This weekend I was out at the soccer park coaching my daughter's soccer team. Like many soccer players these days my daughter plays almost exclusively on synthetic turf fields. While I'm the coach, many of our team's parents know that I am also an environmental chemist. You can probably guess the question I heard most this weekend: Is this turf safe for my kids?
The basis for this question was a series of reports in the local media (The Province, CBC etc.... ) about the possible cancer risk associated with turf fields. The basis for these reports was a short documentary on ESPN called "The Turf War" by Julie Foudy. The documentary presents some strong anecdotal evidence that something may be making soccer goalies sick and hypothesizes that this is caused by those little rubber tire crumbs used on synthetic turf.
As a chemist, the suggestion of a risk associated with an inert material like shredded tire crumbs seemed chemically implausible, but having seen the documentary I chose to do a bit more research. What I found reassured me. The toxicological research on the topic was pretty much unanimous in saying that rubber tire crumbs do not appear to pose a significant risk to players. As one study put it:
Outdoor and indoor synthetic turf fields are not associated with elevated adverse health risks...cancer and non-cancer risk levels were at or below de minimis levels of concern.
For those of you who have read my writing you will remember that a de minimis risk is a risk that is sufficiently small that risk assessors and toxicologists agree to essentially ignore it.
So the question arises: Why all the fuss? Well the answer is one of risk communication and a misunderstanding of chemistry.
When analytical chemists were asked to investigate the crushed rubber crumbs, they did what chemists do and looked at the composition of the material. They recognized that the rubber was pretty much inert. That means it does not react chemically in normal conditions. To analyze the material they thus had to undertake what the EPA calls "aggressive" extractions. For the metals they do something called "microwave mineralization" while for the polycyclic aromatic hydrocarbons they typically do a "soxhlet extraction". Doing these tests they found a number of contaminants of concern which opened this Pandora 's Box of concern.
The problem is that these analytical tests do not mimic natural processes. For the non-chemists out there you can imagine these analyses as the equivalent of a prison-break. High security prisons contain some of the most dangerous people in the world. Each prisoner poses a real risk to your health but as long as the prison is secure the risk posed by these prisoners to the general population is minimal (a de minimis risk). A soxhlet extraction is the equivalent of tearing out the fences, walls and bars from the prison to let the prisoners free. In real life we don't typically see people tearing down prisons to release the prisoners and at the soccer field we do not see the rubber crumbs exposed to a soxhlet extraction.
Some might ask: well our stomachs are pretty aggressive at breaking down organic molecules? Well the toxicologists have tested that out as well. When the crumbs were tested with synthetic digestive fluids the contaminants had zero or near-zero bioaccessibility. That means that our bodies cannot access the contaminants locked in those crumbs.
Online, I have seen a number of people point out that the Material Data Safety Sheet (MSDS) for the crumbs recommends that people spreading them wear respirators. Ironically, the primary reason for that is not the rubber crumbs but rather an additive included in the material to make it spread more easily: Talc. Yes talc the white dust you use to dry babies' bottoms before putting on diapers. Talc is what is called a respirable particulate and when inhaled in large quantities is a Class 2B possible carcinogen, thus the requirement for respirators.
A bit ironic that the only bioaccessible possible carcinogen in the tire crumbs is the same material we use to keep babies' bottoms dry?
I think the Toronto Department of Human Health put it best when describing the risks of turf fields:
Third generation artificial turf is not expected to result in exposure to toxic substances at levels that pose a significant risk to human health provided it is properly installed and maintained and users follow good hygienic practices.
You will notice the final warning about hygiene? Well that is there because another risk these fields have is that they may get a build-up of bacteria. In BC, where our fields see a lot of rain, this is not a major issue, but in summer it might help to rinse the fields regularly to keep them clean. Even in summer, however, the research indicates that the fields aren't as bad as some would have you believe.
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