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Differences in indirect risk methodologies: dioxin emissions from combustion facilities
K L Hentz1, S W Pirages, K A Williams
1Karch & Associates, Incorporated, Washington, DC 20036.
Regulatory Toxicology and Pharmacology : RTP
|August 1, 1994
Summary
Estimating indirect risks from industrial waste combustion requires careful methodology. Different EPA guidance documents yield vastly different risk estimates, highlighting the need for site-specific data and realistic assumptions.
Area of Science:
- Environmental Science
- Risk Assessment
- Toxicology
Background:
- Current guidance for indirect risk evaluations is evolving.
- Estimates of indirect risks from industrial waste combustion are increasingly demanded by the Environmental Protection Agency (EPA) and the public.
- Two distinct guidance documents exist for these risk estimations: one specific to dioxin exposures and a more general one.
Purpose of the Study:
- To compare indirect risk estimates derived from two different EPA guidance methodologies.
- To identify key assumptions contributing to discrepancies in risk estimates.
- To assess the impact of specific exposure pathways and the toxic equivalency approach on risk calculations.
Main Methods:
- Comparative analysis of risk estimation methodologies from two EPA guidance documents.
- Evaluation of assumptions including vapor uptake, food consumption rates, and soil dermal contact.
- Assessment of the influence of an individual exposure pathway on overall risk estimates.
- Application of a toxic equivalency approach to evaluate its effect on risk reduction.
Main Results:
- Indirect risk estimates varied by as much as 30-fold for the same exposure pathway between the two methodologies.
- Assumptions regarding vapor uptake, food consumption rates, and the proportion of locally consumed food significantly influenced the final estimates.
- A major difference was observed in assumptions about soil dermal contact in children.
- The toxic equivalency approach reduced risk estimates by 16- to 18-fold.
Conclusions:
- Discrepancies in indirect risk estimates stem from differing assumptions in EPA guidance documents, particularly concerning soil dermal contact for children.
- EPA default assumptions are often overly conservative and unrealistic, underscoring the necessity of site-specific data for accurate risk assessment of combustor emissions.
- Employing a toxic equivalency approach can substantially decrease risk estimates, suggesting its potential utility in risk management.