Exploring the presence and distribution of microplastics in subterranean estuaries from southwest India

Rivers, surface runoff, and the wind all transport microplastics (MPs) to the ocean. There is a knowledge gap concerning the distribution of microplastics in transitional subterranean estuaries. Here, we report the presence of microplastics in the pore water, groundwater, and sea water from four locations in southwest India. Pore water, groundwater, and seawater had mean MP abundances (± standard deviations) of 0.75 (±0.66), 0.15 (±0.1), and 0.11 (±0.07) MPs/l, respectively. Fibres were the dominant category of MPs found. Fourier-transformed infrared spectroscopy revealed the presence of polymers like polyester, low-density polyethylene, and polystyrene. Possible sources of microplastic are fishing activities, tourism, and coastal residents. The microplastics-derived risk assessment scores indicate severe risk to the ecosystems. Fibrous microplastics in pore water indicate that these linear particles can migrate vertically through sandy sediments, reaching subterranean estuaries. We believe submarine groundwater discharge can act as a possible pathway for microplastics to enter the oceans. [Display omitted] •Distribution of microplastics (MPs) in subterranean estuaries of coastal Karnataka•Pore water had mean MP abundance (± s.d.) of 0.75 (±0.66) MPs/l.•Groundwater and seawater had 0.15 (±0.1) and 0.11 (±0.07) MPs/l, respectively.•Polymers of MPs are polyester, low-density polyethylene, and polystyrene.•Submarine groundwater discharge can possibly transfer MPs to the oceans.