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.

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.

Environmental context: Tyre rubber particles, from both driving and reuse of tyre rubber, are pollutants that carry toxic chemicals into the environment. We investigated the long-term effects that these particles have on small aquatic organisms and found that they drastically reduce their ability to reproduce. Continued exposure of aquatic invertebrates to tyre-related pollutants, has the potential to affect the population by inhibiting reproduction into future generations. Rationale: High levels of rubber microplastics in aquatic environments are often attributed to particles from driven tyres; however, the use of recycled or crumb rubber particles in outdoor surfaces is another source. Chronic toxicity assessments with tyres are limited, and there is a need to evaluate effects of rubber particles from different sources to better understand their role in conferring toxicity. Methodology: We investigated the effect of chronic exposure of Daphnia magna to micro-sized (1–20 µm, 3.13 × 104–1.25 × 105 particles mL–1) and nano-sized (<1 µm, 1.25 × 105–1.00 × 107 particles mL–1) synthetic rubber particles. These included tyre particles (TPs) and two types of rubber from recycled tyres (called recycled rubber, RR, and crumb rubber, CR). Mortality, reproduction and moulting were assessed daily, and growth was measured at the end of the exposure. Additionally, the F1 generation was reared to assess multigenerational effects. Results: Chronic exposure to micro-rubber particles had severe effects, delaying, decreasing and even eliminating reproduction starting at 6.25 × 105 particles mL–1. Chronic exposure to nano-rubber particles had less severe effects, but delayed and decreased reproduction at the highest exposure level, 5.00 × 107 particles mL–1. Exposure to nano-rubber in the parental generation affected reproduction in the F1 generation. Discussion: This is the first comparison of chronic and generational toxicity between different sizes and compositions of rubber particles. The reproductive affects of chronic exposure to rubber particles could have devastating impacts on populations of Daphnia. Research is needed to identify which components leached from rubber particles affect reproductive ability.