For example, electric eels can store charge via concentration gradients of biochemically common alkali metal ions across the membranes of electroplaque cells. In contrast, most batteries used for storing charge require biochemically foreign, toxic elements, such as lead and cadmium. Because of this strategic difference, manmade technologies often distribute throughout the environment persistent pollutants that are toxic because they contain elements that are used sparingly or not at all in biochemistry. Persistent bioaccumulative pollutants pose the greatest chemical threat to sustainability. They can be grouped into two classes.
New toxicities continue to be discovered for biologically uncommon elements.
The second class consists of degradation-resistant molecules. Many characterized examples originate from the chlorine industry and are also potently bioaccumulative. All are organochlorines. Each compartment represents a separate chemistry so that, for example, thousands of compartments are associated with stratospheric chemistry or with a human cell. An environmentally mobile persistent pollutant can move from compartment to compartment, sampling a large number and finding those compartments that it can perturb.