Haji Mwevura's research while affiliated with University of Dar es Salaam and other places

Water samples from Msimbazi and Kizinga rivers in Dar es Salaam and from the coastal marine environment receiving waters from these rivers were analyzed for various organochlorine pescticide residues using GC-ECD and GC-MS. p,p'-DDE, p,p'-DDT, dieldrin and γ-HCH were the only organochlorine pesticide residues detected at significantly greater concentrations above the detection limits. There was a marked difference in the frequency of pesticide residue detection during the dry and wet seasons. All the wet season samples and 37.5% of the dry season samples revealed presence of p,p-DDE at concentrations ranging from 0.05 to 0.45 mgl-1 and 0.08 to 0.20 mgl-1 respectively. pp'-DDT was detected in 25% of the dry season samples at a concentration range of 0.1-0.4 mgl-1 and in 81% of the wet season samples at concentrations ranging from 0.1 – 0.3 mgl-1. Dieldrin and γ-HCH were only detected during the wet season. Dieldrin amounts ranging between 0.2 and 2.5 mgl-1 were detected in all wet season samples whereas γ-HCH (0.2 mgl-1) was found in only one wet season sample. Recoveries of pesticides ranged from 65 to 108%. The present study suggests that the current levels of pesticides detected in these waters have no acute effects to aquatic biota. However, the levels of total DDT and dieldrin present during the wet season suggest a possibility for chronic effects on aquatic biota. Tanz. J. Sci. Vol. 28(2) 2002: 117-130

Sediment and biota samples were collected from Msimbazi and Kizinga rivers and from the coastal marine environment of Dar es Salaam during both dry and wet seasons. The samples were analyzed for various organochlorine pesticide residues using GC-ECD and GC-MS. Dieldrin, p,p'-DDT, p,p'-DDE, p,p'-DDD, o,p'-DDT and y-HCH were detected at significantly greater concentrations above the method detection limits. Recoveries of pesticide residues ranged 86.5-120% in sediments and 62-102% in biota. The average concentrations of total DDT in sediments for the two seasons were almost the same. Biota samples showed significant difference in levels of residues depending on mode of feeding and age of analyzed biota. p,p'-DDT to total DDT ratios in all matrices indicated recent use of DDT. The levels of residues in sediments suggest possible adverse effects to humans consuming biota that are directly exposed to the sediments. This effect, which is associated with bio-concentration of residues in the tissues of edible aquatic biota, should not affect wildlife. In spite of concern on the adverse effect to humans posed by pesticide residues in sediments, edible biota from the examined water bodies were found to be safe for human consumption.

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.