Environmental Engineering Reference
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causing a harmful or adverse health effect (ATSDR 2009). Factors influencing the LOAEL
include the following:
• The chemical's solubility in body fluids
• The particle size and state of the chemical
• Route of exposure
• Residence time of the chemical in the body
• Individual susceptibility
Dosage units are expressed as the mass of chemical per unit mass of body weight in
mg/kg. These units are employed to evaluate the relative toxicities between animals of
different species and size. To develop the most accurate human exposure limits, exten-
sive animal studies are initially used to establish extrapolated human dosage limits for a
specified chemical, and these estimates are refined by human health studies conducted on
individuals known to have been exposed to the same chemical. The Occupational, Safety,
and Health Administration (OSHA) has established a list of exposure limits for over 600
individual chemicals and refers to exposure limits as permissible exposure limits (PELs)
(ACGIH 2009).
Most chemicals or substances have the potential to exhibit some adverse health effect
on humans or other organisms, given a certain set of circumstances.
Adverse health effect
is defined as a change in body function or cell structure potentially leading to disease or
health problems (ATSDR 2009).
The effect that a specific chemical or substance may exhibit on a living organism is
dependent upon the following factors (USEPA 1989a; USEPA 2005):
• Nature of the chemical or substance
• Concentration
• Route of exposure
• Length of time of exposure
• Individual susceptibility
Chemicals and substances enter the human body through three
routes of exposure
—inhala-
tion, ingestion, and dermal adsorption (USEPA 1989a). When exposure occurs, chemicals
may produce one or more of these symptoms:
• Tissue irritation
• Eye irritation
• Rash
• Dizziness
• Bleeding
• Hair loss
• Loss or depressed vision
• Loss or depressed hearing
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