Weeds in the Garden: Spraying May Be Harmful to Your Health

Weeds in the Garden: Spraying May Be Harmful to Your Health
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Throughout much of the U.S. of A., spring has sprung. Here in North Carolina, lawns are lush and verdant and blooms are everywhere. But with the good stuff comes those pesky weeds. What's a gardener to do?

Many Americans attack their weeds by spraying. Zap those guys with a chemical, kick back, and relax -- another weekend chore taken care of, right? Problem. I for one am not all that relaxed around most of those sprays.

Do You Know What's in your Herbicide?

By far the most popular herbicide is glyphosate -- every year Americans use more than 100 million tons [pdf] of the stuff. Introduced in 1974, glyphosate is now found in 63 pesticide formulations registered in the United States. The most common over-the-counter products are Roundup and Rodeo.

Before running to the store for that bottle of glyphosate, consider the following.

EPA Has Second Thoughts About Glyphosate

In past posts I have noted that there are myriad chemicals in the marketplace whose effect on the environment and human health are not well characterized. Apparently the new folks at the Environmental Protection Agency are concerned about this. On April 15, 2009, EPA announced it will begin screening 67 herbicides and insecticides (for both active and/or inert ingredients) as possible endocrine disruptors. EPA will eventually expand the testing to cover all pesticides.

In its announcement EPA was careful to note that "the list was developed on the basis of exposure potential and should not be construed as a list of known or likely endocrine disruptors."

For those of us concerned about introducing such chemicals into the environment without a full understanding of their effects, this is welcome news. But there are nagging questions:

  1. Are EPA's proposed testing procedures adequate?
  2. Once testing begins, it will take a couple of years to find out if any chemicals are officially labeled as endocrine disruptors. Can we afford to wait that long given the scientific studies already linking significant health impacts to chemicals like glyphosate? (See here, here, and here.)

So while we wait for the results of EPA's mandated tests, caveat emptor. To which I'd add, buyer be aware: before purchasing your next bottle of spray-on weed zapper I suggest checking out EPA's list [pdf] of 67 pesticides. And forewarned that if your favorite weed-killer happens to be Roundup or Rodeo, their active ingredient, glyphosate, is on the list.

And It's Not Just the Active Ingredients

All pesticides are a mixture of an active ingredient (the registered pesticide) with other chemicals such as solvents, surfactants, and emulsifiers -- the so-called inert ingredients.

Because these are considered trade secrets, pesticide manufacturers are not required to list them on the label. But don't be misled by that innocent appellation.

Inert ingredients, which can comprise as much as 99 percent of a pesticide's formulation, are often highly toxic chemicals that can be more hazardous than the active ingredient or can act synergistically to form a more toxic brew when formulated as the pesticide.

Roundup is a case in point. While lab experiments have shown that glyphosate on its own has interfered with gene activity in human placental cells, it is even more toxic when formulated as Roundup. The reason for this, researchers suspect, is that the inert ingredients act to enhance the toxic effect of glyphosate.

So what's a gardener to do? Hold on one second (or scroll to the last paragraph). There's one other biggie worth mentioning here.

Not Just a Problem for Our Lawns -- Roundup's on the Farm

A great boon for Monsanto, Roundup's manufacturer, was the development in 1996 of so-called Roundup Ready crops. Simply put, these hybrids are crops that are engineered to resist the poison glyphosate. So planting Roundup Ready crops allows farmers to slather large amounts of the pesticide on them to kill weeds without damaging the crops themselves.

In 2008 more than 90 percent of U.S. soybean crops were Roundup Ready and more than 60 percent of our corn and cotton acreage was Roundup Ready. Between 1996 and 2007 the use of glyphosate for just these three crops [pdf] went from 25 million pounds to more than 135 million pounds.

But while the use of Roundup on American farms has skyrocketed, there are at least three important caveats to note.

  1. Its efficacy is not all that clear (see here, here, and here);
  2. There is evidence that some weeds are developing a resistance to glyphosate and that weeds with higher glyphosate-resistance are becoming more plentiful (see here and here);
  3. As weed resistance increases, more Roundup is required to maintain crops, reducing the profitability of Roundup Ready cropping systems and increasing the load of pesticides entering our soil, surface waters, and groundwater. In an interesting twist, just as species diversity promotes ecosystem health, here too pest management diversity and crop rotation seem to be the key to the effectiveness of Roundup Ready cropping systems.

So What To Do? Simple Solutions to Consider

For Your Lawn - I would hardly call myself a gardener but I do get out in the yard fromtime to time, mostly to fight the weeds. I don't spray. What I do is pull,and sometimes I even get lucky in my backyard tug-of-war and get the roots. (And sometimes a poison ivy rash on my arms bears witness to the fight.) The agriculture department also has some good tips for fighting weeds.

Regarding Your Fruit and Veggies - And what about those Roundup Ready crops? Are they loaded with an extra dollop of glyphosate? Should we be concerned? (See EPA's Reregistration Eligibility Decision, page 35, and this paper on weed control in Argentina.) I don't know about you, but to me the organic food counter is looking more inviting all the time.

Further Reading

Statistically Speaking: Lawns by the Numbers - A look at how the American love affair with lawns impacts more than just our wallets.

Dr. Bill Chameides is the dean of Duke's Nicholas School of the Environment and a member of the National Academy of Sciences. He blogs regularly at theGreenGrok.com.

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