Article pubs.acs.org/est
Comparison of Batch and Column Tests for the Elution of Artificial Turf System Components O. Krüger,* U. Kalbe, W. Berger, K. Nordhauβ, G. Christoph, and H.-P. Walzel BAM Federal Institute for Materials Research and Testing, Unter den Eichen 87, 12205 Berlin, Germany S Supporting Information *
ABSTRACT: Synthetic athletic tracks and turf areas for outdoor sporting grounds may release contaminants due to the chemical composition of some components. A primary example is that of zinc from reused scrap tires (main constituent, styrene butadiene rubber, SBR), which might be harmful to the environment. Thus, methods for the risk assessment of those materials are required. Laboratory leaching methods like batch and column tests are widely used to examine the soil−groundwater pathway. We tested several components for artificial sporting grounds with batch tests at a liquid to solid (LS) ratio of 2 L/kg and column tests with an LS up to 26.5 L/kg. We found a higher zinc release in the batch test eluates for all granules, ranging from 15% higher to 687% higher versus data from column tests for SBR granules. Accompanying parameters, especially the very high turbidity of one ethylene propylene diene monomer rubber (EPDM) or thermoplastic elastomer (TPE) eluates, reflect the stronger mechanical stress of batch testing. This indicates that batch test procedures might not be suitable for the risk assessment of synthetic sporting ground components. Column tests, on the other hand, represent field conditions more closely and allow for determination of time-dependent contaminants release. turf.5 They found no contaminants in groundwater underneath sport fields and only low concentrations of heavy metals in the rainwater runoff (0.06 mg/L zinc). Batch tests with rubber granules according to the synthetic precipitation leaching procedure (SPLP, LS 20 L/kg at pH 4.2) led to mean zinc concentrations in the eluate of 1.95 mg/L.5 Furthermore, they detected aniline, phenol, and benzothiazole. In column test eluates, conducted with water as leachant (LS 6 L/kg) and a flow rate of 2 mL/min, they found lower zinc concentrations with a mean value of 0.29 mg/L. The Swiss Federal Office for Sports (BASPO) studied the environmental compatibility of synthetic turfs by outdoor lysimeter experiments, but single components were not tested.6,7 They considered the results, including the zinc concentrations, to be not harmful but found indications of possible sorption of zinc at the unbound basic layer. The French Environment and Energy Management Agency (ADEME) conducted lysimeter experiments with rubber granules in synthetic turfs.8 They generally found low concentrations of contaminants; e.g., zinc was, with one exception of 0.5 mg/L, below typical rainwater concentrations. In Germany, the construction and quality control of synthetic sporting grounds is regulated by tentative standards for synthetic turf areas9 and synthetic surfaces, respectively.10
1. INTRODUCTION Synthetic turf fields and athletic tracks for sporting grounds are well-established and widely used in nearly all sports.1 Since newly manufactured plastics and recycled materials, like styrene butadiene rubber (SBR) from scrap tires, are used in their construction, there is a growing concern about possible environmental and health impacts due to contaminant release.2 Rubber granules contain leachable heavy metals and organic contaminants. SBR contains up to 17 g/kg zinc1,3 that is used in the form of zinc oxide as catalyst during the vulcanization process. Due to softening agents containing polycyclic aromatic hydrocarbons (PAH), scrap tires may comprise up to 77 mg/kg PAH (16 EPA-PAH) and up to 3 mg/kg benzo[a]pyrene.4 Li et al. identified 10 volatile substances in commercially available rubber granules, with benzothiazole as the most common component.2 So far, little is known about possible hazardous impacts of synthetic sporting grounds on the environment and public health. Hofstra detected zinc release from virgin materials of 4− 12 mg/kg in upflow column tests.3 From materials that were aged for three years on an outdoor sporting ground, he observed a release up to 57 mg/kg. He reasoned that degradation of granules due to weathering led to an increased leachability of zinc. Bocca et al. conducted batch tests of weathered rubber granules with a liquid to solid ratio (LS) of 10 L/kg and found zinc concentrations up to 2.3 mg/L.1 The New York State Department of Health studied possible release of contaminants from rubber granules used as infill for synthetic © 2012 American Chemical Society
Received: Revised: Accepted: Published: 13085
March 29, 2012 October 9, 2012 November 15, 2012 November 15, 2012 dx.doi.org/10.1021/es301227y | Environ. Sci. Technol. 2012, 46, 13085−13092
Environmental Science & Technology
Article
batch and percolation tests with an LS of 10 L/kg and found comparable results for inorganic parameters (+20% up to −35% in batch tests).19 López Meza and Garrabrants et al. checked granular waste materials like ashes, construction debris, and concrete and found column and batch tests also to give comparable Cr and Cu concentrations.20 Al-Abed and Jegadeesan et al. conducted batch tests with LS of 5, 10, 20, and 50 L/kg and column tests up to 22.73 L/kg of granular mineral processing waste and found corresponding heavy metal release profiles for both methods.21 They point out that batch tests might overestimate the release due to the different experimental procedures, in particular the end-over-end tumbling during batch testing. Kalbe and Berger et al. and Grathwohl and Susset found better reproducibility of column tests for various soils and waste materials.12,13 They mention that batch tests might be prone to analytical artifacts, especially because of the liquid−solid separation steps, which are mostly not necessary for column tests. We conducted batch tests with an LS of 2 L/kg and column tests with an LS up to 26.5 L/kg to study the behavior of synthetic sports flooring components at different elution methods. We compared accompanying parameters like pH, electric conductivity, turbidity of the eluates, and the contaminant release with a special emphasis on zinc and PAH, which are the most significant contaminats, according to literature and pretests.
The one for synthetic turf areas stipulated two consecutive 24 h batch elutions of the respective sample with LS 10 L/kg, whereby only the second eluate had to be analyzed.9 In the framework of the further development of this standard draft, it has recently been substituted by DIN SPEC 18035,11 which specifies for the investigation of the leaching behavior a singlestep batch test procedure at an LS of 10 L/kg. Research in the field of waste reutilization indicated that this LS ratio might not be appropriate.12,13 For this reason, the procedure must be evaluated in terms of reliable environmental compatibility assessment. Artificial turfs are multilayered constructions permeable to water. They consist of an unbound basic layer of mineral aggregates of at least 20 cm, and this layer can be omitted if the building ground fulfils the requirements concerning water permeability, freeze resistance, and grain size distribution. The bound elastic basic layer may consist of a pure elastic layer, a bound layer with or without mineral components, or an asphalt layer. SBR from recycled scrap tires is often a major component here. The artificial turf itself, which is produced from polyethylene or polypropylene, can either be left without infill or be filled with rubber granules and quartz sand or with quartz sand alone. Common infill materials are SBR, ethylene propylene diene monomer rubber (EPDM), or thermoplastic elastomer (TPE). Producers usually consider the specific composition of their granules confidential. Synthetic surfaces used for tracks, runways, playgrounds, and minipitches also consist of an unbound basic layer and a bound elastic basic layer. They have a single- or multilayered flooring of SBR and/ or EPDM as top layer. So far, no appropriate methods for the risk assessment of synthetic sports grounds are available at a European level. However, a lysimeter test is under development within the responsible standardization committee of CEN TC 217, taking into account the assessment of contaminant release from the turf system. The normative annex of this draft provides additionally a column test procedure for single components of turf systems. Since the sporting grounds may affect soil and groundwater, respective relevant regulations have to be considered. Leaching tests are already established as important tools for the determination of possible impacts on the soil−groundwater pathway.14 Validated standards for batch and column tests are available in Germany, stipulating an LS ratio of 2 L/kg. The batch test allows for compliance testing,15,16 whereas the column test is suitable for both compliance test and basic characterization.17 The former displays a snapshot of the leaching of contaminants; the latter shows the time dependence of contaminant release. Although the methods differ significantly, both are likely to be permitted for the risk assessment according to the regulations. Thus, a comparison of their respective results is of great importance. Whereas column tests constitute a more realistic simulation of actual field conditions, the friction during the batch test may lead to enhanced mobilization of colloids. Since contaminants are often colloid-linked, this may lead to an overestimation of pollutants.18 To simulate realistic soil water conditions and to avoid this overestimation, the eluate has to be centrifuged and/or filtered. Usually, this can be dropped for column tests, due to less mechanical strain. Several authors researched the differences of batch and column tests of various waste materials but not of scrap tires and/or artificial turf systems. Hage and Mulder tested several calcium minerals with
2. MATERIALS AND METHODS 2.1. Materials Acquisition and Sample Preparation. We received test materials of artificial turf system components from six German producers and their respective suppliers straight from the factory. Table 1 shows the description of the materials together with the coding used in this work. We homogenized the granular materials and took representative subsamples using a rotary sample divider or a sample splitter.22,23 For batch tests of the prefabricated elastic layer material (R, B, and EL 1), we cut the samples to pieces of approximately 1−3 cm size. We obtained one granule type in three different grain sizes (SBR 2, 3, 4) to determine the possible influence of the grain size on leaching. 2.2. Leaching Methods. We performed the batch tests according to the respective German standards for organic16 and inorganic contaminants15 at a liquid to solid ratio (LS) of 2 L/ kg. The standard requires a minimum sample amount of 100 g in the case of a maximum grain size of 2 mm and 250 g for 2− 10 mm particles to ensure representativeness. We mixed the respective samples with a 2-fold amount of doubly distilled water24 in a glass bottle and shook it in an end-over-end tumbler for 24 h at 7 rpm. After 15 min of sedimentation we decanted the supernatant and centrifuged it for 30 min at 20000g in a Beckmann Coulter Avanti J-E centrifuge with JA-14 fixed angle rotor and 250 mL stainless steel cups. Then we conducted pressure filtration through a 0.45 μm cellulose nitrate membrane filter for inorganic analysis or a 0.7 μm glass fiber microfilter for organic analysis, respectively. We collected eluates from column tests for both organic and inorganic analysis according to the German standard.17 We used glass columns with an internal diameter of 5.86 cm filled to a height of 10.5−16 cm. All materials except TS 5 (0−32 mm) comply with the stipulation of the maximum grain size being less than half of the internal diameter. We believe this to be negligible, since
