Chemodynamics of pesticide residues and other persistent organic pollutants within the ruf1ji delta and dolphins from the coastal waters of Zanzibar

This thesis reports on investigations of the chemodynamics of pesticides used in Rufiji Delta with emphasis on their bioavailability and accumulation in organisms within the coastal areas of Tanzania. The investigation revealed the presence of a wide range of organic pollutants including OCs (DDTs, cyclodienes and technical HCH), OPPs, carbonate herbicide and natural brominated compounds. The OPPs showed low bioaccumulation ability by dominating other pollutant groups in water and soil samples but in relatively low concentrations in sediments, prawns and fishes, and they were not detected in crab, birds and dolphin matrices. The OCs particularly DDTs indicated very high accumulation capacity and were the predominating anthropogenic pollutants in sediments and biota tissues. The natural brominated compounds were measured at high concentrations, more than ten times those of DDTs. The study also revealed current use of OPPs and y-HCH in mangrove rice farms and previously used OCs. There were no strong spatial variations of the measured pollutants within the study areas but all OPPs and y-HCH gave strong temporal variations that were governed by pesticide use in the delta. The other pollutants were quite stable throughout the study period showing their ubiquitous nature. Soil and sediments sorption experiments indicated that the marine sediments play a more important role in sequestering chlorpyrifos than freshwater sediments however heavy rains may reduce trapping efficiency of the sediments and thus making the pesticides more bioavailable. Egrets accumulated significantly higher concentrations of residues than yellow-billed storks, but not pelicans. There were no geographical or species variations of pollutants in dolphins, although the brominated natural compounds were found in higher concentrations in the northern part of Unguja Island indicating presence of potential source of the compounds. Finally, the study demonstrated presence of maternal transfer of the residues from mother to newborns via both placental and lactation transfer routes.