When I hear talking about forever chemicals, they are usually described as “chemicals are not affected by naturally occurring reactions, and that accumulate in the bodies of living beings”. By accumulating, they cause all sorts of health issues.
What I don’t understand is how they cause these health issues. If these chemicals do not participate in regular reactions, how do they cause issues?
I am not claiming that the research in the subject is wrong, I am missing the link between “these things don’t react with anything” and “these things still cause all sorts of health problems”.
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So your body is broadly controlled by hormones. The hormone is a specific shape like a key, and it falls into specific shaped receivers in your body. When it does that, the signal is acted on.
Plastics as they break down can be these same shapes so they accidentally fit into the receiver slots for the hormones. Making your body do things it shouldn’t.
This is one serious way they effect us. An example is a plastic called BPA which just so happens to be the same shape as estrogen, so children of either gender drinking from cups made of it might grow boobs, or go into puberty at a young age
Depends somewhat on the specific chemical, but the general idea is that the chemical is stable relative to most naturally occurring compounds so does not react in nature with most of what it might encounter. Some of the chemicals can react with particular conditions or compounds that themselves are fairly stable, and in some cases, that is one possible reason they can be a problem (by destroying or modifying chemicals required for body functions).
Often, though, the problem compound is similar in form to some other useful compound (like, say some sort of hormone), at least in part, so it will interact with the things normally targeted by the hormone (or whatever compound it is similar to). It is a problem because it can either trigger responses that should not be turned on, or interfere with mechanisms (by blocking receptors) that ought to be initiated by the expected and useful compound being mimicked.
To understand this fully, you have to understand that many organic molecules are fairly large and made up of different functional groups at different locations on the larger molecule, and thus have a fairly specific shape and reactivity that varies from region to region in the molecule. Like a key only works for a matching lock, many organic compounds only “fit” together with its target, and it is the only compound produced by the body which will fit. Having a similar shaped compound from elsewhere that can fit the lock, well, that can be a problem and disrupt the way the system ought to be working, by locking, or unlocking, a chain of processes.
So imagine our bodies as a tightly controlled system. Everything is connected and everything needs to work together in a specific way to help keep us alive and functioning. Harmful chemicals are so because they interact with something that interferes with the tightly controlled system. For example: cyanide goes into cells and stops them from producing energy. No energy means cell death, if enough cells die, tissues, then organs, then you die.
These chemicals are not cyanide, but any chemical has the potential to interfere with something it should not. Our bodies are sometimes able to compensate but you don’t want that. Bottom line, do not let unknown chemicals in your body if you can avoid it.
competitive inhibitors obstruct enzyme activity without getting “used up” doing that.
Let’s make up a forever chemical called anti-starch, it’s a competitive inhibitor for amylase, the enzyme that breaks starch into sugar that we can then absorb and use. At a “normal” level of presence, 1/100 times your amylase enzyme tries to digest a starch it latches onto an anti-starch instead, translating to a 1% reduction in how efficiently you digest starch, so you only get 99% of the energy out of a potato.
But because it builds up indefinitely as you get older that ratio starts to go up and up and eventually you’re only like 20-30% effective at digesting starch, and can die of starvation despite eating thousands of calories of potatoes.
This same thing can happen with literally any substance that is “competitive” with a natural substance – hormone receptors, enzymes, even neurotransmitters. These substances are essentially just clogging the pipeline and making our systems less and less efficient over time. Most of the time this is easily solved by just making more of the appropriate receptor/enzyme – in the above anti-starch example your body would just make more amylase until it was able to digest at 100% efficiency – but some things are harder to fix or upgrade to overcome the clog, and so they eventually degrade function so far that you can’t survive.
Not at all a doctor, but as I understand it:
Your body is a serious of complex pumps and tubes, built to move volumes of organic compounds to places they need to be.
If you put things in the tube that arent supposed to be there, you are going to be using some of that tube’s “bandwidth” to move something around that really isn’t supposed to be there.
Thats before you even consider how that something will react to the recipients waiting at the outflows from the tubes.
Say your heart is supposed to be pumping 100 abstract units of blood to your brain. As other stuff starts to build in your vascular system, the tube still moves 100 total abstract units, but now its 99 blood and 1 junk. This is fine, if the brain can make do, but over time as this junk accumulates, the throughput continues to drop, putting stress on the brain until finally it starts to break down due to lack of blood units per heart beat.
Basically your body fills up with junk that blocks it from doing what its supposed to.
Lots of great but long answers here. Our understanding can be boiled down to “they get in the way”.
Sometimes they get in the way because they look like a key, so the body puts them into a particular lock, but since they aren’t the real key the door doesn’t open.
Sometimes they get in the way like a bunch of cars at rush hour when you’re just trying to get to work.
These chemicals are small, but so is everything else in your body, and there isn’t any room for unnecessary stuff. It causes all sorts of confusion and mayhem.
The replies so far are accurate as far as possible mechanisms of toxicity, which is your question. But it helps to zoom out a bit- in order to do an experiment, you need a control group. Give one set of rats a dose of halogenated hydrocarbons, raise a second group of rats without them, compare their disease rates. But [these chemicals are in wild animals everywhere except Antarctica](https://www.theguardian.com/environment/2023/feb/22/animal-toxic-pfas-contamination-study) and even [on top of Mt. Everest.](https://www.theguardian.com/environment/2023/feb/22/animal-toxic-pfas-contamination-study) These chemicals are used in the factories that package food for lab animals, and they’re used in the farming process, so it is exceptionally difficult to raise lab animals without them. Now, one might start with the assumption that rats with *tiny* quantitates of these chemicals are going to show tiny effects, and larger doses will show larger but similar effects. That is how most toxins work. But other chemicals, like dioxin, the main contaminant in Agent Orange, and Bisphenol A, the hormone mimic in plastic, [have strongly non-linear dose- response curves.](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2475953/) Tiny doses may have the same response as larger doses, because they have already saturated the sensitive receptors they bind to. *Both of those chemicals are highly persistent in the environment and are sometimes described under the umbrella term “forever chemicals”, although that term is more often applied to precursors of chemicals like Teflon.
It was irresponsible to release these things without fully testing the health consequences, and now they are so widespread that it is difficult to raise a rat with zero exposure as a comparison subject. I think it is most reasonable to be only mildly alarmed, the rate of cancer has mostly increased only mildly since the chemicals have been invented, and most of that increase is due to people getting fatter and living longer. But comparison is difficult- cigarette smoke and coal smoke was everywhere when these things were invented. Before cigarettes and coal were widespread, people died young of infectious disease, and medical diagnosis was wildly inaccurate, so we really have only a foggy idea what the cancer rate was before the year 1900.
The PFAS chemicals we know the most about are toxic at very low exposure levels to humans and wildlife. Some of them, like pfos are bioaccumulative, which means their concentration builds up in your cells over time.
Not all the toxicology is published, but PFOS scared a lot of people when they realized how low those levels were.
Medically, PFOS causes liver & thyroid damage, lowered fertility, increases obesity, hormone suppression and antibody suppression.
Each individual PFAS chemical has its own toxicology characteristics.
Depends somewhat on the specific chemical, but the general idea is that the chemical is stable relative to most naturally occurring compounds so does not react in nature with most of what it might encounter. Some of the chemicals can react with particular conditions or compounds that themselves are fairly stable, and in some cases, that is one possible reason they can be a problem (by destroying or modifying chemicals required for body functions).
Often, though, the problem compound is similar in form to some other useful compound (like, say some sort of hormone), at least in part, so it will interact with the things normally targeted by the hormone (or whatever compound it is similar to). It is a problem because it can either trigger responses that should not be turned on, or interfere with mechanisms (by blocking receptors) that ought to be initiated by the expected and useful compound being mimicked.
To understand this fully, you have to understand that many organic molecules are fairly large and made up of different functional groups at different locations on the larger molecule, and thus have a fairly specific shape and reactivity that varies from region to region in the molecule. Like a key only works for a matching lock, many organic compounds only “fit” together with its target, and it is the only compound produced by the body which will fit. Having a similar shaped compound from elsewhere that can fit the lock, well, that can be a problem and disrupt the way the system ought to be working, by locking, or unlocking, a chain of processes.
I think one real risks is the bioaccumulation and biomagnification as the forever chemicals move up through the foodchains.
They might be completely safe at the level that everyone’s exposed to right now, but the issue with never going away is that the exposure levels will only keep going up.
Look at the case of the pesticide DDT in the USA. DDT is very safe (to most non-insects) at low levels, but it takes a very long time to break down.
What ended up happening is that the DDT sprayed on crops and farms would go into runoff or rodents and work it’s way into the ecosystem and start moving up the food chain. DDT accumulates in the bodies of fish and mice in normal levels, but animals higher in the food chain would consume dozens of these prey animals and it would start accumulating in higher levels in those animals.
In the case of DDT it was discovered that it was weakening the eggshells of Bald Eagles, and it nearly brought the animal to extinction.
Luckily, we were able to ban DDT in time, and it slowly broke down in the environment before the Bald Eagle went extinct, but a ‘forever chemical’ won’t be as easy to recover from.
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