Sodium tetrahydroborate

Toxicological Summary

Workers - Hazard via inhalation route

Systemic effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

5.1 mg/m³

Most sensitive endpoint:

developmental toxicity / teratogenicity

Route of original study:

Oral

DNEL related information

Overall assessment factor (AF):

12.5

Modified dose descriptor starting point:

NOAEC

Acute/short term exposure

DNEL related information

Local effects

Acute/short term exposure

DNEL related information

Workers - Hazard via dermal route

Systemic effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

240 mg/kg bw/day

Most sensitive endpoint:

developmental toxicity / teratogenicity

Route of original study:

Oral

DNEL related information

Overall assessment factor (AF):

30

Acute/short term exposure

DNEL related information

Local effects

Long term exposure

Hazard assessment conclusion:

medium hazard (no threshold derived)

Most sensitive endpoint:

skin irritation/corrosion

Acute/short term exposure

Hazard assessment conclusion:

medium hazard (no threshold derived)

Most sensitive endpoint:

skin irritation/corrosion

Workers - Hazard for the eyes

Local effects

Hazard assessment conclusion:

medium hazard (no threshold derived)

Additional information - workers

  

Worker-DNEL_{long-term, inhalation, systemic}

No animal studies for the inhalation route are available for sodium borohydride or boric acid. Therefore a NOAEC was extrapolated from the boric acid oral key study using the BMDL₀₅ of 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. As recommended by Chapter R.8 from the Guidance on IR and CSA the remaining inter-species differences are covered by applying the factor 2.5 for toxicodynamic differences and the factor 5 for intraspecies variability within the working population. 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/m³ or 5.1 mg NaBH4 / m³

Worker-DNELlong-term, inhalation, systemic

The dermal DNEL refers to mg Sodiumborohydride/kg bw/day and is derived from data on boric acid. No relevant animal studies for the dermal route are available. Therefore a NOAEC was extrapolated from the boric acid oral key study using the BMDL05 of 10.3 mg B/kg bw/day (36 mg NaBH4/kg bw/day). For risk assessment of borates a dermal absorption of 0.5 % is used as a worst case approach. The assessment factors applied are for interspecies variability (5) and intraspecies variability (6).

The dermal DNEL is derived for information purpose. Corrosivity of SBH will determine the PPE requirements.

Local Effects

_{Respiratory irritation may be an endpoint of relevance, especially for a corrosive substance such as sodium borohydride. To take this into consideration, the mouse RD50 of 0.44mg/l (IUCLID Section 7.9.3, Hilaski 2001) was extrapolated to a human respiratory irritation LOAEL based on the correlation published by Kuwabara et al. 2007 (EHS 115:1609 -1616):}

_{log RD50 = 1.16 (log LOAEL) + 0.77}

_{The extrapolated human LOAEL is 0.1069 mg/l, or 107 mg/m3. Considering that the DNEL for systemic effects is 5.1 mg/m3, it can be reasonably assumed that the long-term systemic inhalation DNEL is also protective of respiratory irritation effects.}

A DNEL dermal for acute local effects will not be derived due to the corrosivity of the substance. A qualitative risk assessment is provided to evaluate risk management measures.

 

General Population - Hazard via inhalation route

Systemic effects

Acute/short term exposure

DNEL related information

Local effects

Acute/short term exposure

DNEL related information

General Population - Hazard via dermal route

Systemic effects

Acute/short term exposure

DNEL related information

General Population - Hazard via oral route

Systemic effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

0.17 mg/kg bw/day

Most sensitive endpoint:

developmental toxicity / teratogenicity

Route of original study:

Oral

DNEL related information

Overall assessment factor (AF):

60

Modified dose descriptor starting point:

BMDL05

Value:

10.3 mg/kg bw/day

Acute/short term exposure

DNEL related information

Additional information - General Population

Sodium borohydride is not applied in any consumer use, so that DNELs for the general populations are not required. The DNEL is only depicted for information purpose.