Composition and distribution of organochlorine pesticide residues in surface sediments from the Wu-Shi River estuary, Taiwan Ruey-An Doong a, * , Chin-Kai Peng a , Yuh-Chang Sun b , Pei-Lin Liao a a Department of Nuclear Science, National Tsing Hua University, 101, sec. 2, Kuang-Fu Rd., Hsinchu 30013, Taiwan, ROC b Nuclear Science and Technology Development Center, National Tsing Hua University, Hsinchu 30013, Taiwan, ROC Abstract Thecontaminationoforganochlorinepesticides(OCPs)insedimentsfromtheWu-ShiRiverestuarywasinvestigatedtoevaluate thepollutionpotentialsanddistributionofOCPsincentralTaiwan.Atotalof19sedimentsampleswerecollectedatfivesampling stationsalongtheRiverestuary.TheconcentrationsofOCPswereintherangeof0.99–14.5ng/g-dryweight(dw)for RHCH(a-, b-, c-, d-HCH), 0.46–13.4 ng/g-dw for Rcyclodiene and 0.53–11.4 ng/g-dw for RDDT (p; p 0 -DDD, p; p 0 -DDE, p; p 0 -DDT). The mean concentrationsof RHCH, Rcyclodieneand RDDTwere3.79,4.87and2.51ng/g-dw,respectively.ThetotalconcentrationsofOCPs correspond to 1.73–71.9 lg/g-OC when normalized to TOC contents. Among the organochlorine pesticides, endosulfan sulfate, b- HCH,and p; p 0 -DDDwerethemostdominantcompoundsinthesedimentswiththeaverageconcentrationsof1.97,3.43and2.08 ng/g, respectively. Also, different contamination patterns among sampling seasons were observed. The measured concentrations of OCPs collected in spring were higher than those in autumn and winter. A linear relationship between sediment characteristics and OCP residues was also demonstrated. The results obtained in this study show that there still exist a variety of organochlorine pesticide residues in the sediments from the near shore of central Taiwan. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: Organochlorine pesticides; Wu-Shi River estuary; Sediments; Distribution 1. Introduction A large variety of hydrophobic organic substances, suchasorganochlorinepesticides(OCPs)andpolycyclic aromatic hydrocarbons (PAHs) are transported into riverine and estuarine environments through different input pathways, such as discharge of domestic sewage and industrial wastewater, runoff from nonpoint sour- ces,andatmosphericdeposition.Althoughsedimentsdo not constitute a direct measure of the degree of aquatic pollution, they offer an irreplaceable aid in recon- structing the historical inputs of anthropogenic pollu- tants based on spatial and temporal profile descriptions of contamination in sediment samples (Hendy and Peake,1996).Therefore,theinvestigationofdistribution of anthropogenically hydrophobic organic compounds in sediments can provide a valuable record of contami- nation in the river or estuary environments. The understanding of the contamination of orga- nochlorine pesticides in the riverine and estuarine envi- ronmentsisofgreatconcernbecauseofthedetectionof the pesticide residues in various environmental media (Pereira et al., 1996; Hong et al., 1999; Doong et al., 1999). In spite of numerous countries have withdrawn the registered usage of OCPs for many years, these man-made chemicals still persist at considerable levels worldwide (Fowler, 1990; Hendy and Peake, 1996; Sarkar et al., 1997). In Taiwan, a broad spectrum of pesticides was used for agricultural activities as well as vector controls. Hexachlorocyclohexane (HCH), endo- sulfan and DDT were employed extensively from the early 1950s for the control of soil-dwelling insects until the production ban commenced in 1974. It is estimated that 2:5  10 7 kg of pesticides was released into the environments annually since the 1950–1970s and con- stituted a long-term source of contamination to aquatic ecosystem via soil erosion and agricultural runoff. Long-range transport (LRT) is also another possible routeforthecontaminationoforganochlorinepesticides in sediments. Some organochlorine pesticides, such as * Corresponding author. Tel.: +886-3-5726785; fax: +886-3- 5718649. E-mail address: radoong@mx.nthu.edu.tw (R.-A. Doong). 0025-326X/02/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. PII:S0025-326X(02)00102-9 www.elsevier.com/locate/marpolbul Marine Pollution Bulletin 45 (2002) 246–253