updated August 2020
We are sometimes too much in awe of our own creations. When we see problems emanating from either technology or chemical compounds, we often think that our creations are neutral. It supposedly all depends on “how we use them”. But that only applies in certain cases. The rationalization oversimplifies the reality, and it’s too reminiscent of the way people defend a certain country’s rampant production and lack of control of the military. Here is an attempt at classifying chemical compounds, both man-made and natural ones, that will hopefully reveal some nuances when we consider how compounds serve our interests.
Water is the superhero molecule. The molecule’s properties are quite special, making it essential for life on earth and probably elsewhere. Fairly resistant to temperature changes, large bodies of water slowly absorb or release heat to the atmosphere and nearby coast. During photosynthesis, water can lose electrons to excited chlorophyll molecules, creating oxygen for respiration and acidic ions that set up a potential difference invested in storing energy. It is a remarkable solvent, dissolving important ions, proteins and sugar molecules.
Physically, it’s not always helpful or innocuous. No homeowner wants it leaking through roofs or pipes or it will invite rot. Water can also kill or cause brain damage by filling lungs. Its undiscriminating abilities as a solvent allow toxins to tag along on its way to drinking sources and bodily fluids. But none of those issues are the result of water’s own chemical properties.
Nitrogen: Aside from serving as a raw material for amino acids, relatively inert nitrogen is needed in the atmosphere to attenuate the strong oxidizing abilities of oxygen. Invert proportions of nitrogen and oxygen in the air and the higher concentration of oxygen would lead to an explosive atmosphere.
2. Almost Superheroes
Sodium chloride, a compound containing two ions essential to animal life, reminds us that in certain cases, the poison is the dose. If a child ingests about four tablespoons of rock salt, it will lead to acute toxicity. For most plants a much lower concentration is lethal. Phosphates, a component of natural and synthetic fertilizers are needed to assemble ATP and DNA, but in excess they can lead to the eutrophication of lakes.
3. Neither Good nor Bad Substances: Depends On the Life Form’s Point of View
Potato plants, not only produce those familiar, edible tubers but also poisonous berries filled with alkaloids (solanine and chaconine) that protect them from most herbivores and fungi. Even tubers produce poisons when exposed to light. Some varieties investigated for possible cultivation had to be rejected because, even when underground, their tubers produced excessive toxins. From the point of view of the potato, the alkaloids increase its chances of survival— poisonous for us but essential from the plant’s vantage point.
Oxygen in diluted form is essential to all aerobic organisms, allowing them to extract energy from food, but to anaerobes, it’s a poison. Another example is the tough matrix consisting of lignin and cellulose, commonly known as wood, which is useless to a starving man, wonderful to a builder, and of course a highly supportive material for any living tree. Aside from the main constituents of wood, there are also aromatic compounds that offer additional protection from insects. But some of these compounds, at least in cases of excessive occupational exposure to hardwood dust (more than 8-hour time-weighted average 5 mg/m3 ), nasal cancer could result.
4. Sometimes It Does Depend Mostly On How Humans Use Them
The classic example of nitroglycerin reveals how the impact of some molecules is the result of individual choices. In small quantities it can be used as a vasodilator to treat angina. It can be an ingredient of dynamite, which in turn can be used to either build roads or to wreak havoc. In nitroglycerin’s category are many drugs which, regardless of legal status, when used appropriately, lead to favorable outcomes. When indigenous South Americans chew on coca leaves, the small amount of cocaine present helps them adapt to higher altitudes. It can also be used as an anesthetic in nose, throat and oral cavity surgery.
But if cocaine is heavily relied upon for recreational purposes it can become psychologically addictive, and in pregnant women it is passed on to the fetus, leading to developmental complications.
This classification also appeared in a previous version of this essay. being the mostly familiar, it was the only one retained by the majority of students! Education is not as easy as we sometimes pretend it is.
5. Supervillains: Substances That Would Have Been Best Left Unsynthesized
If a chemist reacts elemental mercury with methyl iodide and elemental sodium, he will produce two substances. One, sodium iodide, contains ions that would fall into our essential substance category. But the other compound, dimethyl mercury is one of the strongest known neurotoxins. A concentration of only 5 ppm (0.005 g of poison per kg of body weight) is considered lethal. Although it can be used to calibrate NMR instruments for mercury detection, less toxic salts can be used as substitutes, and presently, its use in research is widely discouraged.
In 1995, Karen Wetterhahn, a Darmouth College chemist specializing in toxic substances, accidentally spilled some drops of dimethyl mercury on her latex gloves. Before removing them, she cleaned up the area in the fumehood. She had been taking the recommended precautions. Whoever wrote up the materials safety sheet(MSDS) for dimethyl mercury at the time was unaware that dimethyl mercury can penetrate latex, neoprene and PVC. The MSDS sheet reportedly vaguely, ” Wear appropriate chemical-resistant gloves.” But once it finds its way through latex gloves, dimethyl mercury penetrates the skin within seconds.
Her log book revealed that she only worked with the neurotoxin for one day. Four months after the single exposure from the spillage, she was admitted to the hospital suffering from a loss of speech, balance and gait. She had also lost weight and suffered from brief episodes of nausea and diarrhea. A blood analysis revealed 4 ppm of mercury, twenty times the toxic level. They tried chelation therapy, which attempts to chemically bond the metal for purposes of excretion. But regardless, because Hg metabolites had already bonded to proteins in her brain, it was too late. She eventually fell into a coma with spontaneous moments of agitation and crying.
On June 8, 1996, Karen Wetterhahn died at the age of 48.
6. The Unpredictables
Millions of compounds have been made in the last hundred years. Often they are mass produced for one specific purpose and yet with unforeseen circumstances. A classic example are the chlorofluorocarbons. They were put on the market to replace the more toxic refrigerant ammonia, but then they turned out to be sources of atomic chlorine which catalyzes the breakdown of ozone. Even their less destructive replacements turned out to be powerful greenhouse gases.
Unpredictables include hundreds of substances known as chemical mutagens. Mostly man made, they affect DNA, sometimes leading to cancer and other health issues. Charlotte Auerbach, a scientist who got her doctorate in Britain after losing her teaching job in Nazi Germany, was the first to reveal that a compound can damage DNA. By exposing fruit flies to the vapors of the liquid “mustard gas”, she revealed that mustard gas is an alkylating agent. It adds chemical groups to DNA leading to mispairings.
The disposal of mustard gas found in Germany after World War II was done irresponsibly. It was dumped into the Baltic Sea, where it polymerized into beads that were later mistaken for fossilized resin (amber). When it has been collected it has led to severe health problems.
Other mutagens cause damage by raising the number of free radicals in the body to precarious levels. These types of mutagens include several compounds in cigarette smoke, certain forms of air pollution and some pesticides such as tetrachlorodibenzodioxin, TCDD, and maleic hydrazide.
Other unpredictables are not mutagens but can also have long-term consequences by inducing complications at concentrations that are far less than those considered toxic. Examples include perfluoroalkyl and polyfluoroalkyl substances (PFAS), widely used in industrial applications, such as firefighting foams, Scotchguard, non-stick pans, paper and textile coatings. These compounds act as endocrine disruptors which mimic or interfere with hormones produced by the endocrine system and lead to developmental, reproductive, brain, immune disorders and other problems in certain animals. Their impact on humans could be similar.