In vivo and in vitro methods for evaluating soil arsenic bioavailability: relevant to human health risk assessment.

Arsenic (As) is the most frequently occurring contaminant on the priority list of hazardous substances, which lists substances of greatest public health concern to people living at or near U.S. National Priorities List site. Accurate assessment of human health risks from exposure to As-contaminated soils depends on estimating its bioavailability, defined as the fraction of ingested As absorbed across the gastrointestinal barrier and available for systemic distribution and metabolism. Arsenic bioavailability varies among soils and is influenced by site-specific soil physical and chemical characteristics and internal biological factors. This review describes the state-of-the science that supports our understanding of oral bioavailability of soil As, the methods that are currently being explored for estimating soil As relative bioavailability (RBA), and future research areas that could improve our prediction of the oral RBA of soil As in humans. The following topics are addressed: (1) As soil geochemistry; (2) As toxicology; (3) in vivo models for estimating As RBA; (4) in vitro bioaccessibility methods; and (5) conclusions and research needs.

Lead exposure in young children over a 5-year period from urban environments using alternative exposure measures with the US EPA IEUBK model - A trial.

The US Environmental Protection Agency (EPA) Integrated Exposure Uptake Biokinetic (IEUBK) model has been widely used to predict blood lead (PbB) levels in children especially around industrial sites. Exposure variables have strongly focussed on the major contribution of lead (Pb) in soil and interior dust to total intake and, in many studies, site-specific data for air, water, diet and measured PbB were not available. We have applied the IEUBK model to a comprehensive data set, including measured PbB, for 108 children monitored over a 5-year period in Sydney, New South Wales, Australia. To use this data set, we have substituted available data (with or without modification) for standard inputs as needed. For example, as an alternative measure for soil Pb concentration (µg/g), we have substituted exterior dust sweepings Pb concentration (µg/g). As alternative measures for interior dust Pb concentration (µg/g) we have used 1) 30-day cumulative petri dish deposition data (PDD) (as µg Pb/m2/30days), or 2) hand wipe data (as µg Pb/hand). For comparison, simulations were also undertaken with estimates of dust Pb concentration derived from a prior regression of dust Pb concentration (µg/g) on dust Pb loading (µg/ft2) as concentration is the unit specified for the Model. Simulations for each subject using observed data aggregated over the 5-year interval of the study, the most usual application of the IEUBK model, showed using Wilcoxon tests that there was a significant difference between the observed values and the values predicted by the Model containing soil with hand wipes (p < 0.001), and soil and PDD (p = 0.026) but not those for the other two sets of predictors, based on sweepings and PDD or sweepings and wipes. Overall, simulations of the Model using alternative exposure measures of petri dish dust (and possibly hand wipes) instead of vacuum cleaner dust and dust sweepings instead of soil provide predicted PbB which are generally consistent with each other and observed values. The predicted geometric mean PbBs were 2.17 ( ± 1.24) µg/dL for soil with PDD, 1.95 ( ± 1.17) µg/dL for soil with hand wipes, 2.36 ( ± 1.75) µg/dL for sweepings with PDD, and 2.15 ( ± 1.69) for sweepings with hand wipes. These results are in good agreement with the observed geometric mean PbB of 2.46 ( ± 0.99) µg/dL. In contrast to all other IEUBK model studies to our knowledge, we have stratified the data over the age ranges from 1 to 5 years. The median of the predicted values was lower than that for the observed values for every combination of age and set of measures; in some cases, the difference was statistically significant. The differences between observed and predicted PbB tended to be greatest for the soil plus wipes measure and for the oldest age group. Use of 'default dust' values calculated from the site-specific soil values, a common application of the IEUBK model, results in predicted PbB about 22% (range 0 to 52%) higher than those from soil with PDD data sets. Geometric mean contributions estimated from the Model to total Pb intake for a child aged 1-2 years was 0.09% for air, 42% for diet, 5.3% for water and 42% for soil and dust. Our results indicate that it is feasible to use alternative measures of soil and dust exposure to provide reliable predictions of PbB in urban environments.

Estimating Children's Soil/Dust Ingestion Rates through Retrospective Analyses of Blood Lead Biomonitoring from the Bunker Hill Superfund Site in Idaho.

BACKGROUND: Soil/dust ingestion rates are important variables in assessing children's health risks in contaminated environments. Current estimates are based largely on soil tracer methodology, which is limited by analytical uncertainty, small sample size, and short study duration. OBJECTIVES: The objective was to estimate site-specific soil/dust ingestion rates through reevaluation of the lead absorption dose-response relationship using new bioavailability data from the Bunker Hill Mining and Metallurgical Complex Superfund Site (BHSS) in Idaho, USA. METHODS: The U.S. Environmental Protection Agency (EPA) in vitro bioavailability methodology was applied to archived BHSS soil and dust samples. Using age-specific biokinetic slope factors, we related bioavailable lead from these sources to children's blood lead levels (BLLs) monitored during cleanup from 1988 through 2002. Quantitative regression analyses and exposure assessment guidance were used to develop candidate soil/dust source partition scenarios estimating lead intake, allowing estimation of age-specific soil/dust ingestion rates. These ingestion rate and bioavailability estimates were simultaneously applied to the U.S. EPA Integrated Exposure Uptake Biokinetic Model for Lead in Children to determine those combinations best approximating observed BLLs. RESULTS: Absolute soil and house dust bioavailability averaged 33% (SD ± 4%) and 28% (SD ± 6%), respectively. Estimated BHSS age-specific soil/dust ingestion rates are 86-94 mg/day for 6-month- to 2-year-old children and 51-67 mg/day for 2- to 9-year-old children. CONCLUSIONS: Soil/dust ingestion rate estimates for 1- to 9-year-old children at the BHSS are lower than those commonly used in human health risk assessment. A substantial component of children's exposure comes from sources beyond the immediate home environment. CITATION: von Lindern I, Spalinger S, Stifelman ML, Stanek LW, Bartrem C. 2016. Estimating children's soil/dust ingestion rates through retrospective analyses of blood lead biomonitoring from the Bunker Hill Superfund Site in Idaho. Environ Health Perspect 124:1462-1470; http://dx.doi.org/10.1289/ehp.1510144.

Using doubly-labeled water measurements of human energy expenditure to estimate inhalation rates.

Doubly-labeled water (DLW) data is recognized as an improvement over alternative methods to quantify human energy expenditure. Previously, energy expenditure has been estimated indirectly using heart-rate monitoring, calorimetry, or accelerometer measurements. Inhalation rate estimates can benefit from improved energy expenditure estimates using equations developed by Layton. DLW methods are advantageous for several reasons: the database is robust, they are direct measures, subjects are free-living, and the observation period is longer than what is possible from staged activity measures. DLW energy data is an improvement over previous inhalation estimates based on dietary recall survey data. Mean long-term inhalation rates of 16 m3/day and 13 m3/day, for physically active adult men and women, respectively, were derived based on DLW estimates of energy expended. The range of human energy expenditure is narrow with the maximum energy expenditure not likely greater than twice the minimum.

A case study of lead contamination cleanup effectiveness at Bunker Hill.

A review of cleanup effectiveness at Bunker Hill Superfund Site (BHSS) has shown that yard soil cleanup is an effective tool for reducing house dust lead concentrations, thereby reducing children's blood lead levels. This review has also shown that contiguous cleanup of residences has a three-fold greater reduction of children's blood lead levels compared with cleaning only those homes where children currently reside by reducing exposures attributable to neighboring properties. This review underscores the importance of a community-wide, preventative approach to controlling lead contamination in soil and house dust. This review has further characterized the need for careful design, implementation, and perpetual maintenance of a community-wide lead cleanup. Several key areas of importance to maintain large scale mining/smelting remedies in the Bunker Hill area were analyzed and noted for further action, including: infrastructure, institutional controls for homeowner projects (post cleanup), erosion control for undeveloped hillsides with potential to impact the developed valley floor, drainage improvements and flood control, waste piles, and increasing the rate at which cleanup proceeds. Focusing on these areas is crucial to minimizing recontamination at a large scale lead cleanup.