Common Contaminants in Urban Watersheds - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 229

• Nausea
• Anxiety
• Narcosis
• Headache
• Vomiting
• Diarrhea
• Pain
• Fever
• Tremors
• Shortness or difficulty in breathing
• Psychotic behavior
• Euphoria
• Cancer
• Death
• And others
Human response to exposure of a chemical is described as acute or chronic. An acute
response is generally characterized as a single high dose with rapid onset and disap-
pearance of symptoms. Chronic response involves a stimulus lingering for a period of
time (USEPA 2009a). Exposure to a contaminant may not trigger an immediate response.
Instead, there is a latency period —a duration of time without observable effects. Certain
chemicals or substances such as asbestos and forms of mercury have a latency period of
up to 10-20 years (USEPA 2005).
Exposure to some chemicals or substances may result in the development of cancer,
and any chemical, substance, radionuclide, or radiation contributing to the develop-
ment or propagation of cancer is termed a carcinogen (United States Department of
Health and Human Services 2005). Cancer exists when cells in the body become abnor-
mal and grow or multiply out of control (ATSDR 2009). There is also often some selec-
tivity involved with chemical exposure, as some chemicals may target certain organs,
parts of the body, or reproduction. For example, teratogens may have an adverse affect
on a developing fetus, mutagens may induce genetic changes that could affect future
generations through reproduction, and hepatotoxins are chemicals posing a risk of liver
damage.
Carcinogens are grouped into five general categories (ACGIH 2009):
• Group A1: Confirmed human carcinogen
• Group A2: Suspected human carcinogen
• Group A3: Confirmed animal carcinogen with unknown relevance to humans
• Group A4: Not classified as a human carcinogen
• Group A5: Not suspected as a human carcinogen
It is much more difficult to evaluate the toxicity of a mixture of contaminants compared
to a single chemical compound or substance. This is because the interaction of a mixture