Parameter Tree:
EARTH SCIENCE > HUMAN DIMENSIONS > ENVIRONMENTAL IMPACTS > HEAVY METALS CONCENTRATION

Definition:
Heavy Metals are any of the high atomic weight metals such as lead, mercury, cadmium, and zinc.

Reference:
Nebel, Bernard J. and Richard T. Wright. 1998. Environmental Science: the Way the World Works.-6th ed. Prentice Hall, Inc. Upper Saddle River, New Jersey.