Application of neutron activation analysis to the monitoring of trace elements in Brazilian foodstuffs

Due to lack of data on trace element levels in Brazilian foodstuffs, nuclear analytical techniques were used to determine about twenty elements in foods samples collected from local markets of the city of Sao Paulo. Drinking water was also analyzed. The methods employed were mainly instrumental and radiochemical neutron activation analysis. In the case of the analysis of toxic elements, such as mercury, selenium, arsenic and antimony, the purely instrumental approach failed in yielding results for very low concentrations of these elements. For INAA, samples and multielemental synthetic standards were irradiated in the IEA R1 research reactor for periods of time ranging from minutes to several hours, under thermal neutron fluxes from 1011 to 1013 n·cm-2·s-1; after suitable cooling times, γ-ray spectra were measured using a Ge(Li) or Ge solid state detector. The RNAA approach involved the distillation of mercury and selenium in HBr medium; selenium was then reduced to the metal form with sodium metabisulphide and mercury was precipitated as sulphide with thioacetamide. For water analysis, a preconcentration procedure based on retention of several elements in a Chelex-100 resin was employed. The elements retained were Hg, Cr, Zn, Fe, Co while Se was measured in the effluent after absorption on active charcoal. The levels of the trace inorganic elements determined in the Brazilian foodstuffs analyzed were always below the levels established by the existing regulations in our country. (author). 16 refs, 18 tabs