Water Detective: Tracing the Source of Widespread Arsenic Poisoning

Charles Harvey traces the source of widespread arsenic poisoning in Bangladesh, setting the stage for programs that could benefit 20 million people.

When a new U.S. president takes office, the first official announcements often undo policies set under the previous administration. In 2001, for example, President George W. Bush notoriously suspended a new standard for arsenic in drinking water that had been announced late in the Clinton administration. The new rule cut the allowed level of arsenic from 0.05 micrograms per liter of water to 0.01, bringing the U.S. in line with the European Union and the World Health Organization.

Arsenic was known to cause cancer, but the earlier limit had been considered safe for decades. Under Clinton, however, the Environmental Protection Agency concluded that arsenic probably was carcinogenic even at extremely low doses.
When Bush’s EPA suspended the new standard, environmental and public health advocates erupted. Facing lawsuits, a barrage of bad press and a National Academy of Sciences report concluding that even the Clinton standard might not be strict enough, the Bush administration backed down.

The debate made national headlines for months, but hardly anyone mentioned a glaring fact: Millions of people in developing countries drink groundwater contaminated with much higher levels of arsenic than the old U.S. standard, every day. The problem is especially acute in South Asia, where large rivers — the Mekong, Ganges and Irrawaddy, among them — carry arsenic-rich sediments down from the Himalayas. In 1998, the British Geological Survey estimated that 20 million to 30 million people in Bangladesh alone relied on water containing more than 0.05 micrograms of arsenic per liter. In 2002, the World Health Organization called Bangladesh’s arsenic crisis “the world’s largest mass poisoning of a population in history.”

Cruelly, Bangladeshis were getting sick because they followed the advice of international development agencies. In the 1970s, those agencies advised people in rural Bangladesh to drill “tube wells” — deep shafts made by driving a tube into the earth — for drinking water to avoid the waterborne diseases that had historically plagued the area. By the time scientists realized that much of the country’s groundwater was laden with arsenic, villagers were already showing telltale signs: blotchy skin, sores and elevated rates of skin cancer. Many will develop lung, bladder, liver or kidney cancer in the next 10 to 20 years.

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There are ways to manage arsenic in drinking water: You can filter the water, treat it with chemicals, harvest rainwater or tap into cleaner aquifers. But to choose the right strategy — especially in developing countries where few people can afford or maintain complex technical systems — it’s critical, first, to find the source of the contaminant. After a decade of painstaking scientific detective work, MIT civil engineering professor Charles Harvey found arsenic in an odd place.

Harvey was a junior professor of environmental engineering, specializing in hydrology, when he first learned about drinking water contamination in the Ganges Delta. Hardly anyone in his field was paying attention to the issue, but Harvey had written a dissertation on the movement of dissolved substances through aquifers. He’d also spent a year in medical school before switching to engineering and understood that the contamination represented both an important public health problem and an interesting scientific puzzle.

“Most people who cared about it were talking about quick solutions, but I wanted to understand why arsenic concentrations in the water were so high,” says Harvey, who has been a faculty member at MIT for more than a decade but looks boyish enough to pass as a doctoral student. His cluttered office in the university’s Parsons Laboratory has a view of MIT’s newest campus landmark, a hyper-modern student center designed by Frank Gehry. But the Parsons building is old-style MIT — a concrete shoebox seemingly designed to mask the complexity of what goes on inside.

In 1999, Harvey convinced Shafiqul Islam, an MIT alumnus from Bangladesh who was teaching engineering at the University of Cincinnati, to visit Bangladesh with him to set up a study. They went without funding in hand, which Harvey admits was “kind of crazy.” Graham Fogg, a professor of hydrology at the University of California, Davis, agrees but says the venture is to Harvey’s credit. “It’s really hard to mobilize and do that kind of project across the world, and Charlie did it at a time in his career when his focus was supposed to be on basic research in the laboratory,” Fogg says. “He’s very unassuming, but he wasn’t afraid to follow through on a project that he thought was important.”

Harvey and Islam found a research site, made contacts at the Bangladesh University of Engineering and Technology and gathered preliminary data. The next year, they received a National Science Foundation grant to characterize where the arsenic in underground water was coming from. Munshiganj, the district where they worked, is in central Bangladesh and one of the country’s most important rice-growing zones. Lying at the intersection of the Ganges, Brahmaputra and Meghna river floodplains, Munshiganj is flooded from July through November during monsoon season.

“The whole place is under water, so people dig out flood-control ponds and then use the excavated soil to raise up roads and houses,” Harvey says. “Every village is like a little island.” Villagers also use the ponds for other purposes; some bathe in them, others raise fish, and many families use them for sewage disposal. The water cycle reverses from December through May: Very little rain falls, so farmers run irrigation pumps, drawing up groundwater for their rice fields.

When Harvey and his colleagues started drilling wells to determine why arsenic levels were so high, they found that concentrations peaked at depths of about 30 meters — unfortunately, the same level at which many tube wells drew their drinking water. Testing groundwater at this depth, they found that it contained high levels of methane, which is released when microbes break down organic materials under oxygen-free conditions — for example, when they are buried in saturated soil.

Normally bacteria use oxygen to metabolize their food, but when it’s not available they can use metals instead. The group theorized that bacteria were using iron oxide particles in the soil to break down organic material, such as human and animal wastes, in the process releasing arsenic bound up with the oxides. To test this explanation, they mixed groundwater with molasses, an easily degraded organic material, and injected it back into a well. Arsenic concentrations in the well rose for several days, then fell, supporting the scenario that microbes were breaking down the molasses by “breathing” rust, releasing arsenic as a byproduct. (This technique is also used to clean up contaminated groundwater at industrial and military sites: Engineers inject harmless organic substances like molasses, whey or vegetable oil, stimulating bacterial activity that breaks down toxic pollutants into more benign byproducts.)

But the mystery was far from solved. Harvey and his team knew how the arsenic was being generated, but they had no idea where the organic material that fed the process releasing the poison came from. To answer that question, they used radiocarbon dating to measure the age of organic material containing carbon at different depths in the aquifer. Some of it turned out to be less than 50 years old, which suggested that groundwater pumping in the dry season was drawing “young” water from the surface down into the aquifer, carrying organic carbon with it.

Here, Harvey saw, hydrology could help pinpoint the arsenic source. In 2002, he brought a team of graduate students in to connect the dots between surface and underground water by constructing a water balance — that is, a detailed account of water flowing in and out of a 6-square-mile area, both above and below ground.”That’s a routine process, but it hadn’t been done in this area,” he says. Using modeling and natural tracers, they developed a picture of a layered groundwater system: Rice-field water was in a top layer, water seeping down from flood-control ponds settled in a middle layer, and “older” water that had been there since before the area was developed was on the bottom.

“The total supply of groundwater doesn’t change too much in Bangladesh because the monsoon system returns an immense amount of water every year,” Harvey explains. But, he says, development has changed discharge and recharge patterns. Historically, water had tended to move through the system horizontally. In monsoon season, the aquifer filled up from direct rainfall and seepage through the bottom and side beds of rising rivers; in dry months, the pattern reversed, with groundwater flowing back through streambeds to recharge rivers or upward to the roots of growing plants.

But now farmers were pumping groundwater up to irrigate their fields during the dry season and, by doing so, creating a downward pressure that pulled water from the surface. There was a surprise, though; not much of the water being sucked underground came straight down through the bottoms of flooded rice fields. Farmers plowed the fields in December, during the rainy season, when they were wet and mucky. The plowing broke up cracks and pores in the soil, so little water penetrated deep underground.

Actually, it seems, rice fields were filtering arsenic out of the system. Harvey and his students analyzed the chemistry of water in rice fields and found that it was very clean and saturated with oxygen generated by photosynthesis. Ultimately, other researchers found, arsenic washed out of the rice fields when they flooded during monsoon seasons.

Putting together all of these puzzle pieces, including chemical analyses of water from the rice fields, flood-control ponds and underground reservoirs, Harvey and his students concluded that water from the man-made ponds was seeping into the ground, carrying organic carbon with it. Once the organic material was deep underground, bacteria broke it down, using iron oxide and releasing arsenic.

For many reasons — the area’s complex hydrology, limited funding and the logistics of doing field research in a developing country — finding and fitting these pieces together took seven years. Over the course of the project, Harvey and his students studied water in some 50 irrigation wells, 40 to 50 drinking water wells and 80 monitoring wells. The team constructed vacuum chambers to suck water into impermeable bags that were transported thousands of miles to MIT for analysis. The group published its findings that the flood-control ponds were the key link in the chain that led to elevated arsenic levels in 2009.

Scott Fendorf, a professor of soil chemistry at Stanford, has studied arsenic poisoning in Cambodia, which has a geological history much like Bangladesh’s but has not been developed as intensively in recent years. “Charlie’s work and ours have been nice complements,” Fendorf says. “His findings show us what’s happening in a place that humans have modified, and we can play off of them.” Specifically, he says, Harvey’s work shows that flood-control ponds are causing the problem, not rice cultivation. That’s a critical distinction for countries, including Cambodia, that are less developed than Bangladesh but may follow a similar path.

M.King Hubbert, a geophysicist who died in 1989, is best known for correctly predicting in 1956 that U.S. domestic oil production would peak within 10 to 15 years. (It happened in 1970.) But he also wrote many books and articles on groundwater and structural geology issues. In 2008, the National Ground Water Association presented Charlie Harvey with its M. King Hubbert Award, which recognizes major scientific and engineering contributions to the field of groundwater hydrology.

“Charlie’s work in Bangladesh is high-quality applied research that has given us fundamental new knowledge about groundwater arsenic transport. It also points toward science-based solutions to a major public health problem,” says UC Davis’ Graham Fogg, who nominated Harvey for the award. “You don’t find many young scientists who have such a strong scientific foundation and also care about wider social relevance.”

As Harvey sees it, arsenic contamination in Bangladesh is an example of a larger problem occurring in many places around the world: Land-use changes over the past 50 years have had delayed impacts – underground. Harvey’s findings in Bangladesh, therefore, may help mitigate arsenic poisoning in other countries. “Everything we do in the water sector rests on our understanding of how physical systems work,” says Winston Yu, who earned his Ph.D. in Harvey’s lab and is now a water resource specialist with the World Bank. “In Bangladesh, we found that the prerequisites for mobilizing arsenic were a very hydraulically dynamic environment, a monsoon climate and a society that was extracting huge amounts of water and cycling it through the system at an intense rate.

“Those findings have applications to all sorts of other delta environments, like Cambodia, West Bengal and potentially Nepal.”

Early this year, Bangladesh’s finance minister, Abul Maal Abdul Muhith, promised that his government would make the nation arsenic free by 2013. That’s a worthwhile target, but one unlikely to be hit: According to UNICEF, about 20 million people in Bangladesh use well water that contains more than the national limit of 0.05 micrograms of arsenic per liter. But Harvey’s research offers some starting points for a program that would reduce the number of people drinking arsenic-laced well water. First, he says, villagers shouldn’t dig more flood-control ponds. And they shouldn’t drill new wells downstream from existing ponds or other water bodies where carbon-rich soils are saturated with water for long time periods — for example, stagnant slow-moving rivers.

In the United States, where arsenic hot spots are scattered mainly around the West and Southwest, homeowners can buy water filters, starting at around $150. But filtration is much too expensive for most Bangladeshis. “Median income in the U.S. is $50,000. In Bangladesh it’s $600. It’s a totally different context,” says Shafiqul Islam, who now teaches at Tufts University.

Harvey is planning a new project in concert with environmental scientists and physicians; it will drill some deep wells into older aquifers and monitor whether they draw contaminated water from shallower depths. But deep wells aren’t a perfect solution: They’re much more expensive than shallow wells, and village families like to have their own wells instead of pooling money to drill a deeper one. Moreover, according to the World Bank’s Yu, Bangladeshi government agencies are very hesitant to allow drilling into deep aquifers, fearing it could make the arsenic problem worse. Harvey would also like to try installing some shallow drinking water wells in rice fields, building on his finding that rice-field water at Mushinganj was surprisingly clean and arsenic-free, but shallow wells may not produce enough pressure to pump water to the surface.

To come anywhere close to its 2013 arsenic-free target, Bangladesh’s government will have to organize widespread water-testing programs and public education campaigns that persuade villagers to shift away from tainted tube wells. It will have to convince international aid agencies that the political will exists to drill new wells, run pipes or make other upgrades to connect citizens to safe water supplies, and then community leaders and social workers will have to persuade Bangladeshis to trust those new sources. It’s a complex undertaking to deliver what should be one of life’s simplest things — a drink of clean water — but thanks to Harvey, it will be based on a clear assessment of the depth of the problem.