Despite numerous studies on the contamination
of organophosphate
triesters (tri-OPEs) in indoor environments, organophosphate diesters
(di-OPEs) have rarely been investigated. The present study aimed to
investigate whether di-OPEs coexist with tri-OPEs in house dust collected
from Guangzhou (n = 30), South China and the city
of Carbondale (n = 17) located in the Midwestern
United States (U.S.). Median concentrations of bis(2-butoxyethyl)
phosphate (BBOEP), bis(1-chloro-2-propyl) phosphate (BCIPP), bis(1,3-dichloro-2-propyl)
phosphate (BDCIPP), bis(2-ethylhexyl) phosphate (BEHP), bis(2-methylphenyl
phosphate) (BMPP), and diphenyl phosphate (DPHP) were determined to
be 15.9, < LOQ, 33.6, 654, 9.5, and 605 ng/g in South China house
dust, and 1580, 90.6, 234, 867, 4.0, and 6500 ng/g in Midwestern U.S.
dust, respectively. The total concentrations of di-OPEs (referred
to ΣdiOPEs) constituted an average of 22.9% and 21.3%
of the total concentrations of tri-OPEs in dust from these two locations,
respectively. Median concentration ratios of DPHP and BEHP to their
respective tri-OPEs (i.e., TPHP and TEHP) were determined to be 1.1
and 1.0 in South China dust and 3.7 and 1.4 in Midwestern U.S. dust,
respectively, indicating possible commercial applications for these
two di-OPEs. Correlative analyses reveal chemical- and region-specific
relationships between di-OPEs and their respective tri-OPEs, suggesting
that the relative importance of different sources (e.g., direct commercial
use, impurity in tri-OPE formulas, and tri-OPE degradation) could
vary for different di-OPEs. Our findings demonstrate wide occurrences
of di-OPEs in an indoor environment from the studied locations and
raise concerns on human exposure to dust associated di-OPEs. Future
studies are needed to explore more possible di-OPEs in indoor environments
and elucidate their sources, human exposure pathways, and toxicokinetics.
