OPTICS ‘More necessary than the sun’ Coal brought prosperity — and sickness — to Bosnia. A phrase uttered by a worker in the 1990s came to define the struggles of a region dealing with the pollution caused by one of its main industries. Text and photos by MATTEO TREVISANin Zenica, Bosnia and Herzegovina A boy suffering from chronic respiratory problems plays at home, a few dozen meters from the the steel plant in Zenica, Bosnia and Herzegovina. His father says they can never drink coffee in the garden because it fills up with black dust within minutes — and they…