Industries are responsible for four types of pollution: (i) Air pollution is caused by the presence of high proportion of undesirable gases, such as sulphur dioxide and carbon monoxide. Smoke is emitted by chemical and paper factories, brick kilns, refineries and smelting plants, and burning of fossil fuels in big and small factories. (ii) Water pollution is caused by organic and inorganic industrial wastes and effluents discharged into rivers. The main culprits in this regard are paper, pulp, chemical, textile and dyeing, petroleum refineries and electroplating industries that let out dyes, detergents, acids, salts and heavy metals like lead and mercury, pesticides, fertilisers, synthetic chemicals with carbon, plastics and rubber, etc., into the water bodies. (iii) Noise pollution is due to industrial and construction activities. Machinery, factory equipment, generators, saws and pneumatic and electric drills cause hearing problems and irritation.