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

Toxicological Summary

Workers - Hazard via inhalation route

Systemic effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

10.95 mg/m³

Most sensitive endpoint:

repeated dose toxicity

DNEL related information

Overall assessment factor (AF):

12.5

Modified dose descriptor starting point:

NOAEC

Acute/short term exposure

Hazard assessment conclusion:

no hazard identified

DNEL related information

Local effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

18.4 mg/m³

Most sensitive endpoint:

irritation (respiratory tract)

DNEL related information

Dose descriptor:

NOAEC

Acute/short term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

18.4 mg/m³

Most sensitive endpoint:

irritation (respiratory tract)

DNEL related information

Dose descriptor starting point:

NOAEC

Workers - Hazard via dermal route

Systemic effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

500.1 mg/kg bw/day

Most sensitive endpoint:

developmental toxicity / teratogenicity

DNEL related information

Overall assessment factor (AF):

30

Modified dose descriptor starting point:

NOAEL

Acute/short term exposure

Hazard assessment conclusion:

no DNEL required: short term exposure controlled by conditions for long-term

DNEL related information

Local effects

Long term exposure

Hazard assessment conclusion:

no hazard identified

Acute/short term exposure

Hazard assessment conclusion:

no DNEL required: short term exposure controlled by conditions for long-term

Workers - Hazard for the eyes

Local effects

Hazard assessment conclusion:

low hazard (no threshold derived)

Additional information - workers

Assessment entity approach

"Brazing fluxes" are mixtures of boron-containing constituents (potassium(fluoro)borates), which undergo chemical exchanges (anion exchange) and condensation reactions (e.g. formation of oligoborates, polyborates) upon mixing and further manufacturing. This results in a complex mixture of potassium borates, which cannot be fully chemically characterised for substance identity. Thus, according to the definition under REACH, such brazing fluxes must be described as a UVCB substance.

 

An assessment entity approach is followed based on the transformation products of this UVCB uppon dissolution in aqueous media. The substance is highly soluble and forms complex boron, potassium and fluoride constituents. The quantitatively predominant transformation product of this UVCB is represented by boric acid, which is assumed to be the determinant of human health effects because of its classification and its toxicity. For this reason, the assessment is based on information for “borates” (including potassium borate, boric acid and other borate substances).

 

Based on the information provided below, it may safely be assumed that under physiological conditions the chemical speciation of most of the unknown potassium boron compounds corresponds to boric acid. Thus, from a chemical point of view, there is no reason to assume that brazing fluxes would behave differently than boric acid and/or borates under physiological conditions.

 

The basis of this assessment entity approach is further justified by the following reasoning:

In aqueous solutions at physiological and acidic pH, low concentrations of simple inorganic 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). This leads to the conclusion that the main species in the plasma of mammals and in the environment is undissociated boric acid. Since other borates dissociate to form boric acid in aqueous solutions, they too can be considered to exist as undissociated boric acid under the same conditions.

For comparative purposes, exposures to borates are often expressed in terms of boron (B) equivalents based on the fraction of boron in the source substance on a molecular weight basis. Some studies express dose in terms of B, whereas other studies express the dose in units of boric acid. Since the systemic effects and some of the local effects can be traced back to boric acid, results from one substance can be transferred to also evaluate the another substance on the basis of boron equivalents. Therefore data obtained from studies with these borates can be read across in the human health assessment for each individual substance. Conversion factors are given in the table below.

 

Substance		Formula		Conversion factor for equivalent dose of B (multiply by)
Boric acid		H3BO3		0.1748
Boric Oxide		B2O3		0.311
Disodium tetraborate anhydrous		Na2B4O7		0.2149
Disodium tetraborate pentahydrate		Na2B4O7•5H2O		0.1484
Disodium tetraborate decahydrate		Na2B4O7•10H2O		0.1134
Disodium octaborate tetrahydrate		Na2B8O13·4H2O		0.2096
Sodium metaborate (anhydrous)		NaBO2		0.1643
Sodium metaborate (dihydrate)		NaBO2·2H2O		0.1062
Sodium metaborate (tetrahydrate)		NaBO2·4H2O		0.0784
Sodium pentaborate (anhydrous)		NaB5O8		0.2636
Sodium pentaborate (pentahydrate)		NaB5O8∙5H2O		0.1832
Dipotassium tetraborate (anhydrous)		K2B4O7		0.185
Dipotassium tetraborate (tetrahydrate)		K2B4O7^.4H2O		0.1415
Potassium pentaborate (anhydrous)		B5KO8		0.244
Potassium pentaborate (tetrahydrate)		B5KO8^.4H2O		0.1843

 

Reference:

WHO. Guidelines for drinking-water quality, Addendum to Volume 1, 1998

Worker-DNEL_{acute, inhalation, local} (for `borates`)

Local effects of borates on the respiratory system have been investigated in animals in four acute inhalation studies (Wnorowski, 1994a, b, 1997) and two Alarie-tests (Krystofiak & Schaper, 1996; Kirkpatrick, 2010). Further, studies in humans were conducted, two small studies (12 probands) under laboratory conditions (Cain et al., 2004, 2008) and three studies on exposed workers (Garabrant et al., 1984, 1985, Wegman et al., 1991). In two studies by Woskie et al. (1994, 1998) the methods used by Wegman et al. (1991) were evaluated and determinants of human susceptibility to the irritant effect of borates were examined.

Borates act as sensory irritants, indicated by the effects observed in humans (i. e. nose, eye and throat irritation; sneezing) and by the results of the Alarie-tests by Kirkpatrick (2010), which demonstrated a depression of the respiratory frequency in mice after exposure to sodium borate. Many of the irritant symptoms (sensory irritation of the nose and throat, cough, phlegm production and broncho-constriction, as evidenced by a decrease in FEV1) are part of the respiratory defense reflex, the function of which is to protect the body from inhaled irritants. This reflex can be triggered by agents that stimulate receptors in the respiratory tract e. g. on the trigeminal nerve (Wegman et al., 1991, Nielsen et al., 2007, Krystofiak & Schaper, 1996; Kirkpatrick, 2010). The actual mechanism, however, has not yet been elucidated.

The relationship between total dust and inhalable dust air sampling results for borates is important in reconstructing measures of past exposures for comparison with current exposures. The samplers designed for the inhalable fraction collect larger dust particles more efficiently than do the total dust samplers so that in dust environments containing large particles the inhalable dust sampler will collect larger proportions of the airborne mass than the total dust sampler. Several studies have demonstrated that the 37-mm total dust sampler equipment under-samples suspended particles by factors ranging from 1.2 to 4.0 compared to the IOM sampler (Culver et al. 1994; Tsai et al. 1995; Werner et al. 1996; Katchen et al. 1998; Teikari et al. 2003). The dust particles associated with borate mining and processing typically have mass median aerodynamic diameters of 10-15 µm (81) and in this environment the IOM sampler collects between 2 and 3 times more mass per unit volume of air than the total dust sampler (Shen et al. 1991; Culver et al. 1994; Katchen et al. 1998). A conversion factor of 2.5 has been suggested for converting “total” personal exposure measures from industries similar to the borate mining and processing facility to equivalent inhalable aerosol exposures (Werner et al. 1996) further supported by paired 37-mm closed face cassette and 25 mm IOM sampling at a borax facility in(Shen et al. 1991).

A BMDL₀₅of 0.94 mg B/m³can be derived from the study by Wegman et al. (1991) is based on the incidence of any symptom of nose, eye and throat irritation, sneezing, breathlessness and coughing during exposure periods of 15 minutes to disodium tetraborates. A limitation of this study is that the subjects being questioned about irritant responses during their work could see the dust in the air and were able to judge visibly the intensity of their exposure. Much of the dust to which the workers were expsosed was an alkaline dust containing unspecified sodium borates which is capable of some sensory stimulation. Despite certain deficiencies of the study the results of the study allow the derivation of a dose-response curve. Since the number of individuals tested was large enough and as the investigation was carried out in a population of workers no assessment factor is needed to come up for inter-individual variability. A correction factor of 2.5 has to be applied, as the total dust sampler methodology used in this study underestimated the actual exposure levels.

The acute irritant effects which build the basis for the BMDL₀₅of the Wegman-study have been reported by several authors as a consequence of borate exposures. Garabrant et al. (1984 and 1985) who investigated large numbers of borate exposed workers reported dryness of mouth, nose and throat, eye irritation, dry cough, nosebleeds, sore throat, productive cough, shortness of breath, and chest tightness. A NOEC for respiratory irritation of 0.6 mg B/m³based on total dust (IOM equivalent of 1.5 mg B/m³) was derived by Garabrant et al. (1985). Due to several limitations of this study it cannot be used for DNEL derivations, however, the results are useful for the weight of evidence approach.

A NOAEL for irritation from boron of 1.5 mg B/m³(10 mg/m³of sodium tetraborate pentahydrate) among male and female human volunteers under controlled laboratory conditions was derived from Cain et al. (2004). At 10 mg/m³(1.5 mg B/m³) sodium tetraborate pentahydrate increased nasal secretion was observed, but not at 5 mg/m³(0.75 mg B/m³). The increased nasal secretion occurred in the absence of other irritating effects at concentration below that which volunteers considered irritatingand was not seen in subsequent study by Cain et al. 2008. Materials that cause mechanical or chemesthetic sensations in mucosal tissue may produce reflex responses as well, including an increase in secretions and blood flow to the tissue. Since a similar increase in secretion was not observed in the later study, the increase in secretion was likely mechanical in nature due to the increase particle deposition in the nose rather than a chemesthetic response to boron. Similarly, Cain et al. (2008) reported a NOAEL for irritation among human volunteers inhaling boric acid of 1.75 mg B/m³(10 mg/m³of boric acid). 

The transitional Annex XV dossier reports that a NOEC of 0.75 mg B/m³was derived from Cain et al. (2004) with a LOEC of 1.4 mg B/m³based on increased nasal secretion. However, the increased nasal secretion was likely due to mechanical sensations in the mucosal tissue by the inrease particulate diposition in the nose rather than sensory irritation caused by boron. The transitional dossier also reports that a LOEC of 0.44 in a comparable study in 2008. However, the authors of the study clearly state the levels of exposure did not reach the level considered irritating by subjects “…the highest levels studied here lay at the edge of where people would agree that feel in the nose becomes irritating, about 17-18 % carbon dioxide. None of the functions actually reached that concentration, though those for 2.5 mg/m³calcium oxide and 10 mg/m³sodium borate came close. ”

An airway sensory irritation respiratory depression (RD₅₀) study of sodium tetraborate pentahydrate was conducted in male Swiss-Webster mice based on the ASTM E981-04 (2004) standard test method of estimating sensory irritancy of airborne chemicals. The ASTM E981-04 sensory iritancy test (Alarie assay) has been demonstrated to be a reliable test for estimating sensory irritancy of airborne irritants and RD50s are a basis, at least partially, for OELs by ACGIH (Kuwabara et al. 2007).   The REACH implementation guideline (Chapter R.8) acknowledges the use of the Alarie assay in assessing respiratory irritation. The ASTM standard uses the value of 0.03 x RD50 for estimation of threshold limitvalues (TLV). Alarie et al. (2001) has established that a value of 0.01 x RD₅₀as the concentration where no sensory irritation would be seen in humans.

It was not possible to achieve an RD50 for sodium tetraborate pentahydrate. Based on the results in the mouse sensory irritation model, the RD50 for is greater than 1704 mg/m³(maximum achievable exposure) for sodium tetraborate pentahydrate. Therefore, although the highest achievable concentration was below the RD50 value for sodium tetraborate pentahydrate, based on the high aerosol concentrations achieved with %RD values below 50 %, it is sodium borates have a low potency as sensory irritants. Decreases in respiratory rate less than 12% are graded as no irritation (ASTM E981-04; 2002). The lowest exposure tested of 186 mg/m³sodium tetraborate pentahydrate resulted in a reduced respiration rate of 11% is graded as no irritation. The practical side of these results is that occupational exposure limit of 10 mg/m³total particulates will prevent any sensory irritation in workers. Due to the alkaline nature of sodium metaborate, effects would be similar to sodium tetraborate.

The ECHA guidelines recommend extrapolating from the RD10 values. However, there is no correlation or extrapolation established for TLVs or human health effects for the RD10. Furthermore RD10 value is below the limit of detection of 12 % for this assay. The RD50 is the relevant value since extrapolation and correlation to humans uses this value.

The DNEL based on 0.01 x the maximum achievable concentration for sodium tetraborate pentahydrate, 0.01 x 1704 mg/m³= 17.04 mg/m³or 2.52 mg B/m³.

Worker-DNEL_{acute, inhalation, local}= 2.52 mg B/m³,13.6 mg/m³Dipotassium tetraborate anhydrous, 17.8 mg/m³dipotassium tetraborate tetrahydrate

Worker-DNEL_{long-term, inhalation, systemic} (for `borates`)

This route is not relevant for systemic effects in the general population, but in the occupational setting considerable boron dust concentrations may arise.

No animal studies for the inhalation route are available. Therefore a NOAEC was extrapolated from the oral key study using the the BMDL₀₅of 10.3 mg B/kg bw/day. An eight hour workday and an according respiratory volume of 10 m³are assumed. The corrected inhalatory NOAEC of 18.16 mg B/m³was calculated as recommended by Chapter R.8 from the Guidance on IR and CSA using the following equation: 

Corrected Inhalatory NOAEC = oral BMDL₅x (1/ sRV_rat) x (ABS_oral-rat/ ABS_inh-rat) x (sRV_human/ wRV)

Corrected Inhalatory NOAEC = 10.3 mg B/kg bw/day x (1/ 0.38m³/kg/d) x (100 %/ 100 %) x (6.7 m³(8h) / 10 m³(8h))

Corrected Inhalatory NOAEC = 18.16 mg B/m³

sRV: standard Respiratory Volume

ABS: Absorption,

wRV: worker Respiratory Volume

sRV_rat= 0,38 m³/day

sRV_human= 6,7 m³/day (8h);

sRV_{human, moderate work}= 10 m³/day (8h)

ABS_oral-rat= ABS_inh-human= 100 %

 

Absorption of boric acid and tetraborates via the oral route is close to 100 %. Due to the good water solubility of the compounds and studies in animals and humans a realistic worst case assumption of 100 % absorption via the inhalation route is justified. Borates exist predominantly as un-dissociated boric acid in dilute aqueous solution at physiological pH, it is not further metabolized, therefore it can be concluded that the main species in the plasma of mammals is un-dissociated boric acid, and as such can exert its toxic effects in the target organs. The toxicokinetics of boric acid and disodium tetraborates are similar in rats and humans with regard to absorption, distribution, and metabolism. Differences exist for renal clearance, which is approximately 3 times faster in rats compared to humans. The physiological process of renal clearance is affected by the basal metabolic rate. In the above stated formular differences with regard to metabolic rate between rats and humans are considered. The remaining inter-species differences are covered by applying the factor 2.5 for toxicodynamic differences. An additional factor for uncertainties caused by route-to-route extrapolation was considered not necessary.

Worker-DNEL_{long-term, inhalation, systemic}= (18.16 mg B/m³) /(2.5 x 5) =1.45 mg B/m³or:

Dipotassium tetraborate (anhydrous): 7.8 mg/m³

Dipotassium tetraborate (tetrahydrate): 10.2 mg/m³

 

Worker-DNEL_{long-term, dermal, systemic} (for `borates`)

For risk assessment of borates a dermal absorption of 0.5 % is used as a worst case approach. Dermal absorption is not regarded relevant for the general population, however, it is considered for workers. A Worker-DNEL_{long-term, dermal, systemic}is derived from the oral BMDL₀₅10.3 mg B/kg bw/day. The assessment factors applied are for interspecies variability (5) and intraspecies variability (6). A DNEL of 0.34 mg B/kg bw/day was obtained for workers. A body weight for workers of 70 kg was assumed.

Worker-DNEL_{long-term, dermal, systemic}= (10.3 mg B/kg bw/day) / (6 x 5) = 0.34 mg B/kg bw/day or:

Dipotassium tetraborate (anhydrous): 1.8 mg/kg bw/day

Dipotassium tetraborate (tetrahydrate): 2.4 mg/kg bw/day

 

External DNEL value = (0.34 mgB/kg bw/day) /0.5% dermal absorption value = 68 mg B/kg bw/day or:

Dipotassium tetraborate (anhydrous): 367.7 mg/kg bw/day

Dipotassium tetraborate (tetrahydrate): 480.6 mg/kg bw/day

Derivation of DNELS for “brazing fluxes”

 

From the above stated DNELs on the “analogous” borates and based on a boron content of 13.7 wt-% (worst case) for brazing fluxes, the following DNEL values are derived based on a stoichiometric recalculation according to the “boron” content:

Worker	Boric acid/borates	Brazing fluxes (13.7 wt-% B content as worst case [factor 7.3]
Dermal, systemic, chronic (mg B/kg bw/day)	68.5(AF 30)	500.05
Inhalation, systemic chronic (mg B/m3)	1.5(AF 12.5)	10.95
Inhalation, local, acute (mg B/m3)	2.52	18.40
General population
Oral, acute, chronic (mg B/kg bw/day)	0.2(AF 60)	1.46
Dermal, systemic, chronic (mg B/kg bw/day)	34.3(AF 60)	250.39
Inhalation, systemic chronic (mg B/m3)	0.7(AF 25)	5.11
Oral, systemic, chronic (mg B/kg bw/day)	0.2(AF 60)	1.46

 

General Population - Hazard via inhalation route

Systemic effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

5.11 mg/m³

Most sensitive endpoint:

repeated dose toxicity

DNEL related information

Overall assessment factor (AF):

25

Modified dose descriptor starting point:

NOAEC

Acute/short term exposure

Hazard assessment conclusion:

no hazard identified

DNEL related information

Local effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

18.4 mg/m³

Most sensitive endpoint:

irritation (respiratory tract)

DNEL related information

Dose descriptor:

NOAEC

Acute/short term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

18.4 mg/m³

Most sensitive endpoint:

irritation (respiratory tract)

DNEL related information

Dose descriptor starting point:

NOAEC

General Population - Hazard via dermal route

Systemic effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

250.39 mg/kg bw/day

Most sensitive endpoint:

developmental toxicity / teratogenicity

DNEL related information

Overall assessment factor (AF):

60

Modified dose descriptor starting point:

BMDL05

Acute/short term exposure

Hazard assessment conclusion:

no DNEL required: short term exposure controlled by conditions for long-term

DNEL related information

Local effects

Long term exposure

Hazard assessment conclusion:

no hazard identified

Acute/short term exposure

Hazard assessment conclusion:

no DNEL required: short term exposure controlled by conditions for long-term

General Population - Hazard via oral route

Systemic effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

1.46 mg/kg bw/day

Most sensitive endpoint:

developmental toxicity / teratogenicity

DNEL related information

Overall assessment factor (AF):

60

Modified dose descriptor starting point:

BMDL05

Acute/short term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

1.46 mg/kg bw/day

Most sensitive endpoint:

developmental toxicity / teratogenicity

DNEL related information

Overall assessment factor (AF):

60

Modified dose descriptor starting point:

BMDL05

General Population - Hazard for the eyes

Local effects

Hazard assessment conclusion:

low hazard (no threshold derived)

Additional information - General Population

In the assessment of the human health toxicity 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 boric acid and complex potassium borate 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

"Brazing fluxes" are mixtures of boron-containing constituents (potassium(fluoro)borates), which undergo chemical exchanges (anion exchange) and condensation reactions (e.g. formation of oligoborates, polyborates) upon mixing and further manufacturing. This results in a complex mixture of potassium borates, which cannot be fully chemically characterised for substance identity. Thus, according to the definition under REACH, such brazing fluxes must be described as a UVCB substance.

 

An assessment entity approach is followed based on the transformation products of this UVCB uppon dissolution in aqueous media. The substance is highly soluble and forms complex boron, potassium and fluoride constituents.The quantitatively predominanttransformation productof this UVCB is represented by boric acid, which is assumed to be the determinant of human health effects because of its classification and its toxicity. For this reason, the assessment is based on information for “borates” (including potassium borate, boric acid and other borate substances).

 

Based on the information provided below, it may safely be assumed that under physiological conditions the chemical speciation of most of the unknown potassium boron compounds corresponds to boric acid. Thus, from a chemical point of view, there is no reason to assume that brazing fluxes would behave differently than boric acid and/or borates under physiological conditions.

 

The basis of this assessment entity approach is further justified by the following reasoning:

In aqueous solutions at physiological and acidic pH, low concentrations of simple inorganic 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). This leads to the conclusion that the main species in the plasma of mammals and in the environment is undissociated boric acid. Since other borates dissociate to form boric acid in aqueous solutions, they too can be considered to exist as undissociated boric acid under the same conditions.

For comparative purposes, exposures to borates are often expressed in terms of boron (B) equivalents based on the fraction of boron in the source substance on a molecular weight basis. Some studies express dose in terms of B, whereas other studies express the dose in units of boric acid. Since the systemic effects and some of the local effects can be traced back to boric acid, results from one substance can be transferred to also evaluate the another substance on the basis of boron equivalents. Therefore data obtained from studies with these borates can read across in the human health assessment for each individual substance. Conversion factors are given in the table below.

Substance		Formula		Conversion factor for equivalent dose of B (multiply by)
Boric acid		H3BO3		0.1748
Boric Oxide		B2O3		0.311
Disodium tetraborate anhydrous		Na2B4O7		0.2149
Disodium tetraborate pentahydrate		Na2B4O7•5H2O		0.1484
Disodium tetraborate decahydrate		Na2B4O7•10H2O		0.1134
Disodium octaborate tetrahydrate		Na2B8O13·4H2O		0.2096
Sodium metaborate (anhydrous)		NaBO2		0.1643
Sodium metaborate (dihydrate)		NaBO2·2H2O		0.1062
Sodium metaborate (tetrahydrate)		NaBO2·4H2O		0.0784
Sodium pentaborate (anhydrous)		NaB5O8		0.2636
Sodium pentaborate (pentahydrate)		NaB5O8∙5H2O		0.1832
Dipotassium tetraborate (anhydrous)		K2B4O7		0.185
Dipotassium tetraborate (tetrahydrate)		K2B4O7^.4H2O		0.1415
Potassium pentaborate (anhydrous)		B5KO8		0.244
Potassium pentaborate (tetrahydrate)		B5KO8^.4H2O		0.1843

Reference:

WHO. Guidelines for drinking-water quality, Addendum to Volume 1, 1998

General population DNEL_{long-term, oral, systemic} (for `borates`)

With regard to developmental effects no human data exist. The available data from animal studies are sufficient to conclude that prenatal exposure to boron (specifically boric acid and disodium tetraborates) by the oral route can cause developmental toxicity. Developmental effects were seen in three different mammalian species, rat, mouse and rabbit, with the rat being most sensitive. From the most robust study in rats (Price et al., 1996) the lowest NOAEL = 9.6 mg B/kg bw/day can be derived for reduced foetal body weight per litter, increase in wavy ribs and increased incidence in short rib XIII. Other effects seen at maternally toxic doses were visceral malformations like enlarged ventricles and cardiovascular effects.

Several epidemiological studies on fertility effects of borates have been carried out in workers and populations living in areas with high environmental levels of boron. Truhaut et al., 1964, Tarasenko, 1972, Krasovskii et al., 1976, Whorton, 1994, Tuccar, 1998 and Sayli, 1998, 2001, 2003.

In general the need for good epidemiological studies on male and female fertility, as well as on developmental toxicity was clearly identified by several national and international panels (BfR, 2005; EFSA, 2004; Commission Working, 2004; WHO, 1998; ECETOC, 1995; US EPA, 2004).

Male infertility was observed in breeding studies in rats, mice and deer mice. The underlying cause for male infertility was identified to be testicular atrophy. A series of studies has been published that provide insight as to the mechanistic nature of the lesion in rats. Good correlation between doses inducing spermatogenic arrest and infertility could be derived. The effects were reversible at lower doses, but no recovery was possible at doses at which germ cell loss was observed. Germinal depletion correlated well with increased plasma levels of FSH. Levels of other hormones, like testosterone and LH were not always affected. A NOAEL of 17.5 mg B/kg bw/day in rats (Weir, 1966a, b) could be derived.

Two 3-generation studies in rats with boric acid and disodium tetraborate decahydrate (Weir, 1966c, d) and a continuous breeding study in mice with boric acid (Fail et al., 1991) further substantiate the effects seen in males.

The NOAEL of 9.6 mg/kg body weight per day is based on the critical developmental effect of decreased fetal body weight in rats. Allen et al. (1996) developed a benchmark dose based on the studies of Heindel et al. (1992), Price, Marr & Myers (1994) and Price et al. (1996a). The benchmark dose is defined as the 95% lower bound on the dose corresponding to a 5% decrease in the mean fetal weight (BMDL₀₅) and was used by the United States Environmental Protection Agency in its re-evaluation (USEPA, 2004) and by WHO in its guideline for boron in drinking water (2009). The BMDL₀₅of 10.3 mg/kg body weight per day as boron is close to the Price et al. (1996a) NOAEL of 9.6 mg/kg body weight per day. The uncertainty factor used by WHO was derived following the methodology of Doursen et al. (1998).

The most appropriate TK uncertainty factor for intraspecies variability is based on available data in pregnant humans for variation in glomerular filtration rate (GFR) as a surrogate for the clearance and elimination of B. This choice is most appropriate because the pregnant human is the population associated with B's critical effect. Furthermore, B's elimination is the kinetic area with the most variability, absorption and distribution of B are expected to be very similar among humans and B is not metabolized. Based on division of the mean glomerular filtration rate by the glomerular filtration rate at two standard deviations below the mean to address variability for approximately 95 % of the population, the toxicokinetic component of interspecies variation is 1.8 (compared with the default value for this component of 3.2). As there are insufficient data to serve as a basis for replacement of the default value for the toxicodynamic component of the uncertainty factor for intraspecies variation, the total uncertainty factor for intraspecies variation is 1.8 x 3.2 = 5.76 (rounded to 6). Data are inadequate to determine a different uncertainty factor for interspecies variation; therefore, the default value of 10 is used (Doursen et al., 1998), giving a total uncertainty factor of 60. The appropriate uncertainty factor for other areas of uncertainty, and specifically for database uncertainty, is 1-fold.

The uncertainty factor (UF) of 60 used in derivation of the DNEL is more conservative than UFs previously used by several other national and international panels where UFs ranging from 25 to 30 have been used (IEHR 1995, ECETOC 1995, IPCS 1998, NAS FNB 2000; See Appendix E). The default factor of 100 (10 x 10) was used under the Biocidal Products Directive in 2009, and a total UF of 150 for the general population in the Transitional Annex XV dossier in 2009. The default UF of 100 was also recently used by the ECHA Committee for Risk Assessment (RAC) in their opinion on new scientific evidence on the use of boric acid and borates in photographic applications by consumers adopted 29 April 2010. However, the default value was used because of insufficient time for an in-depth assessment of the toxicokinetic data. The RAC acknowledged that the 10 x 10 was an overly conservative and that there was good scientific justification to derogate from the default values. Further the RAC recongnized the UF of 60 used by WHO in deriving its Guidelines for Drinking Water Quality (2002 & 2009) for boron, and that EFSA in 2004 also ustilsed a combined UF of 60 (Minutes of the 10^thmeeting of the Committee for Risk Assessment, 16-18 march 2010).

More recently an UF of 60 was used bytheScientific Committee on Health and Environmental Risks (SCHER)2010Derogation on the Drinking Water Directive 98/83/ECfor Boron (SCHER 2010), and theScientific Committee on Consumer Safety(SCCS) 2010 opinion onBoron compounds(SCCS 2010).

The European Centre for Ecotoxicology and Toxicology of Chemicals (ECETOC) is developing guidance on the use of assessment (AF) when deriving DNELs (ECETOC 2010). When substance-specific data documenting intra-species variability are available, the use of‘informed’ AF, rather than the default AF provided in the ECHA guidance is proposed. Such data can be toxicokinetic or toxicodynamic data, and demonstrate either the absence of variability between humans, or on the contrary indicate that some parts of the population may require additional consideration (e. g. young children, the elderly).

In the absence of substance-specific data, ECETOC guidance is to deviate from the default AF of 10 (general population) and 5 (workers) as recommended by the ECHA R8 and to use default values of 5 and 3, for workers and the general population respectively. These values have been proposed in the ECETOC guidances (2003, 2010).

In the case where allometric scaling is already applied (systemic effects), it is proposed to use an overall additional factor covering the total (inter- and intra-species) variability, of 5 for the general population and 3 for the workplace. In the case where local effects in the respiratory tract are of concern, the intraspecies factors of 5 and 3 are considered to also provide coverage for toxicodynamic differences. This is relevant since compared to rats; humans seem to be less susceptible to the toxic local effects in the respiratory tract associated with inhalation of inorganic metal compounds (Oberdörster, 1995; Mauderly, 1997; ILSI, 2000; Nikula et al., 2001; Greim and Ziegler-Skylakakis, 2007).

The basis provided by ECETOC for the use of the reduced AFs includes:

· both the ECHA guidance (R8) and ECETOC recognise that, when substance- or category-specific information is available, there may be scientific justification for deviating from default AFs

· statistical analysis of the variability of toxicodynamic and toxicokinetic parameters within several published datasets has shown that the intra-species variability between humans can be covered by an AF of 5 for the general population and an AF of 3 for the more homogeneous worker population

· It is anticipated that a low variability in response would be seen in human populations exposed to boric acid that does not undergo extensive metabolism (and have lower genetic polymorphisms) than in populations exposed to substances that required more extensive metabolism.

· if allometric scaling is used, although some interspecies variability may remain, it is estimated that this residual variability is largely accounted for in the default assessment factor proposed for intra-species variability, because of the inherent interdependency of those two variables. In the case where local effects in the respiratory tract are of concern, the intraspecies factors of 5 and 3 are considered to also provide coverage for toxicodynamic differences

Although the more conservative AF was used in derivation of the DNEL in this CSR a reevaluation of the appropriate AF to use will be conducted upon final publication of the ECETOC guidelines that may result in a reduction of the AFs as outline by ECETOC guidance.

General population-DNEL_{long-term, oral, systemic}= (10.3 mg B/kg bw/day) / (6 x 10) =0.17 mg B/kg bw/day or: 

Dipotassium tetraborate (anhydrous):0.92 mg/kg bw/day

Dipotassium tetraborate (tetrahydrate): 1.2 mg/kg bw/day

Derivation of DNELS for “brazing fluxes”

 

From the above stated DNELs on the “analogous” borates and based on a boron content of 13.7 wt-% (worst case) for brazing fluxes, the following DNEL values are derived based on a stoichiometric recalculation according to the “boron” content:

Worker	Boric acid/borates	Brazing fluxes (13.7 wt-% B content as worst case [factor 7.3]
Dermal, systemic, chronic (mg B/kg bw/day)	68.5(AF 30)	500.05
Inhalation, systemic chronic (mg B/m3)	1.5(AF 12.5)	10.95
Inhalation, local, acute (mg B/m3)	2.52	18.40
General population
Oral, acute, chronic (mg B/kg bw/day)	0.2(AF 60)	1.46
Dermal, systemic, chronic (mg B/kg bw/day)	34.3(AF 60)	250.39
Inhalation, systemic chronic (mg B/m3)	0.7(AF 25)	5.11
Oral, systemic, chronic (mg B/kg bw/day)	0.2(AF 60)	1.46