Ambient water quality criteria derived using probabilistic risk assessment

Area of Science:

• Environmental Science
• Risk Assessment
• Toxicology

Background:

• National ambient water quality criteria (AWQC) are typically derived using a deterministic approach by the US Environmental Protection Agency (USEPA).
• This deterministic method has been criticized for compounded conservatism and an inability to specify population protection levels.
• Probabilistic risk assessment (PRA) is proposed as a more transparent and robust alternative for deriving AWQC.

Purpose of the Study:

• To introduce a novel PRA method for deriving AWQC.
• To quantitatively compare the PRA approach with the USEPA's deterministic method using national inputs.
• To provide regulators and stakeholders with a better understanding of different AWQC derivation methods.

Main Methods:

• Developed and applied a PRA methodology for AWQC derivation.
• Utilized national input data consistent with USEPA guidance.
• Conducted case studies comparing probabilistically derived AWQC with USEPA's 2015 recommendations.

Main Results:

• The PRA approach reduces compounded conservatism by using entire data distributions instead of point estimates.
• PRA-based AWQC demonstrably protect specific segments of the exposed population.
• Quantitative comparisons highlight differences between deterministic and PRA-derived AWQC.

Conclusions:

• The proposed PRA method provides a scientifically defensible alternative for deriving AWQC.
• This study offers valuable insights into the assumption- and method-specific differences between criteria.
• Findings will aid water quality managers and regulators in selecting appropriate AWQC derivation approaches.