Human exposures from dioxin in soil--a meeting report

Area of Science:

• Environmental Science
• Toxicology
• Risk Assessment

Background:

• A 1984 risk assessment set a "level of concern" for dioxin in soil at 1 part per billion (ppb).
• This assessment relied on assumptions, particularly regarding soil ingestion rates by toddlers.
• The original authors cautioned against using this level as a universal standard due to site-specific factors.

Purpose of the Study:

• To re-evaluate dioxin exposure assessments in light of new research.
• To discuss the importance of site-specific data in determining acceptable dioxin levels in soil.
• To address the discrepancy between assumed and actual soil ingestion rates.

Main Methods:

• A workshop convened 50 experts to discuss published and new research on exposure estimation.
• Review of studies on soil ingestion rates in children and bioavailability of dioxin.
• Analysis of dioxin half-lives in various soil types.

Main Results:

• Average soil ingestion by children is significantly lower than previously assumed (0.04 g/day vs. 10 g/day).
• However, some children ingest high amounts of soil (e.g., 5 g/day), raising questions about risk management for average vs. extreme exposures.
• Dioxin half-lives and bioavailability vary widely depending on soil characteristics, emphasizing the need for site-specific data.

Conclusions:

• The 1 ppb level of concern for dioxin in soil should not be a de facto standard.
• Exposure assessment guidelines should incorporate site-specific data and consider planned land use.
• Risk management decisions must balance average and extreme exposure scenarios and address potential future land use changes.