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CLASSIFICATION OF CHEMICALS (ELEMENTS) BY THEIR TOXICITY

All substances that adversely affect beneficial animals and humans are divided into groups according to their degree of acute or chronic toxicity, the level of functional or material cumulation, and chemical affiliation.

Criteria of toxicity of substances. Chemical toxicity is usually characterized by the following criteria: LD5o (SK5o), LD (SK) 6, LD (SK) 84, the maximum inactive dose, or concentration (max. ND or max. NK), the minimum effective dose is the threshold dose or concentration (min. DD or min. DC).

LD50, or SK.50, is the dose of a toxic substance that causes the death of 50% of individuals that received a toxic substance. Typically, the LDso score is determined on white mice or white rats with a single administration of the toxic substance inside or outside.

LD (SK)] 6 and LD (SK) 84 - doses that cause the death of 16 and 84% of individuals. These indicators characterize the minimum and maximum lethal doses, which are determined by the calculation method when calculating the LD5o value

In veterinary toxicology, the LD50 value is mainly determined for birds (chickens, chickens). For large animals (sheep, cattle, horses, pigs), it is advisable to determine the TD5o indicator - the dose that causes visible signs of intoxication in 50% of individuals with a single injection of the substance inside or for external use.

The maximum inactive dose, or concentration (max. ND or max. NK), is the maximum dose or concentration that can be set by the most sensitive toxicological tests, not causing a toxic effect. An exception is the indicator of suppression of blood cholinesterase activity, which is the main biochemical test in the toxicological assessment of the action of organophosphorus compounds. It is believed that the inhibition of the activity of this enzyme to 20% is safe for the animal. With the toxicological characteristics of these compounds, the maximum inactive dose, or concentration, is one that causes inhibition of the activity of blood cholinesterase by no more than 20%.

The minimum effective dose, or concentration (min. DD or min. DC), is the threshold dose, or concentration, of the substance that causes the initial signs of intoxication, which can be set by one or more of the most sensitive tests.

In addition to these criteria, for some substances that can enter the body of animals for a long time, an indicator such as cumulation is established. It is characterized by a cumulation coefficient. Cumulation can be functional and material and is determined by the coefficient of functional or material cumulation.

The coefficient of functional cumulation expresses the ratio of the T / LZo mask with repeated administration of the substance inside to the LZO with its single administration in the same way.

The material cumulation coefficient expresses the ratio of the level of substance residues in the tissue in mg / kg of mass to the level of its content in the feed. Typically, the coefficient of material cumulation is determined by the tissue in which the substance accumulates or remains in the greatest quantities. For example, for lipidophilic pesticides of the organochlorine group, such a coefficient is determined by adipose tissue, and for mercury-containing compounds by the kidneys.

For chemicals intended for external treatment of animals (insectoacaricides), the skin-oral coefficient is determined.

The knee-oral coefficient is the ratio of LD5o (TD5o) with a single external use to LD5o (TD5o) with a single oral administration.

Toxicity indicators. There is no unified classification of chemicals by their toxicity to animals. However, there is a classification accepted for pesticides. It can be adopted for other chemical compounds or elements with pronounced biological activity. In accordance with this classification, toxicity pesticides are divided into four groups depending on the LD5o values ​​for white mice or white rats with a single oral administration:

I. Strong toxic substances - LD5o up to 50 mg / kg;

I. Highly toxic - LD5o 50-200 mg / kg;

III. Medium toxic - LD5o 200-1000 mg / kg;

IV. Low toxicity - LD5o more than 1000 mg / kg. A similar division of biologically active substances into

groups can be carried out for birds when determining for them the indicator LD50-

The degree of toxicity of substances for fish is determined by the SK50 indicator - the concentration that causes the death of 50% of individuals at 72-96-hour exposure. V.V. Metelev et al. (1971) proposed the Don Hertie classification (1951), according to which all substances according to toxicity to fish according to SK5o are divided into five groups:

I. Highly toxic - up to 1 mg / l;

II. Highly toxic - 1 - 10 mg / l;

III. Moderately toxic - 10-100 mg / l;

IV. Weakly toxic - 100-1000 mg / l;

V. Very slightly toxic substances - more than 1000 mg / l. The degree of toxicity of pesticides for bees is determined by

index, which is the ratio of the concentration of the pesticide used to process crops to the total indicator of the contact and intestinal effects of the toxicant on the bee (S. S. Nazarov, 1967).
However, such an index is difficult to determine and can vary significantly, since the concentration and consumption rate of the pesticide can vary depending on the type of pests and the nature of the treatments themselves (large-volume, low-volume and ultra-volume spraying). Therefore, with a certain degree of conditionality, substances for toxicity to bees are divided into groups of LD50 per bee with topical application of the pesticide to the mid back of the insect in the form of an acetone solution:

I. Highly toxic - up to 1 mcg / individual;

II. Medium toxic - 1 - 10 mcg / individual;

III. Low toxicity - 10-100 mcg / individual;

IV. Non-toxic - more than 100 mcg / individual.

According to skin-resorptive toxicity, substances are divided into three groups (L. I. Medved, 1977) according to the results of studies in rats or rabbits:

I. Pronounced toxicity - LD5o less than 300 mg / kg, skin-oral coefficient less than 1;

II. Severe toxicity - LD5o 300-1000 mg / kg, skin-oral coefficient of 1-3;

III. Mild toxicity - LD5o more than 1000 mg / kg, skin-oral coefficient more than 3.

For example, if the LD50, when delivered through the skin, is 300 mg / kg of the animal’s mass, and when introduced into the stomach, 400 mg / kg, then the skin-oral coefficient will be 0.75, i.e. less than one.

When studying skin-resorptive toxicity in large animals for drugs intended for external use, a safety factor is usually determined - the concentration of the solution or emulsion of the pesticide that causes the initial clinical signs of intoxication or has an effect on the skin at a working concentration recommended for the fight against ectoparasites. According to this indicator, drugs are divided into three groups:

I. Highly hazardous - safety factor up to 3;

II. Moderately dangerous - up to 3-5;

III. Low-hazard - more than 5.

According to the functional cumulation, poisons are divided into four groups (L. I. Medved, 1977):

I. Over cumulation - cumulation coefficient less than 1; P. Severe - cumulation coefficient 1-3;

III. Moderate - cumulation coefficient 3-5;

IV. Mild - cumulation coefficient of more than 5.

Cumulation coefficient is the ratio of the total dose of a substance that caused the death of 50% of experimental animals with repeated administration to the dose that caused the death of 50% of animals in a single exposure.

Functional cumulation is usually determined on white mice or rats. To do this, the test substances are administered for 4 months on an empty stomach in the stomach of animals in doses equal to 1/10, 1/20, 1/50 LDso, established in acute experiments. Practice shows that the value of the coefficient of functional cumulation can vary in significant sizes depending on the dose.

In veterinary toxicology, material cumulation is of the greatest importance. The sanitary value of the poison, which characterizes the degree of its accumulation in animal tissues and its penetration into food products of animal origin, depends on its level.

For example, when calves were fed with the gamma-isomer HCH in the amount of 5 mg / kg feed in fat, the maximum content of residues of this substance equal to 25 mg / kg of tissue was found. The coefficient of material cumulation of the gamma isomer of HCH will be 25/5 = 5.

According to this indicator, all toxic substances are divided into four groups:

I. Supercumulation - the coefficient of material cumulation is more than 5;

II. Expressed - coefficient from 1 to 5;



III. Weak - coefficient from 0.1 to 1.0;

IV. Very weak - coefficient less than 0.1. Toxic substances related to the degree of material

cumulation to group I, it is impractical to allow for use in veterinary practice, as well as for the processing of fodder or other crops, the processed products of which are fed to farm animals. This group includes a very limited amount of toxic substances: DDT; some compounds of diene synthesis; preparations containing arsenic and mercury. Group II preparations are allowed for use on farm animals, fodder and industrial crops used in animal feed, in meadows and pastures with the establishment of regulations for their use. Compounds of groups III and IV do not represent a great sanitary hazard and can be allowed without restrictions for the treatment of forage crops, meadows and pastures, if by toxicity they belong to the group of medium and low toxic substances. If their toxicity corresponds to the toxicants of groups I and II, they can be approved for the treatment of plants used in animal feed only after studying the dynamics of residues on plants and establishing relevant regulations. The use of compounds of groups III and IV on farm animals, regardless of toxicological affiliation, is allowed only after the establishment of regulations for their use.
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CLASSIFICATION OF CHEMICALS (ELEMENTS) BY THEIR TOXICITY

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