Fragments of plastic smaller than 1 μm have raised concerns about the potential risks they pose to the environment. Research will have to answer a number of questions to establish what the realistic ...risks are.
Tire wear particles (TWP), generated from tire material during use on roads have gained increasing attention as part of organic particulate contaminants, such as microplastic, in aquatic ...environments. The available information on properties and generation of TWP, analytical techniques to determine TWP, emissions, occurrence and behavior and ecotoxicological effects of TWP are reviewed with a focus on surface water as a potential receptor. TWP emissions are traffic related and contribute 5–30% to non-exhaust emissions from traffic. The mass of TWP generated is estimated at 1,327,000 t/a for the European Union, 1,120,000 t/a for the United States and 133,000 t/a for Germany. For Germany, this is equivalent to four times the amount of pesticides used. The mass of TWP ultimately entering the aquatic environment strongly depends on the extent of collection and treatment of road runoff, which is highly variable. For the German highways it is estimated that up to 11,000 t/a of TWP reach surface waters. Data on TWP concentrations in the environment, including surface waters are fragmentary, which is also due to the lack of suitable analytical methods for their determination. Information on TWP properties such as density and size distribution are missing; this hampers assessing the fate of TWP in the aquatic environment. Effects in the aquatic environment may stem from TWP itself or from compounds released from TWP. It is concluded that reliable knowledge on transport mechanism to surface waters, concentrations in surface waters and sediments, effects of aging, environmental half-lives of TWP as well as effects on aquatic organisms are missing. These aspects need to be addressed to allow for the assessment of risk of TWP in an aquatic environment.
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•Knowledge on TWP emissions, fate, and effects in the aquatic environment is reviewed.•Knowledge gaps regarding environmental relevance of TWP are identified.•TWP emissions entering the aquatic environment are below 20% of the total TWP emissions.•There is hardly any information about TWP effects at environmentally relevant concentrations.
The environmental fate of tire and road wear particles (TRWPs) receives increasing attention due to the per capita emission volumes of 0.2–5.5 kg/(cap year) and recent reports on the environmental ...hazard of TRWP constituents. It is expected that aging impacts TRWPs fate in the environment but detailed knowledge is quite limited, yet. Making use of information on tire aging, the available knowledge on environmental aging processes such as thermooxidation, photooxidation, ozonolysis, shear stress, biodegradation and leaching is reviewed here. Experimental techniques to simulate aging are addressed as are analytical techniques to determine aging induced changes of TRWPs, covering physical and chemical properties. The suitability of various tire wear test materials is discussed. Findings and methods from tire aging can be partially applied to study aging of TRWPs in the environment. There is a complex interplay between aging processes in the environment that needs to be considered in future aging studies. In addition to existing basic qualitative understanding of the aging processes, quantitative understanding of TRWP aging is largely lacking. Aging in the environment needs to consider the TRWPs as well as chemicals released. Next steps for filling the gaps in knowledge on aging of TRWPs in the environment are elaborated.
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•Knowledge on tire aging is partially applicable to tire and road wear particles (TRWPs).•Suitability of various TRWP test materials for aging studies is evaluated.•Aging processes have a joint impact on TRWP properties and composition.•Quantitative understanding of TRWP aging is lacking.•Future research needs on TRWP aging are identified.
A variant of suspect screening by liquid chromatography–high-resolution mass spectrometry (LC-HRMS) is proposed in this study: Samples of a potential source of contamination and of an environmental ...sample close to this source are first analyzed in a non-targeted manner to select source-related suspects and to identify them. The suspect list compiled from such an exercise is then applied to LC-HRMS data of environmental samples to ascribe and to identify persistent and mobile contaminants in the water cycle that may originate from the source under study. This approach was applied to tire crumb rubber (source) and road dust (close to source); by comparison of the two data sets, 88% of the features detected in tire leachate could be excluded. Of the 48 suspects remaining, a total of 41 could be tentatively identified as either related to hexamethoxymethyl melamine or cyclic amines, benzothiazoles, or glycols. Subsequently, environmental samples were searched for these suspects: 85% were determined in an urban creek after a combined sewer overflow and 67% in the influent of a municipal wastewater treatment plant (WWTP). These exceptionally high rates of positive findings prove that this source-related smart suspect screening effectively directs the effort of selecting and identifying unknown contaminants to those related to the source of interest. The WWTP effluent and the urban creek during dry weather also showed the presence of numerous contaminants that may stem from tire and road wear particles (TRWP) in road runoff. Contribution from other sources, however, cannot be ruled out.
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Tire and road wear particles (TRWPs) are one of the main sources of particulate traffic emissions, but measured data on TRWP contents in the environment are scarce. This study aims at identifying ...organic compounds suitable as quantitative markers for TRWPs by a tiered multistep selection process involving nontarget screening and subsequent identification by liquid-chromatography high-resolution mass spectrometry. Starting from several thousands of signals recorded in the extract of tire particles, the rigorous selection process considered source specificity, tendency of leaching, analytical sensitivity and precision, and stability during aging. It led to three transformation products of N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6-PPD) as the most suitable marker candidates: N-formyl-6-PPD, hydroxylated N-1,3-dimethylbutyl-N-phenyl quinone diimine, and 6-PPD-quinone. A linear response in standard addition experiments with tire particles and the correlation with TRWP contents in a diverse set of environmental samples imply that these compounds are promising candidates as markers for the quantification of TRWPs. Organic markers for TRWP contents in the environment would allow TRWP quantification with the traditional tandem MS (LC–MS/MS) equipment of an organic trace analytical laboratory and, thus, allow easy generation of data on TRWP occurrence in sediments and soils and other environmental matrices.
In this study, a method for the determination of tire and road wear particle (TRWP) contents in particulate samples from road environment was developed. Zn was identified as the most suitable ...elemental marker for TRWP, due to its high concentration in tire tread and the possibility of separation from other Zn sources. The mean concentration of 21 tire samples was 8.7 ± 2.0 mg Zn/g. Before quantification in samples from road environment, TRWP were separated from the particulate matrix by density separation. Method development was conducted using shredded tread particles (TP) as a surrogate for TRWP. Recovery of TP from spiked sediment was 95 ± 17% in a concentration range of 2 - 200 mg TP/g. TP determination was not affected by other Zn containing solids or spiked Zn-salts. By adjusting the density of the separation solution to 1.9 g/cm³, more than 90% of total TRWP were separated from the sample matrix. TRWP concentrations in particulate matter collected in two road runoff treatment systems ranged from 0.38 to 150 mg TRWP/g. Differences in quantified TRWP contents of the two systems indicate changes in particle dynamics due to ageing and aggregation processes. The developed method allows TRWP determination in road runoff and in environments that are influenced by road traffic. The validated separation procedure can also be applied for TRWP characterization in future studies.
•Density separation is able to enrich TRWP.•Density separation can be a powerful tool for TRWP characterization.•TRWP density was determined and may change upon ageing.•Zn is the best suited elemental marker for TRWP quantification.•Samples from road environment were analyzed for TRWP.
Abstract
Plastic items from urban, freshwater and marine environments as well as from household items and electric supplies were analyzed for their metals and metalloids arsenic, barium, bismuth, cadmium, ...cobalt, chromium, copper, manganese, nickel, iron, lead, antimony, tin and zinc. Total metal contents ranged from 3 μg/kg (5th percentile) up to 7 g/kg (95th percentile). The median content of most metals was below 1 mg/kg and did not exceed legal limits. Iron and zinc were the metals with the highest contents, with medians of approximately 50 mg/kg. Multivariate statistics (k-means clustering and principal component analysis) did not reveal a polymer specific metal composition except for samples of tire tread rubber that was obtained from passenger car tires. Investigation on the potential origin of the metals in plastics revealed that pigments were the most likely source. In comparison to natural and anthropogenic materials in rivers, oceans and air, the metal content of plastic items was within the same order of magnitude, except for antimony and zinc contents. Literature data on the adsorption capacities of plastics suggested that the inherent content of barium, iron, antimony and zinc was dominating the total content in the studied samples. Compared to suspended sediments in rivers, the metal flux into marine environment transported with plastic items was found to be negligible due to the three orders of magnitude lower masses. The different properties, however, may consequently lead to the transport of plastics and their constituents into pristine and remote environments which natural particulate matter may not reach.
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•Tire rubber had a specific metal fingerprint in contrast to other polymers.•Pigments are the likely origin of most metals in plastics.•Metal flux transported with plastics is small compared to river sediments.
A recently developed multimethod for the determination of 150 pesticide metabolites was exemplarily applied to 58 samples of groundwater and surface water. 37 of these metabolites were detected in at ...least two samples with a concentration ≥0.025 μg/L. The detected metabolites were ranked according to their concentration and frequency of detection. Findings are clearly dominated by metabolites of chloroacetanilide herbicides, but metabolites of sulfonylurea and thiocarbamate herbicides and other herbicides (dichlobenil) together with metabolites of some fungicides (tolylfluanid, chlorothalonil, trifloxystrobin) were also prominent. A number of 17 of the ranked metabolites are denoted as emerging metabolites because no reports on their previous detection in groundwater or surface water were found. Most of them, however, were correctly predicted to occur in the summary reports of the European pesticide approval process. Median total concentrations of the analysed pesticide metabolites summed up to 0.62 μg/L in groundwater and 0.33 μg/L in surface waters. While the concentration of the individual metabolites is usually low (<0.1 μg/L) the diversity of metabolites found in one sample can be large; between two and six metabolites were detected most frequently (maximum of 12 metabolites). Runoff from urban surfaces was investigated in this study and also here previously undetected pesticide (biocide) metabolites were detected. The emerging pesticide metabolites detected in environmental water samples in this study require more extended monitoring.
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•Ground and surface waters analysed for 150 pesticide metabolites.•17 of the 27 highly ranked metabolites reported for the first time.•Individual concentration usually below 0.1 μg/L but up to 12 metabolites per sample.
Tire and road wear particles (TRWPs) are a major component of non-exhaust traffic emissions, but knowledge about their physico-chemical properties is limited. Road dust of a highway tunnel was ...fractionated by size and density, and fractions were analyzed for TRWPs, metals, seven tire tread indicator chemicals (benzothiazoles, 6-PPD and DPG) and effects in in-vitro bioassays. TRWP content in tunnel dust was very high (11–12%). The peak of the TRWP mass distribution was in the size fraction 20–50 μm, with 31–36% of the total TRWP mass and a content of up to 260 mg/g. The mass of organic tire constituents peaked in the smallest analyzed size fractions (<20 μm) with 35–55% of their total mass. They also peaked in the density fraction 1.3–1.7 g/cm³, indicating a lower TRWP density and a higher contribution of TP to TRWP (approx. 75%) than expected. Video-based shape analysis and SEM showed elongated particles, likely TRWPs, to be present in those size and density fractions ascribed to TRWPs by chemical analysis. But also irregular heteroagglomerates could be found. Solvent extracts of size and density fractions induced effects in bioassays indicative of the activation of the arylhydrocarbon receptor (AhR-CALUX) and the adaptive response to oxidative stress (AREc32). Similar comprehensive characterization of road dust from other sites may be needed to decide on whether TRWPs occurring in high concentrations in tunnel dust are suited as representative test materials for analytical purposes and TRWP fate studies.
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•Tire and road wear particles (TRWPs) in tunnel dust: smaller and less dense than in road simulators.•Mass distributions of tire constituents had maxima in the size fraction <20 μm.•Density of TRWPs was mostly in the range of 1.3–1.7 g/cm³.•Elongated particles were identified in size and density fractions.•Solvent extracts of tunnel dust activated oxidative stress response in bioassays.
Persistent and mobile organic substances (PM substances) are a threat to the quality of our water resources. While screening studies revealed widespread occurrence of many PM substances, rapid trace ...analytical methods for their quantification in large sample sets are missing. We developed a quick and generic analytical method for highly mobile analytes in surface water, groundwater, and drinking water samples based on enrichment through azeotrope evaporation (4 mL water and 21 mL acetonitrile), supercritical fluid chromatography (SFC) coupled to high-resolution mass spectrometry (HRMS), and quantification using a compound-specific correction factor for apparent recovery. The method was validated using 17 PM substances. Sample preparation recoveries were between 60 and 110% for the vast majority of PM substances. Strong matrix effects (most commonly suppressive) were observed, necessitating a correction for apparent recoveries in quantification. Apparent recoveries were neither concentration dependent nor dependent on the water matrix (surface or drinking water). Method detection and quantification limits were in the single- to double-digit ng L
−1
ranges, precision expressed as relative standard deviation of quadruplicate quantifications was on average < 10%, and trueness experiments showed quantitative results within ± 30% of the theoretical value in 77% of quantifications. Application of the method to surface water, groundwater, raw water, and finished drinking water revealed the presence of acesulfame and trifluoromethanesulfonic acid up to 70 and 19 μg L
−1
, respectively. Melamine, diphenylguanidine,
p
-dimethylbenzenesulfonic acid, and 4-hydroxy-1-(2-hydroxyethyl)-2,2,6,6-tetramethylpiperidine were found in high ng L
−1
concentrations.
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