Evaluation of residual level and distribution characteristics of organochlorine pesticides in agricultural soils in South Korea.

In this study, we evaluated the residual levels and distribution characteristics of 10 organochlorine pesticides (OCPs) in the soil of agricultural lands (paddy field, vegetable field, and orchard, n = 150) nationwide. As a result of the investigation, 3-10 types of OCPs were detected in combination in 144 locations (96%) of the total 150 locations. Among those OCPs, dichlorodiphenyltrichloroethane (DDT) and endosulfan were detected in high amounts. The geometric mean concentrations of DDT and endosulfan were ∑DDT 0.31 ng g-1 (ND-2187.18 ng g-1) and ∑endosulfan 0.33 ng g-1 (ND-312.68 ng g-1), respectively. OCP concentrations were generally higher in orchards than in other agricultural fields due to a large amount of pesticides used. DDT in two orchards was detected at 2187.18 ng g-1 and 1061.78 ng g-1, exceeding the levels stated in the Canadian DDT Soil Quality Guidance (SQG, 700 ng g-1). The result of applying the isomer ratio to evaluate the recent or past use of DDT, endosulfan, and hexachlorocyclohexane (HCH), which had a high detection rate, showed that it could be attributable to historical usage. DDT and HCH showed statistically similar residual distribution patterns; however, endosulfan did not show a clear correlation with DDT and HCH due to the effect of its recent use. Thus, the results of evaluation of OCP residual levels and distribution characteristics can be used for the soil management policy of OCPs in agricultural lands in Korea.

Evaluation of soil flushing of complex contaminated soil: an experimental and modeling simulation study.

The removal of heavy metals (Zn and Pb) and heavy petroleum oils (HPOs) from a soil with complex contamination was examined by soil flushing. Desorption and transport behaviors of the complex contaminants were assessed by batch and continuous flow reactor experiments and through modeling simulations. Flushing a one-dimensional flow column packed with complex contaminated soil sequentially with citric acid then a surfactant resulted in the removal of 85.6% of Zn, 62% of Pb, and 31.6% of HPO. The desorption distribution coefficients, KUbatch and KLbatch, converged to constant values as Ce increased. An equilibrium model (ADR) and nonequilibrium models (TSNE and TRNE) were used to predict the desorption and transport of complex contaminants. The nonequilibrium models demonstrated better fits with the experimental values obtained from the column test than the equilibrium model. The ranges of KUbatch and KLbatch were very close to those of KUfit and KLfit determined from model simulations. The parameters (R, ß, ω, α, and f) determined from model simulations were useful for characterizing the transport of contaminants within the soil matrix. The results of this study provide useful information for the operational parameters of the flushing process for soils with complex contamination.