Toxicity, transport, and fate of forest herbicides

Abstract

Public opposition to use of herbicides in forests typically centers around concerns over potential toxicity to wildlife. Characterization of the risk of silvicultural herbicides to wildlife requires an understanding of herbicide toxicity and environmental fate and transport. The fate and chemistry of herbicides and adjuvants within environmental media determine how and which organisms may be exposed and duration of those exposures. The nature of the toxicity of herbicides, adjuvants, and their decomposition products, and levels at which those toxic responses may be observed, determine which organisms or life stages may be most susceptible to any toxic effects and which exposure concentrations and durations can be considered safe. In general, herbicides most commonly used for vegetation management in forestry (glyphosate, triclopyr, imazapyr, sulfometuron, metsulfuron methyl, hexazinone) degrade quickly once they enter the environment and thus are neither persistent nor bioaccumulative. Because modern herbicides have been designed to target biochemical processes unique to plants, they exhibit a low level of direct toxicity to animals. When used according to label instructions, modern silvicultural herbicides pose little risk to wildlife.