Ecological and health risk assessment of potentially toxic elements in Ewaso Nyiro River surface water, Kenya

摘要

Ewaso Nyiro basin covers an area of about 210,226 km~2, 36.3%, of Kenya drainage area and bears 5.8% of Kenya waterpotential with an annual yield of 1469 million m~3. The river is the principal source of domestic and irrigation water tothe arid north of Kenya. To determine metal and nutrient concentration of Ewaso Nyiro River surface water, a total of 30water samples, 15 samples each for dry (February) and wet (August) seasons of 2019, were collected. Chromium, lead,iron, manganese, cobalt, cadmium, mercury, selenium, molybdenum, boron, copper, zinc, arsenic, nickel, aluminum, totalphosphorus and nitrate were analyzed in the two seasons. Ecological risk assessment was determined by calculatingcontamination factor, pollution load index and ecological risk index. Multivariate statistical analysis was used to inferpollutants association and identify their potential sources. Cadmium, arsenic, lead, molybdenum, mercury, seleniumand nickel were not detected in both seasons, while manganese, iron and aluminum were the main pollutants identified.Ewaso Nyiro irrigation water had a manganese contamination factor of 9.17, implying it was very contaminated.Twenty-seven and 40% of sampled sites in dry and wet seasons, respectively, had more than 0.3 mg/L of iron that isrecommended by USEPA in drinking water. Herbicides, leached fertilizer and fuel leaking into the river water were theprimary sources of anthropogenic pollution.