Prostate, kidney and ovarian diseases, obesity, and birth abnormalities seen in second and third generation offspring of rats exposed to glyphosate
Washington State University researchers have found a variety of diseases and other health problems in the second- and third-generation offspring of rats exposed to glyphosate, the key ingredient of the world's most popular weedkiller, Roundup. In the first study of its kind, the researchers saw descendants of exposed rats developing prostate, kidney and ovarian diseases, obesity, and birth abnormalities.
These adverse transgenerational effects were found to correlate with changes in epigenetic (DNA methylation) patterns in sperm. It is proposed that alterations in gene function caused by these inherited epigenetic DNA methylation changes resulted in damage to various organs and birth defects in the latter generations of animals.
The study was led by Prof Michael Skinner, a WSU professor of biological sciences, who has over the years championed the phenomenon of chemical pollutant-induced transgenerational effects via epigenetic mechanisms. In this study, Prof Skinner and his colleagues exposed pregnant rats to glyphosate between their eighth and 14th days of gestation. The dose – half the amount expected to show no adverse effect (the "no observable adverse effect level" or NOAEL for short) – produced no apparent ill effects on either the parents or the first generation of offspring.
But writing in the journal Scientific Reports, the researchers say they saw "dramatic increases" in several pathologies affecting the second and third generations. The second generation had "significant increases" in testis, ovary and mammary gland diseases, as well as obesity. In third-generation males, the researchers saw a 30 percent increase in prostate disease - three times that of the control population. The third generation of females had a 40 percent increase in kidney disease, or four times that of the controls.
More than one-third of the second-generation mothers had unsuccessful pregnancies, with most of those affected dying. Two out of five males and females in the third generation were obese.
Tumour development was also monitored in males and females, and found to increase in the second generation glyphosate female lineage, but not the first or third generation glyphosate lineages. The most common type of tumour to develop in the males and females was mammary (breast) adenoma.
Skinner and his colleagues call this phenomenon "generational toxicology". It has been observed over the years from exposures to fungicides and other pesticides, jet fuel, the plastics compound bisphenol A, the insect repellant DEET and the herbicide atrazine. At work are epigenetic changes such as alterations in DNA methylation patterns, that are intimately involved in turning genes on and off, often because of environmental factors including exposure to toxic chemical pollutants.
Skinner said he decided to study glyphosate "due to it being one of the most commonly used compounds worldwide".
Glyphosate has been the subject of numerous studies about its health effects. The Skinner study is the third in the past few months out of Washington alone. A University of Washington study published in February found the chemical increased the risk of non-Hodgkin lymphoma by as much as 41 percent. A Washington State University study published in December found state residents living close to areas subject to treatments with the herbicide are one-third more likely to die an early death from Parkinson's disease.
The chemical's generational toxicology represents a new downside that Skinner and his colleagues said should be incorporated into estimates of its risk.
"The ability of glyphosate and other environmental toxicants to impact our future generations needs to be considered," they write, "and is potentially as important as the direct exposure toxicology done today for risk assessment".
The research blows a hole in the notion of the NOAEL as it is calculated on the basis of industry-sponsored toxicology studies. Regulators use this NOAEL to work out supposedly safe levels of exposure for consumers and spray applicators. The problem is that the studies used to determine the NOAEL are outdated and insensitive. This new study clearly shows that focusing on toxicity evaluation by direct exposure, while ignoring transgenerational effects, is yet another major limitation of the current regulatory system that results in a failure to protect public health.
The OECD, which sets standards for industry toxicology studies used for regulatory approvals, only expects the studies to examine effects up until the weaning of the second generation of offspring – and the effects looked for in the second generation are extremely limited. In this way many second-generation and all third-generation effects, such as those revealed in the new study, will be missed. Thus these regulatory standards fail to protect public health.
Strengths and limitations of the study
Toxicological research in rats is considered relevant to humans, so there can be no doubt that from the point of view of the suitability of the experimental animal, these results raise strong concerns for human health. The aim of the study was to test the effects of a dose of glyphosate officially classed as harmless across several generations. It successfully meets this aim.
However, critics will point to several aspects of the study that may limit its applicability to human health:
* A comparison of glyphosate and a representative Roundup formulation at the same glyphosate concentration should ideally have been conducted.
* It tested fairly high doses of glyphosate (albeit below the level deemed by regulators to cause harm), repeated over just a few days of pregnancy, whereas typical human exposures will be at a far lower level and repeated over a longer period. It is well known that low doses can produce stronger toxic effects than higher doses, especially on the hormone (endocrine) system.
* The route of glyphosate administration was intraperitoneal injection (i.e, direct delivery within the abdominal cavity). This is not realistic because if the glyphosate was administered by the more commonly accepted route of oral ingestion, only a portion of the dose would be absorbed into the body tissues and the rest would be excreted. The OECD, which sets standards for industry toxicology studies used for regulatory approvals, recommends oral ingestion, dermal exposure, or inhalation as methods of administration that are "relevant" to human health.
* Although changes in epigenetic (DNA methylation) patterns in sperm were seen and proposed to underlie the transgenerational inheritance of glyphosate ill effects, no effort was made to see if there were also alterations in the epigenetic DNA methylation and gene expression status, which could account for the observed organ damage and birth defects.
The new paper contains one major blunder: it claims that the IARC classification of glyphosate as a probable human carcinogen in 2015 was retracted in 2016. This is false – the verdict was never retracted and stands as valid.
In support of this claim of retraction, the authors reference a Monsanto-sponsored review that took issue with IARC's conclusion that there was strong evidence that glyphosate was genotoxic (a mechanism for carcinogenicity). The Monsanto-sponsored paper predictably concluded that evidence for glyphosate's genotoxicity was "largely unconvincing". But the opinion of the Monsanto-sponsored authors does not affect IARC's verdict in any way.
We expect that the authors of the new study will issue a correction on this point to the publishing journal, Scientific Reports.
The new study:
Assessment of glyphosate induced epigenetic transgenerational inheritance of pathologies and sperm epimutations: Generational toxicology
Deepika Kubsad, Eric E. Nilsson, Stephanie E. King, Ingrid Sadler-Riggleman, Daniel Beck& Michael K. Skinner
Scientific Reports volume 9, Article number: 6372 (2019)
Ancestral environmental exposures to a variety of factors and toxicants have been shown to promote the epigenetic transgenerational inheritance of adult onset disease. One of the most widely used agricultural pesticides worldwide is the herbicide glyphosate (N-(phosphonomethyl)glycine), commonly known as Roundup. There are an increasing number of conflicting reports regarding the direct exposure toxicity (risk) of glyphosate, but no rigorous investigations on the generational actions. The current study using a transient exposure of gestating F0 generation female rats found negligible impacts of glyphosate on the directly exposed F0 generation, or F1 generation offspring pathology. In contrast, dramatic increases in pathologies in the F2 generation grand-offspring, and F3 transgenerational great-grand-offspring were observed. The transgenerational pathologies observed include prostate disease, obesity, kidney disease, ovarian disease, and parturition (birth) abnormalities. Epigenetic analysis of the F1, F2 and F3 generation sperm identified differential DNA methylation regions (DMRs). A number of DMR associated genes were identified and previously shown to be involved in pathologies. Therefore, we propose glyphosate can induce the transgenerational inheritance of disease and germline (e.g. sperm) epimutations. Observations suggest the generational toxicology of glyphosate needs to be considered in the disease etiology of future generations.
Image of Michael Skinner: Washington State University