Can efforts to untangle sources of contamination in the food chain counteract the “largest mass poisoning in history”?

Hashem Mondal had not been feeling well. A rickshaw puller in rural Bangladesh, he noticed that on sunny days he tired easily, and his skin became itchy and prickly. That was about a year and a half ago. Shortly afterward, his skin became mottled with dark brown patches, and lesions festered on the palms of his hands and soles of his feet. It was more than an inconvenience. A rickshaw puller’s livelihood (US $2 on a good day) is earned through his feet and hands.

Unbeknownst to Mondal, he had joined tens of millions of Bangladeshis as another victim of arsenicosis—arsenic poisoning— in what the World Health Organization (WHO) has called the “largest mass poisoning of a population in history.” In a poignant and bizarre tale, this health threat arose from a humanitarian effort in the 1970s to bring clean drinking water to Bangladesh and curb deadly water-borne diseases such as typhoid, dysentery, and diarrhea. Thousands of tubewells were drilled throughout the country. The incidence of water-borne diseases decreased dramatically. What was not foreseen was that the nation’s shallow aquifers would become increasingly contaminated with arsenic. Arsenic was part of the silt deposited throughout the lowland basin of Bangladesh and West Bengal in India as the Himalayas eroded. As large amounts of irrigation water were pumped over the land in the winter, the arsenic was released into the water for drinking and agriculture.

The maximum level of arsenic in water viewed as safe by the WHO is 10 parts per billion (ppb); the official Bangladeshi threshold is 50 ppb in drinking water. In rural Bangladesh, many wells pump water with arsenic concentrations exceeding 500 ppb. The well Mondal fetched his water from later tested at 400 ppb, and his early symptoms of arsenicocis are typical. Longer exposure often results in cancer. It is estimated that arsenic in drinking water will cause as many as 270,000 cancer deaths in Bangladesh in coming years. There may also be effects related to diabetes, vascular diseases, and reproduction. The poor cannot afford the bottled water, meat, or even lentils that could counteract the toxin’s effects.

Arsenic: Flowing through
the food chain?

Not surprisingly, arsenic has become a top priority of the government and of aid organizations. Until recently, research and remediation focused almost exclusively on drinking water. Key links between arsenic and agriculture, specifically irrigated land and crops, had been largely overlooked.

“Arsenic in irrigation water poses a potential threat to soils and crops, the food chain generally, and consequently to human health,” says CIMMYT agronomist Craig Meisner. “On average, a Bangladeshi adult drinks about 4 to 5 liters of water a day and consumes about 450 grams of rice. Assuming 200 ppb arsenic in the drinking water and about 0.5 milligrams per kilogram in rice grain, the total daily intake of arsenic would be around 1.2 milligrams, which may not be safe.”

The problem as it relates to the food chain and human health is multifaceted (see figure). According to CIMMYT affiliate scientist G.M. Panaullah, “There are questions about how much arsenic is actually absorbed by the plant, and then how much of that is taken into the grain and straw under diverse conditions and farm management systems. Then, does arsenic in the grain actually pose a health hazard, and if so, at what levels and under what conditions? Consider also that the straw is fed to animals and burned as fuel. Will people be affected by drinking the milk or eating the meat of those animals? Will the smoke from a straw-fueled fire prove harmful?”

Much more information and knowledge are needed. “At this point,” Panaullah says, “we do not want to alarm people about circumstances that ultimately may not prove to be hazardous. On the other hand, it’s critical that we determine what is happening in the fields and the food chain, and start formulating responses.”

“Mainly, we are grateful
that someone is trying to help”

CIMMYT, together with the Bangladesh Agricultural Research Institute (BARI), the Bangladesh Rice Research Institute (BRRI), the Bangladesh Institute of Nuclear Agriculture (BINA), the Bangladesh Agricultural University, and Cornell and Texas A&M Universities, is tackling these issues through a USAID-funded project. The project will assess arsenic contamination in irrigation water and soils, study the effects of arsenic on crop yield and grain and straw composition and quality, and develop mitigation technologies for safe agriculture and food. To accomplish this, the project provided rigorous training for Bangladeshi scientists and research technicians at the US universities. The project is also sponsoring PhD programs for four Bangladeshi students.

During 2002 and early 2003, a preliminary assessment was conducted at 450 shallow tubewell sites in five representative areas in eastern, central, and western Bangladesh. Irrigation water, soil samples, and grain and straw samples were collected from all sites and analyzed by the recently trained Bangladeshi team, with results confirmed in the US university labs.

The farm of Yusuf Ali Sarker in Faridpur was typical of the research sites. The farmer works with officials of the Department of Agricultural Extension and BINA scientists to set up sampling regimes for testing irrigation water at different distances from the well, boring soil samples at different field sites, and collecting grain and straw at different distances from the wellhead and from different varieties of rice. The project team regularly visits the site and monitors data collection.

Ali Sarker has little if any formal education, but he fully realizes the magnitude of the situation. “When the government began testing the tubewells five or six years ago, I became aware of the problem,” he says. “The well where I get my drinking water tested red [the designation for a dangerous well—in this case, 181 ppb or 18 times the WHO acceptable limit], but what can I do? I’m poor and no man can live without water. So I’m working with the scientists and extension workers to see what we can do. Mainly, we are grateful that someone is trying to help.”

Early results

By sampling soil, water, grain, and straw, researchers learn how arsenic enters the food chain.

The project has already made useful discoveries, while confirming that the path from water to soil to crops to food is complex. Rice grain and straw analyses revealed unusually high levels of arsenic in grain (0.8–1.0 mg/kg) at a few sites, but more generally the range was 0.2–0.4 mg/kg. Panaullah says that a general rule of thumb emerged that arsenic concentrations were on the order of 1:10:100, grain:straw:root. Notably for farming systems research, in some soils, rice grown under anaerobic conditions had arsenic levels 10-20 times greater than wheat, which is grown under aerobic conditions. It is anticipated that similar ratios will be found between rice and crops such as maize and potatoes.

Water and soil arsenic concentrations do not always correlate well with each other, however, and individually they do not always correlate to high arsenic concentrations in plants. High and low arsenic concentrations in both irrigation water and soil consistently result in plants with high and low arsenic concentrations, respectively. But the scientists report that “there is a large middle ground where the picture is muddled.” Mineralogy, soil texture, or factors related to irrigation, such as flow rate and distance from the wellhead, may play a role. These are some of the possibilities investigated at the farms of Ali Sarker and others.

Following data collection and analysis, says Meisner, the project will issue a risk assessment. “It will tell farmers that if they have a well with this level of arsenic and their crop is this or that distance from the wellhead, here is what the impact will be.” Depending on the research conclusions, substituting maize, wheat, or other crops for boro rice (irrigated winter rice), or accelerating the adoption of water-conserving technologies such as zero tillage and bed planting, might be an important response to the problem.

Even at this early stage, Panaullah, Meisner, and the project team feel that they can make a positive impact on the health and livelihoods of Bangladeshis. The rickshaw puller’s illness was recognized in a chance encounter with project staff who directed him to a doctor and have followed up with him since then. His strength is returning and the painful lesions receding. “It is gratifying to see he’s getting better,” Panaullah comments. “Now just imagine if we can do that for millions more.”

	For more information:
	c.meisner@cgiar.org

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February, 2004