Meta-Analysis Results from Children’s Soil and Dust Ingestion Rate Studies
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Ingestion of soil and dust by children is a potential source of exposure to environmental contaminants. However, robust data for this exposure factor are lacking for many of the children’s age groups of interest to EPA. We conducted a literature search to identify available soil and dust ingestion rates for children based on published results from three main types of studies: trace element-based mass-balance (MB) studies, biokinetic studies, and activity pattern studies. Our goal was to pool the results from all three categories of studies using alternative meta-analysis approaches. Our focus was to derive pooled estimates of total soil plus dust ingestion rates, along with their confidence intervals for various age groups of children of interest to EPA, within the age range from 0 to 21 years old. First, we evaluated the reliability of tracers used in different MB studies and the physical interpretation of reported results. We concluded that the published “soil” ingestion rates did not always represent “soil” or “soil plus dust” ingestion rates, depending on the tracers used. We then developed a novel approach to physically estimate soil plus dust ingestion rates by adjusting the data from published (Best Tracer Method) MB studies. These modified results were then pooled with estimates of soil plus dust ingestion rates derived from biokinetic and activity pattern studies as part of the meta-analysis. Results from the meta-analysis were produced for each age group and study type, as well as for all three study types combined. Several different statistical methods were used to calculate the estimates and their confidence intervals for the mean total soil plus dust ingestion rates. Specifically, we used a fixed effects method (inverse variance method), two different random effects methods, and the maximum likelihood method. This analysis produced estimates of soil and dust ingestion rates in finer age ranges than presented in current guidance. We compared several of our results with existing recommendations for various age groups from EPA’s Exposure Factors Handbook. This presentation will share details on the approach and results generated.