Occurrence and ordination of dichlorodiphenyltrichloroethane and hexachlorocyclohexane in agricultural soils from Guangzhou, China

Abstract

On a global scale tropical regions in developing countries are thought to be significant source areas of organochlorine pesticides (OCPs), owing to a long history of widespread use and only a recent production ban or restriction on the application of these pesticides. In the present study, 32 soil samples were collected in 2004 from agriculture lands around the urban area of Guangzhou, in southern China, and analyzed for residues of OCPs including p,p'-DDT, p,p'-DDE, p,p'-DDD, and alpha-, beta-, gamma-, and delta-HCH. The dry weight concentrations of SigmaHCH (SigmaHCH = alpha-HCH + beta-HCH + gamma-HCH + delta-HCH) ranged from 0.2 to 103.9 ng/g, with a median of 4.4 ng/g. Residues of SigmaDDT (SigmaDDT = p,p'-DDT + p,p'-DDE + p,p'-DDD) ranged from 7.6 to 662.9 ng/g, with a median of 67.3 ng/g. The predominance of beta-HCH among HCHs in most soil samples suggested that they were from historical contamination rather than recent input. The mean HCH alpha/gamma-ratio of 2.72 was lower than that of technical HCHs, possibly due to more loss of alpha-HCH via evaporation from soil with time, conversion of gamma-HCH to alpha-HCH or recent application of lindane in the region. The mean ratio of (DDE + DDD)/SigmaDDT was 0.54, indicating that quite a portion of DDT in soils was degraded since its official ban in 1983. Higher DDT concentrations with lower (DDE + DDD)/SigmaDDT ratios at a few sites suggested possible local DDT sources via the application of Dicofol. A positive but weak correlation (r = 0.449, p < 0.01) between DDT residues and TOC contents implied that soil organic matter might enhance adsorption of DDT in soils in the tropical regions. Hierarchical cluster analysis and principal component analysis were also performed to study the distribution and compositional patterns of OCPs as well as their sources and environmental fates within the study area.