Chromium hydroxide nitrate (Cr(OH)(NO3)2)

Toxicity to soil microorganisms

Administrative data

Endpoint:

toxicity to soil microorganisms

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Justification for type of information:

Although many publication note that Cr III is less toxic than Cr VI, this research covers the conversion of Cr VI to Cr III under microbial influence. The use of microbial innoculation is used in remdiation of Cr VI contaminiated soils and this paper considered tolerance to Cr VI.
The fact that the micro-organisms survive the Cr VI and then thrive in the Cr III enriched media demonstrates toxicity to Cr III to be significanty lower than Cr VI.

Cross-reference

Cross-reference 1

Reason / purpose for cross-reference:

data waiving: supporting information

Reference

Endpoint:

toxicity to microorganisms, other

Type of information:

experimental study

Adequacy of study:

key study

Study period:

5 hours

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Qualifier:

no guideline followed

Principles of method if other than guideline:

Bucillus cereus was cultured in a nutrient broth which supplemented with Fe+2, Fe+3, Cr+3, Cd+2 separately, or in combination with each other, at 37° C for 5 hours. Bacterial growth was measured every half – hour, using spectrophotometer.

GLP compliance:

no

Specific details on test material used for the study:

Cr+3 as Cr Cl3 6H20

Vehicle:

no

Details on test solutions:

Cr+3: 533 mg of CrCl 3, 6H2O were dissolved in 50 ml distilled water and then made to 100 ml to prepare 20 mM/L of chromium chloride

Test organisms (species):

Bacillus sp.

Details on inoculum:

Nutrient agar (N.A.) and nutrient broth (N.B.) (Merk) were prepared as manufacturer recommendation.Bacillus cereus ATCC (American Type Culture Collection) 11778, NCTC (National Collection of Type Culture) 1032 was used and cultivated on N.A. using streak plate method. The plate was incubated for 24 hours at 37ºC and then stored in the fridge.

Test type:

other: Agar plate

Water media type:

freshwater

Total exposure duration:

5 h

Test temperature:

37 C

Nominal and measured concentrations:

1, 5 and 10 ml of chromium stock solution was added to 199, 195 and 190 ml of Nutrient Broth and mixed well in order to have 0.1, 0.5 and 1mM concentrations of these elements.

Key result

Duration:

5 h

Dose descriptor:

EC50

Effect conc.:

ca. 50 mg/L

Nominal / measured:

nominal

Conc. based on:

other: Cr (OH)3

Basis for effect:

growth inhibition

Duration:

5 h

Dose descriptor:

EC50

Effect conc.:

ca. 25 mg/L

Nominal / measured:

nominal

Conc. based on:

element

Remarks:

Cr3+

Basis for effect:

growth inhibition

Details on results:

Although the figures cited are entered as 'EC50', inhibition was ca 2% at the concentrations indicated. A precise EC50 was not determined.

These finding revealed that Cr3+ has partial inhibitory effects on the growth of bacteria. Bacterial growth was reduced to 79% and 76.7% using 0.1 mM/L (5.2 mg/l) and 0.5 mM/L (26 mg/l) concentration of chromium, respectively

This equates to inhibition of ca 25% at ca 96.5 mg/l Ca (OH)(NO3)2

Validity criteria fulfilled:

not specified

Conclusions:

These finding revealed that Cr3+ has partial inhibitory effects on the growth of bacteria. Bacterial growth was reduced to 79% and 76.7% using 0.1 mM/L (5.2 mg/l) and 0.5 mM/L (26 mg/l) concentration of chromium, respectivelyThis equates to inhibition of ca 25% at ca 96.5 mg/l Ca (OH)(NO3)2

Executive summary:

This scientifically valid study shows limited inhibition of bactial growth at approximatley 96.5 mg/l equivalent of the hydroxynitrate.

Cross-reference 2

Reason / purpose for cross-reference:

data waiving: supporting information

Reference

Endpoint:

toxicity to microorganisms, other

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

supporting study

Study period:

24 hour, plate method

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Justification for type of information:

As with all inorganic salts, the significance for toxicity or environmental assessment is the presence of specific ions that will form when in solution or when in biological systems.In the case of Cr III salts, the counter ion will have an effect on solubility and this is itself dependant on the type of media being used and in particular the pH of that media. It is generally accepted that in the case of metal salts, testing with salts that are soluble in the respective test media will ensure maximum exposure of the metal ions. This will include chlorides and nitrates as being more soluble and will indeed have relevance when dissolved in acid media, such as if ingested.Read-across to other chromium III salts is therefore considered valid as long as the exposure in the test system is greater than wold be expected for the substance under review for registration.

Qualifier:

no guideline followed

Version / remarks:

Bacterial regrowth assessed using streaked nutrient agar medium in test tube

Principles of method if other than guideline:

Streaked nutrient agar method adopted from Mgbemena et al. (2012).

GLP compliance:

no

Specific details on test material used for the study:

Laboratory grade

Vehicle:

no

Details on test solutions:

0, 5, 50, 100, and 500 mg/L CrCl3

Test organisms (species):

other: Azotobacter S8, Bacillus subtilis, Pseudomonas putida

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

24 h

Remarks on exposure duration:

To allow significant growth of cultures

Details on test conditions:

Incubated 24 hours at 37 C

Reference substance (positive control):

no

Duration:

24 h

Dose descriptor:

NOEC

Effect conc.:

ca. 5 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth inhibition

Key result

Duration:

24 h

Dose descriptor:

EC50

Effect conc.:

ca. 50 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth inhibition

Duration:

24 h

Dose descriptor:

EC100

Effect conc.:

ca. 100 - 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth inhibition

Details on results:

Lowest concentration to significnatly inhibit the growth of Azotobacter S8, Bacillus subtilis and Pseudomonas putida was found to be ranging from 50 to 100 mg/L Chromium(III).

Validity criteria fulfilled:

not specified

Conclusions:

Lowest concentration to significnatly inhibit the growth of Azotobacter S8, Bacillus subtilis and Pseudomonas putida was found to be ranging from 50 to 100 mg/L Chromium(III).

Executive summary:

Scientifically valid study examining effects on growth in three species of bacteria

Data source

Reference

Reference Type:

publication

Title:

Unnamed

Year:

2017

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

EPA OPPTS 850.5100 (Soil Microbial Community Toxicity Test)

Principles of method if other than guideline:

The effect of Cr on Pseudomonas aeruginosa growth was checked by comparing the growth of Pseudomonas aeruginosa in medium containing certain concentration of chromium and in medium without chromium.

GLP compliance:

not specified

Test material

Test material information

Constituent 1

Reference substance name:

Potassium dichromate

EC Number:

231-906-6

EC Name:

Potassium dichromate

Cas Number:

7778-50-9

Molecular formula:

Cr2H2O7.2K

IUPAC Name:

Potassium dichromate

Specific details on test material used for the study:

Specific details not provided

Sampling and analysis

Analytical monitoring:

yes

Test substrate

Vehicle:

yes

Details on preparation and application of test substrate:

Water

Test organisms

Test organisms (inoculum):

soil

Study design

Total exposure duration:

24 h

Test conditions

Test temperature:

These plates were incubated at 37ºC

Moisture:

In water based media

Details on test conditions:

Nutrient agar used

Nominal and measured concentrations:

Nominal 0, 20, 50, 100, 150, 200 ppm

Reference substance (positive control):

no

Results and discussion

Effect concentrations

Effect concentrations 1

Duration:

24 h

Dose descriptor:

EC100

Effect conc.:

> 50 other: ppm

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: Cell growth

Effect concentrations 2

Duration:

24 h

Dose descriptor:

EC0

Effect conc.:

ca. 50 other: ppm

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: Cell growth

Details on results:

Pseudomonas aeruginosa grew normally up to at least 50 ppm of Cr (VI), and was killed at 100 ppm of Cr (VI)
Biotransformation efficiency of Cr (VI) into Cr (III)

Applicant's summary and conclusion

Validity criteria fulfilled:

not specified

Conclusions:

Although many publication note that Cr III is less toxic than Cr VI, this research covers the conversion of Cr VI to Cr III under microbial influence. The use of microbial innoculation is used in remdiation of Cr VI contaminiated soils and this paper considered tolerance to Cr VI.
The fact that the micro-organisms survive the Cr VI and then thrive in the Cr III enriched media demonstrates toxicity to Cr III to be significanty lower than Cr VI.
It was also found that Pseudomonas aeruginosa reduced Cr (VI) into Cr (III) with the conversion efficiency of 94% after and extended 48h treatment.

Executive summary:

Chromium 3+ exists in natural soils and is well tolerated by micro-organisms.