|Abstract or Summary
- Comparison of the toxic effects of six herbicide formulations in simultaneous moving water and static water bioassays showed that mortality of coho salmon, Oncorhynchus kisutch (Walbaum), was less in the moving water tests. The moving water tests were conducted in troughs with powered paddlewheels while the static tests were conducted either in five-gallon glass jars or in troughs with immobilized paddlewheels. Of the six herbicides tested, least differences in results were obtained with Daxtron. In a representative experiment all fish were dead in less than 24 hours in the static tests at 100 and 115 ppm. while in the moving water tests 60% mortality occurred in 100 ppm. and 100% mortality in 115 ppm. at 72 hours. Of the other five
herbicides, Dow M-3083, Tordon 101, TD 191, Pramitol 25E, and Kalzate A, the most dramatic differences in bioassay results were obtained with TD 191 and Pramitol 25E. For example, in one experiment with TD 191 50% mortality, for the duration of the bioassay, occurred in 0.42 ppm. in the static tests but 0.75 ppm. was
required to obtain the same mortality in the moving water tests. In the same experiment 90% mortality occurred within 96 hours in 1 ppm. in the moving water tests but all fish in the static tests were dead at
24 hours in 0.56 ppm. In bioassays using Pramitol 25E all deaths occurred within the first 24 hours with none thereafter. In a typical experiment there was 10% mortality in 11.5 ppm. in the moving water tests with no deaths in lower concentrations, while there was 100% mortality in 8.7 ppm. and 70% mortality in 6.5 ppm. in the static tests. For the remaining three chemicals, typical results are listed below: Dow M-3083- All fish in the static tests died within 24 hours in 49 ppm. while in moving water tests 48 hours in 65 ppm. was required to kill all fish. Tordon 101- In the static tests mortality was 100% in 56 ppm. at 72 hours while in the moving water tests mortality was 40% under the same conditions. Kalzate A- In 180 ppm. there were no deaths in the moving water tests but in the static tests mortality was 60% in less than 72 hours. Apparently agitation of the solutions caused the differences observed between the moving water and static water bioassays rather than exercising the test fish, possibly by increasing the opportunity for sorption of the toxicant or by promoting seeding and growth of microorganisms capable of breaking down the toxicant.