The risks associated with other activities, including the exposure to various chemicals, cannot be readily assessed and quantified. Historical data on risks of chemical exposure may involve a single, very high exposure that has resulted in an immediately observable form of injury. Assessment of the risks of chemical exposures that do not cause immediately observable forms of injury or disease is far more complicated. Exposure Assessment quantifies the amount and duration of exposure to a chemical via all possible routes, such as by consuming contaminated water or food or inhaling polluted air. Risk Characterization is an estimate of the potential incidence of any adverse health effects, such as acute poisoning or cancer in a population likely to be exposed to a given chemical.
Any chemical can be toxic if the dose is high enough.
Toxicity is considered acute if the effects are evident almost immediately after exposure to a chemical. Examples of acute health effects are nausea, lung irritation, skin rash, vomiting, dizziness, and even death. The concentrations of chemicals in groundwater, however, are seldom high enough to cause acute toxicity. Examples of chronic health effects include cancer, birth defects, organ damage, nervous system disorders, and immune system damage. There is no direct evidence linking groundwater contamination by pesticides to any chronic health effects.