Freshwater food webs are increasingly exposed to microplastics—particles smaller than 5 millimeters—that originate from tire wear, synthetic textiles, plastic fragmentation, and wastewater. Research by Albert Koelmans, Wageningen University, synthesizes how these particles move and persist in rivers, lakes, and sediments, creating new pathways of exposure for aquatic organisms.
Pathways and exposure
Microplastics enter freshwater systems through urban runoff, sewage effluent, atmospheric deposition, and direct littering. Once present, small size and buoyancy determine whether particles stay suspended, settle into sediments, or become resuspended during floods. Studies led by Sherri Mason, State University of New York College at Fredonia, documented widespread microplastic contamination in the Laurentian Great Lakes, highlighting how large freshwater basins near dense human populations concentrate these pollutants. Exposure is spatially heterogeneous: urban and industrial watersheds tend to show higher concentrations than remote headwaters, but localized inputs can make small streams hotspots for contamination.Primary consumers such as zooplankton, insect larvae, and benthic invertebrates ingest microplastics while feeding. Classic laboratory and field observations, first synthesized by Richard Thompson, University of Plymouth, and expanded by Chelsea M. Rochman, University of Toronto, show ingestion across many taxa. Ingestion can be accidental when particles resemble food or unavoidable when feeding mechanisms lack selectivity.
Ecological effects and trophic transfer
The direct consequences begin with physical impacts: gut blockage, reduced feeding efficiency, abrasion, and altered energy budgets. Tamara Galloway, University of Exeter, reported physiological stress responses in fish exposed to microplastics, including reduced growth and changes in behavior in controlled experiments. These sublethal effects can scale up: when invertebrate prey carry microplastics, predators ingest both prey and associated particles, enabling trophic transfer. Albert Koelmans, Wageningen University, emphasizes that the degree of transfer depends on particle retention by prey, predator diet breadth, and the capacity for egestion.Microplastics also act as vectors for chemicals. Plastics can sorb persistent organic pollutants and metals from water and later desorb them in the digestive tracts of organisms, potentially increasing bioavailability. Chelsea M. Rochman, University of Toronto, has shown interactions between plastic particles and contaminants that may amplify exposure risks beyond the plastics themselves. However, the magnitude of contaminant-mediated harm in natural freshwater food webs remains an active area of research, with context-dependent outcomes.
Broader relevance and consequences
Ecosystem-level consequences include altered nutrient cycling when key invertebrate populations decline, shifts in predator–prey dynamics, and reduced productivity of fisheries that communities depend on. In many Indigenous and rural territories, where fish and freshwater invertebrates form cultural and subsistence staples, contamination can affect food security and cultural practices. Urban rivers used for recreation can pose additional human exposure risks through ingestion or contact.Policy and management responses require reducing source inputs, improving wastewater filtration, and integrating microplastic monitoring into freshwater conservation. The scientific consensus, informed by work from Koelmans at Wageningen University, Rochman at University of Toronto, Galloway at University of Exeter, and Mason at SUNY Fredonia, is clear that microplastics create multiple, interacting pressures on freshwater food webs—pressures whose ecological and social consequences will depend on local environmental conditions and human use patterns. Understanding which species and habitats are most vulnerable remains essential for targeted intervention.