Presence of metals and metalloids in crumb rubber used as infill of worldwide synthetic turf pitches: Exposure and risk assessment

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.

Waste rubber - Black pollution reframed as a global issue: Ecological challenges and sustainability initiatives

In contrast to "white pollution" originating from waste plastics, waste rubber is often referred to as "black pollution." The quantity and variety of waste rubber are increasing at an alarming rate, with a considerable fraction entering the global ecosystem via various pathways. This study presents the first critical review of waste rubber research with a focus on the risks associated with toxicant discharge and existing problems in waste rubber disposal, management, and recycling practices. We aim to obtain a comprehensive understanding of current research, particularly regarding the ecological impacts of these wastes, highlight major gaps, and propose the most significant research directions. A total of 192 studies published in journals were critically analysed. The importance of conducting long-term and large-scale experiments and developing efficient waste rubber recycling systems is also emphasised. This study highlights the need to address the challenges posed by waste rubber pollution and offers insights and references for undertaking ecological risk assessments and understanding the mechanisms underlying toxicant behaviour. Suggestions and countermeasures are proposed with ecosystem sustainability as the ultimate goal. Further long-term, comprehensive, and systematic research in this area is required.

Hazardous elements in plastic and rubber granules as infill material from sports facilities? Field Portable-XRF spectroscopy as 'white analytical technique' reveals hazardous elements in fall sports facilities in Rzeszów (Podkarpackie, Poland)

Plastic and rubber granules are commonly used as infill material in all-weather sports facilities, providing an ideal activity surface for millions of Europeans on a daily basis. However, concerns have been raised about the presence of hazardous elements in these granules, which can pose risks both to the environment and human health. Our study focusses on the elemental composition of rubber granules used in fall sports facilities in Rzeszów, (Podkarpackie, Poland) using field portable X-ray fluorescence (FP-XRF) as a non-destructive and 'white analytical technique'. The results show the content of Zn, Fe, Cr, Ba, Br, Ti, Cu, Cd, As, Au, Bi, Pb, Ni, Sb, and Sn in the rubber granule samples. This study highlights the need for stringent quality control measures and regulations to ensure the safety of all-weather sports facilities and protect the well-being of sportsman. When modern FP-XRF spectrometry is employed as a "white analytical technique," for the first time it becomes possible to identify the presence of hazardous elements, addressing the pressing concerns highlighted by the ECHA and enabling proactive measures to mitigate potential risks. This approach ensures the protection of the health and sustainability of sports facilities, contributing to the ongoing hot topics in the field.

Are volatile methylsiloxanes in downcycled tire microplastics? Levels and human exposure estimation in synthetic turf football fields

Downcycled rubber, derived from end-of-life tires (ELTs), is frequently applied as crumb rubber (CR) as infill of synthetic turf in sports facilities. This practice has been questioned in recent years as numerous studies have reported the presence of potentially hazardous chemicals in this material. CR particles fall into the category of microplastics (MPs), making them possible vectors for emerging micropollutants. A preliminary study where volatile methylsiloxanes (VMSs) were found in CR originated the hypothesis that VMSs are present in this material worldwide. Consequently, the present work evaluates for the first time the levels and trends of seven VMSs in CR from synthetic turf football fields, while attempting to identify the main sources and impacts of these chemicals. A total of 135 CR samples and 12 other of alternative materials were analyzed, employing an ultrasound-assisted dispersive solid-phase extraction followed by gas chromatography-mass spectrometry (GC-MS), and the presence of VMSs was confirmed in all samples, in total concentrations ranging from 1.60 to 5089 ng.g-1. The levels were higher in commercial CR (before field application), a reflection of the use of VMS-containing additives in tire production and/or the degradation of silicone polymers employed in vehicles. The VMSs generally decreased over time on the turf, as expected given their volatile nature and the wearing of the material. Finally, the human exposure doses to VMSs in CR (by dermal absorption and ingestion) for people in contact with synthetic turf in football fields were negligible (maximum total exposure of 20.5 ng.kgBW-1.year-1) in comparison with the European Chemicals Agency (ECHA) reference doses: 1.35 × 109 ng.kgBW-1.year-1 for D4 and 1.83 × 109 ng.kgBW-1.year-1 for D5. Nevertheless, more knowledge on exposure through inhalation and the combined effects of all substances is necessary to provide further corroboration. This work proved the presence of VMSs in CR from ELTs, another family of chemical of concern to take into account when studying MPs as vectors of other contaminants.

Emerging Health Risks of Crumb Rubber: Inhalation of Environmentally Persistent Free Radicals via Saliva During Artificial Turf Activities

Crumb rubber (CR) is a commonly used infill material in artificial turf worldwide. However, the potential health risk associated with exposure to CR containing environmentally persistent free radicals (EPFRs) remains under investigation. Herein, we observed the widespread presence of CR particles in the range of 2.8-51.4 μg/m3 and EPFRs exceeding 6 × 1015 spins/g in the ambient air surrounding artificial turf fields. Notably, the abundance of these particles tended to increase with the number of operating years of the playing fields. Furthermore, by analyzing saliva samples from 200 participants, we established for the first time that EPFR-carrying CR could be found in saliva specimens, suggesting the potential for inhaling them through the oral cavity and their exposure to the human body. After 40 min of exercise on the turf, we detected a substantial presence of EPFRs, reaching as high as (1.15 ± 1.00) × 1016 spins of EPFR per 10 mL of saliva. Moreover, the presence of EPFRs considerably increased the oxidative potential of CR, leading to the inactivation of Ca2+, redox reactions, and changes in spatial binding of the α-1,4-chain of salivary amylase to Ca2+, all of which could influence human saliva health. Our study provides insights into a new pathway of human exposure to CR with EPFRs in artificial turf infill, indicating an increased human health risk of CR exposure.

A simple method for microwave-assisted preparation of tire samples

Heavy metals content in tires affects the safety of soil and agricultural products. The digestion method is a pretreatment for determining heavy metals in tire samples, and will affect the efficiency and accuracy of the heavy metal determination. The microwave digestion process and reagents for tire samples are not currently standardized. Therefore, this study attempts to provide an appropriate method of resolution for scholars. All digestion processes were performed in Mars One. We tested 15 different acid mixtures to determine the best reagent type and dose and then investigated the effect of maximum temperature, holding time, and sample grams on the degree of digestion. In summary, the best condition to digest the tire sample was a mixture of 3 ml HNO3 and 7 ml H2SO4, taking 0.1 (± 0.0005) g tire sample, at the maximum digestion temperature of 220 °C for 25 min. The experimental conclusion will provide a reliable experimental method for scientists using MARS One to study heavy metals in tires. At the same time, researchers using the MARS series can also find valuable references in this paper.

Temperature and nitrogen-induced modification of activated carbons for efficient catalytic ozonation of salicylic acid as a model emerging pollutant

The occurrence of emerging pollutants on effluents of wastewater treatment plants makes unfeasible their reutilization and consequently to comply with the sixth goal of 2030 Agenda for sustainable development. Thus, it is extremely important to find ways to remove these pollutants without compromising the quality of reclaimed water. Ozonation has been successfully explored for this purpose, but it still presents limitations towards some oxidant-resistant pollutants. To surpass this, the conversion of ozone (O3) into more reactive species is required, which can be accomplished by using catalysts. Carbon catalysts, such as activated carbons (ACs), represent a more environmentally attractive option than traditional metal-based catalysts, with the advantage of being easily modified to tune their textural and surface properties to the reaction chemistry. In this study, two different sources of ACs were tested in the catalytic ozonation of a frequently detected emerging pollutant: salicylic acid (SalAc). These ACs were submitted to thermal treatment under H2 and functionalization with N precursors, such as melamine and poly(ethyleneimine), to induce changes in the surface properties, especially in the nitrogen content. Although no correlation was found between the N-content and catalytic activity, the thermal treatment under H2 increased the mesopores surface area (Smeso), which reflected in greater catalytic activity. As that, the best-performing AC was the one with the highest Smeso, which revealed also to be resistant to O3 and able to convert O3 into more reactive species, evidenced by the capacity of oxalic acid, a well-known ozone-resistant by-product. The same AC was then submitted to three consecutive reutilization cycles and a more significant activity loss was observed in terms of SalAc degradation rate (⁓ 40%) then total organic carbon removal (⁓ 25%), from the first to the third cycle. This decline in efficiency was ascribed to the presence of by-products adhered to the catalyst surface, which impede its ability to react effectively with O3.

A new look at rubber recycling and recreational surfaces: The inorganic and OPE chemistry of vulcanised elastomers used in playgrounds and sports facilities

We revisit current understanding of the chemical complexity of different kinds of particulate vulcanised elastomers widely used in playgrounds and sports fields, adding new data on trace element and organophosphate ester contents of used tyre and EDPM crumb rubber. Enrichments in elements such as Zn, S, Co, Bi and Nd relate to the vulcanised mixtures created during manufacture. Zinc concentrations vary across an order of magnitude, being highest in our used tyre particulate samples (up to 2.4 %). In contrast, other trace element variations are due to coloured pigments causing increases in Cu and Zr (blue), Cr (green), and Fe and Sn (red and yellow) concentrations. The use of pale fillers such as CaCO₃ and clay minerals (rather than carbon black) strongly influences Ca and Al concentrations, which are much higher in the coloured EPDM than in black used tyre crumb rubber. Representatives from all three of the main organophosphate ester (OPE) groups, namely chlorinated (e.g. TCEP, TCIPP, TDCPP), alkyl (e.g. TEHP, TEP, TNBP, TBOEP) and aryl (e.g. TPHP, EHDPP, TCP) were identified, confirming how these chemicals are commonly used in modern rubber compounding as flame retardants and plasticisers. Elevated concentrations of TEHP (up to 117 μg/g) in coloured-coated used tyre turf infill crumb rubbers were traced to the coating rather than the crumb rubber itself. The presence and weathering behaviour of OPEs in recreational crumb rubber materials deserve closer investigation. The ecological "onehealth" impact of potentially toxic substances present in recreational crumb rubbers will depend on if and how they are released during play and sports activities, maintenance procedures, and natural weathering. We argue that detailed chemical data on these materials should be available to buyers, as manufacturers strive to reduce ecotoxin content as part of the quest towards sustainable use and recycling of vulcanised elastomers.