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Final Progress Reports: Columbia University: Bioavailability of Soil PB and AS in Humans

Superfund Research Program

Bioavailability of Soil PB and AS in Humans

Project Leader: Conrad B. Blum (College of Physicians & Surgeons, C.U.)
Grant Number: P42ES010349
Funding Period: 2000 - 2006

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Final Progress Reports

Year:   2005 

The primary aims of Dr. Blum’s project are to 1) determine estimates of the bioavailability of lead (Pb) in soils from a mining site, smelting site and urban site; 2) to test the hypothesis that phosphate-based soil amending agents reduce this bioavailability in adult humans; and 3) to examine the correlation between the human and in vitro estimates of bioavailability in these soils.  This study involves the ingestion of tiny amounts of sterilized soils, which contain lead but no other contaminants of concern.  The method utilizes the technique known as stable isotope dilution, and takes advantage of the fact that the presence of non-radioactive isotopes of lead in soil allows one to track tiny amounts of lead that are actually absorbed into blood.

A total of 20 volunteer subjects have completed the protocol designed to assess the bioavailability of lead in soil.  The first 12 study participants were randomly assigned to ingest either the phosphate amended or non-amended soil.  This soil from a former smelting site in Joplin, MO, was treated with 1% phosphate at the site, by the U.S. EPA, and sampled at 6 month intervals.  Blum’s team evaluated an “amended” and “non-amended” soil specimen that was sampled 18 months post-treatment.  Final Pb isotope and bioavailability data were analyzed in the Geochemistry Core Laboratory.

The findings, are extremely interesting and potentially important.  Among the 6 subjects who received the non-amended soil, the mean Pb bioavailability was 34.7%.  In contrast, among those who received the phosphate-amended soil, mean Pb bioavailability was 19.9%, significantly less.  While there is a wide range of inter-individual variability, this represents an average reduction in bioavailability of 43%. 

Studies evaluating the bioavailability of these same soil samples in animals, by Casteel et al, and in an in vitro system, by Ruby et al, reported a 38% reduction in bioavailability, by both methods, validating the relative effect that phosphate inactivation has on soil lead bioavailability in these samples.  It is particularly important to note that this work to date appears to validate the use of the in vitro and animal models, in that the values obtained for bioavailability in all three systems are coherent with each other.

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