Application of Sequential Solvent Extraction for Characterization of Long Time Aging of Organochlorine Pesticides in Agricultural Soil

Abstract

Long time aging of organochlorine pesticides (OCPs) in agricultural soil was characterized by the sequential solvent extraction using series of shaking with 50% methanol-aq and n-buthanol, and finally soxhlet extracted with dichlorormethane. First, the extractability and the organic carbon normalized adsorption coefficient (Koc) of OCPs by these solvents were calculated to characterize the sequential extraction using 3 type soils. The 50% methanol-aq extractability of OCPs with low n-octanol water partition coefficient (Kow) values in soil with low organic carbon content tended to be high. The Koc of OCPs extracted by 50% methanol-aq tended to be related with Kow.
The exhaustive and the sequential extraction were applied to the paddy soil preserved since 1960s to characterize the long time aging of OCPs in soils. Although OCPs concentrations in paddy soil obtained by the exhaustive extraction have decreased since 1960s, recent decreasing rate is very slow. The half-lives of OCPs for disappearance from the paddy soils were estimated to be ∼5 years from 1960s to 1970s, around 10 years from 1980s to 1990s, respectively. The extractability of α-HCH with the 50% methanol-aq by shaking has been decreased. Additionally, the extractability of α-HCH with the dichlorormethane by soxhlet has been increased gradually. On the other hand, the changes in temporal extractabilities of dieldrin and p,p′-DDT was not found. These results can be indicated that long time aging of α-HCH among OCPs in agricultural soil for a half century can be found by the sequential solvent extraction.