Organochlorine pesticides (OCPs) in wetland soils under different land uses along a 100-year chronosequence of reclamation in a Chinese estuary

Soil profiles were collected at a depth of 30 cm in ditch wetlands (DWs), riverine wetlands (RiWs) and reclaimed wetlands (ReWs) along a 100-year chronosequence of reclamation in the Pearl River Delta. In total, 16 OCPs were measured to investigate the effects of wetland reclamation and reclamation history on OCP levels. Our results showed that average Sigma DDTs, HCB, MXC, and Sigma OCPs were higher in surface soils of DWs compared to RiWs and ReWs. Both D30 and D20 soils contained the highest Sigma OCP levels, followed by D40 and D100 soils; lower Sigma OCP levels occurred in D10 soils. Higher Sigma OCP levels were observed in the younger RiWs than in the older ones, and surface soils exhibited higher Sigma OCP concentrations in the older ReWs compared with younger ReWs. The predominant percentages of gamma-HCH in Sigma HCHs (>42%) and aldrin in Sigma DRINs (>46%) in most samples reflected the recent use of lindane and aldrin. The presence of dominant DDT isomers (p,p'-DDE and p,p'-DDD) indicated the historical input of DDT and significant aerobic degradation of the compound. Generally, DW soils had a higher ecotoxicological risk of OCPs than RiW and ReW soils, and the top 30 cm soils had higher ecotoxicological risks of HCHs than of DDTs.