Toxicological Evaluation of Contamination by Potentially Toxic Elements (PTEs) and Related Risks in the Surface Waters of Three Tidal Streams of the Niger Delta, Nigeria

Abstract

This work investigated the physicochemical parameters and potentially toxic elements (PTEs) in the surface water samples collected from three tidal streams (Bonny, Krakrama and Buguma) in the Niger Delta, Nigeria. Potentially toxic elements such as arsenic (As), boron (B), cadmium (Cd), cobalt, (Co), chromium (Cr), lead (Pb), nickel (Ni) and selenium (Se) were analysed using atomic absorption spectrophotometer. Physicochemical parameters were evaluated in situ using portable instruments and also in the laboratory. These parameters and PTEs were used to compute the water quality index, comprehensive pollution index, pollution load index, metal evaluation index, and toxicity load index. The ecological and health risks were also analysed. The PTEs found in the water samples were higher than the acceptable limit by WHO standards and followed the trend of Ni > Pb > Cr > Co > Se > As > Cd > B. Nickel was the most abundant element in water with the maximal concentration of 5510 µg L-1. The calculated contamination indices concluded that the streams were extensively polluted. Based on the permissible toxicity loads, maximum of 99%, 100%, 98%, 98%, 100%, 99%, and 97% of As, Cd, Co, Cr, Pb, Ni and Se respectively should be removed from the surface water of the streams in the Niger Delta to address safety and health. The PTEs in water exerted very high ecological risks. Overall, the estimated lifetime cancer risk of PTEs due to ingestion of water at Bonny, Krakrama and Buguma streams were 5.72 x 10-3, 2.88 x 10-3 and 2.3 x 10-3 respectively. The results guide controlling the PTE pollution and important information on PTEs for the formulation of the necessary remediation policies to improve water quality and protect the human health of dwellers along the Niger Delta.