Occurrence and health risk assessment of trace and heavy metals in four wastewater treatment plants and their receiving surface waters in Gauteng Province, South Africa
摘要
Wastewater treatment plants (WWTPs) receive high volumes of domestic and industrial effluents, which are endowed with varying levels of metallic elements. If not properly treated WWTPs effluents discharged into river systems contribute to their contamination. This work reports on the ubiquitous detection of metals (As, Cd, Co, Cr, Cu, Fe, Mn, Pb, Ni, Zn) in WWTPs influents, effluents, sludge and water from the receiving rivers located in the Gauteng Province in South Africa. In wastewater, calculated mean metal concentrations ranged between 0.132 and 4.914 mg L−1. Comparatively in the surface water, the concentrations ranged between 0.127 and 4.631 mg L−1. In effluents As, Cr and Pb exceeded the permissible values for safe river discharge whilst surface water concentrations for As, Cd, Co, Fe, Mn, Ni and Pb exceeded the threshold values for agricultural and domestic use. These presented possible non carcinogenic and carcinogenic risks to individuals exposed to surface water through ingestion and dermal contact. In activated and digested sludge metal concentrations ranged from 16.425 to 2466 mg kg−1 with Zn and Cd being the most and least abundant respectively. Human health risk assessments for workers and farmers handling sludge revealed probable non-carcinogenic and carcinogenic risks emanating from incidental sludge ingestion. The findings of this work highlight the indiscriminate distribution of metals in the environment and support the calls for the upgrade of WWTPs to increase their efficiency in contaminant removal.