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

Abstract

Ewaso Nyiro basin covers an area of about 210,226 km2, 36.3%, of Kenya drainage area and bears 5.8% of Kenya water potential with an annual yield of 1469 million m3. The river is the principal source of domestic and irrigation water to the arid north of Kenya. To determine metal and nutrient concentration of Ewaso Nyiro River surface water, a total of 30 water 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, total phosphorus and nitrate were analyzed in the two seasons. Ecological risk assessment was determined by calculating contamination factor, pollution load index and ecological risk index. Multivariate statistical analysis was used to infer pollutants association and identify their potential sources. Cadmium, arsenic, lead, molybdenum, mercury, selenium and 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 is recommended by USEPA in drinking water. Herbicides, leached fertilizer and fuel leaking into the river water were the primary sources of anthropogenic pollution.

Health and ecological risk assessment of heavy metals in water and sediments within a data scarce urban catchment in Tanzania – A case of Ngerengere River, Morogoro Municipality

“…5 Heavy metals concentrations, were found to be higher in both sediment and water samples around the midstream and downstream reaches of the Ngerengere river and its tributaries, likely due to the presence of point and non-point sources of pollution. 7 Generally, for water samples, the highest heavy metal concentrations were in dry season where the recorded concentrations were 0.09±0.01 mg/L, 0.25±0.01 mg/L, 0.03±0.02 mg/L, 0.73±0.04 mg/L, 0.03±0.02 mg/L and 0.19±0.02 mg/L for Pb, Cr, Cd, Cu, Zn and Ni respectively. The observed results poses serious health risks to humans and has toxic effects on fish and other aquatic organisms.…”

“…This is primarily due to the prevalence, long-lasting nature, inherent toxicity, inability to degrade, widespread distribution, accumulation in organisms, and amplification through the food chain. [5][6][7] In the field of environmental studies, the term "heavy metals" refers to metals and metalloids characterized by a high atomic weight and a specific gravity five times greater than that of water at 4 °C. Hence, heavy metals are categorized into essential ones such as Zinc (Zn), Copper (Cu), Iron (Fe), Manganese (Mn), etc., and non-essential or toxic heavy metals including Arsenic (As), Cadmium (Cd), Lead (Pb), Mercury (Hg), etc.…”

Water Quality Assessment for the Egyptian Northern Wetlands (Manzala and Burullus) Using WQI and MI Indices

“…Heavy metals (HMs) are considered the most significant pollutants in the aquatic environments due to their persistence, teratogenicity, mutagenicity, carcinogenicity, and ability to bioaccumulate in food chains (Yang et al, 2017;Karimi et al, 2020;Zhao et al, 2020). Several known exposure pathways to HMs include ingestion via drinking water, feeding on aquatic organisms, dermal contact, and consuming agricultural products irrigated by contaminated water (Mbuthia et al, 2014;Biswas et al, 2017;Yang et al, 2017;Njuguna et al, 2020). Additionally, HMs may be generated by natural sources or anthropogenic activities (Mohammadi et al, 2020;Shams et al, 2020) and pose serious threats to human health safety (Setia et al, 2020;Renu et al, 2021).…”