Time trend of BHCs and DDTs in a sedimentary core in Macao estuary, Southern China

BHCs and DDTs in a Pb-210 dated sedimentary core in Macao estuary were anal ysed with supercritical CO2 extraction and GC-ECD. The concentrations of BH Cs in the core sediment dated from 1962 ranged from trace level (< MDL) to 82.4 ng/g, and those of DDTs ranged from trace level(<MDL) to 79.0 ng/g. Th e highest concentrations of both DDTs and BHCs were found in sediment dated 1993, which correspond to a sharp decrease in cultivated land area and a g reatly expanded capital construction investment scale in Zhuhai in 1992-199 4. Vertical variations of (DDD + DDE)/DDT and DDE/DDD ratios indicated that DDTs deposited after 1985 were subjected to more on-land weathering proces s than those deposited before 1985. The authors suggested that the organoch lorine pesticide residue in soils might have been mobilized by large-scale land transformation, which greatly contributed, after the production ban, t o the DDTs in sediments in Macao estuary. Significant decreases in concentr ations of BHCs and DDTs were observed in sediments deposited after 1993. (C ) 1999 Elsevier Science Ltd, All rights reserved.