Occurrence, sources and treatment of contaminants of emerging concern and heavy metals in effluent and receiving waters in Mzuzu city, Malawi

Abstract

Effluent from municipal wastewater has recently been one of the major sources of pollution in the environment. This study quantified the selected heavy metals (HM) ((lead (Pb), chromium (Cr), cadmium (Cd), arsenic (As) and mercury (Hg)) and antibiotics (amoxicillin, erythromycin, bactrim, tetracycline, gentamicin and ciprofloxacin) as contaminants of emerging concern (CECs) in effluent and receiving water bodies in Mzuzu City in the wet and the dry seasons. The samples (n = 208) were collected from the 3 waste stabilization ponds (WSPs), 3 water bodies and analyzed using Atomic Absorption Spectrophotometer for HM and High-Performance Liquid Chromatography for antibiotics. Statistical analysis was done using IBM SPSS version 20 and R statistical software tools. Detection of the selected heavy metals ranged from 51.85 to 85.19 % and antibiotics ranged from 14.81 to 96.3 %. The mean concentrations of heavy metals in the wet season and the dry season were (Pb: 0.34±0.08 mg/L; and Cr: 0.12±0.05 mg/L) and (Pb: 0.03±0.02 mg/L, Cr: 0.01±0.01 mg/L and Cd: 0.004±0.0001 mg/L), respectively. The mean concentration of antibiotics ranged from below the detectable limit to 51.4±1.26 µg/L in the wet season and 0.13±0.01 µg/L to 158.58±65.85 µg/L in the dry season. There were significant seasonal variations (p < 0.05) in the occurrence, distribution and sources of HM and antibiotics in both seasons. Major antibiotics and heavy metals sources in the aquatic environment were the anthropogenic activities and effluent from WSPs. Mineralization and temperature affected the distribution of antibiotics and heavy metals in the study area. The removal of HM from WSPs in both seasons ranged from -17.95 to 100 % while antibiotics removal ranged from -1837.6 to 100 %. The results showed that WSPs are conducive to removing HM more than antibiotics. Proper treatment and disposal of waste and wastewater in the environment is key in reducing the occurrence of HM and CECs in the environment thereby protecting human and aquatic life.