Borate cobalt(2+) C3/C8/C10 carboxylates salts

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

1.06 µg/L

Assessment factor:

2

Extrapolation method:

sensitivity distribution

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

2.36 µg/L

Assessment factor:

3

Extrapolation method:

sensitivity distribution

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

0.37 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

53.8 mg/kg sediment dw

Assessment factor:

10

Extrapolation method:

assessment factor

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

69.8 mg/kg sediment dw

Assessment factor:

10

Extrapolation method:

assessment factor

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

10.9 mg/kg soil dw

Assessment factor:

2

Extrapolation method:

sensitivity distribution

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

Read-across statement

Under environmentally-relevant conditions, metal carboxylate salts readily dissociate from an ionic bonded salt into metal ions and free carboxylic acid upon dissolution in aqueous media. Dissociation is a reversible process and the proportion of dissociated salt present is dependent on the pH and composition of the solution and the metal-ligand dissociation constant of the salt. Predictions of stability of metal carboxylates (propionate, valerate, isovalerate and benzoate salts for Ca, K, Zn, Mn and Co) in a standard ISO 6341 medium (2 mMCaCl2, 0.5 mM MgSO4, 0.77 mM NaHCO3 and 0.077 mM KCl, pH 6 and 8) clearly show that monodentate ligands such as carboxylic acids have no potential for complexing metal ions in solution (<<1% of metal complexed at 0.001 mM; Visual minteq. Version 3.0, update of 18 October 2012. http://www2.lwr.kth.se/English/OurSoftware/vminteq/index.html). Complexation of the liberated free metal ion with ligands present in the natural environment (e.g. dissolved organic matter) will further increase the degree of dissociation of the metal-carboxylate salts.

Upon dissolution and dissociation of metal carboxylates into the metal ion and carboxylate anion, both constituent ions will each show its proper partitioning, degradation, and bioaccumulation behaviour in the environment. The environmental fate and behaviour for the metal and organic moieties is predicted to be clearly different from each other, resulting in a different relative distribution over the environmental compartments (water, air, sediment and soil). Because the relative exposure to both constituent ions in the various environmental compartments is hence predicted to be different from the original composition of the metal carboxylate, data for the ecotoxicological properties of metal carboxylates tested as such are also considered less relevant and a read-across approach to separate data for both the metal cation and carboxylate anion is preferred.

Physicochemical and ecotoxicological data for the individual dissociation products (i.e., metal and carboxylic acids) are therefore essential to understanding the environmental fate and toxicological characteristics of the metal carboxylate salts. Environmental fate and effects data developed with the free acid, or a simple salt that would readily dissociate (e.g. the sodium salt), can serve as surrogate data for the carboxylic acid component of each cobalt carboxylate salt. Similarly, data for the metal ions can be represented by fate and toxicity data generated with simple metal salts (e.g. chloride or nitrate salts). For example, the potential hazards associated with cobalt acetate can be estimated through the evaluation of the cobalt free ion, tested as cobalt dichloride, and the acetate moiety, tested as sodium acetate. Thus, data for each individual carboxylic acid (tested as the free acid or Na, K or Ca salt) and the individual metal (tested as the free metal, metal chloride, other simple metal salt) can be used to “read-across” to characterize the hazard of a cobalt carboxylate compound.

Most testing efforts generally suggest that the test material will dissociate in water into its cationic and anionic components and that the effects noted can be attributed to the individual components, as occurs for ionic salts at concentrations of environmental concern. The USEPA, in their guidance document for derivation of ambient water quality criteria (USEPA 1985), states: “The toxic metal [for testing] should be added in the form of an inorganic salt having relatively high solubility. Nitrate salts are generally acceptable; chloride and sulphate salts of many metals are also acceptable.” For this reason, testing is usually done with a readily soluble metal salt, where the anionic component is not likely to “overshadow” the cation’s contribution to any observed toxicity.

For the most part, this is considered to be an environmentally “conservative” approach, and therefore metals testing is generally done with chloride or nitrate salts.

For most metal-containing compounds, it is the potentially bioavailable metal ion that is liberated (in greater or lesser amounts) upon contact with water that is the moiety of ecotoxicological concern. Therefore, the solubility of the metal carboxylates has to be taken into account and compared with the effect concentrations for dissolved metals. The solubility of the metal carboxylates is generally above the range of effects concentrations for dissolved metals in the aquatic environment and therefore ecotoxicity data for soluble metal salts can be directly used in a read-across approach for the metal carboxylates. As a conservative approach, the ecotoxicological properties of the carboxylic acid can be considered, if it is believed that this may significantly contribute to the toxicity of the salt.

In case both the metal and organic moieties require a risk assessment (e.g. because both are classified as hazardous to the aquatic environment or have L(E)C50 values < 100 mg/l; REACH Guidance on information requirements and chemical safety assessment, chapter B.8 Scope of exposure assessment), the dose additivity approach can be used to explain the ecotoxicological effects of the metal carboxylate based on the data for the individual moieties. As stated in a toxicity assessment of chemical mixtures opinion for the European Commission (Scientific Committee on Consumer Safety (SCCS), Scientific Committee on Health and Environmental Risks (SCHER), and Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR) [2011] “Preliminary opinion on Toxicity and Assessment of Chemical Mixtures,” the dose/concentration addition method should be preferred over the independent action approach if no mode of action information is available.

In the framework of the European REACH regulation (EC 1907/2006), some measured data on solubility, behaviour and toxicity of a range of metal carboxylates (e.g. some zinc carboxylates) were collected in order to support this read-across approach or for the purpose of classification and labeling under the European CLP regulation (EC 1272/2008). These data are available on the REACH dissemination website (http://echa.europa.eu/web/guest/information-on-chemicals/registered-substances) after registration.

Empirical data from chronic toxicity tests conducted with the cladoceran, Ceriodaphnia dubia, and the fathead minnow, Pimephales promelas, as part of the Cobalt Development Institute (CDI) research programme, support the proposed “read-across” approach for evaluating the toxicity of cobalt inorganic and carboxylate salts compounds. Cobalt 10% effect concentrations (i.e., EC10 values) for all five of the compounds tested were statistically similar to one another, suggesting that the free cobalt ion dictates the chronic toxicity of all of the compounds or, at the very least, the EC10 values of the compounds are a conservative estimator of cobalt toxicity. It is also apparent that the addition of the boron atom, in the case of the cobalt borate complexes, does not contribute to the toxicity of the salt; this is likely due to the reduced toxicity of boron, compared with cobalt and the fact that cobalt is present in a 3:1 ratio to boron in these materials.

Ceriodaphnia dubia 10% effect concentrations (EC10) for cobalt compounds

Test material       EC10 (95% CI; μg dissolved Co/L)

Cobalt dichloride       7.9 (0.7-86.4)

Cobalt hydroxide oxide       11.6 (9.8-13.8)

Cobalt bis (2-ethylhexanoate)       19.7 (14.7-26.4)

Cobalt borate neodecanoate       15.1 (7.0 – 32.6)

Cobalt stearate       23.3 (14.7-37.0)

Cobalt resinate       8.4 (4.0-17.6)

      

Fathead minnow (Pimephales promelas) 10% effect concentrations EC10) for cobalt compounds

Test material       EC10 (95% CI; μg dissolved Co/L)

Cobalt dichloride       350 (210-590)

Cobalt naphthenate       206 (94-452)

Cobalt neodecanoate       204 (17-2503)

Cobalt resinate       187 (164 - 213)

These findings are sufficient justification for the implementation of a “read-across strategy” using results obtained in tests conducted with soluble cobalt salts (e.g., cobalt dichloride), and this is applicable for all relevant environmental endpoints (aquatic toxicity, sediment toxicity, terrestrial toxicity, toxicity to microorganisms, toxicity to birds, and toxicity to mammals). Cobalt dichloride, the most frequently tested compound, is a readily soluble substance and yields free cobalt(II) ions upon dissolution, i.e., the same speciation form that is relevant upon dissolution of cobalt metal, cobalt inorganic salts, and cobalt carboxylate salts.

It should be noted that all effects levels from these studies are expressed as dissolved cobalt (i.e., operationally defined as that portion passing through a 0.45 μm filter).

With reference to the RAAF (ECHA, 2017), criteria for a category approach Scenario 5 with Appendices C are met for the cobalt category substances as detailed in Appendix 1.3 of the CSR. Due to the absence of substance specific information for the majority of substances within the cobalt category, the approach will read-across data from representative source substances to all other members of the read-across group. Salt reaction of borate, cobalt(2+) and C3/C8/C10 carboxylates can be considered as part of this read-across group.

Conclusion on classification

Environmental classification of the Salt reaction of borate, cobalt(2+) and C3/C8/C10 carboxylates is derived from the environmental classification of its 3 main constituents as a worst case scenario. The proposed self-classification is as follows:

- Acute 1 (M = 1) and Chronic 2

For classification purposes, Ecotoxicity Reference Values (ERVs) should be derived using the “lowest value” approach. For metals ERVs are derived using data from one or more soluble metal substances, and in most cases, test data are reported on a “dissolved” metal concentration basis. In the assessment for Co, the aquatic toxicity classifications of Co metal and Co compounds are derived by comparing the quantity of dissolved Co liberated during an OECD Transformation/Dissolution test (OECD 29) with the ERVs derived from laboratory toxicity tests developed with a soluble cobalt compound (e.g. cobalt dichloride). In the case of Co, single acute and chronic ERVs are available without consideration of factors that might affect Co bioavailability or toxicity (i.e. pH, DOC, hardness).

 

The acute ERV is based on available ecotoxicity data for an plant species, Lemna minor, while the chronic ERV is based on available ecotoxicity data for the epibenthic invertebrate, Hyalella azteca. The reported Co ERVs are as follows:

           Acute:            Lemna minor             52.0μg/L

           Chronic:         Hyalella azteca         7.6μg/L

 

As outlined in the CLP guidance (ECHA 2017), substance-specific ERVs can be developed using the following equation:

ERVsubstance = ERVCo × MWsubstance / (n × MWCo)

where n is the stoichiometric number of Co atoms in the substance molecule.

A full description of ERV derivation is provided as attachment to endpoint summary of IUCLID section 6.

The EU CLP guidance document (ECHA 2017) permits consideration of the “environmental transformation” of metals in the environment, including removal from the water column and deposition and sequestration in sediments, much the same way as the concept of “rapid degradation” is considered for organic chemicals. To indicate “rapid removal” for a metal, it is assumed that one must demonstrate greater than 70% removal of soluble metal within 28 days of addition to the water column, as is the case with organic compounds. Furthermore, one must demonstrate that the potential for metal remobilisation from sediments is limited, for example by changes in metal speciation, remineralisation and permanent burial in the sediment. If these conditions are met, the metal is considered “rapidly removable” and poses lower chronic environmental risk. Results of modelling using the Unit World Model (UWM) and initial empirical testing via the extended transformation/dissolution protocol (e-TDp) indicate that the cobalt ion satisfies the requirements for “rapid” metals removal, i.e. > 70% removal from the water column in 28 days, and the limited sediment remobilisation potential under most environmental conditions.

(i) Cobalt borate neodecanoate:

The lowest available acute reference values are:

Algae, Pseudokirchneriella subcapitata (following OECD Method 201)          

EC50: 0.551 mg/L (0.121 mg Co/L)

Invertebrate, Daphnia magna (following OECD Method 202)          

EC50: 9.2 mg/L (2.6 mg Co/L)

No compound specific acute data are available for fish species (but are typically least sensitive trophic group)

Data classify substance as Acute 1; M = 1

Available chronic EC10value for algae is:

Algae, Pseudokirchneriella subcapitata (following OECD Method 201)            

EC10: 0.182 mg/L (0.040 mg Co/L)

Invertebrate, Ceriodaphnia dubia (following USEPA 2002)          

EC10: 0.068 mg/L (0.015 mg Co/L)

No compound specific chronic data are available for fish species

Chronic data for invertebrates classify substance as Chronic 1 (M = 1) or 2 depending on rapid removal

Chronic tests take precedence over acute data for chronic classification, so acute algae and invertebrate values not considered under surrogate scheme

There is no evidence for bioaccumulation or biomagnification in the environment

Proposed self-classification:

Acute 1 (M = 1) and Chronic 2

(ii) Cobalt borate 2-ethylhexanoate:

Water solubility is 2.69 g Co/L at 20C

Expected to be readily soluble under TDp as well

Molecular weight is 665.29 g/mol

Substance-specific ERVs are:

Acute ERV: 195.7 μg/L– <1mg/L so Acute 1

Chronic ERV: 28.6 μg/L– between 10 and 100μg/L so Chronic 1 (M=1) or Chronic 2 depending on rapid removal

Proposed self-classification: Acute 1 (M = 1) and Chronic 2

(iii) Cobalt borate propionate

Water solubility is 12.2 g Co/L at 20C

Expected to be readily soluble under TDp as well

Molecular weight is 454.84 g/mol

Substance-specific ERVs are:

Acute ERV: 133.8 μg/L– <1mg/L so Acute 1

Chronic ERV: 19.6 μg/L– between 10 and 100μg/L so Chronic 1 (M=1) or Chronic 2 depending on rapid removal

Proposed self-classification:

Acute 1 (M = 1) and Chronic 2

• Proposed self-classification for target substance:

Acute 1 (M = 1) and Chronic 2