Seasonal variations in microplastics in a coastal wetland in southwest India as well as their risks to Sillago sihama and Gerres filamentosus

Abstract

Microplastics are minute plastic particles ranging from 1 µm to 5 mm in size. Mangroves are crucial ecosystems with roles in carbon sequestration, shoreline protection, and habitat for diverse species. Despite their significance, the extent of microplastic pollution in mangroves, especially in India, remains inadequately understood. To address this gap, we conducted a seasonal sampling in the Kota mangrove ecosystem at different water column depths. Our analysis revealed average microplastic abundances of 0.93 (monsoon), 3.71 (post-monsoon), and 2.92 MPs/L (pre-monsoon). The average microplastic abundances were 19.88 and 15.86 microplastics/individual for Gerres filamentosus and Sillago sihama, respectively. Fibrous microplastics smaller than 1 mm were dominant. Transparent microplastics dominated the water column (28.57% in monsoon, 77.45% in post-monsoon, and 49.24% in pre-monsoon), and they were also prevalent in S. sihama (49.55%) and G. filamentosus (41.51%). This points towards greater bioavailability and suggests that transparent microplastics are often mistaken for prey. Anthropogenic influence is a major factor that governs microplastic distribution than season in Kota mangroves. Fourier transform infrared spectroscopy revealed that polypropylene was the dominant polymer in both water column as well as in S. sihama and G. filamentosus. We identified aquaculture, tourism, and local activities as probable sources of microplastic pollution. The monitoring data is crucial as it provides insights into microplastics pollution in two economically important fish species that are largely consumed by the local population. Exposure to microplastics from the consumption of these fish may cause serious health issues for human beings.