The Methylation of Metals and Metalloids in Aquatic Systems

This chapter will focus on the formation processes and fate of the more common methylated metals and metalloids in the aquatic environment, focusing on both the ocean and freshwa‐ ter ecosystems. In addition to the formation of the methylated compounds, the biotic and abiotic degradation of these compounds in the natural environment will also be discussed. The formation pathways and the microbes responsible for environmental methylation of dif‐ ferent elements will be examined in detail with the focus on the organometallic or organic metalloid compounds of Hg, As, Sb and Se. Methylated compounds of other metal(loids)s will also be discussed. Such compounds are defined here as those in which the attachment of the organic moiety to the metal/metalloid ion is directly through a carbon-metal bound. Most of these bonds are covalent, especially for the metals and metalloids which have filled d and f orbitals [1]. There is an ever growing field of organometallic chemistry related to the use of manufactured transition metal compounds as catalysts or in organic production syn‐ thesis, or for other uses (e.g. alkylated Pb and butylated Sn compounds). These compounds will not be discussed in detail.