Glyphosate – Pro and Con

Should you use Monsanto’s Roundup/Rodeo/Pondmaster, etc. in your garden? Is it dangerous? Are there long term consequences?

Here are answers by people who say they know. Somebody is lying, I think. You decide.

The Pro answer is written by A Pesticide Information Project of Cooperative Extension Offices at University of California at Davis, Cornell University, Michigan State University and Oregon State University. Major support and funding was provided by the USDA/Extension Service/National Agricultural Pesticide Impact Assessment Program. The report was revised in May, 1994, and is part of EXTOXNET (Extension Toxicology Network), which is archived at Oregon State University. It is exactly as given, except for the “Exposure guidelines.”

The Con answer is written by Caroline Cox, editor of the Journal of Pesticide Reform, Fall and Winter, 1995, with support by the Northwest Coalition for Alternatives to Pesticides, P O Box 1393, Eugene OR 97440. (541) 344-5044. You can write to Caroline Cox and send $4 for the two issues. Mine came slowly — at least three months. (I sometimes take three months to answer letters, too….)


Fate in humans or animals
Glyphosate is poorly absorbed from the digestive tract and is largely excreted unchanged by mammals. Ten days after treatment there were only minute amounts in the tissues of rats fed glyphosate for three weeks (3).

Cows, chickens and pigs fed small amounts had undetectable levels (less than 0.05 ppm) in muscle tissue and fat. Levels in milk and eggs were also undetectable (less than 0.025 ppm). Nearly all glyphosate residues were rapidly eliminated by fish that had been exposed for 10 to 14 days once these fish were transferred to glyphosate-free water. Glyphosate has no significant potential to accumulate in animal tissue (9).

Ecological effects
Glyphosate is only slightly toxic to wild birds. The LC50** in both mallards and bobwhite quail is greater than 4500 ppm. The bioaccumulation factor in chicken muscle, fat, eggs and liver was as low as 1/10,000 (4).

Glyphosate is practically non-toxic to fish. However, Roundup was more toxic to fish than was glyphosate. In rainbow trout, for instance, the 96-hour LC50** was 8.3 mg/l with Roundup and 38 ppm with glyphosate. The LC50 for glyphosate was 120 mg/l for bluegill sunfish….


Human exposure and ecological effects:
Residues of the commonly-used herbicide glyphosate have been found in a variety of fruits and vegetables. Residues can be detected long after glyphosate treatments have been made. Lettuce, carrots and barley planted a year after glyphosate treatment contained residue at harvest(4).

In California, where reporting of pesticide-caused illnesses is more comprehensive than in other states, glyphosate exposure has the third most commonly-reported causes of pesticide illness among agricultural workers. For landscape maintenance workers, glyphosate ranked highest(9). (Although the third largest, almost half were not given.)

Glyphosate can drift away from the site of its application. Maximum drift distance of 400 to 800 meters (1300 to 2600′) have been measured. From an airplane application(17).

Glyphosate residues in soil have persisted over a year. The highest persistence was 1-3 years in 11 Swedish forestry sites(28) .

Although not expected for an herbicide, glyphosate exposure damages or reduces the population of many animals, including beneficial insets, fish, birds and earthworms. In many cases glyphosate is directly toxic; for example, concentrations as low as 10 parts per million can kill fish and 1/20 of typical application rates caused delayed development in earthworms….