In the early 20th century - enthusiastically supported by the U.S. government - the most popular pesticides were arsenic compounds. How popular? In the year 1929, almost 30 million pounds of lead arsenate and calcium arsenate were spread across this country's fields and orchards.

And how enthusiastic was the government? Well, in 1935, on a weekly radio program sponsored by the U.S. Food and Drug Administration, the host suggested that the old-time school rhyme "A is for Apple" be changed as follows:

A is for Arsenate/Lead if you please/Protector of Apples/Against Archenemies.

Yes, that enthusiastic.

Still, the FDA was besieged by angry fruit growers demanding to know why the government was alerting consumers to the fact that farmers put poisons on fruit and vegetables. And the U.S. Department of Agriculture - an agency far more enthusiastic about pesticides - wrote an angry letter to the FDA head: "We urge very strongly that when radio talks of this kind are under consideration, full weight be given to the probable reaction of growers to them and its resultant effect on the relations existing between Department representatives and the industry."

I'm indebted to the work of public health historian, James Whorton, for the information above. A more detailed history of arsenic pesticides can be found in his 1974 book, Before Silent Spring: Pesticides and Public Health in pre-DDT America. As the book title indicates, the arsenate pesticides were edged out in the years after World War II, with the rise of chlorinated hydrocarbon pesticides, like DDT, and organophosphates, like malathion. Even so, arsenate pesticides were not officially bannedin the United States until the 1980s. (And modified arsenic pesticides such as MMA and DMA are still approved for use on cotton).

Their story remains a fascinating one. An important one. And one that still affects us. The residues of lead arsenate and calcium arsenate still haunt us, tainting acres of farmland still in use today. Scientists say that a major source of inorganic arsenic in rice from the American southeast is from pesticide residues, seeping from lands once used to raise cotton. During the early 20th century, calcium arsenate was the number one pesticide used by growers to fight the cotton boll weevil. "There's a legacy of arsenic in some of those fields," Joshua Hamilton, a senior toxicologist with the Marine Biological Laboratory, told me recently.

In other countries, the use of arsenic pesticides continued longer. China, for instance, reportedly continued using the pesticides past the year 2000. And continued illegal use of lead arsenate is suspected there, partly due to the arsenic contamination of apple juice concentrate imported from China and used in drinks in this country.

According to the FDA: "Juices, particularly apple juice, are frequently consumed by young children, who are the most susceptible population to exposure to arsenic and other heavy metals. Since FY2005, through FDA's toxic elements in foods program, the agency conducts targeted testing for arsenic in apple juice. FDA started looking at arsenic (and lead) in apple and other juices more closely under this program due to the increase of juice and juice concentrates imports into the United States." The agency is scheduled to announce the details of a study on arsenic in the American diet later this month.

We should remember that tests of arsenic in food products shows only trace, in the part-per-billion, amounts. In apple juice, the highest reported finding, according to Consumer Reports, was 55 ppb. A recent Dartmouth College study of arsenic in rice products found levels ranging from 7 to 128 parts ppb. These are not, in anyway, acutely toxic levels. But it's also worth remembering that arsenic can be dangerous at very low levels, linked to diseases ranging from diabetes to heart disease. It's for that reason that the U.S. Environmental Protection Agency sets a standard of 10 ppb for drinking water and, as Inoted in an earlier post, some public health researchers would like to see that standard pushed even lower.

One of the reasons that so many people would like the FDA to release its own report is that you can't really compare a drinking water standard to a food standard. We consume water every day. We might eat a cereal bar - one of the products tested by Dartmouth - a couple times a week. So in order to make sense of those higher food numbers for arsenic, it would be very helpful to get a reading from our leading food regulatory agency.

As we wait on that report, I've started wondering if geography labeling of foods would be a useful plan for consumers. Beyond what I buy at the local farmers' market, I'd like to know what's served up in the grocery story, where my apple juice comes from, where my rice is grown, and so on. And it's that point that brings us back to the story of arsenic pesticides and how they were used - and where.

There's actually a very long historyhere because arsenic is a very old poison; in Europe it was used to kill rats during the black plague years of the 14th century. Compared to that, farmers were actually slow to adopt the use of poisonous compounds on their crops. Arsenic pesticides didn't arrive in the United States until the 1860s, when they were used to fight the Colorado potato beetle. Lead arsenate wasn't introduced until the 1890s when it was used against the gypsy moth. From that point on, though, U.S. farmers embraced it. My home state of Wisconsin offers this warning and adviceeven today for people who farm or live where old orchards once stood.

By the 1920s, U.S. fruit growers were plastering on lead arsenate in such amounts that they were starting to poison their customers. In 1919, the Boston Health Department destroyed arsenic contaminated apples because people were getting sick. The follow year, it had to do it again. In 1919, California health officials discovered with alarm that arsenic residues tended to stick to fruit, meaning the poison was hard to remove. A historyfrom Washington State University notes, however, that until the DDT era farmers continued to use the compounds because they were the most effective. That report also notes that arsenic tends to concentrate in the top layer of the soil and - thankfully - that most food crops don't take it up in any measurable way.

Rice is an exception to that. Scientists have discovered that the rice plant, because it's designed to pull silicon out of the soil (it strengthens the grain) does the same with the structurally similar arsenic. Researchers at Dartmouth College's Toxic Metals Superfund Research program note that rice has been described as a natural arsenic accumulator. Most of this accumulation, of course, is due to naturally occurring arsenic in soil and water. But some is due to residual contamination from arsenate pesticides - and that's what makes rice from the United States so interesting in this regard.

In a piece evaluating rice toxicity, Nancy Shute at NPR's The Salt noted earlier this year: "In the United States, a 2007 report found that rice from the south-central United States contains almost twice as much arsenic as rice from California, on average, because arsenic-based pesticides were used earlier for growing cotton." She added that the FDA had told her that it was those areas - rich with calcium arsenate residue - that were of particular concern.

That report was summarized in Environmental Health Perspectives under the title "Food Safety: U.S. Rice Serves up Arsenic." Here's the basic data summary: *Total arsenic levels in the 107 south central rice samples averaged 0.30 μg/g, compared to an average of 0.17 μg/g in the 27 California samples. A white rice sample from Louisiana ranked highest in total arsenic (0.66 μg/g), and an organic brown rice from California ranked lowest (0.10 μg/g). *Microgram per gram (μg/g) is equivalent to part-per-million.

The higher arsenic rice from Louisiana, Texas and Arkansas is, of course, grown across the old cotton belt region. And this is, of course, is the legacy that worries Joshua Hamilton, and others studying the low-dose effects of arsenic. And although an FDA standard would be helpful, I don't want to leave you with the impression that everything waits on that action. Already, scientists are working to develop species of rice less prone to uptake arsenic from the soil. Research also suggests that if growers use less water in their rice production, arsenic uptake could be reduced. And some scientists have even looked at ways that consumers might make rice safer, such as washing it before cooking.If you're really worried, basmati rice from India and jasmine rice from Thailand routinely test lower in arsenic (reinforcing my sense that geographic-labeling is a good idea)

All of this tells you that people are paying attention, looking for ways to reduce risk and serving up a healthier diet. We haven't figured it all out yet. But we have come a long way - a very long way - And from the days of singing - or at least rhyming - our praise of arsenic in agriculture.

Note: This is the third in a series on arsenic in public health.

Images: 1) Dusting cotton, 1934/USDAgov/Flicker 2) Virginia Tech Pesticide Programs