Toxicity assessment of leachates from rubber and mineral-based infill materials on marine plankton

Crumb rubber, derived from recycled tyres, has been used as a sustainable, low-cost infill material. However, growing evidence suggests that tyre crumb rubber leachates can be highly toxic, underscoring the need for comprehensive risk assessments of different types of rubber and the development of safer alternatives. This study evaluated the acute toxicity of leachates from various infill materials, including black recycled tyre rubbers, coloured thermoplastic rubbers, and a mineral-based material ("Bioflex"), on key models of marine plankton. Specifically, we determined the effects of micronised crumb rubber leachates on the microalga Rhodomonas salina, embryos and nauplii of the copepod Acartia tonsa, and early developmental stages of the sea urchin Arbacia lixula. We also evaluated the toxicity of leachates extracted using an organic solvent compared to those obtained using filtered seawater, using R. salina as a model organism. Toxicity varied significantly among rubber types, with EC₅₀ values ranging from 22.1mgL^-1 to >1505mgL^-1, depending on the organism, and biological endpoint. One of the tested tyre rubber crumbs consistently exhibited high toxicity across all test species, with EC₅₀ values as low as 50mgL^-1 for specific life stages. Among thermoplastic rubbers, green crumb rubber also showed high toxicity towards R. salina, with an EC₅₀ of 25.7mgL^-1. In contrast, the mineral-based material was only toxic to the early stages of A. lixula, exhibiting relatively low toxicity (EC₅₀ = 2305mgL^-1). In most cases, the toxicity of seawater-based leachates was comparable to that of solvent-based extracts, indicating that most toxic compounds affecting R. salina are water-soluble. Metal analysis revealed that the mineral-based material contained lower concentrations of toxic metals, such as zinc, and lower levels of polycyclic aromatic hydrocarbons than the other rubbers. This may partially explain its reduced toxicity to plankton. Our findings demonstrate that leachates from recycled crumb rubber and thermoplastic rubbers are toxic to marine plankton, although the effects are species-specific and dependent on the material composition. Our results also suggest that mineral-based infill materials (e.g., "Bioflex") are ecologically safer alternatives to rubbers. Overall, this study indicates that leachate pollution from recycled tyre rubber and thermoplastic rubber particles poses a potential risk to the pelagic food web, highlighting the importance of restricting or banning their use in areas near sensitive aquatic environments.