Fate and Transport of Forestry Herbicides in the South: Research Knowledge and Needs

A review of the fate and environmental risks associated with the use of hexasinone, imasapyr, sulfometuron methyl, and triclopyr in pine silviculture in the South is presented. Herbicides used in forestry can contaminate surface waters to varying degrees depending on the application rate , method of application, product formulation, and site specific characteristics, but streamside management zones (SMZ) greatly reduce stream contamination. Highest concentrations measured in streams occurred in short duration pulses during the first two or three storm events following application. Stream contamination usually declined rapidly thereafter. The highest concentrations of herbicides observed in streams are usually lower than concentrations determined to be safe by the Environmental Protection Agency’s Office of Drinking Water for domestic drinking water. Persistence of herbicides on treated sites is affected by many factors. Half-life in vegetation is ususally < 40 days and from 7-180 days in soil. Environmental Impact Statements and Risk Assessments completed for the southen United States concluded that: (1) no member of the public, including sensitive individuals, should be affected by typical exposures to herbicides or associated chemicals used for vegetation management in the South; (2) the risk of dying or from cancer is greater after drinking 40 diet sodas with saccharin, consuming a total of 2.7 kg (6 lb) of peanut butter, drinking 750 L (200 gal) of water from Miami or New Orleans, or smoking two cigarettes than it is from exposure to herbicides used in the South, even for workers; and (3) care needs to be taken with herbicides concerning threatened and endangered species. More research is needed for new herbicides because: (1) analytical problems are greater for new herbicides which are used at very low rates and biodegrade rapidly; (2) new herbicides should be screened for toxicity against threatened and endangered plant species; and (3) research should define the role of SMZs in reducing stream contamination so that SMZ size can be prescribed on a site specific basis. ’ Paper presented at Sixth Biennial Southern Silvicultural Research Gonference, Memphis, TN, Oct. 30-Nov. 1, 1990. z Research Ecologist, Southern Forest Exp. Sta., Auburn, AL; and Soil Scientist, Southeastern Forest Exp. Sta., Gainesville, FL. Introduction There are many issues surrounding use of herbicides in forestry and most of these seem to have arisen from an association with agricultural food crop uses. The distinction between intensive forest management use of herbicides and agricultural is significant, but seldom presented. While agricul-