Metal speciation and bioavailability: revisiting the ‘big questions’

Environmental context. Four decades of research on metal speciation and bioavailability have failed to answer the ‘big questions’ of the ecological consequences of metal stress. Important, though still insufficient, insights have been gained from analytical approaches derived from inorganic environmental chemistry (targeting the quantification of free metal ion or ‘labile’ metal concentrations) and from organic environmental chemistry (focusing on the structure of ambient metal species). The ‘omics’ approach, not yet widely applied to this topic, offers the possibility of providing sufficient information to identify a quantitative signature of metal stress.