When 23,000 new cancer patients checked into the Mahavir Cancer Institute last year, Dr. Ashok Ghosh, a professor at the institute in Bihar, India, drew a connection between the patients’ symptoms and the region’s increasingly-polluted groundwater supply.

Since 2004, when he began testing the state’s 44,000 tubewells, Ghosh found that about 30% had water with arsenic concentrations higher than 10 parts per billion (ppb), which is the permissible limit according to World Health Organization guidelines. 

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Years later, millions of people have begun to show symptoms of arsenic poisoning which can lead to cancer.

"When I joined the cancer hospital, I started checking blood, hair and nail samples of cancer patients and found they have very clear-cut symptoms of arsenic poisoning," Ghosh told CNN. "I saw 6 and 7-year-old children coming with cancer. These children don't chew tobacco or smoke. It was very disturbing, and I could not sleep."

Reports have shown that 17 of Bihar’s 38 districts have groundwater with arsenic concentrations far above the permissible limit. In some districts, hand pumps have severe concentrations of the toxin — and a handful are above 1,500 ppb. 

"It is a slow poison,” Ghosh added. “Symptoms appear after continuous ingestion over five to 12 years.”

According to the International Agency for Research on Cancer, the toxin is highly carcinogenic.

Chronic arsenic poisoning has been linked to several different kinds of cancer, including skin, bladder, kidney, and lung. Symptoms may include pigmentation and keratosis, and lead to respiratory and vascular diseases, neuropathy, and liver fibrosis. 

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"The cause of the upsurge in arsenic concentration is the overuse of groundwater for irrigation and drinking, which happens when withdrawal rates exceed recharge rate," Ghosh explained, adding that the aquifer’s chemistry changes from years of overuse. "There is no law here to check excessive groundwater withdrawal."

Up until the 1970s, people in India consumed surface water from tanks, ponds, and open wells. But in order to prevent gastrointestinal diseases like diarrhea, people became dependent on groundwater from tubewells that were installed in the Ganges delta, which is higher in arsenic concentrations due to silt containing arsenopyrite that washes in from the Himalayas. 

Government support is crucial, Ghosh emphasized. Without a grassroots educational program or a system set in place that distinguishes high arsenic sources from low ones, millions more in the highly-impoverished state may be exposed. 

“The presence of this contaminant threatens enjoyment of the human right to water, negatively impacting upon people’s health, economy and social wellbeing,” the study states. “This in turn thwarts people’s enjoyment of the rights to health, education and development.”