Acute sublethal and lethal effects of tire wear particle leachate on larval fathead minnows (Pimephales promelas)

Tire wear particles are a specific class of microplastics that are shed from tires when they are abraded by pavement. These particles contain a multitude of compounds, such as synthetic chemicals, heavy metals, and antioxidants. Many of these chemicals can be leached into water under certain conditions and enter waterways through stormwater runoff. To assess how tire wear particle leachate affects aquatic life, acute (24 hr) toxicity tests using leachate produced over 7-day and 14-day periods were performed on larval (7 day old - 30 day old) fathead minnows (Pimephales promelas). To assess sublethal effects, EthoVision behavior tracking software was used, as well as feeding assays and manual ethograms. To assess lethal effects, the mortality rate of the different treatment groups (control, 7-day, 14-day) was assessed. A dilution study was conducted to identify the mortality rate of possibly more environmentally relevant leachate concentrations. Behavioral changes were observed in both the 7- and 14-day leachate treatments, with an overall decrease in mobility. Any time spent mobile was characterized by erratic behaviors that are indicative of neurological dysfunction. Leachate lethality increased with concentration, with the 75-100 % 14-day leachate solutions exhibiting the highest mortality. The LC₅₀ of the 14-day leachate was determined to be 76 %. This study highlights both behavioral and lethal effects of tire wear particle leachate on early life stages of freshwater fish.