technical guidance documents - Institute for Health and Consumer ...

EFFECTS ASSESSMENT
bioaccumulation and biomagnification. For certain chemicals, for which the octanol/water
partition coefficient cannot be measured properly, a high adsorptive capacity (of which
log Kp > 3 may be an indication) can be additional evidence of bioaccumulation potential.
Hydrolysis
The effect of hydrolysis may be a significant factor for substances discharged mainly to the
aquatic environment: the concentration of a substance in water is reduced by hydrolysis so the
extent of bioconcentration in aquatic organisms would also be reduced. Where the half-life, at
environmentally relevant pH values (4-9) and temperature, is less than 12 hours, it can be
assumed that the rate of hydrolysis is greater than that for uptake by the exposed organisms.
Hence, the likelihood of bioaccumulation is greatly reduced. In these cases, it may sometimes be
appropriate to perform a BCF test on the hydrolysis products, if identified, instead of the parent
substance. However, it should be noted that, in most cases hydrolysis products are more
hydrophilic and as a consequence will have a lower potential for bioaccumulation.
Degradation
Both biotic and abiotic degradation may lead to relatively low concentrations of a substance in
the aquatic environment and thus to low concentrations in aquatic organisms. However, the
uptake rate may still be greater than the rate of the degradation processes, leading to high BCF
values even for readily biodegradable substances. Therefore ready biodegradability does not
preclude a bioaccumulation potential, but for most substances concentrations will be low in
aquatic organisms.
At the base-set level, only scarce information on the kinetics of degradation is available. For new
substances even at higher tonnages, a request for such information would need to be justified; it
can be requested only on a case-by-case basis at level 2. For existing substances information on
degradation kinetics may be available.
If persistent metabolites are formed in substantial amounts the bioaccumulation potential of these
substances should also be assessed. However, for most substances information will be scarce.
From experiments with mammals information may be obtained on the formation of possible
metabolites, although extrapolation of results should be treated with care.
Molecular mass
Certain classes of substances with a molecular mass greater than 700 are not readily taken up by
fish, because of possible steric hindrance at passage of gill membranes or cell membranes of
respiratory organs. These substances are unlikely to bioaccumulate significantly (regardless of
the log Kow-value).
Summary of indications of bioaccumulation potential
Taking the factors mentioned above into account will indicate whether or not there is potential
for bioaccumulation. In summary: if, at base-set level, a substance:
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