Updated July 6. See below.

Yesterday,organic farming activist Andrew Kimbrell, the executive director of the Center for Food Safety, wrote a piece for Huffington Post called "Obama Organic Family Garden: Swimming in Sludge?" in which he suggests that lead levels in the Obama's garden -- said to test at 93 parts per million -- are high enough to consider avoiding that soil for growing fruits and vegetables. Says Kimbrell:

Lead is highly toxic to children's developing organs and brain functions -- however, [lead levels in the Obama's garden are] below the 400 ppm the EPA suggests is a threat to human health.

This comes after a revelation in Mother Jones online magazine that composted, sewage-sludge fertilizer was probably used on the White House's South Lawn (above -- and just look how nice and green it is!) back in the Clinton years. Sewage sludge is defined as municipal waste (city sewer poop!) that is treated, composted, and used as fertilizer in agriculture. Yum!

While the dangers of sewage sludge are many, and warnings are warranted, for Kimbrell, his assertion that 93 ppm is "alarming contamination" got him in hot water today, with the biggest counterpunch coming from Eddie Gehman Kohan who edits the terrific blog Obama Foodorama (another version of her blog post also appeared at Huffington Post). Eddie stacks up a big ol' pile of experts to refute the assertion that 93 ppm is at all dangerous or that Michelle Obama is endangering Sasha and Malia's young brains. From Dr. David L. Johnson, professor of Environmental Chemistry, Environmental Science, and Forestry at the State University of New York:

“I have no concerns at all about growing vegetables in soil with a reading of 93 ppm,” Dr. Johnson said.

That's the lowdown, and, really, there's not much more to be said (though, could we have gotten a pediatrician and/or human brain development expert to weigh in on that lead level maybe?), but there's LOTS more discussion from Dr. Johnson and other environmental scientists in the Obama Foodorama post, and it's worth reading, especially if you garden in a city and worry about lead levels. (Lead levels are at 34 ppm in the El Dragón Garden, in case you were worried about los dragoncitos!).

But while it seems clear that Kimbrell may have overreached on his 93 ppm argument, I'd like to place some of his other well-made points back in play. Namely, that while Sasha and Malia are no doubt fine, sewage sludge use IS a problem in this country. From Kimbrell's article:

So what is sludge, really? A stinking, sticky, dark-grey to black paste, it's everything homeowners, hospitals and industries put down their toilets and drains. Every material-turned-waste that our society produces (including prescription drugs and the sweepings of slaughterhouses), and that wastewater treatment plants are capable of removing from sewage, becomes sludge. The end product is a concentrated mass of heavy metals and carcinogenic, teratogenic, and hormone-disrupting chemicals, replete with antibiotic-resistant bacteria. There are some 80,000 to 90,000 industrial chemicals, including a host of dioxin-like deadly substances, which are allowed to be present in sludge under current EPA rules. What's worse, there's no way of knowing which toxic chemicals and heavy metals are entering the wastewater stream at any given time or in what concentrations. Sludge is always an unknown quantity, and therefore, assessing whether sludge is safe to use for growing food, is -- in practice -- impossible.

In short, it's what hasn't been tested for that's far more disturbing. Indeed, here's what writer Catherine Price concluded about sewage sludge's agricultural use, just two months ago at Grist:

Given the inconsistency and toxicity of the ingredients in sludge, the loopholes in its regulations and the mounting criticisms against its use, I kept reaching the same conclusion: despite the ...insistence on the safety of spreading sludge on land, we should be looking for alternatives. The United States will never stop producing shit. But there must be a better way to deal with it.

It's the chaotic, variability of using sewage sludge on farmland generaly speaking that should give us pause -- and maybe Michelle and Barack do want to test their garden, just to be sure. Due to a total lack of regulating the product's history or application, after all, municipal sewage sludge was excluded from use in organic farming by the USDA, despite a concerted effort by Big Ag and food manufacturers to include it. Indeed, turning a blind eye to sewage sludge's presence would be frowned upon by most longtime organic farmers and gardeners.

The scientists quoted in the Obama Foodorama piece make it clear that sewage sludge toxins will have probably have leached from the Obamagarden's soil by now. Nevertheless, I wish Eddie had gone just one step further in her argument and made the point that continued agricultural use of sewage sludge is a problem in the US -- 7 million metric tons get used on conventional farm fields every year, despite the fact that we really have absolutely no way of knowing what its doing to public health, the quality of our food, or our soil, rivers, and oceans. I'd hate to see her post used as ammo by Big Ag that municipal sewage sludge is safe.

But I'm guessing all that and more is coming in the counter-counter punch from Kimbrell, the Center for Food Safety, or other sludge detractors. Grab yer popcorn and update your RSS feeds, kids. I think there's more coming...

**UPDATED July 6: Andrew Kimbrell returns fire in the Huffington Post.

It's a good response, namely this:

As for the lead issue, it is mostly the soil I worry about. I'm sure that Ms. Kohan and the folks she interviewed are aware that a leading way that small children get poisoned is through contact with lead-contaminated soils (on their fingers and then in their mouths) and residues on food. This is becoming increasingly serious: the CDC has found that "blood lead levels once considered safe are now considered hazardous, with no known threshold." Even very low levels can have severe adverse impacts on the central nervous system and other critical biological systems in children.

As for the 93 ppm standard, by analogy I would bring to your attention a recent case settled in December 15, 2008, where Massachusetts Attorney General Martha Coakley, along with the Attorneys General of 38 other states, reached a settlement agreement with Mattel, Inc., over excessive concentrations of lead paint in the company's toys in 2007. Under the settlement, the new standards are 90 ppm for lead paint and surface coatings, and 300 ppm total lead for substrates.

The "no known threshold" for safe lead levels is compelling. So is the 90 ppm in lead paint. But as Obama Foodorama's soil scientists said,you'll find those levels in an urban environment even without sewage sludge use. We live in a thoroughly toxic society -- this isn't news.

But it does compel parents who garden fruits and vegetables to test their soil, do a little research, and decide for themselves what's safe.

**UPDATED AGAIN July 6

Writer Josh Harkinson of Mother Jones responds as well. (h/t to @whitehead on Twitter.)