Even the release of treated effluents to waters is not without environmental repercussions, because these effluents are a prime source of nutrients and subsequent eutrophication. The chemicals used in wastewater treatment can also have toxic effects. Chlorine, for example, is both toxic to aquatic organisms in its own right and can also combine with some organic compounds in the effluent to form organochlorines such as chloroform and various chloramines, which may be carcinogenic or directly toxic. Industrial Pollutants Especially in the developing world, industry is concentrated in urban centers, resulting in severe water pollution problems in most large cities. Major sources of water pollution include chemical- intensive industries such as tanneries, metal plating operations, pulp mills, and refineries.
Urban runoff is another source of industrial pollutants.
In Jakarta Bay in Indonesia, where untreated industrial wastes are discharged by some 30,000 small industries such as batik factories, heavy metal accumulations are alarmingly high. Cleaning up contaminated sediments is extremely difficult and costly.