Temporal Trends in Phthalate Exposures: Findings from the National Health and Nutrition Examination Survey, 2001-2010

BACKGROUND: Phthalates are ubiquitous environmental contaminants. Because of potential adverse effects on human health, butylbenzyl phthalate [BBzP; metabolite, monobenzyl phthalate (MBzP)], di-n-butyl phthalate [DnBP; metabolite, mono-n-butyl phthalate (MnBP)], and di(2-ethylhexyl) phthalate (DEHP) are being replaced by substitutes including other phthalates; however, little is known about consequent trends in population-level exposures. OBJECTIVE: We examined temporal trends in urinary concentrations of phthalate metabolites in the general U. S. population and whether trends vary by sociodemographic characteristics. METHODS: We combined data on 11 phthalate metabolites for 11,071 participants from five cycles of the National Health and Nutrition Examination Survey (2001-2010). Percent changes and least square geometric means (LSGMs) were calculated from multivariate regression models. RESULTS: LSGM concentrations of monoethyl phthalate, MnBP, MBzP, and SDEHP metabolites decreased between 2001-2002 and 2009-2010 [ percent change (95% CI): -42% (- 49, - 34); -17% (-23, -9); -32% (-39, -23) and -37% (-46, -26), respectively]. In contrast, LSGM concentrations of monoisobutyl phthalate, mono(3-carboxypropyl) phthalate (MCPP), monocarboxyoctyl phthalate, and monocarboxynonyl phthalate (MCNP) increased over the study period [percent change (95% CI): 206% (178, 236); 25% (8, 45); 149% (102, 207); and 15% (1, 30), respectively]. Trends varied by subpopulations for certain phthalates. For example, LSGM concentrations of SDEHP metabolites, MCPP, and MCNP were higher in children than adults, but the gap between groups narrowed over time (P-interaction < 0.01). CONCLUSIONS: Exposure of the U. S. population to phthalates has changed in the last decade. Data gaps make it difficult to explain trends, but legislative activity and advocacy campaigns by non-governmental organizations may play a role in changing trends.