FOS-SUR-MER, France — The line of giant chimneys ceaselessly belching smoke in the air stretches to the horizon in one of the most polluted industrial zones in Europe.

For years, the inhabitants of Fos-sur-Mer, France, accepted their illnesses — for example, a cancer rate that is double the national average — in exchange for jobs in the nearly 200 factories, warehouses, gas terminals and industrial sheds that surround them.

Doctors’ waiting rooms were often full. At the cemetery, tombstones recorded the deaths of young men cut down in their prime. In addition to the cancer rate, the asthma rate is also considerably higher than the national average, according to a publicly funded health study.

But enough got to be enough. Citizens in this otherwise sun-dappled corner of the Mediterranean, just west of Marseille, decided not long ago that they would take action, whatever their misgivings about losing their jobs.