鈥淣ot everything that can be counted, counts, and not everything that counts can be counted.鈥� That quote is commonly attributed to Einstein although there is no evidence he ever said it. Even if he did, he certainly didn鈥檛 have toxicology in mind. But the concept is very relevant to toxicology, especially these days when substances can be detected at the part per trillion level. How small is a part per trillion? That would be 1 cent in 10 million dollars or one second in 32,000 years, which is longer than human civilization. Detection of substances at such trace amounts is a feather in the cap of analytical chemists. But that feather can stir up some dust. And that dust can contain a host of perfluoroalkyl substances, or 鈥淧FAS.鈥� Potentially nasty stuff!
Analyze some household dust and there they are. They are also in our air, our food, and in our water. More disturbingly, in our bloodstream. They have been there for decades, we just didn鈥檛 know it since our analytical capabilities were limited to the parts per billion level (ppb), a thousand times larger than parts per trillion (ppt). Industry has been producing these chemicals for some eighty years on account of their great practical utility. PFAS are resistant to moisture, oil and assorted 鈥渄irt.鈥� They can be found in water-repellant clothing, grease-resistant pizza boxes, stain-resistant furniture, soil-resistant carpets, nonstick cookware, personal care products, paints, ski wax, dental floss, electronics, construction materials and fire fighting foams. Their usefulness is beyond question, but there is a question, a significant one, about their impact on the environment and on our health.
Fluorine atoms form very strong bonds to carbon, and these perfluoroalkyl substances have many such bonds. Indeed, it is the presence of fluorine atoms on the periphery of these molecules that accounts for the desirable properties. But the strength of the carbon-fluorine bonds also makes PFAS resistant to breakdown in the environment, which is why they have been labeled as 鈥渇orever chemicals.鈥�
Look for them, and you will find them. Test just about any sample of water anywhere, and as long as the testing equipment (liquid chromatography tandem mass spectrometry) is sophisticated enough, there will be some PFAS detected. This is usually expressed as nanograms per liter, which is equivalent to parts per trillion. How do these substances end up in water? A myriad ways. Just ask yourself where the nail polish, shampoo or shaving foam you used go. Down the drain. How about that hamburger wrapper, microwave popcorn bag, or stain-resistant carpet you no longer want? They go to a landfill from where their PFAS content can leach out into waterways and into crops if that water is used to irrigate fields. Then of course there are the manufacturing plants all over the world that either produce or use PFAS, some of which inadvertently or callously is discharged into water. Wastewater treatment plants can remove PFAS, but the contaminated sludge can end up as fertilizer, providing another entry point of PFAS into our food supply. It comes as no surprise then that some PFAS can be detected in almost everyone鈥檚 blood. There they can be 鈥渃ounted鈥� but the critical question is whether they 鈥渃ount, when it comes to affecting our health. In some cases, depending on extent of exposure, they may. Determining to what extent is extremely challenging.
There are many issues. To start with, PFAS represent a large family of substances that have a common feature in that they contain lots of fluorine atoms, but the skeleton to which these are attached can vary from a few to a long chain of carbon atoms. The properties of one PFAS, including its potential toxicity, can vary dramatically from that of another. Over 8000 of these compounds have been produced and some 600 are in common use. As far as toxicity goes, studies have mostly focused on PFOA (perfluorooctanoic acid) and PFOS (perfluorooctane sulfonate), historically the most widely used PFAS, both of which have been banned from production. So at this point, just determining that a sample of drinking water, or some food, contains PFAS, cannot give us a complete picture of toxicity. It is a question of which specific ones are present and what is known about them, which unfortunately, isn鈥檛 much. Still, it is reasonable to assume that we would rather not have these chemicals find their way into our bloodstream.
There are essentially three ways to get a handle on the potential toxicity of a substance. There are 鈥渋n vitro鈥� studies, in which the effects of a chemical on living cells are investigated. Animals, mostly rats or mice, can be fed varying doses of the substance, but since humans are not giant Petri dishes, and mice are not tiny humans, there is always inherent uncertainty in extrapolating results to people. Since ethically, people cannot be experimented upon, data has to be drawn from epidemiological studies. This can involve examining workers who because of their occupation are exposed to the substance in question, generally at much higher doses than the population. Perhaps the most meaningful information comes by testing blood samples from a cross-section of the general population to see whether the presence of specific substances is associated with disease.
The in vitro studies show that PFAS can disrupt cell function in various ways, and animal feeding studies suggest developmental toxicity, liver toxicity, and possible immune system effects, although at doses higher than what humans are generally exposed to. The most concerning data come from associations between PFAS in human serum samples and disease. Serum is the liquid left when blood cells are removed, and can be analyzed for the presence of various chemicals. Numerous studies have shown an association between higher blood levels of PFAS and impaired thyroid function, liver disease, kidney cancer, reproductive problems, reduced immune function, obesity, and an increase in blood cholesterol. As usual, we have to note that an association cannot prove cause and effect. Confounding factors are always possible. Perhaps people have higher blood levels of PFAS because they are eating more processed foods and it is poor nutrition that is causing the health issues. Nevertheless, taking everything into account, a strong case can be made for reducing any exposure to perfluoroalkyl substances.
Regulating agencies around the world are looking at tap water as a significant route of exposure with a view towards limiting the amount of PFAS that can be present. The numbers being tossed around are in the range of 30-70 nanograms per liter, with Canada targeting the lowest figure. Samples taken across the country are generally below 30 nanograms per liter, but there are locations where the concentration can be up to 80-100. Whether that presents a risk cannot be determined at this point. That would involve relating disease patterns to concentrations of PFAS in tap water and controlling for all confounders such as diet, activity level, air quality, pre-existing conditions and other environmental contaminants such as phthalates, bisphenol A, pesticides and a host of others. This is almost undoable.
Where then does all this this leave us? There is not much we can do about the PFAS already out there, but regulations can be introduced about limiting production and eliminating non-essential uses. We don鈥檛 need PFAS is cosmetics or in pizza boxes, and stain-resistant carpets are not critical to life. As far as tap water goes, activated carbon filters can remove some PFAS, and a filter made with cyclodextrins derived from corn starch (Purefast) can bind most PFAS and fits into a Brita filter. A reverse osmosis system removes almost all contaminants from water, including PFAS but is expensive and is likely an overkill. We just don鈥檛 know if the traces of PFAS in water are harmful or not. Unfortunately, our ability to collect data has outstripped our ability to interpret what the data mean.
