Stress of Soil Moisture and Temperature Exacerbates the Toxicity of Tire Wear Particles to Soil Fauna: Tracking the Role of Additives through Host Microbiota

Tire wear particles (TWPs) are considered as an emerging threat to soil fauna. However, how TWP toxicity to soil fauna responds to the stress of soil moisture and temperature remains unclear. We assessed the toxicity of environmentally relevant TWPs to the soil model species Enchytraeus crypticus under three soil moisture and two temperature gradients. Typical thermoplastic polypropylene (PP) was selected for comparison. Results showed that compared with PP, TWPs exerted stronger toxicity, including decreasing the worm growth, survival and reproduction rates, disturbing the soil and worm gut microbiota, and leaching more diverse and higher contents of additives. Stress of soil moisture and temperature exacerbated TWP toxicity mainly through affecting the leaching and transformation of additives. Fourteen mediated additives significantly contributed to the shift of the gut microbiota under soil moisture and temperature stress, among which 1,3-diphenylguanidine, N,N'-bis(methylphenyl)-1,4-benzenediamine quinone, N-tert-butyl-2-benzothiazolesulfenamide, and 2-aminobenzothiazole were identified as the main drivers. In addition, this study provided the first clear evidence that increased soil moisture and temperature promoted the transformation of additives in the soil. Our study revealed the non-negligible aggravated toxicity of TWPs to soil fauna under stress of soil moisture and temperature, providing novel insights into the environmental behavior of additives.

Environmental Implication (maximum limit:100 words)

Tire wear particles (TWPs) have become an emerging threat to the environment and soil is the major sink for TWPs. However, it is still unknown about whether and how the toxicity of TWPs to soil fauna responds to soil moisture and temperature. We represent the first to demonstrate that stress of soil moisture and temperature exacerbates TWP toxicity to soil fauna mainly through mediating additive leaching and transformation, and provide the first clear evidence that increased soil moisture and temperature promote the transformation of additives in the soil, helping understand the environmental behavior and risks of TWPs.