Impact of tyre wear particles and tyre leachate on the freshwater angiosperm Lemna minor

Environmental context Understanding the ecotoxicity of tyre wear particles (TWPs), an increasing pollution source, is necessary for managing environmental risk. This study combines a tyre leachate ecotoxicity assessment and absorption and uptake of TWPs into plants. It was demonstrated that the risk of TWPs entering the food chain through the two studied aquatic plants is low, but managing the leachate levels in the local ecosystems is crucial. Rationale Tyre wear particles (TWPs) have been increasingly recognised as a major contributor of low size-range microplastics that are easily accessible to organisms. The present study aimed to expand on the limited ecotoxicity assessments of aquatic plants exposed to TWPs and understand the potential for TWP trophic transfer from the bottom of the food web. Methodology Here, the surface absorbance of TWPs was investigated using Lemna minor as a model organism for angiosperm plants. Growth inhibition caused by tyre leachate was investigated following the Organisation for Economic Cooperation and Development’s protocol #221, with leachate characterised for 14 common tyre additive chemicals previously detected in Australia’s environment. TWP environmental uptake was assessed using Persicaria sp. collected from a local creek affected by highway runoff in Brisbane. Results The results demonstrated that tyre leachate negatively affected L. minor growth and development at TWP concentrations above levels previously reported in the Australian environment (>1 mg mL–1 TWPs). A possible cause was nutrient deficiency due to stunted root development. TWP agglomerates absorbed to frond surfaces, but TWP uptake into plants could not be confirmed with the methods used. Analysis of TWP-exposed wild plants reported no detectable TWPs. Discussion Aquatic plants serve as food for fish, amphibians, and aquatic birds. This study observed TWP accumulation on L. minor surfaces, suggesting potential entry into the food web. However, the levels detected in lab-cultivated L. minor and wild Persicaria sp. suggest a low risk of trophic transfer in similar scenarios. Thus, although current environmental concentrations of TWPs may not threaten higher organisms from plants, high leachate levels can still harm aquatic vegetation.