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Spatial Distribution of Hexachlorocyclohexanes in Agricultural Soils in Zhejiang Province, China, and Correlations with Elevation and Temperature Anping Zhang,† Weiping Liu,‡,†,* Hejin Yuan,† Shanshan Zhou,† Yushan Su,§ and Yi-Fan Li§,†,#,* †
International Joint Research Center for Persistent Toxic Substances (IJRC-PTS), Zhejiang University of Technology, Hangzhou 310032, China ‡ IJRC-PTS, MOE Key Laboratory of Environmental Remediation & Ecosystem Health, Zhejiang University, Hangzhou 310058, China § Science and Technology Branch, Environment Canada, Toronto, Ontario M3H5T4, Canada # IJRC-PTS, State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090, China
bS Supporting Information ABSTRACT: Large quantities of hexachlorocyclohexanes (HCHs) were historically applied to soils in Zhejiang, a hilly province of eastern China, yet very limited information is publicly available for the present levels and residue characteristics of HCHs in the region. In this work, concentrations of HCHs and enantiomeric fractions (EFs) of R-isomer were analyzed in 58 agricultural soil samples (020 cm) collected in Zhejiang province. On the basis of the ratio of R-HCH/β-HCH and the fact that HCHs were banned in 1983 for agricultural use in China, fresh application of technical HCHs in a large quantity was unlikely in this province. Significant correlation was found between soil concentrations and elevation (R = 0.52, P < 0.001) and temperature (R = 0.55, P < 0.0001), but not between soil concentrations and total technical usage (R = 0.24, P = 0.1), suggesting a typical secondary distribution pattern. The soil residue inventories of HCHs derived from the relationship between concentration and elevation indicated 14.2 tons of HCHs left in agricultural soils in plain areas with the average elevation less than 100 m, and 61.6 tons of HCHs left in mountain soils with the average elevation higher than 100 m. It was also found that EFs of R-HCH were significantly negatively correlated with carbon biomass (Cbio) in soils. This implies that Cbio might have important impact on orientation and extent of enantioselective degradation of R-HCH in the region, which is, according to our knowledge, the first report of this kind.
’ INTRODUCTION Hexachlorocyclohexanes (HCHs) were used as pesticides worldwide,1,2 and classified as persistent organic pollutants (POPs) under the Stockholm Convention on POPs (http://chm.pops. int). Two types of HCHs products were used around the world: technical HCHs and lindane. The former mainly contains R-HCH, β-HCH, and γ-HCH, and the latter consists of almost pure (>99%) γ-HCH. China had been a major producer and consumer of technical HCHs from the 1950s until its ban on production and agricultural use was enforced in 1983. In over 30 years, total production of technical HCHs (4.9 million tones) in China accounted for 33% of the world total production.3 Even after the ban of technical HCHs, 3200 tons of Lindane (almost pure γ-HCH) was still used in forest management between 1991 and 2000.4 Zhejiang province, an eastern coastal mountainous province of China, is one of districts that had record high organochlorine pesticides (OCPs) application in China.5,6 Li et al. (7) developed r 2011 American Chemical Society
usage inventories of technical HCHs from 1952 to 1984 with 1/6° latitude by 1/4° longitude resolution (around 24 by 24 km) for China, and the portion in Zhejiang province is presented in Figure SI-1 of the Supporting Information. The total usage of technical HCHs in Zhejiang Province was approximately 300 kt from 1952 to 1984. In Zhejiang, hills and mountains account for 70.4% of the total area in the province; plains and basins make up 23.2%; and the remaining 6.4% is composed of rivers and lakes. The climate records indicated average annual temperature of mountain is lower than that of plain in Zhejiang. Moreover, the temperature difference between mountain and plain quickly increased during the period of 19812006, because the temperature in plain Received: February 12, 2011 Accepted: June 17, 2011 Revised: April 23, 2011 Published: July 01, 2011 6303
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Environmental Science & Technology increased much faster than that in mountain under the influence of global climate change.8 To assess redistribution of HCHs under the conditions of complicated landform and climate, it is very important to carry out research on HCHs residues in the province. However, up to now there has been no scientific report on soil residue of HCHs in Zhejiang province. The objectives of this study were to report soil residues of HCHs at 58 locations in Zhejiang and to study the distribution pattern of HCHs in the soil more than 2 decades after the ban of technical HCHs in the province. The enantiomeric fraction of R-HCH was also quantified for all samples because the enantiomeric signature in soil residues is useful to evaluate environmental sources and pathways of chiral pollutants.911
’ MATERIALS AND METHODS Details of this section can be found in the Supporting Information, and a brief description is given below. Materials. All HCHs analytical standards were purchased from Dr. Ehrenstorfer GmbH, Augsburg, Germany. All solvents used were HPLC or glass-distilled grade. Anhydrous granular sodium sulfate was obtained from Hangzhou Huipu Co. Ltd., China, and baked at 400 °C overnight before use. Other reagents were analytical grade. Sample Collection. Fifty-eight soil samples were collected in agricultural soils in eleven prefecture-level divisions of Zhejiang province in 2006 and 2007. The locations of the sampling sites are shown in Figure SI-2 of the Supporting Information and the selected physicochemical and microbial parameters including moisture content (MC), pH values (pH(KCl)), total organic carbon (TOC), clay ( 0.05). Overall averaged EF was 0.500 ( 0.005 (n = 9) in the R-HCH standard. At a 95% confidence interval with 8 degrees of freedom, soil samples are considered as racemic when their EF values fall between 0.496 and 0.504. Racemic standards of R-HCH were added to a control soil before extraction. The EFs of recovered compounds are not significantly different from racemic (p > 0.05), demonstrating that the extraction and cleanup processes did not alter enantiomer fractions in soil samples.
’ RESULTS AND DISCUSSION Soil Concentrations of HCHs. Concentrations of HCHs at each sampling site are shown in Figure 1, and concentrations of individual HCH isomers are presented in Table SI-2 of the Supporting Information. Table 1 summarizes statistical results of HCHs soil concentrations. Among all HCH isomers, β-HCH was the most abundant isomer with a mean of 2.67 ng/g dry weight (dw) and a range from below detection limit (BDL) to 27.5 ng/g dw, followed by R-HCH, with a mean of 1.86 ng/g dw and a range from BDL to 24.9 ng/g dw. The concentration levels of HCHs in Zhejiang province were comparable to those reported in other areas in China (Table SI-3 of the Supporting Information), such as Guangzhou,14 the suburbs of Beijing,15 and the Haihe Plain,16 but much lower than those in soils irrigated with wastewater in Tianjin, China.17 Technical HCHs produced in China contains 71% R-HCH, 6% β-HCH, 14% γ-HCH, and 9% δ-HCH, and Lindane consists 6304
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Environmental Science & Technology
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of 99% γ-HCH.7,16,18 Table 2 presents correlations among soil concentrations of HCHs isomers and total HCHs. Strong correlations among R-, γ-, and β-HCH (R g 0.51) suggest similar sources likely originated from historic use of technical HCHs. The highest correlation was found between β-HCH and the total HCHs with R = 0.91, which is not surprising because β-HCH was the most stable isomer and tends to stay in the source area.2,19 The ratio of R-HCH/γ-HCH is between 5 and 7 in the technical HCHs and nearly zero in lindane. The ratios of R-HCH / γ-HCH can be used to evaluate whether the source was from technical HCHs or lindane.15,18 HCH isomer ratios in each soil sample are given in Table SI-2 of the Supporting Information, showing the ratios of R-HCH /γ-HCH were below 5.0 in most of soil samples in this work. It indicates that HCHs residues at these sites were most likely from historic use of technical HCHs. The ratio of R-HCH/β-HCH is another useful indicator to assess if technical HCHs were recently applied in the region.16 In this study, ratios of R-HCH/β-HCH of all samples (with mean value of 0.88 in plain and 0.75 in mountain) were below that in technical HCHs (i.e., 11.8), except at several sampling sites, where β-HCH was undetectable. The results suggested that fresh application of technical HCHs in a large quantity is unlikely in Zhejiang province. Influence of Site Elevation and Temperature on HCH Concentrations. Figure SI-3 of the Supporting Information
shows gridded elevation with different resolutions. If we define cells with elevation
