Appendix D - Dossier (PDF) - Tera

date: 20–JUL–2005
3. Environmental Fate and Pathways Substance ID: 71–43–2
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Exposure duration was not reported , although it may be
inferrred that this was 96 hr.
The ratio of air/water used in the test systems is also not
reported. It is unclear whether the test system water was
supersaturated with oxygen prior to the test commencing, as
the size of the fish and the assumed test duration would
have exhausted dissolved oxygen under normal saturated
conditions (8 – 9 ppm)
Although the investigators noted
poor organism health (sluggishness, erratic swimming) as
signs of intoxication, the aurthors’ opinion is that the
determined uptake and elimination rates are reasonably
accurate estimates which were not significantly influenced
by stress due to combined toxic aqueous concentrations.
The development of an exposure system suitable for studying
the uptake and elimination kinetics in fish of volatile
chemicals is discussed. Uptake (k1) and elimination rate
(k2) constants in fathead minnows (Pimephales promelas) were
determined for a mixture of benzene and toluene, and used to
estimate bioconcentration factor (BCFkin) values.
Exposure experiments with 10 females per exposure were
conducted in triplicate. Headspace concentrations of
injected benzene & toluene in a closed system (12 L glass
dessicator w/ 9L appropriate diluent water) were allowed to
achieve steady state between air–water phases prior to
addition of fish. Automated sampling and analysis of the
air by inline GC/FID provided a concentration–time profile
that was then fit to differential equations using numerical
integration methods.
Assumptions for the mathematical description of the system
are a)instantaneous distribution of chemical between water
and air (Kaw),and b) a first order one–compartment model
describing the kinetics of chemical in fish. Rates were
derived from the water concentrations, which were determined
based on onecompartment analysis (air) with (Cw) calculated
from GC results of headspace analysis of the system both
empty (Cref; _concentration in air in :M/L) and when
containing the water phase (Ci).
Result: Uptake rate constants increased with increasing
octanol–water partition coefficient (Kow), whereas the
elimination rate constants were inversely related to Kow.
Kaw values experimentally determined were approximately 26%
lower than values reported in the literature. Since steady
state concentrations were reached during fish exposure,
biotransformation was not expected to have occurred, since
chemical concentration did not decrease over time. Uptake
rate constants increase
Benzene
Kaw Cwumol/L Log P:Calculated Log P:Measured
0.224 0.18+/–0.01 48+/–7 2.13
Appendix D: Benzene SIDS Dossier
Uptake–k1,L/kg/hr Elimination–k2,(1/hr) BCFkin (ml/g)
7+/–1 0.384+/–0.074 19
– 218/957 –