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A straw man proposal for a quantitative definition of the RfD
Dale Hattis1, Sandra Baird, Robert Goble
1Center for Technology, Environment, and Development, George Perkins Marsh Institute, Clark University, 950 Main Street, Worcester, MA 01610, USA. dhattis@aol.com
Drug and Chemical Toxicology
|October 16, 2002
Summary
This study proposes a new numerical calculation for reference doses (RfDs) to better account for uncertainty and variability in chemical risk assessment. Current RfDs may not meet desired risk criteria, highlighting the need for improved methods in toxicology.
Area of Science:
- Toxicology and Risk Assessment
- Environmental Health Sciences
- Biostatistics
Background:
- Current reference doses (RfDs) aim to protect public health but have limitations in explicitly addressing uncertainty and variability.
- Existing RfDs may not consistently achieve desired risk management goals across diverse populations.
- There is a need for more precise and transparent methods for calculating RfDs that reflect real-world exposure scenarios and human sensitivities.
Purpose of the Study:
- To evaluate a proposed numerical calculation for RfDs that incorporates both uncertainty and variability.
- To assess the feasibility and implications of a new RfD definition for regulatory applications.
- To compare the proposed RfD calculation with existing methods and analyze their impact on current regulatory values.
Main Methods:
- A straw man proposal for a numerical RfD definition was developed and evaluated against specific criteria.
- Existing uncertainty factors were applied to 18 randomly selected chemical entries from the Integrated Risk Information System (IRIS).
- Quantitative probabilistic performance objectives for RfDs were specified and assessed using distributional information on human variability.
Main Results:
- Analysis suggests current RfDs meet a 1/100,000 risk criterion with only slightly better than 50% confidence.
- Current RfDs often fall short of achieving the 1/100,000 risk criterion with 95% confidence, by approximately an order of magnitude.
- Human inter-individual variability in response to chemical doses is the most significant source of uncertainty.
Conclusions:
- It is feasible to establish quantitative probabilistic performance objectives for RfDs and assess current values against them.
- Preliminary risk estimates near current RfDs and their uncertainties can be determined.
- Harmonizing cancer and non-cancer risk assessments is possible, fostering open discussion and encouraging better data collection on human susceptibility.