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Ecotoxicological information

Short-term toxicity to aquatic invertebrates

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Administrative data

Endpoint:
short-term toxicity to aquatic invertebrates
Type of information:
experimental study
Remarks:
reported in a publication
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Remarks:
review article
Justification for type of information:
REPORTING FORMAT FOR THE ANALOGUE APPROACH
see target record
Cross-referenceopen allclose all
Reason / purpose for cross-reference:
reference to same study
Reference
Endpoint:
long-term toxicity to aquatic invertebrates
Type of information:
experimental study
Remarks:
reported in a publication
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Remarks:
review article
Reason / purpose for cross-reference:
reference to same study
Reason / purpose for cross-reference:
reference to same study
Qualifier:
no guideline required
Principles of method if other than guideline:
Review of literature data
GLP compliance:
no
Analytical monitoring:
not specified
Vehicle:
not specified
Test organisms (species):
Daphnia magna
Details on test organisms:
TEST ORGANISM
- Common name: Water flea
- Strain/clone: Daphnia magna Straus
Test type:
semi-static
Water media type:
freshwater
Total exposure duration:
21 d
Hardness:
150 resp. 166 mg/L
Test temperature:
20 resp. 19.2 °C
pH:
6.7 - 8.1 resp. 7.1 - 8.7
Details on test conditions:
TEST SYSTEM
- Renewal rate of test solution (frequency/flow rate): 3 times weekly

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Lake Huron water resp. Carbon-filtered well water
Reference substance (positive control):
not specified
Duration:
21 d
Dose descriptor:
LC50
Effect conc.:
52.2 mg/L
Nominal / measured:
not specified
Conc. based on:
element
Remarks:
boron
Basis for effect:
not specified
Remarks on result:
other: corresponding to 395.5 mg/L BHO2.K
Remarks:
Lake Huron water, 20°C, pH 6.7 - 8.1, Hardness 150 mg/l
Duration:
21 d
Dose descriptor:
NOEC
Effect conc.:
6.4 mg/L
Nominal / measured:
not specified
Conc. based on:
element
Remarks:
boron
Basis for effect:
not specified
Remarks on result:
other: corresponding to 48.5 mg/L BHO2.K
Remarks:
Lake Huron water, 20°C, pH 6.7 - 8.1, Hardness 150 mg/l
Duration:
21 d
Dose descriptor:
LOEC
Effect conc.:
13.6 mg/L
Nominal / measured:
not specified
Conc. based on:
element
Remarks:
boron
Basis for effect:
not specified
Remarks on result:
other: corresponding to 103 mg/L BHO2.K
Remarks:
Lake Huron water, 20°C, pH 6.7 - 8.1, Hardness 150 mg/l
Duration:
21 d
Dose descriptor:
LC50
Effect conc.:
53.2 mg/L
Nominal / measured:
not specified
Conc. based on:
element
Remarks:
boron
Basis for effect:
not specified
Remarks on result:
other: corresponding to 403.1 mg/L BHO2.K
Remarks:
Carbon-filtered well water, 19.2°C, pH 7.1 - 8.7, hardness 166 mg/L
Key result
Duration:
21 d
Dose descriptor:
NOEC
Effect conc.:
6 mg/L
Nominal / measured:
not specified
Conc. based on:
element
Remarks:
boron
Basis for effect:
not specified
Remarks on result:
other: corresponding to 45.5 mg/L BHO2.K
Remarks:
Carbon-filtered well water, 19.2°C, pH 7.1 - 8.7, hardness 166 mg/L / lowest available value
Key result
Duration:
21 d
Dose descriptor:
LOEC
Effect conc.:
13 mg/L
Nominal / measured:
not specified
Conc. based on:
element
Remarks:
boron
Basis for effect:
not specified
Remarks on result:
other: corresponding to 98.5 mg/L BHO2.K
Remarks:
Carbon-filtered well water, 19.2°C, pH 7.1 - 8.7, hardness 166 mg/L
Validity criteria fulfilled:
not specified
Conclusions:
The present information was based on a literature review of various suitable read-across substances all belonging to the group of borates, the relevant information on short term toxicity in daphnia magna was taken from boric acid. The lowest available chronic NOEC was 6 mg/L, which corresponds to 45.5 mg/l BHO2.K. So the available data shows that neither boron nor potassium metaborate needs to be classified as chronic aquatic toxic acc. Regulation 1272/2008, as all NOECs were above the limit value for classification of 1 mg/l for Non-rapidly degradable substances for which there are adequate chronic toxicity data available.
Executive summary:

A literature review of showed that boron / potassium metaborate gave consistently NOECs > 1 mg/l.

Reason / purpose for cross-reference:
reference to same study
Reference
Endpoint:
short-term toxicity to fish
Type of information:
experimental study
Remarks:
reported in a publication
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Reason / purpose for cross-reference:
reference to same study
Reason / purpose for cross-reference:
reference to same study
Qualifier:
no guideline required
Principles of method if other than guideline:
Review of literature data
GLP compliance:
no
Analytical monitoring:
not specified
Vehicle:
not specified
Test organisms (species):
other: Mosquito fish and Coho salmon, among others
Details on test organisms:
Mosquito fish (Gambusia affinis), adult females
Coho salmon (0. kisutch), under yearlings, 1.8-3.8 g
Test type:
other: static & static renewal
Water media type:
other: freshwater and seawater
Total exposure duration:
96 h
Test temperature:
20-23°C or 22-26°C or 8°C
pH:
5.4-7.3 or 8.6-9.1 (freshwater fish)
Salinity:
28 promiile (seawater fish)
Reference substance (positive control):
not required
Duration:
96 h
Dose descriptor:
LC50
Remarks:
Mosquito fish, boric acid (TLm)
Effect conc.:
978 mg/L
Nominal / measured:
not specified
Conc. based on:
element
Remarks:
boron
Basis for effect:
mortality (fish)
Remarks on result:
other: corresponding to 7409.7 mg/L BHO2.K
Remarks:
20-23°C; pH 5.4-7.3; turbidity 210-250 mg / liter, static
Duration:
96 h
Dose descriptor:
LC50
Remarks:
Mosquito fish, sodium tetraborate (TLm)
Effect conc.:
408 mg/L
Nominal / measured:
not specified
Conc. based on:
element
Remarks:
boron
Basis for effect:
mortality (fish)
Remarks on result:
other: corresponding to 3091.2 mg/L BHO2.K
Remarks:
22-26°C; pH 8.6-9.1; turbidity 410-650 mg / liter, static
Duration:
96 h
Dose descriptor:
LC50
Remarks:
Coho Salmon, sodium metaborate
Effect conc.:
40 mg/L
Nominal / measured:
not specified
Conc. based on:
element
Remarks:
boron
Basis for effect:
mortality (fish)
Remarks on result:
other: corresponding to 303.1 mg/L BHO2.K
Remarks:
Seawater; 8°C; salinity 28 promille, static renewal (daily)
Validity criteria fulfilled:
not specified
Conclusions:
The present information was based on a literature review of various suitable read-across substances all belonging to the group of borates. The lowest available LC50 value was 40 mg/L in an seawater organism, which corresponds to 303 mg/l BHO2.K, the other values were a magnitude higher. So the available data shows that potassium metaborate does not need to be classified as aquatic toxic acc. Regulation 1272/2008, as all LC50 values for potassium metaborate were calculated to be above the limit value for classification of 100 mg/l.
Executive summary:

A literature review of showed that potassium metaborate gave consistently LC50 values > 100 mg/l.

Reason / purpose for cross-reference:
read-across source
Remarks:
target record
Reference
Endpoint:
short-term toxicity to aquatic invertebrates
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Remarks:
reported in a publication
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Remarks:
review article, read-across substance
Justification for type of information:
1. HYPOTHESIS FOR THE ANALOGUE APPROACH
Borates in general dissociate immediately upon contact with water and are converted rapidly into i.a. boric acid. This includes salts of boric acid (borates), metaboric acid (metaborates), hydrated borates (hydroborates) or borax. Boron compounds are highly soluble in water, and upon dissolving form essentially two species, undissociated boric acid (H3BO3) and borate anion (B(OH)4- [Soucek, Environmental Toxicology and Chemistry, Vol. 30, No. 8, pp. 1906–1914, 2011]. Orthoboric acid (Short: Boric acid, H3BO3) is a weak monobasic acid, which does not act as a proton donator but OH- acceptor (Lewis base) according to the following equilibrium:
B(OH)3 + 2 H2O ↔ B(OH)4- + H3O+ pKs = 9.2
Metaboric acid ((HBO2)n is formed during heating >90°C via intermolecular condensation while releasing a water molecule. Upon solubilisation in water, orthoboric acid is formed again. In diluted solutions practically only the monomeric H3BO3 are present [Riedel, Anorganische Chemie, de Gruyter, 1999]. A study by Zhu et al. [Zhu FY, Journal of Molecular Structure, Volume 1070, 24 July 2014, Pages 80-85] shows that the main borate species in aqueous KB(OH)4 solutions is B(OH)4−. This ion is in an equilibrium with H3BO3.
So in aqueous solutions at physiological and acidic pH, low concentrations of simple inorganic borates such as boric acid, disodium tetraborate decahydrate, disodium tetraborate pentahydrate, boric oxide and disodium octaborate tetrahydrate will predominantly exist as undissociated boric acid [WHO, Environmental Health Criteria 204, boron, World Health Organization, Geneva, 1998]. Also borax readily dissolves in water to form undissociated boric acid (H3BO3) and borate anion (B(OH)4-) [Soucek, 2011]. Most of the simple inorganic borates exist predominantly as undissociated boric acid in dilute aqueous solution at physiological pH [Hubbard SA, Biological Trace Element Research Vol. 66, 1998]. In aqueous solution, the metaborate ion is rapidly converted to the borate anion and the weakly dissociated boric acid by the sequential reactions shown by the following equations [Antia NJ, 1975, J. Fish. Res. Board Can. 32: 2487-2494]:
BO2- + 2 H2O → B(OH)4-
B(OH)4- + H3O+ ↔ B(OH)3 + 2 H2O
So if metaboric acid (resp. borates) is dissolved in water, orthoboric acid is formed [Riedel, 1999].
So summarizing, upon contact with water, potassium metaborate dissociates immediately into potassium and metaborate ions, whereas the latter is converted rapidly into boric acid.
As stated above, in diluted solutions and biologically relevant pH values, only undissociated boric acid is present, irrespective of which borate was dissolved in water, which so also applies to potassium metaborate. This is applicable for both ecotoxicity tests (usual limit concentration: 100 mg/l) as well as toxicological studies. Borates are readily absorbed orally in humans and animals [Hubbard, 1998], so the expected plasma levels are maximally as high as the applied dose, which still indicates that the boron species dissolved in plasma is H3BO3.
In consequence, data from boric acid and also all types of borates mentioned above, may be used to cover data gaps for potassium metaborate via read-across.

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
Target: Potassium metaborate, CAS 13709-94-9, EC 237-262-2, BKO2, MW = 81.9081 g/mol, SMILES [K+].[O-]B=O
Source: Boric acid / Orthoboric acid, CAS 10043-35-3, EC 233-139-2, H3BO3, MW = 61.83 g/mol, SMILES OB(O)O
Source: Borax / di-Sodium tetraborate decahydrate / sodium borate, CAS 1303-96-4, EC 603-411-9, Na2B4O7 *10H2O, MW = 381.365, SMILES (anhydrous) [Na+].[Na+].[O-]B(OB=O)OB([O-])OB=O
Source: Sodium tetraborate pentahydrate / Boron sodium oxide, pentahydrate, CAS 12179-04-3, EC 601-808-1, B4-O7.2Na.5H2-O, MW = 291.291 g/mol, SMILES B(=O)OB([O-])OB([O-])OB=O.O.O.O.O.O.[Na+].[Na+]
Source: Disodium octaborate tetrahydrate / Boron sodium oxide, tetrahydrate, CAS ‎12280-03-4, EC 602-894-3, B8Na2O13
Source: Sodium metaborate tetrahydrate / Boric acid, sodium salt, tetrahydrate, CAS 10555-76-7, EC 600-663-1
Source: Dipotassium tetraborate / boron potassium oxide, CAS 1332-77-0, EC 215-575-5, B4K2O7, MW = 233.4358, SMILES [K+].[K+].[O-]B([O-])[O-].[O-]B([O-])[O-].[O-]B([O-])[O-].[O-]B([O-])[O-]
Source: Diammonium tetraborate tetrahydrate / azane;2-hydroxy-4-[(4-hydroxy-1,3,2,4-dioxadiboretan-2-yl)oxy]-1,3,2,4-dioxadiboretane;tetrahydrate, CAS 10135-84-9; 12228-87-4, B4H16N2O11, MW = 263.371, SMILES B1(OB(O1)OB2OB(O2)O)O.N.N.O.O.O.O
Source: Zinc borate, hydrate / dodecaboron tetrazinc docosaoxide heptahydrate / Boron zinc hydroxide oxide / hexaboron dizinc undecaoxide, CAS 138265-88-0, EC 235-804-2, B12Zn4(OH)14O15, MW = 425.7 g/mol

There are no impurities known in neither target nor source chemical(s) which may affect the feasibility of the read-across approach.

3. ANALOGUE APPROACH JUSTIFICATION
As obvious in detail from the available data matrix, all borates exhibit similar (eco-)toxicological properties.
With regard to ecotoxicity, all available studies on various borates on fish, invertebrates, and algae, both short and long term, consistently indicate that, recalculated from the molecular weight, Potassium metaborate does not need to be classified as aquatic toxic (acute and chronic) according to Regulation 1272/2008 and amendments.
Similarly, with regard to human-relevant endpoints, Potassium metaborate does not need to be classified as acutely toxic, as consistently indicated by various borates in also various species.
Both boric acid and borax do not trigger classification as skin sensitizing, no further study data is available, However, Sodium Borate and Boric Acid are used in cosmetics in various functions, and no sensitizing reactions induced by these cosmetic products have been reported.
Borax and Boric acid were similarly non-mutagenic in the Ames Test, and the non-genotoxic potential is further supported by a negative chromosome aberration test. Both Borax and Boric however gave in different species, although via partially species-specific mode of actions, indication that they interfere via a certain threshold with reproduction. Proof via human data is however not available.
Further, all borates chosen for read-across, incl. the registered substance itself, are highly soluble in water, and upon dissolving form essentially two species, undissociated boric acid (H3BO3) and borate anion (B(OH)4-. Hence, read-across is further based on common breakdown products.
So summarizing, read-across is justified via similar (eco-)toxicological effects and common breakdown products.

4. DATA MATRIX
See attachment
Reason / purpose for cross-reference:
read-across source
Qualifier:
no guideline required
Principles of method if other than guideline:
Review of literature data
GLP compliance:
no
Analytical monitoring:
not specified
Vehicle:
not specified
Test organisms (species):
Daphnia magna
Details on test organisms:
TEST ORGANISM
- Common name: Water flea
- Strain/clone: Daphnia magna Straus
Test type:
static
Water media type:
freshwater
Total exposure duration:
48 h
Hardness:
150 resp. 166 mg/L
Test temperature:
20 resp. 19.2 °C
pH:
6.7 - 8.1 resp. 7.1 - 8.7
Details on test conditions:
TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Lake Huron water resp. Carbon-filtered well water
Reference substance (positive control):
not specified
Key result
Duration:
48 h
Dose descriptor:
LC50
Effect conc.:
133 mg/L
Nominal / measured:
not specified
Conc. based on:
element
Remarks:
boron
Basis for effect:
not specified
Remarks on result:
other: corresponding to 1007.7 mg/L BHO2.K
Remarks:
Lake Huron water, 20°C, pH 6.7 - 8.1, Hardness 150 mg/l
Duration:
48 h
Dose descriptor:
LC50
Effect conc.:
226 mg/L
Nominal / measured:
not specified
Conc. based on:
element
Remarks:
boron
Basis for effect:
not specified
Remarks on result:
other: corresponding to 1712.3 mg/L BHO2.K
Remarks:
Carbon-filtered well water, 19.2°C, pH 7.1 - 8.7, hardness 166 mg/L
Validity criteria fulfilled:
not specified
Conclusions:
The present information was based on a literature review of various suitable read-across substances all belonging to the group of borates, the relevant information on short term toxicity in daphnia magna was taken from boric acid. The lowest available LC50 value was 133 mg/L, which corresponds to 1007 mg/l BHO2.K. So the available data shows that neither boron nor potassium metaborate needs to be classified as aquatic toxic acc. Regulation 1272/2008, as all LC50 values were above the limit value for classification of 100 mg/l.
Executive summary:

A literature review of showed that boron / potassium metaborate gave consistently LC50 values > 100 mg/l.

Data source

Reference
Reference Type:
review article or handbook
Title:
Safety Assessment of Boron in Aquatic and Terrestrial Environments
Author:
Butterwick L, De Oude N, Raymond K
Year:
1989
Bibliographic source:
ECOTOXICOLOGY AND ENVIRONMENTAL SAFETY 17, 339-371 (1989)

Materials and methods

Test guideline
Qualifier:
no guideline required
Principles of method if other than guideline:
Review of literature data
GLP compliance:
no

Test material

Constituent 1
Chemical structure
Reference substance name:
Boric acid
EC Number:
233-139-2
EC Name:
Boric acid
Cas Number:
10043-35-3
Molecular formula:
H3BO3
IUPAC Name:
Boric acid
Test material form:
solid: particulate/powder
Details on test material:
White odourless crystalline powder
Melting point: 168 - 171 °C
Water solubility: 49.5 g/l
pH-value: 3.8 - 4.8
Decomposition temperature: ca. 100 - 130 °C
Formation of metaboric acid by loss of water. At 160 deg C a glassy melt of boron trioxide is formed by further loss of water.
LD50 oral rat: 2660 mg/kg

Sampling and analysis

Analytical monitoring:
not specified

Test solutions

Vehicle:
not specified

Test organisms

Test organisms (species):
Daphnia magna
Details on test organisms:
TEST ORGANISM
- Common name: Water flea
- Strain/clone: Daphnia magna Straus

Study design

Test type:
static
Water media type:
freshwater
Total exposure duration:
48 h

Test conditions

Hardness:
150 resp. 166 mg/L
Test temperature:
20 resp. 19.2 °C
pH:
6.7 - 8.1 resp. 7.1 - 8.7
Details on test conditions:
TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Lake Huron water resp. Carbon-filtered well water
Reference substance (positive control):
not specified

Results and discussion

Effect concentrationsopen allclose all
Key result
Duration:
48 h
Dose descriptor:
LC50
Effect conc.:
133 mg/L
Nominal / measured:
not specified
Conc. based on:
element
Remarks:
boron
Basis for effect:
not specified
Remarks on result:
other: corresponding to 1007.7 mg/L BHO2.K
Remarks:
Lake Huron water, 20°C, pH 6.7 - 8.1, Hardness 150 mg/l
Duration:
48 h
Dose descriptor:
LC50
Effect conc.:
226 mg/L
Nominal / measured:
not specified
Conc. based on:
element
Remarks:
boron
Basis for effect:
not specified
Remarks on result:
other: corresponding to 1712.3 mg/L BHO2.K
Remarks:
Carbon-filtered well water, 19.2°C, pH 7.1 - 8.7, hardness 166 mg/L

Applicant's summary and conclusion

Validity criteria fulfilled:
not specified
Conclusions:
The present information was based on a literature review of various suitable read-across substances all belonging to the group of borates, the relevant information on short term toxicity in daphnia magna was taken from boric acid. The lowest available LC50 value was 133 mg/L, which corresponds to 1007 mg/l BHO2.K. So the available data shows that neither boron nor potassium metaborate needs to be classified as aquatic toxic acc. Regulation 1272/2008, as all LC50 values were above the limit value for classification of 100 mg/l.
Executive summary:

A literature review of showed that boron / potassium metaborate gave consistently LC50 values > 100 mg/l.