ABSTRACT
Metalloids such as arsenic and antimony, and metals such as mercury, lead, and tin-which occupy a similar location to metalloids in the periodic system-all tend to form stable covalent bonds with organic groups. Some authorities regard tin as a metalloid. By contrast, metals such as sodium, potassium, calcium, strontium, and barium, which belong to groups 1 and 2 of the periodic system, do not form covalent bonds with organic groups. The compounds used as examples here all possess covalent linkages between a metal and an organic group-most commonly an alkyl group. The elements in question are mercury, tin, lead, and arsenic, all of which are appreciably toxic in their inorganic forms as well as in their organometallic forms. The attachment of the organic group to the metal can bring fundamental changes in its chemical properties, and consequently in its environmental fate and toxic action. In particular, the attachment of alkyl or other nonpolar groups to metals increases lipophilicity and thereby enhances movement into and across biological membranes, storage in fat depots, and adsorption by the colloids of soils and sediments. Thus, the question of speciation is critical to understanding the ecotoxicology of these metals.
