Abstract
Despite the global occurrence of microplastic contamination on sandy beaches, evidence of microplastic distribution within beaches remains contradictory. When conflicting evidence is used to inform sampling surveys, it increases uncertainty in resulting data. Moreover, it hampers spatially explicit risk characterization of microplastic pollution to intertidal fauna. We aimed to guide sampling designs for microplastic monitoring on beaches, and to quantify macroinfauna exposure to microplastics. Microplastic abundance, quantified between 5 mm–66 μm, lacked a significant zonation across the top sediment layer of sub-terrestrial, upper and lower midlittoral, and swash zones at two sites with varying anthropogenic influence on a microtidal dissipative beach in Uruguay. Microplastic abundance decreased exponentially with increasing grain size, as revealed by Bayesian Poisson regression, although the decrease was less steep compared to prior knowledge regarding sediment – plastic interactions obtained for large (millimeter-sized) industrial pellets. Significant differences in microplastic contamination between the two sites with varying anthropogenic influence likely related to their proximity to a freshwater canal. Corresponding field measurements of body burdens of fibers and irregular particles were significantly lower for the polychaete Euzonus (Thoracophelia) furcifera, despite its preference for finer sediments with higher microplastic loads, compared to the isopods Excirolana braziliensis and Excirolana armata. Results provide critical insights toward representative sampling of microplastics within beach sites. Specifically, we caution against sampling limited to the drift line, and instead recommend: 1) reporting beach morphodynamic characteristics; 2) using clearly defined, ecologically-informed zonation schemes; and 3) accounting for sediment grain size as a covariate to normalize among reported contamination levels. The results contribute valuable baseline data toward realistic exposure landscapes relative to the sediment grain size preferences of macroinfauna, needed to inform laboratory experiments.
Highlights
Plastic materials are used in a diverse range of products, with their success, in part, due to characteristics such as longevity, strength, ease of manipulation, and low production costs (Andrady and Neal, 2009)
A recent study did observe a higher abundance of industrial microplastic pellets on beaches with very fine, fine, and medium sand compared to coarser sediments in the Laurentian Great Lakes of North America (Corcoran et al, 2020). These results argue for increased attention to the role of sediment grain size in microplastic deposition patterns
The number of microplastics (
Summary
Plastic materials are used in a diverse range of products, with their success, in part, due to characteristics such as longevity, strength, ease of manipulation, and low production costs (Andrady and Neal, 2009). The large amount of plastics currently being produced has created environmental contamination on a global scale (Borrelle et al, 2020). This contamination is augmented because many plastics have a long lifespan, yet are only single or short-term use, and appropriate waste management is generally lacking (Borrelle et al, 2020). The small size of microplastics makes them available to organisms throughout aquatic food webs (Au et al, 2017). A wide range of physical and chemical ef fects of microplastics on individual organisms has been documented (Haegerbaeumer et al, 2019), resulting from direct interactions with
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