Spatial distribution patterns and identification of microplastics on intertidal sediments from urban and semi-natural SW Atlantic estuaries

Although estuaries act as a sink of many pollutants, the assessment of microplastics pollution in these transition environments remain scarce or unknown. Sediments from estuarine intertidal areas possess a great ecological concern but also could act as a sink of both buoyant and non-buoyant plastic debris. In this work, we have compared microplastic abundances and their main characteristics (size, shape, colour and polymer type) on intertidal sediments from SW Atlantic Argentinean estuaries (Samborombón, Mar Chiquita, Quequén Grande and Bahía Blanca). The mean microplastics abundance in surface sediments among estuaries was ranged from 0 to 1030 ± 657 items per kg d. w. Upper intertidal areas have shown significant higher microplastic abundances in comparison with lower intertidal zones (p < 0.05). In general, higher mean abundances were observed in surface (0–10 cm) compared to deeper sediments (10–30 cm), which revealed recent deposition trends of microplastics particles. However, higher microplastic abundances were observed in deeper sediments from Bahía Blanca (p < 0.05). Large (MPs, 1–5 mm) and small microplastics (MMPs, 1–0.1 mm) were observed in sediments from all estuaries, representing from 17 to 100% of total microplastics abundance. In terms of shape, fragments and films forms were dominant in all samples while fibers and foams were moderately or poorly represented. White, black, blue and transparent particles were observed as the main colour contribution of microplastics in sediments. The most common polymers identified included polyethylene, polyethylene terephthalate/polyester, polyvinyl chloride and polypropylene. The results showed that microplastic characteristics are different among the estuarine environments, which suggests different anthropogenic sources. Besides, deeper sediments should also be included on intertidal sediment monitoring to identify potential environmental liabilities from anthropogenically impacted estuaries.