From Spat to Adult: Investigating Microplastic Accumulation in <i>Crassostrea hongkongensis</i> of Varying Sizes

Although bivalves are widely recognized as indicators of microplastic pollution, evidence of bioaccumulation shows high variability across studies due to exposure duration and depuration rates. This study examined microplastic ingestion in wild oysters of varying sizes (spat to adult) over three months in the Maowei Sea, a mariculture bay in China. Results revealed a positive correlation between oyster size and microplastic ingestion per individual, with larger oysters accumulating more microplastics, primarily in the visceral mass and mantle compared with the gills. However, when normalized by tissue mass, smaller oysters exhibited markedly higher burdens. Specifically, microplastic counts increased by ∼0.53 particles per individual per 1 cm increase in shell length, while the concentration decreased by ∼0.48 particles per gram of tissue per 1 cm increase. This inverse relationship highlights that size is a critical factor influencing the microplastic exposure risk per unit biomass. Additionally, a negative correlation between catalase (CAT) enzyme activity and microplastic exposure over two months provided field-based evidence of oxidative stress. To our knowledge, this study provides the first evidence of a size-dependent pattern in microplastic accumulation among wild oysters from spat to adult; notably, this effect manifests only across broad developmental stages rather than within shorter time scales.