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Comparing the effects of conventional and biodegradable plastic mulch particles and their leachates on Chironomus riparius
Summary
Scientists tested how regular plastic farm mulch versus "biodegradable" plastic mulch affects aquatic insect larvae when they break down in water. Surprisingly, the biodegradable plastic's chemical runoff delayed the insects' development at high concentrations, while regular plastic caused no harm at all—suggesting that "biodegradable" doesn't automatically mean safer for the environment. This matters because these plastics are marketed as eco-friendly alternatives, but this study shows we need more research on their real-world effects before assuming they're better for ecosystems (and ultimately, us).
Agricultural mulches are commonly employed to enhance crop yields, these mulches are typically made of conventional plastic such as polyethylene (PE). As an alternative, mulches can be made of biodegradable plastics. However, both plastics are prone to weathering, causing plastic fragments and unintended leachate to end up in the adjacent water systems. Plastic leachates can contain various chemical additives depending on plastic type, yet their effects are poorly studied. Here, we exposed Chironomus riparius larvae through the water phase to artificially weathered plastic particles of conventional linear low-density PE and biodegradable starch-based polybutylene adipate terephthalate (PBAT). To test the role of leaching in toxicity, we exposed the C. riparius larvae to particles of both plastics in leached and unleached form in concentrations up to 10 g/L, and the corresponding leachate in concentrations of a maximum of 100 g/L. None of the tested solutions of conventional PE plastic mulch induced any effects on survival, development or behaviour of the C. riparius larvae. In contrast, we observed developmental effects on the emergence time of the larvae after exposure to the highest concentrations of BPAT leachate. These effects were independent of gender, both emergence of male and female adults were delayed at 10 g/L. Although this study only finds limited impacts and only restricted to high concentrations of the PBAT leachate, we still plea that it is crucial to understand the toxicity of biodegradable plastics on a range of organisms before considering them a more sustainable alternative to conventional plastics.