Assessment of reference values for mercury in urine: the results of an Italian polycentric study

The results of a polycentric study to assess the reference values of urinary mercury (U-Hg) in four Italian cities are presented. A total of 383 subjects were selected on the basis of standardised criteria by a questionnaire on personal habits, lifestyle, occupational or non-occupational exposure to Hg, medical history, number and area of dental amalgams. U-Hg was determined by hydride generation atomic absorption method (HG-AAS), with a detection limit of 0.5 μg/l and by flow injection (FI) inductively coupled plasma mass spectrometry (ICP-MS), with a detection limit of 0.03 μg/l. The median value of U-Hg, determined by HG-AAS, was 0.78 μg/g creatinine (0.75 for males and 0.83 for females), with 5° and 95° percentiles, respectively, of 0.17 and 3.66 μg/g creatinine. When determined by FI ICP-MS, the median value was 0.79 μg/ g creatinine (0.77 for males and 0.79 for females) with 5° and 95° percentiles of, respectively, 0.12 and 5.02 μg/g creatinine. Among the independent variables, city of origin, area of dental amalgams, fish intake and tobacco smoking significantly influenced the U-Hg levels. The U-Hg reference values from this survey are lower than those from other recent investigations, probably due to characteristics and selection of the examined individuals and to the strict control of pre-analytical and analytical factors of variability.