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EC number: 218-320-6
CAS number: 2116-84-9
1011 l/kg (0.80 µg a.i./l); 384 (4.4 µg a.i./l)
2992 l/kg (0.80 µg a.i./l); 1208 (4.4 µg a.i./l)
normalised (to 5%) values are:
934 l/kg (0.80 µg a.i./l); 255 l/kg (4.4 µg a.i./l) and BCFk 2765 l/kg
(0.80 µg a.i./l); 803 l/kg (4.4 µg a.i./l).
BCF value of 2765 is used as a worst case. Depuration rate constants:
0.161 d-1(0.8 µg a.i./l); 0.0125 d-1(4.4 µg a.i./l).
Steady-state BCF values of
1011 l/kg (0.80 µg a. i. /l) and 384 (4.4 µg a. i. /l) and kinetic BCF
values of 2992 l/kg (0.80 µg a. i. /l) and 1208 (4.4 µg a. i. /l) were
determined for tris(trimethylsiloxy)phenylsilane in a reliable study
conducted according to an appropriate test protocol, and in compliance
normalised (to 5%) values are: BCFss= 934 l/kg (0.80 µg
a.i./l) and 255 l/kg (4.4 µg a.i./l) and BCFk= 2765 l/kg
(0.80 µg a.i./l) and 803 l/kg (4.4 µg a.i./l).
bioconcentration (BCF) studies are most validly applied
to substances with log Kow values between 1.5 and 6.
Practical experience suggests that if the aqueous solubility of the
substance is low (i.e. below ~0.01 to 0.1 mg/l) (REACH Guidance R.11;
ECHA, 2014), fish bioconcentration studies might not provide a reliable
BCF value because it is very difficult to maintain exposure
concentrations. Dietary bioaccumulation (BMF) tests are practically much
easier to conduct for poorly water-soluble substances, because a higher
and more constant exposure to the substance can be administered via the
diet than via water. In addition, potential bioaccumulation for such
substances may be expected to be predominantly from
uptake via feed, as substances with low water solubility and high Koc
will usually partition from water to organic matter.
there are limitations with laboratory studies such as BCF and BMF
studies with highly lipophilic and adsorbing substances. Such studies
assess the partitioning from water or food to an organism within a
certain timescale. The studies aim to achieve steady-state conditions,
although for highly lipophilic and adsorbing substances such
steady-state conditions are difficult to achieve. In addition, the
nature of BCF and BMF values as ratio values, means that they are
dependent on the concentration in the exposure media (water, food),
which adds to uncertainty in the values obtained.
highly lipophilic and adsorbing substances, both routes of uptake are
likely to be significant in a BCF study, because the substance can be
absorbed by food from the water.
uptake routes can also occur in a BMF study, with exposure occurring via
water due to desorption from food, and potential egestion of substance
in the faeces and subsequent desorption to the water phase. Although
such concentrations in water are likely to be low, they may result in
significant uptake via water for highly lipophilic substances.
al. (2013) put forward the use of elimination half-life as a metric
for the bioaccumulation potential of chemicals. Using the commonly
accepted BMF and TMF threshold of 1, the authors derive a threshold
value for kelimination of >0.01 d-1 (half-life
70d) as indicative of a substance that does not bioaccumulate.
rates from BCF and BMF studies, being independent of exposure
concentration and route of exposure, are considered to be a more
reliable metric to assess bioaccumulation potential than the ratio BCF
and BMF values obtained from such studies.
The depuration rate
constants of 0.161 d-1(0.8 µg a.i./l) and 0.0125 d-1(4.4
µg a.i./l) obtained from the BCF study with tris(trimethylsiloxy)phenylsilane
are considered to be valid and to carry most weight for bioaccumulation
assessment of the substance. These rates are indicative of a substance
which does not bioaccumulate.
L. P.et al., 2012 has described fugacity ratios as a method to
compare laboratory and field measured bioaccumulation endpoints. By
converting data such as BCF and BSAF (biota-sediment accumulation
factor) to dimensionless fugacity ratios, differences in numerical
scales and unit are eliminated.
is an equilibrium criterion and can be used to assess the relative
thermodynamic status (chemical activity or chemical potential) of a
system comprised of multiple phases or compartments (Burkhard, L. P.et
al., 2012). At thermodynamic equilibrium, the chemical fugacities in
the different phases are equal. A fugacity ratio between an organism and
a reference phase (e. g. water) that is greater than 1, indicates that
the chemical in the organism is at a higher fugacity (or chemical
activity) than the reference phase.
fugacity of a chemical in a specific medium can be calculated from the
measured chemical concentration by the following equation:
f = C/Z
is the fugacity (Pa), C is concentration (mol/m3) and Z is
the fugacity capacity (mol(m3. Pa)).
relevant equation for calculating the biota-water fugacity ratio (Fbiota-water)
BCFWD/LW/ Klwx ¿l/ ¿B
BCFWD/LW is the ratio of the steady-state lipid-normalised
chemical concentration in biota (µg-chemical/kg-lipid) to freely
dissolved chemical concentration in water (µg-dissolved
chemical/L-water), Klw is
the lipid-water partition coefficient and ¿l is the
density of lipid and ¿B is the density of biota.
be assumed that n-octanol and lipid are equivalent with respect
to their capacity to store organic chemicals, i.e. Klw= Kow.
For some substances with specific interactions with the organic phase,
this assumption is not sufficiently accurate. Measurement of Klw values
for siloxane substances is in progress. Initial laboratory work with
olive oil as lipid substitute indicates that the assumption that Klw=
Kow is appropriate (Reference: Dow Corning Corporation,
personal communication). However, the calculated
fugacity ratios presented here should be used with caution at this stage.
table below presents fugacity ratios calculated from the BCF data for tris(trimethylsiloxy)phenylsilane,
using Kow for Klw.
fugacity ratios for tris(trimethylsiloxy)phenylsilane
0.80 µg a.i./l
4.4 µg a.i./l
log Kow 9
fugacity-based BCFs directly reflect the thermodynamic equilibrium
status of the chemical between the two media included in the ratio
calculations. The fugacity ratios calculated are all below 1, indicating
that the chemical in the organism tends to be at a lower fugacity (or
chemical activity) than in the water. It should be noted however, that
the BCF studies may not have reached true steady-state in the timescale
of the laboratory studies. The fugacity ratios indicates that uptake may
be less than expected on thermodynamic grounds, suggesting that
elimination is faster than might be expected on grounds of lipophilicity
Burkhard, L. P., Arnot, J. A., Embry, M. R., Farley, K. J., Hoke, R. A., Kitano, M., Leslie, H. A., Lotufo, G. R., Parkerton, T. F., Sappington, K. G., Tomy, G. T. and Woodburn, K. B. (2012). Comparing Laboratory and Field Measured Bioaccumulation Endpoints. Integrated Environmental Assessment and Management 8, 17-31.
Goss, K-U., Brown, T. N. and Endo, S. (2013). Elimination half-life as a metric for the bioaccumulation potential of chemicals in aquatic and terrestrial food chains. Environmental Toxicology and Chemistry 32, 1663-1671.
Peter Fisk Associates. (2014i). Peter Fisk Associates. Siloxane analogue report. PFA.300.005.008.R1
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