Vector-amplified toxicity of microplastics and heavy metals in aquatic invertebrates: mechanistic insights and implications for sustainable aquaculture

The co-occurrence of microplastics (MPs) and heavy metals (HMs) in aquatic environments represents an emerging threat to sustainable aquaculture due to their persistence, bioaccumulation, and synergistic toxicity. This review synthesizes mechanistic and quantitative evidence primarily from aquatic invertebrate studies, particularly crustaceans and mollusks, to evaluate adsorption dynamics, bioaccumulation patterns, and toxicity pathways associated with MP–HM complexes. Polyethylene and polystyrene MPs exhibit high adsorption capacities for metals such as Cu² + and Cd² + , with distribution coefficients (Kd) typically ranging from 10³ to ~3 × 10 4 L kg⁻¹ under varying environmental conditions. Co-exposure studies demonstrate amplified toxicological effects: Cd-laden MPs increased metal accumulation in Daphnia magna by ~35%, while Crassostrea gigas showed a 2.4-fold increase in oxidative stress biomarkers. In Litopenaeus vannamei , combined exposure to MPs and Cu resulted in ~30% inhibition of acetylcholinesterase activity, indicating neurotoxicity. Overall, MP–HM interactions intensified oxidative and neurotoxic responses by 1.5–3 times compared to single-contaminant exposure, confirming vector-mediated toxicity. From an aquaculture perspective, MPs serve as active carriers that modify metal bioavailability and internal distribution, increasing exposure risks through contaminated feeds, pond water, and sediment reservoirs. These processes can impair fish and shrimp health, reduce production efficiency, and compromise food safety. Addressing this dual-contaminant challenge requires innovation-driven management strategies, including improved feed sourcing and quality control, sediment remediation, and integrated biosecurity frameworks. This review provides a mechanistic foundation to inform risk assessment and supports the development of adaptive, sustainability-oriented interventions to mitigate MP–HM co-contamination in aquaculture systems.