Polychlorinated biphenyls (PCBs) and organochloride pesticides (OCPs) in sediment from the Beibu Gulf, China: Occurrence, spatial-temporal distribution, source, historical variation and ecological risks

Abstract

This study comprehensively analyzed 11 polychlorinated biphenyls (PCBs) and 16 organochlorine pesticides (OCPs) in 87 surface sediment samples collected across two seasons and in a sediment core from the Beibu Gulf, China. Overall, only a limited number and low concentrations of PCBs and OCPs were detected. In surface sediments, ΣPCBs concentrations were higher in summer (mean: 0.27 ± 0.37 ng/g dw) compared to winter (mean: 0.07 ± 0.06 ng/g dw), while ΣOCPs showed no significant seasonal variation (summer, mean: 0.19 ± 0.19 ng/g dw; winter, mean: 0.17 ± 0.07 ng/g dw). 4,4′-trichlorobiphenyl (PCB 28), 2,3,5,6-Tetrachlorobiphenyl (PCB 65) and p,p’-Dichlorodiphenyldichloroethylene (p,p’-DDE) were the most predominant contaminants, with average concentrations accounting for >90 % of the ΣPCBs and ΣOCPs, respectively. Spatial distribution revealed higher ΣPCBs concentrations in the southern Beibu Gulf compared to other areas. Industrial productions, shipping activities, as well as ocean current transport appear to be key sources of PCBs in studied region, while the aerobic degradation of residual DDT likely explains the widespread presence of DDE. In sediment core, both ΣPCBs and ΣOCPs exhibited parabolic variation trends along the sediment core depth, reflecting historical use in the Beibu Gulf, with recent declines in new inputs. Risk assessments indicated that PCBs and OCPs in Beibu Gulf sediments pose minimal ecological risks. These findings offer valuable scientific insights to support future research on typical organic pollutants in the Beibu Gulf.