No 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/LC(50) 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/LC(50) 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/LC(50) values and the limited conditions under which toxicity was observed, TRWP should be considered a low risk to aquatic ecosystems under acute exposure scenarios.

Tire and road wear particles (TRWP) consist of a complex mixture of rubber, and pavement released from tires during use on road surfaces. Subsequent transport of the TRWP into freshwater sediments has raised some concern about the potential adverse effects on aquatic organisms. Previous studies have shown some potential for toxicity for tread particles, however, toxicity studies of TRWP collected from a road simulator system revealed no acute toxicity to green algae, daphnids, or fathead minnows at concentrations up to 10,000 mg/kg under conditions representative of receiving water bodies. In this study, the chronic toxicity of TRWP was evaluated in four aquatic species. Test animals were exposed to whole sediment spiked with TRWP at concentrations up to 10,000 mg/kg sediment or elutriates from spiked sediment. Exposure to TRWP spiked sediment caused mild growth inhibition in Chironomus dilutus but had no adverse effect on growth or reproduction in Hyalella azteca. Exposure to TRWP elutriates resulted in slightly diminished survival in larval Pimephales promelas but had no adverse effect on growth or reproduction in Ceriodaphnia dubia. No other endpoints in these species were affected. These results, together with previous studies demonstrating no acute toxicity of TRWP, indicate that under typical exposure conditions TRWP in sediments pose a low risk of toxicity to aquatic organisms.

Tire and road wear particles (TRWP) are produced during the interaction of a tire with the roadway surface when the vehicle is in motion. In order to assess the potential global environmental and human health impact of TRWP, air and sediment samples were collected in 3 watersheds: the Seine River watershed in France, the Yodo River watershed in Japan, and the Chesapeake Bay watershed in the U.S. TRWP was quantified in these samples using a pyrolysis GC-MS marker specific to tires. A wide diversity of areas were sampled including environmental protection areas, recreational areas, commercial districts, residential zones and more remote rural areas. In all cases, the presence of an identifiable source of vehicle traffic was mandatory. For sediment, the overall average tread concentration was 1000 ppm dry weight with a range of < 14 to 5800 ppm dry weight (n=149) and grain size classification as sand or silt/clay was a significant determinant of tread concentration. For air the overall average concentration was 0.080 g/m 3 with a range of < 0.002 g/m 3 to 0.67 g/m 3 (n=81) and a non-significant trend of increasing average tread particle concentration in air with increased population density and traffic load. This study represents the most comprehensive analysis of environmental levels of TRWP to date, with approximately 75 PM10 samples and 150 sediment samples collected on three continents. The results of this study will be used to understand the potential human and environmental risk of exposure to TRWP.

The manganese superoxide dismutase (MnSOD) ala16val polymorphism has been associated with various diseases including breast cancer. In the present study, we investigated levels of MnSOD protein, enzymatic activity and mRNA with respect to MnSOD genotype in several human breast carcinoma cell lines and in mouse embryonic fibroblasts (MEF), developed from the MnSOD knockout mouse, stably expressing human MnSOD-ala and MnSOD-val. In human breast cell lines, the MnSOD-ala allele was associated with increased levels of MnSOD protein and MnSOD protein per unit mRNA. In the MEF transformants, MnSOD activity correlated fairly well with MnSOD protein levels. MnSOD mRNA expression was significantly lower in MnSOD-ala versus MnSODval lines. MnSOD protein and activity levels were not related to MnSOD genotype in the transformed MEF, although, as observed in the human breast cell lines, the MEF human MnSOD-ala lines produced significantly more human MnSOD protein per unit mRNA than the human MnSOD-val lines. This suggests that there is more efficient production of MnSOD-ala protein compared to MnSOD-val protein. Examination of several indicators of reactive oxygen species levels, including superoxide and hydrogen peroxide, in wild type MEF and in MEF expressing similar elevated amounts of MnSOD-ala or val activity did not show differences related to the levels of MnSOD protein expression. In conclusion, in both human breast carcinoma cell lines and MEF cell lines stably transfected with human MnSOD, the MnSOD-ala allele was associated with increased production of MnSOD protein per unit mRNA indicating a possible imbalance in MnSOD protein production from the MnSOD-val mRNA.