Exploring the Environmental Impact of Tire-Derived Materials Using LC-MS/MS

In the United States, approximately 290 million scrap tires are produced each year. This substantial waste stream poses significant disposal challenges. Recycling end-of-life tires into new and alternative materials has gained traction due to the widespread availability, durability, and versatility of tire-derived rubber products. These materials are now commonly used in gardening, track-and-field surfaces, playground fill, and as additives in building materials such as concrete and asphalt. However, the environmental impact of these tire-derived materials is a growing concern. 

To address this, a research team led by Jonathan Navarro Ramos from the State University of New York at Buffalo conducted an in-depth study to evaluate the potential for these materials to produce leachate containing chemicals that could pose environmental risks. Their study utilized advanced liquid chromatography-tandem mass spectrometry (LC-MS/MS) techniques to quantify potentially toxic chemicals in simulated leachate from four widely used tire-derived materials: rubber mulch, rubber-modified asphalt, crumb rubber, and rubber aggregate. 

The team began by collecting and filtering 250 mL leachate samples from each of the four tire-derived materials. To ensure accurate measurements, they spiked the samples with isotopically labeled standards. These standards act as benchmarks, allowing the researchers to account for any potential losses during sample preparation and analysis. The next step involved solid-phase extraction (SPE) with hydrophilic lipophilic balance (HLB) sorbent material. This technique is essential for cleaning up the samples by separating the target analytes from other components in the leachate. After extraction, the samples were eluted, evaporated to dryness via an N-EVAP evaporation workstation, and reconstituted in the starting mobile phase. Before analysis, the samples were spiked with an internal standard (D10-Carbamazepine) to further ensure precise quantification during the LC-MS/MS analysis. 

The researchers focused on quantifying four key chemicals of interest: 6PPD-Quinone, N-(1,3 dimethylbutyl)N'phenyl-p-phenylenediamine (6PPD), 1,3-Diphenylguanidine (1,3-DPG), and Hexamethoxymethylmelamine (HMMM). The analysis was performed using an Agilent 6460 A triple quadrupole mass spectrometer equipped with a 1200 HPLC system. Chromatographic separation was achieved using a Restek Raptor C18 analytical column, which is designed to effectively separate the target analytes from other components in the sample. 

For quantification, the team employed isotope dilution, a technique that involves adding a known quantity of isotopically labeled standard to the sample.  

The study revealed significant findings regarding the leaching of chemicals from tire-derived materials. Notably, the researchers observed leaching of 6PPD and 6PPD-Q at levels up to 0.14 ppb in rubber-modified asphalt even after 28 days. In rubber mulch, levels as high as 3.08 ppb after 7 days and 9.01 ppb after 28 days of leaching exposure were detected. These findings indicate that tire-derived materials can leach potentially toxic chemicals over time, raising concerns about their environmental impact. 

This research highlights the potential environmental impact of tire-derived materials through the leaching of potentially toxic chemicals. The study demonstrates the efficacy of LC-MS/MS in quantifying trace levels of contaminants in complex matrices, showcasing the power of advanced analytical techniques in environmental chemistry. 

This study underscores the importance of continuous monitoring and evaluation of recycled materials to ensure their safety and sustainability. As chemists and environmental scientists, leveraging the capabilities of LC-MS/MS can provide deeper insights into the environmental impacts of various materials, contributing to more informed and responsible practices in material recycling and waste management.