Comparison of Batch and Column Tests for the Elution of Artificial Turf System Components

Comparison of Batch and Column Tests for the Elution of ArtificialTurf System ComponentsO. Kruger,* 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 outdoorsporting grounds may release contaminants due to the chemicalcomposition of some components. A primary example is that ofzinc from reused scrap tires (main constituent, styrene butadienerubber, 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 arewidely used to examine the soil−groundwater pathway. Wetested several components for artificial sporting grounds withbatch tests at a liquid to solid (LS) ratio of 2 L/kg and columntests with an LS up to 26.5 L/kg. We found a higher zinc releasein the batch test eluates for all granules, ranging from 15% higherto 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) orthermoplastic elastomer (TPE) eluates, reflect the stronger mechanical stress of batch testing. This indicates that batch testprocedures might not be suitable for the risk assessment of synthetic sporting ground components. Column tests, on the otherhand, represent field conditions more closely and allow for determination of time-dependent contaminants release.

1. INTRODUCTION

Synthetic turf fields and athletic tracks for sporting grounds arewell-established and widely used in nearly all sports.1 Sincenewly manufactured plastics and recycled materials, like styrenebutadiene rubber (SBR) from scrap tires, are used in theirconstruction, there is a growing concern about possibleenvironmental and health impacts due to contaminant release.2

Rubber granules contain leachable heavy metals and organiccontaminants. SBR contains up to 17 g/kg zinc1,3 that is used inthe form of zinc oxide as catalyst during the vulcanizationprocess. Due to softening agents containing polycyclic aromatichydrocarbons (PAH), scrap tires may comprise up to 77 mg/kgPAH (16 EPA-PAH) and up to 3 mg/kg benzo[a]pyrene.4 Liet al. identified 10 volatile substances in commercially availablerubber granules, with benzothiazole as the most commoncomponent.2

So far, little is known about possible hazardous impacts ofsynthetic sporting grounds on the environment and publichealth. Hofstra detected zinc release from virgin materials of 4−12 mg/kg in upflow column tests.3 From materials that wereaged for three years on an outdoor sporting ground, heobserved a release up to 57 mg/kg. He reasoned thatdegradation of granules due to weathering led to an increasedleachability of zinc. Bocca et al. conducted batch tests ofweathered rubber granules with a liquid to solid ratio (LS) of10 L/kg and found zinc concentrations up to 2.3 mg/L.1 TheNew York State Department of Health studied possible releaseof contaminants from rubber granules used as infill for synthetic

turf.5 They found no contaminants in groundwater underneathsport fields and only low concentrations of heavy metals in therainwater runoff (0.06 mg/L zinc). Batch tests with rubbergranules according to the synthetic precipitation leachingprocedure (SPLP, LS 20 L/kg at pH 4.2) led to mean zincconcentrations in the eluate of 1.95 mg/L.5 Furthermore, theydetected aniline, phenol, and benzothiazole. In column testeluates, conducted with water as leachant (LS 6 L/kg) and aflow rate of 2 mL/min, they found lower zinc concentrationswith a mean value of 0.29 mg/L. The Swiss Federal Office forSports (BASPO) studied the environmental compatibility ofsynthetic turfs by outdoor lysimeter experiments, but singlecomponents were not tested.6,7 They considered the results,including the zinc concentrations, to be not harmful but foundindications of possible sorption of zinc at the unbound basiclayer. The French Environment and Energy ManagementAgency (ADEME) conducted lysimeter experiments withrubber granules in synthetic turfs.8 They generally found lowconcentrations of contaminants; e.g., zinc was, with oneexception 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 forsynthetic turf areas9 and synthetic surfaces, respectively.10

Received: March 29, 2012Revised: October 9, 2012Accepted: November 15, 2012Published: November 15, 2012

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© 2012 American Chemical Society 13085 dx.doi.org/10.1021/es301227y | Environ. Sci. Technol. 2012, 46, 13085−13092

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The one for synthetic turf areas stipulated two consecutive 24 hbatch elutions of the respective sample with LS 10 L/kg,whereby only the second eluate had to be analyzed.9 In theframework of the further development of this standard draft, ithas recently been substituted by DIN SPEC 18035,11 whichspecifies for the investigation of the leaching behavior a single-step batch test procedure at an LS of 10 L/kg. Research in thefield of waste reutilization indicated that this LS ratio might notbe appropriate.12,13 For this reason, the procedure must beevaluated in terms of reliable environmental compatibilityassessment.Artificial turfs are multilayered constructions permeable to

water. They consist of an unbound basic layer of mineralaggregates of at least 20 cm, and this layer can be omitted if thebuilding ground fulfils the requirements concerning waterpermeability, freeze resistance, and grain size distribution. Thebound elastic basic layer may consist of a pure elastic layer, abound layer with or without mineral components, or an asphaltlayer. SBR from recycled scrap tires is often a major componenthere. The artificial turf itself, which is produced frompolyethylene or polypropylene, can either be left without infillor be filled with rubber granules and quartz sand or with quartzsand alone. Common infill materials are SBR, ethylenepropylene diene monomer rubber (EPDM), or thermoplasticelastomer (TPE). Producers usually consider the specificcomposition of their granules confidential. Synthetic surfacesused for tracks, runways, playgrounds, and minipitches alsoconsist of an unbound basic layer and a bound elastic basiclayer. 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 theresponsible standardization committee of CEN TC 217, takinginto account the assessment of contaminant release from theturf system. The normative annex of this draft providesadditionally a column test procedure for single components ofturf systems.Since the sporting grounds may affect soil and groundwater,

respective relevant regulations have to be considered. Leachingtests are already established as important tools for thedetermination of possible impacts on the soil−groundwaterpathway.14 Validated standards for batch and column tests areavailable in Germany, stipulating an LS ratio of 2 L/kg. Thebatch test allows for compliance testing,15,16 whereas thecolumn test is suitable for both compliance test and basiccharacterization.17 The former displays a snapshot of theleaching of contaminants; the latter shows the time dependenceof contaminant release.Although the methods differ significantly, both are likely to

be permitted for the risk assessment according to theregulations. Thus, a comparison of their respective results isof great importance. Whereas column tests constitute a morerealistic simulation of actual field conditions, the friction duringthe batch test may lead to enhanced mobilization of colloids.Since contaminants are often colloid-linked, this may lead to anoverestimation of pollutants.18 To simulate realistic soil waterconditions and to avoid this overestimation, the eluate has to becentrifuged and/or filtered. Usually, this can be dropped forcolumn tests, due to less mechanical strain. Several authorsresearched the differences of batch and column tests of variouswaste materials but not of scrap tires and/or artificial turfsystems. Hage and Mulder tested several calcium minerals with

batch and percolation tests with an LS of 10 L/kg and foundcomparable results for inorganic parameters (+20% up to−35% in batch tests).19 Lopez Meza and Garrabrants et al.checked granular waste materials like ashes, construction debris,and concrete and found column and batch tests also to givecomparable Cr and Cu concentrations.20 Al-Abed andJegadeesan 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 granularmineral processing waste and found corresponding heavy metalrelease profiles for both methods.21 They point out that batchtests might overestimate the release due to the differentexperimental procedures, in particular the end-over-endtumbling during batch testing. Kalbe and Berger et al. andGrathwohl and Susset found better reproducibility of columntests for various soils and waste materials.12,13 They mentionthat batch tests might be prone to analytical artifacts, especiallybecause of the liquid−solid separation steps, which are mostlynot 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 ofsynthetic sports flooring components at different elutionmethods. We compared accompanying parameters like pH,electric conductivity, turbidity of the eluates, and thecontaminant release with a special emphasis on zinc andPAH, which are the most significant contaminats, according toliterature and pretests.

2. MATERIALS AND METHODS2.1. Materials Acquisition and Sample Preparation.

We received test materials of artificial turf system componentsfrom six German producers and their respective suppliersstraight from the factory. Table 1 shows the description of thematerials together with the coding used in this work. Wehomogenized the granular materials and took representativesubsamples using a rotary sample divider or a samplesplitter.22,23 For batch tests of the prefabricated elastic layermaterial (R, B, and EL 1), we cut the samples to pieces ofapproximately 1−3 cm size. We obtained one granule type inthree different grain sizes (SBR 2, 3, 4) to determine thepossible influence of the grain size on leaching.

2.2. Leaching Methods. We performed the batch testsaccording to the respective German standards for organic16 andinorganic contaminants15 at a liquid to solid ratio (LS) of 2 L/kg. The standard requires a minimum sample amount of 100 gin the case of a maximum grain size of 2 mm and 250 g for 2−10 mm particles to ensure representativeness. We mixed therespective samples with a 2-fold amount of doubly distilledwater24 in a glass bottle and shook it in an end-over-endtumbler for 24 h at 7 rpm. After 15 min of sedimentation wedecanted the supernatant and centrifuged it for 30 min at20000g in a Beckmann Coulter Avanti J-E centrifuge with JA-14fixed angle rotor and 250 mL stainless steel cups. Then weconducted pressure filtration through a 0.45 μm cellulosenitrate membrane filter for inorganic analysis or a 0.7 μm glassfiber microfilter for organic analysis, respectively.We collected eluates from column tests for both organic and

inorganic analysis according to the German standard.17 Weused glass columns with an internal diameter of 5.86 cm filledto a height of 10.5−16 cm. All materials except TS 5 (0−32mm) comply with the stipulation of the maximum grain sizebeing less than half of the internal diameter. We believe this tobe negligible, since <5% is above the limit of 29.3 mm and thusdid not disturb the flow paths through the column. Again,

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doubly distilled water was used as leachant. We carried out thetests as basic characterization. Differing from the standard, wecollected not only the fractions at LS 0.3, 1, 2, and 4 L/kg, butalso at higher LS up to 26.5 L/kg, to observe possible time-delayed release of contaminants, especially zinc.3 An LS of 1corresponds approximately to 2 years of precipitation in thefield, depending on actual climate conditions. We collected theeluates in glass bottles, preserved them,25 and analyzed themwithout further treatment. Due to limited sample amounts, weconducted column experiments in addition to batch tests onlyfor selected components (SBR 5−9; EPDM 1−3; TPE 1; SI 3;TS 2, 4, 5). We carried out all experiments in triplicate.To compare the contaminant release (given in mg/kg) in

batch and column tests, we calculated the release in relation tothe amount of the solid matter of the sample by multiplying therespective contaminant concentrations with the LS. For thecolumn tests, we determined the release for each fraction andsummed up (cumulated) the results of all fractions up to LS 2L/kg.2.3. Analytical Methods. We measured pH values with a

Schott CG 841 pH-meter equipped with a WTW SenTix 41pH electrode, the electric conductivity with a WTW LF 437microprocessor conductivity meter, and the turbidity with aHach 2100 IS turbidity meter. For the determination of zincsolid matter content, we digested 0.5 g of sample with 8 mL ofHNO3 and 2 mL of H2O2 on the basis of DIN ISO 11466.26

We measured element concentrations according to DIN EN

ISO 11885,27 without matrix adjustment using a ThermoScientific Iris Intrepid II XSP inductively coupled plasmaoptical emission spectrometer (ICP-OES). We measured PAHas the sum of 15 EPA-PAH with high-performance liquidchromatography (HPLC) and stir bar sorptive extraction(SBSE) sample preparation as described recently.28 We usedan Agilent 1200 Series HPLC system with fluorescencedetector. Since acenaphthylene is not available to fluorescencedetection, we did not measure or discuss it in this work. Weused a Zorbax Eclipse PAH column of 4.6 × 100 mm with 1.8μm particle size for separation.

3. RESULTS

Table 2 shows the zinc and PAH concentrations in batch testeluates of artificial turf system components. Other heavy metalslike lead or cadmium were under the limit of quantitation(LOQ); thus, we concentrated on zinc as inorganiccontaminant. pH, electric conductivity, and turbidities beforeand after the filtration step are given. The table also states therelative standard deviations unless the parameters were underthe LOQ (0.03 mg/L) or only one measurement wasperformed due to low amounts of eluate. The zincconcentrations varied between LOQ and 4.52 mg/L with thetwo exceptions of SBR 7 (129 mg/L) and EL 1 (10.1 mg/L).The PAH concentrations varied between 0.07 and 3.41 μg/L.The turbidity before filtration varied significantly, with thehighest values for the EPDM, TPE, and some sand eluates (SI,TS 1, TS 4). After filtration, only the eluates of SBR 7 and 9,EPDM 1, SI 2 and 3, R 1, and TS 4 were above 20 formazinenephelometric units (FNU). pH values of all eluates werebetween 6.37 and 9.63 with a mean value of 7.69. Theconductivity of the eluates varied between 15 and 334 μS/cmwith the exceptions of EPDM 1 (3793 μS/cm), R 1 (1336 μS/cm), and R 2 (928 μS/cm). To check possible causes of thehigh conductivities, we checked alkaline and earth alkalineconcentrations of the respective eluate for significantly highvalues. Sodium, potassium, and calcium were above 20 and 10mg/L each in the R 1 and R 2 eluates, respectively. The EPDM1 batch test eluates contained 1065 mg/L sodium, and theconcentrations in the column test amounts ranged from 656 to177 mg/L. The relative standard deviations fluctuate stronglyon a high level, with the respective mean values of the Zn, PAH,and turbidity RSDs all above 30%.Figure 1 shows the zinc release at LS 2 L/kg (given in mg/

kg) of the tested components calculated from the batch testresults plotted versus those from the column tests whose resultsare shown in Figure 2. The left part represents an enlargedfraction of the right one to show the results in the range of 0−4mg/kg. Points above the diagonal indicate higher zinc release inbatch tests. In all cases, the zinc release was higher in batchtests. We found the highest relative excess (difference of batchand column test release divided by column test release) for theEPDM eluates, where very little zinc was released during thecolumn experiments. For the SBR granules, the relative excessfindings ranged from 15% (SBR 6) to 687% (SBR 9). SBR 7showed the maximum zinc release (258 mg/kg) from the batchtest, which was also significantly higher than that from thecolumn test, which was 197 mg/kg at LS 2.8 L/kg. Since wecompare this with batch test results at LS 2, we interpolated thecolumn test result for LS 2 to check whether this differenceaffects the conclusion. The release at LS 2 was estimated as 206mg/kg, less than 5% higher than at LS 2.8.

Table 1. Coding of Tested Materials

component description

SBR 1−9 styrene butadiene rubber (recycled rubbergranules from scrap tires)

SBR 1, 5−7, 9 0.8−2.0 mm, of various producersSBR 2 0.2−0.8 mmSBR 3 0.8−2.0 mmSBR 4 2.0−4.0 mmSBR 8 0.8−2.0 mm, coated with green-colored

polyurethaneEPDM 1−3 ethylene propylene diene monomer (new

synthetic granules)EPDM 1 0.8−2.0 mm, foamed granulate,

peroxide-linked, no longer in useEPDM 2, 3 0.8−2.0 mm, sulfur cross-linked

TPE 1, 2 thermoplastic elastomer (granules from newsynthetic material)

TPE 1 0.5−2.0 mmTPE 2 0.5−1.2 mm

SI sand infill (quartz sand 0.25−1.25 mm)R synthetic turf

R 1 straight fibersR 2 curly fibers

B 1−3 synthetic sports flooringB 1 SBR with a sprayed layer of EPDMB 2 SBR layer and EPDM layer (50:50)B 3 pure EPDM layer

EL 1 bound elastic basic layer, without mineralcomponents, meter goods

ET 1, 2 bound elastic basic layer, with mineralcomponents

TS 1−5 unbound basic layer (gravel, split)TS 1, 5 gravel 0−32 mmTS 2 split 0−8 mmTS 3 split 2−8 mmTS 4 quartz filter sand 0.6−1.0 mm



Figure 2 shows zinc and PAH concentrations in the columntest eluates of the tested components as well as their pH andelectric conductivity. The values are plotted versus LS. We didnot plot the zinc concentrations of the SBR 7 eluates, since thevalues were too high for a mutual illustration (LS [L/kg], Zn[mg/L]: 0.16, 133; 0.52, 92.4; 1.0, 56.0; 2.8, 25.5). Figure 3shows no zinc values, since the respective concentrations werebelow the LOQ, with the exception of the first eluates (0.3 L/

kg) of EPDM 2, EPDM 3, and TPE 1, which were slightlyabove LOQ (0.045−0.048 mg/L).The zinc concentrations (Figure 2) generally declined from

high values in the first eluate fractions (between 1755 μg/L forSBR 5 and 44 μg/L for SBR 8) to values below LOQ. SBR 9showed a slight increase at LS 7.8 L/kg, SBR 6 an increase fromLOQ at 11.6 L/kg to 1220 μg/kg at LS 26.5 L/kg, and SBR 5rose from the minimum of 357 μg/L at 8.3 L/kg to 4110 μg/L

Table 2. Batch Test Results (LS 2 L/kg) of Artificial Turf System Components

compdZn

(mg/L)RSD(%)

PAHa

(μg/L) RSDturbidity beforefiltration (FNU)

RSD(%)

turbidity afterfiltration (FNU)

RSD(%) pH

RSD(%)

conductivity(μS/cm)

RSD(%)

SBR 1 3.59 9.5 ndb − 75.8 15.8 34.3 78.6 6.76 8.7 57.1 54.6SBR 2 0.90 62.6 1.42 13.4 − − 3.39 28.6 6.80 3.1 364 10.0SBR 3 1.31 31.6 1.39 35.8 6.04 34.5 5.12 23.4 6.91 4.2 189 2.4SBR 4 0.69 44.7 1.49 8.9 8.74 41.1 5.56 7.7 6.80 3.7 103 4.8SBR 5 4.52 3.7 0.68 24.7 − − 4.86 21.4 7.12 0.4 179 3.4SBR 6 0.84 6.3 0.45 28.9 128 14.9 50.1 38.3 7.49 2.7 138 1.2SBR 7 129 23.0 0.41 11.8 58.5 46.1 25.2 25.6 7.32 2.0 334 2.4SBR 8 0.08 42.4 1.18 4.9 112 42.6 12.9 74.9 8.13 0.4 152 3.1SBR 9 1.55 16.1 1.29 8.5 46.0 7.9 35.2 72.4 7.57 1.5 166 29.6EPDM 1 0.75 2.8 0.21 10.0 npc − 75.9 1.8 9.63 0.1 3793 0.8EPDM 2 1.05 125 0.20 39.3 1079 1.9 1.45 62.8 7.80 0.3 149 13.4EPDM 3 0.20 7.7 0.93 − 800 17.2 0.82 11.0 8.01 1.5 209 1.2TPE 1 <0.03 − 0.10 − 621 31.6 0.98 100 7.56 0.5 220 3.2TPE 2 <0.03 − 0.11 6.4 333 45.0 0.30 16.7 7.48 0.9 220 1.8TPE 3 <0.03 − 0.52 16.4 − − 0.74 24.3 8.50 0.4 64.6 2.0SI 1 0.06 43.7 3.41 57.8 648 34.6 2.29 52.8 7.04 4.3 35.5 10.8SI 2 0.07 39.6 0.14 17.1 npc − 42.0 58.3 6.37 2.0 15.0 11.5SI 3 0.11 10.7 0.23 60.0 418 2.0 153 14.1 6.89 4.6 20.3 34.9R 1 0.46 29.3 0.86 29.1 121 1.3 32.6 10.6 7.67 0.5 1336 1.6R 2 0.44 2.0 1.42 82.5 31.6 5.1 12.5 13.0 7.82 0.1 928 1.6B 1 0.27 0.8 1.13 1.2 0.37 16.4 0.23 17.4 7.88 1.4 72.0 2.0B 2 0.18 6.3 0.75 13.3 2.44 109 0.91 80.2 8.02 1.0 91.5 7.3B 3 0.15 77.3 0.65 9.0 6.03 53.6 3.43 22.2 8.10 1.7 137 3.7EL 1 10.1 13.1 0.52 − 6.01 − 2.20 − 6.59 − 72.5 −ET 1 0.20 64.1 0.07 36.0 200 47.8 11.3 27.6 7.86 4.3 101 4.3ET 2 0.26 1.1 0.74 9.9 ndb − ndb − ndb − ndb −TS 1 <0.03 − 0.28 28.1 533 8.8 0.42 2.4 7.90 8.0 223 5.4TS 2 0.06 50.7 1.13 63.9 10.1 49.2 0.55 12.7 8.41 0.7 243 8.4TS 3 <0.03 − 1.24 92.7 9.56 19.9 0.44 15.9 9.04 0.8 89.2 7.6TS 4 <0.03 − 0.75 2.8 444 49.7 47.5 22.5 8.17 1.2 22.9 14.8TS 5 <0.03 − 0.75 201 13.4 31.3 5.44 1.7 8.84 0.5 20.9 36.6aSum of 15 EPA-PAH (without acenaphthylene). bNot determined. cMeasurement not possible; turbidity too high.

Figure 1. Comparison of zinc release from artificial turf system components in batch and column tests at a liquid to solid ratio (LS) of 2 L/kg.



Figure 2. Zinc, PAH, pH, and conductivity of column test eluates of artificial turf system components.

Figure 3. PAH, pH, and conductivity of column test eluates of artificial turf system components.



at 10.6 L/kg. PAH values of SBR 6 and 8 showed a clear declinefrom 2.3 μg/L at 0.3 L/kg to values below 0.5 μg/L. SBRincreased again to 0.95 μg/L at 26.5 L/kg. SBR 9 showed aslight decrease while fluctuating around 2.5 μg/L, whereas SBR5 increased slightly from 0.7 to 0.9 μg/L. PAH values for TS 2fluctuated around 0.10 μg/L. The pH values of the eluatesalternated around 7 with the exception of TS 2, which rosefrom 3.3 to 4.1 during the column experiments. For SBR 5, thepH increased from 6.3 (8.3 L/kg) to 6.9 (9.4 L/kg). Theelectric conductivity declined throughout the experiments from724 μS/cm (TS 2) to 94 μS/cm (SBR 5). SBR 9 showed aslight increase in conductivity at LS 7.8 L/kg, and SBR 5increased from 28 μS/cm (8.3 L/kg) to 75 μS/cm (10.6 L/kg).Figure 3 shows that the PAH concentrations of EPDM and

TPE eluates decline during the column tests. EPDM 3 and TPE1 eluates started with high values (7.2 and 5.3 μg/L), whereasPAH concentrations in EPDM 1 and 2 eluates were lower (0.2and 0.8 μg/L). We did not display the PAH results for SI 3, TS4, and TS 5, since the values were generally below 0.2 μg/L.The pH values alternated around 7 for all components butEPDM 1 (9.3) and TS 4, which declined from 6.3 to 5.0. Theconductivities declined steadily with higher LS ratios withstarting values between 222 μS/cm (EPDM 3) and 27 μS/cm(TS 4), with the exception of EPDM 1, where theconductivities were about an order of magnitude higher(2545 μS/cm at LS 0.2 L/kg).

4. DISCUSSIONThe higher zinc concentrations in batch test eluates (Figure 1)might be due to additional zinc release because of the frictionthe particles experience during tumbling. Batch test conditionsdo not simulate actual field conditions, where the materials arebeing percolated and not tumbled but partly stressed by users.Thus, batch test procedures require centrifugation and filtrationas sample preparation prior to analysis.13,14 These proceduresmay not be suitable for plastic granules material, since the batchtests are prone to higher uncertainties in determination ofpotential zinc release compared to column tests due to lowersample amounts. In addition, the fluctuating turbidity of thebatch test eluates before the filtration indicates a differentbehavior of the various artificial turf system components underbatch test conditions. After filtration, eight eluates still had aturbidity above the boundary limit allowed by the standard (20FNU).15,16 Since the leaching results of different grain sizefractions of SBR (Table 2; SBR 2, 3, 4) showed no distincttrend, we assume no significant effect of the grain size on theleaching of zinc and PAH.Column tests on the other hand are closer to field conditions

and thus not prone to excess findings due to mechanicalfriction. Usually, the self-filtration capacity of the packed samplematerial supersedes subsequent sample preparation. Columntests also allow for observation of the time-dependent leachingbehavior (expressed as LS ratio, Figures 2 and 3), in order toidentify aspects such as the delayed zinc release from SBR 5 and6. Presumably, this is due to zinc reservoirs, which are notaccessible until the later course of the elution. This may bebecause of different solubility, matrix effects, and/or Zn bindingsites. Rowley et al. conducted replacement experiments (Znexchanged by Pb, Cd, Hg) and assume two types of Zn bindingsites with different sorption capacities from which zinc can bereleased under different boundary conditions.29 They do notspecify these sites. Zinc in rubber tires is usually present asZnO.30,31 For SBR 5, the strong increase of the zinc

concentration at higher LS ratios correlates with a rise in pHand conductivity values, whereas we found nothing similar inthe case of SBR 6. This might be due to the considerably lowerincrease of zinc concentration in the eluate. Electricconductivity decreases with higher LS ratios according to thelower release of ionic components. The stable pH valuesaround 7 throughout the column experiments indicate that therespective components have no acid−base-related effects on theeluate. Only for TS 2 and TS 4, the increasing and decreasingpH, respectively, show influence on the eluate, presumably dueto sorption and/or desorption processes on the particlesurfaces. Further research is recommended to determinepossible causes of the time-delayed zinc release.The results given in Table S1 (Supporting Information)

show no correlation between zinc solid matter content and therelease from the respective batch tests. There seems to be nocausal relation between leachable zinc and its respective solidmatter content.The unbound base layer TS 2 showed a very different

behavior, with high pH and low zinc concentrations in thebatch test eluates and vice versa in the column test eluates(Table 2 and Figure 2). The zinc release at LS 2 L/kg was 0.12mg/kg in the batch test and 2.3 mg/kg in the column test.Since we used the same material, but different batches receivedat different times, we have to assume differences in the testmaterial. Samples from each batch were homogeneous andrepresentative according to the sample preparation proceduresdescribed in the Materials and Methods (section 2.1). The TS 2material emphasizes the importance of the quality of the baselayer material for the zinc release from artificial turf systems. Atlow pH values, this material releases significant amounts of zinc,probably due to the increased solubility of zinc species at lowerpH.32,33 This means that natural mineral aggregates maycontribute to the overall contaminant release dependent on theinherent geogenic zinc concentration and the field conditions,especially regarding pH value. We recommend further researchto determine the possible influence of the base layer on thecontaminant release, especially ad- and desorption experiments.In case of the EPDM 1 eluates, we measured a Na

concentration of 1066 mg/L, which was 2 orders of magnitudehigher than the mean value of all other eluates (10.6 mg/L).This might be the reason for the high electric conductivity. Thisand the high pH in the EPDM 1 eluates may be caused by theproduction method of this peroxide-linked foamed granule.Due to industrial secrecy, we have no information about theexact chemical composition of the granule and the foamingprocess. The exceptionally high zinc concentrations in the SBR7 eluates may be due to unintended use of tires with high zincconcentrations (e.g., truck tires) during production.3,30 Batchtest eluates of one of the materials (EPDM, TPE, SI) show ahigh turbidity (Table 1), presumably because of fine particlesreleased during tumbling. Whereas filtration efficiently reducesthe turbidity of some eluates (EPDM, TPE, SI), it is much lessefficient for SBR eluates. This is probably due to the differentparticle size distribution. The conductivity of the eluates wasnot significantly altered by filtration. Results before filtration(data not shown) were very similar to those measured afterfiltration (difference less than 5% for most of the eluates).The PAH concentrations in the batch test eluates (Table 2)

fluctuated on the same level without clear distinction betweenthe different groups of components. The column test eluates ofgranules (Figures 2 and 3) show a decrease with higher LSratios only for SBR 6, SBR 8, EPDM 3, and TPE 1, indicating a



slow and steady release in the other cases and, especially forSBR 9, a considerably large reservoir of leachable PAH.We observed high relative deviations especially for Zn, PAH,

and turbidity of the batch test eluates, despite the fact that wetook representative subsamples according to relevant stand-ards.22,23 This might be due to inhomogeneities caused byconglomeration34 and/or heterogeneities on particle surfaces.35

Apparently, the subsamples used for batch tests (usually 100−250 g, depending on the grain size) were too small tocompensate for inhomogeneities. Presumably, column tests aremore suitable, since they easily allow for larger sample amounts(200−3000 g or more, depending on the column dimensions)and thus better representativeness. The mean values of therespective RSDs for SBR 5, 6, 9 and TS 2 were lower forcolumn tests than for batch tests (zinc 13% vs 23%, PAH 15%vs 31%).We found higher zinc release from the tested rubber granules

in batch test eluates than in column test eluates. This might bedue to the additional agitation and/or friction during thetumbling process, which produces additional particles withadditional surface area.12 Apparently, the sample preparationprocedures prior to analysis, including centrifugation andfiltration, are not sufficient to level out these effects. Columntests provide conditions closer to actual field conditions andavoid excess findings due to friction. Furthermore, column testsenable the determination of the time-dependent leachingbehavior of contaminants, whereby effects such as a delayedrelease of contaminants can be observed. In addition, largeramounts of materials used in column tests allow for betterrepresentativeness of the tested subsamples. Considering therisk assessment of artificial turf systems, emphasis should beplaced not only on the plastic components but also on mineralaggregates used for basic layers, which might contribute to therelease of contaminants, especially of zinc. For a thorough andrealistic risk assessment, column tests of complete artificial turfsystems, simulating the actual installation, may be morerealistic. This would also allow for the determination ofpossible interactions of the single components. We recommendfurther research on the influence of intermittent test conditions,aging by weather influences (including sprinkling, freeze/thawcycles, UV irradiation), and friction from users on the leachingof contaminants.

■ ASSOCIATED CONTENT

*S Supporting InformationWe compared zinc release and solid matter content of selectedcomponents to determine whether there is a correlationbetween these values. This material is available free of chargevia the Internet at http://pubs.acs.org/.

■ AUTHOR INFORMATION

Corresponding Author*E-mail: [email protected]; phone: +49 30 8104 3861;fax: +49 30 8104 1437.

NotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTS

The research was funded by BISpBundesinstitut furSportwissenschaft, the German Federal Institute for SportsScience.

■ REFERENCES(1) Bocca, B.; Forte, G.; Petrucci, F.; Costantini, S.; Izzo, P. Metalscontained and leached from rubber granulates used in synthetic turfareas. Sci. Total Environ. 2009, 407 (7), 2183−2190.(2) Li, X.; Berger, W.; Musante, C.; Mattina, M. I. Characterization ofsubstances released from crumb rubber material used on artificial turffields. Chemosphere 2010, 80 (3), 279−285.(3) Hofstra, U. Leaching of Zinc from Recycled Rubber Taking inAccount the Degradation of the Rubber. WASCON 2009; ISCOWA:Utrecht, The Netherlands, 2009.(4) Wengert, S. Gesundheitsgefahrdung durch Schadstoffe imKunstrasen?, Eidgenossisches Department des Innern (EDI), Bundesamtfu r Gesundheit (BAG) ; 2007.(5) Lim, L.; Walker, R. An Assessment of Chemical Leaching, Releases toAir and Temperature at Crumb-Rubber Infilled Synthetic Turf Fields;New York State Department of Environmental Conservation: Albany,NY, 2009.(6) Muller, E. Umweltvertra glichkeit von Kunststoffrasen: Resultate einesFeldversuches, BASPO-Tagung, 13.9.2007, Magglingen, CH 2007.(7) Stauffer, W.; Muller, E.; Held, M. Untersuchungen zurUmweltvertra glichkeit von Sportplatz-Kunststoffbela gen mittels Lysimetern,12. Gumpensteiner Lysimetertagung, Irdning, 2007.(8) Moretto, R. Environmental and Health Assessment of the Use ofElastomer Granulates (Virgin and from Used Tires) As Filling in ThirdGeneration Artificial Turf; Technical Report, ADEME/Aliapur/FieldTurf Tarkett, 2007.(9) DIN V 18035−7:2002−06, SportplatzeTeil 7: Kunststoffrasen-flachen (Sports groundsPart 7: Synthetic turf areas); GermanStandardization Organization.(10) DIN V 18035−6:2004−10, SportplatzeTeil 6: Kunststoff-flachen (Sporting groundsPart 6: Synthetic surfaces); GermanStandardization Organization.(11) DIN SPEC 18035−7:2011−06, SportplatzeTeil 7: Kunst-stoffrasenflachen (Sports groundsPart 7: Synthetic turf areas);German Standardization Organization.(12) Grathwohl, P.; Susset, B. Comparison of percolation to batchand sequential leaching tests: Theory and data. Waste Manage. 2009,29 (10), 2681−2688.(13) Kalbe, U.; Berger, W.; Eckardt, J.; Simon, F. G. Evaluation ofleaching and extraction procedures for soil and waste. Waste Manage.2008, 28, 1027−1038.(14) Susset, B.; Grathwohl, P. Leaching standards for mineralrecycling materialsA harmonized regulatory concept for theupcoming German Recycling Decree. Waste Manage. 2011, 31 (2),201−214.(15) DIN 19529:2009−01, Elution von FeststoffenSchuttelverfah-ren mit einem Wasser/Feststoffverha ltnis von 2 l/kg zurUntersuchung der Elution von anorganischen Stoffen fur Materialienmit einer Korngrosse bis 32 mmUbereinstimmungsuntersuchung(Leaching of solid materialsBatch test at a liquid to solid ratio of 2 l/kg for the examination of the leaching behaviour of inorganicsubstances for materials with a particle size up to 32 mmCompliance test); German Standardization Organization.(16) E DIN 19527:2010−05, Elution von FeststoffenSchuttelver-fahren zur Untersuchung des Elutionsverhaltens von organischenStoffen mit einem Wasser/FeststoffVerhaltnis von 2 l/kg (Leachingof solid materialsBatch test at a liquid to solid ratio of 2 l/kg for theexamination of the leaching behaviour of organic substances); GermanStandardization Organization.(17) DIN 19528:2009−01, Elution von FeststoffenPerkolations-verfahren zur gemeinsamen Untersuchung des Elutionsverhaltens vonorganischen and anorganischen Stoffen fur Materialien mit einerKorngrosse bis 32 mmGrundlegende Charakterisierung mit einemausfuhrlichen Saulenversuch and Ubereinstimmungsuntersuchung miteinem Saulenschnelltest (Leaching of solid materialsPercolationmethod for the joint examination of the leaching behaviour of organicand inorganic substances for materials with a particle size up to 32mmBasic characterization using a comprehensive column test and



http://pubs.acs.org/

mailto:[email protected]

compliance test using a quick column test); German StandardizationOrganization.(18) Kogel-Knabner, I.; Totsche, K. U. Influence of dissolved andcolloidal phase humic substances on the transport of hydrophobicorganic contaminants in soils. Phys. Chem. Earth 1998, 23 (2), 179−185.(19) Hage, J. L. T.; Mulder, E. Preliminary assessment of three newEuropean leaching tests. Waste Manage. 2004, 24, 165−172.(20) Lopez Meza, S.; Garrabrants, A. C.; van der Sloot, H.; Kosson,D. S. Comparison of the release of constituents from granularmaterials under batch and column testing. Waste Manage. 2008, 28(10), 1853−1867.(21) Al-Abed, S. R.; Jegadeesan, G.; Purandare, J.; Allen, D. Leachingbehavior of mineral processing waste: Comparison of batch andcolumn investigations. J. Hazard. Mater. 2008, 153 (3), 1088−1092.(22) ISO 23909:2008−04, Soil qualityPreparation of laboratorysamples from large samples; International Standardization Organ-ization.(23) DIN 19747:2009−07, Untersuchung von FeststoffenProbenvorbehandlung, -vorbereitung and -aufarbeitung fur chemische,biologische and physikalische Untersuchungen (Investigation ofsolidsPretreatment, preparation and processing of samples forchemical, biological and physical investigations); German Stand-ardization Organisation.(24) DIN ISO 3696:1991−06, Wasser fur analytische Zwecke;Anforderungen and Prufungen; Identisch mit ISO 3696:1987 (Waterfor analytical laboratory use; specification and test methods; identicalwith ISO 3696:1987); German Standardization Organisation.(25) DIN EN ISO 5667−3:2004−05, WasserbeschaffenheitProbenahmeTeil 3: Anleitung zur Konservierung and Handhabungvon Wasserproben (Water qualitySamplingPart 3: Guidance onthe preservation and handling of water samples); German Stand-ardization Organisation.(26) DIN ISO 11466:1997−06, BodenbeschaffenheitExtraktion inKonigswasser loslicher Spurenelemente (Soil qualityExtraction oftrace elements soluble in aqua regia); Deutsches Institut fur Normung(German Standardization Organization).(27) DIN EN ISO 11885:2009−09, WasserbeschaffenheitBestimmung von ausgewahlten Elementen durch induktiv gekoppeltePlasma-Atom-Emissionsspektrometrie (ICP-OES) (Water qualityDetermination of selected elements by inductively coupled plasmaoptical emission spectroscopy (ICP-OES)); German StandardizationOrganization.(28) Kruger, O.; Christoph, G.; Kalbe, U.; Berger, W. Comparison ofstir bar sorptive extraction (SBSE) and liquid−liquid extraction (LLE)for the analysis of polycyclic aromatic hydrocarbons (PAH) incomplex aqueous matrices. Talanta 2011, 85, 1428−34.(29) Rowley, A. G.; Husband, F. M.; Cunningham, A. B. Mechanismsof metal adsorption from aqueous solutions by waste tyre rubber.Water Res. 1984, 18, 981−984.(30) Smolders, E.; Degryse, F. Fate and effect of zinc from tire debrisin soil. Environ. Sci. Technol. 2002, 36 (17), 3706−3710.(31) Councell, T. B.; Duckenfield, K. U.; Landa, E. R.; Callender, E.Tire-wear particles as a source of zinc to the environment. Environ. Sci.Technol. 2004, 38 (15), 4206−4214.(32) Reich, J.; Pasel, C.; Luckas, M.; Herbell, J.-D. Moglichkeiten undGrenzen thermodynamischer Gleichgewichtsrechnungen bei derBestimmung bei der freisetzung von Zink aus Schlacken derSondermullverbrennung. Chem. Ing. Tech. 2000, 72, 763−771.(33) Bian, S.-W.; Mudunkotuwa, I. A.; Rupasinghe, T.; Grassian, V.H. Aggregation and dissolution of 4 nm ZnO nanoparticles in aqueousenvironments: Influence of pH, ionic strength, size, and adsorption ofhumic acid. Langmuir 2011, 27 (10), 6059−6068.(34) Buekens, A. G. Some observations on the recycling of plasticsand rubber. Conserv. Recycl. 1977, 1 (3−4), 247−271.(35) Segre, N.; Monteiro, P. J. M.; Sposito, G. Surface character-ization of recycled tire rubber to be used in cement paste matrix. J.Colloid Interface Sci. 2002, 248 (2), 521−523.



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Comparison of Batch and Column Tests for the Elution of Artificial Turf System Components