Polychlorinated biphenyl pollution as an unintentional major contaminant in the Pearl River Delta, China

The highly industrialized Pearl River Delta (PRD) region in China serves as a critical region for Polychlorinated biphenyls(PCB)contamination research. Despite its prominence, previous studies have predominantly focused on conventional PCB congeners, with no comprehensive investigation encompassing all 209 PCB congeners conducted to date.This study provides a detailed analysis of the distribution, composition, and sources of the 209 PCB congeners in the PRD. The results reveal that the concentration of ∑209PCBs ranges from 34 to 5218 ng/kg, with an average of 1372 ± 1417 ng/kg. The PCB composition is dominated by 2Cl congeners, followed by 5Cl, with all other congeners contributing less than 10 %. The identified primary sources of PCBs include terrestrial input such as rainfall runoff (67.3 %), sewage treatment(10.25 %), organic pigment production and emissions (8.54 %), and unintentional emissions (4.01 %). Over the past 40 years (1980-2017), PCB concentrations in the study area have generally increased, peaking in 2017 before experiencing a sharp decline in 2021. Additionally, the composition of PCBs has shifted from predominantly 4Cl to 2Cl, primarily due to a reduction in e-waste imports. The study shows that non-technical PCBs now account for 57.68 %, indicating that unintentional emissions have become a major pollution source. The main environmental factors influencing PCB concentration changes are the volume of e-waste imports and industrial wastewater discharge. Currently, the potential ecological risk of PCB pollution in the PRD is relatively low.