|Lerch, Robert - Bob|
Submitted to: Symposium on the Fate and Chemistry of Modern Pesticides Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 6/11/2004
Publication Date: 8/16/2004
Citation: Lin, C.H., Lerch, R.N., Garrett, H.E., George, M.R. 2004. The immobilization and detoxification of atrazine and balance (isoxaflutole) by selected forage species. In: Proceedings of the Symposium on the Fate and Chemistry of Modern Pesticides, August 16-19, 2004, Vail, CO. p. 32. Interpretive Summary:
Technical Abstract: A lysimeter study with six forage species (bare ground, orchardgrass, tall fescue, timothy, smooth bromegrass, and switchgrass) was established to evaluate phyto-degradation pathways and the potential to enhance soil degradation of atrazine (ATR) and Balance (isoxaflutole, IXF). Treatments received either 1500 ng of ATR or 240 ng of IXF. Soil and above ground plant tissue were sampled 25 days following herbicide application. Concentrations of ATR, IXF and their metabolites in soil and plant tissues were isolated by extraction followed by solid phase or liquid-liquid extraction. Determination of the herbicide residues was accomplished by gas chromatography or high performance liquid chromatography with mass spectral detection. The results showed that forage species, especially switchgrass, significantly enhanced the degradation of ATR in the soil compared to the control through N-dealkylation and/or hydrolysis. Switchgrass treatments had an average of 81% of their soil ATR residues in the form of less toxic metabolites. Smooth bromegrass, timothy, orchardgrass and tall fescue also showed enhanced soil degradation compared to the control. Phyto-degradation of ATR occurred via hydrolysis in switchgrass while the C3 forage species showed varying degrees of N-dealkylation in proportion to their ATR tolerance. In contrast, the degradation of diketonitrile (DKN), the initial degradation product and biologically active form of IXF, in soil appears to be an abiotic process as none of the forage species significantly affected DKN degradation. The results also indicated that plant uptake of Balance residues was strongly correlated with transpiration rates of the forages. Phyto-degradation of DKN to the non-phytotoxic benzoic acid metabolite was strongly correlated to tolerance of forages to this new herbicide. Field implementation of grass buffer strips utilizing the forages tested here can enhance biological degradation of ATR and reduce its off-site transport. The apparent abiotic soil degradation of DKN implies that physical trapping is likely to be the primary mechanism for decreasing off-site DKN transport.