Environmental impact of residue Tire & Road Wear Particle on gammarids and potential ecological consequences.

The environmental impact of Tire and Road Wear Particles (TRWP), arising from tire-road friction, has raised significant concerns. Like microplastics, TRWP contaminate air, water, and soil, with considerable annual emissions and runoff into freshwater ecosystems. Among TRWP compounds, 6PPD-Q, leached from tire particles, shows varying toxicity across species, notably affecting fish and invertebrates. This study investigates the effects of 6PPD-Q on Gammarus amphipods, a key species in freshwater ecosystems, to better understand its potential ecological and policy implications. Using recirculating water systems with 9 independent incubators, Gammarus amphipods were exposed to 6PPD-Q at concentrations (1.5 and 3.0 µg/L) relevant to peri-alpine lakes. Males and females were separately tested across treatments, and multiple biodemographic endpoints were monitored, including survival, feeding rate, behavior, and reproductive traits. Results revealed sublethal effects included a significant reduction in feeding rate and behavioral alterations at 1.5 µg/L, such as decreased swimming speed, reduced distance travelled. Furthemore a moderate increase in male mortality (14%) was observed at 3 µg/L. Although oocyte size increased at 3 µg/L, the number of oocytes and embryos did not significantly differ between treatments. These results suggest that even at low concentrations, 6PPD-Q may impair key physiological and behavioral functions in Gammarus, potentially through neurotoxic mechanisms. Given the ecological role of amphipods in detritus processing and trophic transfer, such impairments could compromise energy flow within freshwater food webs. While some observed effects showed high variability, they warrant further investigation to assess potential long-term and population-level consequences.