The acceptable level of arsenic in drinking water has been set at 50 parts per billion (PPB) or 0.05 microgrammes per litre of drinking water in Bangladesh, while the approved global standard set by the World Health Organization (WHO) is 10PPB.
According to new field surveys of arsenic contamination in soil, water and plants in various parts of the country by scientists from Japan's Nihon University and local researchers, arsenic was found in all types of crops in the worst-affected areas.
An earlier survey by scientists of the School of Biological Sciences, University of Aberdeen, UK, analysed 330 samples of “aman” (rain-fed) and “boro” (irrigated) rice, 94 vegetables and 50 pulse and spice samples for arsenic and found that the districts with the highest mean arsenic rice grain levels were all in the south-west.
The districts were Faridpur (boro) with 0.51, Satkhira (boro) 0.38 and (aman) 0.36, Chuadanga (boro) 0.32 and Meherpur (boro) 0.29 microgrammes per gramme. Boro rice contained significantly more arsenic than aman rice, mainly because boro rice is irrigated with ground-water containing arsenic.
”Daily consumption of rice with a total arsenic level of 0.08 microgrammes per gramme of rice would be equivalent to a drinking-water arsenic level of 10 microgrammes per litre of water,” the research found.
Rice represents about 70 percent of the daily calorie intake, according to specialists.
A long-standing problem
Levels of arsenic in the drinking water are so high in Bangladesh that the WHO has described it as “the largest mass poisoning of a population in history”.
In rural Bangladesh, many wells pump water with arsenic concentrations exceeding 500 microgrammes per litre. Groundwater is contaminated with arsenic in 61 out 64 districts.
According to a 2006 UN Food and Agriculture Organization (FAO) report, people might be exposed to arsenic not only through drinking water, but indirectly through food crops irrigated by contaminated groundwater.
”Where concentrations of arsenic in soil and water are high, we found a correlation with high arsenic content in crops,” said Sasha Koo-Oshima, an FAO water quality and environmental expert.
Several studies have also reported a correlation between arsenic in soil and reduction in crop yields, particularly in rice. Since rice is the staple food, arsenic contamination could also negatively impact food security if concentrations reach levels toxic to crops.
”Arsenic contamination of groundwater in Bangladesh threatens the health of up to 30 million people,” according to the FAO.
But Ehteshamul Haque, chief engineer of the government’s department of public health engineering’s (DPHE) arsenic mitigation project, is less worried.
“Arsenic is flowing into agricultural products via irrigation water, but in very insignificant quantities,” Haque told IRIN on 19 September. “A lot of research is required before we could ascertain how much arsenic is accruing into the food chain and what harm it can cause to the consumers,” he said.
He also said the World Bank-DPHE arsenic mitigation project expired in June 2007 and had not been renewed. “What we are doing is continuing with the remnants of the project,” he said.
Cutting back on irrigation
”The Bangladesh Rice Research Institute (BRRI) estimates that farmers could apply up to 40 percent less irrigation water without any yield losses,” the 2006 FAO report said. “If water input can be reduced so that the soil conditions become more aerobic, the solubility of arsenic - and therefore its uptake - would be minimised as well.”
Another option is to promote cropping patterns that require less irrigation water, which could be done by replacing boro rice with wheat and maize, for instance, which require less water, the report stated.
”Roughly 50 percent of the present boro acreage of some four million hectares in Bangladesh is agro-ecologically suitable for non-flooded dry-land crops like maize and wheat. These crops may be a good alternative to boro rice in an arsenic management strategy because boro rice is grown in an anaerobic [irrigated] environment where arsenic becomes much more bio-available than in the aerobic [dry] growing conditions for wheat and maize,” Muhammad Panaullah, a senior soil scientist, told IRIN. He played a lead role in investigating the transmission of arsenic from ground-water to soil to crops under a project of the International Maize and Wheat Improvement Center (CIMMYT), US Agency for International Development (USAID) and Cornell University (CU) in 2002-2006.