2004-05 Speciation of Metallic Compounds

When we think of metals with respect to human health we tend to categorize them as toxic or non-toxic without consideration to what form they are in.

The B.C. Contaminated Sites Regulation has a lower limit for arsenic of 15 mg/kg while edible seafood products such as crab and lobster commonly contain between 20 and 30 mg/kg arsenic. Kelp sold as a health supplement may contain up to 50 mg/kg. Similarly, the BC CSR limits tin in agricultural soil to 5 mg/kg while canned pineapple may contain up to 250 mg/kg. These apparent contradictions are based on the form of the metals assumed to be present in various situations. 

Most metals are present in a variety of compounds, both inorganic and organically bound. The toxicological properties of metals however can vary greatly based on oxidation state. In addition, how the metal behaves in the environment in terms of mobility and bioavailability and how the metal reacts to treatment methods is very much a function of the chemical form rather than total concentration. Unfortunately, any information about chemical form is lost in the digestion process.

Recent developments in analytical chemistry involving interfacing separation techniques such as gas or liquid chromatography with sensitive, specific detection methods such as ICP Mass Spectroscopy have opened the door for more selective identification and quantitation of metallic species. “Soft” extraction techniques which do not alter the chemical form of the metals can be employed to solubilize the compounds of interest. The resulting extract can be run through a chromatography column to separate the compounds and then introduced into an ICPMS for positive detection.