Now let me explain what I mean, and how I can answer this very generic question in a catch-all way without specifying the item/substance/compound to which I refer. Because he said it so well that it doesn’t need rephrasing, I’ll quote the Renaissance-era botanist Philippus Aureolus Paracelsus, who said:
All substances are poisons; there is none that is not a poison. The right dose differentiates a poison from a remedy.
Phrased more generally, this is simply that any substance can be either safe or toxic; the dose (quantity) to which one is exposed is what makes the difference. I’ve mentioned in previous posts (like this one about oxybenzone in sunscreen) that the notoriously jumpy Environmental Working Group (EWG) systematically fails to recognize this particular principle; they have a tendency to vilify anything that proves toxic in any dose, under any conditions. This attitude, however well intentioned, leads us to some interesting places. Pause for a moment and check out the cautionary website DHMO.org. Note that the highly toxic dihydrogen monoxide (DHMO) is associated with cancer (it’s found in every tumor ever identified), has serious environmental impact (it’s a major greenhouse gas and overexposure is associated with thousands upon thousands of deaths every year), and, per the website:
[DHMO's] basis is the highly reactive hydroxyl radical, a species shown to mutate DNA, denature proteins, disrupt cell membranes, and chemically alter critical neurotransmitters.
Sounds horrid, doesn’t it? No doubt we should ban it. Except that…DHMO.org is a joke website, and dihydrogen monoxide is the almost never-used, formal chemical name for water.
None of the information on DHMO.org is false, which is what makes it both amusing and apropos to this discussion. Water does, in fact, directly result in many deaths. Not only through “overexposure” via flooding and/or drowning, but also through overconsumption. For instance, in 2007, a radio station held a contest (“Hold your wee for a Wii”), the idea of which was to drink as much water as possible without a bathroom break; the caller who drank the most would win a coveted Wii game console. Contestant Jennifer Strange won (and then lost) by consuming more than 2 gallons of water in the space of less than an hour. She died shortly thereafter of hyponatremia, a condition in which there is an insufficient concentration of sodium in the body fluids to support life (sodium is critical to cellular function, neural conduction, muscular contraction, brain function, and so forth). This is not the only incident of water toxicity on record; similar cases have resulted from fraternity hazings, bizarre diet plans, and overconsumption of water during endurance sporting events like marathons.
On the other hand, there are substances that we typically consider highly toxic that are, in the right dose, of great medicinal utility. Clostridium botulinum is a species of bacteria that produces botulinum toxin, generally considered the deadliest substance on Earth. The average 150 pound man would have a 50:50 chance of survival if exposed to merely 341 ng (that’s less than a millionth of a gram) of pure botulinum toxin. Regardless, marketed under the trade name Botox, botulinum toxin is used for cosmetic purposes (wrinkle treatment and prevention). Of perhaps greater medical importance, it’s also used to ease the painful symptoms of temporomandibular joint syndrome (TMJ) and other spasmodic disorders, and mitigate the symptoms of diabetic neuropathy (damage to peripheral nerves, often in the feet, due to diabetes).
Further complicating matters, our perception that “natural” substances are somehow safer or better for us than “artificial” substances is misinformed. A simple example is the flavoring agents found in many foods. While the common perception is that natural flavors come from the food of which they taste (strawberry flavor, for instance, comes from strawberries), nothing could be further from the truth. In reality, natural and artificial flavors are generally identical chemicals, collected or produced in different ways.* Natural almond flavor, for instance, isn’t a mixture of “natural substances” that come from almonds. Instead, it’s a chemical called benzaldehyde that is extracted from peach pits. Artificial almond flavor is also benzaldehyde, but unlike natural almond flavor, the artificial stuff is made in the lab. Funnily enough, it’s possible to get benzaldehyde made in the lab much more pure than that extracted from peach pits. Further, the stuff that comes from peach pits — the natural almond flavor, remember — contains small amounts of deadly cyanide that occurs naturally in those same peach pits (one of many reasons it’s not wise to eat the pits of stone fruit).
*Eric Schlosser’s excellent book Fast Food Nation contains a very interesting chapter on this topic, for further reading.
Where does this leave us, in trying to avoid toxins? First, as a chemist, let me just say that the word toxin is very often misused in popular sources and conversation, and the word chemical is almost always misused. “Chemicals” are not bad things that cause harm and should be avoided. Instead, they are matter; they are what makes up the physical universe. Nothing that has mass and occupies space — nothing we touch, eat, drink, breathe — is not chemical. There’s no such thing as chemical-free bread, shampoo, or paint. Water is a chemical (and — let’s not forget — a toxic one at that). With regard to toxins, the word is used too often in a vague, handwaving sense on the Interwebs. I see pop-authors (who are generally trying to sell something) write about how Product X contains “toxins,” and should therefore be avoided, or Product Y (which they’re selling) contains no toxins.* I’m not sure what these folks mean when they say “toxins” (and since they rarely name said toxins, I’m not sure they know either); after all, let’s not forget that all substances are toxic in the right dose.
*Or worse yet, Product Y (which they’re selling) is a detoxifying agent. This is ridiculous; almost all humans (with the exception of a few with significant disease) are possessed of one of the most powerful detoxifying mechanisms known to man — a liver. Livers work really well, particularly when they’re left alone to do their job.
This is not to say that we should all go about our business with no concern whatsoever for the things we touch/eat/drink/breathe; it’s simply to say that we simultaneously worry too much and worry too little about “chemicals.” To take one particular example, a few scare-articles about bisphenol A (BPA) have some of us so worried (and confused) that we’re willing to shell out extra cash for BPA-free diaper wipe containers, toys, and even a bath toy organizer. In reality, if BPA has any effect at all in doses to which we’re routinely exposed (which has not yet been established), it would require significant physical contact with the compound to absorb it. Holding, playing with, or storing one’s bath toys in a BPA-containing item would not be a problem, particularly given that while the absorption rate of BPA through human skin hasn’t been thoroughly evaluated or established, it nevertheless appears to be significantly lower than the (already modest) rate of absorption through the skin of other animals (Marquet et al). Based upon the current research, might it be worth avoiding storing food in BPA-containing plastics? Possibly. This is because food might leech BPA out of the plastic in sufficient quantities to possibly have some effect on people (because we eat the food, which gives it an easy route into the system). Is it worth it to avoid all BPA in our houses, however? Simply, no. And on that note, it particularly amuses me to watch women with painted nails shopping for BPA-free toys for their daughters (also with painted nails), given that the exposure to potentially harmful substances (like toluene) is much greater when one physically paints said chemicals on one’s body.*
*For those who are curious, I do paint my nails, because I really don’t think this is that big a deal. But it’s certainly a more significant exposure to chemicals (ew! chemicals!) than touching a rubber ducky in the tub.
So, we worry too much. But we also worry too little. In our desire for the “natural” (whatever that means), we choose the cyanide-laced flavoring agent over the one made under strict conditions and control in the lab. We go to the natural foods store and buy herbs to treat our ailments — which are essentially unregulated for either safety or efficacy, and which may interact unsafely with prescription and over-the-counter drugs or be toxic in their own right — rather than using the “unnatural chemicals” prescribed by medical professionals, despite the fact that the latter have undergone many years of pre-marketing research, followed by decades of post-marketing surveillance. We’re more willing to expose our children to the 1/330 risk of death due to the measles than the 1/3000 risk of a moderate side effect of measles vaccination (e.g. seizure with no permanent effects, mild rash), and immeasurably small risk of serious side effect. We further eschew the vaccination because, in a complete failure to understand the mechanics of human immunity, we have come to believe that “natural” immunity from disease is superior to “artificial” immunity from vaccination. When it comes to the “natural” versus the “toxic” and/or “chemical,” we’re chasing flies out of the chicken coop while the foxes sneak in.
So what do we do about it? This is difficult. We know that all substances are toxic in the right (wrong?) dose, but when it comes to many substances, we still don’t know what that dose is. Some exposures are unavoidable (by virtue of living in a city, for instance, one is going to be exposed to a certain amount of benzene from exhaust, industrial processes, etc). Some exposures are avoidable, but avoiding them reduces quality of life (no one HAS to eat foods containing coloring agents, for instance, many of which are of questionable safety, but the complete avoidance of these would make for a stoic existence, particularly for children). In most cases, when it comes to toxic chemicals (and once more, all substances are chemicals, and all chemicals are toxic when one is exposed to them…all together now…in the right dose), one must do a risk-to-benefit analysis. Some cases are relatively clear. Is codeine toxic? Yes, in the right dose. Is it worth the risk to take codeine for recreational purposes? Probably not. Is it worth the risk to take codeine after a painful surgery? Probably. Is water toxic? Yes, in the right dose. Is it worth the risk to drink water when one is thirsty? Absolutely. Is it worth the risk to drink water to win a contest? Probably not. Some cases are less so, as with the previous example of BPA. With the evidence still equivocal, financial means and convenience likely become a large part of the decision. Those of greater means or with greater willingness to be inconvenienced might buy the BPA-free rubbery ducky, the BPA-free cabinet safety locks. Others might decide to buy the BPA-free food storage, but be content with the plain old, BPA-containing bath caddy. Regardless of these personal decisions when it comes to substances of yet-unknown safety, it’s worth remembering that the media, the product manufacturers, and the fad-authors capitalize upon the lucrative combination of public confusion and fear, and that the words “chemical,” “toxic,” “artificial,” and “natural” are as powerful as they are misused and misunderstood.
Marquet et al. In vivo and ex vivo percutaneous absorption of [14C]-bisphenol A in rats: a possible extrapolation to human absorption? Arch Toxicol. 2011 Sep;85(9):1035-43. Epub 2011 Feb 2.