Individual and combined dietary exposure to polyethylene microplastics and cadmium in Litopenaeus vannamei: biological effects and bioaccumulation

Although polyethylene microplastics (PE-MPs) have been documented to adsorb heavy metals, such as cadmium (Cd) in aquatic environments, the effects of their combined ingestion on marine organisms remain scarcely understood. This study evaluated the individual and combined effects of spherical PE-MPs (53-63 μm) and Cd on survival, growth, and bioaccumulation in juvenile shrimps Litopenaeus vannamei exposed via feeding for 21 days. Individual (300 mg kg^-1 PE-MPs and 30 mg kg^-1 Cd) and combined exposures did not affect survival rates. However, the final weight was significantly lower in the combined treatment (3.8 ± 0.1 g) compared to the control (4.3 ± 0.2 g), suggesting that co-exposure to PE-MPs and Cd adversely affected growth. The highest PE-MPs accumulation at 21 days under the combined treatments was observed in the gastrointestinal tract (GIT) (981.7 ± 70.8 MP g^-1). Cadmium (Cd) accumulation followed the order hepatopancreas (HP) > GIT > gills (GL) > exoskeleton (EX) > muscle (MU), reaching its highest concentration in the HP of the combined treatment (91.7 ± 1.4 μg g^-1), even higher than in the treatment with Cd alone (80.5 ± 5.6 μg g^-1). Overall, dietary co-exposure to PE-MPs and Cd for 21 days reduced growth and increased the bioaccumulation of both contaminants, suggesting that combined exposure may modify contaminant bioavailability and retention. Further studies are needed to elucidate the metabolic mechanisms associated with this response.