Distribution of Persistent Organic Pollutants in Soil and ... - Springer Link

1 downloads 117 Views 291KB Size Report
soil and grass samples from the Mt. Qomolangma (Everest) area, central Himalayas, China, from the elevation range 4700 to 5620 m. We analyzed all samples ...
Arch. Environ. Contam. Toxicol. 52, 153–162 (2007) DOI: 10.1007/s00244-006-0111-6

Distribution of Persistent Organic Pollutants in Soil and Grasses Around Mt. Qomolangma, China X.-P. Wang,1 T.-D. Yao,1 Z.-Y. Cong,1 X.-L. Yan,1,2 S.-C. Kang,1 Y. Zhang2 1 2

Institute of Tibetan Plateau Research, Chinese Academy of Sciences, P. O. Box 2871, Beijing 100085, China School of Chemistry and Engineerings, Shanxi University, 36 Wucheng Road, Taiyuan 030006, China

Received: 31 May 2006 /Accepted: 4 September 2006

Abstract. Previous literature has reported the fate of persistent organic pollutants (POPs) in mountainous regions, but the Himalayas have received little attention, and few results from this region have been published. The present study collected soil and grass samples from the Mt. Qomolangma (Everest) area, central Himalayas, China, from the elevation range 4700 to 5620 m. We analyzed all samples for organochlorine pesticides (OCPs) to determine the level of OCP contamination in the Qomolangma region. The soil samples contained 0.385 to 6.06 ng g–1 of DDT only, and these concentrations were lower than those from Europe and mountains close to industrial emissions. Our study detected a number of OCPs in the grass samples, such as hexachlorocyclohexane (HCH) (0.354 to 7.82 ng g–1), hexachlorobenzene (HCB) (0.0156 to 1.25 ng g–1), endosulfan (0.105 to 3.14 ng g–1), and DDT components (1.08 to 6.99 ng g–1). Their concentrations were higher than those in pine needles from Alberta, Canada. Our measurements of HCH and DDT in grass samples showed the same or slightly higher concentration levels than reported in moss from Mt. Qomolangma 15 years ago. This result and the analysis of isomer ratios (a/c-HCH and p-pÕ-DDE/p-pÕ-DDT) indicate recent releases of OCPs from a nearby region, possibly from dicofol use in India. We also investigated the elevation distribution of OCPs and found that HCH and HCB were progressively concentrated in colder, higher elevation sites. A bioconcentration factor (BCF) of grass was calculated, and the BCF values increased with the increasing elevation, indicating that the cold condensation of POPs at high-elevation sites may increase the potential threat to vegetation and the food chain in the mountain ecosystem.

In past decades, the ‘‘grasshopper-effect’’ model has successfully explained how persistent organic pollutants (POPs) can migrate to polar regions through repeated evaporation, atmospheric transport, and deposition (Wania and Mackay 1995, 1996). Recently, interest has increased in quantifying organic contaminant levels in mountain ecosystems to study how these

Correspondence to: X.-P. Wang; email: [email protected]

contaminants may impact humans through either aquatic or terrestrial pathways (Daly and Wania 2005). Organic contamination in high mountains may pose a threat to mountain ecosystems themselves. However, mountain regions also serve as the primary water supply for lowlands. Contamination of snow and lake water in high mountain regions has the potential to impact drinking and agriculture water supplies. High-altitude vegetation may be at risk, and livestock and top predators in the mountain regions may bioaccumulate organic compounds through food chains. Chemicals enter the mountain system from atmospheric sources, either by dry deposition, resulting in air–snow, air–water, air–soil, and air–vegetation gaseous partitioning, or by wet deposition, which leads to POP scavenging and capture by snow. In mountain regions, chemical uptake by grasses can be affected by the air–grass equilibrium partitioning, water–grass exchange during exposure to melt water, and the uptake and transfer of pollutants from soil to grass. Investigations of the levels of POPs in snow, soil, and grasses in these regions provide critical information for assessing human and animal health risks. Although many researchers have studied the role of mountains in POP distribution and transportation, some major mountain regions, such as the Himalayas, have received minimal attention. Little work on contaminants in the central Himalayas has been reported. The Himalayan Mountains wedge between India and China. Mt. Qomolangma (8844 m) reaches the highest elevation in the Himalayas and in the world (Loewen et al. 2005). The huge Himalayan mountain chain lies adjacent to the worldÕs most densely populated countries, including India, Pakistan, Bangladesh, and China. In the past, the Indian subcontinent and China have heavily used organochlorine pesticides (OCPs), such as hexachlorocyclohexanes (HCHs) and DDT (Loewen et al. 2005). The current findings of increased POP levels in these high mountain regions point to the importance of a cold-condensation effect on the enhanced POP concentrations at high elevations. Because of the usage history and behavior of POPs, investigations regarding ecologic and ecotoxicologic effects of POPs in the Himalayan region provide an important and valuable assessment of potential risks. The grasses Jidou (O. glacialis Benth.ex Bge) and Rouzi (T. rupifragum Schrenk) dominate the ground cover of the Himalayan region below 5800 m. They are long living, high in lipids, and

154

X.-P. Wang et al.

Pure, Fluka) were glass-to-glass distilled twice, and the solvent checks showed that there were no interferences with the target compounds. Standards of HCHs, HCB, DDT components, a-HCHD6, and p-pÕ-DDE-D8 were purchased from Dr. Ehrenstorfer GmbH, Germany. The term ÔDDT componentsÕ in the text refers to DDTrelated compounds, including p-pÕ-DDT and o-pÕ-DDT and their metabolites, DDE, and DDD.

Fig. 1. Location of research area (Fang et al. 2004)

provide the main food for yaks and sheep. Because Tibetan people depend heavily on yak meat and yak and sheep dairy products, the terrestrial food chain near Mt. Qomolangma consists of grasses, yaks and sheep, and humans. The objective of this study was to investigate the levels and distribution patterns of OCPs in snow, soil, and grasses from 4700 to 5600 m elevation around the northern slope of Mt. Qomolangma. Our study investigated trends of these pollutants with elevation and the accumulation of pollutants in grasses.

Materials and Methods Sample Collection A fresh snow sample was collected in April 8, 2005, and grass and soil samples were collected in April 2005, from the north slope of Mt. Qomolangma (Fig. 1; Rongbuk Valley [N 28.30, E 87.04 to approximately N 28.29, E 87.03). With the increase of elevation (from 4700 to 5600 m), 13 Jidou, 11 Rouzi, and 24 soil samples were collected. Grass samples were wrapped in clean aluminum foil, stored in sealable plastic bags, and stored at –18C until extraction. The soil samples were obtained by shaking the loosely adhering soil from the roots of the Jidou and Rouzi grass samples. The soil samples were separated before freezing and subsequent analysis for OCP contaminants.

Extraction and Cleanup Soil. A 10-g freeze-dried soil sample was Soxhlet extracted with 200 ml mixed solvent (n-hexane/acetone 1:1 v:v) for 24 hours. Each sample was spiked with a-HCH-D6 and p-pÕ-DDE-D8 as recovery surrogates. The extract was concentrated and cleaned with a column (30 cm in length and 1 cm i.d.) of 5 g Florisil (Pesticide pure grade, 60/100 mesh, Supelco, activated at 130C for 24 hours and stored in a sealed desiccator before use) and 2-cm-thick anhydrous sodium sulfate. The OCPs were then eluted with 20 ml n-hexane and dichloromethane (19:1 v:v) and n-hexane and dichloromethane (2:1 v:v), respectively. The elution was concentrated to 1 ml with a stream of purified nitrogen. Mirex was spiked as an internal standard before analysis. N-hexane, dichloromethane, and acetone (Pesticide

Plants. A 5-g sample of grass was placed in a clean 50-ml amber glass vial, spiked with recovery surrogate, and sonicated for 30 minutes in a 8:2 mixture of n-hexane and acetone covering the vegetation in an ultrasonic cleaner. The solvent was decanted, and grass samples were sonicated once more with a fresh portion of the mixture (8:2 n-hexane and acetone). Sulfuric acid was used for cleanup. A Florisil column was used after decreasing the volume with a rotary evaporator. The n-hexane and dichloromethane (19:1) and n-hexane and dichloromethane (2:1) were used to elute the column, and the combined elution was concentrated to 1 ml and the internal standards (Mirex, 10 pg) spiked before analysis.

Snow. A snow sample was melted in a clean room in its closed-field container (= 2 L water equivalent). To minimize re-equilibrium of pesticides with the atmosphere, the sample was extracted as soon as the last bit of snow melted. Then the melted water sample was extracted with pesticide-grade dichloromethane (DCM) in a Goulden liquid–liquid extractor. The DCM extract was evaporated under vacuum, exchanged into hexane, and analyzed by gas chromatography– mass spectrometry–mass (MS) detection.

Analysis. OCPs in all samples and field blanks were analyzed using a gas chromatograph with an ion-trap mass spectrometer (Finnigan Trace GC/PolarisQ). A 30 m x 250 lm i.d. HP-5MS capillary column was used for separation. High-purity helium was used as a carrier gas at a constant flow rate of 1.0 ml min–1. Each sample (1 L) was injected under splitless injection mode. The mass spectrometer was operated in 70-eV electron impact mode. When the mass spectrometer is using an ion-trap as the mass separator, the MS-MS mode can be used to achieve high sensitivity. The analytic conditions for MS-MS determination and limits of detection of target compounds are listed in Table 1. The oven temperature for OCP detection was 100C held for 2 minutes, ramped up at 25C/min to 170 C, at 8C/min to 225C, at 0.7C/min to 235C, and then at 25C/min to 260C and held for 2 minutes. The temperature of the injector was 250C, and the temperature of transfer line was 280C. Total organic matter of the soil sample was determined using a total organic carbon analyzer (Shimadzu 5000-A). Quality control. One ml surrogate (a-HCH-D6, p-pÕ-DDE-D8 10 pg/ ll) was added to each sample (snow, soil, and vegetation) before extraction. The recovery of OCP laboratory surrogates for soil and grass samples were 104% € 18.3% for a-HCH-D6 and 95% € 4.6% for p-pÕ-DDE-D8. The recovery of surrogates for snow sample were 97.2% € 8.1% for a-HCH-D6 and 96% € 3.7% for p-pÕ-DDE-D8. The accuracy of the method was assessed by analysis of the National Institute of Standards and Technology standard reference material 1944 New York/ New Jersey Waterway Sediment, and values within 60% to 115% of the certified values were obtained. Table 2 lists the certified values of this reference material and the detected values in this study. Aluminum foil used for storage of grass samples was rinsed with acetone and hexane before heating for 12 hours at 200C. All glassware was washed with detergent, rinsed in triplicate with tap water followed by deionized water, rinsed with redistilled acetone and

155

POPs Around Mt. Qomolangma, China

Table 1. Analytic conditions for MS-MS determination Ion selection (m/e) Target compound

Parent (width)

Daughter

Detection limit (pg)

Values of procedure blank (pg)

a-HCH c-HCH HCB p,pÕ-DDE p,pÕ-DDD o,pÕ-DDT

181(4) 181(4) 284(4) 318(4) 235(4) 235(4)

0.41 0.33 0.75 0.88 0.14 0.18

LOD LOD 5.4 LOD LOD LOD

p,pÕ-DDT

235(4)

0.5

LOD

o,pÕ-DDE

318(4)

0.47

LOD

o,pÕ-DDD

235(4)

0.11

LOD

a-Endosulfan b-Endosulfan

195(4) 195(4)

145–148 145–148 247–249 246–248 165–167 199–203 165–167 199–203 165–167 198–203 246–250 165–167 199–203 158–162 158–162

1.15 1.03

LOD LOD

LOD = Limit of defection.

Table 2. Certified values of NIST standard reference material 1944 New York/ New Jersey Waterway Sediment and the detected values in this studya Concentration (ng g)1)

Compound NIST value

p-pÕ-DDT o-pÕ-DDD o-pÕ-DDE p-pÕ-DDD p-pÕ-DDE a-HCH Naphthalene Phenanthrene Acenaphthene Anthracene Perylene Chrysene Fluoranthene Fluorene Benzo[a]fluoranthene Benzo[a]pyrene Benzo[b]fluoranthene Benzo[ghi]perylene Benzo[k]fluoranthene Indeno[1,2,3-cd]pyrene

0.119 0.038 0.019 0.108 0.086 0.002 1.65 5.27 0.57 1.77 1.17 4.86 8.92 0.85 0.78 4.3 3.87 2.84 2.3 2.78

This study Minimal

Maximal

0.102 0.041 0.017 0.087 0.073 0.0023 2.24 5.45 0.57 1.75 0.98 4.53 9.04 0.835 0.65 4.19 3.43 1.98 2.55 2.57

0.124 0.045 0.021 0.114 0.099 0.0028 2.33 5.62 0.59 1.82 1.22 4.87 9.23 0.879 0.79 4.8 3.69 2.67 2.69 2.94

Value range (%) 85–104 107–118 89–110 80–105 84–115 80–90 135–141 103–106 100–104 98–102 83–107 93–105 101–103 98–103 83–101 97–111 88–95 69–94 110–116 92–106

SD 0.0083 0.0025 0.0037 0.0092 0.0056 0.00033 0.053 0.047 0.016 0.024 0.078 0.35 0.29 0.077 0.046 1.02 0.55 0.89 0.38 0.64

a

The internal standard used for OCP detection is Mirex, and 10 pg Mirex was added to each extractant before analysis. One microliter surrogate (a-HCH-D6, p-pÕ-DDE-D8, 10 pg/ll) was added to each sample before extraction. The absolute amount of recovery surrogates is 10 pg, which is the same as that of internal standard. The recovery of OCP laboratory surrogates was 104% € 18.3% for a-HCH-D6 and 95% € 4.6% for p-pÕDDE-D8. hexane, and heated for 12 hours at 200C. Glass Pasteur pipettes used for transfer of solvents and sample extractant were also heated for 12 hours at 200C. To monitor potential laboratory contamination, procedure blanks were processed after every 10 sample extractions. Most of the OCPs (the exception being HCB) in procedural blanks were lower than the method detection limit, and all samples were extracted and analyzed in triplicate; all data were blank corrected before analysis by subtracting the mean blank concentration from extract concentration (for HCB only).

Results and Discussion Levels of HCHs and DDT Components in Soil and Grass Samples Table 3 lists the number of samples and the concentrations of total organic carbon (mgC/g) for soil samples. Table 4 lists the concentrations of OCPs in soil detected in this study and the

X.-P. Wang et al.

156

Table 3. Number of samples and TOC of soils Increase (m)

Rouzi

Jidou

Soil

TOC (mgC/g)

4600 4800 5210 5440 5620

3 3 2 3 2

2 2 2 3 2

5 5 4 6 4

10.4 2.86 2.87 2.94 2.88

TOC = Total organic carbon.

Table 4. Concentrations of main OCPs in soils (ng g)1) from Mt. Qomolangma and other mountain areas Target compound

This study

Pyrenees Mountains, Europea

Woodland regions of Austriab

Holy Cross mountain, Polandc

Giant Mountains, Czech-Polish borderd

Teide, Atlantice

a-HCH c-HCH HCB p,pÕ-DDE p,pÕ-DDD o,pÕ-DDT p,pÕ-DDT o,pÕ-DDE o,pÕ-DDD Sum of DDT components a-Endosulfan b-Endosulfan

ND ND ND 0.111–2.03 0.0132–0.153 0.0289–0.315 0.0822–2.91 0.0504–0.428 0.00991–0.223 0.385–6.06 ND ND

0.13–0.80 – 0.06–0.40 – – – – – – 0.42–10 – –

– –