Access Type

Open Access Thesis

Date of Award

January 2020

Degree Type

Thesis

Degree Name

M.S.

Department

Civil and Environmental Engineering

First Advisor

Shawn P. McElmurry

Abstract

Historical and contemporary use of lead (Pb) in gasoline, paints, and industry have caused lead to be ubiquitous in the urban soil environment, disproportionately affecting low-income minority children. As soil is a major exposure pathway for children, an effective remediation technique for lead-contaminated soil is urgently needed. Common remediation techniques, such as excavation or soil capping, are expensive and environmentally destructive, especially on a city-wide residential basis. Decreasing the bioavailability of lead, or the fraction which is retained by the human body, may be a more economically and environmentally conscious option for remediating lead in urban environments.

Research has demonstrated that the addition of phosphates to lead-contaminated soil promotes the formation of insoluble minerals (i.e. pyromorphite) that can reduce bioavailability. Previous work typically focused on sites with high concentrations of lead, such as sites proximate to smelters or mining. It is unclear if urban residential properties, with relatively low levels of lead contamination, can be successfully remediated using phosphate amendments. Apatite, in the form of bone meal, may be an ideal phosphate amendment for lead-contaminated soils, as it is readily available, low-cost, contains significant amounts of phosphate, and it is suggested to be less likely to cause eutrophication compared to other phosphate sources. In-vitro bioaccessibility (IVBA) tests, which simulate a child’s digestive system, are often used to predict bioavailability of metals from soil.

In this study, a liquified bone meal soil amendment was applied to residential soils across Detroit, Michigan to determine if this treatment is effective at reducing IVBA. Soil characteristics were evaluated before and after treatment to determine their impact on IVBA. The initial mean Detroit soil IVBA was 39%. The total lead concentration (mg/kg), organic matter content (%) content and soil pH were the most important predictors of IVBA before treatment. Soils with organic matter (OM) 1% and 2.5% greater than the mean OM content (5%) had IVBA measurements 8.6% and 18.2%, respectively, greater than average soils. Soils with pH values 0.1 and 0.5 less than the mean (7.8) had IVBA measurements 2.2% and 10.7%, respectively, lower than the average soils. Overall, the application of bone meal amendment (5g P per 4 ft2) resulted in a 9.8% decrease in IVBA. This reduction in IVBA was attributed to changes in soil pH and phosphate content. To assess the potential impact of this reduction, a sensitivity analysis was performed using the US EPA’s Integrated Exposure Uptake Biokinetic (IEUBK) model. Based on default exposure assumptions in the IEUBK model, if the remediation were to be applied across all soils, the geometric mean of blood lead levels (BLLs) in children under the age of seven is expected to decrease 6.7%. The results of this study suggest bone meal may be a suitable remediation strategy for reducing lead bioavailability in Detroit.

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