Use of Biochar Amendments to Mitigate Soil Pb Toxicity to People and Waterfowl.
On this page:
Biochar can improve plant growth and reduce metal bioavailability to plants in metal-contaminated soil but the ability of biochar to reduce gastrointestinal bioavailability of heavy metals to people and waterfowl remains unknown. In this project, Pb-contaminated soil and sediment from three sites with distinct contaminant legacies were amended with 2% biochar (17 unique chars) and incubated for six months. The soils and sediment were analyzed for changes in in vitro Pb bioaccessibility post incubation according to four variations of EPA’s standard soil Pb bioaccessibility assay (EPA Method 1340 at pH 1.5 and 2.5, dried and sieved and wet and not sieved), the Avian Ohio State University In Vitro Gastrointestinal bioaccessibility assay, and the Mehlich 3 soil nutrient test.
Results from one upland and one wetland site are currently available. Biochar amendments to the upland soil contaminated by aerial smelter deposits reduced Pb bioaccessibility (EPA Method 1340, pH 2.5, dry) by up to 13% relative to control. In the wetland sediment contaminated by alluvial mining deposits, all pots including the control increased in Pb bioaccessibility after six months. This increase is likely due to oxidation of reduced Pb compounds over the course of the experiment and illustrates the influence of redox conditions in determining Pb toxicity. Remediation strategies that disturb reduced sediments, including incorporating biochar, may inadvertently exacerbate Pb bioaccessibility by converting sparingly soluble reduced Pb compounds to more soluble, oxidized species. Results also illustrate that the drying and sieving step in the standard operating procedure for determining soil Pb bioaccessibility to humans (EPA Method 1340) increases Pb extractability by an average of 48% compared to sediment samples processed wet and not sieved. To avoid overestimating Pb risk to organisms exposed to Pb in reduced form (e.g. waterfowl), bioaccessibility metrics must preserve relevant Pb redox conditions for the target organism.