Occurrence and Distribution of Organochlorine Pesticides in the Water, Sediment and Bivalves from the Estuarine and Riverine Ecosystem of South India

This study examined the distribution and partitioning of organochlorine pesticides (OCPs) across water, sediment, and three bivalve species (Crassostrea madrasensis, Meretrix casta and Villorita cyprinoides) in estuarine and riverine ecosystems along India’s southern coast adjoining the eastern Arabian Sea. Gas chromatographic analysis revealed frequent detection of ΣHCH, heptachlors, aldrin, dieldrin, endrin, and ΣDDT, with ΣHCH and cyclodienes dominating all matrices. River associated sites consistently exhibited higher OCP burdens than estuarine sites, reflecting strong input from upstream catchments. Bioaccumulation indices (BCF and BSAF), demonstrated inter species difference, with Crassostrea madrasensis showing the highest retention of lipophilic compounds particularly HCH isomers and cyclodienes, positioning it as a sensitive sentinel organism. Multivariate analysis (PCA) highlighted sediment as a long-term reservoir of DDTs and confirmed widespread bioavailability of HCH and cyclodienes. These findings underscore the persistence of banned OCPs in tropical estuarine environments and emphasize the need for continuous monitoring and stricter control of non-point agricultural input to prevent future accumulation and associated risk.