On the outskirts of Dhaka, around 250 brick kilns are operating without clearance certificate from the Department of Environment (DoE) in Keraniganj.   Sources said there are 300 brick kilns in Keraniganj and adjacent areas including Rajendrapur, Doleshwar, Jajira and Mollahat. Among them, 250 are operating illegally.   Unlimited burning of firewood in the brick kilns is causing air pollution which is now a major concern for the residents of Dhaka and nearby areas.   Sources said the brick kilns are affecting the environment and the health of the locals, particularly the young and the old. Many of them are suffering from respiratory problems.   Moreover, a number of brick kilns set up on arable land in Rajendrapur, Doleshwar, Jajira and Mollahat area in Keraniganj are also destroying the fertile topsoil.