Polycyclic Aromatic Hydrocarbons in Biochar and Their Bioavailabilty
Type of DegreeMaster's Thesis
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Biochar may be utilized as a soil-amendment to sequester carbon and enhance soil fertility through improved nutrient retention, increased plant-available water, and improved drainage for excess water. Before biochar can be applied on a widespread scale, potential threats to the soil environment must be evaluated. In this study, total and bioavailable polycyclic aromatic hydrocarbons (PAHs) were evaluated for nine slow pyrolysis biochars and three gasification biochars. Slow pyrolysis biochars were produced from loblolly pine (Pinus taeda), sorghum (Sorghum bicolor), and switchgrass (Panicum virgatum) feedstocks at temperatures of 400, 550, and 700°C. Gasification biochars were produced from hardwood and switchgrass feedstocks at a temperature of 1,100°C and pine feedstocks at 1,000°C. Total PAH concentrations ranged from 1.7 μg/g of pine char produced at 550°C to 31,957 μg/g of pine char at 1,000°C. A significantly higher concentration of PAHs was found in slow pyrolysis chars produced from sorghum stalks and gasification chars produced from pine. Concentrations of bioavailable PAHs in gasification biochars were further evaluated using polyoxymethylene (POM) passive samplers and PAH uptake from lettuce and soybean plants grown in two soil types. Bioavailable PAH concentrations ranged from 0.04 μg/g in blank POM assays to 27.89 μg/g in pine biochar POM assays. Bioavailable PAH concentrations ranged from 0.51 to 5.11 μg/g for lettuce plants grown in a Compass soil and 0.60 to 0.80 μg/g for lettuce plants grown in a Waynesboro soil. Bioavailable PAH concentrations ranged from 0.29 to 2.49 μg/g for soybean plants grown in a Compass soil and 0.31 to 0.34 μg/g for soybean plants grown in a Waynesboro soil. Although soybean and lettuce plants were only able to assimilate small amounts of the total solvent-extractable PAHs, plant uptake due to biochar amendment may still pose a hazard to humans.