Sedimentary records of DDT and HCH in the Pearl River Delta, South China

Tropical regions in developing countries are thought to be significant sources of organochlorine pesticides in the global context owing to high rate of use and only a recent production ban or restriction on application of these pesticides In the present paper DDT and HCH in eight(210) Pb dated sedimentary cores from the Pearl River Delta South China were analyzed in order to reconstruct the time trends of these persistent organic pollutants in this tropical region The sedimentary inventories of SigmaDDT and SigmaHCH through the cores ranged from 36 6 to 1109 5 ng/cm(2) and from 112 to 226 3 ng/cm(2) respectively and their spatial distribution implies that the water flows from the Humen Jiaomen Hongqili and Hengmen outlets rather than the Xijiang flow from Modaomen outlet supplied the major historical input of DDT to the estuary Although a production ban of technical HCH and DDT was imposed in China in 1983 their sedimentary fluxes display increasing trends or strong rebounds in the 1990s as recorded in the core profiles characteristic of the increasing ratios of (DDE + DDD)/DDT and DDE/DDT It is suggested that an enhanced land soil runoff in the process of large scale land transform as well as a higher river water flow in early 1990s had mobilized these pesticides from soil to the sedimentary system in the region.