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United States Department of Agriculture

Agricultural Research Service

Research Project: PRACTICES TO PROTECT WATER QUALITY AND CONSERVE SOIL AND WATER RESOURCES IN AGRONOMIC AND HORTICULTURAL SYSTEMS IN THE NORTH CENTRAL US

Location: Soil and Water Management Research

Title: Comparative sorption, desorption and leaching potential of aminocyclopyrachlor and picloram

Authors
item Oliveira, Rubem -
item Alonso, Diego -
item Koskinen, William
item Papiernik, Sharon

Submitted to: Journal of Environmental Science and Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 31, 2013
Publication Date: September 5, 2013
Citation: Oliveira, R.S., Alonso, D.G., Koskinen, W.C., Papiernik, S.K. 2013. Comparative sorption, desorption and leaching potential of aminocyclopyrachlor and picloram. Journal of Environmental Science and Health. 48(12):1049-1057.

Interpretive Summary: Aminocyclopyrachlor is a newly registered herbicide for the control of broadleaf weeds, grasses, vines and woody species in non-crops, turf, sod farms, and residential areas. At typical soil pH levels, aminocyclopyrachlor is in the anionic form. Anionic pesticides are generally weakly retained by most soil and sediment components and are subject to potential offsite transport. The present study was aimed at characterizing the potential mobility of aminocycloprachlor in soils; there is very little published information on this subject. Potential mobility is controlled by sorption/desorption processes in soil. Sorption was relatively low in all soils, which would indicate moderate mobility in soils. Desorption studies showed that once aminocycloprachlor was bound to soils, it was difficult to desorb, further decreasing its potential mobility for offsite transport. Similar results were found for picloram, a herbicide that has been in use for many years. Using the current information for aminocycloprachlor, or using picloram data as respresentative of aminocycloprachlor behavior, scientists can now more accurately predict the potential for offsite transport of aminocycloprachlor, although more information is needed to determine the sorption of aged residues and degradation.

Technical Abstract: Aminocyclopyrachlor and picloram sorption, desorption and leaching potential were investigated in three soils from Minnesota and Hawaii. Aminocyclopyrachlor and picloram sorption fit the Freundlich equation and was independent of concentration for aminocyclopyrachlor (1/n = 1), but not for picloram (1/n 0.80-0.90). Freundlich sorption coefficients for aminocyclopyrachlor were lowest in the eroded and depositional Minnesota soils (0.04 and 0.12 µmol (1-1/n) L1/n kg-1) and the highest in Molokai soil (0.31 µmol (1-1/n) L1/n kg-1). For picloram, Freundlich sorption Kf was lower in the eroded (0.28 µmol (1-1/n) L1/n kg-1) as compared to the depositional Minnesota soil (0.75 µmol (1-1/n) L1/n kg-1). Comparing soil to soil, Kf for picloram was consistently higher than those found for aminocyclopyrachlor. Desorption of aminocyclopyrachlor and picloram was hysteretic on all three soils. With regard to the theoretical leaching potential based on GUS, leaching potential of both herbicides was considered to be similar. Aminocyclopyrachlor would be ranked as leacher in all three soils if t1/2 was > 12.7 days. To be ranked as non-leacher in all three soils, aminocyclopyrachlor t1/2 would have to be < 3.3 days. Calculated half-life that would rank picloram as leacher was calculated to be ~15.6 d.

Last Modified: 9/1/2014
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