Toxicity and Carcinogenic Health Risks of Trace Metal Residues in Selected Water Resources Contaminated by Wastewater Effluent

Abstract

Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) was used to detect the presence of 28 trace metal residues in water and sediment samples taken from four surface water resource sites polluted by wastewater effluent. The selected sites are tributaries of the main river within the area of Mangaung which supplies freshwater to communities. These trace metal residues included aluminium (Al), arsenic (As), indium (In), lithium (Li), manganese (Mn), thallium (Tl), silver (Ag), boron (B), barium (Ba), bismuth (Bi), gallium (Ga), strontium (Sr), antimony (Sb), beryllium (Be), molybdenum (Mo), titanium (Ti), cadmium (Cd), lead (Pb), vanadium (V), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), nickel (Ni), selenium (Se), zinc (Zn), mercury (Hg) and magnesium (Mg). Statistical analysis was performed, including calculating means and performing the Spearman’s rank correlation test. Various indices were computed, including the Heavy Metal Evaluation Index (HEI), Heavy Metal Toxicity Load (HMTL), and the general exposure pathway Human Health Risk Assessment Index. All the trace metals were detected at high concentrations, specifically above the World Health Organisation (WHO) limits in water samples. Interestingly, the following significantly elevated maximum concentrations were observed in water and sediment samples for V (114.11 mg/L and 175 mg/g), Li (66.33 mg/L and 242 mg/g), Ba (48.33 mg/L and 67.49 mg/g), B (38.33 mg/L and 354.67 mg/g) and Fe (37.78 mg/L and 535 mg/g), respectively. Sr presented the most significant trace metal pollutant at all sites, with HEI below 20. As, Cd, Cr, Co, Ni, Zn, Ba and Mn had HMTL values above the stipulated limit, indicating potential for toxic health effects. In terms of human health risk, all the trace metals had a CDI of above 0.00001 mg/kg/day, except for Mo. Only V had a hazard quotient (HQ) > 1. Conversely, incremental lifetime cancer risk (ILCR) greater than 0.0001 was exhibited by As at site 1 (0.000105), 2 (0.000117), 3(0.00011) and 4 (0.00014), and for Cr, site 1 (0.01241), 2(0.01312), 3(0.01353), and 4 (0.01353), these results indicate a carcinogenic risk at all sites. Significant differences in chronic daily intake (CDI) values for various trace metals, including AlCDI, InCDI, HgCDI, MnCDI, VCDI, CoCDI, CuCDI, AsCDI, CdCDI, TiCDI, NiCDI, FeCDI, SeCDI, BCDI, MgCDI, TlCDI and CrCDI, were observed (p-value < 0.05). The results of the current study show significantly elevated trace metal concentrations, posing an elevated cancer risk to humans over a lifetime.