Levels of organic and inorganic mercury in human blood predicted from measurements of total mercury.

The toxicologically relevant mercury species inorganic and organic Hg in blood are frequently determined by separate measurements of total Hg and of inorganic Hg, with their difference indicating organic Hg. It is shown that the different partition of inorganic and organic Hg between erythrocytes and plasma (e/p ratio) can be used to calculate the concentrations of either Hg species in either blood constituent from measurement of total Hg only. This was tested on the blood of different groups of volunteers. The calculated concentrations of inorganic and organic Hg in cells and plasma were then compared by linear regression with their previously measured counterparts. An accurate prediction has been found for individual levels of inorganic Hg in plasma and organic Hg in cells. These calculated levels were little affected by variations of the e/p ratios. The coincidence between calculated and measured levels of inorganic Hg in cells and organic Hg in plasma was more sensitive to alterations of the e/p ratios. In conclusion, the relevant concentrations of inorganic Hg in plasma and organic Hg in cells can reliably be calculated from measurements of total Hg and from assumed e/p ratios. This means a sizeable reduction of analytical work, and also provides specific information in cases of low-level co-exposure to both Hg species. Besides the possibility to introduce automated analyses of total Hg in mercury speciation in blood, the proposed calculation scheme has the potential to easily enlarge the data base in epidemiological and toxicological surveys of mercury exposure.

Inter-individual variations of human mercury exposure biomarkers: a cross-sectional assessment.

BACKGROUND: Biomarkers for mercury (Hg) exposure have frequently been used to assess exposure and risk in various groups of the general population. We have evaluated the most frequently used biomarkers and the physiology on which they are based, to explore the inter-individual variations and their suitability for exposure assessment. METHODS: Concentrations of total Hg (THg), inorganic Hg (IHg) and organic Hg (OHg, assumed to be methylmercury; MeHg) were determined in whole blood, red blood cells, plasma, hair and urine from Swedish men and women. An automated multiple injection cold vapour atomic fluorescence spectrophotometry analytical system for Hg analysis was developed, which provided high sensitivity, accuracy, and precision. The distribution of the various mercury forms in the different biological media was explored. RESULTS: About 90% of the mercury found in the red blood cells was in the form of MeHg with small inter-individual variations, and part of the IHg found in the red blood cells could be attributed to demethylated MeHg. THg in plasma was associated with both IHg and MeHg, with large inter-individual variations in the distribution between red blood cells and plasma. THg in hair reflects MeHg exposure at all exposure levels, and not IHg exposure. The small fraction of IHg in hair is most probably emanating from demethylated MeHg. The inter-individual variation in the blood to hair ratio was very large. The variability seemed to decrease with increasing OHg in blood, most probably due to more frequent fish consumption and thereby blood concentrations approaching steady state. THg in urine reflected IHg exposure, also at very low IHg exposure levels. CONCLUSION: The use of THg concentration in whole blood as a proxy for MeHg exposure will give rise to an overestimation of the MeHg exposure depending on the degree of IHg exposure, why speciation of mercury forms is needed. THg in RBC and hair are suitable proxies for MeHg exposure. Using THg concentration in plasma as a measure of IHg exposure can lead to significant exposure misclassification. THg in urine is a suitable proxy for IHg exposure.

Blood organic mercury and dietary mercury intake: National Health and Nutrition Examination Survey, 1999 and 2000.

Blood organic mercury (i.e., methyl mercury) concentrations among 1,709 women who were participants in the National Health and Nutrition Examination Survey (NHANES) in 1999 and 2000 (1999-2000 NHANES) were 0.6 microg/L at the 50th percentile and ranged from concentrations that were nondetectable (5th percentile) to 6.7 microg/L (95th percentile). Blood organic/methyl mercury reflects methyl mercury intake from fish and shellfish as determined from a methyl mercury exposure parameter based on 24-hr dietary recall, 30-day food frequency, and mean concentrations of mercury in the fish/shellfish species reported as consumed (multiple correlation coefficient > 0.5). Blood organic/methyl mercury concentrations were lowest among Mexican Americans and highest among participants who designated themselves in the Other racial/ethnic category, which includes Asians, Native Americans, and Pacific Islanders. Blood organic/methyl mercury concentrations were ~1.5 times higher among women 30-49 years of age than among women 16-29 years of age. Blood mercury (BHg) concentrations were seven times higher among women who reported eating nine or more fish and/or shellfish meals within the past 30 days than among women who reported no fish and/or shellfish consumption in the past 30 days. Blood organic/methyl mercury concentrations greater than or equal to 5.8 microg/L were lowest among Mexican Americans (2.0%) and highest among examinees in the Other racial/ethnic category (21.7%). Based on the distribution of BHg concentrations among the adult female participants in 1999-2000 NHANES and the number of U.S. births in 2000, > 300,000 newborns each year in the United States may have been exposed in utero to methyl mercury concentrations higher than those considered to be without increased risk of adverse neurodevelopmental effects associated with methyl mercury exposure.

Factors affecting blood mercury concentrations in practicing dentists.

It has been suggested that mercury vapor may be transformed into highly toxic organomercury compounds by micro-organisms in the oral cavity and gastrointestinal tract. If this hypothesis is correct, practicing dentists might be expected to have concentrations of organic mercury in their blood higher than that found in non-dentists. Blood mercury concentrations of practicing dentists and non-dentists were determined by means of cold-vapor atomic absorption spectrophotometry. Potential sources of mercury exposure were identified in both dentists and non-dentists through a questionnaire completed at the time of sampling. Concentrations of total and inorganic blood mercury were significantly higher in dentists than in non-dentists. The organomercury concentrations of the two groups were not statistically different (p greater than or equal to 0.05). The high concentration of inorganic mercury in the blood of dentists was not related to the organomercury level, suggesting that biotransformation of inorganic mercury to organomercury does not occur in vivo. However, the concentration of blood organomercury was positively correlated with the frequency of fish consumption. There was no correlation between the number of amalgam restorations and the concentration of inorganic blood mercury for both groups. Accidental mercury spills in the dental operatory may contribute most to the concentration of inorganic blood mercury in the blood of dentists.