| Abstract: | In aquatic situations it was expected that adsorption by sediments and suspended solids would influence the movement of glyphosate away from the application zone and attenuate its phytotoxicity. However, the results of two experiments showed that only a minor proportion of glyphosate was adsorbed onto suspended solids, even in turbid irrigation water. Phytotoxicity, as measured by the effect on the root growth of safflower (Carthamus tinctorius L.), was not significantly reduced. Where glyphosate was intentionally injected into flowing water of contrasting quality to simulate incidental contamination of water during foliage treatment, adsorption by benthic sediments attenuated loads of glyphosate only slowly. The attenuation was 13–27% for each kilometre of travel downstream, as compared to 31% observed previously. However, when glyphosate was sprayed onto the sediment exposed after channel draining, less than 7% of the glyphosate applied was subsequently eluted. Consequently, draining before treatment should be an effective strategy for minimising the contamination of irrigation water. |
