Test chamber and forensic microscopy investigation of the transfer of brominated flame retardants into indoor dust via abrasion of source materials

Brominated flame retardants (BFRs) have been detected in indoor dust in many studies, at concentrations spanning several orders of magnitude. Limited information is available on the pathways via which BFRs migrate from treated products into dust, yet the different mechanisms hypothesized to date may provide an explanation for the range of reported concentrations. In particular, transfer of BFRs to dust via abrasion of particles or fibers from treated products may explain elevated concentrations (up to 210mgg^-1) of low volatility BFRs like decabromodiphenyl ether (BDE-209). In this study, an indoor dust sample containing a low concentration of hexabromocyclododecane, or HBCD, (110ngg^-1 σHBCDs) was placed on the floor of an in-house test chamber. A fabric curtain treated with HBCDs was placed on a mesh shelf 3cm above the chamber floor and abrasion induced using a stirrer bar. This induced abrasion generated fibers of the curtain, which contaminated the dust, and σHBCD concentrations in the dust increased to between 4020 and 52 500ngg^-1 for four different abrasion experiment times. The highly contaminated dust (σHBCD at 52 500ngg^-1) together with three archived dust samples from various UK microenvironments, were investigated with forensic microscopy techniques. These techniques included Micro X-ray fluorescent spectroscopy, scanning emission microscopy coupled with an energy dispersive X-ray spectrometer, Fourier transform infrared spectroscopy with further BFR analysis on LC-MS/MS. Using these techniques, fibers or particles abraded from a product treated with BFRs were identified in all dust samples, thereby accounting for the elevated concentrations detected in the original dust (3500 to 88 800ngg^-1 σHBCD and 24 000 to 1438 000ngg^-1 for BDE-209). This study shows how test chamber experiments alongside forensic microscopy techniques, can provide valuable insights into the pathways via which BFRs contaminate indoor dust.