Magnesium metaborate

Endpoint summary

Additional information

General considerations

Due to the low aqueous solubility of < 1.0 mg C/L and complex nature of the test item for the purposes of testing the test item was prepared as a Water Accommodated Fraction (WAF) for the testing of acute toxicity towards fish, aquatic invertebrates and algae with a maximum of 50 mg/L to prevent overloading the aqueous phase with undissolved test item.

This procedure is in accordance with the OECD Guidance document on aquatic toxicity testing of difficult substances and mixtures (Series on testing and assessment - Number 23; OECD, 2000). The term WAF is applied to aqueous media containing only the fraction of multi-component substances that is dissolved and / or present as a stable dispersion or emulsion. These fractions are prepared individually and not by serial dilution of a single stock WAF. As the term indicates, only a fraction of the total mass of multi-component substances responsible for the composition may be present in the WAF.

The dissolved test item may have been one or several components of the test item. Given that the toxicity cannot be attributed to a single component or a mixture of components, but to the test item as a whole, the results were based on nominal loading rates only.

The "loading rate" is the mass to volume ratio of the mixture to medium used in the preparation. The obtained LL50/ EL50 values are comparable to LC50/ EC50 values, as well as the NOELR (No Observable Effect Loading Rate) to NOEC (No Observable Effect Concentration).

Toxicity to fish

In the GLP key study (Ablitt, 2017b) the acute toxicity of the test item to rainbow trout (Oncorhynchus mykiss) was assessed via the OECD Guidelines for Testing of Chemicals (1992) No 203, "Fish, Acute Toxicity Test" referenced as Method C.1 of Commission Regulation (EC) No. 440/2008.

Since the threshold of 50 mg/L loading rate WAF was the lowest EL₅₀value from either the Algal Growth Inhibition study or Acute Toxicity to Daphnia magna study, the study has been conducted as "Limit test" with 50 mg/L loading rate WAF.

Seven fish were exposed to a Water Accommodated Fraction (WAF) of the test item, at a single nominal loading rate of 50 mg/L for a period of 96 hours at a temperature of 14 °C to 15 ºC under semi-static test conditions. The number of mortalities and any sub-lethal effects of exposure in each test and control vessel were determined 3 and 6 hours after the start of exposure and then daily throughout the test until termination after 96 hours.

Exposure of rainbow trout to the test item gave LL₅₀ values of greater than 50 mg/L loading rate WAF. The No Observed Effect Loading Rate was 50 mg/L loading rate WAF.

Toxicity to aquatic invertebrates

In the key study (Ablitt, 207c) the acute toxicity of the test substance towards Daphnia magna was determined according to OECD Guideline 202 and Method C.2 of Commission Directive 92/69/EEC in compliance with GLP. Following a preliminary range-finding test, twenty daphnids (4 replicates of 5 animals) were exposed to a Water Accommodated Fraction (WAF) of the test item at a nominal loading rate of 50 mg/L for 48 hours at a temperature of 21 °C to 22 °C under static test conditions. The test item was a complex mixture containing 53% mineral oil. At the Sponsors request an additional vessel was prepared containing mineral oil at the same concentration as in the test item preparations; 26.5 mg/L.

Immobilization and any adverse reactions to exposure were recorded after 24 and 48 hours.

Exposure of Daphnia magna to the test item gave EL₅₀ values of greater than 50 mg/L loading rate WAF. The No Observed Effect Loading Rate was 50 mg/L loading rate WAF.

It was considered unnecessary and unrealistic to test at concentrations in excess of 50 mg/L.

Toxicity to aquatic algae

A GLP study (Ablitt, 2017a) was performed to assess the effect of the test item on the growth of the green alga Pseudokirchneriella subcapitata. The method followed was designed to be compatible with the OECD Guidelines for Testing of Chemicals (2006) No 201, "Freshwater Alga and Cyanobacteria, Growth Inhibition Test" referenced as Method C.3 of Commission Regulation (EC) 761/2009.

Following a preliminary range-finding test, Pseudokirchneriella subcapitata was exposed to a Water Accommodated Fraction (WAF) of the test item, at a single nominal loading rate of 50 mg/L (six replicate flasks) for 72 hours, under constant illumination and shaking at a temperature of 24 ± 1 °C.

The test item was a complex mixture containing 53% mineral oil. At the Sponsors request additional vessels were prepared containing mineral oil at the same concentration as in the test item preparation; 26.5 mg/L.

Total Organic Carbon (TOC) analysis of the test preparations performed at 0 and 72 hours showed measured concentrations of less than the Limit of Quantification (LOQ) of the analytical method employed, determined to be 1.0 mg C/L, were obtained.

Exposure of Pseudokirchneriella subcapitata to the test item gave EL₅₀ values of greater than 50 mg/L loading rate WAF. The No Observed Effect Loading Rate was 50 mg/L loading rate WAF.

Toxicity to aquatic microorganisms

A GLP key study (Bayliss, 2016b) was performed to assess the effect of the test item on the respiration of activated sewage sludge. The method followed was designed to be compatible with the OECD Guidelines for Testing of Chemicals (2010) No. 209 "Activated Sludge, Respiration Inhibition Test (Carbon and Ammonium Oxidation)". Activated sewage sludge was exposed to an aqueous dispersion of the test item at concentrations of 10, 100 and 1000 mg/L (3 replicates of the 1000 mg/L test concentration) for a period of 3 hours at measured temperatures of between 20 and 21 °C. Synthetic sewage was added as a respiratory substrate. 3,5-dichlorophenol was used as reference item (concentrations: 3.2, 10, 32 mg/L) and additional vessels were prepared containing mineral oil at the same concentrations as in the test item preparations: 5.3, 53 and 530 mg/L.

The effect of the test item on the respiration of activated sewage sludge micro-organisms gave a 3-Hour EC₅₀ value of greater than 1000 mg/L. The No Observed Effect Concentration (NOEC) after 3 hours exposure was 1000 mg/L. The reference item gave a 3-Hour EC₅₀ value of 9.0 mg/L, 95% confidence limits 7.1 to 11 mg/L.

Toxicity towards other aquatic organisms

No further investigations are triggered under REACH.