PESTICIDE RESIDUES IN COASTAL DAR ES SALAAM 91 Corresponding Author: HM. E-mail:mwevura@chem.udsm.ac.tz or mwevura@hotmail.com Western Indian Ocean J. Mar. Sci. Vol. 1, No. 1, pp. 91–96, 2002 © 2002 WIOMSA Organochlorine Pesticide Residues in Edible Biota from the Coastal Area of Dar es Salaam City Haji Mwevura, Othman C. Othman and George L. Mhehe Chemistry Department, University of Dar es Salaam, P.O. Box 35061, Dar es Salaam, Tanzania Key words: biota, organochlorine, pesticides, pollution, marine, baseline studies, Tanzania Abstract—This paper reports on the levels of organochlorine pesticide residues in edible biota from the coastal area of Dar es Salaam city, Tanzania. Samples were collected from the Msimbazi and Kizinga rivers and from the coastal marine environment receiving waters from these rivers. The samples were analysed for various organochlorine pesticide residues using GC-ECD and the results confirmed with GC-MS. Dieldrin, p,p'-DDT, p,p'-DDE, p,p'-DDD, o,p'-DDT and γ- HCH were the only organochlorines detected at concentrations above the method detection limits (MDL). The samples showed significant differences in levels of residues depending on location, mode of feeding and age/size of analysed biota. p,p'-DDT to total DDT ratios in biota indicated recent contamination of DDT. Biota from mangrove areas showed highest level of residues followed by those from fresh water while lowest concentrations were detected in biota from marine coastal water. In spite of concerns on the adverse effects to humans posed by pesticide residues in sediments reported from previous studies, edible biota from the examined water bodies are safe for human consumption. INTRODUCTION Organochlorine pesticides have been extensively used for agriculture and vector control purposes in Tanzania. The pesticides applied on land eventually find their way to the aquatic environment, thus contaminating it. The pesticides are transported to aquatic bodies by rain runoff, rivers and streams and associate with biotic and abiotic macroparticles (Colombo et al., 1990). They are removed from the surface to the benthic layers by settling of the particles into the water column (Allan, 1986). The lipophilic nature, hydrophobicity and low chemical and biological degradation rates of organochlorine pesticides have led to their accumulation in biological tissues and subsequent magnification of concentrations in organisms progressing up the food chain (Swackhamer et al., 1988; Vassilopoulou & Georgakopoulous-Gregoriades, 1993). Consumption of biota from contaminated aquatic body is considered to be an important route of exposure to persistent organochlorine compounds (Johansen et al., 1996). Humans, being a final link in the food chain, are mostly affected, and consequently the general public has become increasingly concerned about the potential risk to human health from consumption of such polluted biota. Furthermore, organochlorine pesticides in the aquatic environment have been reported to cause reproductive depression in aquatic biota (Helle et al., 1976). Detectable levels of organochlorine pesticide residues have been reported in the coastal waters and sediments of Dar es Salaam (Machiwa, 2000; Mwevura et al., 2001) and in some cases the detected residues were suspected to cause long-term effects to aquatic biota and human health (Mwevura, 2000). The objectives of this study were therefore, to determine the baseline concentrations and