Industrial Toxicology
Industrial
toxicology which aims to protect the health of the
workers who may be exposed to a toxic substance either
directly or indirectly through their workplace activities
The traditional definition of toxicology is "the science of poisons."
A more descriptive definition of
toxicology is "the study of the adverse effects of
chemicals or physical agents on living organisms".
Toxicity is the ability of a chemical molecule or compound to produce injury once it reaches a susceptible site in or on the body.
Toxicity hazard is the probability that injury will occur considering the manner in which the substance is used.
Dose-Response Relationship
The potential toxicity (harmful action) inherent in a
substance is exhibited only when that substance comes in contact with a
biological system. A chemical normally thought of as “harmless” may
evoke a toxic response if added to a biological system in sufficient
amount. The toxic potency of a chemical is thus defined by the response
that is produced in a biological system .
The
dose-response relationship is a fundamental and essential concept in
toxicology. It correlates exposures and the spectrum of induced
effects. Generally, the higher the dose, the more severe the
response. The dose-response relationship is based on observed data from
experimental animal, human clinical, or cell studies.
Knowledge of the dose-response relationship:
1.establishes causality
that the chemical has in fact induced the observed effects
2.establishes the
lowest dose where an induced effect occurs - the threshold effect
3.determines the rate
at which injury builds up - the slope for the dose response.
"All substances are poisons;
there is none which is not a poison.
The right dose differentiates a poison
from a remedy.”
Paracelsus (1493-1541)
LD50: LD
stands for "Lethal Dose".
LD50 is the amount of a material, given all at once, which
causes the death of 50% (one half) of a group of test animals. The LD50 is
one way to measure the short-term poisoning potential (acute toxicity) of a material.
Acute toxicity
is the ability of a chemical to cause ill effects relatively soon after one
oral administration or a 4-hour exposure to a chemical in air.
LC50: The concentration of a chemical in an environment (generally air or water) which produces death in 50% of an exposed population of test animals in a specified time frame
Normally expressed as (mg/l) milligrams of substance per liter of air or water (or as ppm)
Routes of Entry into the Body
There are four main routes by which hazardous chemicals enter the body
- Inhalation: Absorption through the respiratory tract (Most important in terms of severity)
- Skin absorption or absorption through the mucous membranes
- Ingestion: Absorption through the digestive tract, it can occur through eating or smoking with contaminated hands or in contaminated work areas.
- Injection: Introduction of toxin into bloodstream; can occur by accidental needle stick or puncture of skin with a sharp object.
Types of Effects
Acute poisoning is characterized by rapid absorption of the substance when the exposure is sudden and severe. Normally, a single large exposure is involved. Examples are carbon monoxide or cyanide poisoning.
Chronic poisoning is characterized by prolonged or repeated exposures of a duration measured in days, months or years. Symptoms may not be immediately apparent. Examples are lead or mercury poisoning, or pesticide exposure.
Local refers to the site of action of an agent where the action takes place at the point or area of contact. The site may be skin, mucous membranes, the respiratory tract, gastrointestinal system, eyes etc. Absorption does not necessarily occur. Examples are strong acids or alkalis.
Systemic refers to a site of action other than the point of contact and presupposes absorption has taken place. For example, an inhaled material may act on the liver. For example, inhaled benzene affects the bone marrow.
Cumulative poisons are characterized by materials that tend to build up in the body as a result of numerous chronic exposures. The effects are not seen until a critical body burden is reached.
Examples are heavy metals.
Synergistic or potentiating effects occur when two or more hazardous materials present at the same time have a resulting action greater than the effect predicted based on the individual substances. For example, workers exposed to benzene may show a direct toxicity in hematopoietic tissue and therefore be more susceptible to oxygen-displacing agents such as carbon monoxide.
Factors Affecting Toxicity
- Rate of entry and route of exposure - how fast the toxic dose is delivered and by what means.
- Age - can affect the capacity to repair damaged tissue.
- Previous exposure - can lead to tolerance, increased sensitivity, or make no difference.
- State of health, medications, physical condition, and life style - can affect the toxic response, Pre-existing disease can result in increased sensitivity.
- Environmental factors - temperature and pressure, for example, can affect exposure.
- Host factors - genetic predisposition and the sex of the exposed individual.
Physical Class Affects on Toxicity
When considering the toxicity of gases and vapors, the solubility of the substance is a key factor. Highly soluble materials like ammonia irritate the upper respiratory tract. On the other hand, relatively insoluble materials like nitrogen dioxide penetrate deep into the lung. Fat soluble materials, like pesticides, tend to have longer residence times in the body.
An aerosol is composed of solid or liquid particles of microscopic size dispersed in a gaseous medium. The toxic potential of an aerosol is only partially described by its concentration in milligrams per cubic meter (mg/m3). For a proper assessment of the toxic hazard, the size of the aerosol’s particles is important. Particles above 1 micrometer tend to deposit in the upper respiratory tract. Particles less than 1 micrometer in diameter enter the lung. Very small particles (< 0.2 μm) are generally not deposited.
Physiological Classifications of Toxic Materials
Irritants are materials that cause inflammation of mucous membranes with which they come in contact. Inflammation of tissue results from concentration far below those needed to cause corrosion. Examples include: Ammonia, Alkaline Dusts And Mists, Hydrogen Chloride/Hydrogen Fluoride, Halogens, Ozone, Phosgene, Diethyl/Dimethyl Sulfate, Nitrogen Dioxide, Phosphorus Chlorides, Arsenic Trichloride
Irritants can also cause changes in the mechanics of respiration and lung function. Examples include:
sulfur dioxide, acetic acid, formaldehyde, formic acid, sulfuric acid, acrolein.
Long-term exposure to irritants can result in increased mucous secretions and chronic bronchitis.
A primary irritant exerts no systemic toxic action because the products formed on the tissue of the respiratory tract are non-toxic or because the irritant action is far in excess of any systemic toxic action. Example: Hydrogen Chloride.
A secondary irritant’s effect on mucous membranes is over-shadowed by a systemic effect resulting from absorption.Examples include: hydrogen sulfide, aromatic hydrocarbons; Exposure to a secondary irritant can result in pulmonary edema, hemorrhage, and tissue necrosis.
Corrosives are chemicals which may cause visible destruction of or irreversible alterations in living tissue by chemical action at the site of contact. Examples include:Sulfuric acid, Potassium hydroxide, Chromic acid, Sodium hydroxide
Asphyxiants have the ability to deprive tissue of oxygen. Simple asphyxiants are inert gases that displace oxygen.Examples include: Nitrogen, Helium, Carbon Dioxide, Argon.
Chemical asphyxiants render the body incapable of utilizing an adequate oxygen supply. They are toxic at very low concentrations (few ppm). Examples include:- Carbon Monoxide, Cyanides, Hydrogen Sulfide
Primary anesthetics have a depressant effect upon the central nervous system. Particularly the brain.
Examples include: Halogenated Hydrocarbons, Alcohols
Hepatotoxic agents cause damage to the liver. Examples include:- Carbon Tetrachloride, Nitro-amines, Tetra-chloroethane
Nephrotoxic agents cause damage to the kidneys. Examples include: Halogenated Hydrocarbons, Uranium compounds
Neurotoxic agents damage the nervous system. The nervous system is especially sensitive to organometallic compounds and certain sulfide compounds. Examples include:Trialkyl Tin Compounds, Methyl Mercury, Organic Phosphorus Insecticides, Manganese,Tetraethyl Lead, Carbon Disulfide, Thallium
Hematopoietic (blood) system agents either directly affect blood cells or bone marrow. Examples include:-Nitrites, Aniline,Toluidine, Nitrobenzene, Benzene.
Pulmonary tissue (lungs) agents can be toxic, through other mean than by immediate irritant action. Fibrotic changes can be caused by free crystalline silica and asbestos. Other dusts can cause restrictive disease called pneumoconiosis.
Examples include:- Coal Dust, Cotton Dust, Silica Dust & Asbestos Fibres etc.
A teratogen (embryo toxic or fetotoxic agent) is an agent which interferes with normal embryonic development without damage to the mother or lethal effect on the fetus. Effects are not hereditary. Examples include:- Lead, Dibromo Dichloropropane
A mutagen is a chemical agent which may able to react with nucleophilic structures such as DNA. Mutations can occur on the gene level (gene mutations) when, for example, one nucleotide base-pair is change to another. Mutations can also occur on the chromosomal level (chromosomal mutations) when the number of chromosomal units or their morphological structure is altered.
Examples of mutagens include most Radioisotopes, Barium Permanganate & Methyl Isocyanate.
Sensitizers causes a substantial proportion of exposed people to develop an allergic reaction in
normal tissue after repeated exposure to the chemical. The reaction may be as mild as a rash
(contact dermatitis) or as serious as anaphylactic shock.
Examples include:- Epoxides, Nickel Compounds, Chromium Compounds, Chlorinated Hydrocarbons, Formaldehyde, Amines, Toluene Di-isocyanate
Target Organ Effects
The following is a target organ categorization of effects which may occur from exposure to hazardous chemicals, including examples of signs and symptoms and chemicals which have been
found to cause such effects.
Hepatotoxins (liver)
Signs and symptoms:
Jaundice, Liver Enlargement
Example chemicals:
Carbon Tetrachloride, Nitrosamines, Chloroform, Toluene, Perchloroethylene, Cresol, Dimethylsulfate
Nephrotoxins (kidney)
Signs and symptoms:
Edema, Proteinuria
Example chemicals:
Halogenated Hydrocarbons, Uranium, Chloroform,
Mercury, Dimethyl Sulfate
Neurotoxins (nervous system)
Signs and symptoms:
Narcosis, Behavioral Changes, Decreased Muscle Coordination
Example chemicals:
Mercury, Carbon Disulfide, Benzene, Carbon Tetrachloride, Lead, Mercury, Nitrobenzene
Hematopoietic (blood) system
Signs and symptoms:
Cyanosis, Loss Of Consciousness
Example chemicals:
Carbon Monoxide, Cyanides, Nitrobenzene, Aniline, Arsenic, Benzene, Toluene
Pulmonary (lung) system
Signs and symptoms:
Cough, Chest tightness, Shortness of Breath
Example chemicals:
Silica Asbestos, Nitrogen Dioxide, Ozone, Hydrogensulfide, Chromium, Nickel, Alcohol
Reproductive system (mutations and teratogenesis)
Signs and symptoms:
Birth Defects, Sterility
Example chemicals:
Lead, Dibromo Dichloropropane
Skin (dermal layer)
Signs and symptoms:
Defatting Of Skin, Rashes, Irritation
Example chemicals:
Ketones, Chlorinated Compounds, Alcohols, Nickel, Phenol, Trichloroethylene
Eye or vision
Signs and symptoms:
Conjunctivitis, Corneal Damage
Example chemicals:
Organic Solvents, Acids, Cresol, Quinone, Hydroquinone, Benzyl Chloride, Butyl Alcohol, Bases
Absorption,
Distribution, And Excretion Of Toxic Substances
This information is collected and present in order to create awareness.
