Arsenic is naturally occurring in groundwater in many places around the globe and, therefore, in our food supply. This is why you might have seen reports in the news about the presence of arsenic in baby cereals made with rice.
While we’ve known about the acute toxicity of arsenic for a long time, the health effects of low levels of arsenic are less well understood. What are the hazards of small amounts of arsenic consumed over a long period? How much should parents worry about arsenic in baby cereal, fruit juices, or their drinking water?
How does arsenic get into water and food?
Arsenic comes in two forms: organic and inorganic.
Inorganic arsenic is naturally present in the earth’s crust, and it’s bound to oxygen or combined with a metal-like sodium. Inorganic arsenic is soluble in water, which is why it’s found in drinking water and soil in many parts of the world. This means it can get taken up by plant roots. By this same route, it can also enter our food through prior use of arsenic-containing pesticides.
Among different types of rice, brown rice tends to contain higher levels of arsenic than white rice because the arsenic accumulates more in the outer coating, which is removed in white rice. Studies have suggested that rice grown in the south-central U.S. appears to have higher levels of arsenic than that produced in other states and countries.
Rice has higher arsenic levels than other grains because it absorbs so much arsenic. Adam Chambers/U.S. Department of Agriculture/Flickr, CC BY
According to a 2007 study, this may be because of previous use of arsenic-based pesticides to control the boll weevil pest on cotton. From the 1930s to the 1960s, approximately 10 to 15 pounds of arsenic-based pesticides were used per acre for every planting.
Arsenic compounds were also used to reduce debris in mechanized harvesting of cotton; by causing the plants to drop their leaves, it made machine harvesting easier. When these products were used, they typically applied 3 to 4.5 pounds per acre per planting.
For instance, in the state of Texas, typical naturally occurring arsenic levels in soil average six parts per million (ppm). But as a result of previous use of arsenic-containing pesticides and desiccant products, these fields can average 40 ppm, with some areas far higher.
Whether from pesticides or desiccants, once arsenic gets into the soil, it does not break down. So, if fields that once held cotton are switched to cultivate rice, it may result in high levels of arsenic in that rice.
What does arsenic exposure do to health?
Arsenic, unlike lead, does not accumulate in the human body, and most of it is eliminated in urine in a matter of hours. What remains tends to concentrate in hair, nails, skin, and to a lesser extent in bones and teeth. How arsenic affects the body varies depending upon the organ system and whether the arsenic’s chemical form in food or water is organic or inorganic.
Long-term exposure to inorganic arsenic is associated with a range of health effects, including skin, bladder, kidney, and lung cancer, as well as diabetes, heart disease, and damage to blood vessels and the nervous system.
My research interests have included the potential adverse effects of arsenic on pregnancy. Research shows arsenic is a reproductive toxin to the developing fetus. Animal studies have found that arsenic exposure can lead to congenital disabilities and pregnancy loss. Human studies found increased rates of stillbirths in communities near metal smelters and arsenic production facilities, where people were potentially exposed to elevated levels of arsenic in air, house dust, or drinking water.
The presence of arsenic in rice has been under scrutiny for several years. For instance, a 2012 scientific study conducted by Dartmouth found that children in the U.S. who ate rice had significantly higher levels of arsenic in their urine than those who did not. This same group conducted a detailed study of arsenic levels and rice consumption of New Hampshire children in the first year of life. A 2016 study, also from Dartmouth, found that infants who ate baby rice cereal had concentrations of arsenic in their urine twice as high as did infants who ate no rice.
However, at present, there has been little research into the adverse health effects of arsenic in food at these levels.
When it comes to the potential health effects of ingested arsenic on children, most of our knowledge comes from studies of populations with high levels of arsenic in their drinking water (greater than 50 mg/L). A mg/L is an amount equivalent to a single drop in a large tanker truck. For instance, studies of children in areas of Bangladesh found reductions in their measured IQ.
A study from Columbia’s Mailman School of Public Health also found decreases in IQ in children in the U.S., but at arsenic levels an order of magnitude lower (greater than five mg/L) than the Bangladesh study. At present, the Environmental Protection Agency defines the acceptable level of arsenic in drinking water as 10 mg/L. The Columbia study clearly suggests that the current arsenic in drinking standards may not be sufficient to protect children from these developmental effects.