Abstract
Previous studies have indicated that tire tread particles are toxic to aquatic species, but few studies have evaluated the toxicity of such particles using sediment, the likely reservoir of tire wear particles in the environment. In this study, the acute toxicity of tire and road wear particles (TRWP) was assessed in Pseudokirchneriella subcapita, Daphnia magna, and Pimephales promelas using a sediment elutriate (100, 500, 1000 or 10000 mg/l TRWP). Under standard test temperature conditions, no concentration response was observed and EC/LC50 values were greater than 10,000 mg/l. Additional tests using D. magna were performed both with and without sediment in elutriates collected under heated conditions designed to promote the release of chemicals from the rubber matrix to understand what environmental factors may influence the toxicity of TRWP. Toxicity was only observed for elutriates generated from TRWP leached under high-temperature conditions and the lowest EC/LC50 value was 5,000 mg/l. In an effort to identify potential toxic chemical constituent(s) in the heated leachates, toxicity identification evaluation (TIE) studies and chemical analysis of the leachate were conducted. The TIE coupled with chemical analysis (liquid chromatography/mass spectrometry/mass spectrometry [LC/MS/MS] and inductively coupled plasma/mass spectrometry [ICP/MS]) of the leachate identified zinc and aniline as candidate toxicants. However, based on the high EC/LC50 values and the limited conditions under which toxicity was observed, TRWP should be considered a low risk to aquatic ecosystems under acute exposure scenarios.
Highlights
Road dust has become a topic of interest, in relation to ecological impacts on aquatic environments, which are believed to be the ultimate repository for road dust in the environment as a result of roadway runoff
Previous studies have indicated that tire tread particles are toxic to aquatic species, but few studies have evaluated the toxicity of such particles using sediment, the likely reservoir of tire wear particles in the environment
IC50 = 1.29 g/l; daphnid EC50 = 4 g/l; fathead LC50 = 4.8 g/l) were consistent with previous reference toxicity tests performed at Pacific EcoRisk, indicating that these organisms were responding in a typical fashion
Summary
Road dust has become a topic of interest, in relation to ecological impacts on aquatic environments, which are believed to be the ultimate repository for road dust in the environment as a result of roadway runoff. The TRWP were shown to be markedly different from a tread particle (TP) generated through laboratory mechanical abrasion of the tread or grinding of tread pieces. Zinc has been identified as an agent causing toxicity in several studies (Gualtieri et al 2005b; Nelson et al 1994; Wik et al 2009), the release of zinc from TP has been shown to vary based on surface area (particle size), loading rates, and extraction conditions (Gualtieri et al 2005b). While zinc can be leached from TP in the laboratory, under real world conditions, the presence of TP in a soil or sediment matrix increases the pH, which significantly hinders the leaching of Zn and movement into the pore water (Smolders and Degryse 2002; European Commission 2008)
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