Module 3: Toxicology - Section 3: Linking Chemical Exposures and Health Effects

TOX 3.4: Mechanisms Of Disease Causation

MECHANISMS OF DISEASE CAUSATION:

Chemical substances exert their effects through various mechanisms:

• Acute:

  The effect is exerted immediately or within a few hours of exposure (implies rapid accumulation at the target organ site; the severity of the reaction is directly proportional to the exposure dose rate) e.g. chemical asphyxiants (cyanide, carbon monoxide, hydrogen sulphide, nitrogen dioxide), irritants (chlorine, sulphur dioxide, ammonia) and corrosives (acids).

• Chronic:

  The effect is exerted after months or years of exposure (implies gradual accumulation at the target organ site; severity is directly proportional to the exposure dose rate) e.g. heavy metallic toxins such as lead. Certain substances demonstrate a delayed effect following a prolonged latency period (can occur with prolonged exposure or transient exposure) e.g. carcinogens such as asbestos.

• Allergenic:

  The effect is exerted through the immune system (multiple initial doses result in sensitisation with the accumulation of antibodies; subsequent low-level exposure triggers a response; pronounced individual susceptibility) e.g. respiratory and skin sensitisers (chrome, nickel, platinum salts).