Micro- and mesoplastic contaminants in marine diving ducks: A first assessments from the coast of Japan

Plastic pollution poses a serious threat to seabirds, yet the relationship between plastics and molluscivorous species remains severely understudied despite high risk of exposure to plastics in sediments and contaminated prey. As coastal benthic environments are hotspots for plastic contamination, seaducks that dive and forage on mollusks (predominantly benthic bivalves and gastropods) in coastal habitats may be particularly vulnerable. This study presents the first assessment of plastic contamination in two molluscivorous seaducks: Black Scoters (Melanitta americana) and Stejneger's Scoters (M. stejnegeri), which winter along Japan's Pacific coast. Gizzard samples from 10 individuals were analyzed using Fourier transform infrared spectroscopy after alkaline and acid digestion and density separation, providing an initial assessment of plastic contamination. Microplastics were found in all samples, with a median of 240 particles per bird, corresponding to 7.3 particles g (gizzard content). Diet and foraging habitat may drive this high plastic burden. 99.8% of the plastics were < 200 μm (a size class not considered during previous seaduck studies) and were predominantly fragments (>98% in both species) which may originate from contaminated prey. Polyethylene and polypropylene were the most common polymers identified, accounting for 78.1% of all detected plastics. However, the presence of two polystyrene microplastic pellets and one polystyrene mesoplastic sphere is a unique finding, which is potentially linked to the scoters' foraging behavior. Given seaducks' high exposure and potential health risks associated with their feeding ecology, as well as anatomical and physiological traits, further research should include quantification of nanoplastics in tissues due to the greater toxicological risks involved.