July 24, 2025 by Ed Stutt

The Environment Agency has published a report authored by wca scientists that reviewed chemical additives in tyres and identified the substances that should be prioritised for further assessment. wca, working with the EA, undertook a review of the hazards associated with commonly identified tyre additives and produced prioritisation rankings based on both hazard metrics and tonnage, and a risk assessment that used exposure modelling to predict concentrations in UK surface waters.

The report and supporting materials are available on the Environment Agency website at: https://www.gov.uk/government/publications/hazard-screening-and-uk-risk-prioritisation-for-tyre-additives

The release of chemicals used in the production of rubber tyres is a concern for potential harm to the environment because tens of thousands of tonnes of tyre wear particles (TWP) are released every year on UK roads, from where they can find their way into streams and rivers.

The initial hazard-focussed ranking exercise prioritised well known and data-rich environmental pollutants such as octylphenol, zinc and dibutyl phthalate. Exposure modelling was then undertaken using a model developed by the Agency to predict the release of chemicals from TWP as input to the EUSES model, which was used for estimating concentrations in UK surface waters. The risk- based prioritisation using this modelling gave a very different set of priority chemicals and highlighted the greatest concern as coming from phenylenediamine derivatives (PPDs) used as antiozonants and benzothiazole vulcanising agents. Risks levels were estimated for different environmental compartments and sediment was identified as the most sensitive compartment for the majority of substances considered.

Recommendations were made for a more detailed review of the highest priority substances, particularly PPDs. Furthermore, monitoring should be undertaken for the substances ranked highest by the risk-based prioritisation, with a focus on the environmental compartments identified as most sensitive for each substance.