For decades, farmers and homeowners alike have been eradicating unwanted weeds and vegetation with Roundup. While it’s been an effective herbicide and widely used in the US, its main ingredient has been causing much debate in recent years with claims linking its use to cancer and other conditions. Now, scientists are finding that exposure to this weed killer could also be responsible for damaging the health of future generations via inherited epigenetic defects.
Glyphosate, or N-(phosphonomethyl) glycine was first discovered in 1950 and later commercialized as Roundup in the 1970s by Monsanto due to its herbicidal effectiveness. It was originally presented as having no harmful effect on animals since it acts to inhibit a vital enzymatic pathway found uniquely in plants. The inhibition causes a protein deficiency, which leads to plant death. Because mammals lack this biochemical pathway, have higher metabolic rates, and can eliminate this type of chemical rapidly, the assumption has been that glyphosate is safe for humans and other mammals.
Over the years, glyphosate has been evaluated by regulatory agencies and research institutions with conflicting reports regarding its toxicity. In 2015, the International Agency for Research on Cancer (IARC) declared that it was “probably carcinogenic” based on the prevalence of kidney and liver tumors in animal feeding studies. The statement was then retracted in 2016 after further evaluation. However, evidence continues to accumulate in scientific literature associating this chemical with cancer as well as numerous other adverse health conditions.
Most assessments have only examined glyphosate’s direct exposure effects on individuals. Its impact on succeeding generations had not been reviewed, until just recently. In a first time study published in Scientific Reports, a research team at Washington State University (WSU) looked at how environmental exposure to this chemical might promote the induction of disease and pathology in subsequent generations. This particular occurrence is what they call “generational toxicology” and the mechanism implicated is epigenetic transgenerational inheritance.
Epigenetic transgenerational inheritance refers to the transmission of epigenetic information through the germline (sperm or egg) which leads to phenotypic variations or diseases in future offspring. Epigenetics describes any process that can alter gene activity but does not change the DNA sequence. These processes which can be passed on to daughter cells include DNA methylation, RNA methylation, histone modifications, chromatin structure, and more. Environmental factors can induce epigenetic changes at critical developmental periods, such as in early embryo and during primordial germ cell reprogramming. As well, adult exposure during preconception has also been shown to promote the transgenerational inheritance of certain diseases.
Previous studies on mice have demonstrated that epigenetic marks can be altered by toxins and pollution and then persist across multiple generations. Human studies have also shown epigenetic inheritance in responses to nutrition, smoking, stress, and other environmental exposures. Here the researchers found that descendants of glyphosate exposed rats developed kidney, prostate and ovarian diseases, as well as obesity and congenital disabilities.
In performing the study, the researchers subjected pregnant rats to the herbicide throughout days 8 to 14 of gestation. The dose they were given was only half the no observable adverse effect level or NOAEL amount. As expected, the amount did not bring about any noticeable ill effects on the parents, nor did it negatively affect the first-generation progeny. On the other hand, they reported “dramatic increases” in several pathologies affecting the second (F2) and third (F3) generations.
The F2 offspring showed considerable increases in diseases of the testis, ovaries and mammary glands, plus had higher rates of obesity. The male F3 generation exhibited a 30 percent increase in prostate disease, and the female F3 group had a 40 percent increase in kidney disease. These third-generation results were respectively 3 to 4 times greater than the control populations. Moreover, the group witnessed one-third of the F2 mothers either die during pregnancy or fail to deliver their babies, and two-fifths of the F3 population was well over normal weight levels.
Although additional research is needed to identify the specific molecular factors involved here, the results taken as a whole suggest that glyphosate causes generational toxicology even though its direct contact appears to be of low or negligible danger.
As the authors wrote, “The ability of glyphosate and other environmental toxicants to impact our future generations needs to be considered and is potentially as important as the direct exposure toxicology done today for risk assessment.”
Source: Kubsad, D. et al (2019). Assessment of Glyphosate Induced Epigenetic Transgenerational Inheritance of Pathologies and Sperm Epimutations: Generational Toxicology. Scientific Reports 2019, Apr 23;9(1):6372.
Reference: Eric Sorensen, WSU researchers see health effects across generations from popular weed killer. Washington State University News, April 23, 2019.