Metal and metalloid speciation in plants: Overview, instrumentation, approaches and commonly assessed elements

• Metal(loid) speciation in plants is used in bio-accumulation, -remediation and -fortification studies.
• Sample preparation for metal(loid) speciation studies is critical.
• Metal(loid) species can either be separated by sequential extractions or column separations.
• Detection methods for speciation include XAS, HPLC-ICP-MS, CE-ICP-MS, HPLC-ICP-OES and AAS.
• Commonly speciated elements in plants are As, Se, Sb, Cd, Pb, Mn and Ni.

The ability of plants to hyper-accumulate metals and metalloids from the surrounding environment may pose a significant health risk to both humans and animals since plants form a substantial component of diet. This attribute, however, has also been identified as a useful tool in bioremediation and biomonitoring studies; where assimilated metals and metalloids in plants often correlate to environmental exposure. Since the bioavailability and toxicity of these elements depend upon their chemical form, speciation studies are essential in determining their mobility and metabolic pathways. This can be done in a number of ways where sampling, pre-treatment and storage are all important factors affecting speciation. Appropriate analytical techniques for speciation studies can either be direct methods such as XAS, or indirect methods which require species separation prior to analysis. Separation techniques can either be in the form of sequential extractions or column separation and analyte detection often utilises instrumentation such as ESI-MS, ICP-MS and ICP-OES.