Chromium

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

6.5 µg/L

Assessment factor:

2

Extrapolation method:

assessment factor

Marine water

Hazard assessment conclusion:

no data: aquatic toxicity unlikely

STP

Hazard assessment conclusion:

no data: aquatic toxicity unlikely

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

205.7 mg/kg sediment dw

Assessment factor:

1

Extrapolation method:

sensitivity distribution

Sediment (marine water)

Hazard assessment conclusion:

insufficient hazard data available (further information necessary)

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

21.1 mg/kg soil dw

Assessment factor:

1

Extrapolation method:

assessment factor

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

WHO reported in “Concise International Chemical Assessment Document 76 INORGANIC CHROMIUM(III) COMPOUNDS” (2009) that “Chromium (III) is required by only some microorganisms for specific metabolic processes, such as glucose metabolism and enzyme stimulation (Hughes & Poole, 1989). Huffman & Allaway (1973) demonstrated that chromium was not an essential component of plant nutrition.

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 (Mertz, 1969).”

 

According to ECHA’s Guidance on the Application of the CLP Criteria (p 580): “The hazard classification schemes for metals and metal compounds are limited to the acute and long-term hazards posed by metals and metal compounds when they are available (i.e. exist as dissolved metal ions, for example, as M+ when present as M-NO3), and do not take into account exposures to metals and metal compounds that are not dissolved in the water column but may still be bioavailable, such as metals in food…”.

Based on the same guidance the approach to define the ecotoxicity of metals and inorganic metal compounds should consider the enclosed testing strategy:

“The level of the metal ion which may be present in solution following the addition of the metal and/or its compounds, will largely be determined by two processes: the extent to which it can be dissolved, i.e. its water solubility, and the extent to which it can react with the media to transform to water soluble forms. The rate and extent at which this latter process, known as ‘transformation’ for the purposes of this guidance, takes place can vary extensively between different compounds and the metal itself, and is an important factor in determining the appropriate hazard class.”

 

In order to identify and assess the hazard of metals in aquatic environment and in addition to the solubility, pH and medium in which the data has been provided should be considered. To complete the approach and the assessment, the same guidance finally statutes on the T/D to conduct to demonstrate the ecotoxicity potency or non-potency of a metal compound:

“The Full Transformation Dissolution test should be carried out at the pH that maximizes the concentration of dissolved metal ions in solution and that expresses the highest toxicity.

Based on the data from the Full Test, it is possible to generate a concentration of the metal ions in solution after 7-Daysshort-term test) for each of the three loadings (i.e. 1 mg/l as ‘low’, 10 mg/l as ‘medium’ and 100 mg/l as ‘high loading’) used in the test. If the purpose of the test is to assess the long-term hazard of the substance, then the loadings should be 0.01 mg/l, 0.1 mg/l or 1 mg/l depending on the transformation rate and the duration of the test being extended to 28-Days (long-term test).”

 

Based on this guidance, T/D have been performed (according to guidance OECD 29) and including:

• The T/D test of Chromium metal powder at a loading of 1 mg/L at pH 6 and pH 8 resulted in total Chromium and Cr6+ concentrations below the respective reporting limits (Cr: 0.5 µg/L, Cr6+: 0.05 µg/L) 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. (Browers et al., 2018)


• T/D of chromium metal powder (BET specific surface area 0.0035 m2/g) in a screening test resulted at the loading of 100 mg/L in dissolved chromium concentrations that were below the Limit of Detection of 1 µg/L at pH 6 and pH 8 after 24 h (Ullmann, 2009).


• T/D of chromium metal powder (PS < 25 µm, BET specific surface area 0.46 m2/g) resulted at the loading of 100 mg/L in mean dissolved chromium concentrations that were below the Limit of Detection of 1 microg/L at pH 6 and 8 after 24 h, and also at pH 6 after 7-Days.


• T/D of chromium metal powder (BET specific surface area 0.0035 m2/g) resulted at the loading of 100 mg/L in dissolved chromium concentrations that were below the Limit of Detection of 0.01 µg/L at pH 6 after 96 h and below the Limit of Detection of 1 microg/L at pH 8 after 7-Days. Hexavalent chromium concentrations were below the Limit of Detection of 0.01 microg/L in all media. Thus, chromium metal powder is sparingly soluble in environmental media at pH 6 and 8. (Helberg & Wallinder, 2012)

 All these results demonstrate the highly insolubility of chromium at different pH and for short (1 day) to long exposure (28-Days), based on the dissolved concentration which as measured below the limit of detection.

 

The insolubility of metallic chromium and the ubiquitous presence in the environment makes its ecotoxicity very unlikely and also the testing of the environmental degradation and ecotoxicity mainly scientifically unjustified. Due to its highly insolubility, metallic chromium is not classifiable. The toxicity parameters and PNEC values of soluble Cr(3 +)  are orders of magnitude higher than concentrations obtained in the solubility tests of metallic chromium. They are presented in the documentation only for comparison.

For information and for comparison, the PNECs for trivalent chromium have been determined in the ICDA (2010) environmental report. The report includes detailed description of the rationale behind the derivation PNECs.

Acute Aquatic Toxicity:

Acute toxicity: For information and for comparison, the PNECs for trivalent chromium have been determined in the ICDA (2010) environmental. WHO (2009) also assessed EC50 on several aquatic species as follows: “96-h median effective concentrations (EC50s) for one freshwater alga, based on growth, ranged from 0.3 to 0.4 mg chromium (III)/l. A 96-h EC50, based on growth, was reported for a marine diatom at 2 mg chromium (III)/l.

96-h LC50s for freshwater fish range from 3.3 mg/l for the guppy (Poecilia reticulata) to 151 mg/l for the bighead (Aristichthys nobilis), whereas 96-h LC50s of 31.5 and 53 mg/l were reported for marine fish.”

Finally, ICDA (2010) stated on PNEC : ”The PNEC has been calculated as 6.5 µg/L for fresh water, PNEC for marine water is unlikely and should be considered as a worst case of the same order of magnitude as for freshwater.” Based on the Figure IV.4 of the CLP guidance version 5:

- Chromium III is not readily soluble

- Several data on different aquatic species are available and demonstrate in comparison to the T/D test that chromium III dissolution value is always highly below the Limit of detection and also below the Ecotoxicity Reference Values as 0.05 µg/L.

In application to this guidance, Chromium metal do not request to be classified for acute aquatic hazard.

 

Aquatic Long-Term Toxicity:

Regarding the long-term aquatic toxicity, chromium (III) can be also assessed by comparing the dissolved chromium (III) ion level obtained by the T/D tested on several chromium III forms (powders, alloys, etc…) and at a loading rate of 1 mg/L after 28-Days with the lowest chronic ERV as determined for the (soluble) chromium (III) ion.

The ERV is based on the lowest long-term NOEC/EC10 value for aquatic species.

WHO (2009) in “Concise International Chemical Assessment Document 76 INORGANIC CHROMIUM(III) COMPOUNDS” summarized the available toxicity data for chromium (III) have been mainly derived using the water-soluble forms (chromium (III) chloride, chromium (III) nitrate, and chromium potassium sulfate). It has been also concluded in this report that: “In the environment, chromium (III) is likely to be present in much less soluble forms and hence less bioavailable to aquatic organisms.”.

The long-term toxicity for Chromium III water-soluble forms for invertebrates as LC50 are exposed as follows:

“Median lethal concentrations (LC50s) in freshwater invertebrates ranged from 0.1 mg/l (Daphnia pulex) to 442 mg/l (Asellus aquaticus), with a 21-day non-observed-effect concentration (NOEC) (reproduction) of 0.7 mg/l and a life cycle NOEC of 0.047 mg/l for Daphnia magna.”

Several publications also quoted in the same report allow to confirm the absence of long-term effects on fishes:

“Walsh et al. (1994) studied the effect of chromium (III) effluent from a tannery on marine grey mullet (Chelon labrosus). Fish exposed for 2 months to contaminated sediment (46 mg chromium/kg dw) and food (Enteromorpha intestinalis [9.4 mg/kg] and Mytilus edulis [6 mg/kg]) showed no adverse effects on growth, mortality, or gross tissue damage. Significant bioaccumulation was measured in livers of exposed fish; however,

chromium levels in liver samples from fish at the contaminated site were not significantly higher than those of controls.”

ICDA conducted and published in 2010 a voluntary environmental risk assessment report about Metallic Chromium and Trivalent Chromium Compounds in 3 parts:

• Part 1 is about Euras Chromium 3+ releases


• Part 2 is about Euras Cr 3+ PEC calculation


• Part 3 focuses on Euras Cr 3+ risk characterization and includes the PNEC calculation.

Based on 7-Days on different species and studies, treated the data by total risk approach and added risk approach, considered the uncertainties, the PNEC aquatic long-term was concluded to be 6.5 µg/L.

The report concluded on this part:

“In order to be able to conduct the risk characterisation for trivalent chromium in the aquatic environment, a pragmatic approach was followed: the PNEC aquatic for trivalent chromium was estimated by using an provisional assessment factor of 2 on the HC5,50% resulting in an added and total PNEC aquatic of 6.5 μg Cr/L. The latter value results from a dataset that is characterised by a large degree of uncertainty end which clearly do not fulfill all data requirements as stated in the TGD (2003) or by the London workshop (2001).”

 

Hence, the substance chromium (III) is not sufficiently dissolved / bioavailable to cause chronic toxicity at the level of the chronic ERV which are far above the solubility measured during the T/D test as the Limit of Detection.

 

Conclusion on classification

The insolubility of metallic chromium and the ubiquitous presence in the environment makes its ecotoxicity very unlikely and also the testing of the environmental degradation and ecotoxicity mainly scientifically unjustified. The lack of endpoint data from metallic chromium do not allow the derivation of PNECs.

Due to insolubity, metallic chromium is not classfiable. The toxicity parameters and PNEC values of soluble Cr(3 +) are orders of magnitude higher than concentrations obtained in the solubility tests of metallic chromium. They are presented in the documentation only for comparison.