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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 is insufficient data available to derive a PNEC from studies on sediment dwelling organisms. According to the Technical Guidance Document, an equilibrium partitioning approach can be used in the absence of experimental data. 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 sediments, and
the chromium (III) formed is likely to be of much lower water solubility (and bioavailability).
For chromium (VI), a PNECwater of 3.4 µg/L has been derived (statistical
approach). For chromium (III) a worst-case PNEC of
4.7 µg/L was derived.
According to the Technical Guidance Document, the PNECsediment can be
PNECsediment = Ksusp-water/RHOsuso
x PNECwater x 1000
where RHOsusp = density of suspended
matter = 1,150 kg/m3
The following values for Ksusp-water
Chromium (VI) Ksusp-water = 500 m3/m3
(acid conditions); Ksusp-water = 50 m3/m3
Chromium (III) Ksusp-water = 7,500 m3/m3
(acid conditions); Ksusp-water = 75,000
Using these values, the PNECsediment
can be estimated as follows:
For chromium (VI), PNECsediment = 1.5
mg/kg wet weight for acid conditions, and 0.15 mg/kg wet weight for
Similarly, for chromium (III), PNECsediment
= 31 mg/kg wet weight for acid conditions and 307 mg/kg wet weight for
A recent report (Environment Canada, 1997) has derived draft guideline
values for chromium based on the results of numerous field surveys. In
the approach taken, the data on sediment characteristics and the
presence or absence of benthic species was investigated to look for
associations between total chromium concentrations and any adverse
effect seen. Such an approach cannot prove that a given effect was
caused by a given chromium concentration, since it relies on field data
where exposures are likely to be to a wide range of substances. Using
this approach, a draft threshold effect level (level below which adverse
effects are expected to occur
rarely) of 37.3 mg/kg dry weight for freshwater sediments and 52.3 mg/kg
dry weight for marine sediments was derived for total chromium. The
corresponding draft probable effect level (the level above which adverse
effects are expected to occur frequently) was estimated to be 90 mg/kg
dry weight for freshwater sediments and 160.4 mg/kg dry weight for
(again for total chromium).
Given that the vast majority of chromium (VI) entering into sediment
will be converted to chromium (III), the PNECsediment
31 mg/kg wet weight (which is equivalent to around 80 mg/kg on a dry
weight basis) is in reasonable agreement with the draft effect levels
derived by Environment Canada (1997).
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