Heavy metal load in waters and sediments of Karamana River Basin, southwestern India: A COVID-19 lockdown modulation

Abstract

Rapid urbanization and industrialization jointly provoked heavy metal contamination in surface water (SW) and channel sediments (CS) of the riverine ecosystem especially in developing countries like India. Water and sediments are to be considered the most vital gears and useful indicators of the level of contamination in an aquatic environment. Furthermore, it is imperative to assess how COVID 19 lockdown, influenced the Karamana River Basin (KRB) waters catering to the quality water needs of urbanites of a city like Thiruvananthapuram, the capital of Kerala. For an insight into this issue, 84 samples (water = 41; sediment = 41) were collected during the pre-monsoon (i.e., January) of 2021 and 2022 and analysed to generate heavy metal concentration levels in the samples. Our estimate of the Heavy Metal Pollution Index (HPI) of water in the KRB in 2021, during the late peak of Covid-19, indicates that though ∼78.89% of the basin (553.78 km2) stayed within the non-contaminated category, and ∼21.11% (or 148.22 km2) was in the contaminated or very poor category. Contrarily, in 2022 after the withdrawal of lockdown restrictions, the non-contaminated area sharply declined to ∼45.04% (316.15 km2) of the basin and the contaminated area rose to 54.96% (385.85 km2). Furthermore, the Inverse Distance Weighted (IDW) modeling strongly supports that Cr and Fe are the leading heavy metal polluters in the Karamana River (KR) waters during 2021 and 2022. Subsequently, estimated Igeo values in sediments indicate that the uncontaminated area has reduced from 88.89% to 83.73%, and the uncontaminated to the moderately contaminated area rose to 5.16%. Therefore, the shutdown of anthropogenic activities, including small- and medium-scale industries as part of the COVID-19 lockdown, improved the surface water quality of KRB for a short-stint of time, but swung back to normality just after the lifting of lockdown restrictions.