Functionalized Biochar for Reducing Lead (Pb) Bioaccessibility in Contaminated Soils

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Commodities

Practices

• Soil Management: soil analysis, soil chemistry, toxic status mitigation
• Sustainable Communities: urban agriculture

Across communities in the northeastern U.S., urban agriculture fosters neighborhood engagement, stimulates local economies, provides access to fresh produce, and increases the land area utilized for agriculture, thus improving food security. Many low-income neighborhoods can benefit greatly from urban agriculture. However, a major hurdle to popularizing urban agriculture is the potential soil contamination by heavy metals, especially legacy contaminants like lead (Pb). Measurements of total Pb can be misleading since the true health risks depend on the human intake rate and the fraction of contaminant that is bioavailable. As urban agriculture becomes more popular, growers face challenges in accessing reliable soil contamination testing means and deciding on a method to remediate or amend soil to decrease contamination risks. Amendments for remediating contaminated soil, such as biochar, should be tested for their ability to reduce Pb bioaccessibility. Biochar is well-known to have metal-sorbing properties. We propose a novel method of post-processing biochar, functionalizing it by heating it in oxygenic conditions to increase its capacity to decrease bioaccessible Pb in urban soils. If this method is shown to be successful, it may be extremely useful for urban gardeners who wish to reduce the risk of Pb poisoning for themselves and their children. In support of this goal, we are also validating a novel, inexpensive analytical method for detecting the amount of bioaccessible Pb in soils. 

1.1.
Our first objective is to establish methods for analyzing EPA Method 1340 assays using XRF spectroscopy. We will use benchtop XRF to measure bioaccessible Pb in liquid sample extracts. This objective comprises three main tasks: Task 1. Measuring Accuracy and Precision: We will evaluate the accuracy of XRF by comparing it to ICP, which is typically used for measuring bioaccessible Pb. We will test whether the difference between bioaccessible Pb measured by XRF and that measured by ICP for known standards does not exceed 10%. Three replicates on the same liquid samples will be used to assess precision of the method. Task 2. Creating a Regression Equation: We will develop a regression equation for bioaccessible versus total Pb in powder samples. Standards and soil samples with known total ICP values will be used to obtain a regression curve. Establishing this relationship will determine whether the methods are statistically equivalent. Task 3. Regression Curve Validation: To validate the established regression curve, we will measure experimental samples obtained in Objective 2. We will plot ICP measurements on bioaccessible Pb calculated versus XRF measurements on bioaccessible Pb measured to evaluate the agreement between these data. The completion of this objective will determine if XRF can be utilized as a cost-effective alternative to ICP for measuring bioaccessible Pb in liquids.

1.2.
Our second objective is to assess the efficacy of heat-functionalized biochar in immobilizing lead within soil. This objective involves several key tasks: Task 1. Creating Functionalized Biochar: We will alter the surface properties of biochar by heating it under various experimental conditions in an air atmosphere. This process is designed to generate additional chemically active sites on the biochar’s surface which can bond with Pb. Such chemical bonds are generally considered non-reversible, significantly reducing the likelihood of Pb re-entering the solution and thereby immobilizing it within the soil. Task 2. Conditioning Soil-Biochar Mixture: The soil-biochar mixture will be conditioned for two weeks to ensure that Pb redistribution occurs effectively. Task 3. Time Series Experiment: Over six months, we will conduct a time series experiment to monitor the dynamics of bioaccessible Pb. This will help us track how the effectiveness of the biochar application changes over time. These tasks will help us evaluate the long-term effectiveness of the biochar treatment in reducing bioaccessible Pb in soil, and provide valuable insights into the potential of heat-functionalized biochar as a sustainable solution for soil remediation.