(CNN) Pollution caused one in six deaths worldwide in 2019, a new study has revealed -- more than the annual global tolls for war, malaria, HIV, tuberculosis, drugs or alcohol.
The study, published Tuesday by the Lancet Commission on pollution and health, found pollution kills 9 million people every year -- nearly three quarters of them due to harmful air.
According to the study, deaths caused by air pollution and toxic chemical pollution increased by 66% over the past two decades, fueled by uncontrolled urbanization, population growth and a dependence on fossil fuels.
"The health impacts of pollution remain enormous, and low- and middle-income countries bear the brunt of this burden," said Richard Fuller, the study's lead author. "Despite its enormous health, social and economic impacts, pollution prevention is largely overlooked in the international development agenda."
After air pollution, water pollution was the next most fatal threat, causing 1.36 million premature deaths in 2019. Lead pollution was next, followed by "toxic occupational hazards."
The study builds on a 2015 report by the same commission, drawing on data from the Global Burden of Disease Study, an international collaborative effort based at the Institute for Health Metrics and Evaluation.
In the four years between, the deadly impact pollution has on the world did not improve -- making it the largest environmental risk factor for diseases and premature deaths, the study said. It added that an "absence of adequate national or international chemical policy" has exacerbated the deaths.
More than 90% of the deaths occurred in low- and middle-income countries unable to make pollution a priority, such as India and Nigeria, according to the study. High-income countries, meanwhile, had controlled the "worst forms of pollution," the study said.
"It is clear that pollution is a planetary threat, and that its drivers, dispersion, and health impacts transcend local boundaries and demand a global response," said Rachael Kupka, co-author and executive director of the Global Alliance on Health and Pollution.
"Global action on all major modern pollutants is needed."
India recorded the largest number of air pollution-related deaths in 2019, with more than 1.6 million people killed in the nation of 1.3 billion, according to the study.
Pollution levels in nearly all of India are far above World Health Organization guidelines, it added, forcing millions to breathe toxic air every day.
Last year, six of the world's 10 most polluted cities were in India, according to monitoring network IQAir. Bad air could be reducing the life expectancy of hundreds of millions of Indians by as much as nine years, according to a recent study by the Energy Policy Institute at the University of Chicago.
In 2019, the Indian government announced a national clean air campaign, with an aim to reduce particulate pollution by up to 30% by 2024. Specific plans were created for each city; in the capital, Delhi, those plans included measures to reduce road traffic, burn-offs and road dust, and to encourage the use of cleaner fuels.
But in the past few years, India's pollution problem has worsened, partly due to the country's dependency on fossil fuels -- and in particular, coal. At last year's COP26 climate summit in Glasgow, India was among a group of countries that pushed for an 11th-hour amendment to the agreement to phase "down" coal rather than phase it "out".
Meanwhile, Africa saw a decline in deaths from traditional pollution such as unsafe water or poor sanitation practices, the study said -- largely due to improvements in sanitation, water quality and antibiotics. However, the number of air pollution deaths is starting to rise, with economic growth prompting greater urbanization in many African countries.
The Lancet committee urged action with eight recommendations, including increased government funding for pollution control, better pollution data collection, and an independent global body overseeing pollution similar to the United Nations' Intergovernmental Panel on Climate Change.