April Showers

 

  You've probably heard the old adage, "April showers bring May flowers." Well, it's April, and some of you may not have seen the rain yet, and some of you may have already seen more than enough, but either way, there's no debating that it is one of the most important things that happens on our planet. Water is, of course, essential for all life on Earth, and it is for this reason that rain has always been associated with the bringing or renewal of life. Whether filling our streams and lakes or watering our crops, ancient man saw rain as a gift from the gods. And who hasn't felt after warm spring rain that the world is not somehow renewed? After all, what can be more clean or pure than the water that's falling from the sky? Well, it turns out... a lot.

    The unfortunate fact is that we may have already, possibly permanently, contaminated the world's rainwater with toxic "forever chemicals." These chemicals, known as PFAS, or per- and polyfluoroalkyl substances, can be extremely persistent in the environment. They are used widely in both industry and everyday applications, largely to prevent one thing from sticking to another, and are commonly found in food packaging, non-stick cookware, cosmetics, and waterproofing and stain-proofing for textiles. The most familiar are PFOA, or perfluorooctanoic acid, widely known for being used in Teflon, and PFOS, or perfluorooctanesulfonic acid, the functional ingredient in Scotchgard. The use of both of these chemicals has now been eliminated (in the US) due to the numerous adverse health effects associated with them, including endocrine disruption, liver damage, reproductive and developmental disruption, and cancer. For example, it was recently shown that those with high levels of PFOS in their blood were 4.5 times more likely to develop liver cancer. Newer alternatives in the same class of materials are now in use, but unfortunately, it is likely that these substances have many of the same deleterious effects as the old ones. 

    The real issue with this class of chemicals is not just that they have clear negative effects on living systems but, again, the fact that, once in the environment, they persist almost indefinitely. This allows them to become widespread throughout the environment, and they are now found virtually everywhere. One recent study found that all of the world’s rainwater contains detectable levels of PFAS. Even more disturbing is that the concentrations of PFAS in rainwater often exceed the newly revised U.S. EPA advisory levels. In June of 2022, the EPA lowered what it considered to be a safe exposure for PFOA and PFOS after finding, among other effects, that these substances suppressed vaccine response in children. They revised the level from 70 ng/L (nanograms per liter) for a combination of both to just 4 pg/L (picograms per liter) for PFOA and 20 pg/L for PFOS (note that these are extremely small concentrations and the strictest recommendation of any country, but suggest that the U.S. EPA believes them to be highly toxic). Unfortunately, studies show that even rainwater from the remote Tibetan Plateau exceeds the recommended level for PFOA at 55 pg/L, or 14 times greater, and concentrations for both are exceeded in rainwater from both rural and urban environments around the world.

     Even countries with much lower standards are violated by rainwater concentrations. Researchers found the concentration of 4 common PFAS (PFOA, PFOS, (PFHxS) perfluorohexanesulfonic acid, and (PFNA) perfluorononanoic acid) in rainwater often exceeds the Danish EPA’s standard of 2 ng/L for drinking water for the combination of the 4. To put this another way, the Danish EPA would not consider much of the world's rainwater safe to drink. Of course, the environmental implications are clear. While we may be able to treat rainwater to remove these PFAS and make it safe to drink (maybe), this does nothing for the water falling onto our soils and crops and flowing into our lakes, rivers, and streams, as well as the rest of the world's environments. With adverse effects on us and presumably all other life as well, there is a good chance that we are creating a significant environmental problem that we can do little to fix. With thousands of different PFAS being produced in the millions of tons per year, it's a problem that is growing with each passing year.

     So, as I mentioned before, the production and use of PFOA and PFOS have been nearly completely eliminated in the US, but the production of both of these still continues in other countries. American companies have switched to new alternatives. These are essentially extremely similar compounds, but they are made of shorter-chain fluorocarbons. Let me explain. PFAS are very similar to the more familiar hydrocarbons. Carbon can be strung together in chains. Like this: C-C-C-C. This is four carbon atoms bonded together. Carbon has four positions in which it can bind to other elements. In this example, if those sites are filled with hydrogen, you get C4H10, otherwise known as butane. So, carbon and hydrogen together, hence the name hydrocarbon. Fluorocarbons have the same basic structure, but the hydrogen is replaced with fluorine. So we could have C4F10, which is called perfluorobutane. PFOA has a chemical formula of C8HF15O2, which is a lot more complex but follows the same basic structure. We can see that PFOA has 8 carbon atoms, and these are all arranged in a line like this: C-C-C-C-C-C-C-C. It's extremely durable (persistent) because of the fluorine bound to most of the carbons. It causes severe health issues because it takes a long time to be broken down in the body. When it breaks down, it forms shorter-chain PFASs, which are eventually expelled. The new products being used are shorter-chain versions of the old ones. For example, Dupont stopped using PFOA in the production of Teflon, replacing it with a chemical they call GenX. GenX is functionally the same as PFOA except instead of 8 carbon atoms, it has 3. From the standpoint of human exposure, these shorter-chain PFAS are "safer". The short carbon chain means that GenX is in the body for much less time than PFOA, reducing its health effects.

 

    On the surface, this seems like a solution, but there is a catch. Not only have many short-chain PFAS been shown to have similar effects as the long-chain, but they may be even more persistent in the environment. Additionally, due to their smaller size, they are much harder to remove from drinking water. This is why finding widespread PFAS in the world's rain is so concerning. Any long-chain PFAS that we consume will stay in our bodies for years (half-lives are as long as 3 years for many). Short-chains have half lives of just a few days, but with widespread contamination of the world's water and the difficulty in removing them, our near constant exposure to these short-chain PFAS may do just as much harm as their long-chain cousins. I've alluded to this before, but this problem is far-reaching. You may be safe if your drinking water is properly treated, as long as you avoid eating any naturally irrigated crops (plants also take up PFAS from the rainwater they utilize) or eating animals that eat plants or fish that live in water. In fact, a recent study found that eating a single serving of freshwater fish could expose you to PFOS levels equivalent to drinking contaminated water for a month.

 

    Now that you are thoroughly horrified that everything you consume has PFAS in it (it does), what do we do about it? Well, for the PFAS already released into the environment, there's really little we can do. It will continue to cycle around the environment for decades, maybe centuries, until it is finally broken down or sequestered. The real issue is that we are still producing huge quantities of these chemicals and that this continued production only adds millions of tons more PFAS into the environment. The only thing that we can do is ban the use and production of this class of chemicals ASAP. Without drastic action such as this, the concentrations of PFAS in our rain, our food, and within us will only increase. Steps are being taken. One of the largest manufacturers of PFAS, 3M, will end production of these chemicals by the end of 2025. However, their production will likely continue for decades without some sort of international agreement similar to the Montreal Protocol, which banned the use and manufacture of ozone-depleting CFCs. 

References:

Cousins, I. T., Johansson, J. H., Salter, M. E., Sha, B., & Scheringer, M. (2022). Outside the safe operating space of a new planetary boundary for per-and polyfluoroalkyl substances (PFAS). Environmental Science & Technology, 56(16), 11172-11179

Barbo, N., Stoiber, T., Naidenko, O. V., & Andrews, D. Q. (2023). Locally caught freshwater fish across the United States are likely a significant source of exposure to PFOS and other perfluorinated compounds. Environmental Research, 220, 115165.