Glyphosate is absorbed in the gut or through the skin. After oral intake, 30-36% of glyphosate is absorbed in most test animals. Most of the absorption is excreted in the urine. The acute toxicity of glyphosate, measured by the LD50 test is relatively low and in the US, glyphosate itself is classified in Toxicity Category III –which is “slightly toxic and slightly irritating”.
In spite of tests showing low toxicity to animals, consequential poisoning caused by both intentional and accidental introduction to glyphosate have been recorded in humans and laboratory animals. Physicians in Japan first exposed the acute threats of surfactants in glyphosate products in a study of 56 cases of Roundup poisoning. These cases mostly resulted from suicides or attempted suicides, which included nine deaths. They found that the fatalities happened after ingesting about 200 ml (3/4 cup) of glyphosate. A range of symptoms has been noted from acute glyphosate poisoning.
Exposure to small amounts of glyphosate products in the workplace or through accidental contact has been shown to cause serious poisoning symptoms. A study requested by the US Department of Agriculture (USDA) Forest Service found that the use of Roundup with hand applicators or tractor sprayers resulted in a range of exposure to glyphosate despite using special protective clothing. Reports of poisoning incidents are frequent. An assortment of symptoms has been disclosed from various incidents and occupational exposures, including eye and skin irritation, contact dermatitis, eczema, cardiac and respiratory issues, and allergic reactions.
Monsanto (RoundUp) claims that glyphosate does not cause reproductive complications. However, tests with rabbits have determined adverse effects on semen and sperm quality. Other studies at high dosages have reported problems such as decreased litter size and reduced sperm counts in rats.
Some articles suggest that glyphosate can cause chronic health effects in laboratory animals. Lifetime glyphosate feeding studies have exposed reduced weight gain, liver and kidney effects, and deterioration of the eye lens. These effects were found in the higher doses tested. At lower doses inflammation of the stomach’s mucous membrane was shown.
The EPA classifies glyphosate in ‘Group E’- non-carcinogenic for humans. They base this conclusion on three studies conducted between 1979 and 1990, of laboratory animals fed fluctuating doses of glyphosate. Observations include increased testicular tumors in males, increased thyroid cancers in females, increases in kidney tumors in male mice, and an increase in pancreatic and liver tumors in male rats. All effects were discounted for an assortment of reasons. However, a recent Swedish study found that increased rates of non-Hodgkin’s lymphoma were affiliated with exposure to the pesticides Roundup. The scientists stated that “glyphosate deserves further epidemiologic studies”. Another recent study tested the genotoxicity of glyphosate and recorded cytogenetic damage in mouse bone marrow which was more noticeable for Roundup. A DNA-damaging activity of glyphosate and Roundup was also observed in the mice’s liver and kidneys.
Residues in Food
The use of glyphosate may result in residual exposure in crops and animal tissue or drinking water destined for human consumption. The World Health Organization (WHO) found that pre-harvest use of glyphosate results in significant leftovers in the grain and plant material. The WHO also found that glyphosate residues in animal feeds arising from pre-harvest glyphosate treatment of cereals may result in low glyphosate levels in meat, milk and eggs. In storage, remnants of glyphosate are reported to be stable for one year in plant material and for two years in animal products. Glyphosate residues are not monitored in food since methods of analysis are complex and costly. Likewise, the measurement of glyphosate exposure in the general population through diet has not been conducted.
Research by Monsanto showed the existence of glyphosate in most samples of all grains harvested from treated plots. The metabolite, AMPA, was detected at low levels. Studies showing the outcome of glyphosate residues in wheat found that levels in white flour were 10-20% of the levels in wheat, and the bran residues were 2 to 4 times higher than those in wheat. The residues were not lost during baking. Levels of glyphosate in the final bread product depend on how much glyphosate-contaminated flour is diluted with uncontaminated flour. In a 2 year study in Canada, residues of glyphosate in wheat after pre-harvest treatment increased with the rate of application and decreased with seed moisture at the time of application. When the maximum application rate was sprayed at seed moisture of 40% or less, glyphosate residues were found. Glyphosate residues in beer made from barley were 4% of the original level in the barley. Levels of glyphosate in processed oats were found to be 50% of the levels in the pre-harvest treated oats. Cattle, pig and poultry fed a diet of 100mg of glyphosate resulted in significant residues in pig liver and kidney, and in cattle kidney. Levels of glyphosate in milk, eggs and meat were low. Field studies of glyphosate on wild blueberry and raspberry found that residues in the fruit after spraying remained above the maximum permissible level throughout the 61 days of study period. The berries of the 2 species absorbed the glyphosate at different rates. The initial residue value in blueberry was 7.94 ppm and in raspberry was 19.49 ppm. These fruits are typically sprayed in late summer when the fruit is ripe. Contaminated fruit may be eaten by wildlife or picked for human consumption. Residues of glyphosate have been found in strawberries, lettuce, carrots, and barley after they were sprayed. Glyphosate residues were found in some of these food items when they were planted a year after glyphosate was applied.
Monsanto advertises that glyphosate is not considered a threat to drinking water since it is constrained by soil and sediment and is biodegraded quickly. However, glyphosate has the potential to contaminate surface water if it is carried by soil particles suspended in a run-off. Glyphosate has also, on rare occasions, been detected in groundwater. Once in water, glyphosate is not readily broken down by water or sunlight. Dispersion from water is usually due to absorption to sediment or uptake by plants and biodegradation.
Generally, glyphosate residues in water are not monitored because they are extremely difficult to isolate and many authorities do not consider glyphosate to be of major concern as a water contaminant. In the US, routine monitoring for glyphosate in groundwater is infrequent. Glyphosate has been found in seven US wells: 1 in Texas, 6 in Virginia.
Very little research has been done on the effects of glyphosate on aquatic microorganisms or invertebrates but here is what we have learned:
- A study to determine the effects of glyphosate concentrations on carp found that toxic effects included changes in enzyme activity in serum, liver and kidneys and morphological changes in gills, liver and kidneys.
- A study in Louisiana tested the effect of glyphosate on an aquatic snail species, Pseudosuccinea columella. They found that low levels of glyphosate adversely affect snail reproduction. It also found that, at different concentrations, glyphosate can stimulate growth and increase the number of eggs laid containing more than one embryo with the potential to increase the snail population.
- A study examined the DNA damage caused by 5 commercial pesticides, including Roundup, on bullfrog tadpoles. Significant DNA damage was observed for 2 out of 3 concentrations tested. There was a strong linear correlation between DNA damage and dose. The study concluded that Roundup is clastogenic (causes DNA damage) in tadpoles.