Bangladesh may be heading for an epidemic of arsenic poisoning with an estimated 60 million regularly ingesting arsenic through drinking contaminated groundwater, a public health specialist cautioned last week.
More than 7000 people in Bangladesh have already been diagnosed with symptoms of arsenic poisoning but half of the country's population may be at risk, Enamul Karim, vice president of the Bangladesh public health association, said at a conference on international health, which was sponsored by Harvard and the Massachusetts Institute of Technology and held at Harvard University.
Surveys of groundwater used for drinking and cooking have identified unacceptably high concentrations of arsenic in several thousand deep tube wells, Dr Karim said. Some wells contain 0.4 mg/l of arsenic, 40 times the acceptable concentration, he added.
The National Institute of Preventive and Social Medicine in Bangladesh has developed a training manual for doctors to help them recognise the clinical signs of arsenic poisoning. Typical symptoms include keratosis, melanosis, depigmentation, oedema and nephropathy.
The first cases of arsenic poisoning on the Indian subcontinent caused by contaminated groundwater occurred in the neighbouring state of West Bengal in India, which borders Bangladesh. By the mid-1990s, Indian doctors had detected 220 000 cases of chronic arsenic poisoning and had dubbed it the "biggest arsenic calamity in the world" (BMJ 1996;313:9).
Public health experts in Bangladesh said that the government has delayed acknowledging the problem. Over the past two decades, the government has invested heavily in sinking wells and has tried to coax people to rely on the deep tube wells because using surface water puts them at risk of water borne infections.
"Bangladesh faces a dilemma," said Dr Karim. "Do we now ask people to revert to surface water and risk cholera or rotavirus infections or allow them to continue drinking tube well water laced with arsenic?"
He said that Bangladesh did not have the resources to distribute treated water to the affected population, which is scattered across hundreds of villages. Although some companies have developed what they claim are devices to treat water contaminated by arsenic, these require periodic replacement of filters, and most of the population affected by the contaminated water will not be able to afford such devices, he said.
The source of the arsenic is geological. The alluvial sediments in the region are rich in iron pyrites, which contain arsenic, and hydrologists have suggested that excessive groundwater depletion causes arsenic to be released from pyrite decomposition.
"The dose-response relation is still an unresolved research issue," Dr Karim said. Previous studies in Taiwan had suggested that some cancers might be the result of a cumulative effect of arsenic poisoning that show up after 15 to 20 years of ingestion.
In Bangladesh, there have been cases of squamous cell carcinoma that seem to have been attributable to arsenic ingestion and that have occurred within 10 years of exposure, he said. Arsenic contaminated groundwater and the associated toxicity has also been previously reported from Argentina, China, Mexico, Taiwan, and Thailand. But the number of people exposed to the risk had never been as large as on the subcontinent.