Assessing the Biodegradability of Tire Tread Particles and Influencing Factors.

Abrasion of tire tread, caused by friction between vehicle tires and road surfaces, causes release of tire wear particles (TWPs) into various environmental compartments. These TWPs contribute to chemical, microplastic, and particulate matter pollution. Their fate remains largely unknown, especially regarding the extent and form in which they persist in the environment. The present study investigated (1) the biodegradability of tread particles (TPs) in the form of ground tire tread, (2) how accelerated ultraviolet (UV) weathering affects their biodegradability, and (3) which TP constituents are likely contributors to TP biodegradability based on their individual biodegradability. A series of closed-bottle tests, with aerobic aqueous medium inoculated with activated sludge, were carried out for pristine TPs, UV-weathered TPs, and selected TP constituents; natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), and treated distillate aromatic extracts (TDAE). Biodegradation was monitored by manometric respirometry, quantifying biological oxygen consumption over 28 days. Pristine TP biodegradability was found to be 4.5%; UV-weathered TPs showed higher biodegradability of 6.7% and 8.0% with similar and increased inoculum concentrations, respectively. The observed TP biodegradation was mainly attributed to biodegradation of NR and TDAE, with individual biodegradability of 35.4% and 8.0%, respectively; IR and BR showed negligible biodegradability. These findings indicate that biodegradability of individual constituents is decreased by a factor of 2 to 5 when compounded into TPs. Through scanning electron microscopy analysis, biodegradation was found to cause surface erosion. Processes of TP biodegradation are expected to change throughout their lifetime as new constituents are incorporated from the road and others degrade and/or leach out. Tire emissions likely persist as particles with an increased fraction of synthetic rubbers and carbon black. Environ Toxicol Chem 2024;43:31-41. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

When and How to Conduct Ecotoxicological Tests Using Natural Field-Collected Sediment.

In recent years, the sediment compartment has gained more attention when performing toxicity tests, with a growing emphasis on gaining more ecological relevance in testing. Though many standard guidelines recommend using artificially formulated sediment, most sediment studies are using natural sediment collected in the field. Although the use of natural field-collected sediment contributes to more environmentally realistic exposure scenarios and higher well-being for sediment-dwelling organisms, it lowers comparability and reproducibility among studies as a result of, for example, differences in the base sediment depending on sampling site, background contamination, particle size distribution, or organic matter content. The aim of this methodology contribution is to present and discuss best practices related to collecting, handling, describing, and applying natural field-collected sediment in ecotoxicological testing. We propose six recommendations: (1) natural sediment should be collected at a well-studied site, historically and by laboratory analysis; (2) larger quantities of sediment should be collected and stored prior to initiation of an experiment to ensure a uniform sediment base; (3) any sediment used in ecotoxicological testing should be characterized, at the very least, for its water content, organic matter content, pH, and particle size distribution; (4) select spiking method, equilibration time, and experimental setup based on the properties of the contaminant and the research question; (5) include control-, treated similarly to the spiked sediment, and solvent control sediment when appropriate; and (6) quantify experimental exposure concentrations in the overlying water, porewater (if applicable), and bulk sediment at least at the beginning and the end of each experiment. Environ Toxicol Chem 2023;00:1-10. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Implications of circular textile policies for the future regulation of hazardous substances in textiles in the European Union.

The textile industry's business model is currently unsustainable and systemic changes must be made. The transition to a circular textile economy can be a major lever for this. However, it faces multiple issues, including the (in)ability of current legislations to provide sufficient protection regarding hazardous chemicals in recirculating materials. It is therefore crucial to identify legislative gaps that prevent the implementation of a safe circular textile economy, and to identify which chemicals could jeopardize this process. With this study, we aim to identify hazardous substances that could be found in recirculated textiles, to identify and discuss gaps in current regulations covering chemicals in textiles, and to suggest solutions to ensure better safety of circular textiles. We compile and analyze data on 715 chemicals and their associated functions, textile production stage, and hazard data. We also present how chemicals have been regulated over time and discuss regulations' strengths and weaknesses in the perspective of circular economy. We finally discuss the recently proposed Ecodesign regulation, and which key point should be included in the future delegated acts. We found that most of the compiled chemicals present at least one recognized or suspected hazard. Among them, there were 228 CMR (carcinogenic, mutagenic, reprotoxic substances), 25 endocrine disruptors, 322 skin allergens or sensitizers, and 51 respiratory allergens or sensitizers. 30 chemicals completely or partially lack hazard data. 41 chemicals were found to present a risk for consumers, among which 15 recognized or suspected CMR and 36 recognized or suspected allergens/sensitizers. Following the analysis of regulations, we argue that an improved risk assessment of chemicals should consider chemicals specific hazardous properties and product's multiple life cycles, instead of being limited to the product's end-of-life stage. We especially argue that implementing a safe circular textile economy requires that chemicals of concern are eliminated from the market.

Small Butt Harmful: Individual- and Population-Level Impacts of Cigarette Filter Particles on the Deposit-Feeding Polychaete Capitella teleta.

In the marine environment, discarded cigarette filters (CFs) deteriorate and leach filter-associated chemicals. The study aim was to assess the effects of smoked CFs (SCFs) and non-smoked CFs (NCFs) particles on individual life-history traits in the deposit-feeding polychaete Capitella teleta and extrapolate these to possible population-level effects. C. teleta was exposed to sediment-spiked particles of NCFs and SCFs at an environmentally realistic concentration (0.1 mg particles g-1 dw sed) and a 100-fold higher (10 mg particles g-1 dw sed) concentration. Experimental setup incorporated 11 individual endpoints and lasted approximately 6 months. There were significant effects on all endpoints, except from adult body volume and egestion rate, in worms exposed to 10 mg SCF particles g-1 dw sed. Although not statistically significant, there was ≥50% impact on time between reproductive events and number of eggs per female at 0.1 mg SCF particles g-1 dw sed. None of the endpoints was significantly affected by NCFs. Results suggest that SCFs are likely to affect individual life-history traits of C. teleta, whereas the population model suggests that these effects might not transform into population-level effects. The results further indicate that chemicals associated with CFs are the main driver causing the effects rather than the CF particles.

Effects of long-term fertilization with contemporary Danish human urine, composted household waste and sewage sludge on soil nematode abundance and community structure.

It is desirable to recycle the urban waste products human urine, composted household waste and sewage sludge as fertilizers to agricultural fields. This could minimize the use of NPK fertilizer, improve soil structure and store carbon. However, waste products may contain heavy metals, persistent organic pollutants (POP) and plastics, and there are concerns that long-term build-up of these substances will cause unwanted effects on soil health. Nematodes are ubiquitous and numerous in soil ecosystems. Abundance and community structure of soil nematodes can be used as indicators of soil health, as some species are vulnerable to pollution. There are well-developed methods for detecting environmental changes based on nematode community structure. At the long-term CRUCIAL field experiment, where alternative fertilizer products have been applied since 2003, we measured effects of long-term fertilization with human urine, composted household waste and sewage sludge on soil properties (pH, soil organic matter and nitrogen availability), abundance of soil microorganisms (bacteria, fungi, small protozoa and ciliates) and nematode trophic groups compared to plots with unfertilized, NPK and cattle manure treatment. Sampling and assessments were done three times during a growth season. Further, we assessed the composition of nematode communities using metabarcoding. Treatments with a high input of organic matter (cattle manure, composted household waste and sewage sludge) had high abundances of bacteria and thus bacterial grazers (small protozoa, ciliates, and bacterial feeding nematodes). We found a significant correlation between nematode community structure and pH and organic matter. We calculated the nematode Maturity Index 2-5 (pollution indicator) based on metabarcoding data, which did not differ significantly between the treatments. We conclude that long-term fertilization with different types of contemporary Danish urban waste products affects both soil properties and abundance of soil organisms, the latter largely reflecting the organic matter input of the fertilizer treatments. We found no adverse effect on nematode communities that could indicate pollution-induced stress on nematofauna or decreased soil fertility.

The need for environmental regulation of tires: Challenges and recommendations.

The interest in tire wear particles (TWPs), generated from abrasion of tires, have gained traction over the past few years, both in regards to quantifying particulate emissions, leaching of different compounds, toxicity, and analytical methods. The life of a tire, from cradle to end-of-life, crosses over different scenarios during its lifetime and transcends environmental compartments and legislative areas, underlining the need for a collective approach. Sustainability for a tire encompasses the use of raw materials, recycling of raw materials, circular economy and material sourcing. The tire industry is currently making significant efforts towards a greener and more sustainable production considering reduction of CO2-emissions, recycling, material sources and implementing the use of biomass from plants rather than oil-derived alternatives. In this paper, we aim to analyze and discuss the need for environmental regulation of tires in order to provide a series of targeted recommendations for future legislation. Our study shows that the numerous regulations related to tires focus on chemicals, manufacturing, raw materials, use of tires on roads, waste handling, safety and polycyclic aromatic hydrocarbons (PAHs) in different life cycle stages of a tire. However, none directly addresses the contribution of TWPs to the environment. Despite the overall good intentions of the existing regulations, there is a lack of focus on the compounds that partition from the tire and disperse in the environment, their mixture effects, and the transformative products from the parent compounds in the environment. Therefore, a renewed focus is needed on risk assessment of complex mixtures like TWPs. Thus, transparency in regard to use of chemicals in TWP, mixtures, minimization of emissions, and capture of particulate pollution should be a priority.

Long-term effects of sediment-associated silver nanoparticles and silver nitrate on the deposit-feeding polychaete Capitella teleta.

Aquatic sediments are predicted to be an important sink for released silver nanoparticles (AgNPs). Knowing the long-term effects of AgNPs on benthic deposit-feeders is therefore an important step towards assessing their potential environmental risks. The aim of this study was to examine the effects on survival, growth and reproduction of the deposit-feeding polychaete Capitella teleta exposed for ten weeks to sediment-associated un-coated AgNPs or silver nitrate (AgNO3). C. teleta exhibited tolerance towards exposure to both AgNPs and AgNO3. Significant effects were observed for percentage of pairs that reproduced as well as worm growth after eight weeks, but the effects did not show a clear concentration- or Ag type-dependent pattern. Further investigations of long-term effects of un-coated AgNPs in additional sediment-dwelling organisms are needed and should involve comparisons to coated AgNPs.

Comprehending the complexity of microplastic organismal exposures and effects, to improve testing frameworks.

Microplastics (MPs) have been identified as a threat to global ecosystems. Current projections indicate that the negative impacts of MPs will increase in the environment. Traditional toxicity testing does not account for the diversity of MP particles, the inherent diversity in potential exposure routes, and complex impacts in exposed organisms. Here we present and discuss factors influencing organismal exposure to MPs driven by fate and behavior of MPs in different environmental matrices and organisms behavioral niches. We then provide a structured classification of potential effects of MPs, chemical or particulate, generic or specific to MPs. Using these analyses, we discuss appropriateness and limitations of applying traditional, chemical-based ecotoxicity testing for the study of MPs, and propose practical recommendations and guidelines. Future laboratory based studies can be improved to increase understanding of potential real world effects of MPs by careful selection of appropriate exposure systems and conditions, test organism, MP characteristics, endpoints and required controls. We build upon recommendations provided in previous publications and complement them with a list of parameters and practical information that should be checked and/or reported in MP studies.

Tire wear particle and leachate exposures from a pristine and road-worn tire to Hyalella azteca: Comparison of chemical content and biological effects.

Tire emissions have emerged as an environmental contaminant of concern. To fully understand their effects to biota, research is needed from different stages of a tire's lifecycle. In this study we exposed freshwater Hyalella azteca to tire wear particles (TWPs) as particle suspensions or their respective chemical leachates (the chemicals released from tire particles into water) from a pristine (P-TWP) and worn (W-TWP) tire of same make and model. Acute and long-term toxicity experiments on H. azteca showed that P-TWP suspensions were more toxic than W-TWP suspensions with estimated LC50 values of 364 ± 64 particles (0.19 ± 0.03 g L-1) and 3073 ± 211 particles (0.91 ± 0.06 g L-1), respectively. However, leachates from W- and P-TWPs appeared equally toxic, but did not conform to a sigmoidal dose-response pattern and LC50 values could not be derived. In long-term tests (21 d) P-TWP suspensions showed no significant effects on H. azteca mortality (p = 0.970) or reproduction (p = 0.123), but growth was significantly reduced (p = 0.003) at the highest concentration tested (250 particles mL-1 or 0.127 g L-1). Chemical analysis of both particle types and their leachates showed that four compounds, benzothiazole, 1-indanone, aluminum and zinc, consistently leached from TWPs into water. Analysis of the two TWPs showed a difference in the concentration of the various compounds. Specifically, P-TWPs contained significantly more 1-octanethiol, phenanthrene, anthracene and aluminum than W-TWPs, suggesting that they are possible candidates for the increased toxicity observed following P-TWP exposure.

A nationwide assessment of plastic pollution in the Danish realm using citizen science.

Plastic pollution is considered one of today's major environmental problems. Current land-based monitoring programs typically rely on beach litter data and seldom include plastic pollution further inland. We initiated a citizen science project known as the Mass Experiment inviting schools throughout The Danish Realm (Denmark, Greenland and the Faeroe Islands) to collect litter samples of and document plastic pollution in 8 different nature types. In total approximately 57,000 students (6-19 years) collected 374,082 plastic items in 94 out of 98 Danish municipalities over three weeks during fall 2019. The Mass Experiment was the first scientific survey of plastic litter to cover an entire country. Here we show how citizen science, conducted by students, can be used to fill important knowledge gaps in plastic pollution research, increase public awareness, establish large scale clean-up activities and subsequently provide information to political decision-makers aiming for a more sustainable future.

Effects of sediment-associated Cu on Tubifex tubifex - Insights gained by standard ecotoxicological and novel, but simple, bioturbation endpoints.

Sediments serve as both source and sink of contaminants (e.g., Cu) and biologically important materials (e.g., metals, nutrients). Bioturbation by benthic organisms is ecologically relevant as bioturbation affects the physio-chemical characteristics of sediments, thus altering nutrient and contaminant distribution and bioavailability. We examined the effects of sediment-associated Cu on T. tubifex with conventional toxicity endpoints, such as mortality and growth, and less commonly used non-destructive endpoints, such as bioturbation and feeding. An experimental approach was developed to examine the applicability of simple methods to detect effects on bioturbation and feeding. Two experiments were conducted with 7-day exposures to uncontaminated or Cu-spiked natural sediment at six Cu concentrations to examine Cu bioaccumulation and effects. Endpoints included worm mortality, feeding rate and growth (experiment A) and worm bioturbation (particle diffusion and maximum penetration depth, experiment B). A microparticle tracer was placed on the sediment surface and vertical particle transport was followed over time. Adverse effects were detected for all endpoints (bioturbation, feeding rate, growth and survival): a slight positive effect at the lowest Cu concentrations followed by adverse effects at higher concentrations indicating hormesis. These simple, non-destructive endpoints, provided valuable information and demonstrated that sediment-associated contaminants, such as Cu, can influence bioturbation activity, which in turn may affect the distribution of sediment-bound or particulate pollutants, such as the plastic microparticles studied here. Thus, we suggest to use simple endpoints, such as bioturbation and feeding rate, in ecotoxicity testing since these endpoint account for the influence of interactions between pollutants and benthos and, thus, increase ecological relevance.

Ecotoxicology of micronized tire rubber: Past, present and future considerations.

Micronized tire rubber has recently come into focus as black particles that are found in microplastic (MP) samples worldwide. These particles have been found in all environmental compartments with the most likely source being the abrasion of car tires on road surfaces. Thus, it is well founded that tires are a source of MPs and that tire abrasion is a primary source of anthropogenic particulates. Currently, the impact of tires has been viewed through the lens of particulate pollution together with MPs, but this is a relatively new direction for this topic. Previously ecotoxicological research into the environmental consequences of tires has primarily been related to the leached chemicals from tire particulates. This paper aims to (i) highlight similarities and differences of micronized rubber particles with the existing suite of polymer contaminants termed as 'microplastics' or 'plastic debris', (ii) survey the existing literature on environmental presence, fate, and interaction of micronized rubber particles with biota, and lastly (iii) present future research needs that require consideration in order to move this research area forward. Existing knowledge gaps that require attention include; determining the environmental presence and fate of micronized rubber within different environmental compartments, understanding the interaction of rubber particles with biota, particularly as potential impacts have so far been attributed solely to the leachate, and evaluating whether standard ecotoxicological protocols need to be adapted for particulate contaminants in general and specifically to suit rubber particulates and leachate.

Acute and long-term toxicity of micronized car tire wear particles to Hyalella azteca.

Ecotoxicological studies relating to tire wear particles (TWP) have focussed, up until very recently, almost entirely on the released leachate. Little is known about the toxicology effects of TWP dispersed in freshwater. In the present small-scale study we exposed Hyallela azteca to TWP dispersed in water with the aim of (i) determining the potential acute and chronic impacts of TWP exposure (ii) challenging the prevailing idea that tire leachate is the primary causative agent of tire-related toxicity. H. azteca were shown to indescriminately ingest TWP with a gut retention time of 24-48 h. Acute (48 h) TWP exposure followed an expected concentration-response curve from which an LC50 of 3426 ± 172 particles mL-1 was determined, but leachate exposure did not conform to a sigmoidal concentration-response pattern and therefore an LC50 was not derivable. However, toxicity profiles of TWP and leachate appeared to be sufficiently different as to suggest a dissimilar mechanism of toxicity. Mortality, reproductive output (neonate production) and net growth were all significantly impacted at the higher exposure concentrations (500-2000 particles mL-1) following 21 days exposure. Our study demonstrates that TWP exposure elicits short-term and longer-term toxicity on a key freshwater organism.

Microplastic potentiates triclosan toxicity to the marine copepod Acartia tonsa (Dana).

Microplastics (MP) are contaminants of environmental concern partly due to plastics ability to sorb and transport hydrophobic organic contaminants (HOC). The importance of this "vector effect" is currently being debated in the scientific community. This debate largely ignores that the co-exposures of MP and HOC are mixtures of hazardous agents, which can be addressed from a mixture toxicity perspective. In this study, mixture effects of polyethylene microbeads (MP) and triclosan (TCS) (a commonly used antibacterial agent in cosmetics) were assessed on the marine copepod Acartia tonsa. Data indicated that MP potentiate the toxicity of TCS, illustrating the importance of understanding the mixture interaction between plastics and HOC when addressing the environmental importance of the vector effect.

Assessing and managing multiple risks in a changing world-The Roskilde recommendations.

Roskilde University (Denmark) hosted a November 2015 workshop, Environmental Risk-Assessing and Managing Multiple Risks in a Changing World. This Focus article presents the consensus recommendations of 30 attendees from 9 countries regarding implementation of a common currency (ecosystem services) for holistic environmental risk assessment and management; improvements to risk assessment and management in a complex, human-modified, and changing world; appropriate development of protection goals in a 2-stage process; dealing with societal issues; risk-management information needs; conducting risk assessment of risk management; and development of adaptive and flexible regulatory systems. The authors encourage both cross-disciplinary and interdisciplinary approaches to address their 10 recommendations: 1) adopt ecosystem services as a common currency for risk assessment and management; 2) consider cumulative stressors (chemical and nonchemical) and determine which dominate to best manage and restore ecosystem services; 3) fully integrate risk managers and communities of interest into the risk-assessment process; 4) fully integrate risk assessors and communities of interest into the risk-management process; 5) consider socioeconomics and increased transparency in both risk assessment and risk management; 6) recognize the ethical rights of humans and ecosystems to an adequate level of protection; 7) determine relevant reference conditions and the proper ecological context for assessments in human-modified systems; 8) assess risks and benefits to humans and the ecosystem and consider unintended consequences of management actions; 9) avoid excessive conservatism or possible underprotection resulting from sole reliance on binary, numerical benchmarks; and 10) develop adaptive risk-management and regulatory goals based on ranges of uncertainty. Environ Toxicol Chem 2017;36:7-16. © 2016 SETAC.

Deciphering mechanisms of malathion toxicity under pulse exposure of the freshwater cladoceran Daphnia magna.

The organophosphate pesticide (OP) malathion is highly toxic to freshwater invertebrates, including the cladoceran Daphnia magna, a widely used test organism in ecotoxicology. To assess whether toxic effects of malathion are driven primarily by exposure concentration or exposure duration, D. magna was pulse exposed to equivalent integrated doses (duration × concentration): 3 h × 16 µg/L, 24 h × 2 µg/L, and 48 h × 1 µg/L. After recovery periods of 3 h, 24 h, and 48 h, the toxicity of malathion on different biological levels in D. magna was examined by analyzing the following endpoints: survival and immobilization; enzyme activities of acetylcholinesterase (AChE), carboxylesterase (CbE), and glutathione S-transferase (GST); and AChE gene expression. The results showed no difference in survival among equivalent integrated doses. Adverse sublethal effects were driven by exposure concentration rather than pulse duration. Specifically, short pulse exposure to a high concentration of malathion resulted in more immobilized daphnids, lower AChE and CbE activities, and a higher transcript level of AChE gene compared with long pulse exposure to low concentration. The expression of the AChE gene was up-regulated, indicating a compensatory mechanism to cope with enzyme inhibition. The study shows the need for obtaining a better understanding of the processes underlying toxicity under realistic exposure scenarios, so this can be taken into account in environmental risk assessment of pesticides.

Chronic toxicity of silver nanoparticles to Daphnia magna under different feeding conditions.

Despite substantial information on the acute toxicity of silver nanoparticles (AgNP) to aquatic organisms, little is known about their potential chronic effects and the applicability of current test guidelines for testing nanomaterials. The purpose of this study was to study the influence of food availability on toxicity. This was done through a series of Daphnia magna 21-day reproduction tests (OECD 211) using 30 nm citric acid stabilized AgNP aimed at studying the influence of food abundance on the reproductive toxicity of AgNP in D. magna. The experiments were carried out as static renewal tests with exposure concentrations from 10 to 50 µg Ag/L, and test animals were fed green algae Pseudokirchneriella subcapitata in low and high food treatments. The endpoints recorded were survival, growth of parent animals and number of live neonates produced. Detrimental effects of AgNP on survival, growth and reproduction were observed in concentrations higher than 10 µg Ag/L, whereas the animals exposed to 10 µg Ag/L had larger body length and produced more offspring than controls at both food treatments. High food treatment resulted in higher animal survival, growth and reproduction compared to result found for low food treatment.

Microplastics: addressing ecological risk through lessons learned.

Plastic litter is an environmental problem of great concern. Despite the magnitude of the plastic pollution in our water bodies, only limited scientific understanding is available about the risk to the environment, particularly for microplastics. The apparent magnitude of the problem calls for quickly developing sound scientific guidance on the ecological risks of microplastics. The authors suggest that future research into microplastics risks should be guided by lessons learned from the more advanced and better understood areas of (eco) toxicology of engineered nanoparticles and mixture toxicity. Relevant examples of advances in these two fields are provided to help accelerate the scientific learning curve within the relatively unexplored area of microplastics risk assessment. Finally, the authors advocate an expansion of the "vector effect" hypothesis with regard to microplastics risk to help focus research of microplastics environmental risk at different levels of biological and environmental organization.