You Watch Isn't Poisoning You With PFAS

The science behind some truly ridiculous headlines.

Photo by Daniel Cañibano on Unsplash

PFAS - a broad term that describes a group of chemicals - are the new villain when it comes to environmental health. There is a story almost every week about some new study that has found PFAS in something. And there are real concerns about these chemicals - they are very persistent in the environment, they have some associations with ill health, and they are quite hard to get rid of which means they get into everything.

The problem with the PFAS story, however, is how overboard much of the concern has gotten. It seems like all you need is to mention that we’re being exposed to PFAS in any amount through any route to get headlines across the world screaming out the danger. The recent hubbub over watch bands is a perfect example. If you believe the Guardian, New York Post, or dozens of other outlets, there is a serious risk to everyone’s health from wearing a plastic watch band.

However, the data is much less worrying than you might’ve heard. It’s possible that you’re getting exposed to PFAS through a watch band, but it’s a much smaller problem than the headlines are suggesting.

The Study

The study in question is a lab-bench piece of research where the authors took watch bands similar to this one, cut a piece off, and attempted to extract PFAS from them. The process that they used is fairly complex, but it’s not overly damaging to the watch bands. While I’m not the best person to assess PFAS extraction methods, I’ve been told by several colleagues that the methods appear fine for the type of research that they’re doing.

The authors tested a total of 22 watch bands in this experiment. They found detectable levels of PFAS in 11 of them (50%), with levels ranging from 1 to 16,662 parts per billion (ng/g). The median amount of PFAS in these watch bands was 659ng/g.

Picture: PFAS, potentially. Photo by Adrian Regeci on Unsplash

The authors argue that since another study showed that high levels of some PFAS chemicals can also be extracted by human sweat, and since there is some evidence that PFAS can be absorbed through the skin, that watch bands represent a real risk of PFAS exposure. These were highly theoretical studies - the human ‘sweat’ was synthetic, and the absorption was through synthetic ‘skin’ using PFAS dissolved in methanol - but it’s still an interesting argument.

Now, I think there is a possible issue here. The links between ill health and PFAS aren’t nearly as strong as people often present them, but they are certainly concerning. The reason that PFAS became so ubiquitous in our ecosystem in the first place was that people put them in a lot of things and then those things went into landfills and the water system. Ideally, we should be thinking about reducing the levels of PFAS in many of our products if for no other reason than we don’t want them to keep bioaccumulating everywhere.

That being said, the numbers here simply don’t add up. Let’s do a bit of worst-case math.

One of the most popular of this type of watch bands is the Apple watch band. It’s hard to find exact weights for these bands online, but there seems to be a consensus that the fluoroelastomer bands are around 30-40grams. Now, these watch bands are very durable. I haven’t worn one in a long time, but the last time I did it lasted at least a couple of years. But for our worst-case scenario, let’s assume that you have highly acidic sweat that dissolves the entire band over the course of the year.

We’re also going to ignore the fact that most sweat runs off your body, and thus would carry any dissolved PFAS with it. We’ll assume that the 50% rate of PFAS absorption through synthetic skin is the true rate through human skin, and ignore that of the three samples tested to see if synthetic sweat can absorb PFAS only two managed to show any dissolved substance. We’ll also use the highest amount of PFAS that the authors of our original study could detect in any watch bands. Finally, we’ll assume that you are sweating like crazy the entire time, and wearing the band 24/7.

Taking all this into account, a reasonable worst-case scenario is that the entire watch band contains 16,662ng/g of PFAS, and that this is dissolved over 365 days. Around 50% of it enters your body through your skin. This would mean that in one year this source of exposure would give you 333,240 nanograms of the 20 PFAS tested in this study would get into your body.

That sounds very scary! But is it? The daily figure of intake - around 900 nanograms - is about double the European Union’s recommended daily threshold of 4.4 ng/kg of body weight. However, it’s substantially below the Australia/New Zealand limit of 20ng/kg. Whether this is a problematic exposure somewhat depends on where you live in the world. For some context, some drinking water in European countries contains 4,100 nanograms/liter of water, so in many places you could get this level of exposure by drinking a glass from the tap.

Bottom Line

You have to remember, this is in an incredibly implausible worst-case scenario. In the real world, the average watch band takes years to degrade, and never does so fully. You’d be looking at more like 1% of the total PFAS content sitting on your skin for any length of time. There’s also a great deal of uncertainty in the question of whether this can be absorbed through your skin at all - one unreplicated study showing that it might be possible isn’t nearly sufficient data.

A more realistic estimate of the amount of PFAS that a watch band could expose you to, taking the median value of PFAS in the bands that had any and assuming that around 10% of the PFAS in the band is ever in contact with your skin, is perhaps 1,500 nanograms. Total. Over the course of years.

Even assuming you wear it A LOT, which is not necessarily true. Photo by Massimo Sartirana on Unsplash

What this study really shows is the same thing that we sort of knew already - PFAS are ubiquitous. It’s incredibly unlikely that watch bands are actually harming your health through PFAS exposure, but there are simply so many places that you can be exposed to the chemicals that it’s hard to avoid them. This is one of the reasons that the EU recently reduced their limits for drinking water from 1,500ng/kg/day to 4.4ng/kg/day - you get exposed in so many ways to these substances that the cumulative impact could be dangerous even if individual things are not.

Now, I don’t think that argument is very strong for watch bands. Being realistic, the quantity of these chemicals that you’re in contact with is minuscule, and even the hilariously implausible worst-case is close to or under guidelines for total exposure. The headlines were extremely misleading about the real risks here.

But this study does provide yet more incentive to keep working on the potential problem of PFAS. Watch bands get thrown away, which means that these chemicals are going to get into landfills, and some will leach into drinking water. Every source of exposure is important when we’re thinking of our environment as a whole.