Determining the potential human health risks posed by heavy metals present in municipal sewage sludge from a wastewater treatment plant

Abstract

The study looked to establish the elemental composition of heavy metals such as Zn, Mn, Cu, Cr, Ni, Pb, As, and Co, present in sewage sludge and assessed their health risks. Samples were taken from the Gammams Wastewater Treatment Plant in Windhoek, Namibia and used for the analysis. Two samples of sludge were collected twice in the same week. The samples of sewage sludge were subjected to the hot-plate acid digestion method prior to the determination of the heavy metals using an Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). The evaluation of the health risks was performed according to the U.S Environmental Protection Agency (USEPA) and South African Guidelines. Their elemental contents ranged from 65.75 - 82.17 mg/kg for Zn, 29.31 - 56.98 mg/kg for Mn, 21.46 - 49.20 mg/kg for Cu, 19.44 - 29.20 mg/kg for Cr, 2.88 - 3.82 mg/kg for Ni, 1.84 - 4.22 mg/kg for Pb, 0.83 - 1.74 mg/kg for As and 0.26 - 0.98 mg/kg for Co. Each of the levels for the heavy metals were found to be below the standard permissible limits of the two regulations and therefore are considered safe for land-based applications (agriculture) and were also associated with low health risks. The risk assessment is considered for the estimation of potential human health risks which also evaluates the likelihood of adverse health risks. Furthermore, the study revealed that children are more susceptible to carcinogenic and non-carcinogenic health risks in comparison to adults via the ingestion pathway.