Quantification of micropollutants in some water sources in northern Tanzania

Abstract

The loading of micropollutants in freshwater ecosystems to levels exceeding their waste assimilative capacity is a threat to both ecology of the ecosystems and health of the resource users. Some chemical species are of much concern due to their persistence, bioaccumulative and toxicity nature, even at trace levels, while others are of concern due to their contribution to eutrophication, oxygen depletion and other disruptive changes. Despite contamination threats from human activities around catchment areas in Tanzania, specific extent of the impacts are rather not well investigated. In this work, we quantified concentration levels of some major elements, trace elements, dissolved inorganic ions, nutrients and organochlorine pesticide residues in river water and sediments from northern Tanzania. Information on land use practices in the area, which represents potential sources of contamination, was gathered. Samples were collected from pre-selected stations in two different seasons and characterized for physico-chemical parameters. Preparation and instrumental analysis of samples was done by standard analytical protocols. Obtained results indicated contamination by some micropollutants, including some dissolved ionic species in water: Na⁺ (> 200 mg/l), K⁺ (> 25 mg/l), Mg²⁺ (> 50 mg/l) and NO₃^– –N (> 80 mg/l). High concentrations of some toxic metals were also measured in sediment samples, including V (325 mg/kg), Cr (270 mg/kg), Cu (114 mg/kg), Ni (85 mg/l) and Zn (355 mg/kg). Low levels of organochlorine pesticide residues were measured. Concentration levels were compared to water and sediment quality guidelines to establish their ecotoxicological risk implications.

Keywords: Micropollutants; Surface water; Sediments; Contamination; Tanzania