Organochlorine pesticide residues in waters from the coastal area of Dar es Salaam and their effect on aquatic biota

Water samples were collected from Msimbazi and Kizinga rivers in Dar es Salaam and from the coastal marine environment receiving waters from these rivers during both the wet season and the dry season and analysed for various organochlorine pesticide residues using GC-ECD. The pesticides p,p’-DDE, p,p’-DDT, dieldrin and γ-HCH were the only organochlorines detected at significantly greater concentrations above detection limits. There was a marked difference on the frequency of pesticide residue detection during the two seasons. All the wet season samples and 37.5% of the dry season samples contained p,p’-DDE at concentrations ranging from 0.05 to 0.45μg/l and 0.08 to 0.20μg/l respectively. p,p’-DDT was detected in 25% of the dry season samples at a concentration range of 0.1–0.4μg/l and in 81% of the wet season samples at concentrations ranging from 0.1– 0.3μg/l. Dieldrin and γ-HCH were only detected during the wet season. Dieldrin amounts ranging between 0.2 and 2.5μg/l were detected in all wet season samples whereas γ-HCH (0.2μg/l) was found in only one wet season sample. Recoveries of all pesticides ranged from 65 to 108%. This study showed that the current levels of pesticides residues in the studied waters have no acute effects to aquatic biota. However, the levels of total DDT and dieldrin during the wet season might result in chronic effects to aquatic biota.