Pesticide Profile - Glyphosate

Toxicity

Glyphosate can be acutely toxic to non-target plants, including aquatic plants and algae. The effects of this toxicity on natural plant succession alters the ecology of treated areas. In most cases, the plant species diversity will decrease, and along with it, the numbers of insects, mammals and birds utilizing these areas as habitat.

Santillo, D.J. et al (1989), "Response of songbirds to glyphosate-induced habitat changes on clear-cut." Journal of Wildlife Management, v. 53 no. 1, 64-71.

Connor, J.F. and McMillan, L.M. (1990), "Winter utilization by moose of glyphosate-treated cutovers." Alces 26:91-103.

Glyphosate is toxic to mammals:

Most toxicity tests cited by industry and the EPA investigate toxicity through oral exposure routes. The toxicity of glyphosate and the common surfactant POEA is much greater through inhalation routes of exposure, which is a likely exposure scenario for humans residing in areas of Colombia. Experimentally induced inhalation of Roundup by rats produced 100% mortality in 24 hours. Humans ingesting as little as 100 ml of Roundup have died ( suicide attempts using Roundup have a 10-20% success rate.)

Martinez, T.T. and Brown, K. (1991) "Oral and pulmonary toxicology of the surfactant used in Roundup herbicide." Proceedings of the Western Pharmacology Society, v. 34, 43-46.

Adam, A., et al (1997) "The oral and intratracheal toxicities of Roundup and its components on rats." Veterinary and Human Toxicology, Jun 39(3):147-51.

Glyphosate produces toxic effects on mammalian sperm. Glyphosate is a potential endocrine disruptor.

Youssef, M.I., et al (1995), "Toxic effects of carbofuran and glyphosate on semen characteristics in rabbits." Journal of Environmental Science and Health, part B, v. 30, 515-534.

Walsh, LP, et al (2000) "Roundup inhibits steroidogenesis by disrupting steroidogenic acute regulatory (stAR) protein expression." Environmental Health Perspectives, AUG v108(N8):769-776.

Toxic to aquatic organisms including fish and invertebrates:

Studies with fish show that glyphosate can be moderately toxic alone, but when combined with the surfactant normally found in commercial products, the toxicity is greater. Toxicity increases with higher temperatures in fish; one study found that the toxicity of glyphosate doubled in bluegill and in rainbow trout test subjects when the temperature of the water was increased from 45 to 63 degrees F.

Folmar, L.C. et al (1979) "Toxicity of the herbicide glyphosate and several of its formulations to fish and aquatic invertebrates." Archives of Environmental Contamination and Toxicology, v 8, 269-278.

Significant stream drift of midge larva occurred when Roundup was added to test water at 2 mg/L.

Glyphosate can act as a phosphorous source and could stimulate undesirable eutrophication of waterways.

Austin, A.P., et al (1991), "Impact of an organophosphate herbicide (glyphosate) on periphyton communities developed in experimental streams." Bulletin of Environmental Contamination and Toxicology, v. 47, 29-35.

Toxic to soil microbes including nitrogen-fixing bacteria, mycorrhizae, actinomycete, and yeast isolates:

One study found that glyphosate inhibited the growth of 59% of selected naturally occurring soil microbes.

Carlisle, S.M. and Trevors, J.T. (1988), "Glyphosate in the environment." Water, Air, and Soil Pollution 39:409-420.

Glyphosate, by inhibiting the growth of some microbes allows the overgrowth of others. This includes microbial plant pathogens. Fusarium is a naturally occurring soil fungus that is a plant pathogen. Fusarium invades the roots of plants and either kills the plant outright or prevents normal growth. Subsistence farmers in Colombia have noted that fields accidently sprayed with herbicides in attempts to destroy Coca do not produce at the same level as they did prior to being sprayed, and in some cases, no crops grow at all.

Levesque, C.A. (1987), "Effects of glyphosate on Fusarium spp.: its influence on root colonization of weeds, propagule density in the soil, and crop emergence." Can. J Microbiol. Vol 33, pp354-360.

Sanogo, S., et al,(2000) "Effects of herbicides on Fusarium solani f. sp glycines and development of sudden death syndrome in glyphosate-tolerant soybean." Phytopathology, v. 90 (N1): 57-66.

Mycorrhizae are soil fungus that function to increase nutrient uptake by plants through a symbiotic association with the roots. Mycorrhizae have been implicated in the improved resistance to stress, and are necessary for the proper growth and development of most vascular plants. Studies have shown that glyphosate inhibits the growth of mycorrhizae. Killing of beneficial mycorrhizae can result in overgrowth of toxic or pathogenic fungus, such as Fusarium.

Estok, D. et al (1989) , "Effects of the herbicides 2,4-D, glyphosate, hexazinone, and trichopyr on the growth of three species of ectomycorrhizal fungi." Bulletin of Environmental Contamination and Toxicology v 42, pp 835-839.

Levesque, C.A. and Rahe, J.E. (1992), "Herbicidal interactions with fungal root pathogens, with special reference to glyphosate." Annual Review of Phytopathology v.30, 572-602.

Glyphosate destroys nitrogen-fixing bacteria. Plants are dependent on the availability of inorganic nitrogen in the soil. In order to be utilized by plants, nitrogen must be fixed by the addition of oxygen. Nitrification, the oxidative conversion of ammonium ions to nitrate, produces the principle form of nitrogen assimilated by higher plants, and is under control of relatively few species of bacteria.

Hendricks, C.W. (1992), "Effects of glyphosate and nitapyrin on selected bacterial populations in continuous-flow culture." Bulletin of Environmental Contamination and Toxicology v. 49, 417-424.

Glyphosate bound to soil particles may still be toxic and bioavailable to filter feeders, such as crustaceans and molluscs, and potentially other organisms that ingest significant quantities of soil during normal feeding, including bottom-feeding fish, shorebirds, amphibians, and some mammals.

Welten, R., et al. (2000), "Ecotoxicity of contaminated suspended solids for filter feeders (Daphnia magna)." Archives of Env. Contam. And Tox. 39 (3): 315-323.

Glyphosate -Notes on Environmental Fate and Application

Glyphosate's toxicity is compounded by its persistence in the environment. Many studies show that glyphosate remains, chemically unchanged in the environment, for periods of up to a year. Recent research suggests that even when glyphosate binds to soil particles, it will cyclically "desorb" or lose its attraction to soil and become active as an herbicide.

Persistence and degradation

Soil:

"Field half-lives range from 1-174 days, moderately persistent with estimated average half-life of 47 days"

Wauchope, RD, et al. Pesticide Property Database for Environmental Decision Making. Rev. Environ. Contam. Toxicology, 1992.

Weed Science Soc. Of America. Herbicide Handbook 7^th Edition. 1994. Pp 10-58.

"Persisted in soils in Oregon Coast Range with half-life of 55 days"