Benoit Lab

Other

Analysis of shredded tire material used for athletic fields and playgrounds to determine possible health risks

This project is for identification of organic compounds found in crumb rubber and which may be released by leaching with dichloromethane, simulated acid rain or via direct volatilization.  Compounds will be identified qualitatively on all samples, and some compounds will also be quantified on selected samples.  Measurements will be made via gas chromatography-mass spectrometry (GC-MS) by methods detailed below.  Three separate kinds of measurements will be made: (1) total organics extractable with dichloromethane solvent, (2) organics extractable with simulated acid rain, and (3) volatile compounds evading from crumb rubber into the gas phase.  At least 20 different will be analyzed by the three methods.
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Samples are air dried for 3 days, ground in a freezer mill, and passed through a #60 mesh sieve.  The fine fraction (smaller than 60 mesh [250 µm]) will be extracted in parallel with the unground bulk crumb rubber, as the extraction efficiency is anticipated to be dependent on accessible surface area.  Weighed 2 g samples will be added to 30 ml dichloromethane in 40 ml borosilicate glass tubes and placed on a shaker within a fume hood.  Samples will be taken after 30 min and again after three days.  The short term extraction should simulate more immediately accessible contaminants while the long term extraction may be more indicative of maximum contaminant release.
 
Aliquots of filtered extracts are injected in to the inlet of the GC-MS oven, and separated on a 30 m DB-5MS column with a program reaching a maximum temperature of 300 °C.  Library matching (NIST) will be perform and qualitative analysis made, looking especially for organic compounds which have been documented in other studies.  Some of the key compounds will be quantified.  This will be done by introducing known amounts of pure compounds dissolved in dichloromethane to establish a calibration curve for the GC-MS in quantitation mode.
 
In the acid rain leaching study, dried samples will be exposed to a solution designed to simulate acid rain in the Connecticut area.  This solution will have a pH of 4.0 and be composed of equi-molar amounts of nitric and sulfuric acids (approximately 0.1 millinormal of each).  Samples will be extracted with a 3:1 ratio of acid solution to rubber in glass vials on a shaker bath.  Aliquots will be drawn after one hour and 3 days to simulate short and long term contact between rain and the crumb rubber.  After leaching, solutions will be back extracted and concentrated into an immiscible solvent for injection into the GC-MS.
 
In the volatilization part of the project, 1.0 g of air dried crumb rubber will be transferred to a glass, 2mL automated liquid sampling (ALS) vial.  The vial will be crimp-capped and the septum pierced with an SPME needle (Sigma-Aldrich brand or equivalent). The SPME fiber will be exposed for one hour to the headspace over the crumb rubber while the vial is warmed in a heating block to 60 °C.  At the end of this period the SPME fiber will be removed from the vial and desorbed in the inlet of a gas chromatograph (GC, Hewlett Packard model 6890) at 260 °C.  For a few crumb rubbers, samples will be analyzed after exposures of 1, 2, 4, 8, 16, and 24 hours, to determine the relation between exposure time and volatilization.  If appropriate, a longer exposure sample will be collected for all crumb rubber samples.
 
This project is being funded by the Lattner Foundation
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