Toxic trace metal speciation: importance and tools for environmental and biological analysis

Total element determinations of toxic metals, both in environmental and in biological materials or in living organisms, are increasingly demanded by society. This determination of low levels of toxic metals, and also of essential and therapeutic trace elements, is normally accomplished by atomic spectrometry methods, very appropriate for this analytical task (e.g. concentrations below 10 pg.g-’ in tissues, 10 pg.1-l in biological fluids or less than 1 pg.1” in river waters, need today to be monitored). However, every chemist in his laboratory recognises that a trace element, and so a toxic metal, can exist in a given real sample, e.g. a sediment, urine, serum, etc, in a most varied number of physico-chemical forms (e.g. in the case of lead: Pbt2, Pb(OH)2, Pb(OH)i, (CH&Pb, (CH3-CH2)4Pb, etc). More recently, the scientific community has concluded that toxicity, bioavailability, bioactivity, transport in the organism, bio-geological distributionltransportation and, thus, the eventual impact of the toxic element in our body and environment, will be dictated by the particular species or form present in the sample. In this sense, total element determinations by atomic spectroscopy, as discussed before, of a toxic element as As, Hg or Sn are insufficient today, and sometimes misleading, to assess the toxicity of a food or sediment (e.g. arsenobetaine is not toxic, methylmercury is much more toxic than Hg’2 and tributyltin is a most potent biocide, while Sn(IV) is not). Therefore, additional “speciation” information to complement total toxic element determinations is being increasingly demanded, both in environmental and in clinicaVbiologica1 issues (1,2).