Tricarbonyl(methylcyclopentadienyl)manganese

PBT assessment

PBT assessment: overall result

Reference

Name:

tricarbonyl(methylcyclopentadienyl)manganese

Type of composition:

legal entity composition of the substance

State / form:

liquid

Related composition:

tricarbonyl(methylcyclopentadienyl)manganese

Reference substance:

tricarbonyl(methylcyclopentadienyl)manganese

PBT status:

the substance is not PBT / vPvB

Justification:

Introduction :

 

A PBT/vPvB assessment is required for all substances for which a chemical safety assessment (CSA) must be conducted. Methylcyclopentadienyl manganese tricarbonyl (mmt) is an annex IX substance, manufactured between 100 to 1000 tonnes per year, required to be registered under REACH and for which a CSA has to be performed. A substance is considered to be PBT or vPvB if it satisfies the criteria listed in Annex XIII to the REACH regulation. This Annex applies to all organic substances, including organo-metals, which mmt is.

Current guidance from ECHA (Chapter R.11: PBT/vPvB assessment v2.0, November, 2014 also requires PBT/vPvB assessment to include "relevant constituents" including impurities and additives at > or = 0.1 % (w/w). For mmt, there is one known impurity expected to be present at concentrations between 0 and 5 %. This is Cyclopentadienyl manganese tricarbonyl or CMT (EC 235 -142 -4; CASRN 12079 -65 -1). CMT is structurally similar to mmt and is regulated as a member of the "Manganese compounds" category in various jurisdictions such as U.S.A. and Canada. Like mmt, CMT too has not been assessed as PBT or vPvB in any jurisdiction. The two structures are provided as attachment. Due to the high structural similarity and the fact that CMT is not classified as 'hazardous to the environment' in ECHA's CLP inventory, CMT too is not expected to be assessed as PBT or vPvB.

 

1. Criteria for PBT/vPvB assessment

 

The criteria for PBT and vPvB are laid out in Section 1 of Annex XIII to the REACH regulation and reproduced in ECHA Guidance Chapter R.11: PBT/vPvB Assessment v 2.0, November, 2014. The definitive criteria are listed in Table R.11 -1 of the Guidance. Tables R.11 -2 and R.11-3 of the Guidance provide screening and assessment information, according to sections 3.1 and 3.2 of REACH.

 

2. PBT/vPvB assessment

2.1. Persistence

Biodegradation, hydrolysis and photolysis are the common mechanisms of degradation and depletion of chemical substances.

 

2.1.1 Abiotic degradation

 

mmt is highly sensitive to degradation by light. The wavelengths between 340 and 440 nm are the active area. Ter Haar et al. (1975), calculated a half -life of mmt in the air of 8 to 18 seconds assuming a first order kinetics. mmt vapour was discharged into the air in the presence of sunlight, and inorganic and organic manganese were collected downwind. Due to high uncertainties on wind speed measurements, and sampling low quantities of inorganic and organic manganese, no accurate figure is reported. 

In the second experiment, the authors exposed mmt in a quartz tube and a 2593 seconds half-life was measured. The exposure was complex due to the solid decomposition products, which made a quantitative result difficult. Nevertheless, both results clearly indicate half-life in air in the presence of sunlight to be less than 2 minutes. 

Garrison et al. (1995) conducted an experiment to determine the aquatic photolysis of mmt. The test substance mmt photolysed rapidly in RO-purified water exposed to January midday sunlight. The degradation followed first order kinetics with a calculated half-life of 0.93 minutes with a rate coefficient k of 0.74± 0.01/min. and a regression correlation coefficient of 0.9986. The resultant transformation products are methylcyclopentadiene, cyclopentadiene, carbon monoxide and a yellow precipitate identified as a manganese carbonyl. Upon exposure to oxygen, an oxidized solid product of trimanganese tetroxide was formed. 

The hydrolysis of mmt was determined in study conducted by NOTOX in 2008. There was less than 10% decrease in the concentration of mmt in the period of 2.4 and 124 hours. It was concluded that the half-life of the test substance at 25°C is > 1 year. 

Based on the information summarized under chapter “5.1 Stability” of IUCLID5, the only relevant route of abiotic degradation for mmt is photo-degradation. It should be noted, that photo-degradation is not applicable to all different environmental compartments. In case of a spill to the aquatic environment, light degradation will only occur in the top layer of the aquatic compartment. 

 

2.1.2 Biotic degradation

In order to characterize the biodegradation potential of mmt, three studies are available and summarized under chapter 5.2 Biodegradation. An enhanced ready biodegradability study was conducted by NOTOX in 2008, following the OECD 301D guideline but with low initial concentration (1 mg/L) and extended duration (56 days), with analytical monitoring of mmt concentrations. The study reported an average 1 % biodegradation of mmt based on its ThOD (theoretical oxygen demand). The analytical monitoring did not show any significant decrease of the mmt concentration during the test. Based on this result, mmt cannot be considered to be readily biodegradable during the 56 days exposure period.

In a publication by Garrison et al. (1995) both anaerobic and aerobic biodegradation of mmt was tested in sediment and aquifer solids. Half-lives calculated for anaerobic degradation ranged from 165 – 568 days and those for aerobic degradation ranged from 87 – 480 days. Regarding the half-lives of mmt in sediment, no biodegradation was seen in 60 days exposure period. Based on these three studies, mmt is not readily biodegradable, nor does it biodegrade fast in the different environmental compartments. 

In conclusion, abiotic degradation is only realistic through photodegradation since mmt does not hydrolyse. It is not readily biodegradable and there is no clear indication of biodegradation in water, sediment or soil.

Thus, mmt is assessed as P, and potentially vP.

 

2.2. Bioaccumulation

The bioaccumulation potential of mmt was determined in a publication by Garrec et al. (1995). Different aquariums were setup to simulate the natural environment. One aquarium contained only water (distilled), the second contained fresh water and sediment, the third contained aquatic plants, while the last one contained fish. The total exposure time was 9 days and sampling time points in all four systems was performed at: 3h, 6h, 24h, and 3 and 9 days. In the sediment, the mmt concentration factor is in the order of 3.4, but the accumulation is located only at the surface. On the other hand, the accumulation of mmt in living organisms is much higher than reported for the sediment. In the case of aquatic plants, a bioconcentration factor in order of 400 was calculated while for the fish the BCF was around 200, for the total period of 9 days. In conclusion, mmt does not meet the definitive criteria for bioaccumulation. Additionally, there is no existing information regarding mmt biomagnification in the food chain, and the octanol-water partitioning coefficient is 3.4, much lower than 4.5, the screening threshold for a bioaccumulative substance.

 

Thus, mmt is assessed as non-B and non-vB due to the BCF in aquatic species being less than 2000.

 

2.3. Toxicity

The last step for a PBT/vPvB assessment is to assess the toxicity (T) criterion. 

 

Following the toxicity assessment guidance in ECHA’s Chapter R.11 (section R.11.4.1.3), mmt is assessed as not meeting the criteria for T due to the following reasons:

1. The substance has a long-term NOEC of 0.07 mg/L (based on 72 -hour algae study), which is greater than the criterion of 0.01 mg/L.

2. It does not meet the criteria for classification as carcinogenic (category 1A or 1B), germ cell mutagenic (category 1A or 1B), or toxic for reproduction (category 1A, 1B or 2) according to CLP regulation.

3. It does not show evidence of chronic toxicity, as identified by meeting criteria for classification: STOT RE 1 or STOT RE 2 according to CLP regulation.

4. It is not classified as H350, H340, H372, H373, H350i, H360 or H361 according to CLP regulation. 

5. It does not meet the screening criteria for toxicity (Table R.11 -6). The lowest LC/EC50 value reported is 0.21 mg/L for fish (96 -hour test in carp), which is higher than the screening criterion of 0.1 mg/L. 

    

 

Thus, mmt is assessed as non-T.     

 

3. Conclusion:

 

In summary, mmt does not meet the criteria for a PBT or vPvB substance, since the criteria of bioaccumulation and toxicity are not fulfilled.