Polylactic acid microplastics enhance copper bioavailability and host-microbiome toxicity during black soldier fly bioconversion of food waste: Mechanisms and multi-level impacts.

Biodegradable microplastics are increasingly entering food waste (FW) streams, yet their effects on heavy metal behavior during black soldier fly larvae (BSFL) bioconversion remain unclear. This study investigated the combined effects of polylactic acid microplastics (PLA-MPs, 1% w/w) and Cu (100-300 mg/kg ww) in a BSFL-based FW conversion system. The 100-200 mg/kg treatments represented upper-range Cu exposure scenarios relevant to Cu-rich food residues. PLA-MPs increased Cu accumulation in larvae by 14-32% and shifted Cu toward more bioactive fractions in larvae and frass, indicating enhanced Cu mobility and bioavailability. Co-exposure intensified oxidative and detoxification responses, depleted glutathione, increased lipid peroxidation, and altered energy metabolism. Transcriptomic analysis indicated activation of xenobiotic metabolism, glutathione-related detoxification, and immune-associated pathways. PLA-MPs and Cu also reshaped gut and frass microbial communities, increased community stochasticity, suppressed dissolved organic matter humification, and reduced substrate stabilization and bioconversion performance. Partial least squares path modeling further linked Cu activation and migration, host physiological stress, and microbial dysbiosis to reduced bioconversion efficiency. Overall, PLA-MPs enhanced Cu bioavailability and amplified multi-level toxicity during BSFL-mediated FW treatment, highlighting potential risks to the safe valorization of contaminated organic waste.