Air Date: Week of March 23, 2007

A rice field in the southern U.S. (Courtesy of USGS)

A new study shows high levels of arsenic in rice grown in the American South. Rice is often grown in former cotton fields, where arsenic was long used as a pesticide. Living on Earth speaks with Professor Andrew Meharg of the University of Aberdeen, Scotland, who conducted the study.

Transcript

GELLERMAN: In states where cotton was once king, today rice reigns supreme. Consumption of rice in the U.S. has doubled over the last 25 years, and eighty percent of the rice grown here comes from states in the South Central part of the country. A lot of it is grown in former cotton fields. And when cotton was grown there, a lot of these fields were treated with pesticides that contained arsenic.

Dr. Andrew Meharg is a bio-geo-chemist at the University of Aberdeen in Scotland and an expert on arsenic in the environment. He investigated rice from these fields and he found that it contains unusually high levels of the toxic heavy metal.

MEHARG: The lowest levels are in Egyptian rice where you have 0.05 parts per million in the rice. U.S. rice from the south central region has around about 0.3 so that’s 6 times higher than Egyptian rice. It’s typically 4 times higher than Indian rice you would buy so it’s quite substantially more.

GELLERMAN: Well Dr. Meharg, how does arsenic get into rice in the south central region of the United States?

MEHARG: Well it has to be thought of in detail, but there has been a long history of using arsenical pesticides for cotton production, both as a pesticide for the boll weevil and also arsenic was used as a desiccant to remove leaves before boll harvest and that’s been going on for like the last hundred years. So over that time there’s been heavy use of arsenical pesticides in that cotton belt area.

GELLERMAN: Arsenic is a naturally occurring chemical. How do you know that this is not just, you know, part of what’s in the background soil?

MEHARG: Well, there’s a lot of literature out there about concerns, particularly in Arkansas, about rice breeding because when they grow rice on this soils that’d been previously treated with arsenic they suffer from a disease called stripped head where crop yields are decreased and they specifically bred rice to grow on these high arsenical soils. So the fact is there’s been a large breeding program for states such as Arkansas to produce rice, which can withstand high levels of arsenic in soils. And that’s a pretty big clue that arsenic is a problem in those soils.

And when you look at the background geochemical data, which we’ve done for the different rice growing regions, which are a pretty good measure of what’s the background level of arsenic in the environment and what’s the background levels in soils, they’re much lower in the South-Central states than they are for California. Yet we find higher levels in the South-Central U.S. rice states than we do for California. So from the geochemical evidence it would suggest that California should have higher levels of arsenic naturally in rice rather than the south central region.

GELLERMAN: Are there fields in the United States that were once treated with arsenic for non-food crops and now being used to raise food, besides rice?

MEHARG: Historically arsenic was, inorganic arsenicals were used as a first generation pesticide and they were widely used famously for orchard pesticide treatment where they used lead arsenate. The answer to that is yes but the main problem of arsenic in agriculture is really particular for rice due to the way that rice is grown. Basically rice is the only major crop that is grown under water saturated soil conditions, i.e. the soil is flooded. And under those conditions arsenic is mobilized where with other crops they’re grown with plenty of oxygen around the root system and the actual arsenic in bulk is locked in the soil and doesn’t get into the plants to such an extant as for rice.

GELLERMAN: In Bangladesh where they have very high levels of arsenic in the water there’s a huge problem and people manifest arsenic poisoning in a variety of ways, but one of the ways is that they get sores on their hands and their feet, the soles of their feet. Um wouldn’t we expect to see something like that here in the United States?

MEHARG: When you do the risk assessment, the risk assessment has been done for the USA by the US EPA and they’ve actually found that there is a risk for the US based population and that’s why the US levels in water were reduced, because the risk from arsenic to the US population was more perceptible, and above background, particularly for lung and bladder cancers and what we’re finding is that the levels of arsenic in rice for certain subpopulations exceed those current levels for safety and water. And eating high levels of rice, they’re actually well over what they should be consuming.

GELLERMAN: How concerned should the average consumer of rice in the United States be? I think I’m pretty average. I eat rice two times a week or so.

MEHARG: I think the average consumer should not be that concerned. It’s more the people who have high amounts of rice in their diet. And there’s a range of subpopulations which’ll have higher rice levels, amounts of rice in their diets such as Hispanics, Asians, also people who suffer from like, celiac disease where you have gluten intolerances, tend to use rice as a wheat substitute. So it’s those people who are of concern. Also rice is used in baby formula, as well, so that might be a concern it’s really the populations who consume a high amount of rice that should be concerned. And they are substantial again four percent of the US population is of Asian origin and so four percent of 250 million is a lot of people.

GELLERMAN: Well Dr. Meharg I want to thank you very much.

MEHARG: No problem.

GELLERMAN: Dr. Andrew Meharg’s paper on the elevated levels of arsenic in the South-Central United States appears in the latest edition of the journal, Environmental Science and Technology.

 

Links

Market Basket Survey Shows Elevated Levels of As in South Central U.S. Processed Rice Compared to California: Consequences for Human Dietary Exposure in Environmental Science and Technology