Microplastic bioaccumulation in odonata larvae: Integrating evidence from experimental studies in freshwater microcosm

Microplastic (MP) pollution is an emerging global threat to freshwater biodiversity, yet little is known about its biological accumulation and trophic transfer in aquatic food webs. We conducted two complementary laboratory experiments simulating bromeliad-tank ecosystems to assess MP ingestion, bioaccumulation, and ecological effects on aquatic macroinvertebrates, with particular emphasis on odonata larvae (Bromeliagrion rehni). First, we evaluated whether MP ingestion varies across taxonomic groups, body regions, and exposure time. In a second experiment, we tested how different exposure pathways (waterborne vs. prey-mediated) and MP concentrations influence ingestion, growth, and survival in a top predatory insect. MP ingestion occurred widely among macroinvertebrates and varied by exposure duration and body region. Prey-mediated exposure led to significantly greater MP accumulation (10-day exposure) than direct contact with contaminated water. Odonata larvae fed contaminated prey exhibited higher growth rates, potentially due to increased prey vulnerability or compensatory foraging behavior. Environmental MP concentration seems to predict particle ingestion. Prey feeding habits influenced their contamination levels, indicating functional group-specific risks. This study provides experimental evidence of MP bioaccumulation and trophic transfer among freshwater macroinvertebrates and demonstrates how exposure route modulates contaminant uptake and biological responses. Moreover, macroinvertebrates act as key vectors of MP transfer, and dietary exposure may amplify sublethal effects across trophic levels. These findings underscore the need to integrate trophic dynamics into ecotoxicological evaluations and highlight how MP pollution may subtly—but significantly—disrupt freshwater food web structure and function.