TEMPORAL BIOINDICATION OF MICROPLASTICS BY THE ASIAN CLAM, C. FLUMINEA

Microplastics are prevalent in aquatic systems globally, raising concern about possible environmental risks. Ecological risk assessment could be improved with biological monitoring. The Asian clam, C. fluminea, is a proposed bioindicator due to its wide distribution and demonstrated microplastic uptake. However, the Asian clam’s ability to indicate microplastic pollution across temporally variable hydrologic conditions has not been shown despite microplastics being highly affected by seasonal change (e.g., they are often exported by floods and stored in dry months). Ability of a bioindicator to reflect this variation is key to assess risk. Our research thus evaluates the ability of Asian clam to indicate microplastic change over time. Clam, sediment, and water samples were collected monthly November 2021 – May 2022, though presented sediment data are through March only. Most (84%) clam samples (n = 32) contained microplastics. November had the highest average monthly concentration (13.0 ± 2.1 counts/g; n = 5), while the average winter and spring concentration was only 4.4 ± 4.9 counts/g (n = 27). November had notably lower precipitation (22 mm) than the average for subsequent months (75 ± 49 mm), and linear regression analysis showed a negative correlation of average clam microplastic content to monthly discharge (r = -0.74; p = 0.06). Clams may thus be reflecting microplastic storage in dry months and export in wet months. Microplastic types in clam (72% clear fibers, 19% blue fibers, 9% other) more closely resembled that of sediment (61% clear fibers, 12% blue fibers, 27% other) than water (40% clear fibers, 5% blue fibers, 55% other). Dominant microplastic sizes were the same in clam and sediment (respectively 40% and 37% in the 0.5 – 1 mm range), but not water (43% in the 1 – 2 mm range). Monthly microplastic amounts in clam had slight positive trends with the amounts in sediment (r = 0.51) and water (r = 0.20), but no significant correlations. Clams may represent microplastics in sediment better than water, though current data are limited. Ongoing analyses of replicates and more monthly samples will determine if microplastics in clams indicate suspected seasonal variation in sediment and water. Our study results will clarify whether C. fluminea can serve as a bioindicator across seasonally variable hydrologic conditions.