Contribution
of Polybrominated Dibenzo‑<i>p</i>‑dioxins
and Dibenzofurans (PBDD/Fs) to the Toxic
Equivalency of Dioxin-like Compounds in Archived Biosolids from the
U.S. EPA’s 2001 National Sewage Sludge Survey
- Publication date
- Publisher
Abstract
The
World Health Organization recently proposed the inclusion of
brominated congeners in addition to chlorinated congeners when computing
the toxic equivalency (TEQ) of dioxin-like compounds (DLCs) in assessments
of human health risks. In the present study, 12 polybrominated dibenzo-<i>p</i>-dioxins and furans (PBDD/Fs) were analyzed by gas chromatography/high
resolution mass spectrometry in the composited, archived biosolids
that were collected in 32 U.S. states and the District of Columbia
from 94 wastewater treatment plants by the United States Environmental
Protection Agency in its 2001 national sewage sludge survey. Two PBDDs
and five PBDFs were detected in the biosolids composites at varying
frequencies (40–100%) with a total mean concentration of 10,000
ng/kg dry weight (range: 630–42,800), of which 1,2,3,4,6,7,8-hepta-BDF
constituted about 95% by mass. Relative to commercial polybrominated
diphenyl ether (PBDE) formulations, the ratio of PBDD/Fs to PBDEs
in biosolids was 55-times higher (∼0.002% vs ∼0.11%),
which indicates potential PBDE transformation or possibly additional
sources of PBDD/Fs in the environment. The TEQ contribution of PBDD/Fs
was estimated at 162 ng/kg 2,3,7,8-tetrachlorodibenzo-<i>p</i>-dioxin (TCDD) (range: 15–672), which is equivalent to 75%
(range: 12–96%) of the total TEQ in biosolids. The TEQ of DLCs
released annually to U.S. soils as a result of the land application
of biosolids was estimated at 720 g (range: 530–1600 g). Among
all known DLCs determined in biosolids, brominated analogs contributed
370% more TEQ than did chlorinated congeners, which indicates the
need to include brominated DLCs in the exposure and risk assessment
of land-applied biosolids