Potential bioavailability of inorganic compounds from Tire and Road Wear Particles to fish in simulated gastric and intestinal fluids

The potential impact of Tire and Road Wear Particles (TRWP) on aquatic organisms has recently gained attention since the occurrence of TRWP in the aquatic environment has been demonstrated in surface water and sediments of numerous regions. However, data regarding the bioavailability and toxicity of contaminants associated with these particles are still lacking. Several metals enter in the composition of tires including Zinc, used as a catalyst during the vulcanization process of rubber. This study aimed (i) to characterize the elemental composition of Cryogenically Milled Tire Tread (CMTT) and TRWP and (ii) to assess the solubilization potential of inorganic contaminants from CMTT and TRWP in Simulated Gastric Fluids (SFG) and Simulated Intestinal Fluids (SIF) designed to mimic Oncorhynchus mykiss (Rainbow Trout) gut conditions. Our results show an important difference in the elemental composition of CMTT and TRWP due to the input of elements such as Ti, Cr, Mn, Sr, Ba and Pb from the road constituent to the TRWP. In vitro digestion experiments of both CMTT and TRWP showed that solubilization of all metals were enhanced by up to 10-fold in simulated gut fluids compared to solubilization in phosphate buffer solution. Solubilization kinetics to the SGF and SIF were biphasic with a higher solubilization rate of elements within the first hour and a slower solubilization rate up to 26h. For most metals, solubilization rates were higher for TRWP than for CMTT. After digestion time of 26h, from 1% (Co) to 10% (Zn) of total metal in CMTT were solubilized in the gut fluids and the concentration of metals were about 1 – 100 µg/L except for Zn with 7000 µg/L. Our results emphasise the importance of pH, bile surfactants and organic matter in the solubilization of metals from TRWP and brings new insights on the bioavailability of inorganic pollutants from TRWP.