As Bayer AG seeks to discount concerns that Monsanto’s glyphosate-based herbicides cause cancer, several new studies are raising questions about the chemical’s potential impact on reproductive health.

An assortment of animal studies released this summer indicate that glyphosate exposures impact reproductive organs and could threaten fertility, adding fresh evidence that the weed killing agent might be an endocrine disruptor. Endocrine disrupting chemicals may mimic or interfere with the body’s hormones and are linked with developmental and reproductive problems as well as brain and immune system dysfunction.

In a paper published last month in Molecular and Cellular Endocrinology, four researchers from Argentina said that studies contradict assurances by the U.S. Environmental Protection Agency (EPA) that glyphosate is safe.

The new research comes as Bayer is attempting to settle more than 100,000 claims brought in the United States by people who allege exposure to Monsanto’s Roundup and other glyphosate-based herbicide products caused them to develop non-Hodgkin lymphoma. The plaintiffs in the nationwide litigation also claim Monsanto has long sought to hide the risks of its herbicides.

Bayer inherited the Roundup litigation when it bought Monsanto in 2018, shortly before the first of three trial victories for plaintiffs.

The studies also come as consumer groups work to better understand how to reduce their exposure to glyphosate through diet. A study published Aug. 11 found that after switching to an organic diet for just a few days, people could cut the levels of glyphosate found in their urine by more than 70 percent. Notably, the researchers found that the children in the study had much higher levels of glyphosate in their urine than did the adults. Both adults and children saw large drops in the presence of the pesticide following the diet change.

Glyphosate, the active ingredient in Roundup, is the most widely used weed killer in the world. Monsanto introduced glyphosate-tolerant crops in the 1990s to encourage farmers to spray glyphosate directly over whole fields of crops, killing weeds but not the genetically altered crops. The widespread use of glyphosate, by farmers as well as homeowners, utilities and public entities, has drawn growing concern over the years because of its pervasiveness and fears about what it could be doing to human and environmental health. The chemical is now found commonly in food and water and in human urine.

According to the Argentinian scientists, some of the reported effects of glyphosate seen in the new animal studies are due to exposure to high doses; but there is new evidence showing that even low dose exposure could also alter the development of the female reproductive tract, with consequences on fertility. When animals are exposed to glyphosate before puberty, alterations are seen in the development and differentiation of ovarian follicles and the uterus, the scientists said. Additionally, exposure to herbicides made with glyphosate during gestation could alter the development of the offspring. It all adds up to show that glyphosate and glyphosate-based herbicides are endocrine disruptors, the researchers concluded.

Agricultural scientist Don Huber, professor emeritus from Purdue University, said the new research expands on knowledge about the potential scope of damage associated with glyphosate and glyphosate-based herbicides and provides a “better grasp of understanding the seriousness of the exposure that is ubiquitous in our culture now.”

Huber has warned for years that Monsanto’s Roundup might be contributing to fertility problems in livestock.

One noteworthy study published online in July in the journal Food and Chemical Toxicology,  determined that glyphosate or glyphosate-based herbicides disrupted “critical hormonal and uterine molecular targets” in exposed pregnant rats.

A different study recently published in the journal Toxicology and Applied Pharmacology by researchers from Iowa State University looked at glyphosate exposure in mice. The researchers concluded that chronic low-level exposure to glyphosate “alters the ovarian proteome” (a set of expressed proteins in a given type of cell or organism) and “may ultimately impact ovarian function. In a related paper from the same two Iowa State researchers and one additional author, published in Reproductive Toxicology, the researchers said they did not find endocrine disrupting effects in the mice exposed to glyphosate, however.  

Researchers from the University of Georgia reported in the journal Veterinary and Animal Science that consumption by livestock of grain laced with glyphosate residues appeared to carry potential harm for the animals, according to a review of studies on the topic. Based on the literature review, glyphosate-based herbicides appear to act as “reproductive toxicants, having a wide range of effects on both the male and female reproductive systems,” the researchers said.

Alarming results were also seen in sheep. A study published in the journal Environmental Pollution looked at the impacts of glyphosate exposure on the development of the uterus in female lambs. They found changes that they said might affect the female reproductive health of sheep and show glyphosate-based herbicides acting as an endocrine disruptor.

Also published in Environmental Pollution, scientists from Finland and Spain said in a new paper that they had performed the first long-term experiment of the effects of “sub-toxic” glyphosate exposure on poultry. They experimentally exposed female and male quails to glyphosate-based herbicides from the ages of 10 days to 52 weeks.

The researchers concluded that the glyphosate herbicides could “modulate key physiological pathways, antioxidant status, testosterone, and the microbiome” but they did not detect effects on reproduction. They said the effects of glyphosate may not always be visible with “traditional, especially short-term, toxicology testing, and such testing may not fully capture the risks…”

Glyphosate and Neonicotinoids

One of the newest studies looking at glyphosate impacts on health was published this month in the International Journal of Environmental Research and Public Health.  Researchers concluded that glyphosate as well as the insecticides thiacloprid and imidacloprid, were potential endocrine disruptors.

The insecticides are part of the neonicotinoid class of chemicals and are among the most heavily used insecticides in the world.

The researchers said that they monitored the effect of glyphosate and the two neonicotinoids on two critical targets of the endocrine system: Aromatase, the enzyme responsible for estrogen biosynthesis, and estrogen receptor alpha, the main protein promoting estrogen signaling.

Their results were mixed. The researchers said with respect to glyphosate, the weed killer inhibited aromatase activity but the inhibition was “partial and weak.” Importantly the researchers said glyphosate did not induce estrogenic activity. The results were “consistent” with the screening program conducted by U.S. Environmental Protection Agency, which concluded that “there is no convincing evidence of a potential interaction with the estrogen pathway for glyphosate,” they said.

The researchers did see estrogenic activity with imidacloprid and thiacloprid, but at concentrations higher than the pesticide levels measured in human biological samples. The researchers concluded that “low doses of these pesticides should not be considered harmless,” however, because these pesticides, together with other endocrine disrupting chemicals, “might cause an overall estrogenic effect.”

The varying findings come as many countries and localities around the world evaluate whether or not to limit or ban continued use of glyphosate herbicides.

A California appeals court ruled last month that there was “abundant” evidence that glyphosate, together with the other ingredients in Roundup products, caused cancer.