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Ingestion of small-sized and irregularly shaped polyethylene microplastics affect Chironomus riparius life-history traits
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Researchers exposed freshwater midge larvae to irregularly shaped polyethylene microplastics of different size classes and found that larvae preferentially ingested the smallest particles (32-63 micrometers) regardless of what sizes were available. Ingestion of these small particles significantly reduced larval growth and delayed adult emergence at relatively low concentrations. The findings suggest that small, irregularly shaped microplastics, which are the most common form in natural sediments, may pose a greater risk to benthic organisms than larger particles.
Microplastics (MPs) are emerging contaminants of freshwater ecosystems. Once in aquatic systems, most of these plastic particles undergo processes of fragmentation, biofouling, and sedimentation, resulting in increased concentrations of smaller sized and irregularly-shaped particles in the sediment. High levels of MPs in freshwater sediments can denote a potential threat to benthic and sediment-dwelling organisms such as dipteran larvae. This study evaluates the ecotoxicological effect of three pools of irregularly-shaped polyethylene (PE) microplastics (pools containing 90% of the particles within 32-63 μm (size-class A), 63-250 μm (size-class B) and 125-500 μm (size-class C)), with concentrations ranging from 1.25 to 20 g Kg sediment, on the dipteran Chironomus riparius life-history traits. After ten days of exposure, larvae ingested PE particles typically in the 32-63 μm range, even when 90% of the particles possessed higher size (i.e., in size-classes B and C) and the larvae mandible allowed the ingestion of such bigger-sized particles. Thus, the number of ingested particles was higher in size-class A, followed by B and C, and led to a significant reduction with similar magnitude on larval growth (Lowest Observed Effect Concentrations (LOEC) = 2.5 g Kg sediment DW) and a significant delay on imagoes emergence (e.g., LOEC = 1.5 g Kg sediment DW for females). The results from this study show that the ingestion and persistence of small-sized polyethylene microplastics caused significant impairments on life-history traits of C. riparius. Considering their role on freshwater food-webs and the potential persistence of small-sized PE particles in their larval gut, these results also point for the potential adverse effects of small-sized microplastics at the community and ecosystem level.
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