About 3 billion new tires are produced each year and about 800 million tires become waste annually. Global dependence upon tires produced from natural rubber and petroleum-based compounds represents a persistent and complex environmental problem with only partial and often-times, ineffective solutions. Tire emissions may be in the form of whole tires, tire particles, and chemical compounds, each of which is transported through various atmospheric, terrestrial, and aquatic routes in the natural and built environments. Production and use of tires generates multiple heavy metals, plastics, PAH's, and other compounds that can be toxic alone or as chemical cocktails. Used tires require storage space, are energy intensive to recycle, and generally have few post-wear uses that are not also potential sources of pollutants (e.g., crumb rubber, pavements, burning). Tire particles emitted during use are a major component of microplastics in urban runoff and a source of unique and highly potent toxic substances. Thus, tires represent a ubiquitous and complex pollutant that requires a comprehensive examination to develop effective management and remediation. We approach the issue of tire pollution holistically by examining the life cycle of tires across production, emissions, recycling, and disposal. In this paper, we synthesize recent research and data about the environmental and human health risks associated with the production, use, and disposal of tires and discuss gaps in our knowledge about fate and transport, as well as the toxicology of tire particles and chemical leachates. We examine potential management and remediation approaches for addressing exposure risks across the life cycle of tires. We consider tires as pollutants across three levels: tires in their whole state, as particulates, and as a mixture of chemical cocktails. Finally, we discuss information gaps in our understanding of tires as a pollutant and outline key questions to improve our knowledge and ability to manage and remediate tire pollution.

Environmental sampling has documented a diversity of microplastics, including high levels of black rubber- generally identified as tire debris. Though organisms have been shown to ingest tire particles (TPs), past research focused on toxicity of leachate alone, overlooking potential effects of particles. To address these gaps, we assessed the toxicity of micro (1-20 µm) and nano (<1 µm) TPs for two model organisms, embryonic Zebrafish Danio rerio and the crustacean Daphnia magna. To assess effects on development, Zebrafish embryos were exposed to concentrations of TPs or leachate ranging from 0 to 3.0 × 10⁹ particles/ml and 0-100% respectively (n = 4). Greater mortality and sublethal malformations were observed following nano TP and leachate exposures as compared to micro TPs. Unique abnormalities between the exposures indicates that there is both chemical and particle-specific toxicity. We also observed D. magna mortality following a 48 h exposure of neonate to TPs or leachate, ranging from 0 to 3.3 × 10⁹ particles/ml and 0-100% respectively (n = 3). Though, particle-enhancement of toxicity was observed for both Zebrafish and D. magna, overall sensitivity to TPs differed. It is important to identify differential toxicities across species to achieve an understanding of the environmental impacts of TPs and the chemicals they leach.

Potential differences in species susceptibility to nanoparticle (NP) contaminants make the use of multispecies community toxicity testing strategies beneficial in understanding NP risk to aquatic environments. Because of the limited knowledge of zinc oxide (ZnO) NP fate and toxicity, we conducted multispecies exposures and compared the responses of individual species to the same species in a community comprised of algae (Chlamydomonas reinhardtii), bacteria (Escherichia coli), crustaceans (Daphnia magna), and zebrafish (Danio rerio). Different‐sized ZnO particles and ionic Zn were compared to investigate the contribution of particulate and dissolved Zn to aquatic organism toxicity. Each organism and community was exposed to Zn sources at 0.08, 0.8, and 8 mg Zn/L. The present results indicate that all 3 types of Zn elicited differential toxicity among test organisms, with stronger adverse outcomes observed in single species than within a community. The community assay (nanocosm) we developed increased resilience to all Zn exposures by 5 to 10% compared to individual exposures at equivalent concentrations. In addition, the uptake and toxicity of ZnO particles to aquatic communities appear to be driven by rapid dissolution and the concomitant impacts of zinc ion toxicity, and the size of the ZnO particles had little impact on uptake or toxicity. The nanocosm assay could be a useful screening tool for rapidly assessing the potential impacts of nanomaterials to aquatic species. Environ Toxicol Chem 2019;38:591–602. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Silver nanoparticles (AgNPs) are widely used in commerce, however, the effect of their physicochemical properties on toxicity remains debatable because of the confounding presence of Ag⁺ ions. Thus, we designed a series of AgNPs that are stable to surface oxidation and Ag⁺ ion release. AgNPs were coated with a hybrid lipid membrane comprised of L-phosphatidylcholine (PC), sodium oleate (SOA), and a stoichiometric amount of hexanethiol (HT) to produce oxidant-resistant AgNPs, Ag–SOA–PC–HT. The stability of 7-month aged, 20–100 nm Ag–SOA–PC–HT NPs were assessed using UV–Vis, dynamic light scattering (DLS), and inductively coupled plasma mass spectrometry (ICP-MS), while the toxicity of the nanomaterials was assessed using a well-established, 5-day embryonic zebrafish assay at concentrations ranging from 0–12 mg/L. There was no change in the size of the AgNPs from freshly made samples or 7-month aged samples and minimal Ag⁺ ion release (<0.2%) in fishwater (FW) up to seven days. Toxicity studies revealed AgNP size- and concentration-dependent effects. Increased mortality and sublethal morphological abnormalities were observed at higher concentrations with smaller nanoparticle sizes. This study, for the first time, determined the effect of AgNP size on toxicity in the absence of Ag⁺ ions as a confounding variable.

The challenge of evaluating the completeness and quality of (curated) nanomaterial data is addressed.