Exploring the utility of 3D-skin models to evaluate trans-dermal uptake of flame retardants from indoor dust and consumer products

The aim of this research was to evaluate the utility of innovative \(in\) \(vitro\) techniques as an alternatives for human/animal tissues to study the transdermal uptake of organic flame retardants from indoor dust and consumer products. Firstly, we successfully designed and applied an \(in\) \(vitro\) physiologically based extraction test to provide new insights into the dermal bioaccessibility of various FRs from indoor dust. These investigations revealed the bioaccessible fraction for the brominated flame retardants (BFRs) α-, β-and γ- HBCD and TBBPA to 1:1 (sweat/sebum) mixture to be 41%, 47%, 50% and 40%, respectively, while for the phosphate flame retardants (PFRs) TCEP, TCIPP and TDCIPP, the values were 10%, 17% and 19%. With the exception of TBBP A, the presence of cosmetics had a significant effect (p <0.05) on the bioaccessibility of our target FRs from indoor dust. The presence of cosmetics decreased the bioaccessibility of HBCDs from indoor dust, whereas shower gel and sunscreen lotion enhanced the bioaccessibility of target PFRs. Secondly, we developed a protocol for studying dennal uptake of legacy and novel brominated flame retardants using two 3D-HSE (three dimensional human skin equivalent tissue) models, EpiDerm™ and EPISKIN™ in compliance with the OECD guidelines 428. Overall, results showed a significant negative correlation between the permeability constant of FRs and their Log K\(_o\)\(_w\) values. We also mimicked real life exposure scenarios by exposing the skin surface in turn to FR-containing dust, reference material plastics and upholstered fabrics. Our findings showed that under such scenarios dermal exposure to FRs was appreciable for UK adults and toddlers. For example, for dust exposure, our estimates of daily intake indicated toddlers to be 10 times more highly exposed than adults in the presence of sweat and sebum. This differential exposure is likely attributable to more dust adhering to toddler's skin and their higher exposed skin surface area to body weight ratio compared to adults.