A Trace of Arsenic
The cans of baby formula invaded Brian Jackson’s Dartmouth College lab late in 2010. His team picked up an armful of popular brands at the food co-op in Hanover, N.H. Then another armload. Eventually Jackson had a cabinet full of the brightly labeled canisters. Today, he still keeps a few in his office. Not as clutter — that’s not his style. He just likes to keep his toxicology evidence close at hand.
A 47-year-old analytical chemist with sandy-gray hair and blue eyes, Jackson has a chemist’s passion for the picky details of analysis, the skill his colleagues tapped when they asked him to investigate a disturbing possibility: that baby foods and formulas made with rice might contain arsenic, a known carcinogen. Ingested even at the trace levels the scientists suspected, devastating health outcomes could result.
In a first round of tests, arsenic levels in all the products Jackson’s group studied fell within the 10 parts per billion safety limit the EPA sets for water. (There is no limit for arsenic for most foods.) But a short time later, while shopping at the co-op, Jackson noticed two brands of toddler formula, both high-end organic products, that his team had missed on the first sweep.
This time, to the team’s surprise, the arsenic readings flew off the chart.
“My first thought,” Jackson says, “was that I’d better reanalyze these samples in case I’d screwed up.”
His second thought, after confirming the readings, was to wonder: What made the arsenic levels spike in those two cans? In answering that question, Jackson traced not just the story of the metal-loving rice plant, but also the tangled and troubling path of a notorious poison through our past and present.
A naturally occurring metallic element, arsenic permeates the Earth’s crust. Glinting silver-gray in rocks and soils, it mixes with other minerals as it seeps into water supplies, drifts on the dusty plumes of volcanic eruptions and travels on the wind. It also spreads through industrial use, from mining to agriculture.
Arsenic coils like a dark smoke through our history. The word derives from the ancient Greek arsenikon, meaning “potent.” It was used to describe the compound arsenic trioxide, which can be lethal at 100 milligrams, about one-fiftieth of a teaspoon. Arsenic trioxide is famously tasteless and odorless, which helped make it one of the most frequently used homicidal poisons in history.
But in recent years, studies have revealed that exposure to far smaller doses poses a more subtle — but also insidious — threat. The pure element arsenic mixes into many compounds, either organic (in chemical lingo, meaning that it contains carbon) or inorganic (without carbon).
And even at concentrations of parts per billion (ppb), closer to a drop in a swimming pool than a drop in a teacup, long-term exposure to inorganic arsenic — generally considered the most toxic form — has been linked to an increased risk of cancer and other life-threatening illnesses. Although arsenic hasn’t been studied in as much detail as other toxins found in industrial materials, such as mercury or PCBs, scientists say it underscores the finding that minute exposures to such substances can do great harm.
At low doses, arsenic doesn’t overwhelm body systems immediately or even cause death over the course of months. Rather, explains Dartmouth molecular toxicologist Joshua Hamilton, chronic exposure to trace arsenic inflicts damage at a cellular level, increasing the body’s vulnerability to a wide array of sicknesses, including cancer, cardiovascular disease and diabetes. While trace arsenic won’t kill on its own, he says, it “seems to make everything worse.”
For decades, officials have focused on trace arsenic in drinking water as the chemical’s primary public health threat; in 2001, the EPA dropped the limit for arsenic in water from 50 ppb to 10 ppb. But in the past few years, regulators have also begun to worry about exposure from foods and beverages. This summer, concerned about arsenic in pesticide residues found in imported juices, the FDA announced it will limit the amount of arsenic allowed in apple juice to 10 ppb, the same amount permitted in water.
The FDA has also investigated arsenic’s presence in other foods. Chicken, for example, has come under scrutiny because of the longtime use of an arsenic additive in poultry feed. But the top-priority food on the list is rice, which became a focus when researchers realized that it takes up inorganic arsenic from soil far more efficiently than other grains. A July study revealed the first evidence directly linking consumption of rice containing arsenic to genetic damage in humans.
Such findings are especially alarming because rice is a major part of the diet in certain communities, such as those with an Asian heritage, and because rice is a staple for infants and young children, whose developing bodies and brains are especially vulnerable to harm.
It’s that last concern that sparked the formula studies in Jackson’s Dartmouth lab.
Evidence of Harm
The realization that trace amounts of arsenic might pose a health threat began with mysterious outbreaks of disease in Southeast Asia. In the 1960s, scientists in Taiwan traced an outbreak of blackfoot disease, caused when dying blood cells lead to gangrene, to arsenic-contaminated well water. In many wells, arsenic levels exceeded 800 ppb (80 times as high as today’s EPA standards); some wells registered as high as 1 part per million.
Still, researchers didn’t pay serious attention to the problem for decades, after a massive public health crisis came to light in Bangladesh. In the 1970s, villages began drilling wells to prevent the deadly infectious diseases that flourished in warm, sewage-tainted surface waters. As predicted, infectious disease rates dropped.
What was not predicted was the insidious growth of other diseases: lung and bladder cancers, cardiovascular problems, diabetes and severe skin lesions. As part of a search for the cause, geologic tests revealed large deposits of arsenic-rich minerals steadily leaching into groundwater, causing levels in many wells to top 500 ppb.
After investigating the arsenic situation in Bangladesh at the request of the World Health Organization in the late 1990s, Allan Smith, an epidemiologist at the University of California in Berkeley, recommended that officials declare a public health emergency for what he considered “the largest mass poisoning of a population in history.”
Smith had also investigated evidence of similar poisoning in Antofagasta, a Chilean port city that in 1958 had switched from well water to a cheaper supply sluicing down from the Andes. In 1970, city administrators realized arsenic from mountain mineral deposits was contaminating the city’s water supply, with exposures of 500 to 800 ppb for the public at large.
Antofagasta quickly returned to using well water, but those dozen years provided a unique window into the long-term health effects of drinking water containing trace amounts of arsenic. Smith’s analysis showed that Antofagasta residents exposed to the city’s water between 1958 and 1970 had experienced markedly higher rates of bladder and lung cancer.
By his estimates, arsenic accounted for about 7 percent of deaths among Antofagastans age 30 and older. “I believe arsenic poses the highest cancer and mortality risks we know of compared to any other environmental exposure,” Smith says. “The only exposure we can compare it to is active smoking.”
But researchers are also compiling evidence that arsenic poses a health threat at far lower doses than in such highly contaminated water supplies. New York University epidemiologist Yu Chen has followed up on both the Taiwan and Bangladesh findings by looking at water contaminated by arsenic levels of 50 ppb and below.
At this trace exposure, she’s found evidence of troubling changes in blood cells. And in tracking human disease patterns, she’s established a clear link between such low-dose chronic exposure and increases in high blood pressure and heart disease. In one study, she estimated that among Bangladeshis whose drinking water contained as little as 50 ppb of arsenic, exposure accounted for some 29 percent of heart disease deaths.
Animal studies strengthen the case. In one study, Dartmouth’s Hamilton found that arsenic exposure at 10 ppb compromised the immune systems of mice so much that they could not fend off an ordinary influenza infection. In another study, his team found that mice given chow containing trace amounts of arsenic, then exposed to a standard daily dose of ultraviolet light, had higher rates of skin cancers than mice given untainted chow.
“This is a very, very subtle poison at low doses,” Hamilton says. “Each passing year, we’ve discovered health effects at lower and lower doses. There isn’t any other toxicant that we know of that even comes close to arsenic in terms of the number of health effects at the doses we’re seeing and the numbers of people worldwide who are potentially exposed.”