Bioavailability and health risk assessment of potentially toxic elements in salty water environment of Okposi, Southeastern Nigeria

Abstract

This study is to determine some physicochemical parameters and potentially toxic elements (PTE) in water samples collected from a borehole, a stream and a lake in Okposi, Nigeria, for their quality status and the human health risk of exposure to the waters. The physico-chemical properties: pH, electrical conductivity (EC), salinity, nitrate and sulphate, were determined by standard methods, while the level of PTE contamination was analysed by Flame Atomic Absorption Spectroscopy (FAAS). The results show that the levels of physicochemical parameters in the water samples are within the World Health Organisation (WHO) permissible limit. The PTE concentrations (mg/L) in the samples are in the ranges of 0.12–0.35 (Cr); 0.06–0.19 (Cu); 0.24–2.45 (Fe); 0.0–0.06 (Mn); 0.00–0.75 (Pb); and 0.0–02 (Zn). The levels of Cr and Pb in all the samples, except Pb in the downstream water, are above the WHO permissible limits, indicating that the waters are contaminated and unsafe for drinking. PTE form complexes with anions in water at high EC and salinity which reduces availability of toxic metals to organisms. Therefore, toxicity of PTE in the samples is in decreasing order: Upstream > Downstream > Lake water > borehole water. Calculations of hazard quotients shows possible adverse effects on adults and children on dermal contact with the waters due to Cr. Children might get cancer due to Pb on ingestion of water from the studied borehole, the Lake and the Upstream waters. Statistical analysis suggests that the geology of the area influenced PTE contamination of the water bodies.Article highlightsEvaluation of the pollution status of the major water sources (borehole, lake, upstream and downstream) in the study area was conducted since the information will be useful for making decisions that will protect human health by the policy makers and the public.The samples from all the water bodies in the study area were contaminated by chromium. The borehole water samples were contaminated by Iron and Lead; the downstream samples were contaminated by Iron; while samples from the lake and the upstream were contaminated by Lead. They are contaminated because the concentrations of these metals in the water bodies were above the World Health Organisation’s permissible limit for those metals in drinking water. Human exposure to the level of these metals in the water bodies may lead to severe health problems.Based on the bioavailability studies of the metals and the physicochemical parameters of the major water bodies in the study area, the borehole water (ground water) is the safest (best) for drinking and domestic purposes, then, the lake water (safer), followed by the downstream water (safe), while the upstream water has the highest toxicity potential (not safe).