Identifying transfer mechanisms and sources of decabromodiphenyl ether (BDE 209) in indoor environments using environmental forensic microscopy

Abstract

Although the presence of polybrominated diphenyl ethers (PBDEs) in house dust has been linked to consumer products, the mechanism of transfer remains poorly understood. We conjecture that volatilized PBDEs will be associated with dust particles containing organic matter and will be homogeneously distributed in house dust. In contrast, PBDEs arising from weathering or abrasion of polymers should remain bound to particles of the original polymer matrix and will be heterogeneously distributed within the dust. We used scanning electron microscopy and othertools of environmental forensic microscopy to investigate PBDEs in dust, examining U.S. and U.K. dust samples with extremely high levels of BDE 209 (260-2600 microg/g), a nonvolatile compound at room temperature. We found that the bromine in these samples was concentrated in widely scattered, highly contaminated particles. In the house dust samples from Boston (U.S.), bromine was associated with a polymer/organic matrix. These results suggest that the BDE 209 was transferred to dust via physical processes such as abrasion or weathering. In conjunction with more traditional tools of environmental chemistry, such as gas chromatography/mass spectrometry (GC/MS), environmental forensic microscopy provides novel insights into the origins of BDE 209 in dust and their mechanisms of transfer from products.

Figure 1

A large-scale, microscopic XRF image of Boston house dust showing the uneven distribution of bromine, about 0.1% of pixels. Red=bromine, blue=calcium, green=iron. The scanned area is 9.4 mm by 7.8 mm; the pixel size is 0.1 mm by 0.1 mm.

Figure 2

A moderate-scale, composite image created using secondary electrons (shown in blue-green) and backscatter electronics (shown in red). Red areas may contain bromine; this can be confirmed at any given location using EDS.

Figure 3

Close-up, backscattered electron image of a dust particle. EDS shows that the two bright areas, marked 1 and 2, are bromine rich. Areas 3–5 are enriched in calcium or aluminum.

Figure 4

A close-up composite image of a dust particle created using secondary electrons (shown in red) and backscatter electrons (shown in green). EDS showed that the green patches contain bromine, calcium and/or iron.

Figure 5

a). Close-up secondary electron image of a bromine-containing dust particle. b) Elemental map constructed using EDS of the boxed area in 5a (white=carbon, blue=calcium, red=bromine).

Figure 6

Comparison of infrared spectra from clear, elastic material in the dust sample (top) and a reference acrylic material (bottom)

Figure 7

Environmental scanning electron microscopic images using backscatter electrons: a) a British car dust sample containing 2600 µg/g BDE 209, b) close-up of a patch in the center of 7a (circled) that is enriched in bromine as confirmed by EDS. Shiny white areas indicate the presence of bromine.