GMWatch comment on critique of Samsel and Seneff glyphosate review
A new peer-reviewed paper argues that glyphosate-based herbicides are contributing to the modern diseases that are reaching epidemic proportions in recent decades.
The paper suggests mechanisms through which this may be happening.
A critique of the study has been published in the Huffington Post by food writer Tamar Haspel.
Ms Haspel says the paper forms conclusions based on "nonexistent" evidence and that it is an example of "bad science".
We are not in the business of defending the Samsel and Seneff paper. We do see over-extrapolations in it. For example, the authors claim, "glyphosate may ... be the most important factor in the development of multiple chronic diseases and conditions that have become prevalent in Westernized societies."
The evidence in the paper doesn't, in our view, justify the claim that glyphosate is "the most important factor" in the development of these illnesses. We're all exposed to numerous pollutants and it's likely that many play a part. Perhaps some do so through similar mechanisms to those laid out in the paper.
So one day, perhaps, a well-informed critique of this paper will appear. However, Ms Haspel's article is not it. In fact, her arguments unwittingly perpetuate and support the worst deceptions of industry polluters.
Let's go back and look first at the main argument of the Samsel and Seneff paper:
"Glyphosate's inhibition of cytochrome P450 (CYP) enzymes is an overlooked component of its toxicity to mammals. CYP enzymes play crucial roles in biology, one of which is to detoxify xenobiotics. Thus, glyphosate enhances the damaging effects of other food borne chemical residues and environmental toxins."
As a bit of extra explanation, CYP enzymes, also known as cytochrome P450 enzymes, are produced from the cytochrome P450 genes. CYP enzymes are "involved in the formation (synthesis) and breakdown (metabolism) of various molecules and chemicals within cells. Cytochrome P450 enzymes play a role in the synthesis of many molecules including steroid hormones, certain fats (cholesterol and other fatty acids), and acids used to digest fats (bile acids). Additional cytochrome P450 enzymes metabolise external substances, such as medications that are ingested, and internal substances, such as toxins that are formed within cells."
Now let's consider Ms Haspel's arguments in turn, starting with her objection to the main argument of Samsel and Seneff.
1. Ms Haspel says: "The evidence for these mechanisms, and their impact on human health, is all but nonexistent. The authors base their claim about CYP enzymes on two studies, one of liver cells and one of placental cells, which report endocrine disruptions when those cells are exposed to glyphosate. Neither study is CYP-specific."
Both studies cited by the authors and referred to by Ms Haspel address glyphosate's disruption of aromatase, the enzyme responsible for estrogen synthesis. Aromatase is a CYP enzyme. The second study addresses in detail the disruptive effect of Roundup and glyphosate on CYP enzymes.
It's not clear how either study could be more "CYP-specific" if it tried.
Nothing in Ms Haspel's argument contradicts the authors' central thesis.
2. Ms Haspel says, "Samsel and Seneff didn't conduct any studies."
Indeed--that's why the paper is called a "review".
3. Ms Haspel says, "They don't seem interested in the levels at which humans are actually exposed to glyphosate."
Samsel and Seneff focus on plausible mechanisms through which glyphosate/Roundup may contribute to human diseases. Other papers focus on how much glyphosate people are actually exposed to.
Interestingly, both of the studies cited by Samsel and Seneff, which Ms Haspel dismisses as not "CYP-specific", did consider levels to which humans could be exposed. Gasnier and colleagues (2009) found glyphosate herbicides caused endocrine-disrupting effects in human cells tested in vitro (test-tube test) "at doses far below agricultural dilutions" and "around residual authorized levels in transgenic feed". And Richard and colleagues (2005) found "glyphosate acts as a disruptor of mammalian cytochrome P450 aromatase activity from concentrations 100 times lower than the recommended use in agriculture."
These are in vitro studies and would have to be confirmed by in vivo studies (in animals). But one review paper can't do everything.
In light of these facts, perhaps it is Ms Haspel who is not "interested in the levels at which humans are actually exposed to glyphosate".
Meanwhile, it is an old and dirty industry trick, once outright denial of a chemical's ill effects has failed, to argue, "Maybe this substance is dangerous at high doses but humans are not exposed to that much so it's fine to keep it on the market".
Between the evidence emerging that a substance is dangerous and its actually being pulled off the market, there is plenty of "horse trading" over expected levels of exposure by industry and regulators. The discussion often stalls over industry claims that humans can't be exposed to dangerous levels.
Fortunately in Europe, the pitfalls of this argument have become obvious to EU member states. Pitfalls include: endocrine disruptors (such as Roundup and glyphosate) can exercise toxic effects at extremely low doses that have never been properly assessed in regulatory tests; we don't know the effects of bioaccumulation or of combination effects with other toxins, which can make so-called "safe levels" not safe at all; what's safe for one individual may not be safe for a vulnerable individual, such as the developing foetus, young or old people, or people with compromised immune systems; and exposures themselves can vary hugely and are largely uncontrollable by the individual.
Thus the EU Parliament and Council wrote a new pesticide law with a "hazard cut-off" clause, which says that any substance shown to be an endocrine disruptor--and there's evidence that Roundup and glyphosate are endocrine disruptors--is automatically banned. Under the letter of the law, no horse trading is allowed.
Unfortunately, the letter of the law is one thing and implementation another. So horse trading over levels of exposure continues and known endocrine disruptors like Roundup remain on the market.
No one who cares about human health and the environment should encourage industry and regulators in this horse trading. Nor should they imply it's the job of independent scientists or the public to prove a substance is dangerous or that we are exposed to dangerous levels. It isn't. As the European Food Safety Authority (EFSA) likes to remind us, it is the job of industry to prove its products are safe before they are allowed onto the market.
In the EU we need to constantly remind regulators about the letter of the pesticide law and ensure it's enforced. In the EU and elsewhere, the precautionary principle is part of the regulations of many countries and should be used.
Industry has NOT proved that glyphosate and Roundup are safe according to up to date scientific knowledge.
4. Ms Haspel says, "[The authors] simply speculated that, if anyone, anywhere, found that glyphosate could do anything in any organism, that thing must also be happening in humans everywhere."
While we did spot an over-extrapolation (above), Ms Haspel is misrepresenting the study. The authors laid out plausible mechanisms through which glyphosate COULD contribute to certain illnesses. Whether it is happening or not must be confirmed by further studies. It's unacceptable for humans to be exposed in the meantime, however -- based not on this paper, but on the total body of evidence on glyphosate and Roundup.
5. Ms Haspel levels ad hominem arguments against the supposed lack of credentials of the authors. She implies that having "a point of view" on a substance disqualifies one author, Samsel, from the right to be taken seriously.
There are countless replies that could be made to such arguments, including:
i) The system of blind peer review prevents just this kind of prejudice affecting evaluation of a study. The glory of the system is, as one scientist said, "You can be a Nobel prize winner in chemistry or a housewife in Croydon who failed her GCSEs but your paper will be judged solely on its merits."
ii) If we think that the author Samsel's history is important, then we should also look at the work he did before he took on "charitable community investigations of industrial polluters". He seems to have been busy on inventions with industrial applications and working on risky substances.
If we are going to extrapolate from his personal history to make conclusions on the validity of his paper, then we should take all aspects of his history into consideration. A possible extrapolation is: maybe he is someone who's seen both sides.
iii) If we want to get picky about only allowing people with the "right" credentials to publish their view of the toxicity of a substance, then let's apply the same rule in symmetrical fashion to the defenders of GMOs and toxics. Out go the countless plant scientists with no credentials in human biology or toxicology who claim GMOs are "safe" to eat. Out go the media pundits and self-styled "reformed" environmentalists who claim pesticides are safe and beneficial and organic food can kill us. And definitely -- out go food writers who give opinions on scientific reviews of glyphosate safety.
If we go on like this we will soon be left with no one to defend GMOs and toxics. Maybe that'll be a good thing. But if we apply that rule, we must apply it equally to both sides.
iv) The problem with disqualifying people with "points of view" from scientific journals is that almost every scientist has a point of view on GMOs, toxics, or whatever else they're writing about. Those who claim they don't are either strangers to their own psyches or are lying. The important thing is to apply scientific method to one's point of view and see if it holds up.
Ms Haspel should do some research on the scientists who publish papers on GMOs and their associated pesticides. Many have a strong history of lobbying for GM crops; many own patents on GM technologies and have undisclosed industry connections. Numerous well-cited papers claiming glyphosate and Roundup are safe are authored by Monsanto scientists.
Given the choice between an author whose affiliation is Monsanto (especially given the proven bias of industry-affiliated studies) and an author like Samsel whose affiliation used to be with industry but is now with community investigators of industrial polluters, who are we going to believe?
Ms Haspel's ad hominem arguments are red herrings. The rest of her arguments don't hold up.
We look forward with interest to the substantive arguments against this paper.