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The rate and extent to which chromium (III) oxide produces soluble (bio)available ionic and other chromium-bearing species in environmental media is limited. Chromium (III) oxide can be considered environmentally and biologically inert during short- and long-term exposure. Further, the poor solubility of chromium (III) oxide is expected to determine its behaviour and fate in the environment, and subsequently its potential for ecotoxicity. Proprietary studies are not available for chromium (III) oxide. However, the fate and toxicity of chromium (III) oxide in the environment is evaluated by assessing the fate of its ecotoxicologically relevant moiety, the chromium (III) ion, and read-across to data available for other chromium (III) substances is applied.

Reliable data of the soil toxicity of soluble chromium (III) substances are available for annelids and arthropods. Applying the EPM (and a Log Kp (soilds-water in soil) of 3.9 as determined by EPA, 2005), the lowest NOEC reported for soluble chromium (III) substances, i.e. the 21 d NOEC of 40 mg Cr/kg soil dw for reproduction of Eisenia fetida (van Gestel et al., 1991) could be converted into a porewater concentration of 0.005 mg/L chromium, a concentration that is at least 500-fold above the dissolved chromium concentration of < 0.01 microg/L as determined after 28 d in the T/D test (Hedberg and Wallinder, 2012).

Applying a weight-of-evidence approach, a similar low potential can be assumed for the toxicity of chromium (III) oxide to soil microorganisms and plants. This assumption is in line with conclusion of WHO (2009): Even though soluble chromium (III) substances may have some potential for toxicity to soil organisms, „no effects were seen with chromium (III) in the form of the insoluble chromium oxide” according to the CICAD for trivalent chromium substances (WHO, 2009).

Taking into account all reported effect concentrations of soluble chromium (III) substances and the poor solubility of chromium (III) oxide, bioavailability and the potential for toxicity to soil organisms is low.

Additional information

Solubility: The rate and extent to which chromium (III) oxide produces soluble (bio)available ionic and other chromium-bearing species in environmental media is limited. In a short-term transformation/dissolution test with a loading of 100 mg/L, a dissolved Cr concentration of 0.11 microg/L Cr was determined at pH 6 after 7 days whereas dissolved Cr concentrations were below the LOD (< 1 microg/L) at pH 8 (Hedberg and Wallinder, 2012). Transformation/dissolution at a loading of 1 mg/L resulted in dissolved chromium concentrations below the LOD (< 0.01 microg/L) at pH 6 after 7 days and 28 days. Furthermore, chromium (VI) could not be detected during the test (< 0.01 microg/L). In sum, chromium (III) oxide can be considered environmentally and biologically inert during short- and long-term exposure.

Bioaccumulation: Regarding the bioaccumulation potential and according to the CICAD for trivalent chromium substances (WHO, 2009) „Uptake of chromium(III) directly from water is likely to be very low owing to the limited water solubility of trivalent chromium compounds found in the environment and strong adsorption to sediment under most conditions in the environment… Chromium is not expected to biomagnify in the aquatic food-chain… There is no indication of biomagnification of chromium along the terrestrial food-chain.“ Thus, chromium (III) oxide is also not expected to bioaccumulate in aquatic and terrestrial organisms.

Ubiquitousness: Chromium is ubiquitous and a constituent of soil minerals. The global average of Cr in surface soil has been estimated to be 54 mg/kg; soil on serpentine contains as much as 0.2 to 0.4 % Cr, sandy soil and histosols contain on average 47 and 12 mg/kg Cr, respectively (Salminen et al. 2005). Monitoring data for elemental chromium background concentrations in soil are provided by the FOREGS Geochemical Baseline Mapping Programme that offers high quality, multi-purpose homogeneous environmental geochemical baseline data for Europe (Salminen et al. 2005). Samples of three types of soil (organic top layer, minerogenic top and sub soil) were collected at 900 stations, each representing a catchment area of 100 km2, corresponding to a sampling density of about one sample per 4700 km2. Soil parameters such as pH and organic carbon concentrations cover several magnitudes. All soil samples were prepared at the same laboratory, and all samples of particular sample types were analysed by the same method at the same laboratory. Chromium concentrations of topsoils (based on aqua regia digests) range from 1 mg/kg to 2340 mg/kg with 5th and 95th percentiles of 5 and 72 mg/kg, respectively. Monitoring data for elemental chromium concentrations in agricultural soil are provided by GEMAS (Geochemical Mapping of Agricultural and Grazing land Soil) that offers high quality harmonized, freely and interoperable geochemical data for ploughed agricultural soil and for non-cultivated grass land (non-cultivated for at least 10 years) (Reimann et al. 2014). More than 4000 samples of agricultural soil (0–20 cm) and grazing land soil (0–10 cm) were collected in 2008 at an average sample density of 1 site per 2500 km2, following strictly the field manual. Chromium concentrations of agricultural and grassland soils (based on aqua regia digests) range from 0.4 mg/kg to 696 mg/kg with 5th and 95th percentile of 4 and 70 mg/kg, respectively. 

Essentiality: “Chromium(III) is required by only some microorganisms for specific metabolic processes, such as glucose metabolism and enzyme stimulation. Chromium(III), in trace amounts, has been reported to be an essential component of animal nutrition and is most notably associated with glucose and fat metabolism (WHO, 2009).” Further, “natural chromium levels, available for animals living in a specific environment, depend on the natural geological and physico-chemical characteristics of the water, sediments and soils. To ensure appropriate chromium tissue levels without causing toxicity from chromium excess, it is expected that internal chromium levels are homeostatically regulated by all living organisms. Homeostatic regulation of chromium allows organisms, within certain limits, to maintain the physiologically required levels of chromium in their various tissues, both at low and high chromium intakes” (Voluntary Risk Assessment Metallic of Chromium and Trivalent Chromium Compounds by ICDA, 2008 and references therein).

Acute and chronic aquatic hazard potential: The acute and chronic aquatic hazard potential of chromium (III) oxide is assumed to be low as further discussed in the endpoint summary of section 6.1 ‘Cr2O3_Aquatic toxicity’.

In accordance with ECHA guidance on IR & CSA, Part B: Hazard Assessment (V. 2.1, December 2011), „For substances which are classified as harmful, toxic or very toxic to aquatic life (i.e. H412, H411, H410 and H400), an aquatic PNEC can be derived. In these circumstances there are unclassified hazards to the sediment and soil compartments because toxicity to aquatic organisms is used as an indicator of concern for sediment and soil organisms, and a screening risk characterisation is undertaken using the equilibration partitioning method (EPM) to derive PNECs for sediment and soil. Hence quantitative exposure assessment, i.e. derivation of PECs, is mandatory for the water, sediment and soil environmental compartments.

Substances with the only environmental classification as ‘May cause long lasting harmful effects to aquatic life’ (i.e. H413) have been established as persistent in the aquatic environment and potentially bioaccumulative on the basis of test or other data. There are also potential hazards for these substances for the sediment and soil compartments, because these substances are potentially bioaccumulative in all organisms and are also potentially persistent in sediment and soil. Hence exposure assessment is mandatory for the water, sediment and soil environmental compartments, which may be quantitative or qualitative as appropriate. PBT and vPvB substances have been established as persistent and bioaccumulative (and the former also as toxic) in the environment as a whole. Hence qualitative exposure assessment is mandatory for the water, sediment and soil environmental compartments...

If there are ecotoxicity data showing effects in aquatic organisms, but the substance is not classified as dangerous for the aquatic environment, an aquatic PNEC can nevertheless be derived thus indicating a hazard to the aquatic environment. In these circumstances there are also unclassified hazards to the sediment and soil compartments because toxicity to aquatic organisms is used as an indicator of concern for sediment and soil organisms and a screening risk characterisation is undertaken using the equilibration partitioning method (EPM) to derive PNECs for sediment and soil.

Chromium (III) oxide is not classified as harmful, toxic or very toxic to aquatic life or may cause long lasting harmful effects to aquatic life. Chromium (III) oxide is also not an unclassified hazard to the aquatic environment (see section 6.1 ‘Cr2O3_Aquatic toxicity’). Based on the poor solubility, bioavailability, lack of a potential for bioaccumulation and toxicity to aquatic and terrestrial organisms and considering ubiquitousness of chromium (III) oxide and essentiality of chromium, chromium (III) oxide is also not considered an unclassified hazard to the soil compartment.

 

References:

ECB (2005) European Union Risk Assessment Report. 3rd Priority List. Volume: 53. chromium trioxide, sodium chromate, sodium dichromate, ammonium dichromate and potassium dichromate (CAS-No.: 1333-82-0, 7775-11-3, 10588-01-9, 7789-09-5 and 7778-50-9; EINECS-No.: 215-607-8, 231-889-5, 234-190-3,232-143-1 and 231-906-6). ICDA (2008)

Environmental Risk Assessment Report “Metallic chromium and trivalent chromium compounds”. Voluntary Risk Assessment. 3 reports. Draft of December 2008.

Reimann et al. (2014) Chemistry of Europe’s agricultural soils - Part A: Methodology and interpretation of the GEMAS data set.

Salminen et al. (2005) Geochemical Atlas of Europe - Part 1: Background information, Methodology and Maps. EuroGeoSurveys.

WHO (2009) Concise International Chemical Assessment Document 76 (CICAD). Inorganic chromium(III) compounds (evaluation), International Programme of Chemical Safety (IPCS), WHO, Geneva.