Magnesium oxalate

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

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

Adequacy of study:

key study

Study period:

September 11, 2015 to November 10, 2016

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Justification for type of information:

REPORTING FORMAT FOR THE ANALOGUE APPROACH
Further information in a detailed justification report is included as attachment to the same record.

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
For the determination of analogue in this read-across approach, the following points have been considered:
- Chemical speciation and valency (common magnesium cation: Mg2+).
- The water solubility, as it provides a first indication of the availability of the metal ion in the different compartments of interest. The most simplistic approach to hazard evaluation is to assume that the specific metal-containing compound to be evaluated shows the same hazards as the most water-soluble compounds.
- In fluids of organisms and in aqueous media, dissociation of magnesium oxalate takes place immediately, resulting in formation of magnesium cations (Mg2+) and oxalate anions. Thus, any ingestion or absorption of magnesium oxalate by living organisms, in case of systemic consideration, will inevitably result of exposure to the dissociation products.
- Magnesium is an abundant mineral naturally present in the body. It is a cofactor in more than 300 enzyme systems that regulate diverse biochemical reactions in the body, including protein synthesis, muscle and nerve function, blood glucose control, and blood pressure regulation (IOM 1997, Rude 2010, Rude 2012). Magnesium is required for the normal functioning of several biochemical and physiological reactions and pay an essential role in the human body (Rude 2012). An adult body contains approximately 25 g magnesium, with 50% to 60% present in the bones and most of the rest in soft tissues (Volpe 2012). Human Recommended Dietary Allowances (RDA) for magnesium is up to 420mg per day (IOM 1997). For the same reasons (involvement in biochemical and physiological functions), magnesium is also naturally present in various organisms of the environment such as fish, crustacea or vegetables. Besides they are identified as food sources of magnesium (US 2012). Consequently, it can be concluded that magnesium is of low (eco)toxicological relevance when ingested and taken up systemically. Thus, any possible toxicological or ecotoxicological effect triggered by magnesium oxalate exposure can be attributed to oxalate anion.
- Counter ions: the assumption that the oxalate ion is responsible for the common property or effect implies that the toxicity or ecotoxicity of the counter ion present in the compound will be largely irrelevant in producing the effects to be assessed.
- Likely common breakdown products via physical and/or biological processes for the targeted substance (magnesium oxalate) and the analogues identified cannot present strong differences since the structures are very simple and very similar (formation of Mg2+ or oxalate ion).

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
Source chemical information is provided in the “source” endpoint. No impurity affecting the classification is reported for the source chemical.
Information on the impurities of the target chemical are detailed in the attached report.

3. ANALOGUE APPROACH JUSTIFICATION
The main hypothesis for the analogue approach are verified. They are presented in the detailed report attached. The experimental data performed on the substance (tests performed in this REACH registration dossier on strontium peroxide) confirms the analogue approach performed (same results on analogues).

4. DATA MATRIX
A data matrix is presented in the detailed report attached.

Reason / purpose for cross-reference:

read-across source

Test temperature:

Room temperature

pH:

8.1

Key result

Duration:

24 h

Dose descriptor:

EC10

Remarks:

12.61 mg/L

Effect conc.:

> 11.69 - < 13.61 mg/L

Basis for effect:

growth rate

Key result

Duration:

24 h

Dose descriptor:

EC50

Remarks:

37.03 mg/L

Effect conc.:

> 35.64 - < 38.46 mg/L

Basis for effect:

growth rate

Key result

Duration:

24 h

Dose descriptor:

EC10

Remarks:

7.04 mg/L

Effect conc.:

> 6.48 - < 7.64 mg/L

Basis for effect:

biomass

Key result

Duration:

24 h

Dose descriptor:

EC50

Remarks:

25.39 mg/L

Effect conc.:

> 24.38 - < 26.45 mg/L

Basis for effect:

biomass

Key result

Duration:

48 h

Dose descriptor:

EC10

Remarks:

18.89 mg/L

Effect conc.:

> 18.01 - < 19.81 mg/L

Basis for effect:

growth rate

Key result

Duration:

48 h

Dose descriptor:

EC50

Remarks:

31.26 mg/L

Effect conc.:

> 30.25 - < 32.31 mg/L

Basis for effect:

growth rate

Key result

Duration:

48 h

Dose descriptor:

EC10

Remarks:

6.22 mg/L

Effect conc.:

> 5.76 - < 6.71 mg/L

Basis for effect:

biomass

Key result

Duration:

48 h

Dose descriptor:

EC50

Remarks:

20.48 mg/L

Effect conc.:

> 19.69 - < 21.3 mg/L

Basis for effect:

biomass

Key result

Duration:

72 h

Dose descriptor:

EC10

Remarks:

7.55 mg/L

Effect conc.:

> 7.06 - < 8.08 mg/L

Basis for effect:

growth rate

Key result

Duration:

72 h

Dose descriptor:

EC50

Remarks:

20.58 mg/L

Effect conc.:

> 19.83 - < 21.35 mg/L

Basis for effect:

growth rate

Key result

Duration:

72 h

Dose descriptor:

EC10

Remarks:

5.56 mg/L

Effect conc.:

> 5.14 - < 6.01 mg/L

Basis for effect:

biomass

Key result

Duration:

72 h

Dose descriptor:

EC50

Remarks:

19.14 mg/L

Effect conc.:

> 18.39 - < 19.92 mg/L

Basis for effect:

biomass

Details on results:

Based on the test results,
The ErC50 of OXALIC ACID observed for test period of '24' hour for freshwater alga (Pseudokirchneriella subcapitata) was calculated as 37.03 mg/L, with lower confidence limit of 35.64 mg/L and the upper confidence limit of 38.46 mg/L.
The EyC50 of OXALIC ACID observed for a test period of '24' hour for freshwater alga (Pseudokirchneriella subcapitata) was calculated as 25.39 mg/L, with lower confidence limit of 24.38 mg/L and the upper confidence limit of 26.45 mg/L.
The ErC50 of OXALIC ACID observed for test period of '48' hour for freshwater alga (Pseudokirchneriella subcapitata) was calculated as 31.26 mg/L, with lower confidence limit of 30.25 mg/L and the upper confidence limit of 32.31 mg/L.
The EyC50 of OXALIC ACID observed for a test period of '48' hour for freshwater alga (Pseudokirchneriella subcapitata) was calculated as 20.48 mg/L, with lower confidence limit of 19.69 mg/L and the upper confidence limit of 21.30 mg/L
The ErC50 of OXALIC ACID observed for test period of '72' hour for freshwater alga (Pseudokirchneriella subcapitata) was calculated as 20.58 mg/L with lower confidence limit of 19.83 mg/L and the upper confidence limit of 21.35 mg/L.
The EyC50 of OXALIC ACID observed for a test period of '72' hour for freshwater alga (Pseudokirchneriella subcapitata) was calculated as 19.14 mg/L with lower confidence limit of 18.39 mg/L and the upper confidence limit of 19.92 mg/L.

Results with reference substance (positive control):

Growth Inhibition study was performed in Freshwater green Algae (Pseudokirchneriella subcapitata) in accordance with guideline OECD-201 with Potassium Dichromate. The concentrations used were 0.2, 0.5, 1.1, 2.4 and 5.6 mg/L.
Initially on ‘0’ day approximately 18250 algal cells/ml were inoculated in conical flask containing OECD test medium. The volume of OECD test medium was 100 ml each in control and treatment groups. 6 replicates were maintained for control and 3 replicates for each test concentration. Prior to exposure, pre-culture was maintained for a period of 3 days.
On day of exposure algal cells were observed microscopically and cell count was carried out approximately at ‘24’, ‘48’ and ‘72’ hours after exposure with Haemocytometer. Microscopic observations revealed that the algal cells were normal appearance and no abnormality of the algal cell was observed on exposure to the test item.
Average Specific Growth Rate:
The percent inhibition on the average growth rate at the end of ‘72’ hour was 0.03%, 67.13%, 71.90%, 76.58% and 86.93% in test concentrations of 0.2, 0.5, 1.1, 2.4 and 5.6 mg/L respectively.
From the average specific growth rate recorded with the different test concentrations viz., 0.2, 0.5, 1.1, 2.4 and 5.6 mg/L the concentration that inhibits 50% growth (ErC50) of Freshwater green Algae (Pseudokirchneriella subcapitata) was calculated to be 1.20 mg/L, with lower confidence limit of 1.15 mg/L and upper confidence limit of 1.26 mg/L.
The lowest observed effect concentration (LOEC) was calculated as 0.5 mg/L and the no observed effect concentration (NOEC) was recorded as 0.2 mg/L respectively.
Yield:
The percent inhibition on the yield at the end of ‘72’ hour was 0.07%, 54.13%, 92.35%, 93.82% and 99.95% in test concentrations of 0.2, 0.5, 1.1, 2.4 and 5.6 mg/L respectively.
From the yield recorded with the different test concentrations viz., 0.2, 0.5, 1.1, 2.4 and 5.6 mg/L, the concentration that inhibits 50% growth (EyC50) of Freshwater green Algae (Pseudokirchneriella subcapitata) was recorded as 0.67 mg/L, with lower confidence limit of 0.65 mg/L and upper confidence limit of 0.69 mg/L.
The lowest observed effect concentration (LOEC) was calculated as 0.5 mg/L and the no observed effect concentration (NOEC) was recorded as 0.2 mg/L respectively.
Based on the test results,
The ErC50 of Potassium Dichromate observed for a period of ‘72’ hour in freshwater alga (Pseudokirchneriella subcapitata) was calculated as 1.20 mg/L, with lower confidence limit of 1.15 mg/L and upper confidence limit of 1.26 mg/L.
The EyC50 of Potassium Dichromate observed for a period of ‘72’ hour in freshwater alga (Pseudokirchneriella subcapitata) was calculated as 0.67 mg/L, with lower confidence limit of 0.65 mg/L and upper confidence limit of 0.69 mg/L.

Reported statistics and error estimates:

The no observed effect concentration (NOEC) and lowest observed effect concentration (LOEC) for growth rate were recorded as 19.68 mg/L and 53.14 mg/L respectively (24 hours)
The no observed effect concentration (NOEC) and lowest observed effect concentration (LOEC) for growth rate were recorded as 1 mg/L and 2.7 mg/L respectively (48 hours)
The no observed effect concentration (NOEC) and lowest observed effect concentration (LOEC) for yield were recorded as 1 mg/L and 2.70 mg/L respectively (72 hours)
The biomass in the control culture increased exponentially by a factor of more than 16 within the ‘72’ hour test period. This corresponds to a specific growth rate of 1.07 day – 1
The mean coefficient of variation for section-by-section specific growth rates (days 0-1, 1-2 and 2-3 for ‘72’-hours test) in the control cultures was 1.4 %.
The coefficient of variation of average specific growth rate during the whole test period in replicate control cultures did not exceed 7%.

NOEC AND LOEC – AVERAGE GROWTH RATE
	24 hr	48 hr
NOEC	19.68 mg/L	1 mg/L
LOEC	53.14 mg/L	2.7 mg/L

NOEC AND LOEC – YIELD
	24 hr	48 hr
NOEC	19.68 mg/L	1 mg/L
LOEC	53.14 mg/L	2.7 mg/L

Validity criteria fulfilled:

yes

Conclusions:

Based on the test results,
The ErC50 of OXALIC ACID observed for test period of '24' hour for freshwater alga (Pseudokirchneriella subcapitata) was calculated as 37.03 mg/L, with lower confidence limit of 35.64 mg/L and the upper confidence limit of 38.46 mg/L.
The EyC50 of OXALIC ACID observed for a test period of '24' hour for freshwater alga (Pseudokirchneriella subcapitata) was calculated as 25.39 mg/L, with lower confidence limit of 24.38 mg/L and the upper confidence limit of 26.45 mg/L.
The ErC50 of OXALIC ACID observed for test period of '48' hour for freshwater alga (Pseudokirchneriella subcapitata) was calculated as 31.26 mg/L, with lower confidence limit of 30.25 mg/L and the upper confidence limit of 32.31 mg/L.
The EyC50 of OXALIC ACID observed for a test period of '48' hour for freshwater alga (Pseudokirchneriella subcapitata) was calculated as 20.48 mg/L, with lower confidence limit of 19.69 mg/L and the upper confidence limit of 21.30 mg/L
The ErC50 of OXALIC ACID observed for test period of '72' hour for freshwater alga (Pseudokirchneriella subcapitata) was calculated as 20.58 mg/L with lower confidence limit of 19.83 mg/L and the upper confidence limit of 21.35 mg/L.
The EyC50 of OXALIC ACID observed for a test period of '72' hour for freshwater alga (Pseudokirchneriella subcapitata) was calculated as 19.14 mg/L with lower confidence limit of 18.39 mg/L and the upper confidence limit of 19.92 mg/L

These results are considered in a read across approach for magnesium oxalate.

Executive summary:

Growth Inhibition study was conducted inFreshwater green Algae (Pseudokirchneriella subcapitata) in accordance withOECD-201. Guideline with OXALIC ACID. Thetestconcentrationswere selectedas1, 2.70, 7.29, 19.68 and 53.14 mg/L.Test item was dissolved in the testmedium, as per OECD 201. 

Initially on ‘0’ day,approximately 26425 cells/mLwereinoculated inaconical flask containingthe testmedium.The volume oftest medium was 100 mLin controlandeachtreatmentflasks.Sixreplicates were maintained for controland 3 replicates for eachtestconcentration.

Prior to the exposure,pre-culture was maintained for a period of3days. After the exposure on day ‘0’, algal cells were observed microscopically and the cell count was done atapproximately 24, 48 and 72 hoursby usingHaemocytometer. Microscopic observationrevealed if the cells were normal or abnormalinappearance postexposure tothe testitem.

Average Specific Growth Rate:

The percent inhibition on the average growth rate at the end of '24' hour was 0.15%, 3.12%, 5.16%, 11.87% and 76.19% in test concentrations of 1, 2.70, 7.29, 19.68 and 53.14 mg/L respectively.

From the average specific growth rate recorded with the different test concentrations viz., 1, 2.70, 7.29, 19.68 and 53.14 mg/L, the concentration that inhibited 50% growth (ErC50) of Freshwater green Algae (Pseudokirchneriella subcapitata) was calculated to be 37.03 mg/L, with lower confidence limit of 35.64 mg/L and the upper confidence limit of 38.46 mg/L.

The no observed effect concentration (NOEC) and lowest observed effect concentration (LOEC) for growth rate were recorded as 19.68 mg/L and 53.14 mg/L respectively

The percent inhibition on the average growth rate at the end of '48' hour was -0.13%, 1.04%, 1.60%, 6.32% and 100.80% in test concentrations of 1, 2.70, 7.29, 19.68 and 53.14 mg/L respectively.

From the average specific growth rate recorded with the different test concentrations viz., 1, 2.70, 7.29, 19.68 and 53.14 mg/L, the concentration that inhibited 50% growth (ErC50) of Freshwater green Algae (Pseudokirchneriella subcapitata) was calculated to be 31.26 mg/L, with lower confidence limit of 30.25 mg/L and the upper confidence limit of 32.31 mg/L.

The no observed effect concentration (NOEC) and lowest observed effect concentration (LOEC) for growth rate were recorded as 1 mg/L and 2.7 mg/L respectively

The percent inhibition on the average growth rate at the end of '72' hour were 0.06%, 4.72%, 10.07%, 39.27% and 142.23% in test concentrations of 1, 2.70, 7.29, 19.68 and 53.14 mg/L respectively.

From the average specific growth rate recorded with the different test concentrations viz., 1, 2.70, 7.29, 19.68 and 53.14 mg/L, the concentration that inhibited 50% growth (ErC50) of Freshwater green Algae (Pseudokirchneriella subcapitata) was calculated to be 20.58 mg/L, with lower confidence limit of 19.83 mg/L and the upper confidence limit of 21.35 mg/L.

 The no observed effect concentration (NOEC) and lowest observed effect concentration (LOEC) for growth rate were recorded as 1 mg/L and 2.70 mg/L respectively.

Yield:

The percent inhibition on the yield at the end of '24' hour was 0.41%, 7.43%, 11.97%, 25.59% and 91.21% in test concentrations of 1, 2.70, 7.29, 19.68 and 53.14 mg/L respectively.

From the yield recorded with the different test concentrationsviz.,1, 2.70, 7.29, 19.68 and 53.14 mg/L the concentration that inhibited 50% growth (EyC50) of Freshwater green Algae (Pseudokirchneriella subcapitata)was calculated as 25.39 mg/L, with lower confidence limit of 24.38 mg/L and the upper confidence limit of 26.45 mg/L.

The no observed effect concentration (NOEC) and lowest observed effect concentration (LOEC) for yield were recorded as 19.68 mg/L and 53.14 mg/L respectively

The percent inhibition on the yield at the end of '48' hour was 0.02%, 8.90%, 14.03%, 33.79% and 99.31% in test concentrations of 1, 2.70, 7.29, 19.68 and 53.14 mg/L respectively.

From the yield recorded with the different test concentrationsviz.,1, 2.70, 7.29, 19.68 and 53.14 mg/L the concentration that inhibited 50% growth (EyC50) of Freshwater green Algae (Pseudokirchneriella subcapitata)was calculated as 20.48 mg/L, with lower confidence limit of 19.69 mg/L and the upper confidence limit of 21.30 mg/L

The no observed effect concentration (NOEC) and lowest observed effect concentration (LOEC) for yield were recorded as 1 mg/L and 2.7 mg/L respectively

The percent inhibition on the yield at the end of '72' hour was 0.03%, 9.71%, 15.67%, 38.60% and 99.55% in test concentrations of 1, 2.70, 7.29, 19.68 and 53.14 mg/L respectively.

From the yield recorded with the different test concentrationsviz.,1, 2.70, 7.29, 19.68 and 53.14 mg/L, the concentration that inhibited 50% growth (EyC50) of Freshwater green Algae (Pseudokirchneriella subcapitata)was calculated as 19.14 mg/L, with lower confidence limit of 18.39 mg/L and the upper confidence limit of 19.92 mg/L.

The no observed effect concentration (NOEC) and lowest observed effect concentration (LOEC) for yield were recorded as 1 mg/L and 2.70 mg/L respectively

Analytical verification of the test item in the exposure medium sample was carried out in the test item concentrations of1, 7.29 and 53.14 mg/L. The samples at '0' hour and '72' hour were analyzed. The mean recoveries data are given below:

·        '0' hour –94.83%, 95.96% and 94.32% for 1.0 mg/L, 7.29 mg/L and 53.14 mg/L respectively. 

'72' hour –92.82%, 95.06% and 93.81% for 1.0 mg/L, 7.29 mg/L and 53.14 mg/L respectively

This study is considered relevant in a read across purpose and the result is used for the assessment of magnesium oxalate.

Description of key information

Growth Inhibition study was performed in Freshwater green Algae (Pseudokirchneriella subcapitata) in accordance with guideline OECD-201 on oxalic acid. A 72h EC50 growth rate of 20.58mg/L was determined. In a read accross approach, this value is used for magnesium oxalate.

Key value for chemical safety assessment

EC50 for freshwater algae:

20.58 mg/L