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Jul 14

Herbicides are bad. Except when they aren’t.

by azmanam | Categories: science news | (18185 Views)

CornThere is a growing vocal subculture who contend chemical additives are bad (mmmkay).  Anything that isn’t “natural” isn’t “good.”  Vitanet (I won’t bother linking) tells us that “in the past century, modern organic chemistry has synthesized and released into the world an estimated 300,000 xenobiotic (foreign to our normal biology) chemicals. The food processing and food growing industries put an approximate 10,000 xenobiotic chemicals into our food supply alone.”  And the only way to stop this is to buy their detoxification products.  Only naturally grown foods with no chemical additives can save us now.  Unfortunately, toxicologists disagree.

But an ASAP in The Journal of Agriculture and Food Chemistry (doi: 10.1021/jf9013313) provides some new information.  Dean Kopsell from the University of Tennessee shows that mesotrione (a naturally-derived herbicide), used alone or in combination with atrazine (a herbicide banned in the EU), does more than just suppress weed growth.  It also upregulates the formation of nutritionally important carotenoids, specifically zeaxanthin.  Corn is one of the few vegetable sources of zeaxanthin, and the carotenoid is believed to be protective against age-induced macular degeneration.

Basically, mesotrione inhibits the carotenoid biosynthetic pathway resulting in a buildup of phytoene. Mesotrione is also completely metabolized by the plant to nonherbicidal byproducts.  Once the mesotrione is metabolized, carotenoid biosynthesis begins anew, and the surplus of starting materials pushes the biosynthesis to produce more carotenoids.  The authors conclude the mechanistic data is still unclear, but “data from this study suggest the possibility to increase concentrations of nutritionally important kernel carotenoid in sweet corn genotypes through applications of HPPD-inhibiting herbicides such as mesotrione.”

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(PS, I first heard about this story on this week’s ACS podcast Science Elements.  Click here for my science podcast repository.)

10 comments

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  1. Andres

    I think you’re being intellectually dishonest here. Yes, there is a chemical-phobia/anti-chemical movement opposing pesticides and herbicides, among other things. But more scientifically objective opponents of industrial agriculture oppose synthetic chemicals, and aren’t necessarily opposed to GM (“Tomorrow’s Table” talks about this). Sure, there’s a tight correlation between anti-chemical and anti-industrial farming, but don’t group us together. Many would not be opposed to mesotrione because it is a natural product. Atrazine would be another issue, but even then- please don’t confuse those who categorically reject synthetics and those who treat with caution, for the reason that they are not found in the natural world (and there are good reasons to hold such caution).

    Of course, as the pharma industry attests, non-natural products can have (beneficial) biological activity as well. But there’s something to be said about using ‘naturally occurring’ (made in the natural world w/o human intervention) compounds in agriculture, because their formation and use has occurred under biological constraints. For example, a natural pesticide isolated from a plant can’t be intolerantly lethal to all living organisms, since it would kill the producing plant itself. Excuse the crude example, but my point is that evolution has fine-tuned secondary metabolites in plants, fungi, etc as well as constraining them to a chemical-biological space that synthesis simply can’t recognize, unless we understood all the contingencies of the evolutionary process in present organisms at genetic, molecular, and physiological levels.

    1. Mitch

      So you’re arguing, we shouldn’t use a chemical in agriculture until we find a plant or animal that can make it, that way we know it is safe? How does that not sound as silly to you as it does to me? It may take thousands of years of plant evolution until it selects for the same herbicide that works against pests. Or we can just start using it today.

  2. azmanam

    Many would not be opposed to mesotrione because it is a natural product.

    No. No it’s not. It’s a naturally derived product. This is an important point. Researchers from Zeneca (now part of AstraZeneca) noted that few weeds grew around Callistemon citrinus. They studied the plant and isolated the natural product leptospermone In an effort to make a more potent herbicide, the researchers conducted an extensive structure activity relationship study and eventually synthesized mesotrione and found it’s properties to be far superior to leptospermone. Without the discovery of the natural product leptospermone, there would be no naturally derived mesotrione. It’s a small but important distinction.

    don’t confuse those who categorically reject synthetics and those who treat with caution, for the reason that they are not found in the natural world

    That presupposes that if it’s found in the natural world it is ok to abandon caution, does it not? I’ll spare you the hemlock (conium argument as you seem to have done your homework and have no doubt heard this argument before. Bottom line – chemicals are chemicals, regardless of origin. Natural acetic acid tastes as much like vinegar as synthetic acetic acid. Natural strychnine kills rats just as effectively as synthetic strychnine.

    But there’s something to be said about using ‘naturally occurring’ (made in the natural world w/o human intervention) compounds in agriculture, because their formation and use has occurred under biological constraints.

    No, I reject that supposition. Flemming discovered natural penicillin and revolutionized the way we think about bacterial infections. Thanks to tinkering with the ‘naturally occuring’ penicillin core (the beta lactam), we now have several dozen beta lactam antibiotics that work in areas and at lower doses than ‘naturally occurring’ penicillin ever could. Biological constraints arrived at one destination, the laboratory surveyed many more compounds than biological constraints could make, and found ones that were even better (and undoubtedly a lot that were even worse, too).

    I think you’re being intellectually dishonest here.

    I’ll accept that I may be guilty of lumping together and overgeneralizing. To that extent you have my apologies. However, I have very little sympathy for most flavors of the chemical-phobia/anti-chemical/anti-industrial farming movement.

  3. OperationCounterstrike

    For those who are genuinely interested in the subject, read whatever you can about (and/or by) Professor Bruce Ames (at UCBerkeley).

    The standard test for measuring whether or not a compoud is a mutagen is the Ames test.

    His is the argument-stopping word on these kinds of questions.

  4. OperationCounterstrike

    Whether or not Bruce Ames gets a Nobel Prize will depend on how long he lives. It matters, because at UCBerkeley they have special parking places reserved for exclusive use by Nobel Laureates. (It’s notoriously difficult to park on campus; only Nobel Laureates and cripples can count on spending less than thirty minutes looking for a space.)

  5. Chemjobber

    This is a pretty sweet post, dude. Way to bring it.

  6. orgopete

    Oh so close. I wish herbicides might have been considered beneficial as herbicides. I reject teleological or arguments of nature. Chemicals are simply chemicals without regard to origin. Their atoms do not possess properties of goodness or badness, virtue or detriment. Bond formation by an enzyme does not confer a property of goodness to the result.

    Flooding fields with water (rice) or under a foot of soil with a plow (corn and soybeans) are simply ancient means of weed control. In the case of plowing, if you don’t mind eroding the midwest into the Gulf of Mexico, that was a good method of weed control. In deference to sustainability, using a chemical to inhibit phosoenol pyruvate (Roundup) proves enormously beneficial by stopping soil erosion, saving fuel, and producing crops economically. The chemicals for the inhibition do not possess an inordinate danger.

    While working in the agrochemical industry, I came to realize how economics could command usage. Triazine herbicides are very cheap and effective. While they pose some hazards associated with their use, because they are cheap and effective, they have not been banned. The dilemma is that low cost removes incentive for the discovery of more environmentally safe substitutes. It also sustains their use as no cheap substitutes exist. For this reason, if a herbicide poses an environmental risk, I advocate a technology tax could be instituted again the triazine herbicides, for example. It could be phased in to increase the cost of its use. That increase in cost will create an incentive and opportunity for companies to discover environmentally friendly substitutes.

  7. Matt

    There are no easy rules of thumb with a category as all-inclusive as “chemicals.” Glyphosate (roundup) is less toxic to humans than caffeine or aspirin, while many of the old standards (like atrazine) led to extremely serious cases of well-water poisoning in rural areas.

  8. Thomas

    If you are reporting results of a study to which not all of your readers have direct access, I think it would be more honest if you (as the original authors did in the publication) reported that the study was funded by Syngenta. The very company that produces and markets both Atrazine and Mesotrione. I am not saying that this makes the science necessarily bad – but it sure does indicate a conflict of interest.

    And I am certainly opposing your conclusions – and those of the original authors. To me it sounds utterly simplistic to argue that it might increase the health of anybody eating a crop that has been doused in at least three different pesticides, only because the content of common plant components (lutein and zeaxanthin) are marginally increased in some of the investigated genotypes. Especially if one of them (Atrazine) is discussed as a carcinogen and an endocrine disrupter.

    Additionally, there is another good reason why Atrazine is banned in Europe, as it is amongst the herbicides with the longest half-life in the environment – it is far more persistent that most other PSII-inhibiting herbicides. And Cyhalotrin, the insecticide that was used in the study, is highly toxic to bees.

    And furthermore: Atrazine and Mesotrione tamper with the normal physiology of the treated plant. Hence, before glorifying the tiny increase in xanthophylls in the plant it might be advisable to take a look at the total nutrient content of the plant (vitamins, anti-oxidants, minerals, etc.) and at the effect that the pesticides might have on the total yield.

    All in all, simply eating a bit more kale and spinach (both naturally rich in Lutein and Xeaxanthin) might be much healthier, both for yourself and the environment.

  9. analyticallaboratories

    When you look the organic label in the food product on the shelves of the stores, it states “organic food” or “made with organic” it doesn’t mean it is free from herbicide or pesticide contamination, it still contains some trace levels of herbicides or pesticides which are allowed by USDA. I do not concern about herbicides are bad or good, good or bad is depended how we handle it.

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