Some gases, such as mercury vapor and carbon monoxide, are toxic. Other gases, such as carbon dioxide, are not very toxic, but may contribute to the Greenhouse Effect. If left outside in the open air, fine-grained solid wastes and other materials may readily blow into the atmosphere. As mentioned in the Aral Sea discussions on p. 156, microorganisms and toxins may accumulate in dust, blow into the atmosphere and create respiratory and other health problems in humans and wildlife that live down wind. Eventually air pollutants may fall into lakes and streams, where they become water pollutants.
Acid rain is a common example.
If buried, wastes may release contaminants into soils, sediments, groundwater and surface water. If left on the surface, solid wastes may interact with rainwater and produce hazardous liquid wastes, called leachates . Acid mine drainage is a common example of a leachate. Leachates and other liquid wastes may flow as surface runoff into nearby lakes and streams or infiltrate into the subsurface to contaminant groundwater. Dissolved contaminants may readily move between surface and ground waters.