Seasonal variations in the abundance and distribution of microplastic particles in the surface waters of a Southern Indian Lake

Hazardous anthropogenic particles, such as microplastics (MPs) in the lake ecosystems, are a serious concern. In this work, we have investigated the seasonal occurrence and distribution of microplastics in the surface water samples of Lake Manipal in southwest India. The concentration of MPs was found to be higher during the monsoon season (0.423 particles/L) in comparison with the post-monsoon (0.117 particles/L) period. The higher abundance is attributed to the input of storm-water sewers connected to the lake as well as surface runoff during periods of high rainfall. The concentrations of small-sized (0.3-1 mm) microplastics were greater in both seasons. Approximately 96% of the microplastics were fibres, followed by smaller amounts of fragments, pellets, films, and foams. Polyethylene terephthalate (PET) was the principal polymer composition of the microplastics, followed by cellulose. The PET and cellulose fibres were mainly derived from the laundering of clothes in the residential colonies and hostels situated close to the lake. The storm-water sewers were the likely conduit for these PET fibres into the lake. The Pollution Load Index (PLI) data reveals that pollution due to microplastics in Lake Manipal falls within the Level I risk category. The PLI was higher during the monsoon season due to an increased flux of these particles from the nearby region. During the post-monsoon period, the PLI values decreased, suggesting that MPs in the water column may have settled and mixed with the sediments. The baseline data generated in this study is important as different types of birds, amphibians, and other microorganisms are present in the environment of Lake Manipal. We also propose certain policy measures that can be adopted by the regional population to mitigate microplastic pollution in the lake and its vicinity.