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PFOS / PFAS - Should I Be Concerned?

Yeah, probably but to be quite honest I do not know a hell of a lot about this topic, yet. But I plan to know more as I research it to write this post. My interest in writing on the topic comes about due to recent articles and news stories about per- and polyfluorinated / polyfluoroalkyl substances (PFAS/PFOS) and because of my own lack of knowledge about these chemicals and their effects. In all transparency, I am NOT a chemist or a toxicologist - though I've taken a few classes, it is certainly not my area of expertise. I hope I can write this post at a level that is informative for the "average" reader with a similar lack of expertise.

Fairly recently, the rather shocking headlines about eating freshwater fish was pretty concerning. From The Hill article, "Study suggests US freshwater fish highly contaminated with ‘forever chemicals'".

Eating just one serving of freshwater fish each year could have the same effect as drinking water heavily polluted with “forever chemicals” for an entire month, a new study finds.

Of course, that is only true is you are eating fish from PFAS / PFOS contaminated streams or lakes. In Wisconsin, the contaminated places that have made the news are somewhat limited - the Tyco Fire Products plant in the Peshtigo area, Madison around the Dane County Airport and Starkweather Creek, French Island / Town of Campbell near La Crosse, and Fort McCoy - at least as far as we know right now. This is probably not a comprehensive list and more information about contaminated sites and news as well as fish consumption advisories for PFAS are on the WDNR PFAS website. The good news is that contamination (that we know about) is generally rather concentrated around airports and PFAS manufacturing facilities.

The human health effects of PFAS include reduced fertility, increases in some cancers, developmental delay in infants and children, increased cholesterol and obesity, and a reduction in immune system response. There is a lot not yet known about these chemicals - hence the reference to them as "emerging pollutants" or other such names that indicate the fact that their widespread use is much greater than our understanding of their impacts. That seems to be a common theme - we put stuff into the environment before we know what their effects are likely to be. Our history with DDT, PCBs, BPA, and a number of other pollutants are evidence of this.

What Are PFAS / PFOS?

Unless you have been on Mars for the past couple of years, you have heard about these "forever chemicals" and like me, you probably do not know a lot more than that they are an "emerging pollutant" and a "forever chemical". Where we have heard most about PFAS has been associated with fire fighting foams but they are also in a number of non-stick chemicals like Teflon and thousands of water resistant applications. Maybe you remember some chemistry "from back in the day" and remember that fluorine has the highest electronegativities of the reactive elements (FONClBrISCH). This means that fluorine is good at "stealing" or "unequally sharing" electrons of other elements. It's an oxidizing agent and as you may remember, rust is oxidation. PFAS / PFOS are organoflourine compounds meaning that they contain carbon-fluorine bonds which is a strongly polar covalent bond.

Space-filling model of a PFOS.
Space-filling model of a PFOS.

PFAS / PFOS are a collection of thousands of compounds - probably the best known of these is Teflon (Polytetrfluoroethlene). These chemicals have a wide range of industrial uses due to their water-repellent characteristics. They have the unique property of being both hyrdophobic and lipophobic meaning that they repel both water and fats (most substances do one or the other). They are used as water repellents and in polishes, paints, and other surface coatings thus they are plentiful in the environment. Much of the large-scale environmental contamination is associated with the manufacturing and use fire fighting foams and airplane deicing sprays which is why contamination has often been associated with airports.

Probably the most frightening parts of PFAS for most people is their persistence in the environment - "Forever Chemicals" - and the fact that their effects are seen at such low concentrations. For many environmental toxins, state standards are milligrams per liter which is almost exactly 1 part per million. PFAS concentrations as low as 1 part per trillion (1 trillion = a million million or 1,000,000,000,000). Wisconsin raised quite an outrage when they set the state drinking water standard at 70 parts per trillion - several thousand times higher than EPA health advisory recommendations of 0.004 parts per trillion for PFOA and 0.02 parts per trillion for PFOS.(WPR News).

For more reading, just about every state and federal acronym agency you can think of has an interest in PFAS compounds.

Fish Consumption Advisories

This being mostly a fisheries science blog, let's get back to the fishes...

States maintain fish consumption advisories as a public health service to residents and because it is regulated by law. A few important things to understand about fish consumption are that women of childbearing age and children are most at risk - in large part to to smaller body sizes - and that there are significant health benefits of eating fish including omega-3 fatty acids and that they are a source of "good fats". In fact, some archeologists and evolutionary biologists have linked Homo sapiens and Homo neanderthalensis eating of fish and shellfish with brain development (Klein and Bird 2016 and sources within). In terms of their contaminant concentration, not all fishes are created equal. Larger, longer lived predatory fishes will biomagnify some toxins and benthic (bottom-dwelling) fishes may have greater concentrations of some toxins. Lastly, how fish are butchered and cooked can have an effect on toxin concentrations. Removing the fattiest parts of fishes (most toxins are fat soluble and concentrate in fatty tissues) and cooking them in ways that allow fat to leave the fish - like grilling and smoking - can reduce the amount of toxins that are consumed.

Dall-e2 generated Mad Hatter image
Dall-e2 (Open AI) generated Mad Hatter image

In most Midwestern states, methylmercury and PCBs (polychlorinate biphenols) are responsible for most fish consumption advisories. Mercury is an interesting and complicated environmental toxin. Methylmercury is created from the interaction of microbes and elemental mercury, particularly at lower pH levels. Mercury is a neurotoxin - hatters were "mad" because they used mercury compounds to make felt and the Lewis Carroll character was based on Mad Hatters of the day. Over-consumption of mercury can lead to Minamata disease which is named for the Japanese city where it became common due to pollution from a chemical factory that lead to elevated mercury in fish and shellfish. More common effects of mercury are developmental delays in infants, cardiovascular disease, autoimmune disease, and neurological impacts. PCBs are no longer produced in the US but their legacy continues. They were manufactured largely for their ability to transfer heat and were widely used in electric transformers. Like mercury, PBCs bioaccumulate and biomagnify and have neurological and endocrine disrupting effects.

PFOS advisories are relatively recent additions to most state's fish consumption advisories and they tend to be more localized than the advisories for mercury and PCBs - though large sections of the Mississippi and Wisconsin Rivers have PFOS advisories as does Green Bay and Lake Superior. While mercury is more commonly a problem in marine fishes (CITE), PFOS is largely a localized and freshwater issue as are PCBs but at a much larger scales - currently. PFOS seem to have an effect at much lower concentrations, however we admittedly know relatively little about the long-term effects of the consumption of water or fishes containing PFAS/PFOS. Not surprising given that these chemicals and our understanding of their effects are relatively new.

Are Fish Safe and Healthy to Eat?

This, I think, is a more difficult question than it looks at face value. Like most things, I think that the answer is, "Yes, in moderation". I write this as I sip from my Tanqueray and tonic, another toxin I put in my body, usually in moderation. Why this is such a difficult question is largely because studying anything in a large population of humans is problematic at best. Knowing that the effects - which themselves can be hard to measure - are due to eating fish and not other environmental or genetic factors is really difficult. Many of the effects of mercury or PCBs are neurological and measuring the development of children or loss of a few IQ points and linking that to a specific source is nearly impossible. Only at the extremes of toxin consumption are the effects likely to be clear and obvious. While I understand how difficult research questions are in ecology, I have to assume that public health and dealing with humans is likely twice as complicated.

Ramps and Brown Trout
Ramps and a couple of small, plentiful Brown Trout are destined for the grill. Mmmm, ramps and taters.

Fish and shellfish consumption have significant health benefits which is part of the reason that fish consumption has significantly increased in recent decades. As I mentioned above, there is some evidenced that hominid evolution was shaped by the consumption of fish and shellfish (Klein and Bird 2016). While we have certainly heard about the benefits of omega-3 fatty acids, which we are unable to synthesize but can only obtain through our diets. Fishes are an important source of antioxidants, they help in neuroprotection - in fact, there is evidence that they protect against the effects of mercury (Nøstbakken et al. 2012) - and they have a host of other health benefits including liver protection which may offset my gin and tonic. More anecdotally, some of the longest lived human populations are from places like Japan and the Mediterranean where fish consumption is well above worldwide averages.

Source: (Creative Commons).

With all the benefits - and there are many more than I listed as I try to keep these posts relatively short and consumable - there are obviously risks associated with eating fish. The dose makes the poison - and in this case, it is a chronic toxin that is accumulates over time as opposed to an acute toxin that has more immediate effects. Some fishes concentrate more toxins than others - the general "rules" are that toxins accumulate over time, are dependent upon what they eat, and where they live. This is why the fish consumption advisories are almost always organized by species and the frequency of consumption as well as their location. (see the end of the post for fish consumption guides)

In general, there are two types of consumption; eating the fishes you or other catch near your and eating those from commercial sources. Neither is necessarily better than the other. Many marine fishes are high in mercury but so too are some fishes from northern Wisconsin lakes. A study of Wisconsin male anglers that were older - over 50 years old (ouch!) - showed that they ate more than one meal of fish per week and had higher blood mercury levels than the average US population (Christiansen et al. 2016). Now, none of that says that those keeping and eating fishes that are relatively high in mercury or PFOS/PFAS are seeing negative effects of that consumption. Again, with so many other toxins out there, pinpointing medical issues to consumption of something like fishes is rather impossible. As we should all know, correlation does not imply causation. Likewise, a lack of a measured effect does not mean that there is not an effect. Many of the effects of toxins are sub-lethal - like loss of a few IQ points - and are rarely measured.

Maybe one of the most interesting unknowns are how different toxins may have synergistic effects on human health (Gandhi et al. 2017). It is not just what we are consuming fishes with some mercury and/or PFOS but we are ingesting, breathing in, and in contact with any number of other chemicals. Take this year for example and all the air exposure advisories due to wildfires and their smoke. There is every little known about how these things interact with one another.

I think that the last part of this question should be an ecological / environmental one as well. Done correctly, fishes can be harvested in a sustainable way that provides an excellent and healthy source of protein. I have certainly written in different ways about regulations on this blog and how the harvest of abundant smaller trout would likely benefit many Driftless streams. Of course, harvest is not always done in a responsible manner. We are seeing the overfishing of our oceans and fishing down the food web. Because the larger, more desireable fishes like Atlantic Cod (Gadus morhua) and some of the tuna species like bluefin tuna (Thunnus spp.) have been overfished, we are harvesting species that were historically less commercially desirable. This makes choosing healthy and sustainable fishes more difficult. Places like the US Food and Drug Administration and some of the aquariums have lists to help with those choices.

It is a complex issue with few simple answers. Broadly, most people are likely eating well within the proper range. Women of childbearing years and those caring for children should certainly be conscious of their consumption. I am sure we will know much more about PFOS/PFAS in the future and will better understand those risks. Our current lack of knowledge is certainly one of the most significant issues at this point in time. Fear of the unknown is rather justified much of the time.

As always, comments are appreciated and I am happy to share peer reviewed literature.

Literature Cited

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