The contaminant sources just presented are associated with human activities involving the production, use, and disposal of chemicals and products.
It is important to realize that there are also ‘‘natural’’ sources of contaminants.
A major source of such contaminants is drinking water pumped from aquifers composed of sediments and rocks containing naturally occurring elements that dissolve into the groundwater.
One example, that of radioactive contaminants such as radon, was discussed
in the previous section
.Another major example is arsenic, which has become of great concern in recent years. (See Case Study 16.1.)