Magnesium

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

0.41 mg/L

Assessment factor:

100

Extrapolation method:

assessment factor

PNEC freshwater (intermittent releases):

1.4 mg/L

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0.41 mg/L

Assessment factor:

100

Extrapolation method:

assessment factor

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

10.8 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

268 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

268 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

268 mg/kg soil dw

Extrapolation method:

equilibrium partitioning method

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

Added risk approach

Since magnesium is abundantly present in all environmental compartments and the natural magnesium background concentrations are significantly higher compared to the PNEC values, the added risk approach is employed as a pragmatic solution. All PNEC values are therefore based on added magnesium concentrations (PNECadded), without taking into account the natural background in the exposure media. In essence this added risk assessment approach assumes that species are fully adapted to the natural background concentration and therefore that only the anthropogenic added fraction should be regulated or controlled (Appendix R.7.13-2 of the REACH guidance on “Environmental risk assessment for metals and metal compounds”).

Typical baseline background concentrations (from van Nederkassel and Oorts, 2010) and PNECadded values for magnesium in water, sediment and soil:

Compartment	Unit	10th percentile of baseline concentrations	Typical (50th percentile)baseline level	90th percentile of baseline concentrations	PNECadded
Aquatic (freshwater)	mg Mg/L	2.9	7.1	22.0	0.41
Aquatic (marine water)	mg Mg/L		1290		0.41
Sediment (freshwater)	mg Mg/kg dw	2512	6918	19041	268
Soil	mg Mg/kg dw	1459	3930	11051	268

Read-across statement

No data are available on environmental fate and behaviour and ecotoxicity of Mg metal.

The transformation/dissolution test of Mg powder in aqueous media at pH 6 and 8 showed high solubility of Mg metal powder and rapid formation of Mg²⁺ + 2 OH^- + H₂(g). Therefore, Mg is considered as completely soluble under the relevant concentration range. It is assumed that the hydroxyl ions will largely be neutralised in the environment by e.g. precipitation reactions etc., and therefore the chemical safety assessment will be based on elemental Mg concentrations and a read-across approach is proposed from the toxicity data available for soluble Mg salts or monitoring data of elemental Mg concentrations in the environment.

In assessing the ecotoxicity of metals in the various environmental compartments (aquatic, sediment and soil), it is generally assumed that toxicity is not controlled by the total concentration of a metal, but by the bioavailable form. For metals, this bioavailable form is generally accepted to be the free metal-ion in solution. The speciation and chemistry of magnesium in the environment is considered to be rather simple because Mg ions are highly soluble, not readily oxidized or reduced and do not form strong complexes with most inorganic ligands or organic matter. As a conservative approximation, it is therefore assumed that the total soluble magnesium pool is bioavailable.

This read-across from data for soluble Mg salts is only allowed when toxicity is caused by the Mg2+-cation in the substances. Reliable toxicity data are only available for MgSO₄ and MgCl₂ (and their hydrated forms). Both chloride and sulphate are abundantly present in natural environments and are therefore not expected to cause a specific toxic effect and only may effect the organisms by further increasing the ionic strength (salinity). The reliable data for the various endpoints do not differ significantly among the magnesium salts tested when results are expressed on an elemental Mg basis, which points to a similar, common effect. All data reported are based on elemental Mg concentrations.

Conclusion on classification

For Mg metal, no Acute 1/Chronic 1, 2, 3 classification category under CLP is warranted as there was no acute toxicity (L(E)C50) observed to invertebrates and fish up to >100 mg Mg/L. Algae tests with Pseudokirchneriella subcapitata did not show a significant effect on growth rate at 18 mg Mg/L (corresponding to an added dose of 12 mg Mg/L), resulting in an unbounded NOEC of ≥ 18 mg Mg/L, which is above the 1 mg/L threshold for classification based on chronic toxicity. Chronic toxicity data are also available for daphnids with a 21-day NOEC for reproduction of 41 mg Mg/L. Although no chronic data are available for fish, the remaining Chronic 4 classification category under CLP can be removed based on the following arguments:

• Fish are less sensitive compared to aquatic invertebrates based on the acute toxicity data.

• The lowest LC50 for fish is 541 mg Mg/L, which is more than 500 times higher than the chronic threshold concentration level (1 mg/L). This observation strongly suggests that no chronic effects below 1 mg Mg/L are expected for fish.

• No significant chronic effects are noted for both algae and daphnids at a concentration of 1 mg Mg/L

Therefore, there is no need for an environmental classification of magnesium.