Laboratory studies were conducted to investigate the processes of imazaquin and imazethapyr degradation in soil. Microbial degradation of 14C-imazaquin and 14C-imazethapyr was monitored by measuring 14CO2 evolution compared to nonsterile soil. 14CO2 evolution was greatest from carboxyl-labeled imazaquin and imazethapyr compared to ring-labeled imazaquin and imazethapyr. A corn root bioassay indicated nearly complete loss of herbicidal activity in nonsterile soil after 5 mo, but herbicide activity was reduced only 14% in sterile soil. 14CO2 evolution more than doubled when soil temperature increased from 15 to 30 C. Total CO2 production responded similarly. Degradation of imazaquin and imazethapyr increased as soil moisture increased from 15% (-2.4 MPa) to 75% of field capacity (-0.03 MPa).

In response to concern by the U.S. Environmental Protection Agency (EPA) about the health effects of farmworker exposure to 2,4-D and the phenoxy class of herbicides, the U.S. Department of Agriculture (USDA) initiated a benefits assessment in 1993 to determine the economic implications of a complete ban of these materials in agricultural and nonagricultural uses. About 55 million pounds of phenoxy herbicides are used annually in the United States, with 2,4-D comprising 86% of total use or about 47 million pounds of acid equivalent. The severest economic effects would be felt in major field crop applications and in alfalfa forage uses. The total loss of phenoxy herbicides in field crop applications could result in net societal losses, which combine producer and consumer effects of yield, cost, and price changes, approaching $1.2 billion. Greatest yield losses averaged over total planted acres under a total phenoxy herbicide loss scenario would be seen in peanut (13%), alfalfa (5.2%), barley (3.8%), sorghum (2.4%), and wheat (2.2%). Producers of orchard, vineyard, soft fruit, and nut crops could incur losses of $105 million. The estimated aggregate economic impact of losing phenoxy herbicides in the applications included in this paper is a loss of $1.3 billion. These estimates describe the yield and financial impacts of the initial production year after a cancellation. Subsequent years' losses and financial impacts would be less as farmers and markets adjust to the new production situation.