On herbicides

On herbicides

01 May 2006

Got questions about the environment? Ask Umbra.

Dear Umbra,

How do herbicides (organic, if such exist, or non-organic) work?

David Burch
South Bend, Ind.

Ask Umbra continues below

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Dearest David,

Herbicides are considered a subcategory of pesticides, for all you confused by my last pesticide comments. Herbicides kill plants with a vast array of ingenious torture and maiming techniques. (Maiming a plant isn't quite like maiming an animal: plants can grow back broken limbs, and it's hard to deny a plant its food source unless you expend the effort to get the plant out of the ground entirely.) Effective herbicides work at a cellular level to disrupt the functioning of the life-support system of the plant.

One man's weed is another man's salad.

Photo: iStockphoto.

Chemical herbicides may: block enzyme/amino-acid production, block photosynthesis, disrupt cell membranes, stop or accelerate cell division, destroy chlorophyll, stop protein synthesis. A few examples of herbicides allowed under the organic rules are acetic acid (which is basically a component of vinegar) and mixtures containing clove oil, to burn the plant; and some types of soap, to dry the plant. All these result in a mutant plant which can no longer function and dies. Wikipedia will give you a good, more technical description of these actions.

Contact herbicides must be sprayed on the actual plant in order to do their work, while systemic herbicides can be sprayed onto the plant or soil and later be innocently taken up by the plant into itself as part of its nutritional regimen.

Herbicides are popular because they work well at the outset. They do the job and kill target plants. It can hardly be necessary to add that they can also kill and maim non-target plants and animals, and can have undesirable long-term impacts. Hence, we would like to reduce the use of herbicides, particularly on the homeowner front.

Concisely,
Umbra

Yours is to wonder why, hers is to answer (or try). Please send Umbra any nagging question pertaining to the environment -- but first check out her FAQs!

The claims made in this column may not reflect the views of this magazine. Neither the magazine nor the author guarantees that any advice contained in this column is wise or safe. Please use this column at your own risk.

Umbra Fisk is Grist Research Associate II, Hardcover and Periodicals Unit, floors 2B-4B.

Comments: (4 comments)

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Agent Orange in California?

My husband, who grew up in the Imperial Valley in farthest SE California, worked on his daddy's farm. One of the things they grew was cotton, in his estimation a merciless, miserable, horrible crop. He told me that at a certain point in the growth of the crop, soon before the bolls were to be collected, cropdusters would fly overhead dumping some sort of defoliant agent. It was necessary to get rid of the leaves, in order to pick the cotton more easily and efficiently. Or something like that. So now, one of the many worries the poor lamb has to deal with is when all the Agent Orange he inhaled as a kid is going to start kicking in.

Cotton is notoriously one of the most polluting of all crops to raise. But is that sort of defoliant still used, and applied like that? What related health problems are there?

Chickens deserve our true friendship! So do fish! So do other sentient beings! Let us learn to be kind.

by caniscandida at 12:58 PM on 02 May 2006

Cotton Pickin' Bad

The news is not good for conventional cotton farming, even these days. Patagonia (whom I worship for their cool climbing clothes and enviro ways, and who have ONLY used organic cotton for all their products for a decade now) points me to this website about sustainable cotton farming, which in turn has a few handy links, including this one for the Pesticides Action Network.

It appears that defoliants are still used in conventional cotton farming (in fact, there is probably an article telling us so here on Grist). This site, from the U of Georgia, lists a bunch of "harvest aids" mainly defoliants that attempt to, in one way or another, stimulate the plant's natural production of the hormone ethylene, which promotes the 'natural' process of the cotton leaf falling off, or downregulate the natural hormone auxin, which keeps the leaf healthy and on the plant.

From a simple web search, it seems the most common these days is thidiazuron, manufactured by both DuPont and Bayer. It's difficult for me to find out what was most common back when your husband was a kid (assuming that wasn't 2 or 3 years ago!). A search for info on PubMed revealed little - one article on mortality due to defoliant application suggests that, something drastic would have been more likely to happen back when he was a kid, right near the time of crop-dusting. A search for toxicity data on thidiazuron revealed little to be alarmed about - the MSDS states there was no mutageniticy or genotoxicity (ie no broken chromosomes, DNA, etc), no reproductive toxicity and no carcinogenicity noted at up to 1000 ppm (exposure limit is 50 ppm).

I think in general the pesticides/herbicides that are destined for use in crop-dusting are held to a higher standard, safety-wise, than direct-application ones, because of the risk/likelihood of inhalation exposure.

Hope that helps,
Kaela

by kmp at 2:06 PM on 02 May 2006
[ Parent ]

fretting for naught?

Thanks so much, Kaela, for your research. That man o' mine was out in the fields in the '60s, contemporary with whatever was being dumped on Viet Cong trails. But I am sure you are right, anything inhaled or otherwise contacted in too-high concentrations would have affected him sooner rather than later. So now he can go back to fretting about a very different long-term health problem, how he, the palest of palefaces, used to run shirtless all summer long, under that punishing sun. (He was so vain; he'd probably think this post is about him; but he was most definitely justified in believing he was a looker.)

A bit disconcerting, all those question marks in the page on thidiazuron (Gesundheit!). Are there in fact so few medical databases on farmworkers, in California especially -- I mean, because of the importance of agriculture there, and because CA is supposed to lead the country and the world -- , establishing basic information regarding their initial health and data subsequent to their work?

And here are two sentences from the PAN site, on the subject of toxicity testing, that move me to sing with joy:
"Humans are not necessarily similar to rats and other laboratory animals used for testing. Because most test results are extrapolated from rats, mice, dogs or rabbits to humans, noted effects may be different than what humans actually experience."
Funny, that rather reminds me of what George W. Bush has to say to Cindy Sheehan, and others in her situation, regarding the death or wounding of people they love in Iraq. Not what he has to say explicitly, but the reality that underlies it: this sacrifice of yours, and theirs, is perhaps likely not going to do much good for anybody.

Chickens deserve our true friendship! So do fish! So do other sentient beings! Let us learn to be kind.

by caniscandida at 4:05 PM on 02 May 2006

We Dirty Rats

The question marks in the thidiazuron page are, I suspect, because nothing bad has been proven as of yet. In this context, I think they can be taken as a good sign, because I imagine the question mark is the best you get.

It's a good question regarding a database of farmworker's health issues in Cali - I have no idea, but I can imagine the problems would be myriad. 1) A large population of undocumented workers, 2) a transient (ie harvest-driven) work force, 3)the difficulty in pinning any particular health problem on any one toxin, given the vast amount conventional farm workers must be exposed to, 4) money. Who is to pay for blood tests, routine medicals, questionnaires, follow up, etc.,etc? Are there CA farm worker Unions? I would think they might be interested. Otherwise, you're left to public health utilities, and I think they're budget just got slashed to send me a $100 check in the mail.....

As for the health worries, I'm sure there was some nasty stuff that your husband was exposed to (to which your husband was exposed just sounds TOO pompous, even for me). Luckily, he was young, and the young have amazing powers at body house-cleaning, as it were - and presumably, whilst perfoming hard labor on the farm and running about shirtless, he was getting some exercise, which is the number one best way I know of to clear toxins from the bod.

As for our race's similarity to rats... in general, I find many rats much nicer than many people. It is true that animal studies can't always predict human outcomes, but what we don't often hear about is that they can, and do, predict human outcomes quite often. The problem is, that it is the same type of null hypothesis as the questions marks above; no problems in the rat does not necessarily mean no problems in the human, but a problem in the rat (or dog or monkey) can often mean a problem in the human.

As for the fear of skin cancer, yes, that is a serious one. My Mom recently had her first real melanoma removed (she was also a sun worshipper, albeit on the more forgiving East Coast, and has had dozens of the harmless basal cell carcinomas removed). Scary thing, especially when clueless doctors launch into discussions of 5-year survival rates. As I inherited my Dad's red hair and fair skin, I'm sure some of that is in my future as well. The best advice I can offer is to find a good dermatologist, develop a relationship with him/her, go often (once a year, or once every 6 months if you've ever had a suspicious tumor) and know your own body like the back of your hand. Or your husband's, as the case may be. The best defense against melanoma is to catch it (and cut it out) as early as possible. If you see something suspicious, do not hesitate to bully your way into the dermatologist's office. It'll save your peace of mind, and just may save your life.

Kaela

by kmp at 5:04 PM on 02 May 2006
[ Parent ]

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