Search

Tire particles pose a potential threat to terrestrial organisms because they are deposited in large quantities in the soil by tire wear abrasion, and moreover their chemical complexity poses an additional risk. Microplastics can affect several physiological processes in organisms, including those related to immunity. Therefore, we investigated the expression profile of selected immune-related genes (MnSod, Manganese Superoxide dismutase; Cat, Catalase; CypG, Cyclophilin G; Nos, Nitric oxide synthase; Ppae2a, Prophenoloxidase-activating enzyme 2a; Dscam, Down syndrome cell adhesion molecule; Myd88, Myeloid-differentiation factor 88; Toll4, Toll-like receptor 4; Mas-like, Masquerade-like protein) in haemocytes and the digestive gland hepatopancreas of terrestrial crustacean Porcellio scaber after two different time exposures (4 and 14 days) to tire particles in soil. Our results reveal for the first time the response of P. scaber after microplastic exposure at the transcriptome level. We observed time- and tissue-dependent changes in the expression of the analysed genes, with more pronounced alterations in haemocytes after 14 days of exposure. Some minor changes were also observed in hepatopancreas after 4 days. Changes in the expression profile of the analysed genes are a direct indication of a modulated immune status of the test organism, which, however, does not represent an adverse effect on the test organism under the given conditions. Nevertheless, the question remains whether the observed change in immune status affects the immunocompetence of the test organism.

Tire particles (TPs) are a major source of microplastic on land, and considering their chemical composition, they represent a potential hazard for the terrestrial environment. We studied the effects of TPs at environmentally relevant concentrations along a wide concentration gradient (0–160 mg g−1) and tested the effects on plant growth, soil pH and the key ecosystem process of litter decomposition and soil respiration. The addition of TPs negatively affected shoot and root growth already at low concentrations. Tea litter decomposition slightly increased with lower additions of TPs but decreased later on. Soil pH increased until a TP concentration of 80 mg g−1 and leveled off afterwards. Soil respiration clearly increased with increasing concentration of added TPs. Plant growth was likely reduced with starting contamination and stopped when contamination reached a certain level in the soil. The presence of TPs altered a number of biogeochemical soil parameters that can have further effects on plant performance. Considering the quantities of yearly produced TPs, their persistence, and toxic potential, we assume that these particles will eventually have a significant impact on terrestrial ecosystems.

Detection and quantification of tread wear particles in the environment have been a challenge owing to lack of a robust method. This study investigated the applicability of a combination of Simultaneous Thermal Analysis (STA), Fourier Transform Infra-Red (FTIR), and Parallel Factor Analysis (PARAFAC) in the detection and quantification of tire particles from formulated sediments. FTIR spectral data were obtained by heating 20 samples in STA. Among the 20 samples, 12 were tire granules in formulated sediments (TGIS) containing 1%, 2%, 5%, and 10% by mass of tire granules, while the remaining eight contained 0.5, 1, 2.5, and 5 mg of tire granules only (TGO). The PARAFAC models decomposed the trilinear data into three components. Tire rubber materials in tire granules (RM) and a combination of water and carbon dioxide were the components identified in all samples. The linear regression analysis of score values from the PARAFAC models showed that the RM quantity predicted were comparable to measured values in both TGIS and TGO. Decomposing the overlying components in the spectral data into different components, and predicting unknown quantity in both sample types, the method proves robust in identifying and quantifying tire particles from sediments.

Large amounts of rubber particles are dispersed into the environment due to tire wear. The rubber contains a wide range of chemicals, including several of environmental concern. The purpose of this thesis, which is based on six papers [I–VI], was to assess the ecotoxicological hazard and risk associated with tire wear particles, with a main focus on the aquatic environment. A method was developed that enables rapid screening of the toxicity of tire particle leachates [I]. Acute and chronic toxicity of tire particle leachates to aquatic organisms was found to occur at concentrations ranging from 10 to >10 000 mg/l [I–IV]. The toxicity of wear material from different tires was found to vary with more than two orders of magnitude [I¬¬–II]. Toxicity identification studies (TIEs) identified organic compounds [II–IV] and Zn [IV] as the toxic components of tire particle leachates. Zn was also identified as the contaminant in the sediments of detention ponds, receiving road runoff, posing the highest threat to surrounding water bodies, and tire wear particles are a main source of this Zn contamination [V]. The Predicted No Effect Concentration (PNEC) was calculated, according to European chemical risk assessment guidelines, based on long term tests with the cladoceran Ceriodaphnia dubia and the microalgae Pseudokirchneriella subcapitata [IV]. The PNECs are 3.9 mg/l and 0.3 g/kg dw for water and sediments, respectively [VI]. A literature review of markers for tire wear in the environment showed tire particles to be present in surface waters, soils/sediments, air, and biota [VI]. Most of the tire particles are deposited on or close to the road surface and are then further transported by runoff water to receiving waters and sediments. The maximum Predicted Environmental Concentrations (PECs) of tire wear particles in surface water range from 0.03 to 56 mg/l, and the maximum PECs in sediments range from 0.3 to 155 g/kg dw [VI]. Thus, the upper range for PEC/PNEC ratios exceeds unity in both surface waters and sediments, meaning that tire wear particles constitute potential risks for aquatic organisms. The risk for the terrestrial environment is suggested to be restricted to the immediate road surroundings, and it is suggested that more research should be directed towards evaluating the health aspects associated with the inhalation of airborne tire particles [VI]. To conclude, the work presented in this thesis has shown that the contamination from tire wear particles needs to be reduced in order to protect receiving surface waters. This could be achieved by developing tires with more environmentally friendly constituents. Road runoff detention ponds are primary recipients of tire wear particles, and, therefore it is important that construction, environmental monitoring and management of such ponds receive increased attention.