Meta‐Analysis of Mass‐Balance Studies of Soil Ingestion in Children

Abstract

Ingestion of soil by young children may be an important source of exposure to environmental contaminants. Estimates of soil ingestion have been made by several studies using trace elements in a mass-balance approach, but differ substantially between studies and trace elements. We conduct a meta-analysis of four major mass-balance soil ingestion studies conducted on children between one and seven in the summer/fall in the northern United States. The analysis takes advantage of primary data from all studies, and provides a more complete description of soil ingestion among children. The meta-analysis uses data based on the two most reliable trace elements, Al and Si, that have passed a screening to identify and exclude measures with a high likelihood of bias. Details are described in a companion paper. The best linear unbiased predictor is used in a mixed model to estimate soil ingestion for study subjects. Overall, 11% of subject-periods are identified as outliers and excluded from the analysis. An analysis on 216 children based on Al and Si as tracer elements indicates that the mean (median) soil ingestion is 26 mg/day (33 mg/day), with the 95th percentile estimated as 79 mg/day. This systematic approach provides more reliable estimates than individual study results. There is some evidence that soil ingestion increases with a child's age, but insufficient data to distinguish soil ingestion by gender.

Soil ingestion rate determination in a rural population of Alberta, Canada practicing a wilderness lifestyle

“…Such a detailed examination of ingestion rate for First Nations' people may prove very useful for risk assessments of remote contaminated regions or areas being considered for resource exploitation. One would expect that soil ingestion rates will be lower in winter, but this is still speculative since all soil ingestion studies conducted to date have been done in summer and early fall (Stanek et al, 2011).…”

Soil ingestion rates for children under 3 years old in Taiwan

“…were not considered, a positive bias may be introduced. 10 Tracers may be absorbed in the gastrointestinal tract, and hence a negative bias may be introduced. 10 The transit time is defined as the time spent from the tracer ingestion to the tracer output in feces.…”

“…10 Tracers may be absorbed in the gastrointestinal tract, and hence a negative bias may be introduced. 10 The transit time is defined as the time spent from the tracer ingestion to the tracer output in feces. 10 The bias of transit time misalignment can be reduced by extending the duration of study.…”

“…10 The transit time is defined as the time spent from the tracer ingestion to the tracer output in feces. 10 The bias of transit time misalignment can be reduced by extending the duration of study. 21 However, compared with the biokinetic modeling methodology, the tracer element methodology still has advantages because of noninvasive collection of individual biological and environmental samples from the study subjects.…”

“…A number of previous studies have shown various limitations and uncertainties for the tracer element methodology including study duration and location, representativeness of soil tracer element concentrations, adjustments made for tracer element concentrations of non-soil substances, gastrointestinal absorption and transit times, weight of feces, and recovery rates of different tracer elements. [1][2][3][4][5][6][7][8][9][10][11][12][13] The tracer should be abundant and uniform in soils and low in the diet or food. Moreover, it assumed that children primarily ingested soil from their house, and the soil samples could be representative of the entire house.…”