LABORATORY EVALUATION OF IMPACTS OF EXPOSURE CONCENTRATION AND DURATION ON SILVICULTURE HERBICIDE TOXICITY TO AQUATIC PLANTS (LEMNA GIBBA)
Herbicides to control competing vegetation during stand establishment is a key component of intensive silviculture. Although some field studies have shown that modern best management practices effectively reduce movement of herbicides into forest streams, peak stream concentrations of some herbicides still exceed toxicity thresholds for some aquatic plants. Exposure duration is key in determining the magnitude of herbicide effects, and peak stream herbicide concentrations occur for brief periods of time in response to storm runoff. Because toxicity values are typically derived from 7- or 14-day continuous exposures, the short-term exposures associated with forestry herbicide may represent a significant mitigating factor in actual toxicity. We used a hybrid approach to quantify the duration-exposure concentration-toxicity relationship for herbicide mixtures and Lemna, and evaluated recovery from exposure of varying durations. Growth response was measured as frond area and counts, and biomass. Tested herbicides and mixture ratios represented those most commonly used based on application area in the southeast and northwest US, with highest test concentrations calculated using the US Forest Service Risk Assessment upper peak concentration and the highest application rate used by the industry. Test methods and preliminary findings are presented.
Camille Flinders (Primary Presenter/Author), NCASI, firstname.lastname@example.org;
William Arthurs (Co-Presenter/Co-Author), NCASI, email@example.com;
Joan Ikoma (Co-Presenter/Co-Author), NCASI, firstname.lastname@example.org;
Vickie Tatum (Co-Presenter/Co-Author), NCASI, email@example.com;