The problems of water pollution: an overview

Most potentially toxic chemicals eventually find their way into waterways. The most common source of this pollution is from the air. More than 50 percent of the chemical pollution of the Great Lakes is believed to come from airborne pollutants, and the main sources of this pollution are smokestacks (energy plants, nuclear or conventional; trash-to-steam incinerators; industrial factories, chemical and wood pulp) and road traffic exhaust. Chemicals may reach waterways directly through partially filtered or untreated sewage and waterway traffic, both industrial and pleasure; or they may be deposited into the soil and reach rivers and estuaries through leakage (PCBs on cables, landfills, and regular or low-level nuclear waste) or locally from fields (fertilizers, herbicides, phosphates, and other chemicals.