Blood and urine inorganic and organic mercury levels in the United States: The United States National Health and Nutrition Examination Survey 1999-2016

Abstract

Introduction: Mercury is an environmental hazard. Therefore, we studied recent trends in the blood level of organic and inorganic mercury in the United States. Methods: A total of 56 445 participants that had blood mercury and urine mercury measurements in NHANES (The United States National Health and Nutrition Examination Survey) 1999-2016 were included. The organic mercury level was obtained by subtracting the inorganic mercury level from the total mercury level. Results were analysed using SPSS complex sample module version 25. Pregnant women and children aged <20 years were analysed as subgroups. Results: Blood inorganic mercury level and urine mercury level have been decreasing between 1999 and 2016 (P<0.001). Blood inorganic mercury level decreased from (geometric mean [95% confidence interval]) 0.31 (0.31-0.31) μg/L in 1999-2000 to 0.21 (0.21-0.22) μg/L in 2015-2016 (P<0.001). Urine mercury level decreased from 0.75 (0.71-0.80) μg/L in 1999-2000 to 0.16 (0.16-0.17) μg/L in 2015-2016 (P<0.001). In contrast, blood organic mercury level increased from 0.08 (0.07-0.10) μg/L to 0.17 (0.16-0.18) μg/L during 1999-2016. Blood organic mercury increased significantly (P<0.001) from 0.03 (0.02-0.03) μg/L to 0.07 (0.06-0.07) μg/L in children aged <20 years and from 0.14 (0.09-0.21) μg/L to 0.36 (0.16-0.83) μg/L in pregnant women. Conclusion: A steady decline was observed in both blood inorganic mercury level and urine mercury level over the period 1999-2016. However, blood organic mercury levels have been increasing, which is of particular concern for pregnant women and children. Environmental pollution by inorganic mercury has been decreasing. The increase in organic mercury may be related to changes in diet, such as increased consumption of seafood.