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Effect of Biochar type on immobilization of Mercury (Hg) from a Mercury-spiked Soil
Citation:
Betts, A., G. Millard, S. Plunkett, M. Johnson, C. Eckley, AND T. Luxton. Effect of Biochar type on immobilization of Mercury (Hg) from a Mercury-spiked Soil. 2021 ASA, CSSA, SSSA INTERNATIONAL ANNUAL MEETING, Salt Lake City, Utah, November 07 - 10, 2021.
Impact/Purpose:
Mercury (Hg) is a highly toxic metal pollutant that is harmful to both the environment and human health. There are thousands of mercury (Hg) contaminated sites across the U.S. with only a small portion being remediated due to challenges in funding, remote locations with limited access and contamination dispersed over large areas. Biochar is a charcoal material made from agricultural waste which has great potential as a cost-effective remediation technology to both treat Hg and increase fertility to rehabilitate damaged landscapes. However biochar types need to be identified that can treat Hg effectively without adverse side effects. A fraction of biochar is ash with a large amount of salts with the potential to disturb pH and release Hg after rain events and wetting. In our work, we applied a series of biochar types to a Hg contaminated soil mixed with water in rapid screening tests. We compared the change in Hg release to water chemistry and biochar characteristics to identify successful treatment and optimal biochar type. Our results showed that biochars made from animal manures provided the greatest reduction in Hg mobility while biochars made from plant materials had no significant effect on Hg release from the soil. However, the animal manure biochars also had the greatest amount of ash and caused the greatest increase in Hg release if soil was exposed to the water-soluble fraction without the biochar solid. This indicates a risk of downstream adverse effects if animal manure biochars are not applied carefully. The long term significance of these results are to the development of remediation technologies for Hg contaminated soils and sediments. These results could greatly benefit regional partners with sites that contain Hg as this is a significant step in developing a strategy for Hg remediation in soils and sediments. There is increasing need to address the nation’s many mercury (Hg) contaminated sites and prevent Hg from entering downstream waterways where it can contribute to elevated fish Hg and become an ecological and human health risk. This risk disproportionately impacts Tribal communities’ ability to harvest fish at subsistence levels, which are protected under established treaties.
Description:
Biochar (BC) is pyrolyzed carbonaceous material utilized for soil amending at many contaminated sites. Biochar can improve soil fertility for revegetation efforts and potentially sequester both organic and inorganic contaminants. However, BC applied to Mercury (Hg) contaminated soils and sediments can potentially release Hg so BC selection and application method need to be done carefully. The water-soluble fraction of some biochars include alkaline salts and dissolved organic carbon which have the potential to increase Hg transport after wetting. To find the best biochar for immobilizing Hg in soil, a range of biochars were applied to soil from multiple feedstocks (wheat straw, douglas fir, white oak, poultry litter, swine solids and a GAC standard) and produced at multiple temperatures (300, 500, 700 and 900 C). Additionally, we tested biochars before and after water extraction to see if the water-soluble fraction of BC can potentially cause release of Hg from the soil. From the experimental leachate, total dissolved Hg was measured as well as dissolved organic carbon, UV absorbance at 254nm for SUVA, anions, cations and pH and EC. Trends of Hg retention or release with chemical parameters and their implication for use of biochars as soil amendments in Hg contaminated soil and sediments will be discussed.