In late May, the organic baby formula maker Nature's One announceda goal of "zero arsenic" in its product. Good, you say. Great. Makes perfect sense. Or it would except for this question - why is a poison like arsenic, of all things, an issue in baby formula?

Read a little further in the Nature's One press release, and you'll find a direct link to the problem. The linkgoes to a February study, published in the Journal of Applied Chemistry, titled "Arsenic Concentration and Speciation in Infant Formula and First Foods."

That study, I want to emphasize, found nothing panic worthy, nothing but very trace levels of arsenic in formula and baby food. But, still, as I wrote last week, arsenic can have health effects at a surprisingly low dose. It's no wonder that Nature's One so determinedly wants none of it.

But there are other things to wonder about here. Such as - why does arsenic so inconveniently turn up in the food supply? And are public health officials doing anything to protect us in this regard? These are connected questions but I'll give you one heads up on the latter. In the United States, the Environmental Protection Agency sets a safety limitof ten parts per billion for arsenic in drinking water. But - to the frustration of advocates and scientists - the Food and Drug Administration offers no safety standard for arsenic in food .

And that matters because study I cited is just one of many telling us that there is some risk here. The word speciation in that title refers to the type of arsenic. The basic division is between organic (a carbon-containing compound) and inorganic arsenic. It's a big division actually. Our bodies metabolize organic arsenic compounds efficiently and they are not particularly dangerous. Inorganic arsenic, by contrast, is notably dangerous. And it's that more poisonous variation that turned up in the baby formulas and cereals.

And here, as they say, is where the story gets interesting.

The researchers of that study, based at Dartmouth College, identified rice as the primary source of inorganic arsenic. They found it (again, in very tiny amounts) in rice syrup used to sweeten baby formula, rice cereal, rice flour used in making crackers and cookies. This does not mean that rice is by by nature a poisonous plant. It isn't.

But both soil and groundwater can contain arsenic - as a naturally occurring element and as a residue from the use of arsenic-based pesticides. And , as the Dartmouth scientists noted, "Although As (arsenic) is not readily taken up by crops or transported to the edible parts, a notable exception is rice...The magnitude of this uptake varies widely between cultivars but the ability to take up elevated concentrations of As (in comparison with other cereal crops) appears to be a trait found in the entire rice germplasm."

In other words, rice turns out to be outstandingly good at absorbing arsenic from the environment and storing it. One reason is that the plant is designedto easily absorb the mineral silicon which helps give rice grains their elegantly smooth structure. The crystalline structure of arsenic is just close enough that rice plants readily uptake arsenic as well. In fact, a toxic metal study, also from Dartmouth, describes rice as "a natural arsenic accumulator."

The efficiency of this system also means that the arsenic tends to be absorbed directly in its more toxic inorganic from rather than being converted to an organic form of arsenic. And rice, experts say, seems to be a primary source of arsenic in the human diet.. Or as a newly published book by Andrew Meharg, at the University of Aberdeen in Scotland, Rice and Arsenic, puts it, "Rice is the major exposure route globally to the non-threshold carcinogen inorganic arsenic."

Scientists and public health officials - although not the general public - have known this for years. I won't inundate you with the studies that have piled up since, say, the year 2000 but here's a few: from 2002 "Arsenic Uptake and Accumulation in Rice (irrigated with contaminated water); from 2003 "Uptake Kinetics of Arsenic Species in Rice", from 2005, "Bioavailability of Inorganic Arsenic in Cooked Rice"and from 2008, "Arsenic in Rice, II: Arsenic speciation in U.S. Grain and Implications for U.S. Health." Recently, though, the public started to catch on. There was widespread coverage of a February study from Dartmouth this year, "Arsenic, Organic Foods, and Brown Rice Syrup," which cited unexpected amounts of inorganic arsenicin everything from infant formula to snack bars, especially compounds containing rice or sweetened with brown organic rice syrup as a healthier alternative to high fructose corn syrup.

I wrote about that last study earlier in a post called On Rice and Arsenicso I won't dwell on it in detail here except to talk about some of the fallout. Although I'm focusing on rice here, it's important to recognize that it's not only source of concern in the American diet. I can easily think of two others that have come up in the last year.

One involves the use of commercial poultry feed that contains organic arsenic as an additive. This additive was approved by the FDA in the 1950s, both to kills parasites and to improve the look of packaged chicken (the arsenic caused blood vessels to explode and the meat to look pinker). The argument had been this was only harmless organic arsenic but last year FDA tests found that it was metabolizing into the toxic inorganic form. The pharmaceutical giant, Pfizer, suspended salesof the feed, Roxarsone, pending future tests. The FDA did not ban continued use of feed already on the market, however, or move to prohibit future use. Impatient with the federal delay, Maryland is now moving to ban Roxarsone itself.

The other, as you may remember, involves apple juice. That issue was first raised by the Tampa Bay Times in 2010 and amplified by Dr. Mehmet Ozin 2011. In November of last year, Consumer Reports publishedits own testson both arsenic and lead in fruit juice. In December, the magazine publicized yet another study on arsenic and rice. Both the magazine and Consumer's Union, the related advocacy group, have been asking the FDA to take some official action on arsenic in the food supply, to set safety standards for American consumers.

"We need to come up with a universal standard," agreed Joshua Hamilton, a senior toxicologist at the Marine Biological Laboratory in Woods Hole, Massachusetts, and author of numerous studies on low-dose effects of arsenic. In an interviewwith NPR's The Salt, Andrew Meharg, author of Arsenic and Rice, made the same point: "The safety thresholds for chronic (inorganic) arsenic in water are well established. Food needs to be put on the same footing as water standards."

And this, I think, is exactly right. The lack of such a standard leaves everyone uncertain as to what is safe and what is not. It's unfair to the makers of baby formula and juice packs and other products. American rice producers, for instance, have been left sounding either defensive or uncertain as what to do. As California's Lundberg Farm notes in some frustration on its website, "as yet there are no federal or state standards in regard to testing or as to what are safe levels." And it's unfair to the rest of us too, parents and consumers trying to figure out what's safe in the food supply and what isn't.

Which brings me back, as promised to the FDA. Following that Dartmouth report on poison levels in brown rice syrup, the agency announcedthat it was doing its own study of the issue. The federal report was scheduled be completed last month. Obviously, it wasn't so I've been asking the FDA's public affairs office about it (in fact, making a pest of myself for the last three weeks) and I'm told that the report should be finished by the end of this month. Do I expect the federal agency to suddenly have all the answers to a complicated environmental poison? I don't. But do I expect agency officials to live up to their responsibilities to public health and safety and set some minimal guidelines?

I absolutely do. I am counting on a late June report? I'm absolutely not. But here's hoping that the FDA proves me wrong.

(Note: This is the second of a series of posts I plan to write on arsenic and public health. The first, Is Arsenic the Worst Chemical in the World, was published last week).

Images: 1) White arsenic/Wikimedia Commons 2)* Brown Rice/Wikimedia Commons*