indsutrialtoxicology

Industrial Toxicology

Industrial toxicology is a science that deals with potential harmful effects of materials, products and wastes on health and environments. Toxicology combines the knowledge from the following fields:

Chemistry

Biology

Pharmacology

Physiology

Pathology

Methods for Assessing Toxicity:

Toxicity data for substances come from many sources, most often from controlled studies. Because all chemicals can become toxic under a specific condition, the studies manage not only the amount of chemical involved, but also the conditions of exposure. Nearly all substances fail to exhibit effects at very low exposure levels, but at some level, effects begin to appear. This suggests a threshold level for effects, above which increased concentrations will produce more severe effects. Also, as exposure levels increase, the effects are likely to occur in a larger portion of the population. The following is the list of methods used for the assessment of toxicity:

Human Experimentation

Human Experience

Animal Studies

Microorganism Testing

Human Experimentation: One way to collect data on toxicity of materials is application of the experiment to human subjects. In general, this method is limited to the cases when a serious concern for some disease or illness is present. When a pharmaceutical substance appears to have high benefit and relatively low risk as a result of many other tests, the FDA may approve testing in humans. There is virtually no opportunity to perform general testing of substances on human subjects. Therefore, toxicity data must come from other than human tests.

Human Experience: Sometimes accidental exposures provide opportunities to compile data on the toxicity of a substance. The exposures may be acute or chronic. In accidental exposures there is no control over the exposure and generally it is difficult to draw a conclusion from a single occurrence. Researchers must estimate the exposure levels using epidemiological procedures. After a pattern of disease appears that could be related to some exposure, further testing will be necessary in order to draw a conclusion.

Animal Studies: Most toxicity data come from controlled and replicated animal studies. A problem in toxicity testing involves time. Some substances produce disease in a portion of a population after a long latency period or chronic exposure. To replicate slow exposure or wait for latency periods would be very expensive. As a result, many toxicity test procedures involve high dose rates.

Microorganism Testing: This is a short-term test for toxicity , which monitors the growth patterns of a bacteria with and without exposure to a toxic chemical. These test do not include the variables that animal studies do in the mathematical models for generalizing test results to humans.

Dose and Response Relationship:

In the science of industrial toxicology no chemical should be viewed as entirely safe or entirely harmful. An excessive concentration of any substance will produce a harmful or an undesirable effect in animals or humans. The dose-response relationship is the most important factor in the study of industrial toxicology in humans. This relationship determines the safe and the harmful concentrations of a chemical for biological mechanisms in animals. The following figure shows the Dose-Response relationship.

The dose-response relationship for any given chemical will vary with the species of animal used in the laboratory test program. A family of dose-response curves for a particular chemical can be developed for various animals, such as mice, rats, guinea pigs, and rabbits. Some types of animals are more sensitive than others to a given chemical, and because animal sensitivity can vary greatly among species, the extrapolation of dose-response data from one test animal to another animal species should be attempted with extreme caution. The same concern should be used in trying to apply laboratory animal toxicity data to human effects.

Figure 1. Dose-Response Curve

Dose Threshold: The dose threshold is the minimum dose required to produce a measurable effect.

Lethal Dose: A lethal dose of a given substance is the dose that is highly likely to cause death. Such doses are established through experiments on animals. Lethal dose is usually given by ingestion or injection. A subscript indicates the portion of the experimental population died from that dose. LD ₅₀ means that 50 % of a test population died from a dose.

TDL: Lowest published lethal dose.

Lethal Concentration (LC): Lethal concentration is applied only to airborne concentrations. A lethal concentration of an inhaled substance is the concentration that is highly likely to result in death. Lethal concentration is taken into the body through inhalation of airborne toxic chemicals. A subscript indicates the portion of the experimental population died from that dose. LC10 means that 10 % died from an inhaled concentration.

TCL: Lowest published lethal concentration.

Health Effects of Toxic Chemicals:

Health effects for different chemicals vary considerably. The likelihood and degree of damage depend on type and form of substance, the type and rate of exposure and what happens to the substance in the body. Most hazardous materials affect particular organs of the body. For example, some damage tissue, such as skin and eyes, on contact, some affect respiration and some affect the nervous system. Often general symptoms, such as headache, and nausea, are confused with symptoms of other diseases.

Latency Period: Some chemical have immediate effects. An example is strong acid or caustic contacting tissue and destroying it. (Chemical burns). Other chemical may not show immediate effects. The delay between exposure and observable effect is a latency period. Some carcinogens have a latency period as long as 40 years.

Local versus Systemic Effects: Local effects occur when substances cause injury to skin, eyes, or respiratory tracts. Systemic effects occur when substances enter the body and produce damage to organs or biological functions. Kidney dysfunction or failure, clotting of blood, damage to liver tissue and ulceration in the digestive tract are examples for systemic effects of chemicals.

Asphyxiants: These chemicals do not have direct effects on the body or its organs, but they displace oxygen in a breathing atmosphere. The reduced oxygen content affects the partial pressure of oxygen and inhibits oxygen transport in the blood.

Pneumoconiosis: This is a disease of the lungs resulting from the inhalation of various types of dusts and other particles. The disease has several names depending on the type of material one is exposed to. Asbestosis (Inhalation of asbestos fiber ); Silicosis (Inhalation of free silica dust from mining, sandblasting, quarrying) and Byssinosis (Cotton dust) are examples for different forms of pneumoconiosis.

Dermatitis: There are many forms of skin disorders, many of which result from exposures to chemicals. Dermatitis is a general term for skin disorders. Some forms of dermatitis exhibit reddening; others involve cracking, sores, acne and other disorders.

Conjunctivitis: Inflammation of the conjunctiva which is the delicate membrane that lines the eyelids and covers the exposed surface of the eyeball.

Carcinogens: A substance that produces cancer in animals or human under certain quantified exposures.

Mutagens: A substance that causes changes in the genetic structure in a current generation of animals or humans such that it can cause cancer or some mutation in a later generation. Mutagens cause inheritable changes in chromosomes.

Teratogens: A substance that causes malformations or serious deviations from the normal in a human or animal fetus. Typically teratogens do not cause any exposure effect on the mother but interfere with the normal embryonic development.

Toxicity Rating System:

U = Unknown	Insufficient data are available to asses the toxic hazard of the chemical.
0 = No toxicity	Produces no toxic effect under normal conditions.
1 = Low, Slight Toxicity	Slight effects on skin, eyes and mucous membrane. (Reversible changes)
2= Moderate	This type of chemicals may cause reversible or irreversible changes in the human body not necessarily severe enough to cause serious impairment or threaten life.
3 = High Severe Toxicity	This type of chemicals cause irreversible changes, disfigurement and permanent impairment. Sufficient severity may threaten life.

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Last Update: February 26, 2000

By: Serdar Z. Elgun