Absorbing phthalates from the air: experimental evidence for substantial transdermal uptake of diethyl- and di(n-butyl) phthalate vapors

Toxicological and epidemiologic studies have shown associations between phthalate esters and various adverse health effects. Fundamental considerations indicate that lower molecular weight phthalates are dermally absorbed from air at rates comparable to or larger than inhalation intake. Yet this pathway has not been experimentally evaluated and has been largely overlooked when assessing exposure to phthalate esters. Hence we designed a study to investigate transdermal uptake, directly from air, of diethyl phthalate (DEP) and di(n-butyl) phthalate (DnBP). Six human subjects were exposed for six hours in a chamber containing known concentrations of DEP and DnBP in air. In one set of experiments the subjects wore a hood and breathed phthalate free air. In another set of experiments the subjects were exposed without a hood. All urinations were collected from the initiation of exposure until 54 hours later. Metabolites of DEP and DnBP were measured in these samples and used to calculate parent phthalate intake. For DEP the median dermal uptake directly from air was comparable to inhalation intake, while for DnBP the median dermal uptake was 80% of inhalation intake. For other semivolatile organic compounds (SVOCs) whose molecular weight and octanol/air partition coefficients (Kow) are in a “Goldilocks zone”, direct absorption from air is also anticipated to be significant.