Reactions ofEuglena gracilisto Fluometuron, MSMA, Metribuzin, and Glyphosate

Abstract

Investigations were conducted onEuglena gracilisKlebs strain Z to determine the effects of fluometuron [1,2-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea], MSMA (monosodium methanearsonate), glyphosate [N-(phosphonomethyl)glycine], and metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] on cell number, chlorophyll content, and photosynthesis. Euglena cell number was reduced by 65% or more after 48 h with fluometuron levels above 4 X 10-5M. MSMA at 6 X 10-4M reduced cell number 42% after 144 h exposure. Chlorophyll content was reduced 33 to 80% by metribuzin levels of 2 X 10-6M or greater, and fluometuron inhibited chlorophyll content by 30% or more from 4 X 10-6M or greater concentrations. Chlorophyll was reduced 21 to 69% by treatment with glyphosate at 3 X 10-3M, but MSMA appeared to have little effect on chlorophyll except at the high level of 6 X 10-4M at 48 h. Photosynthesis was reduced 50% or more with metribuzin levels above 9 X 10-7M and with fluometuron above 9 X 10-5M. MSMA reduced photosynthesis by 20% at the 6 X 10-3M level, and glyphosate slightly reduced photosynthesis at levels below 1.2 X 10-4M but slightly stimulated it above that level. Chronic effects (Euglena exposed to herbicides 96 h prior to measurement) on photosynthesis indicated a more pronounced reduction from fluometuron than from short-term exposure, little change with glyphosate, but less reduction with metribuzin than from short-term exposure. Metribuzin caused increased respiration rates of 100 to 200% after 100 min of exposure. Respiration was stimulated 20% by glyphosate and relatively unaffected by the other compounds. Removal of Euglena from metribuzin- and fluometuron-treated media to non-treated media resulted in increased levels of chlorophyll to near that of the control. These results suggest that use of these herbicides is not detrimental to non-target algae if the exposure is not intensive.