In-vitro and In-vivo approaches for the measurement of oral bioavailability of lead (Pb) in soil: A critical review

Authors: ZIA, MUNIR - Fauji Fertilizer Company Limited; Codling, Eton; SCHECKEL, KIRK - Environmental Protection Agency (EPA); Chaney, Rufus

Submitted to: Environmental Pollution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/11/2011
Publication Date: 9/15/2011
Citation: Zia, M.H., Codling, E.E., Scheckel, K.G., Chaney, R.L. 2011. In-vitro and In-vivo approaches for the measurement of oral bioavailability of lead (Pb) in soil: A critical review. Environmental Pollution. 159:2320-2327.

Interpretive Summary: Lead, heavy metal in polluted urban areas is an issue of serious environmental concern since the last several decades. There are two kinds of approaches through which one can estimate lead (Pb) risk assessment to living organisms. One approach relies on trials using animals as test objects while the alternate approach, less laborious, opts for inexpensive laboratory simulation extractions that match animal test results. The recent evidence has clearly shown that with aging, and addition of some amendments such as phosphatic fertilizers etc., lead in soil has been transformed to inactive forms and only a minute portion of this is bioavailable. Therefore, urban managers need to revise environmental policies related to lead metal risk assessment.

Technical Abstract: Urban soils are commonly contaminated by Pb and some other elements from house paint, automotive emissions, and general urban emissions. Soil Pb near painted houses can exceed 10,000 mg/kg, while commonly ranging from 500 to 1000 mg/kg. Such high soil Pb levels raise concerns about exposure of children to the soil as play areas or vegetable gardens because young children ingest soil by hand-to-mouth activity. These levels exceed EPA and HUD guidance for soil Pb. However, soils have been fed to test animals and found to have much lower bioavailability of the Pb than assumed by EPA based on study of matrices such as food and water. Soil Pb bioavailability depends on soil properties, time after contamination, and additions of phosphate and organic matter in common soil amendments. Thus, reliable evaluation of the potential hazard to the public greatly depends upon the bioavailability of Pb in soil which may be ingested. Several researchers have shown that In-vivo soil Pb bioavailability tests can be replaced by In-vitro or bioaccessibility tests to save cost and time. Although In-vitro approaches do not represent the entire physiological process controlling the absorption of metals in the gastrointestinal (GI) tract or their dissolution from the soil, these tests are considered useful in assessing broad potential impacts of soil ingestion on human health. On the other hand, present bioaccessibility methods are expensive and laborious except for the new simplified test of Zia, et. al. Recent findings have revealed that fractional bioaccessibility (bioaccessible compared to total) of Pb in urban soils is only 10% of total Pb in soils, far lower than the 60% as bioavailable as food-Pb presumed by the United States Environmental Protection Agency (USEPA) in evaluating risk from soil Pb. This review supports revised recommendations from the USEPA and the United States Department of Agriculture (USDA) for Pb contaminated soils.