the means 1.38, 2.86, 2.06, 0.73, and 1.19 ng g−1 dw, respectively. The mean concentrations of HCHs and DDTs in yak muscle were 1.65 and 0.55 ng g−1 fw (fresh weight), respectively; no significant seasonal differences. The average total concentrations of HCHs, DDTs, HCB, endosulfans, and PCBs in yak milk were 4.46, 0.59, 1.00, 0.27, and 0.097 ng g−1 fat, respectively. Among the POPs investigated, β-HCH and HCB were dominant in yak muscle and liver, whereas β-HCH dominated the yak milk. Consistent with the results of other studies, PCB 153, 138, and 180 were detected in yak milk that is in accordance with the case reported for farmed cow milk in China and other countries. A human health risk was conducted based on the intake of OCPs via consumptions of the yak muscle and milk. Since the daily intake of HCHs and DDTs was lower than WHO or USEPA's acceptable daily intake or minimal risk level, showing that the consumptions of the yak muscle and milk would not pose any immediate risk to local people. © 2014 Elsevier B.V. All rights reserved.

1. Introduction Organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) are persistent organic pollutants (POPs); they have slow degradation rates and have extensive historical uses in agricultural and industrial applications. Some volatile POPs, such as some lower chlorinated PCBs can undergo long range atmospheric transport (LRAT), and therefore they have been globally detected in animals and humans, even in

⁎ Corresponding authors at: National Research Center for Geoanalysis, Xicheng District, 26 Baiwanzhuang Street, Beijing 100037, China. Tel.: +86 10 68999582. E-mail addresses: [email protected] (N. Gai), [email protected] (Y. Yang).

remote areas like the Arctic, where these compounds have never been used (Hansen, 2000; Muir and de Wit, 2010). The United Nation Environment Protection (UNEP) has established a global treaty, known as the Stockholm Convention in 2001; the aims of the convention are to eliminate of production of POPs and control unintentionally produced POPs (UNEP, 2001, 2009a); among the POPs, PCBs, polychlorinated dibenzo-p-dioxin and polychlorinated dibenzofuran (PCDD/Fs), and OCPs such as hexachlorocyclohexanes (HCHs), dichlorodiphenyltrichloroethane (DDT) are of most concerned. Endosulfan is an insecticide that persists in the environment, which was also added to another international treaty, the Rotterdam Convention, which requires government-to-government notification when dangerous pesticides and other chemicals cross international borders (USEPA, 2002).

http://dx.doi.org/10.1016/j.scitotenv.2014.03.074 0048-9697/© 2014 Elsevier B.V. All rights reserved.

Please cite this article as: Pan J, et al, Organochlorine pesticides and polychlorinated biphenyls in grass, yak muscle, liver, and milk in Ruoergai high altitude prairie, t..., Sci Total Environ (2014), http://dx.doi.org/10.1016/j.scitotenv.2014.03.074

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J. Pan et al. / Science of the Total Environment xxx (2014) xxx–xxx

Due to the lipophilic properties, POPs are accumulated in fatty tissues in animals and humans. These compounds bioaccumulate and biomagnify along the food chains and have health impacts on wildlife and human (Tanabe, 2002). Health effects such as endocrine disruption, mutation, and carcinogenicity have been suggested to link with the bioaccumulation of POPs (Hansen, 2000). As mentioned above, these compounds can also be transferred to remote clean areas via LRAT at regional or even global scale (Wania and Mackay, 1993). High mountains and cold regions have been suggested to be the sink and important reservoirs of POPs (Blais et al., 1998). Compared to the low-altitude areas, high-altitude regions have low air temperature and relatively high snow precipitation. Detection of POPs have been observed in air, water, and soils in the high altitude regions of the western China, such as the Himalayas and Tibetan Plateau (Wang et al., 2006, 2007a; Yang et al., 2008; Kang et al., 2009; Pan et al., 2013; Sheng et al., 2013). Previous studies have shown that food is a major route of human exposure to OCPs and PCBs via the consumption of contaminated fish, meat, and dairy products (Duarte-Davidson and Jones, 1994; Darnerud et al., 2006). Several mass balance studies have demonstrated that POPs such as PCBs, PCDD/Fs, and polybrominated diphenyl ethers (PBDEs) of different physico-chemical properties played an important role in their transfer and accumulation from feed to cow tissues and milk (McLachlan, 1993; Thomas et al., 1998, 1999a; Kierkegaard et al., 2007; Tato et al., 2011). In contrast, limited study is available in highland (Tato et al., 2011). In China, only PCBs in butter samples in Lhasa, Tibet have been reported (Wang et al., 2010). In highland pastures, where no agricultural and industrial activities exist, PCBs and OCPs are believed to be coming from atmospheric precipitation into surface water, soils, and grass; PCBs and OCPs are expected to transfer from grass to cow. Yak meat and milk are the main foodstuffs for highland residents in central Asia and high plateau regions of the western China. Consumption of these foodstuffs may be an important exposure route for the local residents to intake PCBs and OCPs. Therefore, it is important to understand how these POPs such as PCBs, HCHs, DDTs, endosulfans, and HCB transfer from grass to cows' tissue and milk in order to evaluate human exposure to these chemicals via dietary exposure in free-range livestock farming in highland plateaus. Ruoergai (Zoige) highland prairie with an average altitude of 3500 m above sea level (a.s.l.) in Qinghai-Tibetan Plateau was selected as the research area to study the levels of typical POP compounds (OCPs and

PCBs) in grass, yak meat and milk in high altitude areas. The present investigation reports the results from a detailed field study conducted to quantify the OCP and PCB levels in grass, yak, meat and milk. Ten OCPs and six indicator PCB congeners were analyzed by a high resolution gas chromatograph–high resolution mass spectrometry (HRGC– HRMS). The aims of this study are to provide information on the composition patterns of the POP compounds in grass and yak samples and to conduct a health risk assessment of local residents on POP exposure via uptake of yak meat and milk. 2. Materials and methods 2.1. Research areas and geographic setting Ruoergai highland prairie is located at the eastern edge of the Qinghai-Tibetan Plateau, north of Sichuan Province, at altitudes of 3200–3600 m a.s.l. It is in the convergence zone of East Asia monsoon and the Qinghai-Tibetan Plateau climate system. The eco-environment is pasture and alpine wetlands; it is one of the largest three grasslands in China having an 808,000 hectare natural grassland in Ruoergai pasture. The economics is mainly free-range livestock farming (yak, sheep, and horse), and most of the population is Tibetan. The climate of Ruoergai highland grassland is characterized by cold weather, with an annual average temperature of 2 °C, and an annual average precipitation of 600 mm, which mostly occurs between June and August. Summer is short (June and July) and the average temperature is 10.8 °C, whereas the average temperature in winter is − 5 °C. The prevailing wind is mainly westerly and northwesterly. The climate of this region has changed dramatically since the 1990s; decreasing precipitation and increasing evaporation trends were observed, and these trends have lead to shrinking of the wetland area; consequently, water resources drastically reduced, grassland degradation, and accelerated soil desertification. 2.2. Sample collection Grass, yak muscle, liver, and milk samples were collected in June and November 2011. The sampling locations are given in Fig. 1. Grass samples (n = 27), mainly Kobresia sp. and Polygonum sp., were collected using a small stainless shovel in five different farms (Heihe Farm,

Fig. 1. Map of sampling locations in the Ruoergai highland prairie.

Please cite this article as: Pan J, et al, Organochlorine pesticides and polychlorinated biphenyls in grass, yak muscle, liver, and milk in Ruoergai high altitude prairie, t..., Sci Total Environ (2014), http://dx.doi.org/10.1016/j.scitotenv.2014.03.074

J. Pan et al. / Science of the Total Environment xxx (2014) xxx–xxx

Tangke, Huahu Lake, Banyou, and National Reserve Area of Ruoergai Wetland) and wrapped in clean aluminum foil, and stored at − 18 °C until extraction. Yak muscle (n = 8) and liver (n = 8) were purchased from local farmers; yak milk samples (n = 10) were collected in five different farms. The samples were preserved in freezer at − 20 °C and transported on ice to the laboratory. The yak samples were minced and homogenized before extraction and clean-up procedures. 2.3. Extraction and instrumental analysis 2.3.1. Reagents and standards Reagents used in the present work were of analytical grade unless specified. Acetone, n-hexane, and dichloromethane (DCM) were from Tianjin Kermel Chemical Reagent Co. Inc., China; methanol was from Jinan Chemical Reagent Co. Inc., China; guaranteed grade of silica gel (0.063–0.200 mm mesh), alumina and sulfuric acid were from Qingdao Chemical Reagent Co. Inc., China; copper chips were from Tianjin Huazhen Chemical Reagent Co. Inc., China; and granular anhydrous sodium sulfate was from Tianjin Tanggu Dengzhong Chemical Reagent Co. Inc., China. A surrogate standard TMX (2,4,5,6-tetrachloro-m-xylene) and fifteen targeted analysis standards were purchased from National Research Center for Certified Reference Materials of China National Institute of Metrology Standards including PCB 28, PCB 52, PCB 101, PCB 138, PCB 153, PCB 180, α-, β-, γ- and δ-HCH, p,p′-DDD, p,p′-DDE, p,p′-DDT, o,p′-DDT, and α- and β-endosulfans. The internal standards were 13C mass-labeled HCHs, DDTs, and PCBs (EC-4937, CIL, USA). All solvents used were of HPLC or glass-distilled grade. Silica gel and alumina were activated at 450 °C overnight for the activated silicaalumina chromatography; the anhydrous sodium sulfate was activated at 650 °C in a furnace for 6 h. All sorbents were stored in sealed containers in desiccators. All glassware materials were cleaned in an ultrasonic cleaner and heated at 350 °C for 12 h. 2.3.2. Extraction and clean-up procedures Samples were spiked with mass-labeled standards and then Soxhlet-extracted with 150 mL DCM for 48 h. Prior to extraction, 2 g copper chips were added in order to remove sulfur. After extraction, the extract was evaporated to 5–10 mL, and further to 1 mL after adding 10–15 mL n-hexane, after that the 1 mL extract was transferred to a 5 mL vial; this step was repeated three times. The extract was passed through a silica–alumina cleanup column (7 mm i.d., from bottom to top: 10 g 3% activated silica, 10 g 3% de-activated alumina, 1 g dehydrated sodium sulfate). The column was eluted with 35 mL 50% DCM in n-hexane and concentrated to 0.5 mL using a rotary evaporator. The extract was further micro-concentrated to 200 μL under a gentle stream of nitrogen for HRGC–HRMS analysis. 2.3.3. HRGC–HRMS analysis The HRGC–HRMS used was a HP-6890 gas chromatograph coupled with Micromass Autospec-Ultima high resolution mass spectrometer. The chromatographic column was HP-5MS (30 m × 0.32 mm × 0.25 μm). The injection inlet temperature was 280 °C. The GC temperature program was as follows: column temperature from 50 °C (2 min) to 180 °C (10 °C min−1), held for 2 min, then to 220 °C Table 1 Limits of quantification (LOQs) for HCH, DDT isomers and PCB congeners. Compound

LOQ (pg g−1)

Compound

LOQ (pg g−1)

TMX α-HCH β-HCH γ-HCH HCB DDE o,p′-DDT Endosulfan

0.149 0.961 0.961 0.932 0.575 0.381 0.676 0.5

p,p′-DDT PCB028 PCB052 PCB101 PCB153 PCB138 PCB180

0.806 0.589 0.165 0.112 0.169 0.137 0.407

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(2 °C min−1), and to 290 °C (10 °C min−1), held for 15 min. The sample (1.0 μL) was injected with splitless injection mode. The HRMS condition was as follows: the ion source temperature was 280 °C; the ionization mode was EI; the electron energy was 40 eV; and the ionization current was 650 μA. The resolution was N3000. Qualification was carried out using retention times and mass ratios; the retention time of a component peak was exactly equal to that of corresponding standard and the mass ratio of the two single ions of a compound was within 0.8–1.0. Internal calibration using corresponding mass-labeled standards was employed for quantification. One blank sample was carried out during each batch (ten samples) of experiment to ensure the cleanness of reagents and laboratory wares. Sampling, reagent, and procedure blanks were assessed during the analysis; no quantifiable target compounds were found in the blank samples. Duplicate analyses were carried out for each batch of experiment to ensure the repeatability of the analytical results. The recoveries for OCPs and PCBs were in the range of 61%–102% and 75%–109%, respectively. Through matrix spike experiment, the LOQ (limit of quantification) for OCPs was 0.38–0.96 pg g−1, and for PCBs was 0.11–0.59 pg g−1 (Table 1). For calculations of mean values, when the concentration of a given compounds was below the LOQ of the method, the value was assumed to be 0. 3. Results and discussions 3.1. Grass The total concentrations of HCHs, DDTs, endosulfans, HCB, and PCBs in grass samples were in the range of 0.82–2.45 (mean: 1.38), 1.6–6.0 (2.88), 1.10–4.38 (1.98), 0.40–1.01 (0.72), 0.71–2.04 (1.18) ng g−1 dw, respectively (Table 2). Among the POPs measured, DDTs (34.7%) and endosulfans (25.0%) were dominant compounds. Among the six PCB indicator congeners, PCB 28, 52, 101, 138, and 153 were detected; PCB 28 and 52 were the dominant congeners, accounting for 80% of the total PCBs. α- and β-endosulfan accounted for the respective 5% and 20% of the POPs in the samples. The composition patterns of the POPs in the grass samples from Ruoergai area are given in Fig. 2. There was no much seasonal difference in the levels of these compounds, with slightly higher levels in winter than in summer except for α-endosulfan. Comparing the POP concentrations with other high mountain or plateau areas, HCHs in Ruoergai grass were lower than those from Mt. Qomolangma (0.354–7.82 ng g−1 dw; Wang et al., 2007a) and the mosses of the Andean mountains (1.2–11 ng g−1 dw; Grimalt et al., 2004), but higher than those in the Antarctic (0.2–0.5 ng g−1 dw; Fuoco et al., 2009). The concentrations of DDTs in the grass samples from Ruoergai were at about the same level to those in grass from Mt. Qomolangma (1.08–6.99 ng g−1 dw; Wang et al., 2007a). Smith et al. (2001) found that different grass species in European pastures had the same ability to absorb the airborne POPs, and therefore could be used as bio-monitor to compare the POPs in different regions over the world. The usage of HCHs and DDTs in China has been banned for more than 20 years. Therefore the most observed HCHs and DDTs in the present study should be the legacy residues from soils in other regions via long-range transport. Until recently, lindane is currently still being used to small extents in China (Li et al., 2008b). The ratio of α-/γ-HCH in technical HCH is between 3 and 7 (Walker et al., 1999). The α-/γHCH ratio in the Ruoergai grass ranged 0.94–1.73, with an average of 1.29, similar to the ratio in Ruoergai soils, which were in the range of 1.0–2.0 (Gai et al., 2014), suggesting that there was an application of lindane in the neighboring regions (Li et al., 2008b). The mean concentrations of p,p′-DDE, one of the metabolite of p,p′-DDT under aerobic condition, was the highest among the four isomers, followed by p,p′-DDT, p,p′-DDD, and o,p′-DDT. Low DDT/DDE ratios (calculated as p,p′-DDT/p,p′-DDE) are indicative of aged sources (Qiu et al., 2004). The present DDT/DDE ratio (0.75 ± 0.24) in the

Please cite this article as: Pan J, et al, Organochlorine pesticides and polychlorinated biphenyls in grass, yak muscle, liver, and milk in Ruoergai high altitude prairie, t..., Sci Total Environ (2014), http://dx.doi.org/10.1016/j.scitotenv.2014.03.074

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Table 2 Concentrations of HCH, DDTs, endosulfan, HCB, and PCB isomers in grass, yak muscle tissue, liver, and milk from Ruoergai highland prairie. ΣHCHs

−1

Grass (ng g (n = 29)

dw)

Yak muscle (ng g−1 fw) Summer (n = 5) Winter (n = 3) Mean of summer and winter Yak liver (ng g−1 fw) (n = 8)

ΣDDTs

Σendosulfans

ΣPCBs

HCB

Mean

SDa

Range

Mean

SDa

Range

Mean

SDa

Range

Mean

SDa

Range

Mean

SDa

0.82–2.45

1.38

0.45

1.60–6.00

2.86

1.01

1.10–4.38

1.98

0.86

0.40–1.01

0.72

0.22

0.71–2.04

1.18

0.36

0.81–2.58 1.01–2.64 0.81–2.64

1.46 1.93 1.65

0.65 1.93 0.76

0.08–0.99 0.29–1.06 0.08–1.06

0.53 0.59 0.55

0.32 0.59 0.30

nd–0.71 0.25–0.3 nd–0.43

0.31 0.31 0.33

0.27 0.10 0.2

0.20–1.19 0.30–1.03 0.20–1.19

0.66 0.74 0.69

0.37 0.39 0.37

nd nd nd

nd nd nd

nd nd nd

4.74

nd–0.78

0.30

0.24

nd–0.40

0.24

0.12

0.05–1.03

0.58

0.34

nd

nd

nd

2.16 3.75 2.98

0.15–0.96 0.27–1.18 0.15–1.18

0.59 0.59 0.59

0.32 0.52 0.35

0.08–0.42 0.24–0.44 0.08–0.44

0.24 0.32 0.27

0.12 0.10 0.12

0.35–1.21 1.10–1.74 0.35–1.74

0.81 1.46 1.00

0.34 0.32 0.45

nd–0.25 nd–0.34 nd–0.34

0.088 0.11 0.097

0.12 0.20 0.13

Range

5.0–19.4

11.4

−1

Yak Milk (ng g fat) Summer (n = 7) Winter (n = 3) Mean of summer and winter

0.90–5.98 2.59–9.74 0.90–9.74

3.45 6.81 4.46

nd: Not detectable, 0 value was used for calculating the mean concentrations when the value b LOQ. a Standard deviation.

grass samples was lower than that reported in Tibetan Plateau (mean: 1.10; Gong et al., 2010), suggesting no current use of DDTs in Ruoergai area. The difference between Ruoergai area and Tibetan Plateau is that Ruoergai has no agriculture whereas barley and other agricultural plants are cultivated in Tibet where possible current use of OCPs has been reported (Li et al., 2008b). HCB concentrations in Ruoergai grass were at about the same level of those in grass from Mt. Qomolangma (0.0156–1.25 ng g−1 dw) in mosses in Antarctic (0.3–0.8 ng g− 1 dw; Wang et al., 2007a; Fuoco et al., 2009). Uptake of HCB into vegetation occurs through both gas phase deposition to aerial plant surfaces, and through uptake by roots from the soil, but the high lipophilicity of HCB with log KOW (octanolwater partition coefficient) = 5.64 and log KOA (octanol-air partition coefficient) = 7.21 (Shen and Wania, 2005) suggests that the main pathway for an uptake of HCB by grass leaves is directly from air–plant exchange (Riederer, 1990). Endosulfans were detected in the grass samples in Ruoergai area where it was not used. The average total concentration of endosulfans in Ruoergai grass (2.06 ± 0.86 ng g−1 dw) was at about the same level of those in grass from Mt. Qomolangma (α-endosulfan: 0.29–3.14; β-endosulfan: 0.105–1.54; Wang et al., 2007a); and characterized by higher β-endosulfan than α-endosulfan in Ruoergai area. The average concentrations of α- and β-endosulfans in the grass from Ruoergai area were 0.41 and 1.64 ng g−1 dw respectively, which were much higher than those in soils (0.05 and 0.28 ng g−1 dw, respectively; Gai et al., 2014). The technical products of endosulfans contain about 70% of α-endosulfan and 30% of β-endosulfan (Gupta and Gupta, 1979). Endosulfans are compounds with persistency and bioaccumulation in the environment (UNEP, 2009b). The α-endosulfan is more

volatile, while the β-endosulfan is generally more adsorptive and persistent (Rice et al., 2002; USEPA, 2002). The total PCB concentrations in the grass samples in Ruoergai area (0.71–2.04 ng g−1) were significantly lower than those of the Himalayas

Fig. 2. Isomer concentrations of OCPs and PCBs in grass samples in Ruoergai highland prairie.

Fig. 3. Isomer concentrations of OCPs and PCBs in (a) yak muscle tissue, (b) liver, and (c) milk samples in Ruoergai highland prairie (*endosulfan).

Please cite this article as: Pan J, et al, Organochlorine pesticides and polychlorinated biphenyls in grass, yak muscle, liver, and milk in Ruoergai high altitude prairie, t..., Sci Total Environ (2014), http://dx.doi.org/10.1016/j.scitotenv.2014.03.074

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(1.94–3.62 ng g−1 dw, mean: 2.60 ng g−1 dw; Gao et al., 2012), and the Antarctic (23–34 ng g−1 dw; Fuoco et al., 2009), but at about the same level as PCBs in grass of Alps (0.32–2.05 ng g−1 dw; Tato et al., 2011), and in the mosses of the Andean mountains (0.24–2.4 ng g− 1 dw; Grimalt et al., 2004). PCB 28 and 52 accounted for about 90% of indicative PCBs were observed in two types of grass samples from the Himalayas (Gao et al., 2012). 3.2. Yak muscle and liver The concentrations of POPs in yak muscle, liver, and milk samples are presented in Table 2 and Fig. 3. Since there were no significant seasonal differences in the concentrations of POPs between the two seasons in muscle tissues and liver samples, the concentrations between the two seasons were pooled. The total concentrations of HCHs, HCHs, DDTs, endosulfans, and HCB in yak muscle tissue were 1.65, 0.55, 0.33, and 0.69 ng g−1 fresh weight (f.w.), respectively; no detectable PCBs were observed in any yak muscle and liver samples. Relative to yak muscle, HCHs in yak liver were higher (11.4 ng g−1 fw). In all types of yak samples, β-HCH was the predominant HCH isomer; yak liver showed the greatest concentrations (mean: 11.1 ng g−1 f.w.), which was 9.4-fold higher than those of muscle (1.18 ng g−1 fw). High contribution of β-HCH to the OCPs has been observed in animal samples from China (e.g. Wang et al., 2007b; Li et al., 2008a). The production and use of HCHs were banned in the 1970s. Due to its persistency and bioaccumulative potention, β-HCH might be accumulated along food chains. Since limited information on OCP and PCB levels in cattle in China is available, the comparison of data will be on captive animals. The total concentrations of OCPs and PCBs in captive giant and red panda from China ranged from 24.8 to 854 ng g−1 fat and 16.4 to 2158 ng g−1 fat, respectively; with p,p′-DDE and β-HCH were the major OCPs in the samples; PCBs 99, 118, 153/132, 170, 180, and 209 were the major PCB congeners (Hu et al., 2008). In Jordon, HCHs and DDTs were found to be 50 and 45 ng g− 1 fat in lamb and beef, correspondingly (Ahmad et al., 2010). The median sum PCBs in the livers of dairy cows in Belgium were found to be 11.7 ng g−1 fat (Petro et al., 2010). In comparison, OCP and PCB concentrations in Ruoergai yak muscle and liver samples were relatively low. The HCH and DDT levels in the yak muscle and liver did not exceed the allowed concentrations in China's food quality standard (GB2762-2005; HCHs: 1 mg kg−1, DDTs: 2 mg kg−1, PCBs: 0.5 mg kg−1) and FAO/WHOs maximum residue limits (γ-HCH: 0.1 mg kg−1 fat, DDTs: 5 mg kg−1 fat) (FAO/WHO, 2004). 3.3. Yak milk The average total concentrations of HCHs, DDTs, HCB, endosulfans, and PCBs in yak milk between summer and winter were in the range

Fig. 4. Relative contribution of different groups of compounds to the total POPs measured in various types of samples from Ruoergai highland prairie.

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of 0.90–9.74 (mean: 4.46), 0.15–1.18 (0.59), 0.35–1.74 (1.00), 0.08–0.44 (0.27), nd–0.34 ng g−1 fat (0.097), respectively. The HCH, DDT, and PCB levels in the yak milk did not exceed the allowed concentrations for HCHs and DDTs (0.020 mg kg−1) in China's fresh milk quality standard (GSWB-200), and the maximum residue limits (γ-HCH: 0.01 mg kg−1; DDT: 0.02 mg kg−1) of FAO/WHO (2004). In yak samples, β-HCH, HCB, and α-HCH were dominant (Fig. 4). The total HCHs in milk in winter (6.81 ng g−1 fat) were significantly higher than those in summer (3.45 ng g−1 fat); this seasonal difference was mainly due to β-HCH. The fat content in Ruoergai yak milk was lower in winter (mean: 5.6% w/w) than in summer (7.2% w/w), and therefore the concentrations on lipid basis may have contributed to the seasonal difference. To eliminate the influence of fat content on the accumulation levels of groups of compounds in different types of samples, Fig. 4 shows the relative contributions of different groups of compounds to the total POPs in various types of samples from Ruoergai highland prairie. It can be seen that the lipophilic compounds DDTs and PCBs showed no obvious seasonal changes. The relatively higher β-HCH levels in yak milk both in summer and winter were possibly due to its resistance to degradation (UNEP, 2007). The carry-over rates for OCPs from feed to milk have been studied for decades. Kapoor and Kalra (1997) reported the value of around 5% carry-over of α-HCH from feed to milk for buffalo. Carry-over percentages between 15 and 55%, and up to 100% for β-HCH have been reported (Heeschen et al., 1983; Bluthgen, 2000). As for γ-HCH and DDT, from feed to milk, carry-over percentages of 2%–4% and 4% have been reported, respectively; less than 79% has been reported for HCB (Bluthgen, 2000). Our results for OCP levels in yak milk were in consistence with the reported carry-over rate data for these compounds. PCB 28 and 52 were not detected in any of the yak samples. These congeners are known to be relatively easily metabolized by cows (Kalantzi et al., 2001). PCB 138, 153, and 180 were the only PCB congeners detected in the yak milk though at very low level (0.037, 0.031, 0.029 ng g − 1 fat, respectively). Highly chlorinated PCBs with the octanol-air partition coefficients log K OA 8–10 are poorly volatile in the cold high plateau environment and tend to bind to the lipids of organism than their lower chlorinated counterparts. The highly chlorinated PCBs also have lower rates of metabolic degradation and therefore biomagnified to a greater extent (Walker, 2001). Through a long-term study of lactating dairy cows, Thomas and et al. (1999b) observed that PCBs in milk were dominated by PCB 118, 138, and 153; all other detectable congeners were found less than half of the concentrations of these three congeners. The carry-over percentage for PCBs 138, 153, and 180 was reported to be approximately 100% (Thomas et al., 1999b). Our results showed that although the yaks are fed on natural grass in free-range grazing, the discriminating carry-over of PCB congeners from grass to yak milk was similar to the cases reported for farmed cows. Sewart and Jones (1996) reported ΣPCB concentrations in samples of unpasteurized bulked milk, taken directly from ten herds of dairy cattle on rural and urban farms in the north west of England were in the range of 3.4–16.4 ng g−1 fat (mean: 8.4 ng g−1 fat), and the dominating PCB congeners were 118, 153, 138 and 180. In Ghana, PCBs in cow milk samples were reported in the ranged 2.1–45 ng g− 1 fat in rural samples and 2.5–87 ng g− 1 fat in urban samples (Asante et al., 2010). In Iran, concentrations of p,p′-DDT and p,p′-DDE in locally produced butter were found in the range of 8.45–46.8 ng g− 1 fat, of which the greatest levels were mainly found in urban areas (Jafari et al., 2008). Limited report has published OCP and PCB levels in cow fresh milk and dairy products in China. Concentrations of PCBs in Tibetan butter were reported to be 0.137–2.518 ng g− 1 f.w. (mean: 0.519 ng g−1 fw; Wang et al., 2010). The total HCHs and DDTs in yogurt in China were found to be 0.6 and 0.5 ng g−1 f.w., respectively (Zhang et al., 2006). The levels of HCHs, DDTs, and PCBs in the yak milk from

Please cite this article as: Pan J, et al, Organochlorine pesticides and polychlorinated biphenyls in grass, yak muscle, liver, and milk in Ruoergai high altitude prairie, t..., Sci Total Environ (2014), http://dx.doi.org/10.1016/j.scitotenv.2014.03.074

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J. Pan et al. / Science of the Total Environment xxx (2014) xxx–xxx

Table 3 Assessment of health risks intake of OCPs and PCBs of local residents via dietary of yak meat and milk in Ruoergai highland prairie. Item

Unit

α-HCH

β-HCH

γ-HCH

HCB

p,p′-DDT

Mean concentration in yak muscle Mean concentration in yak milk ADI or MRL Yak muscle consumption Yak milk consumption Average body weight Daily intake with yak muscle Daily intake with milk EDI EDI/ADI

ng g−1 fw ng L−1 mg kg−1 bw day−1 g L kg mg day−1 mg day−1 mg day−1

0.13 36.66 0.0008a 300 0.5 60 0.00004 0.00002 0.00000097 0.0012

1.18 249.41 0.0006a 300 0.5 60 0.00035 0.00008 0.00000798 0.0133

0.32 2.35 0.005b 300 0.5 60 0.00010 0.00000 0.00000163 0.0003

0.69 65.19 0.00016b 300 0.5 60 0.00021 0.00003 0.00000397 0.0234

0.55 39.67 0.0005a 300 0.5 60 0.00017 0.00002 0.00000309 0.0003

a b

USEPA., 2012. Accessed on http://www.epa.gov/iris/subst/0147.htm. (JMPR, 2002; WHO, 1997).

the remote Ruoergai highland prairie were significantly lower than those reported for farmed cow milk and dairy products in China and other countries. 3.4. Heath risk assessment for OCPs For health risk assessment, the following values will be used: World Health Organization (WHO)'s acceptable daily intakes (ADIs) for γ-HCH (0.005 mg kg−1 bw day−1), ∑ DDTs (0.01 mg kg−1 body weight (b.w.) day− 1) (JMPR 2000), and HCB (0.00016 mg kg− 1 bw day−1) (WHO, 1997). The minimal risk level (MRL) values for α-HCH (0.008 mg kg−1 bw day−1) and β-HCH (0.0006 mg kg−1 bw day−1) (ATSDR, 2005). For p,p′-DDT, 0.0005 mg kg− 1 bw day− 1 is used (USEPA., 2012). Since no ADI values are available for PCBs, the heath risk to the local residents due to an intake of PCBs through dietary is not discussed here. According to these criteria, the heath risk to the local residents due to intake of OCPs via dietary of yak meat and milk can be assessed. The estimated daily intake (EDI) of OCPs was calculated using the following formula: EDI ¼ Ci  Fi

ð1Þ

where Ci is the average concentration of an OCP in the yak muscle or milk; and Fi is the amount of food intake as meat or milk consumed per person in mg kg−1 bw per day. For the calculation of yak milk, the unit mg L−1 was used. The consumption amount of yak meat and milk were based on a survey to the local peoples' dietary habit: 300 g and 0.5 L/person/day, respectively; the body weight was taken as 60 kg. The EDI was compared to the recommended ADI that are provided above (Table 3). The ratios between EDI/ADI for the targeted OCPs in muscle samples to the general population in Ruoergai area were lower than 1.0, suggesting that the exposure levels to these chemicals did not exceed the criteria established by either WHO or USEPA; there were no immediate risk due to the dietary exposure to these chemicals by the consumption of contaminated foodstuffs. It should be pointed out that apart from yak-based foodstuffs, barley is also the important food for the local residents, which was not investigated in this study. Therefore, the present assessment could underestimate the risk. 4. Conclusions The present investigation revealed that several OCPs, such as HCB, DDE, endosulfans, and PCB 28 were the main isomers in grass samples collected from Ruoergai highland prairie. In the six indicator PCB congeners, PCB 28, 52, 101, 138, and 153 were detected in the grass, with PCB 28 and 52 as the predominant congeners, accounting for 80% of the total PCBs. The yak muscle samples were mainly contributed by β-HCH, HCB, DDE, p,p′-DDT, and β-endosulfan; while β-HCH and HCB were dominant compounds in yak milk. The dominances of β-HCH in yak samples

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Please cite this article as: Pan J, et al, Organochlorine pesticides and polychlorinated biphenyls in grass, yak muscle, liver, and milk in Ruoergai high altitude prairie, t..., Sci Total Environ (2014), http://dx.doi.org/10.1016/j.scitotenv.2014.03.074