Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

Abiotic degradation

Phototransformation and hydrolysis are the main abiotic degradation pathways for a substance. Magnesium metaborate is neither susceptible for phototransformation in air, water and soil nor for hydrolysis under environmental conditions.

Phototransformation is not applicable to Boron compounds.

No further information concerning photodegradation in air, water or soil is available. Based on the produced and supplied form of the test substance, no phototransformation in the environmental compartment is expected.

A hydolysis study according to OECD Guideline 111 (Fox, 2017) was not carried out, because the active ingredient in the test item was an inorganic. The test method is not applicable to inorganic substances. Additionally, the test item as a whole would be too insoluble for the test to be performed practically.

Biotic degradation

A 28 day study key study (Bayliss, 2016) was performed to assess the ready bioavailability of the test substance in an aerobic aquaeous medium. The method followed the OECD Guidelines for Testing of Chemicals (1992) No. 301B, "Ready Biodegradability; CO2 Evolution Test" referenced as Method C.4-C of Commission Regulation (EC) No. 440/2008 and US EPA Fate, Transport, and Transformation Test Guidelines OCSPP 835.3110 (Paragraph (m)) and was conducted in compliance with GLP criteria.

The test substance attained 4% biodegradation after 28 days. The results obtained from the mineral oil vessels showed 37% degradation over the test period. Correction of the biodegradation rate of the test substance for mineral oil degradation showed that the test substance achieved 0% biodegradation after 28 days. The test substance therefore cannot be considered to be readily biodegradable under the strict terms and conditions of OECD Guideline No. 301B.

Bioaccumulation

The Bioconcentration factor (BCF) of magnesium metaborate was predicted with BCFBAF v3.01 which is implemented in EPIWIN v4.11. The Bioconcentration factor according to Arnot-Gobas method (upper trophic) is log BCF = -0.05 (BCF = 0.893 L/kg bw). However, the prediction does not fall into the applicability domain of this model, since the substance is inorganic. Nonetheless the bioconcentration is predicted to be low.

Transport and distribution

Determination of the adsorption coefficient was not carried out using the HPLC screening method, designed to be compatible with Method C.19 Adsorption Coefficient of Commission Regulation (EC) No 440/2008 of 30 May 2008 and Method 121 of the OECD Guidelines for Testing of Chemicals, 22 January 2001, as the active ingredient in the test item was an inorganic. The test guidelines state they are not applicable to inorganic substances. A QSAR prediction has been made to allow PNEC derivation using partition-equilibrium method.

The Koc of magnesium metaborate was predicted with KOCWIN v2.00, which is implemented in EPIWIN v4.11. The predicted Koc is 240 L/kg bw [LogKoc: 2.38].

However, this prediction does not fall within the applicability domain of this model, since the query substance is inorganic.

Boric acid as well as other simple boron compoundswill predominantly exist as undissociated boric acid in aqueous solutions in acidic milieu withpH <7, whereas atabout pH 10 the metaborate anion (B(OH)4-) becomes the main species in solution (WHO, 1998).

It is therefore conclusive that in the plasma of mammals and in the environment the main species is undissociated boric acid.

Since other borates like magnesium mentaborate dissociate to form boric acid in aqueous solutions, they too can be considered to exist as undissociated boric acid under the same conditions.

The vapour pressure for boric acid is extremely low so volatilization is expected to be minimal. The same can be expected for magnesium metaborate with a tested vapor pressure of 0.0365 Pa at 25°C (Tremain, 2017a).

Henry's Law constant of magnesium metaborate was calculated based on the measured vapour pressure and water solubility. It is 40.11 Pa m3/mol.