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Water: Water Quality Standards Academy

Basic Course: Supplemental Topics - Health (w)

Exposure Assessment: Parameters and Protection Goals

Human Health Ambient Water Quality Criteria

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  • EPA generally assumes daily exposure over the course of a lifetime.
  • EPA generally assigns a mix of average values and high-end values (e.g., 90th percentile) for exposure parameters such as ingestion rates and body weight.
  • EPA’s criteria are derived to protect the majority of the general population.

See, for example, the equation below for deriving noncarcinogenic effects, which includes the RSC term.


The three exposure terms in the bracketed portion of the equation address the mix of average and 90% values by EPA in deriving the human health AWQC:

Fish/Shellfish Intake (17.5 g/day; 90th percentile estimate for consumption of fish/shellfish from estuarine and fresh waters for adults in the general population). (Note that FI needs to be converted to kg/day for use in the equation.)

Key Point. The parameters shown above are for the general adult population and assume a lifetime exposure. These will be used by EPA for the national recommended water quality criteria when chronic health effects are of concern. However, there are some circumstances where pregnant women or children may be the population of interest. These would be situations where the critical effect on which the RfD is based applies to developmental effects that would impact the fetus during pregnancy or children during their period of physical maturation.
Learn More. Parameter options for select populations.  Proceed to the Learn More Topic. » Note: This link launches a pop-up window.

For informational purposes only–Not official statements of EPA policy.

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