Dermal uptake of hexabromocyclododecane (HBCDD) from skin contact with polystyrene microplastic particles.

Abstract

Despite the listing of HBCDD in Annex A of the Stockholm Convention, the environmental contamination and human health impact of HBCDD is predicted to last for decades due to HBCDD remaining in global in-use products, the waste stream and various consumer products due to uncontrolled recycling e.g., expanded and extruded polystyrene building insulation materials, toys, utensils. Recent studies from different countries have confirmed the presence of polystyrene (PS) microplastics (MPs) in air and dust from various indoor microenvironments. However, the risk arising from dermal exposure to hexabromocyclododecane (HBCDD), which was widely used as additive flame retardant in expanded and extruded PS remains unknown. To address this gap, we experimentally determined the dermal bioavailability of HBCDDs upon skin contact with PS-MPs using a 3-dimensional human skin equivalent model. All three isomers measured, i.e., α-, β- and γ-HBCDD were dermally bioavailable. Whilst the fraction of HBCDDs that accumulated within the skin tissue after 24 h exposure ranged between 5 to ~ 8% of the dose of HBCDD in the exposed PS-MP, complete skin penetration to the bloodstream within 24 h was low for all isomers, evidenced by the dermal flux, <i>J</i>_<i>ss</i> and the apparent permeability coefficient, <i>P</i>_<i>app</i>. Observed differences among HBCDD isomers were driven mostly by their physicochemical properties e.g., Log K_OW and water solubility. Moreover, dermal uptake of HBCDD was greater under a sweaty skin condition. Overall, internal exposure to HBCDDs arising from skin contact with PS-MP was evident, albeit low. However, the possibility of increased risk due to prolonged exposure or higher concentrations of HBCDDs in PS-MPs is plausible and cannot be ignored.