Trends in and factors affecting the observed levels of urinary inorganic and total blood mercury among US children, adolescents, adults, and senior citizens over 2005-2012

•Smokers had lower levels of blood total Hg than nonsmokers.•Those in unclassified racial/ethnic group had the highest levels of total blood Hg.•Levels of total blood Hg decreased over 2005-2012 for children, adolescents, and adults.•Levels of urinary inorganic Hg decreased over 2005-2012 for children, adolescents, and adults.•Among adults and senior citizens, males had higher total blood Hg than females.

Data from National Health and Nutrition Examination Survey (NHANES) for 2005-2012 were used to (i) study adjusted and unadjusted trends in the levels of urinary inorganic mercury (UIHG) and total blood mercury (TBHG) and (ii) factors that affect the observed levels of UIHG and TBHG among children aged 1-5 (CHLD15) and 6-11 (CHLD611) years, adolescents aged 12-19 years (ADOL), adults aged 20-64 years (ADLT), and senior citizens aged > = 65 years (SNR). Decrease in adjusted levels of UIHG for each 2-year NHANES cycle for CHLD611 was 0.08114 ng/L, 0.08379 ng/L for ADOLs, and 0.12 ng/L for ADLTs. Decreases in adjusted levels (AGM) of TBHG for each 2-year NHANES cycle were: 0.0632 ng/L for CHLD15, 0.10239 ng/L for CHLD611, 0.06424 ng/L for ADOLs, and 0.056088 ng/L for ADLTs. Among CHLD15 (0.34 vs. 0.39 μg/L, p < 0.01) and CHLD611 (0.42 vs. 0.44 μg/L, p = 0.04), males had lower AGMs for TBHG than females but among ADLTs (0.84 vs. 0.80 μg/L, p < 0.01) and SNRs (0.82 vs. 0.71 μg/L, p < 0.01) the reverse was true. For UIHG, for ADLTs (0.33 vs. 0.45 μg/L, p < 0.01) and SNRs (0.27 vs. 0.35 μg/L, p < 0.01) males had lower AGMs than females. Irrespective of age, those who were in unclassified race/ethnic group had the highest AGMs when compared with non-Hispanic whites, non-Hispanic blacks, and Mexican Americans and the differences, more often than not, were statistically significant (p < 0.01). Irrespective of age, fish and shellfish consumption during the last 30 days was associated with higher AGMs for both UIHG and TBHG than when fish and shellfish were not consumed and the differences were always statistically significant (p < 0.01). Nonsmoker ADLTs (0.86 vs. 0.78 μg/L, p < 0.01) and SNRs (0.83 vs. 0.71 μg/L, p < 0.01) were found to have higher adjusted levels of TBHG than smokers. It is hypothesized that constituents in tobacco smoke may accelerate excretion of mercury from the body.