Manganese

Additional information on environmental fate and behaviour

Administrative data

Endpoint:

additional information on environmental fate and behaviour

Type of information:

experimental study

Adequacy of study:

key study

Study period:

06 April 2017 to 13 May 2017

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2017

Report date:

2017

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

other: OECD Test Guidance No.29

Deviations:

no

GLP compliance:

yes

Type of study / information:

The objective of this study was to obtain information about the dissolution characteristics of the test material to classify metal containing substances and mixtures according to the UN Globally Harmonized system, the EU Classification, Labelling and Packaging Regulation (Reg. 1272/2008 + amendment No 286/2011) and the EU Dangerous Substance Directive (Dir. 67/548).

Test material

Test material information

1

Reference substance name:

Manganese

EC Number:

231-105-1

EC Name:

Manganese

Cas Number:

7439-96-5

Molecular formula:

Mn

IUPAC Name:

manganese

Test material form:

solid: flakes

Details on test material:

- Physical Appearance: Silver grey, on the flat sides covered with a brown oxide surface film.
- Physical form: Solid (+4 mm LH Flake)
- Density: 7.2 g/cm3
- Storage conditions: Room temperature, in the dark.

Specific details on test material used for the study:

TREATMENT OF TEST MATERIAL PRIOR TO TESTING
- Treatment of test material prior to testing:
The test material is tested at a particle size representative of normal handling and use. A default diameter value of 1 mm of a spherical particle is used in the absence of this information. A spherical particle with a diameter of 1 mm has a surface of 3.14 mm² (4·π·r²) and a volume of 0.524 mm³ (¾·π·r³). In the case of the test material (density 7.2 mg/mm³), a Ø 1 mm spherical reference particle has a volume of 0.524 mm³ and a mass of 3.77 mg. Therefore, a 1 mg/L loading can be achieved by preparing a total free metal surface of 0.83 mm²/L. The preparation of the samples (cutting, embedding and polishing) was beyond the scope of this study and was not performed according to the principles of GLP. However, a brief description of the sample preparation is given below.

The test item embedding, grinding and polishing are performed using, as close as possible, the following procedure:

- Cutting the test material
Pieces of test material were cut to achieve pieces with dimensions to prepare the epoxy resin discs with a final free metal surface of 1-2 mm². Four test item discs were prepared for this study.

- Epoxy Embedding
One piece of the test material was embedded per epoxy resin sample. The polymerisation process was done as directed by Struers as follows: To prepare the resin fluid an amount of hardener was mixed into the correct amount of resin (25 parts of resin / 3 parts of hardener by weight). The mixture was mixed well for approx. 2 minutes without introducing too many air bubbles. The mixture was left to rest for 2 minutes. (Pot life of this mixture: about 30 minutes). The epoxy was carefully poured over the specimen in an achieved mould. A vacuum system was used to reduce air bubbles. The embedded samples were left at room temperature for hardening during at least 12 hours.

- Surface preparation procedure
Each epoxy sample was wet ground with 400 grit, 800 grit, 1200 grit and finally 2000 grit SiC paper in sequence. To avoid maintaining a memory imprint of the grinding scratches deeper into the bulk material matrix, it was important to apply only a very gentle pressure during the grinding. So each sample was ground only for approximately one minute on each grit size paper with very gentle pressure. After wet grinding, the samples were rinsed with ethanol and dried with nitrogen gas to avoid corrosion during the sample preparation.
Polishing was performed using 3, 1 and 0.25 μm diamond paste (DP-Paste M) in turn with ethanol as a lubricant, and with utmost care. To obtain smooth and scratch-free surfaces, the samples were held very gently against the polishing cloth with very little applied pressure. Plenty of ethanol was used as a lubricant to obtain a well-defined surface. Each polishing step with diamond paste took about 5 to 10 minutes, depending on the removal of scratches. After polishing the samples were cleaned with ethanol and quickly dried with cold nitrogen gas.
To remove any residual particles left on the surface after grinding and polishing, all samples were cleaned ultrasonically first in ethanol for 6 minutes followed by ultrasonic cleaning in isopropyl alcohol for 6 min, and a final rinsing with isopropyl alcohol. Isopropyl alcohol was used as the last cleaning medium. After the ultrasonic cleaning, all samples were dried quickly again with cold nitrogen gas.
The polished surface was checked using a microscope. The metal surfaces were free from scratches and spots, so no re-polishing was necessary.

Ageing time (after polishing)
The samples were stored for 2 days before testing.
The required loading of 1 mg/L was achieved by adding an appropriate amount of test medium to the actual exposed free metal surface after embedding.

Results and discussion

Any other information on results incl. tables

The temperature of the test solutions fluctuated between 21.4 and 21.8°C, which was in line with the test conditions of 20 – 23 °C.

The test item has no immediate influence on the pH of the test system. The pH measured in the medium at the start of the test, and in the blank and test item vessels during the test at pH 8 varied from 7.97 to 8.02. The measured data at pH 8 were within the specifications of ± 0.2.

The dissolved oxygen concentration measured in the blank and test item vessels at pH 8 varied from 8.43 to 8.56 mg/L O2. These values were higher than the required value of ± 6 mg/L O2 at 22 °C corresponding with a minimal saturation level in the air of 70 %.

The measured TOC of the test medium was <1.0 mg/L C, and below the required level of 2.0 mg/L C as laid down in the OECD Test Guidance no.29.

The test medium at the start of the test and the blank control vessel during the test showed small concentrations above the detection limit of 0.1 µg/L manganese defined as three times the standard deviation of all blank measurements (N = 9).

At pH 8, the following observations could be made in the test item vessels with an average actual loading of 1 mg/L “surface equivalent” of embedded test material:

An average dissolved manganese concentration of 4.6 ± 0.4 μg/L Mn at the 7 day sampling point and 11.5 ± 1.3 μg/L Mn at the 28 day endpoint was measured with a between‐vessel variation of 9 % and 11 % respectively, which met the <20 % quality criteria at the 7 and 28 days endpoints. The within‐vessel coefficients of variation met the <10 % quality criteria for all test vessels at the 7 and 28 days endpoints.

Based on the average exposed surface area of the Manganese Massive (i.e. 0.83 mm2/L), a manganese release per surface of 0.55 mg/cm2 and 1.4 mg/cm2 was calculated at the 7 days and 28 days extraction endpoints, respectively.

Based on the actual mass equivalent loading (average of three test item vessels at pH 8, 1 mg/L “surface equivalent”), a manganese release of 4.6 μg/mg and 11.5 μg/mg was calculated at the 7 days and 28 days endpoints, respectively.

Applicant's summary and conclusion

Conclusions:

At pH 8, an average manganese concentration of 4.6 µg/L Mn (CV = 8 %) was found after 7 days which increased to 11.5 µg/L Mn (CV = 10 %) after 28 days of exposure at pH 8. The 7 days and 28 days dissolution results corresponded with a manganese release per surface of 0.55 mg/cm² and 1.4 mg/cm², respectively or 4.6 µg/mg and 11.5 µg/mg based on mass equivalent loading of 1 mg/L.

Executive summary:

The extent of transformation/dissolution of the test substance was investigated in a study which was conducted in accordance with the OECD Test Guideline 29.

A study was conducted to determine the rate and pH dependent extent of dissolution of the test material, tested with a target 1 mg/L “surface loading” in standard aqueous solutions at pH 8 (air-buffering) for 28 days at an agitation speed of 100 revolutions per minute (rpm). The short term (acute) transformation/dissolution endpoint was based on the dissolved test material concentrations obtained after 7 days. The long-term (chronic) transformation/dissolution endpoint was based on the dissolved manganese concentrations obtained after 28 days.

Analyses of the concentrations of dissolved test material and the determination of the total organic carbon content (TOC) of the test medium were performed.

All test parameter conditions were fully in accordance with the OECD Test Guidance no.29 requirements.

The measured TOC of the media were <1.0 mg/L C and below the required level of 2.0 mg/L C. The temperature of the test solutions fluctuated between 21.4 and 21.8 °C and corresponded to the required test conditions of 20 – 23 °C.

The pH measured in the medium at the start of the test, and in the blank and test item vessels during the test at pH 8 varied from 7.97 to 8.02. The measured data at pH 8 were within the specifications of ± 0.2.

The dissolved oxygen concentration measured in the blank and test item vessels at pH 8 varied from 8.43 to 8.56 mg/L O2. These values were higher than the required value of ± 6 mg/L O2 at 22 °C corresponding with a minimal saturation level in the air of 70 %.

The test medium at the start of the test and the blank control vessels during the test showed small concentrations above the detection limit of 0.1 μg/L of test material defined as three times the standard deviation of all blank (N=9) measurements.

For the test at pH 8 at a 1 mg/L loading of test material (surface equivalent), average dissolved manganese concentrations of 4.6 μg/L Mn (CV = 8 %) and 11.5 μg/L Mn (CV = 10 %) were found at the 7 days and 28 days endpoints, respectively. Based on the exposed surface area of the test material (i.e. 0.83 mm2/L), a test material release per surface of 0.55 mg/cm2 and 1.4 mg/cm² was calculated at the 7 days and 28 days extraction endpoints, respectively.

At pH 8, an average manganese concentration of 4.6 µg/L Mn (CV = 8 %) was found after 7 days which increased to 11.5 µg/L Mn (CV = 10 %) after 28 days of exposure at pH 8. The 7 days and 28 days dissolution results corresponded with a manganese release per surface of 0.55 mg/cm² and 1.4 mg/cm², respectively or 4.6 µg/mg and 11.5 µg/mg based on mass equivalent loading of 1 mg/L.