ABSTRACT
A casual glance at the periodic table shows that most of the elements (about threefourths) are metals or metalloids.* It often happens in environmental literature that little or no distinction is made between metals and metalloids, especially for the metalloids arsenic, selenium, and antimony. To discuss their chemical behavior, the elemental metals may be divided into three general classes:
1. Alkali metals: Li, Na, K, Rb, Cs, and Fr (periodic table group 1A). 2. Alkaline metals: Be, Mg, Ca, Sr, Ba, and Ra (periodic table group 2A). 3. Metals not in the alkali or alkaline groups include the transition metals (all
the group B periodic table metals), the metals and metalloids in groups 3A through 6A, and metals whose classifications are not based primarily on periodic table groups, the so-called trace or heavy metals.y
Heavy metals in surface waters can be from natural or anthropogenic sources. Currently, anthropogenic inputs of metals exceed natural inputs. Living organisms require trace amounts of some heavy metals, including cobalt, copper, iron, manganese, molybdenum, vanadium, strontium, and zinc. Excessive levels of essential metals, however, can be detrimental to the organism. Nonessential heavy metals of
particular concern because of their toxicity are cadmium, chromium, mercury, lead, arsenic, and antimony.
