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| Last Updated:: 01/04/2016

Toxic Chemicals : Health Effect

Toxic Chemicals: The U.S. Environmental Protection Agency or EPA defines a toxic chemical as any substance which may be harmful to the environment or hazardous to your health if inhaled, ingested or absorbed through the skin.


Natural Toxic Chemicals:

  • Mercury
  • Snake venom
  • Caffeine in coffee, tea, kola and cocoa
  • Arsenic
  • Ricin from castor beans
  • petroleum
  • Hydrogen sulfide
  • Chlorine gas
  • Smoke

TOXICITY is the ability of a substance to produce an unwanted effect when the chemical has reached a sufficient concentration at a certain site in the body.


HAZARD is the probability that this concentration in the body will occur.



  1. An open container of an acid is much more hazardous than a closed container of the same material.
  2. Two liquids may possess the same degree of toxicity but present different degrees of hazard:- One material may be non-irritating to the eyes and nose and odourless. The other may be irritating to the eyes or respiratory system and possess a pungent odour. The latter material, because of its warning properties presents a lesser degree of hazard.


Routes of Entry


There are three primary routes of entry into the body: ingestion, skin or eye absorption, and inhalation.

Ingestion:- This means taking a material into the body by mouth (swallowing). Ingestion of toxic materials may occur as a result of eating in a contaminated work area.

Absorption- Substances that contact the eye and the skin may be either absorbed into the body or cause local effects. For the majority of organic compounds, the contribution from skin absorption to the total exposure should not be neglected.

Inhalation- This means taking a material into the body by breathing it in. In the lungs, very tiny blood vessels are in constant contact with the air we breath in. As a result, airborne contaminants can be easily absorbed through this tissue. In the occupational environment, this is generally the most important route of entry.


Health Effects


Chronic vs Acute

Once a toxic substance has contacted the body it may have either acute (immediate) or chronic (long term) effects.

Example: Spilling acid on your hand will cause immediate harm, i.e. a burn to the skin.

Exposure to asbestos or tobacco smoke may result in lung cancer after as much as twenty years (this is a long term effect).


Exposure - Chronic vs Acute


Exposure can be classified as chronic or acute.

In Chronic exposures, the dose is delivered at some frequency (daily or weekly usually) over a period of time.


In Acute exposures, the dose is delivered in a single event and absorption is rapid. Usually, a chronic exposure occurs at low concentration and acute exposure at high concentration.


Some materials may only cause harm if given acutely, not having any effect in the long term. Other materials may not exhibit an effect in the short term, but may cause problems after prolonged exposure.


Carcinogens - agents/compounds that will induce cancer in humans.


Mutagens - agents that affect the cells of the exposed people in such a way that it may cause cancer in the exposed individiual or an undesirable mutation to occur in some later generation.


Irritants - refers to some sort of aggravation of whatever tissue the material comes in contact with.


Anaesthetics - the main toxic action is the depressant effect upon the Central Nervous System.


Teratogens - Agents or compounds that a pregnant woman takes into her body that generate defects in the fetus.




Target Organ Toxicity:  Many toxins do not produce general effects but are specific to only a few organs.

  • Vinyl chloride:  Liver Cancer


  • Asbestos:  Mesothelioma


  • Paraquat:  Lung Toxicity


  • Cadmium:  Kidney Toxicity



Target organs are often not the site of the highest concentration of a chemical.


  • Lead concentrates in bone, but its effects are mainly seen in soft tissues, such as liver, kidney and blood cells.


  • DDT accumulates in adipose tissue (fat stores), but produces no effects is primarily a central nervous system toxin.



Target organs most frequently affected by toxicants:
    1.  Central nervous system

    2.  Circulatory system (blood, blood-forming system)

    3.  Visceral organs (liver, kidneys, lung)

    4.  Muscle and Bone