Submitted to: Society of Environmental Toxicology and Chemistry Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: July 7, 2014
Publication Date: N/A
Technical Abstract: Glyphosate resistant Palmer amaranth (Amaranthus palmeri) was discovered in central Georgia (USA) in 2006. Subsequent spread of this highly problematic weed throughout the region prompted growers and registrants to seek labels for herbicides that can provide cost-effective control. To this end, the diphenyl-ether, fomesafen (5-(2-chloro-a,a,a-trifluoro-p-tolyloxy)-N-mesyl-2-nitrobenzamide) was labeled for use in cotton production in 2009. Current estimates indicate that up to ½ of all Georgia cotton fields receive annual pre-emergence treatment with herbicides containing this active ingredient. Risk assessments conducted by USEPA during deliberations related to fomesafen use on cotton identified concerns about potential for persistence in soil and aquatic environments, negative impacts on surface and groundwater quality through runoff and leaching, and threats to endangered species. Simulation modeling indicated that the compound is mobile in the environment; however, there are few published studies that have evaluated fomesafen environmental fate and transport. We examined fomesafen runoff using rainfall simulation techniques and found that strip-tillage and post-application irrigation incorporation of the herbicide greatly reduced runoff potential (Potter et al., 2011). In follow-up studies fomesafen aerobic soil dissipation in soil collected from a field that received two consecutive annual treatments was evaluated. We also collected and analyzed deep soil cores and surface runoff and lateral subsurface flow samples from a series of six 0.2 ha fields for three years after they were treated with fomesafen. Our findings showed that fomesafen was relatively persistent with soil DT50>100 days and that leaching potential was high since the compound was detected in soil cores to a depth of 60 cm and in samples of lateral subsurface flow. However, off-site transport via this pathway was found to be small, representing less 0.2 % of the fomesafen applied to fields. Taken together data have indicated that fomesafen is persistent and that substantial quantities of fomesafen may leach under southern Atlantic coastal plain (USA) conditions. Findings also suggest that the compound is retained in the surface environment where it is degraded.