Toxicity of two different size classes of tire particles from mixed end-of-life car tires to the springtail Sinella curviseta.

Tire particles (TPs) are one of the biggest contributors to microplastic pollution, with reported soil concentrations exceeding 1 % close to busy roads. Little research has been done on the impact of TPs on soil organisms. In this study, two size classes of tire particles, 0-75 μm and 75-180 μm, were compared to determine if size does influence their toxicity to the springtail Sinella curviseta. Adult springtails were exposed for three weeks to TPs spiked in LUFA 2.2 natural soil at concentrations between 0.0016 % and 4 % (w/w). TP addition caused an increase of soil pH at the two highest concentrations, and a dose-related increase of soil Zn concentrations, which were higher for the larger TPs. Available (0.01 M CaCl extractable) Zn concentrations also increased, but were far below toxic levels in all cases. Springtail survival was not affected, but reproduction was decreased by 59 % and 39 % at the highest concentration (4 %) compared to the control for the 0-75 μm and 75-180 μm classes, respectively. ECs were 3.50 % TPs in soil for the 0-75 μm class and 6.36 % TPs for the 75-180 μm class, and differed significantly between the two size classes (χ > 3.84, p < 0.05). These results suggest that smaller sized tire particles (0-75 μm) are more toxic to S. curviseta than larger ones (75-180 μm). It may also be concluded that long-term exposure to tire particles may threaten springtail populations at the highest concentrations currently found near roadsides.