Metal speciation

The total content of the classical heavy metals, lead, cadmium and mercury in foodstuffs and animal feeding stuff, is regulated by EU maximum levels. However, for some trace elements their speciation is very important in terms of food and feed safety and information on the total content only does not give adequate information for correct toxicological risk assessment. For example, in the case of arsenic, the inorganic forms are the most toxic while for mercury, methylmercury is the most toxic form. Seafood is the major dietary source for arsenic and mercury in the European population [23]. For speciation analysis of trace elements the use of either LC or GC with inductively coupled plasma MS (GC- and LC/ICPMS) is currently the state-of-the-art [24,25]. These techniques have been known for a couple of decades but their use is not routine yet, probably due to rather expensive instrumentation, the need for skilled personnel and the lack of standardization, thus clearly defining some of the urgent challenges. Another issue is the lack of rapid and simple field sensors for speciation analysis which address at least partly the toxicity of the specific metal forms. In the past, different microbial biosensors were developed and evaluated in aqueous model systems [26,27]. These transcription activation biosensors contain a reporter gene under metal responsive element(s). Once the cell and the responsive element detect a metal/metalloid the responsive element on the DNA will switch on the transcriptional and translational machinery producing firefly luciferase leading to light emission directly responding to the concentration. These metal biosensors determine intrinsically the bioavailable fraction of the metal, giving an estimation of the toxic potential and complementing the chemical methods where total concentration of the metals is determined. The ability of this type of biosensors to work in real food and feed extracts is a major challenge that still needs to be explored. Some people are hesitating to work with such genetically modified bacterial cell biosensors. To overcome these hesitations luminescent cells immobilised onto a fibre dipstick might be applied to metal and metal speciation analysis [28].

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