Atmospheric deposition and fluxes of organochlorine pesticides and coplanar polychlorinated biphenyls in aquatic environments of Hong Kong, China

Concentrations of organochlorine (OC) pesticides and coplanar (dioxin-like) polychlorinated biphenyls (PCBs) in bulk deposition were measured at the Mai Po Marshes Nature Reserve (MPMNR) and A Chau, which are both important habitats for waterbirds in Hong Kong. OC pesticides exempted from the Stockholm Convention were present in greater concentrations than those that have been restricted for use in the region. Among the OC pesticides, HCB, ΣDDTs, and ΣHCHs were detected. Concentrations of HCB were greater at MPMNR than at A Chau, and this finding suggests short-range transport of this compound, which is different from the other OC pesticides. Several environmental factors including seasonal variations in temperature, particulate matter, and rainfall may influence the flux of OC pesticides. Since sources of HCB often coexist with sources of polychlorinated dibenzo-p-dioxins and dibenzofurans (dioxins and furans), the presence of HCB may be a useful surrogate for monitoring airborne dioxins and for understanding their deposition potential. The contribution of atmospheric deposition to the OC pesticide input to the two study sites was small. Concentrations of most OC pesticides in surface waters were greater than would be predicted based on the inputs from atmospheric deposition and sedimentation. The mass balance calculation suggests a net flux of OC pesticides from bottom sediments to the overlying water column.