How likely is it that crops take up glyphosate residues through their roots or show phytotoxic effects?
Numerous soil and plant studies and the extensive knowledge of the physical and chemical properties of glyphosate support the conclusion that it is unlikely that significant levels of glyphosate will reach the rhizosphere and be available for uptake by crop plants. Glyphosate binds very tightly to most soils and sediments in the environment and thus is generally not available for uptake by roots of nearby plants and poses very little risk of damaging the following crops or other plants in the vicinity of the application zone 7,8.
Glyphosate is a foliar-applied herbicide that adsorbs rapidly and binds tightly to most soils. Once glyphosate is adsorbed, very little of it can desorb into water that is in contact with the soil. Although plants generally do have the ability to take up glyphosate through their roots, only minimal amounts of glyphosate are available for uptake by plant roots because of the speed with which it adsorbs to soil.
If plants are grown in a hydroponic solution containing glyphosate, they can take up glyphosate through the roots. Studies designed to promote uptake of glyphosate study its metabolism in plants have shown that significant levels of the glyphosate that is added to a hydroponic solution can be taken up by the plant, thereby demonstrating that it is the lack of availability of glyphosate in soil, rather than the inability of roots to absorb glyphosate, that limits its uptake from soil 11.
Nevertheless, under specific conditions glyphosate uptake from soil can occur. Glyphosate adsorption to soil is reduced in very sandy soils and phytotoxic effects of glyphosate in soil have been observed in tomato seedlings when they were transplanted into sandy soils shortly after glyphosate application. That’s why a 3-day waiting period between the application and the transplanting is typically recommended. Greenhouse experiments of the University of Hohenheim showed that growth and biomass production was strongly impaired but improved with longer waiting times. However, these greenhouse studies utilized extremely high application rates that do not represent normal use patterns.
Last update: 10 October 2012