Study On Assessment Of Dermal And Total Exposure To Phthalate Esters, Including How They Are Related

Phthalate esters(PAE) have been mainly used as plasticizer and widely used in the industry and our daily life. Humans can be exposed to PAE through inhalation, ingestion, and dermal absorption. PAE exposures are associated with various human adverse health effects, including reproductive harm and endocrine disorder. Exposure assessment of PAE is the basis of PAE risk assessment and control. However, even though lack of rele vant scientific evidence, dermal exposure to PAE has been routinely overlooked. Very recent studies indicate that dermal exposure to some PAE are comparable to or even larger than inhalation exposure. However, scientific method and basic data are lacking for assessing PAE dermal exposure and its contribution to PAE total exposure. Therefore, relevant studies have been carried out and presented in this dissertation. The primary conclusions are as follows:(1) A transient model considering the convective mass transfer around human skin has been developed to assess dermal exposure to gas phase chemicals. Analytical solutions to predict dermal dose have been derived. Then, the model is used to predict dermal absorption of gas phase PAE under two typical exposure scenarios, which indicate that the dermally absorbed dose will be largely overestimated by the steady state model, and if bathing does extract PAE stored in skin to a meaningful degree, it could be a valuable intervention method to control PAE dermal exposure. These results provide a basis to predict dermal exposure to gas phase PAE.(2) The PAE levels and its distribution characteristics on different human body locations(i.e. forehead, back, forearm, calf, back-of-hand and palm) have been analyzed for the first time. The results show that DEHP levels on palm > back-of-hand > forearm > forehead in summer while DEHP levels on palm ≈ back of hand > forehead > forearm ≈ back > calf in winter, and Di BP and Dn BP levels on palm > back-of-hand > forearm in summer while Di BP and Dn BP levels on palm ≈ back of hand > forearm ≈ back > calf in winter. The ratios between PAE levels on forehead, forearm, back, calf and hand are found to be log-normally distributed. Based on the measured results, suggestions have been put forward to assess total dermal exposure. In addition, PAE dermal absorbed doses occurring at different body locations and the sum of all body locations have been assessed. The results show that exposures on body locations covered by cloth contribute 55%-80% to total dermal exposure and cannot be neglected. These findings provide guidance for assessing total dermal expo sure to PAE.(3) PAE levels in handwipes and levels of PAE metabolites in urine have been concurrently measured for the same population(3 9 Beijing Children) for the first time. The results show that the concentrations of MEP, Mi BP and Mn BP were significantly higher in summer than in winter while the concentrations of DEHP metabolites were not significantly different. Di BP, Dn BP, BBz P and DEHP levels in handwipes were significantly correlated with levels of their respective metabolites in urine-- Mi BP, Mn BP, MBz P and MEHP-- in samples collected during the summer. Dn BP levels in handwipes were significantly correlated with Mn BP levels in urine in samples collected during the winter. For samples collected during the summer, t he median contribution of PAE dermal absorbed dose to total uptake has been calculated to be 15%, 11%, 7.0% and 4.5% for Di BP, Dn BP, BBz P, and DEHP, respectively. For samples collected during the winter, the median values for Di BP, Dn BP, and DEHP are 33%, 23% and 9.0%, respectively. These results provide basis for PAE exposure and risk control.