03/27/2012 05:17 pm ET Updated May 27, 2012

Chemical Marketplace: The Fine Print on a Common Pesticide, Writ Large

Crossposted with TheGreenGrok.

More than 80,000 chemicals are produced, used, and present in the United States. This is one of their stories.

Do you weed and feed? If so, here are some reasons you may want to reassess the habit.

Spring has sprung early across much of the nation this year, so much so that in some areas peak blooms of cherry blossoms (see here and here) and azaleas have created headaches for the organizers of the festivals held annually in the flowers' honor. On a more personal scale, the early spring has put yard work on the mind.

If your spring routine includes a weed and feed, a little label reading is warranted as there's a good chance your product of choice contains 2,4-D, the most commonly used home and garden herbicide in the United States. In 2007, U.S. homeowners used between eight and 11 million pounds of the stuff, also known as dichlorophenoxyacetic acid, to attack broad-leaved weeds like dandelions and clover; with all uses taken into account (agricultural, industrial, residential and public), Americans used 52-62 million pounds in 2007, the last year for which government data are available.

The Chemical Marketplace
A series that looks at chemicals in everyday consumer products
     2,4-D, your lawn, weed and feed
     Alkylphenols »
     Aluminum and antiperspirants »

     BPAF »
     Dioxin and eggs »
     Flame retardants and pets »
     Fluoride and water »
     Formaldehyde and no-iron shirts
     Insect repellents »
     Nanoparticles and food »
     PAH and seal coats: A no-brainer »
     PBDE and fire retardants »
     PFOA and popcorn »
     Piperonyl Butoxide, a pesticide »
     Propoxur and bedbugs »
     Rotenone, a pesticide »
     Spray foams, sealants, diisocyanates »
     TDCPP and the air »
     Triclosan and toothpaste »
     Trihalomethanes (THM) and

     showering »

Genetically Engineered Crops Set Pesticides Free

Pesticide use has been given a big boost in recent decades by genetically modified crops that allow weed killers to work with impunity. Before genetically modified resistant seeds were available, a farmer had to tinker with pesticide applications finding those that would kill the weeds but not the crops. But with a crop modified to resist a certain pesticide, especially one that would take out all the problem weeds, farmers could spray their crops confident that at the end of the day the weeds would be gone and only the harvest left standing.

All well and good, you might say, but how do you get a plant that's resistant to herbicides? Aha, that's where genetic engineering comes in. You make a few adjustments to the plant's DNA and presto chango!, you've got an herbicide-resistant plant.

And in the specific case of 2,4-D, that's where Dow AgroSciences comes in. Dow is seeking approval from the Food and Drug Administration to market a new set of genetically modified seed offerings for corn, soybeans, and cotton -- seeds designed to allow 2,4-D to be used with impunity along with that other pesticide favorite glyphosate (a k a Roundup), winding up a sort of one-two pesticide-resistant punch.

Time was, genetically engineering seeds to be resistant to just glyphosate was adequate, But those clever, little weeds, all on their own with Darwinian aplomb, have developed resistance to glyphosate (see here and here), so Dow has upped the ante. Will the weeds catch up with this latest attempt to pummel them? Most certainly, but that's probably not a major concern for a company in the business of selling pesticides -- one man's herbicide-resistant weed is another man's potential gold mine.*

2,4-D: Herbicide History, Health, and Hue and Cry

Developed in the early 1940s, 2,4-D is one of the oldest pesticides in use. A member of the phenoxy herbicide family (made notorious as an ingredient in the defoliant Agent Orange), 2,4-D is a type of synthetic plant hormone that kills weeds by causing uncontrollable, unsustainable plant growth. In 2005 the Environmental Protection Agency estimated that 2,4-D was the active ingredient in about 660 products for agricultural and home use. And unless you live in farm country or near a water body that is treated with it, the most common way to encounter 2,4-D is in a product designed to free your lawn of weeds. 2,4-D typically breaks down a few days after being applied but can persist for up to several weeks or more, and so, besides exposure during application or shortly thereafter, there's also the potential to track the stuff into your home where kids and crawling babies are even more susceptible to its poison.

As pesticides go, 2,4-D has some good attributes. As just noted, it is not a persistent pollutant. It's not considered bioaccumulative in humans. (See here and here.) And it does its job, killing weeds, a feature that helps ensure vegetables make it to your supermarket. The stuff also helps keep lots of lawns weed-free.

In its most recent evaluation EPA, concurring with industry's claim that 2,4-D "does not pose any unreasonable risk to humans, animals or the environment when used as directed," approved its reregistration. It did, however, adjust the pesticide's use and labeling, and noted the data gaps for certain types of the health effects.

The reregistration did not sit well with the Natural Resources Defense Council, which petitioned EPA to cancel all uses of 2,4-D. The basis for NRDC's concerns include the following points:

  1. In spite of the lack of strong, scientific proof of a direct causal relationship, studies have shown a possible link between 2,4-D exposure and non-Hodgkin"s lymphoma as well as hormonal problems leading to birth defects and neurological damage in animals;
  2. EPA ignored some studies, and did not evaluate certain pathways of exposure, like lactation and synergistic effects, that could increase 2,4-D's toxicity especially for children;
  3. There are less worrisome alternatives. (More here.)

The Battle Against Weeds Vs. the Battle in the Courts Vs. the Battle With Our Health

Should the FDA approve Dow's 2,4-D-resistant corn, its use in the United States would likely surge. None too happy about such a prospect, NRDC filed suit last month against EPA for inaction on its petition, seeking to compel an agency response within 45 days of a court decision. EPA, which hasn't commented on the suit, is scheduled to revisit 2,4-D in 2013.

Taken together, EPA's reregistration decision and NRDC's petition illustrate the quandary that exists for many chemicals in the marketplace -- while exposure to a given chemical indicates a likely connection to health problems, often the evidence needed to show causal relationships is insufficient and/or the data to evaluate safety are incomplete or ambiguous. While government agencies, companies and nonprofits duke it out in the courts (and scientists plug away in the lab trying to get a more complete picture), we consumers blithely spray our lawns.

In 2005 EPA [pdf] "determined that 2,4-D products, unless labeled and used as specified in this document, would present risks inconsistent with [the Federal Insecticide, Fungicide, and Rodenticide Act] FIFRA." Just how many of us follow the pesticide's application instructions or even read the precautions on the label? I would hazard a guess: not many. A lot of folks assume that if a product can be bought over the counter for home use, its safety doesn't turn on the nuances of all the fine print. And that, my friends, is just not the case. Read the label. Or better yet, skip the weed and feed this year and reach for a dandelion fork.


End Note

* Want to comment on Dow's genetically engineered corn prior to approval? Weigh in before April 27.