Residual Level, Profile and Potential Ecological Risk of Organochlorine Pesticides in Subsurface Sediments from Lakeshore Backfill Site and Lakebed of an Abandoned Oxidation Pond After Desilting for 15 Years

Abstract

The occurrence and distribution of 19 organochlorine pesticides (OCPs), together with microbial ester-linked fatty acid methyl ester (EL-FAME) profiles were investigated in sediments from an abandoned oxidation pond of Ya-Er lake, China, which had been heavily polluted by hexachlorocyclohexanes (HCHs) and chlorobenzenes in 1980s. Subsurface sediment samples were taken from five sediment cores along the transect running from lakeshore to lakebed. The concentration of total OCPs ranged from 29.8 to 941.8 ng g-1 dw, with a mean value of 193.3 ng g-1 dw. Hexachlorobenzene (HCB), HCHs and dichlorodiphenyl-trichloroethanes (DDTs) were the three dominant OCP classes, accounting for 26.5%-97.4%, 1.8%-51.5%, and 0.4%-15.5% of the total, respectively. Hot spots of HCB, HCHs and DDTs were detected in 0.9-2.7 m deep layers of the lakeshore, where was one of the dredged sediment backfill sites for in-situ remediation of the oxidation pond in 2002-2004. High potential risks of HCHs and HCB were still indicated. Historical industrial input (27.2%), recent agricultural input (14.7%), and persistent residuals (14.3%) were the three major identified sources of OCPs, using Absolute Principal Component Scores-Multiple Linear Regression (APCS-MLR). Redundancy analysis of microbial EL-FAME profiles and nine dominant OCPs revealed that the spatial variation in microbial community structure was significantly corresponded with the OCP composition. This is the first study highlighted the concern on historical industrial inputs of OCPs in subsurface sediments of the lakeshore disposal zone. The findings could help to distinguish the artificial backfill sediments from natural polluted sediments for optimization of further desilting plans.