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EC number: 232-140-5
CAS number: 7789-00-6
Information is based on the EU RAR (2005): European Union Risk Assessment Report: chromium trioxide, sodium chromate, sodium dichromate, ammonium dichromate and potassium dichromate, 3rd. Priority List; Volume 53.
There are a number of studies that indicate the chromium (VI) is toxic
to single species of bacteria. However, it is also clear that many
bacteria are tolerant of high concentrations of chromium (VI). Both
single species and mixed population tests can be used to derive a PNEC
for wastewater treatment plants. The available data were summarised in
the review (see endpoint study record) From these data
those which are relevant to the assessment of the wastewater treatment
plant have been selected, and are listed in the table below with the
appropriate assessment factor and resulting PNEC.
The lowest of the PNEC values in the table is 0.21 mg/L, and this will
be used in the risk characterisation.
There is evidence from studies on pilot-scale activated sludge plants
that once acclimated to the presence of chromium (VI), plants can
tolerate up to 10 mg Cr (VI)/L in the influent, with only minor
reductions in efficiency seen at substantially higher concentrations.
This observation indicates that the PNEC derived above may be
overprotective of wastewater treatment plants that regularly receive,
and are therefore acclimated to, chromium (VI) in the influent.
Chromium (III) appears to be much less toxic to micro-organisms than
chromium (VI). A concentration of 10 mg/L promoted growth in some
species of bacteria, and 100 mg/L produced only a small amount of growth
inhibition. The study did not provide a formal NOEC; it is proposed to
use 10 mg/l as the PNEC for chromium (III).
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