Abundance and characteristics of microplastics in beach sediments: Insights into microplastic accumulation in northern Gulf of Mexico estuaries

•Microplastics were found at all locations and in every sample.•More microplastics were found in higher salinity, marine influenced locations.•Polypropylene and polyethylene were the most abundant microplastics.

Microplastics (plastic debris smaller than 5 mm) represent a growing concern worldwide due to increasing amounts of discarded trash. We investigated microplastic debris on sandy shorelines at seven locations in a northern Gulf of Mexico estuary (Mobile Bay, AL) during the summer of 2014. Microplastics were ubiquitous throughout the area studied at concentrations 66-253 × larger than reported for the open ocean. The polymers polypropylene and polyethylene were most abundant, with polystyrene, polyester and aliphatic polyamide also present but in lower quantities. There was a gradient in microplastic abundance, with locations more directly exposed to marine currents and tides having higher microplastic abundance and diversity, as well as a higher contribution by denser polymers (e.g. polyester). These results indicate that microplastic accumulation on shorelines in the northern Gulf of Mexico may be a serious concern, and suggest that exposure to inputs from the Gulf is an important determinant of microplastic abundance.