Organophosphate insecticides. Moscow State Academy of Veterinary Medicine Organophosphorus toxic substances
Lit.: Melnikov N.N., Chemistry and technology of pesticides, M., 1974; Systemic fungicides, trans. from English, M., 1975; Fest S., Schmidt K. J., The chemistry of organophosphorus pesticides, B. – , 1973: Eto M., Organophosphorus pesticides: organic and biological chemistry, Cleveland, 1974.
- - generalized name of a chemical. preparations used as plant protection products; for weed control. P. also include plant growth regulators, defoliants...
Dictionary of microbiology
- - chem. preparations for controlling pests and diseases of the region, weeds, food pests. products, also used for soil fatigue, etc.; basis of chemistry plant protection method...
Agricultural encyclopedic dictionary
- - pesticides, chemicals that have a detrimental effect on organisms harmful to humans, animals and cultivated plants...
- - organophosphorus compounds, a group of derivatives of phosphoric acid esters. There are F. s. contact and systemic action...
Veterinary encyclopedic dictionary
- - chem. tools to combat harmful or unwanted. microorganisms, plants and animals...
Chemical encyclopedia
- - contain in the molecule a phosphorus atom bonded to carbon, for example. trialkylphosphines K3P, acids like RP2...
Natural science. Encyclopedic Dictionary
- - the general name of chemicals used to control weeds, harmful insects, ticks - carriers of dangerous diseases, pathogenic fungi on field crops, etc. They can kill...
Explanatory dictionary of soil science
Ecological dictionary
Glossary of emergency terms
Modern encyclopedia
- - I Pesticides are toxic substances used in agriculture to combat diseases and pests of cultivated plants, weeds - see Agricultural pesticides...
Medical encyclopedia
- - O. v., which are organic esters of phosphoric acids; belong to O. v. nerve agent...
Large medical dictionary
- - a group of toxic nerve agents...
Great Soviet Encyclopedia
- - a wide class of organic compounds containing phosphorus...
Great Soviet Encyclopedia
- - ORGANOPHOSPHORUS compounds - contain in the molecule a phosphorus atom bonded to carbon, for example. trialkylphosphines R3P, acids type RP2...
Large encyclopedic dictionary
"Organophosphate pesticides" in books
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Organophosphorus compounds (OP). Compared to other groups of pesticides, FOS have found the most widespread use. The FOS group includes substances of various chemical structures, which are based on esters of phosphorus acids: octamethyl, metaphos, methylmercaptophos, phosphamide (rogor), karbofos, chlorophos, trichlorometaphos-3, etc.
Characteristic:
Their high insecticidal efficiency
Relatively fast inactivation in the external environment
Relatively low toxicity
Complete absence of toxic properties of their breakdown products (hydrolysis).
Organophosphate pesticides practically do not accumulate in animals and humans
Have low cumulative properties
Ability to be excreted in milk for a long time
With the help of organophosphorus preparations, it is apparently possible to solve the problem of the “ideal pesticide”, which, having a vigorous effect on the object being exterminated, would not linger on the treated plant objects and would be inactivated in a short time.
Select:
Contact organophosphorus preparations that do not penetrate into plant objects (karbofos, metaphos, etc.).
Systemic or intraplant pesticides are characterized by a pronounced ability to penetrate into plants and spread to all their parts, including the edible part. Systemic drugs, as a rule, are significantly more stable in the external environment. Systemic organophosphorus preparations (phosphamide, octamethyl, etc.) are subject to strict regulation; their practical application is limited.
IN mechanism The main effect of organophosphorus pesticides on the body is inhibition of cholinesterase activity, which is associated with phosphorylation of its active centers. There are also changes in catalase activity, a decrease in the content of certain amino acids in blood serum proteins, changes in protein fractions of blood and other biochemical parameters.
When organophosphate compounds enter the gastrointestinal tract, the symptoms of poisoning are characterized primarily by vomiting, abdominal pain, diarrhea, etc. Then lacrimation and signs of damage to the central nervous system (anxiety, fear, dizziness, etc.) appear.
Moderate intoxication is accompanied by gait disturbances, trembling of the hands and head; patients lose the ability to orient themselves in space, etc. In severe forms of poisoning, myopia develops, visual acuity decreases, pupils narrow, convulsions, involuntary urination and feces appear, collapse, coma, pulmonary edema and respiratory paralysis occur.
Sales of food products in which the content of residual quantities of FOS pesticides exceeds permissible levels are carried out:
Organophosphorus pesticides are partially or completely destroyed when exposed to high temperatures. In the first hours (1-2) after treatment of plants and to a lesser extent later, they can be washed off with water.
Fruits and berries can be processed into preserves, marmalade, marmalade, and dried fruits after preliminary washing. Fruits containing residual amounts of organophosphorus pesticides exceeding the MRL by 3-4 times are peeled before processing. Products containing fozalon residues must in all cases be pre-peeled.
Vegetables can be processed into canned food that can be sterilized. Due to the fact that metaphos, chlorophos, thiophos are stored for a long time in an acidic environment, cabbage and other vegetables with the presence of residues of these drugs exceeding permissible levels are not recommended for pickling and pickling.
Due to the fact that organophosphate pesticides accumulate in large quantities in the peel of citrus fruits, the latter can be processed only after peeling (it is prohibited to press citrus fruits with large pesticide residues without first removing the peel). The use of peels in confectionery production (candied fruits, zest, etc.) is also prohibited.
Organophosphorus pesticides comprise a large group of drugs of various chemical structures, which are based on esters of phosphorus acids. Among them, monothiophosphoric acid esters [thiophos (parathiop), metaphos (methyl parathion)], phosphonic acid esters [chlorophos (trichlorfon)], dithiophosphoric acid esters [karbofos (malathion), rogor] occupy a prominent place.
The basis for the widespread use of organophosphorus pesticides in agricultural practice was, first of all, their high insecticidal efficiency and relatively rapid inactivation in the external environment.
By means of organophosphorus preparations, apparently, there will be a real opportunity to solve the problem of the “ideal pesticide,” that is, a pesticide that, having a vigorous effect on the object being exterminated, does not linger on the treated plant objects and is inactivated in a short time. At the same time, residual amounts of pesticides in food products would be completely eliminated and the basic hygienic requirement could be fulfilled - that human food products should be completely free from chemical impurities, including residual amounts of pesticides, even the most insignificant ones.
This approach to the evaluation of pesticides has made it possible to attempt wider approval of highly toxic pesticides for use in agriculture. Indeed, many organophosphate pesticides approved in different countries are highly toxic. Thus, DL50 of parathion (thiophos) is 6-15 mg/kg, methyl parathion (metaphos) 15-25 mg/kg, octamethyl 5-7 mg/kg.
Such highly toxic drugs could be approved for practical use only under the obligatory condition of complete elimination of their residues in processed food crops and foodstuffs.
An important feature of organophosphorus pesticides is their relatively low toxicity, and in some cases the complete absence of toxic properties of the products of their breakdown (hydrolysis). This made it possible to assume the presence in all food products of residual amounts of decomposition products of such highly toxic organophosphorus pesticides as thiophos and metaphos.
Such common pesticides as metaphos and karbofos break down much faster and are almost completely inactivated within a few days after treatment.
The study showed that contact organophosphorus preparations that do not penetrate into plant objects (thiophos, karbofos, metaphos) have properties of low stability in the external environment and rapid disintegration on treated objects.
Other organophosphorus pesticides, classified as systemic or intraplant pesticides, are characterized by a pronounced ability to penetrate into plants and spread to all their parts, including the edible part.
Systemic drugs, as a rule, are significantly more stable in the external environment. Systemic organophosphorus drugs (M-81, phosphamide, octamethyl) are subject to strict regulation and are limited in practical use.
Organophosphorus pesticides are generally less stable in the environment than organochlorine pesticides and many have a half-life of 2-5 days.
Organophosphorus pesticides do not accumulate in the body of animals and humans, since the latter do not have cumulative properties. Organophosphorus pesticides are usually not excreted in the milk of lactating animals.
In the mechanism of action of organophosphorus pesticides on the body, the leading one is inhibition of cholinesterase activity, which is associated with phosphorylation of its active centers. There are also changes in catalase activity, a decrease in the content of certain amino acids in blood serum proteins, changes in protein fractions of blood and other biochemical parameters.
Thus, organophosphorus pesticides, due to their high insecticidal effectiveness, wide range of action, the presence of systemic and contact properties, rapid hydrolyzability in the external environment, the absence of pronounced cumulative properties and the ability to be excreted in milk for a long time, have great prospects.
Most Common Organophosphorus Pesticides
- thiophos
- metaphos
- karbofos
- rogor
- chlorophos
Thiophos
The most toxic and highly persistent organophosphorus pesticides in the external environment include thiophos (DL50 6-15 mg/kg). Residual amounts of non-hydrolyzed thiophos are not allowed in food products, and only thiophos decomposition products that do not have toxic properties are allowed.
Despite the presence of numerous foreign data on the absence of danger from the presence of significant residues of thiophos in agricultural products processed by it, due to its high toxicity, thiophos is not allowed to be used in agriculture.
Karbofos
Karbofos (malathion) is the most typical representative of the group of dithiophosphoric acid esters. Karbofos is a pesticide that is low-toxic for warm-blooded animals and humans and at the same time has high insecticidal activity.
The drug quickly breaks down on treated plant surfaces. The half-life of karbofos does not exceed 1-3 days. It hydrolyzes easily when heating and washing the fruits. The resulting metabolites are easily soluble in water and have low toxicity.
Rogor
Rogor (dimethoate) refers to the esters of dithiophosphoric acid. It is more stable in the external environment compared to karbofos. The half-life of rogor is 2-5 days. Due to the presence of systemic properties, rogor can linger in fruits (apples) for a long time. Rogor is found not only in the skin, but also in the pulp of apples. The pesticide content in apples 15 days after treatment was quite high and amounted to 0.8 mg/kg.
Rogor is found in the organs and tissues of slaughtered animals as a result of the use of feed contaminated with this pesticide. The residual content of rogor in fruits and citrus fruits is allowed in an amount not exceeding 1.5 mg/kg.
Chlorophos
Chlorophos (trichlorophone) is a phosphonic acid ester, discovered as an insecticidal agent in 1952 simultaneously in Germany and the USA. In a short time it has become widespread in agricultural practice, especially for processing cotton and rice. Chlorophos has low toxicity DL50 950-1100 mg/kg.
The positive side of chlorophos is its rapid decomposition in the external environment, its half-life is 1-2 days. In this regard, the residual content of chlorophos in vegetables and fruits during the period of their collection is, as a rule, insignificant.
Thorough washing of vegetables and fruits can significantly reduce the concentration of chlorophos. There is evidence that chlorophos and some other organophosphorus pesticides can be excreted by lactating animals in their milk.
Thus, the danger of chlorophos entering the human body as part of food is low and its use as a pesticide is acceptable to a greater extent than many other organophosphorus pesticides. According to sanitary requirements, the residual content of chlorophos is allowed in all food products in an amount not exceeding 1 mg/kg.
Esters of carbamic acid, or carbamates
These include sevin, tsineb, and ciram.
The basis for the widespread production of carbamates was their many positive aspects. They have a wide spectrum of action, high insecticidal activity and relatively low resistance in the external environment.
At the same time, there is data on some aspects of the adverse effects of carbamates on the animal body: the carcinogenic properties of zineb, the teratogenic effect of sevin, the mutagenic manifestations of zineb and maneb, as well as the adverse effects of some carbamates on reproductive function. Some carbamates are methemoglobin formers.
In the mechanism of toxic action of sevin and other carbamates, the leading role belongs to the blocking effect on cholinesterase and other vital enzyme systems. In this regard, carbamates have much in common with the action of organophosphorus pesticides, however, the severity of the manifestations of the action of carbamates is not as significant as that of FOS.
The toxic effect of carbamates is manifested in the influence on other enzyme systems, in particular on the activity of glycolytic enzymes and energy metabolism in general. Sevin has an inhibitory effect on oxidative processes in tissues, oxidative phosphorylation, and cellular respiration enzymes.
In the clinical picture of sevin intoxication, the leading place is occupied by damage to the central nervous system and parenchymal organs. In this case, not only functional disorders are noted, but also changes of a morphological nature.
Sevin in the form of residues in food products should not be determined by modern laboratory techniques.
Organophosphorus compounds(or FOS) are insecticides and fungicides, derivatives of pentavalent phosphorus, which have similar mechanisms of action on insects.
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The disadvantage of organophosphorus compounds is the emergence of resistant populations and high acute toxicity for mammals, which requires appropriate precautions when using them.
Story
The history of the discovery of the toxic properties of organophosphorus compounds (OPCs) dates back to the beginning of the twentieth century.
At first they attracted attention as chemical warfare agents (sarin gas was synthesized in Germany in 1938). At the end of World War II, industrial installations were made to synthesize the former.
They have been introduced into agricultural production since 1965 to replace persistent and low-ecological ones, and others. FOS turned out to be easy to synthesize and highly effective against insects.
In the 1970s, half of the 20 most abundant compounds in the world were organophosphorus compounds, and 1/5 were methylcarbamates.
FOS have not lost their advantages to this day.
And
Effect on harmful organisms
Organophosphorus compounds are nerve poisons that cause paralysis, including death.
Most organophosphates do not ionize and exhibit significant lipophilic properties, so the substance that is inhaled or swallowed will be easily absorbed.
is as follows: the active substances, when ingested, phosphorylate the protein enzyme acetylcholinesterase (AChE). It is found in nerve tissues and plays an important role in the transmission of nerve impulses. This enzyme belongs to the group of carboxylic acid ester hydrolases. AChE is mainly localized at receptors on the postsynaptic membrane of the synapse and partially in the membrane of the neuron process (axon).Organophosphorus compounds, interacting with esterases, suppress their activity via competitive inhibition. A nerve cell, or neuron, is the main structural element of the nervous system of animals. Neurons transmit information in the form of impulses (nerve signals).
A neuron consists of:
- dendrites (numerous processes) connected to other nerve cells and collecting information;
- axon - a single long process ending in a thickening - a synoptic plaque, and transmitting information.
The membrane of one neuron, which is in contact with another cell (muscle cell or neuron), forms a functional contact between the excitable cells. It distinguishes between the presynaptic part - the end of the axon of the first cell, the synaptic cleft - the intercellular space separating the membranes of contacting cells, and the postsynaptic part - the section of the second cell.
In arthropods, information is transmitted in the form of an electrical signal (current) along the cell membrane. The synaptic cleft is filled with a gel-like substance that has a large electrical capacity, and the signal cannot pass through it. The transmission of an electrical signal (excitation) through the gap is carried out by mediators - the chemical substances norepinephrine and acetylcholine.
Humans and warm-blooded animals have five transmitters (including adrenaline), insects have about 100. When mediators are inactive, they are located in vesicles (synaptic vesicles), isolating them from the cellular contents. When the nerve impulse reaches the presynaptic part, the membrane of the cell terminal is depolarized, which increases its permeability to calcium ions. The latter, entering the presynaptic part, cause the release of the transmitter - the vesicle bursts, and acetylcholine, which is highly reactive, enters the intercellular space and then into the postsynaptic space of another cell, thereby causing an electrical potential.
The role of the enzyme acetylcholinesterase is that it, by hydrolyzing acetylcholine, reduces excitation. The entire process takes place in a matter of fractions of a second (milliseconds). If there is no acetylchoinesterase or it is blocked, then free acetylcholine accumulates in the synaptic cleft, as a result of which the normal passage of nerve impulses is disrupted. Tremor (convulsive muscle activity) occurs, turning into paralysis.
Organophosphorus preparations have a stronger effect on the postembryonic stages of development of insects and mites (adults) and a weaker effect on.
With the systematic use of preparations based on organophosphorus compounds for protection against ticks and insects, producing many generations per season, they quickly acquire group resistance. In the practice of plant protection, it is necessary to prevent development, for which they are used with various.
Application
drugs used in the form can manifest themselves in damage (burns) of leaves and especially flowers and buds.In agriculture
Preparations based on organophosphorus compounds are widely used in agriculture. The names of the drugs, the method of processing, the listing of protected crops can be found in the “Regulations for Use” tab, which exists for each.The most limited use of highly toxic organophosphorus compounds with pronounced cumulative properties, such as and. They are recommended primarily for the protection of grain, industrial, fruit and citrus crops.
Among vegetable crops, only those cultivated for seeds can be processed with them.
Berry fields are allowed to be processed before flowering or after harvesting.
The great advantage of organophosphorus compounds is the presence among them of substances that have the effect ( and ).
These properties of substances are very important, since in the modern assortment there are no others that have such an effect.
In private household plots
. In personal household farming, preparations based on, and are used.Toxic effect
Phosethyl aluminum
Fungicides
Effect on harmful organisms
Application
Toxic effect
Symptoms of intoxication may develop immediately or several hours after exposure. Symptoms may worsen over a day or more and persist for several days.
If the intoxication is mild or the compound is easily excreted from the body, the severity of symptoms may decrease quite quickly, although it may take several weeks for the levels of suppressed blood ChE to normalize. Following acute intoxication, some chronic effects are likely to persist, and weakness and fatigue may persist over time.
When the body is exposed to various organophosphorus compounds, the picture is generally similar. It is caused by the accumulation of acetylcholine (ACh) in nerve endings. Much depends on the route of entry of the poison into the body. If the substance comes into contact with the skin, the initial symptom may be the development of muscle fibrillations in this area. With inhalation, difficulty breathing and miosis first occur, after which the central and autonomic nervous systems are affected. When taken through the stomach, vomiting, intestinal spasms, and later other symptoms of the resorptive effect of substances usually occur.
Herbicides
Among organophosphorus compounds it is a broad-spectrum herbicide and arboricide. This compound has a selective and continuous effect and is used to control annual and perennial weeds.
. has a contact and partially systemic effect. It moves to the underground organs of the plant from the aboveground ones, being absorbed through the leaves. The compound is believed to inhibit phenylalanine biosynthesis.Prevention of this synthesis leads to plant death. Precipitation can wash away the drug residues from the plants into the soil. Plant roots do not absorb glyphosate from the soil.
Abstract on veterinary toxicology on the topic
Completed by a student IV – 6 FVM
Kashtanova Zh. N.
Moscow, 2004
1. General characteristics of the group.
2. Main compounds, their physicochemical properties, toxicity, application in agriculture.
3. Conditions conducive to poisoning.
4.Ways of penetration of poison into the body.
5.Mechanism of toxic action.
6. Absorption, distribution, release of poison.
7. Symptoms.
8. Pathological changes.
9.Diagnostics.
10.First aid and treatment.
11. Prevention.
12. Issues regarding the sale of products containing toxic compounds.
General characteristics of the group.
FOPs are divided into drugs with contact, intestinal and fumigative action. The first kill insects upon contact with their body, the second penetrate the body through the digestive organs, and the third through the respiratory tract. In addition, among the FOPs there are preparations of systemic intra-plant action that can spread throughout the vascular system of plants, making them toxic for sucking pests for a certain time.
Among organophosphorus compounds there are very active insecticides - means to combat insects, acaricides used to kill mites, fungicides - to combat pathogens of plant diseases, herbicides - to destroy weeds, defoliants - means that cause leaves to fall and facilitate ripening and machine harvesting some crops, desiccants - substances that help dry out plants, rotenticides (zoocides) - means for controlling rodents.
Basic compounds, their physicochemical properties, toxicity, application in agriculture.
Based on the chemical structure, POPs can be divided into the following groups:
1) derivatives of phosphoric acid;
thiophosphoric acid derivatives;
dithiophosphoric acid derivatives;
pyrophosphoric acid derivatives;
derivatives of phosphonic acids.
Derivatives of phosphoric acid.
Derivatives of thiophosphoric acid.
Name, basic synonyms |
Chem. Name |
|||||
Abat (diphos |
Derivatives of dithiophosphoric acid.
Name, basic synonyms |
Chem. Name |
|||||
Timet (forate |
Derivatives of pyrophosphoric acid.
Derivatives of phosphonic acids.
OPCs used as pesticides are either crystalline solids or clear or yellowish-brown, often oily liquids. Many of them have a specific unpleasant odor. Most FOPs are heavier than water, with densities ranging from 1.1 to 1.7.
Many POPs are highly soluble in organic solvents - xylene, toluene, acetone, chloroform, etc. However, some drugs (Kilval, Demufos, Chlorophos) are also soluble in water.
The high distribution coefficient of most OPs between oil and water ensures their penetration through various biological membranes, good resorption through intact skin, penetration into the brain through the blood-brain barrier, and the ability to suppress the activity of not only extracellular but also intracellular acetylcholinesterase. However, there are exceptions to this rule. For example, octamethyl, which is oxidized in the body into an even more polar compound phosphoraminoxide, poorly penetrates the blood-brain barrier and does not suppress the activity of brain acetylcholinesterase. Some other compounds that have positively charged onium atoms in their structure behave in the same way.
From a hygiene point of view, a very important property of compounds is their low stability, associated with the ability to hydrolyze under the influence of various environmental factors (acidic, neutral and alkaline environments, exposure to high temperatures, etc.).
Most POPs hydrolyze relatively quickly in an alkaline environment, but can be very stable in neutral and slightly acidic environments. This circumstance can be used to accelerate the destruction of FOP (use of alkalis). However, the opinion that OPPs are quickly destroyed in the external environment is correct only to a certain extent: in acidic soils and in the presence of a slightly acidic environment in plants and animal tissues, some OPPs can persist for a long time.
The hydrolysis of OPP can accelerate with increasing temperature, but even at 30-40ºC in an acidic environment, some of them can persist for several months.
One of the important properties of FOP from a hygiene point of view is their volatility. However, it is more convenient to consider the issue of the volatility of OPPs when describing their toxicity when inhaled into the body.
According to the degree of toxicity, in accordance with the classification of L.I. Medved et al. (1968), FOPs can be divided into 4 groups:
potent toxic substances (LD50 less than 50 mg/kg);
highly toxic substances (50-200 mg/kg);
substances of moderate toxicity (200-1000 mg/kg);
substances of low toxicity (more than 1000 mg/kg).
At the moment, OPs belonging to the SDYAV group have been replaced in agriculture with less toxic substances. This is due to the fact that drugs related to SDYAV cause 86% of poisonings (V.I. Polchenko, 1973), drugs VT - 8%, ST - 6% and MT - 2%.
Until now, from the SDYAV group, only metaphos, which is produced in the form of 20% emulsifiable concentrate, 30% wettable powder and 2.5% dust and is used for the treatment of orchards, vineyards, field, vegetable and melon and technical structures, as well as grains, legumes and tobacco, and octamethyl, produced in the form of a 60% emulsion concentrate and used limitedly only for spraying mulberries, and the berries are prohibited from being eaten.