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Mapping, emissions and environmental and health assessment of chemical substances in artificial turf

Summary and conclusions

In recent years, it has become increasingly popular to use artificial turf as a substitute for natural turf.

Artificial turf is primarily used for football pitches, but it is also becoming increasingly popular for golf greens, school playgrounds and playgrounds in general.

There are a number of advantages in using artificial turf rather than natural turf: The pitches are more hard-wearing and easier to maintain than natural turf pitches, the football season can be extended whatever the weather, and the pitches can be laid in places where it is difficult to get grass to grow. Artificial turf pitches can be used indoors as well as outdoors.

The pitches that have become especially popular are the third-generation pitches. They are characterised by having turf with longer straws (approx. 50-70 mm versus approx. 30 mm previously) and by the pitch infill consisting of a layer of silica sand at the bottom of the loom and a rubber granule layer at the top. The top 20 mm are not filled. Previously, the infill on football pitches was gravel.

The pitches can be laid directly on a smoothed gravel layer, but many pitches are laid with a shock-absorbing pad between the gravel and the artificial turf.

The Danish Football Association, DBU (DBU, 2005) has described the requirements concerning the football functional properties. These requirements were determined by UEFA and FIFA.

Over the past three years, there have been discussions about the possible health and environmental problems associated with the use of artificial turf pitches. This debate arose on the background of Norwegian studies, in particular. A Swedish report published by the Swedish Chemicals Agency (Kemikalieinspektionen) in 2006 supported the concern that the use of artificial turf pitches could have an adverse effect on health and the environment. These concerns relate to both the health risk to the users of artificial turf pitches and to the leaching of chemical substances into the soil and water.

Especially the use of old car tyres in the form of granules has been debated in the Norwegian studies and the Swedish report. It has in several cases been the practice in Denmark, in connection with invitations for tender, to exclude the use of car tyres following from the Norwegian studies and the Swedish report. This has resulted in e.g. grey industrial rubber being used as an alternative.

Against this background, the Danish Environmental Protection Agency has initiated this study of artificial turf pitches, focusing on Danish conditions.

100-120 tonnes of rubber granules are used per pitch as elastic infill in the pitches, unless an elastic pad is used for the base, so the quantities are rather significant.

The study has shown that today (August 2007), 45 artificial turf football pitches have been laid in Denmark. All but one are outdoor pitches. Following 22 interviews with suppliers, municipalities and the Danish Football Association (DBU), there is reason to assume that many more pitches will be laid in the coming years. This is partly due to the excellent technical playing properties of the third-generation pitches, and partly due to the fact that the artificial turf pitches can actually be used for playing sports all 365 days a year.

In order to use the pitches all year, however, it is necessary to salt the pitches during the winter months in order to keep them free of frost and snow. This is one of the aspects that received focus in this study in relation to environmental impacts, as this issue has not previously been investigated in foreign studies, and there is an expectation that using salt impacts the leaching of chemical substances to soil and water, depending on the volume and type of salt (acid or alkaline).

In addition to the Norwegian studies and the Swedish report, a number of results have been published from the Netherlands, Switzerland and France.

The French study was very comprehensive, both as regards the analysis parameters measured and the number of tests. The tests were conducted over a period of one year and covered both the health and environmental aspects of using rubber granules as infill in the pitches.

The conclusion of the French study is that there is no reason for concern in connection with the use of granulated car tyres as infill, neither based on a health nor an environmental assessment. The assessment is based on the low measured values for the emission of substances in relation to the scenarios set up, on which the conclusion is based.

Leaching of chemicals from the artificial turf pitches was studied using a special recovery technique – a so-called lysimeter test. The same applies for a study recently concluded in Switzerland. In lysimeter tests, it is possible to closely approximate “real life” exposure under well-defined test parameters. The lysimeters are constructed in such a way that rainwater or artificial water can be recovered for analysis following passage through the materials and support layers which make up the artificial turf pitches (gravel, elastic pad, artificial turf mat, sand and elastic infill).

The Swiss study included monitoring the sum parameters DOC (dissolved organic carbon), the sum of dissolved organic nitrogen compounds as well as ammonium nitrogen, nitrate nitrogen and nitrite nitrogen. The study furthermore included monitoring the organic substances aniline, alkylated phenylene diamines, benzothiazole, cyclohexylamine, 16 PAHs and the element zinc, as these substances form part of infill based on rubber from car tyres.

After one year of monitoring in Switzerland, the amount of leached substances in almost all tests had dropped to a concentration lower than the detection limit of 0.2 µg/l.

During the study period, no increases of zinc in the drainage water were detected.

One of the conclusions of the Swiss study is that the substances existing on the surface of rubber granules are leached off by rainwater after a short period of time, and there are therefore no reasons for environmental concerns about the use of rubber granules as an infill material.

However, studies on the long-term effects (several years) are lacking.

The Dutch study indicates that there may be increased zinc leaching as a result of ageing of the rubber, which would make zinc more susceptible to leaching. According to one scenario, Dutch threshold values would be exceeded after 11 years (Building Materials Decree (2,100 mg/m²/year)) and after 20 years (Decree on Soil Quality (3,600 mg/m²/year)), respectively. The scenario assumes that the infill is entirely replaced after 10 years of use. If the rubber ages faster than assumed, the threshold values will be exceeded after only 3-4 years. The environmental impact of zinc was assessed at 0.08% of the total zinc impact in the Netherlands, but with an estimated impact of 0.5% if the number of artificial turf pitches is increased from the current 370 to 2,500.

The results from the foreign studies all conclude that on the basis of the measured concentrations of substances that are hazardous to health, there are no health risks in connection with inhalation, neither indoors nor outdoors.

Against this background, and against the background of self-obtained results in connection with preliminary studies under this project in the form of GC/MS headspace analyses conducted on a wide range of infill and artificial turf mat samples, it was decided not to focus on health scenarios in connection with inhalation. In addition, it should be noted that the Danish third-generation pitches are all outdoors, contrary to Norwegian pitches, in particular.

The intention of this study was to supply new information about the health and environmental aspects of the increasing use of artificial turf pitches.

However, as all existing studies show that there are no problems in relation to PAH emissions, this project has not monitored for PAH.

Unlike the foreign studies, however, a larger number of different infill materials and artificial turf mats have been included in this project in order to obtain a better basis of comparison between the different types. The infill materials include granulated tyres, coated tyre granules, thermoplastic elastomers (TPE) with different tinting and, as a new product, coir fibres. All in all, 16 types of infill materials were obtained, eight types of artificial turf mats and two elastic pads. Here, it is important to remember that the term granulated car tyres covers an inhomogeneous mixture, as the infill material could originate from many different types of car tyres.

Furthermore, laboratory studies have been carried out which provide information about leaching of substances from the infill materials, the turf mats and a recycled rubber-based pad as a result of the pitches being salted in winter, as this aspect had not previously been studied. The studies have included road salt in the form of sodium chloride, which is the cheapest de-icing salt, or calcium chloride, which is used in the event of heavy frost. As regards the salt concentration, the leaching tests were based on the recommendations of the Danish Football Association (DBU).

The monitoring included a wide range of organic substances which derive from either the infill or from the artificial turf mats themselves. In particular, there was emphasis on measuring for organic substances which are found in the different tyres as well as their degradation products. Also, particular focus was given to zinc, phthalates and nonylphenols as a consequence of the results from the foreign studies.

Results

A wide range of environmentally harmful substances were found in the contact water (migration medium) from leaching tests on infill, artificial turf and pad, and also a number of substances that are harmful to human health.

For coir infill and “green industrial rubber” infill, substances which have a negative impact on health or the environment were not found in the solvent extract from the materials. However, leaching tests have not been conducted on these to types of infill. It should be emphasised that in one sample of EPDM rubber infill, a content of organic substances was detected (degradation products from peroxide, used in connection with the vulcanisation of the rubber). Therefore, it cannot be excluded that the substances might cause environmental problems, as leaching tests with EPDM rubber infill showed discharge of the substances into the water

Based on the dichloromethane extracts of grey and green industrial rubber, it can be concluded that these were significantly differing types of rubber, even though both infills are labelled industrial rubber by the supplier.

Environmentally harmful substances found in concentrations well above the detection threshold in the contact water are shown in Table 0.1.

Table 0.1 Environmentally harmful substances found in significant concentrations in the contact water in relation to possible health and environmental impacts.

The zinc leaching measured in this study was of the same magnitude as that found in foreign studies. The leaching of phthalates and nonylphenols, however, was higher in this study.

On the basis of the foreign studies, it was assessed that the leaching conditions from a football pitch differ significantly from the conditions in the leaching tests conducted in the laboratory in this study. Therefore, it cannot be concluded on the basis of the laboratory leaching tests alone whether the substances are an environmental risk under practical conditions. This is due to the fact that during laboratory tests, a better contact is created between the fixed material and the contact liquid than is the case in real life on artificial turf pitches as the result of the weather (e.g. rain). An example is that the sample is placed in the simulated rainwater and shaken for 24 hours before the water is analysed. This should be viewed as an absolutely worst case scenario and would therefore overestimate the actual leaching.

The results from leaching in calcium chloride-based contact liquid (simulated salting) showed a significant drop in the amount of leached phthalates as well as significant changes in the concentration of other substances (both higher and lower values). This is due to the fact that commercially available calcium chloride is highly alkaline due to the calcium hydroxide content. An alkaline environment causes hydrolysis reactions which affect a wide range of organic substances, including phthalates. No significant changes in the zinc leaching were detected as a function of the pH and/or ion strength of the contact liquid, regardless of salt type.

Furthermore, leaching tests have shown the same level of zinc in contact water in new infill as in the same infill after approx. two years of use.

Health assessment

Four representative substances were selected for the health assessment:

benzothiazole, dicyclohexylamine, cyclohexanamine and dibutyl phthalate. These substances are present in high concentrations in contact water from the leaching tests and are representative of the harmful substances emitted from the products.

On the basis of the results from foreign exposure studies and own analyses, it was decided to focus exclusively on exposure via skin contact and oral uptake from particles swallowed.

Microscopy of the dust particles from leaching tests has shown a particle size for the finest particles in the order of 10-50 µm, whereas the majority of the particles are approx. 2 mm. With a high content of fine particles, the leaching of health and environmentally harmful substances may increase due to the larger contact area, and the risk of inhalable flying dust is also increased. However, as mentioned, the amount of fine dust in the products is limited. In the assessments of the results, no health risks were found in connection with exposure to the substances, with the exception of a possible allergenic risk for sensitive individuals to benzothiazole and the amines.

Environmental assessment

The substance concentrations in the contact water from the leaching tests were assessed in relation to possible spillover of drainage water to nearby watercourses. It was assessed that there is an environmental risk from a number of the substances found if the drainage water reaches concentrations on a level with those found in the contact water.

It should be emphasised that – as mentioned above – the actual concentrations of chemical substances in the drainage water from third-generation pitches are probably significantly lower than those measured in the laboratory as a consequence of a less efficient natural leaching, because it was assessed that the contact with water is not as efficient as in the laboratory tests.

For some substances, however, the calculations include very large calculated water concentrations in relation to the estimated no-effect concentration (in excess of 100 times), and thus it cannot be ruled out that there may be an environmental risk with the leaching of these substances.

Furthermore, substances were detected, such as peroxide cross-linking chemicals or degradation products thereof, from EPDM infill. These substances were present in very high concentrations in contact water, but there is no data available on environmental risks. The zinc leaching from EPDM infill, however, is significantly lower than from car tyre infill (SBR rubber).

The results from the laboratory tests in this study show that a number of environmentally harmful substances can be leached from elastic infill as well as from artificial turf with a possible environmental risk in the event of drainage water spilling over into nearby watercourses. However, on the basis of the foreign lysimeter tests and pilot studies showing significantly lower leaching than in laboratory tests, it was assessed that measurements of the substance concentrations under real conditions on football pitches are necessary in order to assess the risk. Therefore, this study found no reason to question the conclusions of the elaborate Swiss, French and Dutch studies that rubber granules from car tyres pose no major environmental risk. Here, it should be noted that the Dutch results regarding zinc leaching are not found in this or the French and Swiss studies. On the other hand, it should also be emphasised that these are only short-term studies, and the effect of ageing of rubber granules etc. is therefore unknown.

However, a more recent Dutch study published in the spring of 2008 concludes that over a period of 10-15 years, zinc is not leached in concentrations that constitute any environmental problem. Continued monitoring for zinc in the Swiss study still shows no sign of increased zinc leaching as a result of rubber ageing (U. Hofstra, 2008, Edwin Müller, 2008).

When setting up a monitoring programme for the drainage water, it is possible, when selecting analysis parameters, to benefit from the results from this study and from the foreign studies mentioned in the report. For instance, measurements for PAHs can be excluded, and measurements for phthalates can be added.

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Version 1.0 October 2008, © Danish Environmental Protection Agency