Toenail mercury concentration as a biomarker of methylmercury exposure

The aim of the study was to assess the value of toenail mercury as an alternative biomarker of methylmercury exposure compared with blood and hair. Blood, hair and toenail total mercury concentrations were determined simultaneously in a southern urban sea n = 35 and an eastern rural lake n = 37 group and separately in a central Finnish rural lake n = 39 group. A questionnaire based index was used for estimating frequency of exposure taking into account high vs low mercury fish. Total mercury concentration was determined by cold vapour atomic absorption spectrophotometry. The mean Fish Consumption Frequency Index varied from 4.7 to 9.9 on a scale of 1-20. The blood, hair and toenail mercury mean concentrations ranged from 2.9 to 14.6 g l-1, 0.45 to 1.57 mg kg-1 and 0.20 to 0.54 mg kg-1, respectively. In the combined southern and eastern groups n = 72 sampled simultaneously, the correlations between blood and hair mercury were r = 0.92 and that of blood and toenails r = 0.78 p 0.0001 . In the central Finnish group the correlations were more moderate. In the three groups all three biomarkers correlated highly with the fish consumption index, r = 0.43-0.76 p 0.0001 . Men consumed high mercury fish more frequently than women, 8.6 vs 6.6 n.s. The mean mercury levels of blood and hair were two fold, but toenail mercury levels were only 30 higher in men compared with those of the women. The relative sensitivity slope of the sources decreased in the order, blood hair toenails. In conclusion, toenails, an easily accessible tissue for the estimation of methylmercury exposure, have been shown to be closely correlated with the well established samples for biomarkers, viz. blood and hair mercury.