Chromium

Endpoint summary

Description of key information

The goal of this part of the dossier is to assess the repartition in the different compartments of the environment of chromium III, its bioavailability and its persistence in order to determine its potential toxicity and evaluate the potential risk this substance can represent for environment and afterward exposure, potential impact to human.

This evaluation is based on several parameters to assess mainly as follows:

1. Hydrolysis


2. Biodegradation


3. Adsorption/desorption


4. Bioaccumulation

This section will consider, develop and conclude on these aspects to consider to establish a risk potential of chromium metal.

 

1. Hydrolysis

Referring to the column 2 of REACH annex VIII about specific rules for adaptation, due to the high insolubility of chromium III, hydrolysis assay can be waived (column 2 of REACH Annex VIII).

Transformation/dissolution test conducted on several different materials concluded on the insolubility of chromium metal:

• The transformation/dissolution test (OECD Series on Testing and Assessment Number 29, 2001) of Chromium metal powder at a loading of 1 mg/L at pH 6 and pH 8 resulted in total Chromium and Cr6+ concentrations of < 0.5 µg/L and < 0.05 µg/L, respectively for all measured timepoints (24h, 7d, 28d). Therefore, the extent to which Chromium metal powder can produce soluble available ionic and other metal-bearing species in aqueous media, is limited. Further testing of pure particulate/powder chromium material according to the OECD Series on Testing and Assessment Number 29 (2001) yielded total soluble chromium concentrations of < 1µg/L with loadings up to 100 mg/L for different timepoints (24h, 7d) and pHs (6, 8). In addition, solubility for metallic chromium was tested for chromium oxide (Cr2O3) because metallic chromium is always covered by a thin layer of chromium oxide which protects the ‘inner’ chromium from further oxidation. Test was performed according to OECD T/D test for sparingly soluble metal compounds (Hedberg, Y. and I. Odnevall Wallinder (2009)). NOTE: The following materials have been tested for solubility via the T/D by KTH: FeCr, 316 stainless, Cr, Cr2O3, Fe, Fe3O4. The study concluded that the tested material was practically insoluble.

As a consequence, hydrolysis of metallic chromium is not expected to be a significant mechanism of degradation or decomposition.

 

2. Biodegradation:

Due to the inorganic nature of chromium metal, biodegradation studies can be waived according to Column 2 of REACH Annex VII and Guidance on “Information Requirements and Chemical Safety Assessment Chapter R.7b: Endpoint specific guidance”.

 

3. Adsorption/desorption:

The aim of this part is to indicate the binding capacity of a substance to solid surfaces to define the environmental partitioning behavior and environmental persistence of chromium III.

In 2005, an “European Union Risk Assessment Report” has been published, mainly based on the assessment on 5 different chromium VI substances behavior in the environment. The document also discussed few useful aspects of Cr III prevalence and behavior in the Environment. About the partition of chromium III in environmental compartments this risk assessment report concluded with the enclosed points:

• In general, chromium (III) is more likely to partition to solids in the sediment and soil. For the water column, chromium (VI) and chromium (III) have similar adsorption partition coefficients for suspended solids, which are greater than those found for sediment and soil. Chromium (III) appears to be much more strongly adsorbed to soils and sediments than chromium (VI). The adsorption of chromium (III) onto soil follows the pattern typical of cationic metals and increases with increasing pH (lowering pH results in increased protonation of the adsorbent leading to fewer adsorption sites for the cationic metal) and the organic matter content of the soil and decreases when other competing (metal) cations are present. Certain dissolved organic ligands may also reduce the adsorption of chromium (III) to the solid phase by forming complexes which enhance the solubility of chromium (III) in the aqueous phase (Richard and Bourg 1991).

A second data set published in “European Union Risk Assessment Report” (2005) indicates that chromium (III) species have a strong preference for the solid phase: suspended matter, sediment and soil.

The chromium partitioning behavior can be summarized as follows:

“chromium (III) appears to be much more strongly adsorbed to soils and sediments than chromium (VI). The adsorption of chromium (III) onto soil follows the pattern typical of cationic metals and increases with increasing pH (lowering pH results in increased protonation of the adsorbent leading to fewer adsorption sites for the cationic metal) and the organic matter content of the soil and decreases when other competing (metal) cations are present. Certain dissolved organic ligands may also reduce the adsorption of chromium (III) to the solid phase by forming complexes which enhance the solubility of chromium (III) in the aqueous phase”.

 

Several publications, scored Klimisch 2 demonstrated that:

The solubility of chromium is higher at low pH (below 5.5) and minimum in the environmentally relevant pH range of 7-10. The free trivalent chromium ion predominates at very low pH (< pH 3), typically not found in the environment. Trivalent chromium can bind with naturally occurring DOC. Organically bound Cr (III) but not unbound Cr (III) can stay in solution at higher pH and can also sorb to and desorb from the organic fraction of suspended matter and settled sediment particles. Dissolved Cr(III) forms coordinate complexes with many inorganic and organic ligands. The oxidation of trivalent chromium only occurs in the presence of at least 1% manganese oxide, but this reaction is unlikely under most environmental conditions. It can be concluded that organic matter is expected to convert soluble chromate to insoluble chromium oxide.

Additional information

Metallic chromium is stable in aquatic, soil and sediment. It is an inorganic substance, which is not biodegradable, and it does not bioaccumulate. Due to its insolubility it does not affect the natural background levels of chromium or its its impurities.