The fact is that any substance under certain conditions can become poisonous. Any of them can have a certain negative impact on human health, there is only a question of dose or concentration, intensity and duration of exposure. For example, ordinary water from deep wells contaminated with hazardous chemicals is usually collected in shallow soil layers. There it is absorbed by plants and then together with them can get into our body. So water (more precisely, toxins in it) in a short time can have a significant harmful effect on human health. In addition, life-giving oxygen is, in certain situations and conditions, a truly dangerous toxin. Air, especially in large cities, is polluted by many dangerous substances that threaten health and even often - life.
Toxic can be widely available and used table salt (sodium chloride) and even glucose, of course, if they are consumed in fairly large quantities. Salt-rich sea water is completely unsuitable for drinking precisely because of the high concentration of these salts, which have a high toxicity.
Distilled water is also very dangerous for your health. The paradox is that it is absolutely pure water, but this is what is harmful to it. It does not contain any additional ingredients necessary for life. Such water is absolutely not absorbed by the body, and with constant use it poisons you.
Ideally, noble noble gases are not toxic to humans. So theoretically, nitrogen (the main component of air), hydrogen, or a gas containing simple aliphatic hydrocarbons, such as methane, ethane and propane, is not toxic. But when a person living in poorly ventilated rooms inhales constantly chemically inactive gas - in connection with an increase in its concentration in the atmosphere of the room - it poisons itself. Thus, oxygen is expelled from the air - typical symptoms of acute ischemia of the body occur. So - in theory, a completely non-toxic substance becomes in this particular situation a negative effect on human health.
The concept of toxicity of various substances in accordance with modern knowledge is understood much more widely than before. The list of hazardous substances is not limited to well-known "historical" poisons such as arsenic, cyanide, strychnine, curare, hemlock alkaloids (hemlock), snake venom, toxins contained in some fungi. It is supplemented by numerous substances that, in certain situations and conditions, become toxic from safe. While others may pose a threat to health and even to human life.
The best example of just such a substance, widely consumed in various forms, is ethanol. This is what can be poisoned within one day. The use of very specific doses of ethanol in medicines is safe for most people. Exceeding the same dose or combination with other medicinal and other chemicals can be very dangerous. As a result of adverse drug interactions, ethanol can cause very serious symptoms as a result of damage to organs and systems and impair their function.
It should be noted that there are people with a genetically determined susceptibility to the pathological consequences of substances that are recognized as toxic. Simply put, they can not poison themselves by poisoning any other person. It is difficult to say whether such "immunity" arises as a result of constant contact with a toxin or that there is another reason. Of course, under certain conditions, adaptive defense mechanisms may appear, but there is no scientific justification for this. Simply, there are people who are insensitive, for example, to snake venom. Or those who easily tolerate large doses of ethyl alcohol (in its own way, too, a powerful toxin).
The truth and myths about poisonous substances
Public knowledge of what is dangerous to human health and that does not pose a serious threat is obviously deepening and expanding. But still it is not enough, especially under certain conditions, when, unfortunately, people are often misled.
For example, there is a widespread opinion (even among some doctors) that metallic mercury is a very dangerous poison. Often parents who have a mercury thermometer in their house fear that they will break up and poison everyone in one day. But meanwhile in such thermometers there is no metallic mercury! There is a usual liquid mercury, whose vapors can also be dangerous, but only if they are inhaled with large volumes and for a long time. Metal mercury, in contrast to it, is dangerous even in microdoses, like many inorganic compounds of molten metal.
The toxicity of certain products is determined by many people and is assessed in completely incompetent. For example, based on their taste, flavor and appearance. Many people believe that they have caught a poisonous mushroom just because it is bitter, or because their bottom of the hat does not darken as a result of oppression or under the influence of light. In fact, if the fungus is bitter or not, it darkens under the influence of light. From a toxicological point of view, all this is absolutely irrelevant! Toxicity of fungi depends on the presence of toxic agents in them, which the human nose or other simple methods can not detect.
Many times it happened that some people mistakenly drank various toxic compounds containing ethylene glycol. For example, a brake fluid, which is a very dangerous poison. In almost every case, a person was convinced of the non-toxicity of the liquid, in particular, precisely because it was pleasant to the taste.
Denaturates are almost symbolically considered to be one of the worst and most dangerous poisons for humans. In fact, they are as toxic as other forms of ethyl alcohol.
Natural gas, which is widely used today, is considered highly toxic, whereas once the release of incomplete combustion of carbon monoxide makes it very hazardous to health and life. Natural gas is actually another cause, initially dangerous for humans - it accumulates in enclosed spaces. In addition to removing oxygen from it, it can suddenly explode with great force. An unpleasant odor often causes fear and leads to false judgments about the alleged toxicity. But not all unpleasant smells are toxic! Few people know that the carbon monoxide released from incomplete combustion of natural gas is completely odorless, but several times more dangerous. This is exactly what you can poison - one day there is only a couple of hours opposed. This is enough to get a lethal dose.
Despite the many shortcomings and gaps in knowledge that are available to modern society, people know a lot about the risks of toxicity of various substances. But sometimes there are too many erroneous myths in this area. In any case, the recognition of a threat is better than its denial.