FACTBOX: Millions at risk in pollution blackspots

(Reuters) - China and India's 10 worst pollution blackspots together account for a third of the world's 30 most polluted places, according to a report issued on Wednesday by U.S.-based group the Blacksmith Institute.

Here are some facts on the four places in China and India in Blacksmith's "Dirty Thirty" where pollution potentially affects the lives of more than a million people.

* RANIPET, INDIA -- potentially affected: 3,500,000

-- Tannery waste from the leather tanning industry in Ranipet, a medium-sized town about 100 miles upstream from Chennai, poses a pollution risk to surrounding populations. Uncovered waste made up of chemicals such as sodium chromate could easily leach into ground water supplies, the report says.

-- Clean-up: A factory responsible for about 1.5 million tons of untreated sludge was shut down in 1996, but the report says no real progress has been made to clean up the site.

* LINFEN, CHINA -- potentially affected: 3,000,000

-- Carbon monoxide, sulphur dioxide, arsenic and lead are among the cocktail of air pollutants circulating in Linfen, Shanxi Province, which has the country's worst air quality. Residents in the city, located in the heart of China's enormous coal industry, have reported high rates of bronchitis, pneumonia and lung cancer.

-- Clean-up: Linfen plans to close 160 of 196 iron foundries and 57 of 153 coke and coal processing plants by the end of 2007, and replace small polluting plants with larger cleaner facilities.

* LANZHOU, CHINA -- potentially affected: 3,OOO,000