Shortly after midnight on December 3, 1984, about 40 tons of deadly gas leaked out of a pesticide factory in the central Indian city of Bhopal. The highly toxic methyl isocyanate (MIC) – used as an intermediary chemical for making pesticides – drifted across the city, exposing nearly half a million residents.

Thousands of people died over the next several days, and it's estimated that many thousands more have died from related health issues since. Survivors who are alive today still struggle with a range of debilitating chronic health issues, from cancer to lung disorders to neurological damage.

Now, a new study shows that the accident – often considered the worst industrial disaster in history – affected not just those who were exposed to the gas that night but also the generation of babies still in the womb when the accident happened. In fact, men born in Bhopal in 1985 have a higher risk of cancer, lower education accomplishment and higher rates of disabilities compared with those born before or after 1985.

"The paper is one of the first papers to demonstrate clearly this link between a huge industrial disaster and the effect on children in utero," says Jishnu Das, a public policy professor at Georgetown University and a fellow at the Center for Policy Research in New Delhi.

The results inform an ongoing discussion about "what is owed to future generations" affected by disasters.

The study also found the accident affected health outcomes for people living much farther from the factory than previously known. Most previous studies looked for impacts in people living a few miles away; people as far as 62 miles from Bhopal were affected by the disaster, according to the new study, which received support from the Bill and Melinda Gates Foundation (a funder of NPR and this blog).

A survivor's story

Rehana Bi was 16 years old in 1984 when the accident happened. She lived in a neighborhood right near the pesticide plant along with her three brothers, father and mother, who was eight months pregnant at the time.

The family was fast asleep when some neighbors banged on their door, calling out her father's name, urging him to wake, says Bi. When her parents opened the door, they saw that it was hazy outside.

"There were a lot of people standing outside," she says. "They were all coughing, and no one could see very well."

Their eyes and lungs were burning. "It was as if someone was burning chilies," adds Bi.

She and her family tried to run away from the gas that now filled the air in the neighborhood but the crowds and the chaos meant they didn't get far. Her pregnant mother struggled to move quickly. "So we sat on the side of the road until the morning," she says.

By the end of the day, Rehana Bi's parents and her 3-year-old brother were among the thousands of people who died. In haunting detail, Bi recalls that some relatives saw the 8-month-old fetus in her dead mother's womb moving until the next morning. It was only then, she says, that they were able to find someone to wash the bodies and bury them in keeping with Muslim tradition.

Nearly 39 years later, she herself struggles with high blood pressure and diabetes as does her husband Shamimuddin, whom she married a year after the gas accident. Their health issues keep them from working these days, so the family depends on the earnings of her two sons, who work as daily wage laborers.

Her neighborhood is filled with survivors struggling with a range of health issues in the decades since the disaster, says Rehana Bi, especially cancer.

"There's a lot of people who have cancer," she says. "Many of them have died."

A multigenerational toxic legacy

The range of chronic health issues among survivors of the Bhopal gas accident have been documented by previous studies. But most of those studies have been limited to people directly exposed to methyl isocyanate that night and to people very close to the factory run by Union Carbide India Limited, a subsidiary of an American company.

"A lot of the studies focus on the populations that lived within three kilometers of the site," says Prashant Bharadwaj, an economist at University of California San Diego and an author of the new study.

Bharadwaj and his colleagues used data collected in 2015-2016 by the National Family Health Survey, which asks every family across the country about health, education and economic outcomes.

"It's interviewing women, getting all of their life history, including when they had children, whether those children survived, when those women themselves were born, their educational attainment, their level of health," says study co-author Gordon McCord, also an economist at UCSD. The survey interviewed men, too.

"So we were able to piece all these together to say, okay, let's look at the children who were born in the years right before 1984, in '85, and then afterward," says McCord.

Then they compared the people born in 1985 to those born before and after the accident to see if there was anything distinct about the 1985 cohort, which was exposed to the accident in utero.

They found an increase in pregnancy loss, which they expected, based on previous research.

But the analysis also illuminated something new about those pregnancy losses – the losses were likely to involve male fetuses.

"That 1985 birth cohort was very strange because it had a much lower male-to-female sex ratio" compared to the other birth cohorts in the study, says McCord.

A range of previous studies have shown that, in general, male fetuses are more vulnerable to any adverse effects in utero, says McCord. "And so when you get an adverse health shock to pregnant women, the likelihood of losing the male fetus is a bit higher."

And the males born in 1985 in Bhopal were unlike those who were born before or after, he adds. In fact, they are worse off in terms of health and employment even when compared to those who lived through the disaster.

"They have a higher likelihood of reporting to have cancer," he says. "They have a higher likelihood of reporting a disability that prevents them from being employed. And they on average have two years less of education."

That is "a really big deal" he adds, "because it goes beyond health to saying that these people have broader consequences for their lives, that prevent them from living full out, thriving lives."

The study doesn't prove that in-utero exposure to MIC caused these long-term health and economic impacts, which the study authors acknowledge. Other factors such as lack of access to health care and other aid following the disaster may have also played a role

However, the study is "the best kind of observational study that we can get on the question 'Did the Bhopal disaster lead to deficits in outcomes for children who were in utero at the time?' " says Das.

"The second thing that they show is that the radius of impact is closer to 100 kilometers [62 miles] rather than five," he adds. "That's worth thinking about too."

What does the world owe victims who weren't yet born?

No one in Rehana Bi's family has cancer yet, but she believes that her own exposure to MIC affected the health of her children who were born years later. She's lost two adult children in the last several years – a son who died from tuberculosis and a daughter who died during childbirth. Her remaining daughter is struggling with fertility issues, which Bi thinks is a generational effect of the industrial accident.

"Not only are we finding high rates of cancers, but also all kinds of immunological issues, neuro skeletal issues, musculoskeletal issues and huge number of birth defects in children being born to gas-exposed parents," says Rachna Dhingra, who works with the International Campaign for Justice in Bhopal, an advocacy organization.

The new study "just vindicates our stand that not just people of Bhopal but their children are also going to face a high number of disabilities and diseases in their life," she says.

This is not the first study to suggest that the impacts of the Bhopal disaster go beyond those directly exposed. A controversial, unpublished Indian study had also documented other intergenerational impacts of the Bhopal industrial accident.

Conducted by the Indian Council of Medical Research (ICMR) in 2016, the study found that women who were exposed to MIC themselves, as well as the daughters of women survivors, had a 7 times higher risk of giving birth to a baby with birth defects compared to women who had no history of exposure to MIC.

But that ICMR study has remained mired in controversy over government and cooperate responsibility for the disaster, and has done little to help the families of survivors and their kids. The results were never published in a peer reviewed journal or released publicly. The results came to light only after Dhingra and other activists obtained the findings through India's Right to Information Act.

"Not a single child who was in utero or born after the disaster was ever compensated," says Dhingra.

The Supreme Court in India in March also rejected a plea for more compensation of survivors of the Bhopal accident. "The damages to the people who were directly exposed — all the curtains have been closed," says Dhingra.

But the curtain is still open for figuring out "damages to the next generation," she adds. And that's where she hopes the new study's findings will make a difference.