Spatiotemporal profiling of chemicals of emerging concern in a megacity: a case study of Lagos, Nigeria

Rapid population growth and urbanisation pose risk to the environment and public health. The aim of this study is to undertake a large-scale spatiotemporal chemical profiling of chemicals of emerging concern (CECs) in the rapidly growing megacity of Lagos, Nigeria. A one-week monitoring study was carried out on 63 target compounds at four wastewater treatment plants (WWTPs) and two sewage disposal points (SDPs) which represent different socioeconomic areas in Lagos metropolis. Forty-eight CECs out of 63 monitored were quantified at least once in the influent and effluent samples. Results showed that tramadol and its metabolite O-desmethyltramadol were the highest contributors to the overall CEC concentrations in influent samples. High variability in weekly trends suggests complexity of sample matrix influencing method performance and variability in CECs across sites. High concentrations of target compounds in effluent of WWTP2 and WWTP4 indicate a poor elimination rate. The results from effluent samples from the constructed wetland showed efficient removal of compounds in a natural system. Generally, the concentrations of target analytes in surface water appear to be independent of distance from discharge points. Occurrence of CECs at very high concentrations in effluent samples and the higher concentrations detected upstream of surface water is a cause for concern. The study proposes promoting the use of constructed wetlands in Lagos metropolis for effective removal of CECs and achieves a sustainable and environmentally friendly mode of treatment.