An Investigation of Elemental Soil Composition Testing Methods and Site Assessment Procedure For Determining Trace Elemental Pollutant Concentrations In Urban Soils

Open Access
- Author:
- Dadio, Stephen
- Graduate Program:
- Soil Science
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- May 30, 2024
- Committee Members:
- Ekaterina A Bazilevskaya, Thesis Advisor/Co-Advisor
Justine F Lindemann, Committee Member
Patrick Drohan, Professor in Charge/Director of Graduate Studies
Patrick Joseph Drohan, Thesis Advisor/Co-Advisor
John Thomas Spargo, Committee Member - Keywords:
- Soil science
Urban Soils
Lead
Heavy Metals
Urban Planning
Site Assessment - Abstract:
- Urban gardens and green infrastructure have emerged as a popular and sustainable way to revitalize vacant lots, providing numerous benefits to the physical, social, and economic health of a community. However, green infrastructure efforts encounter potential risks, such as elevated levels of trace elemental pollutants in the soil, which may be evaluated by assessing site soil risks and more accessible or affordable alternative testing. This thesis outlines a comprehensive strategy for evaluating urban soil quality and its suitability for gardening or green infrastructure, with a focus on soil pollutant levels. The first part of this study focused on creating two site assessment procedures, a historic site assessment to predict trace element pollution (TEP) in the soil, and a comprehensive site assessment protocol for urban soils. Using historic maps of Philadelphia, a risk assessment was determined based on a site’s proximity to modern and historic sources of pollution with the goal of predicting elevated concentrations of trace elemental pollutants in the soil using chemical soil analysis as a validation tool. Samples were collected from vacant lot sites and urban garden sites to determine actual concentrations of TEP and nutrients. TEP were generally low except for Pb whose median value was elevated above the new lowered United States Environmental Protection Agency’s screening level of 200 mg kg-1 for residential soils. There was significantly higher Pb at vacant lot sites and significantly higher Mn at garden sites. The historic site assessment approach successfully predicted higher elevated Pb concentrations in medium and high-risk sites compared to low-risk sites. Results also revealed elevated soil nutrient values at garden sites compared to vacant lot sites, likely due to amendment overapplication. A new site assessment protocol was developed, incorporating physical, chemical, and site-specific characteristics from this study and previous literature. Sixteen categories and associated ranking systems were created to help determine the risks impacting a site. The assessment aims to provide a comprehensive evaluation of urban soil health and suitability for green infrastructure. However, confirmatory soil testing practices are still a necessary part of urban soils to pollutant and fertility levels. The second part of the study assessed the ability for four soil testing methods (benchtop X-ray fluorescence (b-XRF), portable XRF (p-XRF), Mehlich-3, and Aqua Regia) to measure actionable thresholds for As, Cd, Mn, Ni, and Pb concentrations when compared the USEPA method 3050B. This was done using regression analysis and USEPA method 6200 standards to determine if the alternative methods could provide screening or statistically equivalent results when compared to USEPA method 3050B. The models were then validated using a test data set that illustrated the model’s ability to provide results with strong agreement to USEPA method 3050B for three actionable Pb levels. The findings highlight that despite the accessibility of p-XRF, it exhibits limitations and should be used primarily for Pb screening while b-XRF demonstrated statistical equivalence for As, Mn, Ni, and Pb. Both XRF methods were unable to detect low Cd concentrations. Aqua Regia showed statistical equivalence for As, Cd, Mn, and Pb and screening levels for Ni, while Mehlich-3 was statistically equivalent Cd and Pb. The study suggests that combining benchtop XRF and Mehlich-3 is an optimal approach for comprehensive assessment of soil pollutants and fertility. Overall, this research contributes to better understanding of urban soil assessment process, providing recommendations for urban planners, policymakers, and community stakeholders aiming to enhance green infrastructure environment and public health.