Are blood lead levels in the United States still declining? The United States National Health Nutrition and Examination Survey 1999-2016

Abstract

Introduction: Lead is a well-documented environmental toxin without a safe blood level. The current upper reference blood lead level (BLL), 5 μg/dL, came from the 97.5th percentile in children aged 1 to 5 years in the US National Health Nutrition and Examination Survey (NHANES) 2007-2010. We studied BLL, as reported in NHANES, to estimate the proportion of children with BLL ≥5 μg/dL. Methods: We analysed 68 877 participants with BLL measurements in NHANES 1999-2016 using SPSS (Window version 25.0; IBM Corp, Armonk [NY], US). Results: In NHANES 1999-2000, 2001-2002, 2003-2004, 2005-2006, 2007-2008, 2009-2010, 2011-2012, 2013-2014, and 2015-2016, the mean BLLs and 95% confidence intervals (CIs) were 1.66 (1.63-1.68), 1.46 (1.44-1.47), 1.43 (1.42-1.44), 1.29 (1.28-1.31), 1.27 (1.26-1.29), 1.12 (1.11-1.13), 0.97 (0.96-0.99), 0.86 (0.85-0.87), and 0.82 (0.81-0.83) μg/dL, respectively (P<0.001). The decline was significant (P<0.05) after stratification by age, sex, ethnicity, and pregnancy status. The estimated proportions (95% CIs) of children aged 1 to 5 years with elevated BLL in 1999-2000, 2001-2002, 2003-2004, 2005-2006, 2007-2008, 2009-2010, 2011-2012, 2013-2014, and 2015-2016 were 9.7% (7.2%-12.8%), 7.4% (6.1%-9.1%), 5.3% (4.3%-6.4%), 2.9% (2.4%-3.6%), 3.1% (2.6%-3.8%), 2.1% (1.7%-2.7%), 2.0% (1.3%-3.0%), 0.5% (0.4%-0.7%), and 1.3% (0.8%-2.3%), respectively (P<0.001). The estimated 97.5th percentile of BLL in children aged 1-5 years, was 3.71 μg/dL in NHANES 2015-2016. Conclusion: In the overall US population BLLs continue to decline. However, in young children aged 1 to 5 years in 2015-2016, BLLs did not decline and appeared to increase. Data for 2017-2018 are needed to verify if this is a trend. Our data suggest that monitoring BLLs in the population is as necessary as ever and that efforts to reduce environmental exposure to lead must not be relaxed.