Global modeling of the role of microplastics in riverine pathogen transport, exposure, and risks

Concern persists that pathogens attaching to microplastics (MPs) may spread farther in rivers and elevate public health risks. Yet whether pathogen flux carried on riverine MP substantially augments transport via river water is unknown. We quantified, under global river conditions, the fraction of pathogen transport attributable to MP attachment. Riverine MP concentrations were simulated with the MARINA-Plastics model and pathogen concentrations with the GloWPa model at a global sub-basin resolution. We assessed Cryptosporidium worldwide and Escherichia coli (E. coli) for China at the same sub-basin resolution. For the first time, outputs from MP and pathogen models were integrated to estimate MP-pathogen binding probabilistically across rivers. Attachment was represented with an empirical Freundlich sorption formulation parameterized from literature data. Predicted MP-bound E. coli concentrations exceeded those of Cryptosporidium, reflecting stronger sorption and higher bacterial abundances. Despite this, under the current modeling framework and parameterization, the contribution of MP to the total pathogen transport flux is minimal and, based on available evidence, does not warrant prioritization as an independent public health risk source. The framework can be extended to evaluate risks from hazardous particles and co-transported contaminants, including other pathogens, metals, and organic chemicals, to inform evidence-based policy and monitoring priorities.