Abstract
2,4βDichlorophenoxyacetic acid (2,4βD) was first registered in 1947 as an agricultural herbicide, and it is still the most widely used herbicide worldwide. Endβuse products, however, are generally formulated as inorganic or amine salts, or as esters. Because of the various forms available, there was concern that by testing only one form, the environmental profile generated might be insufficient to represent all forms. Therefore, as part of the 2,4βD reregistration process in the U.S., 30 soil dissipation studies were conducted with 2,4βD dimethylamine salt and 2,4βD 2βethylhexyl ester over a 2βyear period. Trials were located in seven states and included four cropping practices and bare soil. The results, averaged over all conditions, showed equivalent rates of 2,4βD dissipation in soil when applied as either the amine salt or ester forms. These results also confirm data from earlier field studies in Canada and Washington state showing equivalent 2,4βD dissipation in soil from applications of isooctyl ester, dimethylamine salt, and mixed amine salt forms. The data from the current and former studies show that ester and amine forms have little effect on the rate of dissipation of 2,4βD per se because they are converted rapidly to the same anionic form.