Potassium fluoroborates and potassium fluorohydroxyborates, exothermic reaction products of boron and potassium hydroxides and fluorohydroxides

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

2.02 mg/L

Assessment factor:

2

Extrapolation method:

sensitivity distribution

PNEC freshwater (intermittent releases):

13.7 mg/L

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

2.02 mg/L

Assessment factor:

2

Extrapolation method:

sensitivity distribution

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

10 mg/L

Assessment factor:

1

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

no exposure of sediment expected

Sediment (marine water)

Hazard assessment conclusion:

no exposure of sediment expected

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

5.4 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

In the assessment of the environmental fate and ecotoxicity of this brazing paste ("reaction product of mixed inorganic base and acid resulting in complex boron, potassium and fluoride constituents"), the inorganic UVCB assessment methodology developed under the wing of Eurometaux and explained in the CSR is followed and each of the constituents is assessed.

Following the constituent assessment, the presence of boron as complex potassium borates is identified as critical and requiring a quantitative risk assessment. After careful analysis of the chemical similarities and data available on borate substances, the dipotassium tetraborate (CAS: 1332 -77 -0, EINECS: 215 -575 -5) dossier was selected as basis for the assessment entity for the borate transformation products of the brazing paste. In the following, a justification for the assessment entity approach with data from the dipotassium tetraborate dossier as well as the limited available data on brazing pastes are provided.

Assessment entity approach:

The assessment of the environmental fate and ecotoxicity of this brazing paste is based on its transformation products upon dissolution in water. Boron containing constituents were identified as critical for the assessment and data for dipotassium tetraborate (CAS: 1332 -77 -0, EINECS: 215 -575 -5) were used. This strategy is based upon the assumptions that

i) upon release to the aquatic environment, the brazing flux material will completely dissolve (solubility > 10 g/L) and speciation of the potassium, fluoro and borate constituents in the environment is strongly dependent upon environmental conditions (e.g. pH).In aqueous solutions at environmentally relevant concentrations and pH ranges, low concentrations of simple borates such as boric acid B(OH)₃, potassium pentaborate (K₂B₁₀O₁₆^.8H₂O), potassium tetraborate (K₂B₄O₇^.4H₂O), disodium tetraborate decahydrate (Na₂B₄O₇^.10H₂O; borax), disodium tetraborate pentahydrate (Na₂B₄O₇^.5H₂O; borax pentahydrate), boric oxide (B₂O₃) and disodium octaborate tetrahydrate (Na₂B₈O₁₃^.4H₂O) will predominantly exist as undissociated boric acid. Above pH 9 the metaborate anion B(OH)₄^-becomes the main species in solution (WHO, 1998).After dissolution, the boron compounds from

this brazing paste("reaction product of mixed inorganic base and acid resulting in complex boron, potassium and fluoride constituents") are expected to follow the environmental fate and behaviour as reported for other, soluble borates (e.g. B₄K₂O₇).

ii) ecotoxicity is mainly caused by the boron compounds.

This assumption is supported by the few toxicity data available for the brazing flux material (Table 1). The brazing flux paste tested contained approximately 10% B and toxicity thresholds are ≥10 fold larger then the lowest toxicity data for the corresponding endpoint measured on soluble borate salts or boric acid. It was therefore concluded that the assessment entity approach for B containing transformation products only, as based on the elemental B content of the substance, is conservative for the environmental effects and risk assessment of brazing flux materials.

Table 1: Comparison of toxicity data for brazing flux paste with corresponding most sensitive data for soluble borates.

Endpoint	Brazing flux paste (10% B)	Borates and boric acid
96 -h LC50 for fish	750 mg/L (Brachydanio rerio)	74 mg B/L (Limanda limanda)
Growth inhibition of micro-organisms in STP	190 mg/L (17-h EC10 forPseudomonas putida)	10.0 mg B/L (72-h NOEC forOpercularia bimarginata)

Potassium and fluoride are more abundantly present in natural freshwater environments compared to boron (Table 2). Emissions of brazing flux products are not expected to significantly increase the exposure concentration for potassium and fluoride in the environment and also for this reason they are not considered as critical for the environmental effects assessment of this UVCB substance.

Table 2. Median baseline background concentrations for potassium and fluoride in water, sediment and soil.

Compartment	Unit	Potassium	Fluoride	Boron
Aquatic (freshwater)*	mg/L	1.6	0.1	0.0156
Aquatic (marine)**	mg/L	399	1.3	4.4
Sediment (freshwater)*	mg/kg dw	11050	no data	no data
Topsoil*	mg/kg dw	10560	no data	no data

*: Data for freshwater, sediment and soil from FOREGS. The FOREGS geochemical baselines mapping program represents the end twentieth century state of the surficial environment in Europe. The main aim of the FOREGS (Forum of European Geological Surveys) Geochemical Baseline Mapping Program was to provide high quality, multi-purpose environmental geochemical background data for stream water, stream sediment, floodplain sediment, soil, and humus across Europe. A baseline background concentration was defined as the concentration of an element in the present or past corresponding to very low anthropogenic pressure (i.e., close to the natural background). The FOREGS-data set was published in September 2007 (http://www.gsf.fi/publ/foregsatlas/ForegsData.php) and is considered to be of high quality. A detailed description of sampling methodology, sampling preparation and analysis is given by Salminen et al. (2005).

**: Data for K in marine water from Culkin, F. and R.A. Cox. 1966. Sodium, potassium, magnesium, calcium and strontium in sea water. Deep-Sea Res., 13: 789804; data for F in marine water from Warner, J.B. 1971. Normal fluoride content of seawater. DeepSea Res., 18: 1255-1263; data for B in marine water from Noakes, J.E., and D.W. Hood. 1961. Boron-boric acid complexes in sea water. Deep-Sea Res., 8: 121-129.

When available, both data developed on brazing flux and extracted from the dipotassium tetraborate (CAS: 1332-77-0, EINECS: 215-575-5) dossier are provided. It is important to report that dipotassium tetraborate dossier is based on the assessment of boric acid and borates (as sodium metaborate, anhydrous) analogous substances, as specified in test material details further provided.

PNEC derivation:

Because B is considered as the critical constituent for ecotoxicological effects, PNEC values for this UVCB substance are based on PNEC values for dipotassium tetraborate, expressed as elemental boron concentrations.

PNEC derivation for freshwater

 

Approach for PNEC derivation for freshwater

The available ecotoxicity database for the effect of boron on freshwater organisms is large. Therefore, the use of the statistical extrapolation method is preferred for PNEC derivation rather than the use of an assessment factor on the lowest NOEC, as specified by the Guidance document on information requirements and chemical safety assessment Chapter R.10.3.1.3. The PNEC is based on the 50% confidence value of the 5th percentile value of the chronic effect NOEC/EC10 data (HC5-50) and an additional assessment factor taking into account the uncertainty on the HC5-50 (thus PNEC = HC5-50/AF). The advantage of this statistical extrapolation method is that it uses the whole sensitivity distribution of species in a collection of laboratory test data to derive a PNEC instead of taking only the lowest long-term NOEC.

Overall conclusion on chronic PNEC-freshwater

In conclusion on the subject of the choice of the assessment factor and considering all arguments above for the derivation of the HC5-50 it is felt that the most appropriate AF would be 2.

The assessment factor 2 takes into account:

• The extensive database of chronic boron effects to freshwater organisms covering a representative range of plant, invertebrate and vertebrate species and representing 72 high quality NOECs among 24 different species.
• The extensive database of chronic boron effects to freshwater organisms fulfills therequirements related to the taxonomic groups (families) mentioned in theECHA Guidance (R.10.3.1.3). Indeed, high quality chronic NOEC values are available for 3 unicellular green algal species (Scenedesmus subspicatus,Chlorella pyrenoidosa, Selenstrum capricornutum), 3 higher plant (Spirodella polyrhiza, Lemna minor, Phragmites australis), 1 blue-green alga (Anacystis nidulans), 1 rotifer (Brachionus calyciflorus), 3 crustacean species (Ceriodaphnia dubia, Daphnia magna, Hyalella azteca), 1 insect (Chironomus riparius), 3 protozoans (Entosiphon sulcatum, Paramecium caudatum, Opercularia bimarginata), 3 amphibian species (Xenopus laevis, Rana pipiens, Bufo fowleri)and 6 fish species (Pimephales promelas, Carassius auratus,Oncorhynchus mykiss, Micropterus salmoides, Brachydanio rerio, Ictalurus punctatus).
• The absence of a field or mesocosm study to evaluate the laboratory to field extrapolation. However, field studies have been reported which make use of naturally occurring waters with high boron concentrations. In several cases these fluctuate during the year, so they do provide a means to demonstrate that levels of boron of about 1 mg B/L and higher do not adversely affect local species, including the sensitive species rainbow trout.
• The demonstration of a suitable probability distribution of the chronic boron dataset for the calculation of 5^th percentile values. The use of the best fitting distribution for the derivation of the HC5-50 value minimizes the statistical uncertainties around the HC5-50 value.
• The conclusion that no key species or group of species is consistently below the HC5-50.

Therefore, the proposed freshwater PNEC_{add, freshwater} is based on the best fitting HC5-50 value using an AF of 2, i.e. 2.02 mg B/L.This value, based on added boron concentrations, is therefore taken forward to the risk characterization.

PNEC derivation for marine and estuarine water

In general there exist very limited data on acute and chronic toxicity of boron to marine organisms. Three fish species (Limanda limanda, Menidia beryllina and Cyprinodon vareigatus), two crusteacean species (Americamysis bahia and Litopenaeus vannamei) are represented, one echinoderm species (Anthocidaris crassipina), and 19 algal species are represented.

 

Marine waters contain about 5 mg B/L, (see general discussion of environmental fate and pathways), so it may be expected that marine organisms are more tolerant of boron than freshwater organisms. However the lack of a suitable database prevents direct evaluation of this expectation.

 

The available studies suggest that boron toxicity may vary with salinity. Li et al (2007) reported acute toxicity to the white tiger shrimpLitopeneaus vannei, to be 25 mg B/L at 3‰ and 80 mg B/L at 20‰. Thompson et al. (1976) found underyearling coho salmon more susceptible to boron toxicity (12-d LC50 12.2 mg B/L) in seawater (28 ‰) than in freshwater (12-d LC50 113 mg B/L). However, under natural conditions, coho underyearlings remain in freshwaters, so the salinity itself may have contributed to physiological stress. Similarly, Litopeneaus are reported to show optimal growth at about 20‰. Pillard et al. (2002) measured borate ion toxicity to the mysid shrimp, Americamysis bahia, and reported acute values of 310, 290 and 380mg B₄O₇^-2/L for salinities of 10‰, 20‰, and 31‰, respectively. They concluded however, that the differences in salinity had no distinct impact on the tolerance to borate. More recent study reports from Hicks (2011) have also shown similar NOECs for a 28d test. The most sensitive endpoint was reproduction and gave a NOEC of 16.6 and 18.6 mg B/L for a salinity of espectively 8 and 20 ‰.

 

To address the concern about differential toxicity of boron as a function of salinity, additional studies are needed. These would preferably use organisms that occur in areas of varying salinity, to avoid the confounding factor of salinity itself being a stress on many organisms.

 

Because of the very limited data for marine species, it is proposed that the marine PNEC is the same value as proposed for freshwater organisms. This represents a conservative proposal, given the naturally higher boron concentrations in the marine environment.

 

Based on the PNEC_{add,freshwater} of 2.02 mg B/L derived with anapproach and an assessment factor of 2, it can be assumed that thePNEC_{add, freshwater} also protects the marine environment (open sea). Therefore, thePNEC_{add,merine water} of 2.02 mg B/Lis taken forward to the risk characterization.

   

PNEC derivation for intermittent releases

According to REACH Guidance R.16.2.3 if intermittent release is identified, only short-term effects are considered for the aquatic ecosystem and no-effect levels are derived from short-term toxicity data only. Instead of using an assessment factor, it was opted to consider all available short term toxicity data for freshwater organisms in order to derive the short term PNEC for intermittent release. The statistical extrapolation approach using all short term toxicity data presented in the second tablewere used to construct a ‘short term’ species sensitivity distribution and to derive a HC5-50 value for short term toxicity.

The database of short term boron effects to freshwater organisms represents 46 high quality studies among 20 different species.Acute study endpoints (L(E)C50) are available for 2 unicellular green algal species (Chlorella pyrenoidosa, Selenstrum capricornutum), 3 crustacean species (Ceriodaphnia dubia, Daphnia magna, Hyalella azteca), 2 insect species (Chironomus decorus, Allocaphnia vivipara), 4 mollusc species (Lampsilis siliquoidea, Leguma recta, Sphaerium simile, Megalonaisa nervosa), and 7 fish species (Pimephales promelas,Oncorhynchus kisutch Oncorhynchus tschawytscha, Catastomas latipinnis, Xyrauchen texanus, Ptychocheilus lucius, Gila elegans).

Using the above listed acute toxicity data, a species sensitivity distribution (SSD) and HC5-50 for short term toxicity have been calculated using best fitting approaches as shown in attachment "Cumulative frequency distributions using the Normal distribution". The best fitting curve was the normal distribution function on the log-transformed short term toxicity data. The ETX software (RIVM), using the normal distribution on the log-transformed short term freshwater toxicity data, resulted in a short term HC5-50 value of 27.3 mg B/L (confidence limits between 12.0 and 47.8 mg B/L).

The short term HC5-50 value from the log-normal statistical approach is used as the basis for the PNEC calculation. It is further proposed to apply a similar assessment factor as used in the derivation of the chronic PNEC (i.e. AF = 2).

Hence the proposed short term freshwater PNEC_{add, freshwater} is 13.7 mg B/L.This value, based on added boron concentrations, is therefore taken forward to the risk characterization of intermittent releases.

PNECadded derivation for sediments

According to chapter R.10 of the Guidance on IR and the PNEC for sediment (PNEC_{freshwater, sediment}) should be preferably derived from whole sediment toxicity data for freshwater benthic organisms (sediment-dwelling organisms). In the absence of whole sediment toxicity data for benthic organisms, the PNEC for sediment may provisionally be calculated using the equilibrium partitioning (EP) method.

 

The high water solubility of boric acid and corresponding low sorption to sediment means that a sediment-only exposure is not possible. Standard protocols involve spiking the test substance to the sediment at the initiation of the study. The overlying water is not spiked. However, boric acid will readily dissolve from the sediments during the course of a sediment study, so the test organisms will actually experience both water-borne and sediment-borne exposures.

 

For boron two whole sediment chronic toxicity tests with the midge Chironomus riparius have been performed (Hooftman, 2000 and Gerke, 2011b). The Hooftman study (2000) had a static test design using 6 test concentrations (18-320 mg B/kg dry wt.) spiked in a formulated sediment. Only nominal values were reported by Hooftman. The test resulted in a NOEC value of 180 mg/kg dry wt.

 

In the test design of Gerke (2011b), a formulated sediment was spiked with 6 different B concentrations between 6.5 and 200 mg B/kg (as nominal concentrations). After spiking, dilution water (i.e. overlying water) was added to the prepared formulated sediment where after midge larvae (C. riparius) were added after 2 days of equilibration for 28 days toxicity testing. The test yielded a measured unbounded NOEC of 37.8 mg/kg dry wt (as mean total measured concentration). 

 

Mass balance calculations of B content in the different phases (attachment "Distribution of B in water-solid phase")of the ABC Laboratories test revealed that there is a significant gradual decrease of B concentrations in the solid phase, while an increase of B concentrations in the overlying water is observed during the 30-day testing period. Indeed, at test initiation (after a 2 day equilibration period) 31% of the B load was present in the overlying water, while 38% of the B load was found in the solid phase. However, at test termination (after 30 days), ± 80 % of the B load was present in the water phase, while ± 20 % remained in the solid phase.

The mean overlying water concentration in Gerke (2011b), i.e. 20.9 mg/L (based on geometric mean concentration over the testing period), are at the level of the total NOEC value (i.e. 20.4 mg/L) derived in a similar 28d water-only test withC. riparius(ABC Laboratories, 2011a). In a similar way the boron concentration (i.e. geometric mean t₀-t₂₈= 42 mg/L) measured in the water column at the LOEC level in the Hooftman (2000) study equals the water only LOEC value obtained in the same water only test.

Chronic toxicity of B (as mg B/L in overlying water) for the endpoints survival/emergence in different exposure systems. Exposure towards B occurred 1) via water[1]only (ABC Laboratories, 2011a) and 2) via sediment/water[2](ABC Laboratories, 2011b, Hooftman, 2000).

Exposure system	NOEC (mg B/L)	LOEC (mg B/L)	Reference
Water-only	20.4	43.3	Gerke, 2011a
Water/sediment	≥20.9	>20.9	Gerke, 2011b
	NR	43.1	Hooftman, 2000

NR: not reported

 

It is clear that the chronic toxicity results on survival/emergence for C. riparius could be completely explained by the boron concentrations measured in the water column.Therefore, the additional contribution of boron adsorbed to sediment to the observed toxicity is expected to be negligible. This observation comes as no surprise since the estimated Kd values for boron are very low (mean value of 1.94 and 3.0 L/kg for respectively freshwater and marine sediment; 3.5 L/kg for suspended solids), indicating that boron has no tendency to adsorb to sediments.

 

The weight of evidence provided by the lack of partitioning (Kd estimates) and the results of the water only/whole sediment toxicity tests indicate that it is unlikely that boron will exert toxic effects via the sediment compartment and that the derivation of a PNEC sediment is not warranted for boron and could waived based on exposure considerations.

Calculation of Predicted No Effect Concentration (PNEC soil)

The available ecotoxicity database for the effect of boron on soil organisms is large. Therefore, the use of the statistical extrapolation method is preferred for PNEC derivation rather than the use of an assessment factor on the lowest NOEC, as specified by the Guidance document on information requirements and chemical safety assessment Chapter R.10.3.1.3. The PNEC is based on the 50 % confidence value of the 5th percentile value of the effect NOEC/EC10 data (HC5-50) and an additional assessment factor taking into account the uncertainty on the HC5-50 (thus PNEC = HC5-50/AF). The advantage of this statistical extrapolation method is that it uses the whole sensitivity distribution of species in an ecosystem to derive a PNEC instead of taking only the lowest long-term NOEC.

Overall conclusion on PNECsoil

Because of the large difference in bioavailability between boron naturally present in soils and added soluble B, risks of added soluble boron will be assessed based on added boron. Based on the above uncertainty analysis and the availability of studies on the effects of soil types and ageing on the toxicity of boron to soil organisms, it is proposed to apply anAssessment Factor of 2 on the HC5-50_added of 10.8 mg B/kg dw, resulting in a PNEC_added for the soil compartment of 5.4 mg B/kg dw.

 

The assessment factor of 2 takes into account:

the extensive database of chronic boron effects on terrestrial organisms covering a representative range of plant and invertebrate species, microbial processes and soil conditions for Europe;

that there are no indications that there are some sensitive species or taxonomic groups lacking in the database;

the good fit of the log-logistic distribution to the dataset;

the presence of some NOEC/EC10 values below the HC5-50;

the lack of good field validation;

the small gap between boron deficiency and toxicity for plants; and

information on the relatively limited effect of soil properties and ageing reactions on boron toxicity in soil.Detailed information on PNEC derivation can be found in the attachment "Calculation of Predicted No Effect Concentration (PNEC)".

Conclusion on classification

The classification of this brazing paste ("reaction product of mixed inorganic base and acid resulting in complex boron, potassium and fluoride constituents") for environmental hazards is based on the classification of its boron constituent.

Soluble borate salts and boric acid are not classified as hazardous to the aquatic environment (see data below), and taking into account the maximum concentration of B in this brazing paste (8.9%), it is concluded that this product is not classified as hazardous to the aquatic environment.

 

The lowest values from acute toxicity tests with soluble borates or boric acid judged to be of reliable quality:

• Green algae, Pseudokirchneriella subcapitata (Hansveit and Oldersma, 2000): 72-hr EC₅₀–biomass = 40 mg B/L
• Invertebrate, Daphnids, Daphnia magna (Gersich 1984a): 48-hr LC₅₀= 133 mg B/L
• Fish, Fathead minnow, Pimephales promelas (Soucek et al., 2010): 96-hr LC₅₀= 79.7 mg B/L