Effects of Covid-19 Era on a Subtropical River Basin in Bangladesh: Perspectives of Eco-Restoration Strategies and Probable Human Health Risks

The COVID-19 era has triggered profound effects on normal human life and the environment, as well as freshwater ecosystems worldwide. Despite the numerous influences, a strict COVID-19 lockdown might lead to improving the surface water quality and thus provide an unprecedented opportunity to restore the degraded freshwater resource. Thus, we intend to investigate the spatiotemporal water quality and preliminary health risks of heavy metals (loids) in the Karatoya River basin (KRB), a tropical urban river in Bangladesh. A total of 70 water samples were collected from 35 stations in KRB in 2019 and 2022 during the dry season. The results showed that the concentrations of Ni, Cu, Zn, Pb, Cd, and Cr were significantly reduced by 89.3–99.7% during the post-lockdown period (p<0.05). However, pH, Fe, Mn, and As concentrations increased due to the rise of urban waste, medical waste, and the usage of disinfectants during the post-lockdown phase. In the post-lockdown phase, the heavy metal pollution index (HPI), heavy metal evaluation index (HEI), and Nemerow’s pollution index values lessened by 8.58%, 42.86%, and 22.86%, respectively. Besides, the irrigation water quality indices also improved by 59%–62%. The total hazard index values increased by 24% (children) and 22% (adults) due to the rise in Mn and As concentrations during the lockdown, while total carcinogenic risk values were reduced by 54% (Children) and 53% (adults) during the post-lockdown period. Industrial and agricultural effluents were restricted access during the lockdown period, resulting in a significant improvement in river water quality for heavy metals (loids). Our study confirms that the lockdown has provided a unique opportunity for the remarkable improvement of degraded freshwater resources. Overall, effective long-term management policies and regular monitoring should be put in place to reduce river pollution and keep surface water clean in the future.