Correlative SEM–Raman Microscopy of Inhalable Particles Sampled during Indoor Football on Artificial Turf with Crumb Rubber and Olive-Stone Infills
This study utilizes correlative SEM–Raman microscopy to demonstrate that while replacing crumb rubber with olive-stone infill in indoor artificial turf alters the composition of airborne particles by introducing bioaerosols and increasing particulate matter concentrations, it does not eliminate inhalation exposure, thereby highlighting the need for comprehensive chemical and biological characterization of sustainable materials.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
When we think of the air inside a sports hall, we often imagine the breath of athletes and the dust kicked up by their shoes. We rarely consider the ground beneath them. Artificial turf, the synthetic grass that covers many indoor football pitches, is held in place by a layer of small granules known as infill. For decades, the standard choice has been crumb rubber, tiny pieces of recycled car tires. Recently, as concerns grew about the chemicals in tires, some facilities have switched to "greener" alternatives made from crushed olive stones and sand. But a critical question remains: when players run and slide on these surfaces, what actually becomes airborne? Does swapping a tire-based material for a plant-based one make the air safer to breathe, or does it simply change the type of dust we inhale? This question sits at the intersection of material science and public health, focusing on the invisible particles that can travel deep into our lungs.
A team of researchers set out to answer this by watching two indoor football halls in Norway during actual matches. One hall used the traditional crumb rubber, while the other used the crushed olive stone mixture. They did not just measure the total amount of dust; they wanted to know exactly what that dust was made of. To do this, they collected air samples while games were being played and then used a powerful combination of microscopes. First, they took high-resolution photographs of the individual particles trapped on their filters. Then, using a technique called Raman spectroscopy, they shone a laser on those same particles to read their chemical fingerprints, identifying whether a speck was rubber, stone, plastic, or something else entirely.
The results revealed that both types of flooring release significant amounts of particles into the air during play, but the composition of that air is very different. In the hall with the olive stone infill, the air was filled with particles derived directly from the stones themselves. These stone particles were found indoors but were absent from the outdoor air, proving they came from the turf. Surprisingly, the total mass of dust in this hall was much higher than in the rubber hall. The researchers also discovered that the organic nature of the olive stones allowed fungi to grow on them. They found spores from two types of mold, Aspergillus and Penicillium, in the air of the olive stone hall. These biological particles were not found in the hall with the rubber infill, suggesting that the "natural" material introduced a new kind of health risk: the potential for breathing in mold spores.
In the hall with the crumb rubber, the air contained particles made of rubber, but the researchers faced a challenge in pinpointing their source. Because the rubber in the turf is chemically identical to the rubber worn off car tires on nearby roads, the particles from the turf looked exactly the same as the pollution drifting in from the city. However, the data suggested that the rubber hall was still releasing its own share of rubber dust, likely mixed with the background traffic pollution. The total amount of dust in this hall was significantly lower than in the olive stone hall, and the air contained far fewer biological contaminants.
The study challenges a common assumption: that a biodegradable, plant-based material is inherently safer to breathe than a synthetic one. The findings show that replacing crumb rubber with crushed olive stones does not eliminate particle exposure; it merely shifts the profile of the hazard. Instead of rubber dust, players in the olive stone hall were breathing in stone dust and, potentially, mold spores. The researchers noted that the olive stone hall had a much higher concentration of inhalable dust overall, reaching levels that exceed the World Health Organization's daily safety guidelines for particulate matter. In contrast, the rubber hall had lower dust levels, though it still contained tire-derived particles.
Ultimately, the work demonstrates that swapping one material for another without understanding the full picture of what gets released into the air can lead to unexpected consequences. The "green" alternative introduced biological risks that the synthetic version did not have, while the synthetic version carried chemical risks associated with tire wear. The researchers concluded that sustainable alternatives should not be assumed to be safer without rigorous testing of their chemical and biological emissions. In the context of indoor sports, the ground beneath the players is not just a surface to play on; it is an active source of the air they breathe, and changing its composition changes the air itself.
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