RP10 Aquatic Ecotoxicology
Thursday, 17 November 2005: 8:00 AM - 6:30 PM in Exhibit Hall

(GRU-1117-930240) Do juvenile salmon avoid commonly used aquatic herbicides?

Curran, Catherine¹, Grassley, James¹, grue, christian¹, ¹ University of Washington, seattle, WA, USA

ABSTRACT- Herbicides are frequently used to control exotic or nuisance aquatic plants. However, the use of herbicides to control aquatic weeds has been hampered by concerns directed at the non-target toxicity of active herbicidal ingredients, particularly in light of new State permitting processes in response to a recent Federal Court ruling, requiring states to issue National Pollutant Discharge Elimination System permits for the use of pesticides and adjuvants in aquatic systems. Unfortunately, adequate data on the non-target toxicity of aquatic herbicides are lacking, thereby threatening the permitting process. Recent declines in several species/stocks of salmon and the emphasis to restore these populations heighten concerns in the Pacific Northwest. Behavioral responses such as avoidance can alter the exposure of fish to pesticides and such behavior has been suggested as important in mitigating the hazards aquatic herbicides pose to juvenile salmonids provided suitable uncontaminated habitat is accessible. The aquatic herbicides we selected to study, Sonar® AS (fluridone), REWARD® (diquat), and RENOVATE® 3 (triclopyr), are permitted for use in Washington State. Our objective was to determine if juvenile Chinook salmon (Oncorhynchus tshawytscha) avoid these herbicides. The maximum application rate and ten times the maximum application rate were tested as well as positive controls. We used five replicate uni-directional flow chambers adapted for juvenile Chinook and photographed the position of fish (n=10/chamber) for 15 min (1-min intervals) before chemical exposure, during chemical exposure, and after clean water was re-introduced into the chambers. One water sample from each concentration tested was chemically analyzed. Responses were quantified using a novel method comparing mean position and slopes of lines generated by mean position in the test chambers over time. Juvenile chinook were neither attracted to or avoided the maximum label rates of the herbicides, but were attracted to 10x the maximum label rates of RENOVATE and REWARD.

Key words: aquatic herbicides, salmonids, behavior, avoidance