Submitted to: Environmental Pollution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/5/2011
Publication Date: 1/23/2012
Citation: Sun, K., Gao, B., Ro, K.S., Novak, J.M., Wang, Z., Herbert, S., Xing, B. 2012. Assessment of herbicide sorption by biochars and organic matter associated with soil and sediment. Environmental Pollution. 163:167-173. Interpretive Summary: Worldwide herbicide usage has increased dramatically over the past 20 years due to increasing agriculture production. The quantity of herbicide used in agriculture has also increased because farmers are applying higher application rates to suppress weed growth. The heavy reliance on herbicides has also caused water quality controversy due to the potential of off-site herbicide movement into ground and surface water bodies. To alleviate the controversy surrounding off-site herbicide movement to water sources, innovative strategies are needed to keep herbicides at the application site. It is well known that herbicide sorption by natural soil organic matter minimizes its off-site movement. We conducted laboratory experiments to determine if we could enhance herbicide sorption using agricultural byproducts (chars) produced from various thermal processes. Herbicide sorption characteristics by two different types of char produced from chicken litter were evaluated. One char was produced by dry pyrolysis and another char was made using wet pyrolysis. Chemical characterization beforehand revealed that the dry pyrolyzed char was structurally different to the wet pyrolyzed char. We found that the wet pyrolyzed char had better herbicide sorption characteristics than the dry pyrolyzed char. Differences in herbicide sorption was explained by variations in their chemical structure. These results have important water quality implications because the wet pyrolyzed char could serve as an amendment to minimize off-site herbicide movement.
Technical Abstract: Sorption of two herbicides, fluridone (FLUN) and norflurazon (NORO), by whole sediment, two types of biochars and various soil/sediment organic matter (OM) fractions including nonhydrolyzable carbon (NHC), black carbon (BC) and humic acid (HA) was examined. The single-point organic carbon (OC)-normalized distribution coefficients (KOC) of FLUN and NORO for HA, NHC, and BC were about 3, 14, and 24 times and 3, 16, and 36 times larger than their bulk sediments, respectively, indicating the importance of different OM fractions in herbicide sorption. This study revealed that aliphatic moieties of the hydrothermal biochars and aromatic moieties of NHC samples, respectively, was one of the key factors regulating herbicide sorption. The hydrothermal biochar and condensed OM (i.e., NHC and BC) showed relatively high or similar sorption efficiency for FLUN and NORO compared to the thermal biochar, suggesting that the hydrothermal biochar may serve as an amendment for minimizing off-site herbicide movement.