Characterization of synthetic turf rubber granule infill in Japan: Rubber additives and related compounds

A comprehensive reconnaissance and risk assessment of rubber additives and their transformation products (RATPs) in groundwater: 1,3-Diphenylguanidine (DPG) as a pressing ecological concern

The widespread detection of rubber additives and their transformation products (RATPs) in surface water environments is well-documented, but their pollution characteristics in groundwater remain unclear. This study comprehensively revealed the occurrence and distribution of 27 RATPs in groundwater across southern China (n = 212). RATPs were detected in groundwater at total levels of 1.21-2,345 ng/L. The primary compounds detected were 1,3-Diphenylguanidine (DPG), 1,3-diphenylurea (DPU), and 2-hydroxybenzothiazole (2-OH-BTH), each with a detection frequency of 99.5 % and mean concentrations of 125, 58.4, and 51.2 ng/L, respectively. The spatial distribution of RATPs in groundwater shows significant lateral variations but lacks vertical differences. Correlation analysis indicates a strong relationship between the RATPs pollution levels and both the type of groundwater and the level of urban economic development, with karst water exhibiting particularly high pollution levels. Five RATPs exhibited medium to high ecological risks in groundwater. The daily intake of RATPs via groundwater in South China is 3.61 × 10-8-7.00 × 10-5 mg/(kg·d). According to the multicriteria evaluation approach and persistence, mobility, and toxicity (PMT) assessment, six RATPs, including DPG, have been identified as high-priority pollutants that require significant attention in groundwater management. This study highlights the contamination characteristics and ecological risks associated with RATPs in groundwater, emphasizing the need for increased focus on these widely used yet inadequately evaluated chemicals in future research.

Rubber-derived chemicals in urban sewer networks and receiving waters: Fingerprints, driving factors and ecological impacts

Rubber-derived chemicals (RDCs), which include rubber additives (RAs) and their transformation products (TPs), can be released into aquatic environments when rubber products, such as vehicle tires, are in use or discarded. However, RDCs and associated ecological risks have not been thoroughly investigated inside urban sewer networks and their receiving water bodies. To address these issues, we investigated the RDCs in Hong Kong's municipal sewer networks, including sewage and stormwater, as well as their receiving waters, such as rivers and coastal water. Among 45 target RDCs, the vulcanizing agents and corrosion inhibitors were found to be predominant in the water samples, accounting for 26-66 % and 29-72 % of total concentrations of 45 RDCs (∑45RDC), respectively, while antioxidants and their TPs presented in smaller quantities, accounting for 0.21-26 % and 0-15 % of ∑45RDC, respectively. Ten RAs from five classes were additionally identified by suspect screening. An estimated mass load of ∑45RDC amounting to 1690 kg/month is discharged into the coastal marine environment of Hong Kong, with sewage effluent being the primary source. Population density and vehicle-related factors (e.g., traffic load) were the major drivers shaping the spatial distribution of RDCs in surface water. Based on the ecological risk assessment outcomes, 16 out of 45 RDCs exhibited medium to high risks, and lists of candidate contaminants for various water bodies were proposed to support future risk management in water quality. These findings suggest that RDCs in stormwater and rivers should be carefully monitored, and management strategies should be developed to mitigate their risks.

A systematic review of the environmental and health effects of waste tires recycling

Objectives

With approximately 1.5 billion tires produced annually, the management and disposal of waste tires pose significant environmental challenges worldwide. While tire recycling has the potential to mitigate some environmental issues, existing studies reveal notable gaps and associated risks to human health and the environment, highlighting the need for a comprehensive review.

Methods

This study utilized primary search engines, including Scopus, Web of Science, and PubMed, in conjunction with relevant keywords, to identify pertinent studies published in peer-reviewed journals. Data and information regarding the application of waste tires in environmental and health-related contexts were systematically extracted.

Results

Out of 1275 potential articles, 80 studies met the criteria for inclusion in this review. The majority of these studies focused on the use of discarded tires in the construction sector, with 49 % specifically addressing their application in artificial turf fields.

Conclusions

A comprehensive assessment of the health and environmental implications of various recycling methods is essential to determine their feasibility. The increasing utilization of recycled tires across diverse sectors raises new concerns that warrant such investigations. Understanding the health effects associated with recycled tire products can provide valuable insights for both researchers and policymakers.

Exploring the Human Health Impact of Artificial Turf Worldwide: A Systematic Review

The growing use of artificial turf in place of natural turf in residential, recreational and commercial settings has raised concerns regarding its potential impact on human health. A systematic review of databases revealed 5673 articles of which, 30 were deemed eligible. Those performing total concentration analyses, bioaccessibility analyses or human health risk assessments (HHRAs) of artificial turf fibres or crumb rubber infill were of interest. Health hazards and risks were explored in relation to three groups of chemicals of concern: polycyclic aromatic hydrocarbons (PAH), heavy metals and other rubber additives. Twenty-five studies performed total concentration analyses on samples of artificial turf infill and/or turf fibres. Of these studies, median reported concentrations of eight PAHs, cadmium, mercury and zinc exceeded the European limits used. Eight studies performed bioaccessibility assays using synthetic biofluids and simulated organ systems. PAHs were not found to be bioaccessible except for benzo[a]pyrene in gastric fluid; heavy metals were bioaccessible except arsenic, and rubber additives were mostly bioaccessible except for three plasticisers: diisobutyl phthalate, benzyl butyl phthalate and dibutyl phthalate. Fourteen studies performed HHRAs to determine non-carcinogenic and carcinogenic risk. Cancer risks were identified for ingestion exposure to PAH in children with pica and heavy metal exposure via dermal, inhalation and ingestion pathways. Non-carcinogenic risks were identified for the ingestion of cobalt in a child spectator and the ingestion of arsenic, cobalt, thallium and zinc. Potentially hazardous concentrations of chemicals were found across both artificial turf infill and artificial turf fibre samples; bioaccessibility of these chemicals varied. Definitive conclusions were unable to be derived on the human health risks posed to users of artificial turf under real-world exposure scenarios. Future studies are recommended to explore the risks associated with the potential synergistic toxicities of chemical mixtures found in artificial turf.

Unveiling spatiotemporal distribution, partitioning, and transport mechanisms of tire additives and their transformation products in a highly urbanized estuarine region

Numerous tire additives are high-production volume chemicals that are used extensively worldwide. However, their presence and partitioning behavior remain largely unknown, particularly in marine environments. This study is the first to reveal the spatiotemporal distribution, multimedia partitioning, and transport processing of 22 tire additives and their transformation products (TATPs) in a highly urbanized estuary (n = 166). Nineteen, 18, and 20 TATPs were detectable in water, suspended particulate matter (SPM), and sediments, respectively, with total levels of 59.7-2021 ng/L, 164-6935 ng/g, and 4.66-58.4 ng/g, respectively. The multimedia partitioning mechanisms of TATPs are governed by their molecular weight, hydrophobicity, and biodegradation rate. Mass inventories coupled with model simulations have revealed that substantial quantities of TATPs accumulate within estuarine environments, and these compounds can be continuously transported into the ocean, particularly during the wet season. According to the multi-criteria evaluation approach, four and three TATPs were identified as high-priority pollutants during the dry and wet seasons, respectively. Unexpectedly, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone was only listed as a medium-priority pollutant. This study underscores the importance of marine surveillance and advocates for particular attention to these ubiquitous but underexplored TATPs in future studies.

Granulated rubber in playgrounds and sports fields: A potential source of atmospheric plastic-related contaminants and plastic additives after runoff events

The use of "crumb rubber" coming from recycling materials in outdoor floors like playgrounds has been a frequent practice during the last years. However, these surfaces are object of abrasion and weathering being a potential source of micro and nanoplastics (MNPLs) to the atmosphere and a potential source of human exposure to them. Our main goal has been to expose different crumb rubber materials to summer weathering effects. The released inhalable fractions were sampled for two months with passive samplers and the composition of MNPLs and plastic additives (organic and inorganic) were evaluated. The ecotoxicological effects of leached materials emulating runoff events was evaluated in freshwater micro crustacean Daphnia magna and the green algae Chlorella vulgaris. The analysis of MNPLs showed the presence of polyethylene, polypropylene, polybutadiene, polysiloxanes and polybutylene at concentrations up to 30,426 ng/m3. In the same fraction, we also identified up to 56 plastic additives, including antioxidants, pigments, copolymers, flame retardants, fungicides, lubricants, plasticizers, UV filters and metal ions. Finally, runoff ecotoxicological effects on D. magna and C. vulgaris showed that leached compounds, either from virgin or aged material, would be toxicants for exposed organisms although at concentrations much higher than those expected to be released to the media.

Nationwide occurrence and prioritization of tire additives and their transformation products in lake sediments of China

As a group of emerging contaminants of global concern, tire additives and their transformation products (TATPs) are causing a severe threat to aquatic ecosystems, particularly the highly lethal effects of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6PPD-Q) on certain fish species. Yet, the contamination status of TATPs in the lake ecosystems remains largely uncharacterized. This study conducted the first nationwide monitoring of the distribution characteristics of TATPs in 208 lake sediments collected from five lake regions across China. All the 13 TATPs were identified in lake sediments, with the total levels varying between 1.4 and 1355 ng/g, and 4-hydroxydiphenylamine (4-OH-PPD) as the most dominant. The total levels of TATPs decreased in the following order: Yunnan-Guizhou Plateau > Inner Mongolia-Xinjiang Region, Eastern Plain > Qinghai-Tibet Plateau, and Northeast Plain (p < 0.05). The geographical distribution of TATPs in lake sediments was significantly driven by total organic carbon content, temperature, and population density. N,N'-di-2-naphthyl-p-phenylenediamine, 6PPD-Q, N,N'-diphenyl-p-phenylenediamine, and 4-OH-PPD belonged to high-priority contaminants. Our study emphasizes that emerging pollutant TATPs place significant pressure on lake ecosystems and deserve urgent attention.

Typical Tire Additives in River Water: Leaching, Transformation, and Environmental Risk Assessment

Tire wear particles (TWPs) released during vehicle driving can enter water bodies, leading to leaching of tire additives (TAs) in aquatic environments. However, the transformation behavior and related ecological impacts of TAs and their transformation products (TPs) remain unclear. In this study, laboratory-based simulation experiments and field investigations were conducted to explore the transformation mechanisms and ecological risks of TAs. After being placed in river water for 24 h, about 7-95% of 12 investigated TAs in TWPs were leached. Forty-eight TPs from eight TAs were tentatively identified along with different transformation pathways via suspect screening by high-resolution mass spectrometry. Semiquantitative results indicated that TPs derived from N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylene-diamine (6PPD) were predominant in leachates, while aryl hydrolysis and quinone pathways were the main transformation pathways. Field investigations on urban surface water samples from 16 sites in Hong Kong revealed the occurrence of 17 TAs and 1 TP, with concentrations ranging from 13.9 to 2230 ng/L (median ± standard deviation: 226 ± 534 ng/L). Sixteen TPs from six TAs were additionally identified via suspect screening. It is estimated that 6PPD-quinone and seven TAs could pose medium to high ecological risk, while N-(1,3-dimethylbutyl)-N'-phenyl-p-quinonediimine, a frequently detected TP, was identified as a persistent-bioaccumulative-toxic substance.

Recycled tire rubber materials in the spotlight. Determination of hazardous and lethal substances

One way of recycling end-of-life tires is by shredding them to obtain crumb rubber, a microplastic material (<0.5 mm), used as infill in artificial turf sports fields or as playground flooring. There is emerging concern about the health and environmental consequences that this type of surfaces can cause. This research aims to develop an analytical methodology able to determine 11 compounds of environmental and health concern, including antiozonants such as N-1,3-dimethylbutyl-N'-phenyl-p-phenylenediamine (6PPD) or N, N´-diphenyl-1,4-phenylenediamine (DPPD), and vulcanization and crosslinking agents, such as N-cyclohexylbenzothiazole-2-sulfenamide (CBS), 1,3-di-o-tolylguanidine (DTG) or hexamethoxymethylmelamine (HMMM) from tire rubber. Ultrasound assisted extraction followed by liquid chromatography coupled to tandem mass spectrometry (UAE-LC-MS/MS) is validated demonstrating suitability. The methodology is applied to monitor the target compounds in forty real crumb rubber samples of different origin including, football pitches, outdoor and indoor playgrounds, urban pavements, commercial samples, and tires. Several alternative infill materials, such as sand, cork granulates, thermoplastic elastomers and coconut fibres, are also collected and analysed. All the target analytes are identified and quantified in the crumb rubber samples. The antiozonant 6PPD is present at the highest concentrations up to 0.2 % in new synthetic fields. The tire rubber-derived chemical 6PPD-quinone (2-((4-methylpentan-2-yl)amino)-5-(phenylamino)cyclohexa-2,5-diene-1,4-dione), recently linked to acute mortality in salmons, is found in all types of crumb rubber samples attaining concentrations up to 40 μg g-1 in football pitches. The crosslinking agent HMMM is detected in most of the playing surfaces, at concentrations up to 36 μg g-1. The tested infill alternatives are free of most of the target compounds. To the best of our knowledge, this study is the largest study considering the target compounds in tire rubber particles and the first to focus on these compounds in playgrounds including the analysis of HMMM, 6PPD-quinone and DTG in crumb rubber used as an infill material.

Assembly strategies for rubber-degrading microbial consortia based on omics tools

Numerous microorganisms, including bacteria and fungus, have been identified as capable of degrading rubber. Rubber biodegradation is still understudied due to its high stability and the lack of well-defined pathways and efficient enzymes involved in microorganism metabolism. However, rubber products manufacture and usage cause substantial environmental issues, and present physical-chemical methods involve dangerous chemical solvents, massive energy, and trash with health hazards. Eco-friendly solutions are required in this context, and biotechnological rubber treatment offers considerable promise. The structural and functional enzymes involved in poly (cis-1,4-isoprene) rubber and their cleavage mechanisms have been extensively studied. Similarly, novel bacterial strains capable of degrading polymers have been investigated. In contrast, relatively few studies have been conducted to establish natural rubber (NR) degrading bacterial consortia based on metagenomics, considering process optimization, cost effective approaches and larger scale experiments seeking practical and realistic applications. In light of the obstacles encountered during the constructing NR-degrading consortia, this study proposes the utilization of multi-omics tools to discern the underlying mechanisms and metabolites of rubber degradation, as well as associated enzymes and effective synthesized microbial consortia. In addition, the utilization of omics tool-based methods is suggested as a primary research direction for the development of synthesized microbial consortia in the future.