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Exposure to environmentally derived secondary microplastics and associated trace metals induces oxidative stress, neurotoxicity, and behavioral alterations in the clam Meretrix lyrata
Summary
Scientists found that tiny weathered plastic bits in ocean sediment don't just pollute on their own — they act like magnets for toxic metals like lead and chromium, dragging more of these metals into clams' bodies. This one-two punch caused real damage: it stressed the clams' cells, damaged their nervous systems, and made them worse at burying themselves in sand for safety, leaving them more exposed to predators. Since these clams are a food source in some regions, this research is a reminder that microplastics may make existing pollution problems worse as they travel up the food chain toward us.
Marine microplastics raise significant concerns regarding their combined effects with trace metals (TMs). This study evaluated the biological impacts of environmentally derived secondary microplastics combined with TMs on the benthic bivalve Meretrix lyrata. Clams were exposed for 30 days to sediment enriched with weathered polyethylene (SMPs) (1-500 µm) at contents ranging from 0 to 5000 mg/kg. Results demonstrated that SMPs substantially enhanced the bioaccumulation of lead (Pb) and chromium (Cr), with tissue contents peaking at the 500 mg/kg treatment. This TM accumulation triggered profound physiological stress, characterized by a marked induction of antioxidant defenses, specifically catalase (CAT) and glutathione S-transferase (GST) activities, which increased by up to 101% and 89%, respectively. Concurrently, severe neurotoxicity was evidenced by a maximum 33% inhibition of acetylcholinesterase (AChE) activity. Linear regression revealed a strong negative correlation between AChE inhibition and tissue Pb levels (R = 0.963, p < 0.005). Furthermore, Principal Component Analysis (PCA) corroborated a cascading mechanistic pathway, demonstrating distinct diametric opposition between the Pb-induced oxidative stress cluster (Pb, CAT, GST) and neuro-behavioral endpoints (AChE, burial rate). Consequently, these biochemical disruptions translated into ecologically relevant behavioral impairments, notably a dose-dependent decline in burrowing capacity and a reduced proportion of fully buried clams (B100). This behavioral failure, potentially indicating sediment-avoidance at extreme SMP dosages, theoretically increases their vulnerability to epibenthic predation and environmental fluctuations. Ultimately, these findings highlight the combined effects of weathered microplastics and associated metals, emphasizing the critical need for integrative, multi-level risk assessments of plastic pollution in benthic ecosystems.