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United States Department of Agriculture

Agricultural Research Service

Title: Effect of Biosolids Processing on the Bioavailability of Lead in Urban Soils

item Hallfrisch, Judith

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 1, 2002
Publication Date: January 10, 2003

Interpretive Summary: Soil lead can comprise risk to young children who ingest soil. And because of the dispersal of Pb in urban areas from stack sources, automobiles, and historic Pb paints and pesticides, urban soils are somewhat to severely Pb contaminated. No Federal program exists to protect children against this Pb, and the default approach of removing the contaminated soil depth is very expensive and disruptive. Based on a series of basic studies on Pb uptake by lettuce and soil Pb bioavailability to rats, we found that when such soils were amended with some biosolids and composts, soil Pb because much less bioavailable. This study was a systematic test of different biosolids processing technologies at one treatment works, and two high Fe composted biosolids which had previously reduce soil Pb bioavailability. An urban soil from the inner city of Baltimore was collected, and different processed biosolids were amended to the soil at about 224 t/ha and incubated for 30 days. Soil was then mixed well, sieved, and fed to rats at 5% of diet for 30 days. Bone, kidney, liver and blood Pb showed similar patterns of response to the different biosolids products. In particular, high Fe biosolids or composts caused up to 50% reduction in soil Pb bioavailability. This work indicates that incorporation of low cost biosolids composts into high Pb urban soils can reduce Pb risk to children quickly. At the end of the incubations, several chemical extraction methods were tested on the soils to learn if a rapid inexpensive chemical test may be correlated well with the results of feeding tests. The results strongly support the validity of chemical extractions at pH 2 or above. Further, biosolids composts use improves lawns, making soil harder to ingest.

Technical Abstract: Lead contamination of urban soils due to auto emissions and lead-based paints is one of the most severe environmental problems to date. It may be possible to reduce the bioavailability of Pb in situ through the addition of different amendments to the soil. The amendments may complex the Pb and reduce its solubility in the human gastric system. A range of biosolids from the same treatment plant that had undergone different processing technologies as well as a high Fe biosolids compost and a high Fe, limed biosolids compost were added to a Pb contaminated urban soil at a rate equivalent to 10 g kg-1 soil. After incubation, soils were added to AIN93G Basal Mix and fed to weanling rats. In addition, a series of in vitro procedures to mimic the in vivo study were preformed. Conventional measure of metal availability (DTPA and CaNO3 extractable Pb) in soil were also conducted. Addition of the high Fe compost was able to reduce the bioavailability of soil Pb (as reflected in bone concentration) by 37% over the control soil. All of the compost materials tested showed greater than a 20% reduction in Pb bioavailability. The rapid in vitro procedure carried out at pH 2.2 had the best correlation with the bone data results. The standard soil extracts did not reflect the observed reduction in Pb availability. These results indicate that the addition of high rates of biosolids composts may be able to limit the Pb availability in high Pb urban soils.

Last Modified: 2/26/2015
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