Dichromium trioxalate

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Study period:

28 days

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Justification for type of information:

Performed to guideline studies 2017 with GLP

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

Identification:
chromium oxalate
Physical state/Appearance:
dark green powder
Batch:
Z-09-2715
Purity:
98%
Expiry Date:
17 January 2018
Storage Conditions:
room temperature in the dark

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Initial conc.:

ca. 31 mg/L

Based on:

test mat.

Initial conc.:

ca. 10 mg/L

Based on:

DOC

Details on study design:

Study run for 28 days, with acid purge on Day 29 to displace remaining CO2

Reference substance:

benzoic acid, sodium salt

Key result

Parameter:

% degradation (CO2 evolution)

Value:

ca. 5

Sampling time:

6 d

Key result

Parameter:

% degradation (CO2 evolution)

Value:

ca. 22

Sampling time:

10 d

Key result

Parameter:

% degradation (CO2 evolution)

Value:

ca. 29

Sampling time:

29 d

Results with reference substance:

Valid, acheiving 60 % in 10-day period

Visual observations were made of the test media during the course of the study. At the start of the test, there was undissolved test material visible, but as the test progressed, less was apparent. However it is not clear as to whether this was due to dissolution or due to settling out of undissolved material.

Validity criteria fulfilled:

yes

Interpretation of results:

inherently biodegradable

Conclusions:

Although it was concluded that the substance is not readily biodegrable, it is possible that solublity could have played a part in distorting the results. Oxalic acid and fully water soluble salts of oxalic acid are readily biodegradable and this result was unexectadly low.

It is concluded that the solublity of the material in the test system had an impact on the rate of biodegradation as thre is good evidence of oxalic acid being readily biodegradable. Oxalic acid is found in biological systems and will readily metabolise.

Executive summary:

Although the substance is clearly very soluble in water at high concentrations, observations from ecotoxicity and biodegradation testing suggest that at low concentrations (10 - 100 mg/l) in hardened water, there is a precipitation. This is very likely chromium carbonate or calcium oxalate which are themselves sparingly soluble in water. (The reported solubility for calcium oxalate is ca 0.25 mg/l)

Therefore, under natural environmental conditions, it is likely that there is full dissociation and potential formation of other salts.

Description of key information

Although only slow biodegradation was seen at the concentrations tested, the precipitation of oxalate as a highly insoluble calcium salt will have led to a low level of bioavailability.

Key value for chemical safety assessment

Biodegradation in water:

inherently biodegradable, not fulfilling specific criteria