DDT, Chlordane, and Hexachlorobenzene in the Air of the Pearl River Delta Revisited: A Tale of Source, History, and Monsoon.

Although organochlorine pesticides (OCPs) have been banned for more than three decades, their concentrations have only decreased gradually. This may be largely attributable to their environmental persistence, illegal application, and exemption usage. This study assessed the historic and current regional context for dichlorodiphenyltrichloroethane (DDT), chlordane, and hexachlorobenzene (HCB), which were added to the Stockholm Convention in 2001. An air sampling campaign was carried out in 2018 in nine cities of the Pearl River Delta (PRD), where the historical OCP application was the most intensive in China. Different seasonalities were observed: DDT exhibited higher concentrations in summer than in winter; chlordane showed less seasonal variation, whereas HCB was higher in winter. The unique coupling of summer monsoon with DDT-infused paint usage, winter monsoon with HCB-combustion emission, and local chlordane emission jointly presents a dynamic picture of these OCPs in the PRD air. We used the BETR Global model to back-calculate annual local emissions, which accounted for insignificant contributions to the nationally documented production (<1‰). Local emissions were the main sources of