Smokestacks protruding from the city skyline churn out thick clouds of smoke that merge with the heavy grey lid hanging over the Czech Republic's third largest city of Ostrava.

A typical autumn day in the city, some 350 kilometres (220 miles) east of Prague, that was dubbed the country's steel heart by the 1948-1989 communist regime but has left local people with a dangerous legacy.

Babies born in the city's Radvanice and Bartovice districts require medical treatment an average of four times in their first year for respiratory diseases induced by toxic substances tied to dust particles from local industrial plants.

"The primary impact on children is that they are far more often sick than in any other place, including the rest of Ostrava," says Eva Schallerova, a pediatrician in Radvanice.

Recent research by a Czech Academy of Sciences team has shown that children in Bartovice suffer from respiratory diseases including pneumonia in the first year of their life far more often than elsewhere in the country.

The chief scare is toxic benzo(a)pyrene (BaP), attached to dust particles and singled out by the World Health Organization as "one of the most potent carcinogens".

Besides harming children, the substance damages genetic material, affects foetuses and sperm quality, causes cardiovascular diseases and accelerates the ageing process.

A 2004 EU directive sets a BaP limit of one nanogramme per cubic metre for member countries as of December 31, 2012.

In 2008, scientists in Ostrava logged a jaw-dropping 92 nanogrammes.

These carcinogens cling to dust particles, a by-product of processes such as coking, casting or burning car fuel.

Ostrava became an iron-making centre in 1828, then evolved into the country's "steel heart" as the communists kicked off in 1949 the construction of new steelworks, which are now run by ArcelorMittal.

The global giant's plant is a major local polluter, alongside Russian-owned Evraz Vitkovice Steel and Hungarian chemicals maker Borsodchem.

Environmentalists from the Arnika association singled ArcelorMittal out as the region's top polluter last month in terms of benzo(a)pyrene, dust, greenhouse gases and dioxin emissions.

The company has recently opened a de-dusting plant worth a billion koruna (38 million euros, $50 million), but it still has a long way to go with its environmentally friendly plans stretching to 2015 and beyond.

Some in Ostrava appear prepared to tolerate pollution amid fears that a factory closure would cost them dearer.

"Ostrava's biggest problem is the people -- they have a job and they don't want to lose it. Health is still far from being the top priority here," says the fiftysomething Schallerova, who has lived in Ostrava for 32 years.

The city with 307,426 residents suffers from high unemployment, which reached 11 percent in October against the national average of 7.9 percent.

Its deputy mayor in charge of the environment, Dalibor Madej, is against cranking up pressure on the polluters.

"I'm not saying the environment is not important, but when you lose your job, it affects the quality of your life and subsequently health far more," he said in a recent interview.

Besides, people from Radvanice and Bartovice, where the wind blows ArcelorMittal emissions most of the year, cannot move as the value of their houses has slumped so far that they will never get enough to buy a new place.

The bad news keeps coming -- four Prague scientists from a team led by Radim Sram were stunned to learn they had suffered from genetic damage as a result of a three-week trip to Ostrava.

"A clear increase in micronuclei frequency was observed in all subjects who spent three weeks in the Ostrava region, probably the most polluted area in the EU," reads their study published by the Oxford University's Mutagenesis magazine.

Schallerova, an energetic black-haired woman, points a finger at Madej, who threatened to file charges against Sram for scaremongering.

"They said four scientists were statistically unimportant. But you don't need a hundred people poisoned by a toadstool to know it's dangerous," she said.

Madej has also called Sram's research "a waste of money because they probe into things we all know -- that we have pollution here."

Local people will take little comfort in knowing they can cope with pollution better than the rest of the country -- in a way.

Pavel Rossner, head of another research team, says a gene that identifies DNA breaks and forces repairs is more active in people from Ostrava than in those from Prague.

At a recent seminar, he likened Ostrava citizens to "a mouse who dies when you expose it to a high dose of radiation, but lives if it is gradually exposed to smaller doses first."

But he added that this "adaptive response" did not help really as it accelerates ageing.

The EU has recently allowed Prague to use six billion koruna to help companies in the Ostrava region cut emissions, but even if they did, the immediate future looks bleak.

"Considering the long-term burden, we must assume a transfer of the genetic damage onto future generations," says Sram, adding that "the current burden will affect people in Ostrava over the next 20-30 years."