Effects of Agricultural Pesticides and Nutrients Residue in Weruweru Sub-Catchment, Tanzania
This research presents the agrochemical residues analysis on the study conducted in Weruweru River Sub-catchment, Kilimanjaro region in Tanzania. Agrochemicals have negative consequences on watershed management in the sub-catchment. It compromises water quality and environment, and thus causing threat to human health and aquatic organisms. This study was undertaken to assess the effects of agricultural pesticides and fertilizers and their residue levels in water and sediments samples in the sub-catchment and establish the measures taken to mitigate the negative effects. 30 farmers were involved in a cross-sectional survey to know the types of agrochemical used, knowledge and attitude. Twelve samples each of water and sediment were collected from upper, middle and lower zones of Weruweru River during the dry and rainy seasons and analyzed by gas chromatography (GC-ECD) for Organochlorine (OCls) pesticide residues, and spectrophotometric method for nutrient levels namely NH3-N, NO3--N, NO2--N and PO43--P . In order of the samples for two seasons to be taken in the same points Geographical Positioning System (GPS) was used to locate sampling points. The bed sediment samples were collected at a depth of 0 - 20 cm, while water samples were collected at a depth of 50 cm below surface; all samples were collected from two different points in each zone. The results revealed that farmers have inadequate knowledge on handling, storage, application and disposal methods. All nutrients analyzed were found to be within the acceptable limits in drinking water as per WHO guidelines, except for NH3-N and PO43—P was higher. The concentrations for NH3-N during the dry season ranged from 0.15 to 0.22 mg/l and rainy season ranged from 0.37 to 0.96 mg/l which were higher than the recommended limits in drinking water which range from 0.05 to 0.5 mg/l. Concentration for PO43--P during the dry season ranged from 0.05 to 0.14 mg/l and during rainy season ranged from 0.44 to 0.52 mg/l were higher than natural background levels of PO43--P in river waters which usually range from 0.005 to 0.02 mg/l. Five OCls pesticide residues detected in water samples namely Cyanazine, Alfa-chlordane, p,p’-DDT, p,p’-DDE and Lindane while seven pesticide residues detected in sediment samples namely cyanazine, Alfa-chlordane, Endosulfan sulphate, p,p’-DDT, p,p’-DDE, lindane and cypermethrin. All OCls pesticide residues detected in sediment samples were below the fresh water sediment quality assessment guideline except Lindane and Alfa-chlordane which were higher with the concentrations ranged from bdl to 3180 mg/kg dw and bdl to 64 mg/kg dw respectively. The pesticides detected in water samples were below acceptable limit in drinking water as per WHO guidelines, except Cyanazine and Lindane, the concentration ranged from bdl to 45.7 mg/l and bdl to 3.66 mg/l, respectively. The concentrations detected were higher than acceptable limit in drinking water cyanazine 10 mg/l and lindane 2 mg/l. The findings provide necessary in formations environmental officers in the sub-catchment and may contribute on designing mitigation measures to reduce degradation of water by agrochemicals and developing strategies which will ensure safe water quality to the consumers.