How does bivalve size influence microplastics accumulation?

Microplastics (wasted plastic particles < 5 mm in diameter) are ubiquitously distributed in the marine environment. Filter-feeding and low trophic level bivalves are vulnerable to microplastics accumulation from the surrounding depositional environment, thereby threatening both ecological health and human food safety. Microplastics had been detected in lots of coastal Bivalvia species. However, the influence of biological morphology on the mechanism of microplastics accumulation is not clear. There is also a knowledge gap of which species are preferred for commercial consumption, which creates loopholes in risk identification for food safety. A survey on a commercial popular eaten but under-researched hard clam (Meretrix meretrix; Linnaeus, 1758) from a famous fishery port city in southern China was carried out to comprehensively analyze shell size influence on microplastics accumulation in bivalves and consequently, human intake risk via bivalve consumption. Detected microplastics count in per individual (MCI) was 24.64 ± 19.11 items · individual, and microplastics count per gram (MCG; wet weight with shell) was 0.66 ± 0.54 items · g. When the shell width grew by 1 mm, MCI increased by 1.01 times, but MCG decreased by 0.97 times. Dominant microplastics characteristics found in this study was fiber and fragment. Sizes ranged from 25 to 150 μm, and dark colors (black, red, and blue) were found. The mostly common polymers were polyethene (PE, 40%), polyethylene terephthalate (PET, 23%), and polypropylene (PP, 18%). Estimated annual intake (EAI) risk of microplastics via hard clam consumption by residents was 6652.26 ± 5327.28 items · year · person . The microplastics in bivalves and EAI was relatively high. When shell width grew by 1 mm, EAI decreased by 0.97 times. Therefore, eating a fixed amount of larger hard clams with a relatively low amount of microplastics can reduce EAI risk for consumers. A systematic investigation of emission sources along main coast, where bivalve production is prominent will be useful for food safety control in this region.