The agency says that arsenic enters the food chain mainly through crops absorbing contaminated irrigation water.
An odorless and tasteless semi-metal that occurs naturally in rock and soil, when igested arsenic can lead to a variety of illnesses including skin disorders, gangrene and cancer of the kidneys and bladder.
Currently, 12 Asian countries have reported high arsenic levels in their groundwater resources.
"The problem of high arsenic levels in crops, particularly rice, needs to be urgently addressed by promoting better irrigation and agricultural practices that could reduce arsenic contamination significantly," said FAO water quality and environment officer Sasha Koo-Oshima.
"Arsenic contaminated rice could aggravate human health when consumed with arsenic laden drinking water," she warned.
The agency's warning is contained in a new report entitled "Remediation of Arsenic for Agriculture Sustainability, Food Security and Health in Bangladesh."
Koo-Oshima said, "The widespread addition of arsenic to soils, for example in Bangladesh, is degrading soil quality and causing toxicity to rice. Arsenic contamination is threatening food production, food security and food quality."
A kindergarten student eating rice at a nursery in Bejing, China. (Photo courtesy UN)
Contamination originates in arsenic-rich sediments of the Ganges and Brahmaputra river that filters into groundwater water pumped to the surface through the tube wells.
Bangladesh, where rice is a staple food and consumed in large amounts, has the highest percentage of contaminated shallow tube wells and an estimated 30 million people are dependent on those wells for drinking water and irrigation.
A pilot study conducted in Bangladesh by FAO and Cornell University show that planting rice in raised beds around 15 centimeters above the ground and not in conventional flooded fields reduces the exposure to contaminated irrigation water and produces higher yields.
In addition, the raised bed rice acts as a buffer against floods and drought and serves as a measure in climate adaptation.
A related Cornell University project found that between 30 and 40 percent less irrigation water is needed in the raised bed system. Fertilizers are also captured better, so farmers will need less fertilizers.
"The raised bed system represents a major shift in rice production," said FAO, "but tests show that farmers prefer the new approach due to visibly higher yields, water savings, lower tillage and labour costs and production of a safer crop."
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