Seasonal patterns of microplastics in surface sediments of a Mediterranean lagoon heavily impacted by human activities (Bizerte lagoon, Northern Tunisia)

Abstract

In this paper, we investigated seasonal variations in concentrations of microplastics (MPs) in surface sediments of a lagoon heavily impacted by human activities, located in northern Tunisia (the Bizerte lagoon, southern Mediterranean Sea). Analyses of 112 sediment samples collected from 28 stations between May 2019 and February 2020 revealed significant seasonal variation in concentrations of total MPs, with the highest levels recorded in August 2019 (109.6 ± 59.8 items kg^-1 DS (dry sediment)) and the lowest in February 2020 (33.2 ± 22.0 items kg^-1 DS). In terms of polymer types, polyethylene particles were the most abundant throughout the year, followed by polypropylene, polyvinyl chloride, and polyethylene terephthalate. Spatial variations in total MP concentrations were found to depend on several environmental factors, including proximity to the coastline, level of anthropogenic pressure, location inside the lagoon, and presence/absence of vegetation. The upper 5-cm surface sediment layer of the lagoon was found to contain ~ 9.96 × 10¹⁰ MP particles, equal to ~ 248.97 t of plastic. Similar patterns of microplastic composition and structure were found throughout the year, revealing the same plastic pollution hotspots during all seasons. This indicates that sources of plastic pollution are land-based and originate from coastal urban, industrial, and agricultural areas, as well as from major freshwater streams. The findings of the present work can help to develop an efficient environmental management plan aiming to reduce and/or stop the spread of plastic pollution and its impacts on the socially and economically important ecosystem of the Bizerte lagoon.

Keywords: Human activities; Lagoon; Plastic pollution; Seasonal changes; Sediments; Southern Mediterranean Sea.