The thesis focused on the ecotoxicogical impact of the Kenyan tanning industry due to worldwide concern of the leather processing sector as a major polluter.  The results obtained indicated that the tannery dust, when measured against UK Statutory limits, posed an occupational risk through inhalable and respirable dust particle size functions and their toxic chemical nature.  The processing waste was high in chromium, chlorinated phenols, sulphides, chlorides, COD and BOD levels when analysed.  The treatment lagoons, which were designed to reduce the pollutant load, were found to be inefficient, as all stages of treatment including the discharge point demonstrated high toxicity when screened by lux-marked biosensor.  Measurement of activity of the microbial biomass indicated that river health was equally affected and that the observed high particulate content, colour, low DO (high BOD) and multiple effect of the contaminant was potentially causative.  In summary, the work succeeded in meeting the overall aim of the thesis by identifying the main contaminant risks from the tannery dust and effluent as well as in river water and sediments and, determining contaminant bioavailability in terms of toxicity levels. Three specific objectives were achieved at the end of the investigation: characterisation of effluents and sediments and riverine samples, assessment of ecotoxicity and bioremediation potential of primary contaminants and input of environment risk assessment through development of a quantitative and qualitative risk assessment model.  It was concluded that because ecotoxicity testing in this study had comprised a bacterial assay, the incorporation of higher trophic levels in the determination of more specific  ecotoxicological risk assessment would compliment the work carried out.