Reaction product of mixed inorganic base and acid resulting in complex boron, potassium, fluoride and potassium fluoride constituents

Endpoint summary

Additional information

In the assessment of the environmental fate and ecotoxicity of this UVCB, 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 UVCB 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 brazing flux materials (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 for Pseudomonas putida)	10.0 mg B/L (72-h NOEC for Opercularia 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.