Registration Dossier

Administrative data

Workers - Hazard via inhalation route

Systemic effects

Long term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
2.4 mg/m³
Most sensitive endpoint:
repeated dose toxicity
DNEL related information
DNEL derivation method:
other: Published SCOEL decision for HF and inorganic fluorides
Modified dose descriptor starting point:
NOAEC
Explanation for the modification of the dose descriptor starting point:
Not required
Acute/short term exposure
Hazard assessment conclusion:
low hazard (no threshold derived)
Most sensitive endpoint:
irritation (respiratory tract)
DNEL related information

Local effects

Long term exposure
Hazard assessment conclusion:
medium hazard (no threshold derived)
Most sensitive endpoint:
irritation (respiratory tract)
Acute/short term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
4.1 mg/m³
Most sensitive endpoint:
irritation (respiratory tract)
DNEL related information
DNEL derivation method:
other: Published SCOEL decision for HF and inorganic fluorides
Dose descriptor starting point:
NOAEC

Workers - Hazard via dermal route

Systemic effects

Long term exposure
Hazard assessment conclusion:
low hazard (no threshold derived)
Most sensitive endpoint:
skin irritation/corrosion
Acute/short term exposure
Hazard assessment conclusion:
low hazard (no threshold derived)
Most sensitive endpoint:
skin irritation/corrosion
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

Background: read-across justification

Limited toxicological data are available for the substance. Sodium hydrogen difluoride will dissociate under physiological conditions with the generation of HF and subsequently hydrogen, fluoride and sodium ions. The effects of exposure to the substance will therefore be dominated by local corrosivity and irritation due to the liberated HF and the critical systemic toxicity of the substance will be due to fluoride. Read-across is therefore proposed to studies performed with soluble fluoride compounds such as hydrogen fluoride and sodium fluoride.  The toxicity of the substance is therefore adequately characterised by read-across to supporting substances and without the need for additional vertebrate testing.

The effects of chronic exposure to fluorides is well characterised. The predominant findings of skeletal and dental fluorosis reflect the incorporation of fluoride into the bones and teeth.

The SCOEL have recommended (1998) IOEL values of 1.5 mg/m3(8-hour TWA) for inorganic fluorides (as F-) and 2.5 mg/m3(15-minute STEL) specifically for HF.  They concluded that the 8-hour TWA was sufficient to protect against systemic effects (fluorosis) and that the STEL value for HF was adequate to limit peaks of exposure which could result in irritation. Based upon the study of Largent and Columbus (1960), conducted in volunteers exposed for 6 h/d for 10-50d, the STEL (15 mins) of 3 ppm (2.5 mg/m3) was proposed for HF to limit peaks in exposure which could result in irritation.  As potassium hydrogen difluoride will generate HF following inhalation exposure, this value is also considered to be appropriate.  Correcting for the fluoride content of potassium hydrogen difluoride results in a STEL of 5.1 mg/m3. Correcting the TWA value of 1.5 mg/m3for fluorine content results in a value of 3.1 mg/m3.

DNEL derivation

Workers

Acute/short-term exposure – systemic effects

Dermal DNEL

Sodium hydrogen difluoride is corrosive, therefore dermal contact should be avoided through the use of personal protective equipment (PPE) and appropriate risk management measures (RMMs). The physicochemical properties of the substance indicate that dermal absorption is unlikely under conditions of exposure where the integrity of the skin barrier is maintained. Systemic toxicity is therefore not predicted and systemic dermal DNEL values are not derived.

Inhalation DNEL

Systemic toxicity as a result of acute exposure to the substance is unlikely except in cases of accidental exposure resulting in severe local effects (irritation / corrosion) at the site of contact. The acute local inhalation DNEL is therefore protective of systemic effects.

Acute/short-term exposure – local effects

Dermal DNEL

Sodium hydrogen difluoride is corrosive, therefore dermal contact should be avoided through the use of personal protective equipment (PPE) and appropriate risk management measures (RMMs). In the absence of adequate dose-response data, it is not possible to derive local dermal DNEL values.

Inhalation DNEL

The short-term inhalation DNEL value of 4.1 mg/m3is derived from the SCOEL 15-minute STEL value for HF, corrected for the fluoride content of the substance which will generate HF under physiological conditions.

Long-term exposure – systemic effects

Dermal DNEL

Sodium hydrogen difluoride is corrosive, therefore dermal contact should be avoided through the use of personal protective equipment (PPE) and appropriate risk management measures (RMMs). The physicochemical properties of the substance indicate that dermal absorption is unlikely under conditions of exposure where the integrity of the skin barrier is maintained. Systemic toxicity is therefore not predicted and systemic dermal DNEL values are not derived.

Inhalation DNEL

The long-term inhalation DNEL value of 2.4 mg/m3is derived from the SCOEL 8-hour TWA value for HF, corrected for the fluoride content of the substance which will generate HF under physiological conditions.

Long-term exposure - local effects

Dermal DNEL

Sodium hydrogen difluoride is corrosive, therefore dermal contact should be avoided through the use of personal protective equipment (PPE) and appropriate risk management measures (RMMs). In the absence of adequate dose-response data, it is not possible to derive local dermal DNEL values.

Inhalation DNEL

No dose-response data are available; the short-term DNEL for local inhalation effects and the long-term DNEL for systemic effects following inhalation are protective for long-term local effects following inhalation.

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
Hazard assessment conclusion:
exposure based waiving
DNEL related information

General Population - Hazard via oral route

Systemic effects

Long term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
0.19 mg/kg bw/day
DNEL related information
DNEL derivation method:
other: EFSA tolerable intake for fluoride
Explanation for the modification of the dose descriptor starting point:
Not required
Acute/short term exposure
Hazard assessment conclusion:
DNEL (Derived No Effect Level)
Value:
0.19 mg/kg bw/day
Most sensitive endpoint:
repeated dose toxicity
DNEL related information

General Population - Hazard for the eyes

Additional information - General Population

DNEL values for the general public are of limited relevance, as direct exposure to sodium hydrogen difluoride is not predicted. The substance is not used by the general population in the scenarios envisaged and exposure will only therefore occur indirectly via the environment. DNEL values for acute exposure of the general population are therefore not derived. Sodium bifluoride will react rapidly with water/moisture in the environment to form hydrogen fluoride and subsequently hydrogen, fluoride and sodium ions. These ions will further interact with other ionic species naturally present in the environment. Indirect exposure to the substance per se will therefore not occur; exposure will be to its ultimate ionic dissociation products. Due to the low inherent toxicity and ubiquitous presence in the environment, exposure to sodium is not considered further. It is considered that the relevant indirect exposure will be limited to fluoride.

Acute/short-term exposure

Systemic effects

Dermal DNEL

There are no uses of sodium bifluoride which would result in dermal exposure of the general population.

Inhalation DNEL

There are no uses of sodium hydrogen difluoride which would result in inhalation exposure of the general population. The substance is a non-volatile inorganic solid.

Oral DNEL

Indirect exposure of the general population to fluoride via the environment is unlikely but may theoretically occur from the use of sodium bifluoride.  However the general population are exposed to levels of naturally occurring fluoride in food, naturally occurring and intentionally added fluoride in drinking water.  EFSA (2008) have specified an upper tolerable intake of 7 mg fluoride/day, which is equivalent to a daily intake of 11.4 mg sodium bifluoride or 0.19 mg/kg bw/d assuming a bodyweight of 60 kg. 

Local effects

Dermal DNEL

There are no uses of sodium hydrogen difluoride which would result in dermal exposure of the general population.

Inhalation DNEL

There are no uses of sodium hydrogen difluoride which would result in inhalation exposure of the general population. The substance is a non-volatile inorganic solid.

Long-term exposure

Systemic effects

Dermal DNEL

There are no uses of sodium bifluoride which would result in dermal exposure of the general population.

Inhalation DNEL

There are no uses of sodium hydrogen difluoride which would result in inhalation exposure of the general population. The substance is a non-volatile inorganic solid.

Oral DNEL

Indirect exposure of the general population to fluoride via the environment is unlikely but may theoretically occur from the use of sodium bifluoride.  However the general population are exposed to levels of naturally occurring fluoride in food, naturally occurring and intentionally added fluoride in drinking water.  EFSA (2008) have specified an upper tolerable intake of 7 mg fluoride/day, which is equivalent to a daily intake of 11.4 mg sodium bifluoride or 0.19 mg/kg bw/d assuming a bodyweight of 60 kg.

Local effects

Dermal DNEL

There are no uses of sodium hydrogen difluoride which would result in dermal exposure of the general population.

Inhalation DNEL

There are no uses of sodium hydrogen difluoride which would result in inhalation exposure of the general population. The substance is a non-volatile inorganic solid.