Distribution is a Major Factor Affecting Bioaccumulation
of Decabrominated Diphenyl Ether: Chinese Sturgeon (<i>Acipenser
sinensis</i>) as an Example
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Abstract
While decabromodiphenyl ether (BDE-209) has very low bioavailability
and a rapid biotransformation rate, it exhibits high bioaccumulation
in wildlife. To explore the bioaccumulation mechanism of BDE-209 in
organisms, its toxicokinetic processes were investigated in Chinese
sturgeons from the Yangtze River. Different from less brominated BDEs,
lipids did not play an important role in the distribution of BDE-209
with relatively high concentrations detected in liver (54.5 ±
3.3 ng/g wet weight (ww)), gills (47.4 ± 2.9 ng/g ww), and intestine
(41.9 ± 3.0 ng/g ww), followed by stomach (21.9 ± 9.0 ng/g
ww), muscle (19.1 ± 5.6 ng/g ww), heart (7.5 ± 5.2 ng/g
ww), gonad (6.8 ± 4.9 ng/g ww), adipose (4.9 ± 1.2 ng/g
ww), and egg (2.8 ± 2.3 ng/g ww). In vitro metabolism of BDE-209
by microsomal fractions of Chinese sturgeon found that BDE-209 was
biotransformed rapidly with the rate constant (<i>K</i>)
of 0.039 h<sup>–1</sup> in liver. BDE-126, BDE-154, BDE-188,
BDE-184, BDE-183, BDE-202, BDE-201, and BDE-204/197 were observed
as debrominated products of BDE-209 after incubation, and their formation
rates were 0.026, 0.016, and 0.006 h<sup>–1</sup> for BDE-126
BDE-184, and BDE-154, respectively. The concentration ratios between
heart and intestine for individual PBDEs suggested slow delivery of
BDE-209 among tissues after absorption. A Bayesian hierarchical model
was further developed to estimate partition coefficients in a physiologically
based pharmacokinetic model of BDE-209 in Chinese sturgeon. The estimated
partition coefficients between tissues and blood were higher than
those of less brominated BDE or PCBs in various animals, suggesting
that the low partition ratios from blood to tissues would lead to
high bioaccumulation of BDE-209, especially in absorbing organs