1.4+. Classification of Poisons in Toxicology

There is a large number of different classifications of harmful substances, reflecting, on the one hand, the diversity of the properties of substances and their biological action, and on the other hand, the diversity of approaches to this problem. Classifications of poisons differ by: the purpose of their use, the degree of effect on living organisms, selective toxicity, origin and membership in a specific class of organic compounds, and the nature of the effect of chemical substances on living organisms.

By purpose of use, poisons are divided into:

• -industrial poisons, which are divided into organic solvents, fuels, dyes, refrigerants, chemical reagents, plasticizers;
• -agrochemicals (pesticides), which are divided into insecticides (against insects), fungicides (against bacteria), herbicides (used against weeds) and zoocides (used against rodents);
• -medicinal products;
• -household chemicals (acetic acid as a food additive, sanitation products, personal hygiene products, cosmetics);
• -poisons of animal and plant origin (poisons in mushrooms –aconite, snakes, bees, scorpions);
• -chemical warfare agents (sarin, mustard gas, phosgene).

By degree of effect on living organisms, all harmful substances are divided into four classes: I – extremely toxic; II – highly toxic; III – moderately toxic;

IV – slightly toxic.

By selective toxicity, poisons are distinguished:

• -cardiac (salts of barium, cobalt, cadmium metals);
• -neurotoxic (carbon monoxide, narcotics);

• -pulmonary (nitrogen oxides, ozone, phosgene);

• -hematic (aniline and its derivatives, nitrites);
• -hepatic (chlorinated hydrocarbons, poisonous mushrooms, phenols, aldehydes);
• -renal (heavy metal compounds, ethylene glycol, oxalic acid).

By origin, according to a specific class of organic compounds, harmful substances are subdivided into poisons:

• -of non-biological nature (organic and inorganic substances);
• -of biological nature (bacteria, plants, animals).

By the nature of the effect of chemical substances on living organisms, they are distinguished by mechanism of action:

• -embryotropic and teratogenic (disruption of fetal development);
• -mutagenic (damage to the hereditary apparatus of the cell);
• -carcinogenic (malignant transformation of the cell).

The hygienic classification of poisons proposed by S. D. Zaugolnikov (1970) has received general recognition; it is based on a quantitative assessment of the toxic hazard of chemical substances according to experimental data determining their CL50, DL50 and MAC. Using this classification, a given toxic substance can be assigned to a specific toxicity category characterizing its greater or lesser hazard.

The classification of substances by toxicity category (according to S.D. Zaugolnikov) is presented in Table 4.

Table 4.

Hygienic classification of poisons.

Among chemical substances, a group is distinguished of compounds possessing a certain combination of toxic and physicochemical properties capable of leading to group and mass poisonings in the event of an accident. For such substances, civil defense uses the term

highly hazardous toxic substances (SDYAV). The main criterion for assigning chemical substances to the SDYAV category is the inhalation poisoning coefficient (KVIO), which relates the toxicity of a substance to its volatility and makes it possible to compare the hazard of individual substances. SDYAV includes substances having a KVIO equal to or greater than 30. The higher the KVIO, the more hazardous the SDYAV. To assess the real hazard of these substances, in addition to KVIO, use is made of

an additional accident-hazard indicator - the depth of the damage zone, which characterizes the scale of the spread of chemical substances at their damaging concentrations when released (spilled) into the environment. In this case, a contamination zone of 100 m or more is taken as hazardous from the accident source, which corresponds to the distance of mass development from the railway track permitted by the current SNiP 207-01-89.

On the basis of calculations performed using the criteria given above, the All-Russian Research Institute of Railway Hygiene has developed a list of SDYAV transported by rail, comprising 39 substances: acrylonitrile, inhibited acrolein, sulfurous anhydride, anhydrous ammonia, acetonitrile, acetone cyanohydrin, anhydrous hydrogen fluoride, anhydrous hydrogen chloride, anhydrous dimethylamine, diethylamine, hydrocyanic acid, hydrochloric acid, hydrofluoric acid, inhibited methyl acrylate, methylamine, methyl bromide and chloride, methylvinylchlorosilane, methyldichlorosilane, methyltrichlorosilane, methylchloromethyldichlorosilane, methylchlorosilane, ethylene oxide, liquefied hydrogen sulfide, carbon disulfide, anhydrous trimethylamine, triethylamine, concentrated formaldehyde solution, phosgene, phosphorus trichloride, phosphorus oxychloride, chlorine, chloroform, chloropicrin, stabilized cyanogen chloride, ethylenediamine, ethyl mercaptan.

The list does not include 5 commonly recognized SDYAV substances (arsine, nitrogen oxides, fluorine, ethyleneimine, ethylene sulfide), the transport of which by rail is not carried out.

The safety rules and procedure for eliminating an emergency situation involving dangerous cargo carried by rail are set out in the collection “Safety Rules and Procedure for Eliminating an Emergency Situation with Dangerous Cargo Carried by Rail”. M.- Transport, 1996.

To assess the special hazard of certain chemical cargoes, one more criterion is used, which characterizes a small group of highly toxic substances with moderate volatility. Substances in this group present a high risk of poisoning with severe consequences and persistent contamination of the natural environment. These include, for example, heptyl, hydrazine, tricresyl phosphate, mercury and its compounds, nickel tetracarbonyl and others. Even brief exposure to large doses of these substances can be expected to cause the development of systemic changes in the body of the affected persons that are predominantly irreversible in nature and difficult to treat. Substances in this group are distinguished by high stability at the accident site (evaporation rate of more than a day), which substantially increases the risk of injury. Therefore, these substances are classified as especially hazardous, even though they do not meet some of the inhalation hazard criteria indicated above.