Biogeographic biases in microplastic ingestion research mask biodiversity and consumption risks across benthic invertebrates

Ingestion of microplastics (MPs) by organisms, including humans, is a global issue with potential risks to individual, population, and ecosystem health. Yet significant gaps remain in understanding the global extent of this issue. By harmonizing field observations from 295 sampling sites through a comprehensive framework, we reveal profound research biases in microplastic (MP) burdens across benthic invertebrates, with efforts concentrated on arthropods and molluscs, as well as in the Northern Hemisphere and marine ecosystems. Among the 263 taxa exhibiting MP ingestion, the average burden was 3.44 items/ind and 20.28 items/g, with Europe and coasts having the highest taxa richness, and only 28 highly commercialized species were frequently sampled. Feeding mode and body size, along with organism sample size and MP filter size, significantly influenced MP burden after controlling for methodological differences and phylogenetic constraints, and the two traits exhibited partially distinct patterns across the two units. Chao2 estimation suggests that 54 % of the MP-ingesting taxa would remain undetected even with doubled sampling efforts, with similar patterns emerging across continental and aquatic environment scales. These findings suggest that current efforts to understand microplastic biological ingestion and transportation are insufficient to assess the planetary-scale risks posed by this issue.