Heavy Metals in Wastewater and Sewage Sludge from Selected Municipal Treatment Plants in Eastern Cape Province, South Africa

This study assessed the distribution of five heavy metals (Cd, Pb, Cu, Zn, and Fe) across the various stages of treatment in three selected sewage treatment facilities and their receiving waterbodies in the Eastern Cape Province, South Africa. Aqueous and solid (sludge) samples were collected monthly from September 2015 to February 2016. Quantitation was achieved by atomic absorption spectrometry after necessary sample preparations. Concentrations of heavy metal cations in the sludge generally varied from <DL (below detection limit) to 1.17 mg kg−1, <DL to 0.14 mg kg−1, 27.588 to 69.789 mg kg−1, and <DL to 0.099 mg kg−1 for Cu, Cd, Fe and Pb; while Zn was below detection all through. Similarly, the levels of Cu, Cd, and Fe in the influents, effluents, upstream and downstream across the three plants ranged from <DL–6.588 mg L−1, <DL–0.636 mg L−1, <DL–0.878 mg L−1 and <DL–0.711 mg L−1, respectively; Zn and Pb were less than DL in all the matrices and study locations. All the contaminants were below hazardous levels in all the sludge and aqueous samples except Cd which was higher in effluents and surface waters across the board. Wastewater Treatment Plant (WWTP)-A exhibited better removal capacity for Fe (86.6%), compared to WWTP-B (34.7%) and WWTP-C (56.9%). However, the removal of Cu and Zn was very poor in all the treatment facilities studied. Carcinogenic and non-carcinogenic risks evaluated were sufficiently low. This suggests that the levels of contamination, even with respect to Cd, was minimal. Nevertheless, efforts should be made to keep the concentrations of these contaminants at levels safe for humans and aquatic organisms. Furthermore, the use of the effluents from these facilities for irrigation should be discouraged to prevent unnecessary build-up of metals in the soil and plants grown with such, as well as subsequent bioaccumulation and biomagnification in the food chain.

Determination of levels of some metal contaminants in the freshwater environments of Osun State, Southwest Nigeria: A risk assessment approach to predict health threat

This study evaluated levels of heavy metals and macro-elements in ten major rivers in Osun State, Southwest Nigeria. Triplicate water samples collected from selected rivers were analyzed for metal pollutants by atomic absorption spectrophotometry. Concentrations were obtained as follows: iron: 60-960 μg L^-1; manganese: ND - 3 μg L^-1; chromium 0-2100 μg L^-1; aluminium: 0-800 μg L^-1; copper: 0-1350 μg L^-1; zinc: 10-650 μg L^-1; calcium: 6400-232000 μg L^-1 and magnesium: 2000-71000 μg L^-1 but lead was not detected. While most of the parameters fell within the threshold values for drinking water, iron, chromium, aluminium and calcium exceeded at some locations. The pollution order of the rivers, especially with heavy metals had the order: R8 > R3 > R2 > R5 > R10 > R6 > R4 > R1 > R7 > R9; which implies that R8 and R3 are the most polluted. The health risk assessment results revealed that hazard quotient and hazard index were below the acceptable limit of 1.0, suggesting no substantial non-carcinogenic effect would arise from individual exposure to the elements. However, the carcinogenic risks were 3.18 × 10^-6 and 4.43 × 10^-6 for adults and children, respectively at R8, implying that 1 person in 314,206 adults and 225,836 children drinking from the water may be at risk of having cancer correspondingly. Hence, there is need to moderate the levels of these pollutants in these waterbodies to safeguard public health.