Assessing natural contents of hazardous metals by different analytical methods and its impact on environmental legislative measures.

A variety of analytical techniques are commonly used to assess natural metal concentrations in soils. Despite the choice of the analytical procedure may appear as a scarcely important issue, through an example from the Po Plain we document that for specific hazardous metals the arbitrary choice between separate analytical techniques may have contrasting legislative implications. Comparative analyses of 160 soil samples obtained with X-ray fluorescence (XRF) and aqua-regia inductive coupled plasma mass spectrometry (ICP-MS), respectively, reveal a systematic lower efficiency of Cr determination by ICP-MS (45-60% of XRF determinations), irrespective of the laboratory chosen. Maximum permissible concentrations of Cr for residential and recreational sites were invariably exceeded by sediments deriving from Cr-rich parent rocks after XRF analyses. In contrast, replicate determinations following aqua regia digestion were generally below the threshold values, defining the same soils as unpolluted. This study thus emphasizes the need for strictly standardized procedures of metal determination.