Trace Element Speciation

Trace element speciation is an important factor in the toxicity and movements of trace elements in aquatic ecosystems. Many trace elements have several different chemical forms that can be present at different concentrations, and which may change with inputs and biogeochemical reactions in the system. For example, arsenic is commonly found in two inorganic forms, arsenate and arsenite, and at least two organic forms, monomethyl and dimethyl arsenic. Arsenate is the predominant form in oxygenated waters, while arsenite is the predominant form in sediments and anoxic waters. However, phytoplankton and other biota remove arsenate from the water, convert some to arsenite and release it, and under some conditions, notably phosphorus limitation, release dimethyl arsenic. Dimethyl arsenic, in turn, is converted to monomethyl arsenic and arsenate by bacteria. Arsenate and arsenite are highly toxic forms, while the methyl species are much less toxic. Other metals that have important speciation issues include mercury (inorganic, methyl and dimethyl mercury), selenium (selenate, selenite and organic selenium), chromium (chromate and chromite), and copper (inorganic free copper and organically and inorganically complexed Cu). These speciation issues complicate the analysis of and evaluation of the effects of these trace elements, since complex and difficult analytical techniques are required to accurately analyze separate forms, and the different forms can have dramatically different chemical and biological behaviors in the environment.

The Trace Element Lab has been working in the field of trace element speciation analysis, and evaluations of its consequence for over 20 years. This requires highly skilled chemists, and considerable and expensive equipment. The Trace Element Lab has state of the art equipment for speciation of trace elements, including ICP-MS, Atomic Absorption Spectrometers, ICP-OES, gas chromatographs, and other tools for the job.