Advancing Methodologies Used in Trace Element-Based Mass Balance Studies to Separately Estimate Soil and Dust...

Area of Science:

• Environmental Health
• Toxicology
• Exposure Science

Background:

• Historically, trace element-based mass balance (MB) studies estimated soil ingestion rates for risk assessments in contaminated communities.
• The MB approach cannot distinguish between soil and dust ingestion, despite their differing characteristics.
• Previous alternative methods yielded results inconsistent with MB studies.

Purpose of the Study:

• To evaluate the limitations of the mass balance (MB) methodology for estimating soil ingestion rates.
• To develop a hybrid physical model separating outdoor soil, indoor tracked-in soil, and total dust ingestion exposures in children.
• To characterize environmental and behavioral determinants of children's soil and dust ingestion.

Main Methods:

• Formulated a hybrid physical model integrating data from five MB studies.
• Utilized SHEDS-Soil/Dust time-activity pattern-based modeling runs for new data.
• Explicitly separated outdoor soil, indoor tracked-in soil (dust component), and total dust ingestion pathways.

Main Results:

• Predicted mean soil ingestion rates were 30%-70% lower than MB-based 'total soil' ingestion rates.
• Predicted dust ingestion rates generally exceeded predicted soil ingestion rates.
• Predicted total soil plus dust ingestion rates were up to 60% higher than MB-based 'total soil' rates.

Conclusions:

• The hybrid model provides a more accurate assessment of children's soil and dust ingestion exposures.
• Outdoor soil contributed 29%-70% to total soil ingestion, while tracked-in soil comprised 30%-71% of indoor dust ingestion.
• This refined methodology improves exposure assessment accuracy for children in chemically contaminated environments.