Chlordane had been released into the environment primarily from its application as an insecticide. In the aquatic environment, chlordane is very persistent in the adsorbed state. Trans -nonachlor is the most bioaccumulative of the chlordanes exceeding human health guidelines in fish tissue. As a chlordane constituent, it is also one of the chemicals addressed by the Great Lakes Initiative. In the Lake Michigan Mass Balance, trans -nonachlor will serve as a model for the cyclodiene pesticides.
Mercury occurs naturally in coal and mineral ores.
About 3x10 -6 percent of the earth's crust is made of mercury mostly in combination with sulfur to form more than 25 different minerals. It is used in battery cells, barometers, thermometers, switches, fluorescent lamps, mercury arc lamps producing ultraviolet light, and as a catalyst in the oxidation of organic compounds. It is estimated that about 11,000 metric tons of mercury are released annually to the air, soil, and water through anthropogenic sources. As an elemental metal it is extremely persistent in all media. Mercury is readily sorbed to soil organic matter, clays and some hydrous metal oxides.