Deriving safe short-term chemical exposure values (STEV) for drinking water

Area of Science:

• Environmental Health
• Toxicology
• Water Quality Assessment

Background:

• Temporary chemical exceedances in drinking water pose minimal health risks.
• Short-term exposure values (STEV) are crucial for assessing drinking water safety during brief contamination events.
• Existing toxicity data and regulatory guidelines inform STEV derivation.

Purpose of the Study:

• To calculate and compare STEV for pesticides using three distinct methodologies.
• To evaluate the consistency and conservatism of different STEV calculation approaches.
• To assess the broader applicability of a preferred STEV derivation method.

Main Methods:

• Approach 1: STEV derived from the acute reference dose (ARfD).
• Approach 2: STEV calculated by removing uncertainty factors from current guideline values.
• Approach 3: STEV extrapolated from 1-day and 7-day no observed adverse effect levels (NOAEL) using log-linear regression.

Main Results:

• All three approaches produced comparable STEV for pesticides, typically within one order of magnitude.
• Calculated STEV often overlapped with existing short-term no adverse response levels (SNARL) and health advisories (HA).
• Approach 2, adjusting guideline values with standard extrapolation factors, consistently yielded the most conservative STEV.

Conclusions:

• Multiple methods can effectively derive STEV for drinking water contaminants.
• Approach 2 demonstrates robust applicability for pesticides, disinfection by-products (DBPs), and cyanotoxins.
• Conservative STEV derivation is essential for ensuring public health protection during water quality excursions.