Rubber recycled from end-of-life tyres and its use as infill for artificial turf fields

Artificial turf fields are currently composed of carpets of strands of synthetic grass (PE or PP) kept upright by an “infill” of sand and elastic granules of various kinds, including rubber recycled from end-of-life tyres (ELTs). The rubber’s presence ensures more comfortable playing and a higher durability of the artificial turf. The use of rubber recycled from ELTs also contributes to a decrease in environmental impacts, reducing the consumption of virgin materials derived from non-renewable resources and improving the ecological footprint[1].  This virtuous system is a step toward the circular economy that the European Union is promoting as a solution for a sustainable economic development for the planet’s future.

Rubber recycled from ELTs has the same chemical composition as that of new tyres, as it derives from the simple grinding of the latter, without the addition of any additives or substances of any kind.  In Italy, ELTs are shredded in the industrial chain coordinated by Ecopneus in approximately twenty plants located throughout the country; they work under contract with Ecopneus following specifications that impose a series of constraints regarding the quality of the processing phases (entrance of the material, storage, grinding, and bagging).  Ecopneus has also launched a quality certification process with the help of the company Certiquality.

Study on the safety of ELT rubber for artificial turf infill

The use of infill derived from ELT recycling has been repeatedly challenged in the past due to suspicions that some substances considered toxic and contained in components of vulcanized rubber (such as PAHs, polycyclic aromatic hydrocarbons) could migrate from the rubber granules to players through contact with the skin or inhalation.  Ecopneus launched a set of investigations and scientific analyses in 2014 in order to investigate possible health risks deriving from the use of rubber recycled from ELTs in applications where there could be contact with the user.  The study lasted two years and was developed in three phases: sampling of the tyres and analysis of the PAH content, laboratory tests relative to the potential release of PAHs from black granules to biological fluids, and tests on fields infilled with coated rubber (in Italy, rubber is commonly coated with polyurethane resins and green or brown pigments to improve the infill’s aesthetic value) to verify the effective exposure of players in sports facilities with the artificial turf typically installed in Italy.

The presence of PAH in ELTs: sampling of the tyres and analysis of the content

The sampling plan, supervised by Bureau Veritas, allowed the chemical and toxicological characterization of the rubber recycled from different types of ELTs.  Almost 4000 ELTs were classified at five recycling facilities on the basis of their age and country of origin.  Seventy samples of granules and powder of known origin were delivered to four Italian and foreign[2] laboratories to perform a complete characterization of the rubber.  It was then possible to compare the composition of the rubber recycled from tyres produced in Europe or outside Europe before and after 2010, when the use of aromatic oils (a significant source of PAH contamination) in the production of new tyres was banned[3].  The Mario Negri Pharmacological Research Institute – Research Hospital measured the PAH content in ELT rubber, evaluated its bioavailability, and quantified the risks associated with dermal and inhalation exposure in the most common usage scenarios.

The PAH content in the rubber was found to be very limited in all the samples analysed: the sum of the eight PAHs under restriction entry 28 of the REACH regulation was between 5 and 20 ppm (or mg/kg), i.e. values from 100 to 10,000 times lower than the limit set for mixtures destined for sale to the general public.

The risk of migration of PAHs from ELT rubber granules: laboratory tests

The migration tests in sweat and pulmonary surfactants (simulants of the substances present in the pulmonary alveoli) carried out by the Mario Negri Institute – Research Hospital on black rubber highlighted the low bioavailability of these substances, which remain trapped within the vulcanized rubber and are therefore not absorbed by the human body through either dermal contact or inhalation.  In the migration tests of PAHs in artificial sweat, the maximum release values measured were equivalent to migration factors much less than 0.01% of the content of each substance.  These values make the migration of the rubber’s PAH content through simple dermal contact highly unlikely.  Furthermore, the migration factors measured in different pulmonary surfactant simulants allow PAH bioavailability to be defined as “limited” even under the most extreme conditions.

The exposure and risk assessment performed on artificial turf fields infilled with coated ELT rubber granules

At the same time, the experts at Waste and Chemicals conducted a series of 15 monitoring activities at fields made of natural grass as well as artificial turf fields infilled with coated rubber from ELTs or with organic infills to evaluate the exposure of workers to PAHs during the installation of the rubber infill and of athletes during training matches on the various field types.

In addition to measuring the quality of the air inhaled during the monitoring and the dermal deposition of any rubber powder, the urine of workers and athletes was also analysed.  The latter tests were undertaken to assess any variation in hydroxypyrene concentration following exposure to the rubber that indicated the absorption of PAH: also in this case the analyses excluded exposure to PAHs linked to ELT rubber.  The monitoring performed confirmed what was observed by international studies, i.e. an incremental carcinogenic risk significantly less (by an order of magnitude) than that recommended for the general population of 1×10-6This means that a person exposed on a daily basis to the rubber on the playing fields (e.g. a professional player that trains daily for 3-5 hours) for a substantial period of their lives (e.g. for 20-40 years) has less than a one in a million chance of contracting a disease, even a serious one, due to exposure to the PAHs contained in the infill.  Both during the installation of the infill (workers) and during sports practice (players), the risk of dermal exposure is less than the inhalation risk; it should also be underlined that during all of the monitoring activities performed, the PAH concentration measured in the air was dependent on the local level of air pollution.

Conclusions of the study

All of the analyses performed – both in the laboratory, on black granules, and in the field under real conditions, on coated granules – revealed a reassuring picture that confirms the absence of significant risks for the health of workers and the athletes who play on synthetic fields with ELT recycled rubber infill.  In fact, the rubber recycled from tyres contains very limited quantities of PAHs, well under the maximum thresholds considered safe, and these quantities of PAHs have in any case an insignificant, almost undetectable, degree of bioavailability.  The results are also consistent with the numerous scientific publications of the last decade.

The recent controversy in the Netherlands: the position of Ecopneus

With regard to recent reports in the Dutch press, which have also been reprinted by some Italian newspapers, referring to artificial turf fields with rubber infill, which are suspected of having excessively high contents of toxic substances other than PAHs, we note how, in the absence of traceability regarding the origin of the infill rubber used in these fields, it cannot be assumed that this rubber derives from the recycling of ELTs, nor that there has not been a commingling with other substances, additives or materials, or that environmental contaminants of various kinds may not be present.

The current Italian chain of end-of-life tyre recycling coordinated by Ecopneus is controlled, tracked and also subjected to checks by third parties, therefore allowing these risks to be avoided.  We believe that all countries should engage in the traceability and quality certification of the chain.  Ecopneus has been working on this for several years with significant investments and will continue to do so in the future, as always making the information in its possession available to anyone interested in the topic.

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[1] linked to their extraction, processing, and transport

[2] CERISIE, Tun Abdul Razak Research Center, Biochemical Institute for Environmental Carcinogens (Dr. Grimmer Foundation) and Mario Negri Institute Research Hospital

[3] Point no. 50 of Annex XVII of REACH bans the use, for the production of tyres, of plasticizing oils containing more than 1 mg/kg of BaP or more than 10 mg/kg total of 8 listed PAHs.  The sale of tyres or tread bands for reconstruction that contain the “aromatic” oils above was banned in January 2010.  The progressive elimination of tyres produced with aromatic oils will lead to a further reduction of the PAH content of rubber in the next years; nevertheless, the presence of trace amounts of these substances in carbon black precludes its complete disappearance.