Description of test samples and theirs preparation
84 samples of recycled rubber granules with a particle size of 0.5 to 4 mm, produced for the construction of sport field surfaces, were tested. The samples of rubber granules were collected from 17 sport fields and 67 samples rubber granules were supplied by recyclers. Research included 57 samples of SBR granules and 27 samples of EPDM granules. The numbers of samples in relation to their sources of origin are shown in Fig. one.
The samples were taken from the surface of sport fields with artificial turf in accordance with the laboratory instructions or delivered to the laboratory by recyclers. The mass of the granulate samples delivered for testing was approx. 0.5 kg. Sampling from sport fields was carried out using a scheme based on 6 sampling points, shown in Fig. 2, in accordance with point 4 of the FIFA guidelines: “Quality Program for Football Turf. Handbook of Test Methods for Football Turf”. The number and weight of granular samples and the locations of the granular sampling points on the field indicated in the aforementioned guidelines are indicated in order to obtain a representative homogenized granular sample for the tested field42.
At the designated points (1 ÷ 6), 6 samples of granulate were collected. The collected and secured samples were stabilized in the laboratory conditions of natural drying, in which the moisture of the sample was in equilibrium with the ambient moisture. After stabilization, the samples were purified and homogenized to give a pooled sample. Images of exemplary SBR and EPDM granules used in the study are shown in Fig. 3. The average values of the physical parameters of the tested rubber granules are given in Table 1.
Samples weighing at least 100 g were taken from the granulate samples using the quartering method. This way allowed to ensure full qualitative and quantitative compliance of the sample composition with the composition of the analyzed material. Samples for testing the content of PAHs were grounded by grinding in a cryogenic mill 6770 Freezer/Mill, by SPEX SamplePrep LLC. Samples for testing other substances were not crushed.
The scope and methods of testing rubber granules
The scope of the research on rubber granules included: content determination of the PAHs, leached elements, organotin compounds and PAHs. In all samples of rubber granules, the content of 8 polycyclic aromatic hydrocarbons, resulting from the REACH Regulation, was determined: benzo[a]pyrene (BaP), dibenz[a,h]anthracene (DBAhA), benzo[e]pyrene (BeP), benz[a]anthracene (BaA), chrysene (CHR), benzo[b]fluoranthene (BbFA), benzo[j]fluoranthene (BjFA) and benzo[k]fluoranthene (BkFA). The content of indeno[1,2,3-cd]pyrene (IcdP), benzo[ghi]perylene (BghiP), phenanthrene, anthracene, fluoranthene, pyrene and naphthalene was determined for 38 samples from recyclers, additionally, that the number of PAHs covered by the requirements of the document43 was increased by 7.
The leaching tests of elements and organotin compounds were carried out for 18 samples and the leachability of PAHs and elements were carried out for 4 samples. The tests were carried out with the methods listed below, using the following apparatus.
The content and leachability of PAHs from rubber granules was determined by gas chromatography with tandem mass spectrometry (GC–MS/MS) using a gas chromatograph coupled with a mass detector GCMS/MS/7890B/7000C. The method was chosen because of the high sensitivity and selectivity obtained for low PAHs levels when used GC–MS/MS, compared to other commonly used analytical techniques such as high-performance liquid chromatography (HPLC) combined with UV, fluorescence or diode array detector (DAD). In studies carried out with the use of the above-mentioned techniques trace amount of PAHs identification is easily interfered by sample matrix and other components if only based on retention44.
Determination of leaching of elements: Al, Sb, As, Ba, B, Cd, Co, Cu, Pb, Mn, Hg, Cr, Ni, Se, Sr, Sn, Zn and elution of the Cd, total Cr, Pb, Sn, Zn from rubber granules was carried out by the inductively coupled plasma mass spectrometry (ICP-MS) method with the use of Agilent 7900 ICP-MS (Agilent Technology, Santa Clara, CA, USA). The selected method is featured by a low limit of quantification, which stands out among other instrumental methods used in elemental analysis, such as ICP-OES or AAS (Inductively coupled plasma–optical emission spectrometry or atomic absorption spectrometry). It is also featured by high sensitivity and precision, selectivity enabling the simultaneous determination of many elements in complex matrices in a wide range of concentrations.
Leachability of Cr (III) and Cr (VI) and elution of Cr (VI) from rubber granules were determined by high-performance liquid chromatography with inductively coupled plasma mass spectrometry (HPLC-ICP-MS) using Agilent 7700 Series ICP-MS with Agilent 1260 Infinity series HPLC (Agilent Technology, Santa Clara, CA, USA). The decision to use HPLC in conjunction with ICP-MS was dictated by the need to determine chromium in two oxidation states. In the case of the selected method, the speciation separation of Cr (III) and Cr (VI) takes place on the HPLC column, where Cr (III) and Cr (VI) are adsorbed. In the next step it allows for the separation and determination of Cr (III) and Cr (VI) in the ICP-MS spectrometer. The HPLC-ICP-MS method is featured by a short analysis time and a low detection limit compared to the other spectrophotometric methods used for determination of Cr (VI). The leaching of organotin compounds was assessed on the basis of the results of total Sn leaching.
Cold-vapor atomic absorption spectroscopy (CV-AAS) with the PerkinElmer FIMS 100 mercury analyzer was selected for the Hg leaching study due to the use of a unique technique of mercury vapour measurement at room temperature. Among other alternative methods of Hg determination in aqueous solutions (ICP-MS or GF-AAS (graphite furnace atomic absorption spectrometry)), the selected method is distinguished by a low limit of quantification, simple preparation of samples for analysis, easy elimination of interference and short analysis time.
Tests of the content of PAHs
Shredded samples of rubber granules were subjected to the ultrasonic extraction process for 1 h with the use of toluene as a solvent. Samples were taken from the obtained extract for chromatographic analysis. The analysis was carried out for the following conditions: dispenser operation mode: splitless, carrier gas: Helium: 1.8 ml/min, DB-EUPAH column with dimensions: 20 m × 180 µm × 0.14 µm (the 20 m column is in the form of a coiled wire), injection temperature: 275 °C. The PAHs were identified on the basis of mass spectra and retention times—Table 2.
Tests of the leaching of elements and organotin compounds
Samples of rubber granules for the study of the leaching of organotin elements and compounds were extracted in a solution of hydrochloric acid (HCl), with concentration 0.07 ± 0.005 mol/dm3 in temperature 37 ± 2 °C. Solutions for the determination the Cr(VI) and Cr(III) prepared by diluting the extraction solution to obtain the pH equal to 7.0 ± 0.5 by adding 1 ml of 0.07 mol/dm3 ammonia and 60 µL of 0.1 mol/dm3 EDTA solution. In parallel, a reagent blank was prepared, as the test samples were. The obtained extracts were analyzed by ICP-MS and HPLC-ICP-MS. The analyzes were performed for the isotopes of the elements: Al—27, Sb—121, As—75, Ba—137, B—11, Cd—111, 112, Cr—52, 53, Co—59, Cu—63 , Pb—206, 207, 208, Mn—55, Hg—201, Ni—60, Se—78, Sr—88, Sn—118, 120, Zn—64, 66.
Tests of the leachability of polycyclic aromatic hydrocarbons (PAHs) and elements
Determination of the dry mass of the rubber granulate samples for the leachability tests was carried out in accordance with ISO 11465:199945using a drying oven (Pol-Eco-Apparatus SLW-115 Top, Wodzisław Śląski, Poland) and analytical balances (SARTORIUS, Kostrzyn Wlkp. i Radwag, Radom, Poland).
The rubber granulate samples were dynamically washed with deionized water according to EN 12457-4:200246 providing a ratio of 1 ml of liquid to 1 g of rubber granulate. The pH value of the water used for dynamic leaching did not exceed 6.7. Elution was performed using a bottle/tube roller mixer (Thermo scientific model, Thermo Fisher Scientific (China) Co., Ltd., Shanghai China). After washing, the effluents were left for 15 min and then filtered through 0.45 mm membrane filters using a pressure filtration device.
The leachate obtained from dynamic leaching was subjected to the process of transferring PAHs from the water phase to the organic phase using the algorithm:
SPE column: C18 bed—6 ml/1000 mg;
activation: 10 ml of methanol, 10 ml of methanol:water (40:60) (v:v), flow: 1 ml/min;
sample:eluting solution of methanol (100 ml:10 ml), flow: 0.5 ml/min;
drying: minimum 15 min, maximum flow;
elution: 3 × 3 ml of dichloromethane, flow: 0.5 ml/min.
Collected filters were evaporated using a vacuum evaporator (IKA RV 05 basic, IKA WERKE GMBH & CO.KG, Staufen) up to 1 ml. Evaporated filters were subjected to the chromatographic analysis performed for the conditions as for the determination of PAHs content. The content of eluted PAHs and elements was related to dry mass of the rubber granulate in each sample.
The devices were calibrated and checked on a current basis, including the analysis of control samples, before starting the measurements. Calibrations of the chromatograph, spectrometer and mercury analyzer were performed on solutions of certified reference materials and 2 control samples. The correlation coefficients obtained during the calibration were above 0.995 for all analyzed substances. The analysis of the control samples confirmed the accuracy of the calibration curves, which are the basis for the calculations. Measurements of the content/leachability of the tested substances were carried out for two parallel samples and a reagent blank sample, taking into account the results obtained from it in the analysis of analytical samples. The arithmetic mean of two parallel determinations was assumed as the result of the analytical measurement. Content/leachability conversions of test substances were performed using the GC–MS/MS MassHunter Workstation Software, LCP MHLauncher HPLC-ICP-MS and ACP-MS software and WinLab32 with an AA mercury analyzer FIMS100.