Occupational Toxicology

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Occupational Toxicology is the science that is dedicated to the study of the toxic actions produced by chemical compounds used in industry and which tend to penetrate man as a result of their manipulations and uses.

In broad terms, toxic action or toxicity is understood as the relative capacity of a compound to cause damage through adverse biological effects, once it has reached a susceptible point in the body.

For the development of Industrial Toxicology and knowledge of the adverse effects that chemical pollutants produce on workers, three procedures are used: animal experience with extrapolation to man, epidemiology and chemical analogy.


For systematic intoxication to occur, a means of transporting the poison is necessary, this medium is normally blood. Once the poison enters the bloodstream, it circulates reaching the area where it exerts its action. Later it is deposited or it will be eliminated, transforming itself through metabolic reactions.

We can consider, sequentially, the movement of the toxin inside the organism (kinetics) in the following way: Absorption, Distribution, Location, Accumulation or Fixation and Elimination.

Absorption consists of the passage of the toxic into the circulatory system, for which it will have to cross, in any case, some type of biological membrane, for example: the alveolar membrane. The cell membrane is made up of three layers. Each of these layers has a thickness of 25 A. The two protein layers are responsible for elasticity, resistance and hydrophilicity, and these will be in contact with the aqueous media outside and inside the cell. The lipid intermediate layer is bimolecular and constitutes the main skeleton. This structure will regulate the passage of toxins through it. The lipoid cornea will favor the passage of fat-soluble substances, that is, neutral, but the strong electrical charge of the membrane hinders the passage of ionized substances.

The mechanisms by which a poison can cross the membrane will be: by simple diffusion, by filtration, or by active transport. In the latter case, energy input is required, which is provided by the cell itself.

By diffusion, only neutral molecules can penetrate, and their speed depends on the lipid / water partition coefficient, that is, the ratio of the solubility of the toxin in these media, and the difference in concentrations of the toxin on both sides of the membrane.

There is a form of absorption which is catalyzed diffusion, which requires the presence in the cell membrane of a carrier, which can combine with the toxic substance and move freely through the membrane. Since it is a form of diffusion, the transfer will always be carried out towards lower values of an electrochemical great.

This type of union is specific, the carriers only bind to a limited minimum of substances of similar chemical structure. These substances can compete with each other for the carrier and cause inhibition.

By filtration, small anions can penetrate through the pores of certain cells, due to the groupings of positive charges, which in turn prevent the passage of cations.

Active transport, which allows the passage of electrically charged substances, occurs only with the help of specific enzymes and with the use of energy, provided by the ATP that comes from the oxidative phosphorylation processes that continuously take place inside the cell. The carrier enzyme binds to the toxin to be transported, modifies its structure in such a way as to facilitate its passage through the membrane and once inside the cell the complex unfolds and the cycle is renewed.

Skin absorption

In this type of penetration, the poison must cross many layers of cells until it reaches the capillaries. The poison must be more or less soluble in the different layers of the skin, each with its own chemical characteristics. In general, absorption will be more favorable for fat-soluble compounds such as solvents, being almost nil for metallic compounds, unless there are chelation and protein denaturation phenomena.

The annexes of the skin, glands, hairs, etc., as well as the damaged areas of the skin, significantly modify their absorption capacity with respect to the transepidermal capacity.

Digestive absorption

In this case, the fat-soluble compounds will be easily absorbed and the ionized ones will be influenced by changes in the pH of the digestive tract. The ionization states of the molecules will vary depending on the pH and, as a consequence, their greater or lesser ease of absorption. In the stomach and small intestine there are specialized "carriers" for the absorption of metal ions.

Respiratory absorption

The inhalation route is the most important absorption route in Industrial Hygiene, due to its ease of penetration and its large exchange surface.

Fat-soluble gases and vapors reach the alveolar volume and are diluted in the air already present; absorption occurs by diffusion and will depend on the concentration of the toxin in the alveolar volume, the diffusion coefficient through the alveolar membrane and the partition coefficient between air and blood.

The alveolar concentration will depend on the environmental concentration of the toxin and the exposure time. The partition coefficient will depend on the solubility of the toxin in plasma lipids, its ability to bind to plasma proteins, and its solubility in tissue membranes.

Distribution: When the poison has passed into the blood, it spreads it throughout the body. Incorporation into the blood can be done by simple dissolution or by binding to proteins or blood cells. The speed of diffusion of the toxin depends mainly on the modality of this incorporation into the blood, as well as the route of penetration followed.

Accumulation: Toxic products distributed throughout the body by the blood can be fixed in those organs for which they have the greatest affinity. The most affected organs are usually the most vascularized or those with a constitution rich in lipids. When the fixation does not cause a local effect, it constitutes an accumulation process, which is capable of prolonging the effects of the poison, after ceasing the exposure, due to the progressive release of the accumulated product.

Metabolism: Chemical compounds can be altered by their interaction with the body. This metabolic action tends to transform the molecules of the compound into more water-soluble products in the blood plasma to facilitate their elimination.

This process means detoxification, except in some cases where the first stage of metabolism produces a more toxic product than the starting one.

Elimination: Absorbed toxins can be eliminated from the body by various routes depending on various factors.

The volatile products are partly eliminated by the respiratory route, in a process contrary to their absorption. Most of the compounds are excreted to a great extent in the urine, either unchanged or as products of their metabolism. Some toxins are eliminated by the bile, in which case they can be reabsorbed by the intestine, thus prolonging the intoxication.


The presence of a contaminant in the environment in which an individual is found causes their exposure to the contaminant in question. The consequence of this exposure (external exposure) is that a certain amount of the pollutant may reach or enter the worker's body, producing certain effects (intoxication) on the worker.

The amount of poison that the body absorbs (incorporates) is called the dose. Generally, it is expressed in mg / Kg. subject's weight.

The intensity of the damage in the worker exposed to toxic substances is proportional, however, to a series of factors, some of human nature, others characteristic of the pollutant such as its toxicity, the speed of absorption of the pollutant by the body, concentration and time of exposition.

Since human factors, toxicity and absorption rate are constant for each case, we can say that in a person the concept of exposure,

Given that human factors, toxicity and absorption rate are constant for each case, we can say that in a person the concept of exposure, as a magnitude, integrates two different variable factors: the concentration or level of presence of the contaminant in the environment. and the time or duration of the exposure itself. E = f (c, t


The effect produced by a poison in an organism is not only a function of the dose Three poisonings are known according to the speed of penetration into the organism:

Acute intoxication

It leads to a serious alteration of the organism and manifests itself in a short period of time. For it to occur, acute exposure to the poison and rapid absorption by the body is necessary.

Subacute poisoning

It presents a lower degree of severity than acute poisoning and follows a subclinical course, with no apparent manifestations for some time.

Chronic intoxication

The poison penetrates in small repeated doses over a long period of the life of the subject..


We have specified the toxic effect (or intoxication) in the ability of chemical compounds to produce adverse biological effects. In reality, there are no harmless chemicals. Among these effects there are the following dualities, which are used as a system to classify chemical pollutants:

Local and general

The first appear in the place of contact of the poison with the organism and the second appear in points away from that place.

Acute and chronic

They respond to a distinction from the clinical point of view according to the duration of the evolution of the manifestations.

Reversible and irreversible

It refers to the possibility of recovery of the normal state after the remission of the biological changes produced by the poison.

Cumulative and non-cumulative

Difference between toxins that act by accumulation in the body, being eliminated very slowly, and those whose elimination is much faster, and that act when exposure is intense enough.

Stochastics (quantal) and non-stochastic (graduated)

In the first group, the possibility of the effect occurring increases with the dose of poison received (eg, carcinogens). In the second, it is the intensity or severity of the effect that depends on the dose (eg: corrosives).

He continued treating them about what goes into the subject of industrial hygiene, in this case one of the occupational risks is toxicology, which I dealt with in this post, I like to contribute with the people who have more conscience regarding what it is Occupational Health and Safety that is very important.

Occupational safety, health and welfare.


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