Considerations for estimating daily intake values of non-persistent environmental endocrine disruptors based on urinary biomonitoring data

IntroductionHuman exposure to chemicals may be estimated by back-calculating urinary concentrations resulting from biomonitoring studies if knowledge of the chemical's toxicokinetic properties is available.AimTo review available toxicokinetic data for back-calculating urinary concentrations into daily intake values for bisphenol A, phthalates, parabens and triclosan, and to identify knowledge gaps.MethodsHuman data was evaluated and supplied with relevant animal data. Focus was on recovery of the administered dose, the route of administration and on differences between humans and animals.ResultsTwo human toxicokinetic studies are currently used to conclude that an oral dose of bisphenol A is recoverable in urine and that no free bisphenol A is present in plasma in spite of several contradicting biominotoring studies.Urinary recovery of an oral dose of phthalates in humans is complicated to assess due to extensive metabolism. In animals using 14C-marked phthalates, near-complete recovery is observed. An oral dose of 14C-marked parabens is also almost completely recovered in animals. In both humans and animals however, two unspecific metabolites are formed, which complicates the back-calculation of parabens in humans. The recovery of both oral and dermal triclosan in humans has been studied, but due to background levels of triclosan, the back-calculation is difficult to perform.ConclusionDue to limited data, reasonable estimates of daily intake values based on urinary data are often not possible to obtain. Several knowledge gaps were identified and new studies were suggested. The route of administration used in toxicokinetic studies often does not match realistic scenarios.