Disinfection Byproducts in Drinking Water from the Tap: Variability in Household Calculated Additive Toxicity (CAT)

Area of Science:

• Environmental Chemistry
• Toxicology
• Public Health

Background:

• Calculated additive toxicity (CAT) estimates risk from disinfection byproducts (DBPs) in water.
• Existing regulatory monitoring may not fully capture household exposure to DBPs.

Purpose of the Study:

• Investigate the CAT approach for 21 regulated and unregulated DBPs at the household level.
• Identify key DBPs contributing to toxicity and assess the predictive power of regulated DBPs for unregulated ones.
• Examine household variability in DBP exposure and toxicity.

Main Methods:

• Collected tap water samples from over 120 participants across diverse water systems and conditions.
• Applied the CAT approach using multiple in vitro bioassay potencies.
• Analyzed concentrations of 21 regulated and unregulated DBPs.
• Developed simple linear models to compare regulated vs. unregulated DBP concentrations and CAT.

Main Results:

• Unregulated DBPs, such as haloacetonitriles and iodoacetic acid, were identified as major drivers of toxicity.
• Linear models showed weak predictability (r² < 0.3 for 67%) between regulated and unregulated DBP concentrations and CAT.
• Household-level DBP exposure and associated toxicity showed significant variability.

Conclusions:

• Current regulatory monitoring of DBPs may be insufficient to accurately assess household exposure risks.
• Unregulated DBPs contribute significantly to overall DBP toxicity.
• Future DBP risk assessments should incorporate a wider range of compounds, including unregulated ones.