Phytotoxicity Testing: Foliar spray method
Scientific Advisory Panel Briefing
June 27-29, 2001
PROPOSAL TO UPDATE NON-TARGET PLANT TOXICITY TESTING UNDER NAFTA
Michael Davy, Richard Petrie, and Jerry Smrchek, EPA Ted Kuchnicki and
Derek Francois, PMRA
Joint Presentation By: Health Canada - Pest Management Regulatory Agency and USEPA - Office of Prevention, Pesticides, and Toxic Substances
Appendix 10 (page 94):
Brief description of the methodology for exposure to sprayed glyphosate
Lemna minor (Lockhart et al., 1989).
For application of a spray to the foliar surface of Lemna minor plants, a laboratory sprayer was used consisting of a spray nozzle which moved along a rigid track at a rate and pressure selected by the operator. The sprayer was calibrated using dyes to allow delivery of any desired quantity of material to the surface of the Lemna cultures.
The application rate of glyphosate was that recommended for the control of annual weeds up to 15 cm high. The rate was 2.25 L of Roundup per hectare which is equivalent to 800 g a.i./ha. This rate of application to the surface of the test dishes would produce a concentration of 3.96 g a.i./L.
Exposures were conducted by placing sufficient Lemna fronds in deep Petri dishes with a surface area of 0.00785 m2 and containing 117.8 ml of culture medium. After spraying the exposed plants were allowed to stand for 6, 12 or 24 hours without disturbance. The, 10 normal fronds were selected from each dish and transferred to 125 ml Erlenmeyer flasks where they were grown in clean culture medium. Preliminary experiments showed that the removal of sprayed cultures immediately after spraying resulted in loss of toxicity, presumably by wash-off of the glyphosate from the Lemna fronds. Controls were treated in the same manner except that the dish covers were left in place.
Cultures were grown in a controlled environmental room at 25°C. Light was provided by Gro and Sho lights (GE) at an intensity of about 60 mE·m -2·sec -1 with a photoperiod of 16 hours light and 8 hours dark.
The number of fronds were counted several times over a 2-week period following exposure. At termination of the test, cultures were drained, blotted, weighed then air dried to constant weight at 95°C and re-weighed.
Lockhart, L.W., B.N. Billeck and C.L. Baron. (1989) Bioassays with a floating aquatic plant (Lemna minor) for effects of sprayed and dissolved glyphosate. Hydrobiologia. 188/189: 353-359.
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Revised: March 10, 2002