Seasonal patterns and current sources of DDTs, chlordanes, hexachlorobenzene, and endosulfan in the atmosphere of 37 Chinese cities.

China has a history of large scale production and application of organochlorine pesticides (OCPs) although, data on their nationwide distribution and seasonal variations in the atmosphere is still sparse. Passive air samplers (PAS) were therefore utilized to obtain seasonal data from 37 Chinese cities and three background sites in 2005. Concentrations and spatial and seasonal distribution of dichlorodiphenyltrichloroethanes (DDTs), chlordanes (CHLs), hexachlorobenzene (HCB), and endosulfans (Endo) are presented in this paper, and their potential sources are discussed based on the dataset. It is estimated that ca. 95% of DDTs present in the atmosphere of Chinese cities was still from technical DDT, while only ca. approximately 5% was "dicofol-type of DDT". DDT application for public health control and DDT activated antifouling paint for fishing ships may be the two most important current sources of technical DDT. The DDT concentrations in several Chinese cities seem to match well with the reported DDT concentrations in human breast milk. A low TC/CC ratio was observed across China in the winter to spring, which may provide a fingerprint of Chinese chlordane emission. It was suggested that "weathered" chlordane emitted from urban construction foundations in winter may give the distinctively low TC/CC ratio. The data showed that China is an important global source for HCB. Higher HCB concentrations were observed in winter and spring, and in colder cities, highlighting an important contribution from combustion sources. Samples with higher endosulfan concentrations occurred in the cotton production areas, indicating its major use in killing cotton pests.