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Description of key information

Magnesium methanolate hydrolyses rapedly in contact with moisture or water into methanol and magnesium hydroxide (detailed description in section 5.1.2). Both hydrolysis products are not dangerous for aquatic organisms and no classification is required.

Hydrolysis product methanol:

Methanol is the first and simplest member of the series of aliphatic alcohols. Like other non-reactive, non-ionizable organic chemicals ("neutral organics") such as ketones, ethers, alkyl halides, aryl halides and aromatic hydrocarbons methanol is expected to exert toxicity to aquatic species through simple narcosis.

A large amount of data on the toxicity of methanol is available for a broad spectrum of aquatic organisms (fish, invertebrates and algae).

The results from the most reliable and relevant available studies are listed below

Short-term toxicity

Fish

LC50 (96h) = 28100 mg/L                            Pimephales promelas

LC50 (96h) = 20100 mg/L                            Oncorhynchus mykiss

LC50 (96h) = 15400 mg/L                           Lepomis macrochirus

Daphnids

EC50 (48h) = 18000 mg/L                             Daphnia magna

EC50 (48h) > 10000 mg/L                            Daphnia magna

Green algae

EC50 (96h) ca. 22000 mg/L                         Selenastrum capricornutum

Microorganisms

EC 50: 19800 mg/L                                      activated sludge

IC50: >1000 mg/L                                        activated sludge

IC50: 880 mg/L                                            Nitrosamonas

toxic limit concentration: 530 - 6600 mg/L     Pseudomonas, Microcystis aeruginosa.

All the available data demonstrate consistently the very low acute toxicity to methanol for aquatic organisms 

Long-term toxicity

No fully reliable results and no guideline studies are available concerning long-term toxicity of methanol to aquatic species. Given the Biological Oxygen Demand of methanol and its rapid biodegradation, it is indeed difficult to maintain in long-term tests the required levels of oxygen concentration. Due to this aspect, it also difficult to assess the reliability of studies, in which the oxygen concentration is not well documented.

Since methanol belongs to the category of chemicals acting with a non-specific mode of action (simple narcosis) the chronic toxicity to aquatic organism can be reasonably predicted from data on acute toxicity using an appropriate acute-to-chronic ratio. An ACR of 10 has been proposed in the literature for such kind of chemicals(see for example Raimondo et al., Environ. Toxicol. Chem. 26, 2007; Roex at al., Environ. Toxicol. Chem. Cryo Letters. 2004 Nov-Dec; 25(6):415-2419, 2000).

Taking into account the toxicity mode of action of methanol the chronic toxicity to aquatic organisms can be also reasonably predicted using Structure-Activity Relationship models (QSARs).

The available information and the results from toxicity estimations indicate a very low chronic toxicity of methanol to aquatic organisms, with no-effect levels well above the concentrations which are normally used in limit tests on long-tern toxicity.

 

 Fish

NOEC (predicted chronic value): 447 mg/l   Pimephales promelas

NOEC (200h) = 7900 - 15800 mg/L             Oryzias latipes

Daphnids

NOEC (21 d) = 208 mg/L (predicted)           Daphnia magna

NOEC (21 d) = 122 mg/L                              Daphnia magna

Hydrolysis product magnesium hydroxide:

Magnesium hydroxide has no short-term toxicity to fish. The two key studies for this endpoint concluded that the LC50s for freshwater fish were 306.79 mg/L and 775.8 mg/L, respectively. The supporting studies found that magnesium hydroxide has a very low toxicity to all fish tested.

Long-term toxicity of fish is unlikely to occur based on the physico-chemical properties of magnesium hydroxide, the breakdown pathway of the substance and the fact that magnesium ions are ubiquitous in the natural environment.

Magnesium hydroxide is of low acute toxicity to aquatic organisms and does not meet the criteria to be classified as dangerous under the CLP Regulation (EC) No 1272/2008 nor does it meet the criteria to be classified as persistent, bioaccumulative or toxic under the REACH Regulation.

Reported results on the physico-chemical properties of Magnesium hydroxide show that the substance is only slightly soluble in water (1.78 mg total solids/L at 8.3 pH and 20ºC) and has a low potential to adsorb to sediment (derived sediment-water partition coefficient (Kd) 1.65). Furthermore, Magnesium hydroxide is expected to break down in the environment to water and magnesium over time. Magnesium is ubiquitous in the environment and is an essential plant and animal nutrient.Magnesium sulphate and magnesium chloride, and hence the magnesium ion, all have a very low toxicity to aquatic invertebrates.The recalculated LC50 (96h) for D. Magna was determined as 170.86 mg/L with 100% pure Magnesium hydroxide. Supporting studies on magnesium chloride all shows low long-term toxicity to aquatic invertebrates

Additional information