Using the o,p'-DDT/p,p'-DDT ratio to identify DDT sources in China.

Dichlorodiphenyltrichloroethane (DDT) has been banned in China for decades, and yet high DDT concentrations are still being detected in the Chinese environment. This might be at least partly due to the current use of dicofol formulation, which contains DDT as an impurity. In this study, a method based on the ratios of two DDT isomers, o,p'-DDT and p,p'-DDT, was established and used to estimate the relative contributions of dicofol formulation and those of technical DDT to overall environmental DDT. Based on this method and field data from the literature, we calculated that dicofol formulation contributed >72% of atmospheric DDT in 2004 in the Taihu Lake region, China, and this value was >84% in summer when dicofol was applied for agricultural purposes. Sediment and soil, however, contained mostly residual DDT from the historical use of technical DDT. In most other regions of China, we found that dicofol contributed to a significant fraction of DDT in air samples.