Artificial Turf: Poisonous Pitches?

by Brian Dunning
October 10, 2023

Artificial turf on sports playing fields is no stranger to controversy. Normally, issues around artificial turf have to do with its costs, its durability, whether athletes perform better or worse on it, and whether athletes are more or less likely to be injured on it, all compared to grass fields. But there's another objection to it that you may not have heard of: whether or not artificial turf outgasses harmful chemicals which can impact the health of players and spectators, and also any wildlife that may be in the path of rain runoff. Today we're going to point the skeptical eye at artificial turf, to see whether they are indeed poisonous pitches, or merely fresh, fun fields.

The concern is certainly a plausible one. Artificial turf is made mainly of plastics and rubbers, and those are compounds that do outgas after their manufacture. But the variables here — and thus the complications — are myriad. All of these complications are going to center around the guiding axiom for today, which is that it's the dose that determines the poison. Any compound can be deadly in high enough concentrations — even water and oxygen. And any compound can be safe in low enough concentrations — even ricin, VX, and plutonium. So even if artificial turf puts out horribly toxic chemicals, if the amount is low enough there is no cause for concern.

The compounds coming from artificial turf include known carcinogens, neurotoxicants, mutagens, and endocrine disruptors including polycyclic aromatic hydrocarbons, phthalates, and perfluoroalkyl and polyfluoroalkyl substances (PFAS). Some of the harmful compounds are outgassed as VOCs (volatile organic compounds) and some of it is washed into the environment or can get onto a player's skin as leachate. An environmental scientist could have a field day just listing off all the compounds that come off of artificial turf. Some of this is from the crumb rubber which is shredded from used tires; some of it is from the plastic carpet fibers (basically the fake grass strands); and some of it comes from the tough plastic fiber base. Depending on the brand and type, below that may be a synthetic fabric layer to prevent weeds from growing through; below that a resilient synthetic shock absorbing layer; and below that a foundation of one or more layers of crushed concrete, decomposed granite, gravel, or sand.

All of this results in an overwhelming majority of online articles on the subject declaring artificial turf fields to be chemically dangerous, especially to children. And, of course, there are the inevitable charges of industry conspiring to put profits ahead of children's health. PFAS are universally brought up as the worst offender, so it's worth a quick sidebar to examine PFAS.

There are literally thousands of compounds classed as PFAS. They are used in countless products, and have been for some 75 years. They are one of those man-made chemicals that can be found in trace amounts virtually anywhere in the world — in wildlife, in groundwater sources and the oceans, in soil, in the air, and in plants. What's the harm to people and to wildlife? Well, you can read a thousand articles on the subject, but the answer is we just don't know yet. For decades, the National Institutes of Health, the Environmental Protection Agency, the Centers for Disease Control and Prevention, the Food and Drug Administration, and even the Department of Defense have been researching this. The only thing you can say that's accurate to sum all of this up is that PFAS are one of those things we want to reduce, but we don't really know how dangerous they might be, and at what dose they might pose a risk. There's that all-important axiom again: it's the dose that makes the poison. Your last breath included some environmental PFAS. Was it harmful to you? There's no indication that it was; but there's insufficient data to prove it wasn't.

But we do have some data. So far, every single published study on harm to people from artificial turf has found zero correlation with increased incidence of disease, and that's a very important point. We could end this episode right there, but we won't — because that's too small a data set. There have only been a few such studies, and they've only looked at cancer. And they all include that universal disclaimer that's virtually a given at the end of every published study: "More study is needed." According to all we've been able to learn so far, artificial turf does not increase anyone's risk of cancer. What are the other risks beyond that? We don't know yet.

One thing we do know about these sports fields is that they're outside, or at least inside large arenas. There is plenty of ventilation. Outside in the breeze, you're about as ventilated as it's possible to be. So let's compare this situation to another one that we're all very familiar with, and that also involves the inhalation of outgassed chemicals.

Some research was published in April 2023 about the risk assessment of VOCs in new cars, and it went viral among the automotive press. Researchers took a brand new mid-size SUV plugin hybrid and parked it outside for twelve days, logging the temperature and humidity inside and outside, and recording the VOC concentration at a number of sample points inside the car: the seats, the carpet, the dashboard, the door trim panels, and so on. Importantly, they also measured the AER: the air exchange rate, the rate at which air inside the car circulated out and was replaced with fresh air. The important results include that the VOC concentration is driven mainly by temperature; the hotter it gets inside the car, the more VOCs are outgassed. And the thing most associated with reducing the VOC concentration is — if you can guess — ventilation, the higher the AER, the cleaner the air.

So inside the environment of a new car, what exactly are the health risks of being exposed to those VOCs? They calculated the ILCR (incremental lifetime cancer risk) for taxi drivers (11 hours per day) and for passengers (1.6 hours per day), for the three compounds of most concern: benzene, formaldehyde, and acetaldehyde. An ILCR of 10^-6 or less is considered acceptable; only passenger exposure to benzene was below this level. An ILCR of 10^-6 to 10^-4 indicates low risk, and all the other metrics for both drivers and passengers were within this range, except one: the driver's risk for exposure to formaldehyde was just over 10^-4, which indicates moderate risk.

This study was something of a worst case scenario. Brand new cars outgas VOCs at a much higher rate than used cars, 80% of all outgassing is done after only three months. This study considered a taxi driver spending 11 hours a day inside a brand new car with minimal ventilation for his whole life, to achieve the moderate risk level from a single compound. Those of us who do most of our driving in cars older than three months will never, in our lifetimes, reach even the low risk level.

So this worst case scenario, sitting inside a car with no ventilation, isn't all that bad. It gives some perspective to the risk from playing a sport, or even spectating, on artificial turf, where you're not there for multiple hours every day and where you're outdoors with maximum ventilation.

This may seem like an unfair comparison, but just wait until you hear about a couple of these studies that were done, ostensibly to assess the risk of playing sports on artificial turf. In one study, chicken eggs were injected with crumb rubber leachate, and then after the chicks were hatched, they were assessed for health issues. They showed impaired development and endocrine disruption. This was intended as an analog for athletes who come into transient skin contact with crumb rubber. Clearly it's not; those chicken embryos received a dose incalculably higher than the athletes might ever. In another study — which I found particularly baffling — mummichogs and fathead minnows were placed in a solution of water and the LC₅₀ concentration of leachate (LC₅₀ is the concentration known to be lethal to 50% of test animals), and some of them died. I'm not sure what alternate outcome they expected. This study was to assess the impact of tire wear particles on fish in estuaries, yet it's frequently cited in studies of runoff from artificial turf. Unfortunately this is the quality of study that we have to deal with on this subject — as the authors all note, more and better study is needed.

We learned from the new car interior study that outgassing of VOCs decreases fairly rapidly over time, and so we'd like to know the same thing about leaching of chemicals from crumb rubber. Luckily this has been thoroughly studied. One representative publication from 2003 that assessed runoff from playgrounds found that impacts from leaching disappeared after the crumb rubber had been in place for three months. The amount of leaching is directly proportional to the surface area, and when an old used tire is shredded into crumb rubber, you're now exposing a lot of new surface area that had never been exposed before. After three months, each crumb has pretty much leached out everything it's going to. And so all of these issues with contaminated groundwater or harm to fish in nearby rivers are basically finished three months after installation — and the same goes for any hypothetical harm to athletes who have transient skin contact with the crumb rubber. Outgassing from VOCs and leaching from the rubber simply don't last long enough for any long term impacts to build up.

However, even when we have a firm conclusion based on sufficient data, that conclusion is always provisional, because more data might come out tomorrow. When that happens, the size (and thus the quality) of our data set is improved, and we can draw a new solution that's better supported. On this topic, the most accurate description of our data is that it's inadequate. We do have plenty of experience with artificial turf, and so far we have not observed any negative consequences to the health of athletes, spectators, or impacted wildlife; but that doesn't mean we won't observe such consequences tomorrow. The theory underlying the potential risk is perfectly sound, but the nature of the environments in which these fields are used mean that it's very unlikely that anybody could ever reach an exposure level that toys with our axiom of the day: it's the dose that makes the poison.

Final conclusion #1: Online claims that artificial turf presents a health risk, either to children or anyone else, are not supported by data. Final conclusion #2: That might change in the future. But unless and until it does, go out and enjoy your sports. And now you can resume arguing about all the other issues around artificial turf.

By Brian Dunning
Follow @BrianDunning