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EC number: 215-607-8
CAS number: 1333-82-0
A substantial amount of information is available for the toxicity of
chromium (VI) to terrestrial organisms. In the environment, it is likely
that chromium (VI) will be reduced to chromium (III) in soil, and it is
also likely that such conversion would have taken place in many of the
toxicity tests. The follwoing data are taken from the EU RAR:
For chromium (VI), long-term toxicity data are available for three
trophic levels (plants, earthworms and soil processes/micro-organisms),
with plants generally being the most sensitive species (although a clear
NOEC has not been determined for earthworms, the EC50 values are
generally higher than those found in the plant experiments). The lowest
NOEC from these studies is around 0.35 mg/kg dry weight of soil for
plants. According to the Technical Guidance Document, an assessment
factor of 10 is appropriate and so the PNECsoil can be estimated as
0.035 mg/kg dry weight. Using the water content of soil from the
Technical Guidance Document of 11.8% by weight (20% by volume), this is
equivalent to a PNECsoil of around 0.031 mg/kg on a wet weight of soil
Chromium (III) has generally been shown to be less toxic than chromium
(VI) to soil organisms. One exception to this may be on the effects seen
in some experiments using growth media (no soil) where reduction in root
growth was seen at similar concentration as found for chromium (VI).
Since chromium (III) adsorbs more strongly onto soil than chromium (VI),
it would again be expected that in soils, chromium (III) would be less
toxic than chromium (VI). From the available data, the NOEC for chromium
(III) to plants is of the order of 100 mg Cr/kg soil, with a NOEC of 32
mg Cr/kg dry soil being reported for earthworms, and a NOEC/LOEC of
~100-330 mg Cr/kg soil also being reported. Applying an assessment
factor of 10 to the lowest of these NOECs gives a PNEC for chromium
(III) of approximately 3.2 mg Cr/kg dry soil, which is equivalent to a
PNEC of around 2.8 mg/kg on a wet weight of soil basis. This value is
also lower than the HC5 value for soil processes.
According to the Technical Guidance Document, an equilibrium
partitioning approach can also be used in the derivation of the
PNECsoil. However, such an approach for chromium (VI) should be
considered very tentative in nature as chromium (VI) is likely to be
reduced to chromium (III) under the conditions found in most soils, and
the chromium (III) formed is likely to be of much lower water solubility
For chromium (VI), a PNECwater of 3.4 µg/l has been derived. For
chromium (III) a worst-case PNEC of 4.7 µg/l was derived.
According to the Technical Guidance Document, the PNECsoil can be
PNECsoil = Ksoil-water/RHOsoil
x PNECwater x 1000
where RHOsoil = density of soil = 1,700
The following values for Ksoil-water were derived:
Chromium (VI) Ksoil-water = 75 m3/m3
(acid conditions); Ksoil-water = 3.2 m3/m3
Chromium (III) Ksoil-water = 1,200 m3/m3
(acid conditions); Ksoil-water = 22,500 m3/m3
Using these values, the PNECsoil can be estimated as follows:
For chromium (VI), PNECsoil = 0.15 mg/kg wet weight for acid conditions,
and 0.006 mg/kg wet weight for other conditions. Similarly, for chromium
(III), PNECsoil = 3.3 mg/kg wet weight for acid conditions and 62 mg/kg
wet weight for other conditions.
The PNECsoil estimated for chromium (III) for acidic conditions using
the equilibrium partitioning method is in very good agreement with the
values obtained above using the available toxicity data. For the risk
assessment the PNECs obtained from experimental data will be used. Thus
the PNECsoil for chromium (VI) is taken as 0.031 mg/kg wet weight. The
PNECsoil for chromium (III) is taken to be 2.8 mg/kg wet weight.
For the risk characterisation the PNECsoil for chromium (III) is used,
as the concentrations of chromium in soil are calculated as chromium
(III). It should be noted that the PNEC for chromium (III) is derived
from experiments where a highly soluble (and hence bio available) form
of chromium (III) has been tested. In the environment, chromium (VI) is
likely to be reduced to forms of chromium (III) of limited solubility
and bioavailability, where it is unlikely that the concentration of
'dissolved' and hence available chromium (III) will reach the levels
where effects might be expected. This is seen in experiments with both
soil and aquatic organisms when a form of chromium (III) with low water
solubility has been tested. Similarly, it is clear that there are many
natural soils where the levels of total chromium are above the PNECs
derived here. Again, the main form of the chromium needs to be
considered. In natural soils, the majority of chromium will be present
as low solubility chromium (III) complexes, where bioavailability is
again limited. The PNECs derived are not appropriate for such situations.
Information on Registered Substances comes from registration dossiers which have been assigned a registration number. The assignment of a registration number does however not guarantee that the information in the dossier is correct or that the dossier is compliant with Regulation (EC) No 1907/2006 (the REACH Regulation). This information has not been reviewed or verified by the Agency or any other authority. The content is subject to change without prior notice.Reproduction or further distribution of this information may be subject to copyright protection. Use of the information without obtaining the permission from the owner(s) of the respective information might violate the rights of the owner.
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