The status of pesticide pollution in Tanzania

The paper summarises the findings of recent studies carried out to assess the levels of pesticide residues in water, sediment, soil and some biota collected from different parts of Tanzania. Although the intention is to cover the whole country, so far the studies have focused on areas with known large-scale pesticide use (Southern Lake Victoria and its basin, TPC sugar Plantations in Kilimanjaro region, Dar es Salaam coast, Mahonda-Makoba basin in Zanzibar) and a former pesticide storage area at Vikuge Farm in Coast region). Analysis of the cleaned extracts in GC-ECD/NPD revealed the dominance of organochlorines in all samples. Generally, low levels of residues were found in areas associated with agricultural pesticide use but the levels in the former storage areas were substantially high. DDT and HCH were dominant in all the studied areas. In the former areas, levels of ∑DDT in water, sediments and soil were up to 2 μg L⁻¹, 700 μg kg⁻¹ and 500 μg kg⁻¹, respectively, while those of ∑HCH were up to 0.2 μg L⁻¹, 132 μg kg⁻¹ and 60 μg kg⁻¹, respectively. The levels in aquatic biota were much higher than those in the water most likely due to bioaccumulation. In the former storage area at Vikuge the levels of pesticides in the topsoil were alarmingly high. Their concentrations were up to 282,000 mg kg⁻¹ dry weight for ∑DDT and up to 63,000 mg kg⁻¹ for ∑HCH. A herbicide, pendimethalin N-(1-ethylpropyl)-2,6-dinitro-3,4-xylidine], was also found at concentrations up to 41,000 mg kg⁻¹ dry weight. Thus the total pesticide content in the soil was almost 40%. Following these findings the area is now earmarked to be a demonstration site for a proposed GEF project ‘Bioremediation of POPs impacted soils in East Africa’.