Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 13, 2004
Publication Date: December 1, 2004
Citation: Blume, E., Bischoff, M., Moorman, T.B., Turco, R.F. 2004. Degradation and binding of atrazine in surface and subsurface soils. Journal of Agricultural and Food Chemistry. 52(24):7382-7388.
Interpretive Summary: Atrazine is a herbicide that has been detected in groundwater supplies resulting from leaching through soil from agricultural use. Past research has described the binding and degradation of atrazine in surface soils. This research examined the binding and degradation of atrazine in subsurface soils. We found that atrazine degraded at rates that were much slower than surface soils. At 175 to 220 cm (7.2 ft) below the soil surface atrazine was degraded at a rate that was 3% as fast as the rate in the surface soil. Atrazine was also bound less tightly in the subsurface soil. Atrazine metabolites also followed this pattern. These findings show that once atrazine enters the subsurface environment it will persist longer and leach more quickly than in surface soil. This information will aid development of computer models that predict contamination of groundwater and in the improvement of herbicide application technology to reduce herbicide leaching.
The dissipation of a chemical in the unsaturated and saturated zones of the earth's subsurface will determine if reduction of chemical concentrations to acceptable levels will occur. Chemical properties and microbial biomass and activity were determined in soil samples from the surface (0-15 cm), lower root (50-105 cm), and vadose (175-220 cm) zones across a typical agricultural field from a silty clay loam Fluventic Hapludoll. The soils were also incubated with atrazine and sorption, mineralization, and transformation (formation of bound residues and metabolites) of atrazine determined. Microbial activity was estimated from the mineralization of 14C-benzoate. We observed decreased levels of nutrients (total organic carbon, nitrogen and phosphorous) and microbial biomass and activity with depth. Sorption, mineralization, and formation of bound residues were correlated to chemical and biological properties of the soil. These processes, as well as formation of metabolites were greater in the surface than in the subsurface soils. Sorption coefficients (Kf) declined from 8.17 in the surface to 3.31 in the vadose zone. Rates of atrazine mineralization and bound residues formation were, respectively, 12- to 2.3-fold lower in the vadose than in the surface soil. Dissipation of atrazine decreases with depth in the profile and is a function of chemical and biological properties of the soil.