National secular trends in ambient air volatile organic compound levels and biomarkers of exposure in the United States

Abstract

Background: Exposure to air pollution is a leading cause of global mortality. Volatile organic compounds (VOCs) are constituents of ambient air that could exert adverse health effects.

Objective: To examine the relationship between VOC levels in ambient air and individual-level exposure to VOCs, as assessed by urinary VOC metabolites.

Methods: Secular trends in 11 ambient air VOCs (2005-2013) and individual-level metabolites of 14 VOCs (2005-2014) were assessed using National Monitoring Programs (NMP) and National Health and Nutrition Examination Survey (NHANES) data, respectively. To isolate environmental exposure, individuals reporting exposure to tobacco smoke were excluded. Quantile regression models were used to assess secular trends in VOC exposure, and survey-weighted regression models were built to identify factors associated with VOC exposure.

Results: All annual levels of ambient VOCs decreased from 2005 to 2013 (Range: 12.5%-77.2%). However, 11 of the corresponding VOC metabolites increased during the same time (Range: 0.3%-53.6%). There was a proportional change in patterns of VOC exposure across NHANES waves, with the middle quantiles of exposure showing the largest increase. VOC exposures were significantly associated with age, sex, race, education, and physical inactivity, but not with secular VOC trends.

Discussion: In the United States, individual-level exposure to several VOCs increased between 2005 and 2014 despite a decline in ambient air VOC levels. This inverse relationship suggests that ambient VOCs are not the primary source of VOC exposure, therefore, decreasing ambient VOCs alone may not be sufficient to protect against the adverse health effects associated with VOC exposure.

Keywords: Air pollution; Biomarkers of exposure; Environmental health; NHANES; Secular trends; VOCs; Volatile organic compounds.

Fig. 1.. Percent change in ambient volatile organic compounds and urinary metabolites of volatile organic compounds.

National arithmetic mean percent change for 11 ambient VOCs as reported by the yearly summary statistics for VOC monitoring in the National Monitoring Program (NMP) annual reports from 2005 and to 2013 and geometric mean percent change for 14 corresponding UM-VOCs from 2005–06 to 2013–14 NHANES waves. NHANES = National Health and Nutrition Examination Survey; A, VC, EO = Acrylonitrile, vinyl chloride, ethylene oxide; VOC = volatile organic compound; UM-VOC= urinary metabolite of VOC.

Fig. 2.. Proportion of UM-VOCs attributed to each metabolite by NHANES wave.

Proportion of select UM-VOCs attributed to each metabolite by NHANES wave, (A) 2005–06, (B) 2011–12 and (C) 2013–14. The UM-VOCs represented are metabolite which are significantly changing across the NHANES waves. NHANES= National Health and Nutrition Examination Survey; UM-VOC = urinary metabolite of volatile organic compound.

Fig. 3.. Quantile regression models of cumulative VOC exposure regressed by NHANES wave.

Quantile plot for associations between cumulative VOC exposure score differences by NHANES wave where the 2005–06 NHANES wave is the referent group. The y-axes represent the cumulative VOC exposure score difference. Estimate and 95% confidence intervals are shown for 0.1, 0.2, 0.3, 0.4, 0.5 0.6, 0.7, 0.8 and 0.9 quantiles for NHANES waves (A) 2011–12 vs. 2005–06 and (B) 2013–14 vs. 2005–06. VOC= volatile organic compound; NHANES= National Health and Nutrition Examination Survey

Fig. 4.. Factor analysis path diagram of NHANES urinary metabolites of volatile organic compounds.

Factor analysis of creatinine normalized log transformed UM-VOCs. Loading estimates > 0.3 are indicated by the directed links from factors to variables. The double-headed links show correlations between factors. NHANES= National Health and Nutrition Examination Survey; UM-VOC = urinary metabolite of volatile organic compound.