Registration Dossier

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Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.

The new ECHA CHEM database has been released by ECHA, and it now contains all REACH registration data. There are more details on the transition of ECHA's published data to ECHA CHEM here.

Diss Factsheets

Administrative data

Workers - Hazard via inhalation route

Systemic effects

Long term exposure
Hazard assessment conclusion:
no hazard identified
Acute/short term exposure
Hazard assessment conclusion:
no hazard identified
DNEL related information

Local effects

Long term exposure
Hazard assessment conclusion:
other toxicological threshold
Value:
8 mg/m³
Acute/short term exposure
Hazard assessment conclusion:
other toxicological threshold
Value:
15 mg/m³
DNEL related information

Workers - Hazard via dermal route

Systemic effects

Long term exposure
Hazard assessment conclusion:
no hazard identified
Acute/short term exposure
Hazard assessment conclusion:
no hazard identified
DNEL related information

Local effects

Long term exposure
Hazard assessment conclusion:
high hazard (no threshold derived)
Acute/short term exposure
Hazard assessment conclusion:
high hazard (no threshold derived)

Workers - Hazard for the eyes

Local effects

Hazard assessment conclusion:
high hazard (no threshold derived)

Additional information - workers

The violent and instantaneous hydrolysis of hafnium tetrachlorides was described in E. Barraud et al. / Journal of Solid State Chemistry 179 (2006) and also shown in the hydrolysis report of Zsolt Sárvári, CIToxLab, 2012 ; see section 5.1.2.of the technical dossier.

In water, the decomposition leads to the formation of an oxychloride octahydrate (HfOCl 2 . 8H2O) and slower hydrolysis reactions may also occur by contact with wet air and leads to the formation of an hydrated oxychloride (HfOCl 2 . nH2O) with an hydration rate n ranging between 0 and 8, depending on the temperature, the vapour pressure and the contact time (Barraud, 2006).

The experiment carried out in CitoxLab in 2012 showed that the reaction occurred immediately and the stabilization of the reaction was demonstrated by the pH and also the chloride content, which didn't vary at all after the reaction. The instantaneous hydrolysis was seen by eye with a precipitate formation that could demonstrate the formation of HfO2 very insoluble.

Moreover, when tested for pH, a pH of 1.4 and an acid reserve around 24% HCl equivalent was found with HfCl4 at 10 g/L. This was also confirmed by a Corrositex test performed with HfCl4 that concluded to the corrosivity category 1B (2013, reliability 1).

Hafnium tetrachloride appears then not available in the body due to its quasi-instantaneously degradation on contact with moist skin or mucous membranes.

 

For these reasons, this approach was followed for the hazard characterization of HfCl4:

-      Short term toxicity and local toxicity endpoints were waived, based on corrosive potential and for animal welfare considerations,

-      Repeated toxicity, reprotoxicity and genotoxicity endpoints were based on degradation products; HCl and HfO2 (annex V of REACh regulation). For this last compound, read across was performed with other Hf compounds and justification is given below.

 

Read across justification for long term toxicity, reprotoxicity and genotoxicity endpoints:

The guidance document on information requirements and chemical safety assessment deals with the specific category of metals, metal compounds and other inorganic compounds like Hf coumpounds (section 6.2.5.6.). For this category, the hypothesis is that properties are likely to be similar or follow a similar pattern as a result of the presence of a common metal ion (Hf4+ in this case). However, it is the bioavailability of the metal ion (or a redox form of this ion) at target sites that in most cases determine the occurrence and severity of the effects to be assessed for the read-across of metal substances. Supporting information to assess the bioavailability of the metal ion at the target site can include information on a number of different factors (e.g. physico-chemical properties such as water solubility, particle size and structure,in vivodata on systemic effects or toxicokinetics).

In our case, as mentioned in the literature, the chemistry of Zr and Hf is so similar that they are difficult to separate. The melting and boiling points and the solubility in solvents are the major differences in the chemistry of these two elements (cf. the following comparative table).

In addition, they both have a hexagonal crystalline structure.

Regarding their toxicological profile, it is quite similar: the oral absorption is negligible, the distribution in the organism is similar with the following gradient; squeleton > liver > spleen > lung, mainly excreted via faeces, both element show no toxicity except minor hepatic effects induced by HfO2.

 

 

Hf

HfO2

Zr

ZrO2

Atomic weight

178,5

210,5

91,2

123,2

Atomic radius

155 pm

-

160 pm

-

Crystal structure

hexagonal

-

hexagonal

-

Melting point

2233 °C

2758 °C

1855 °C

2715 °C

Boiling point

4603 °C

5400 °C

4409 °C

4300 °C

Solubility in water

< 8 µg/L

< 8 µg/L

< 50 µg/L

< 55 µg/L

Oral absorption

0,04 – 0,13 %

Negligible

Very low

negligible

Dermal absorption

None

none

none

none

Distribution

Squeleton, liver, spleen, lung

Liver, spleen, lung

Squeleton, liver, spleen, lung

Squeleton, liver, spleen, lung

Excretion

faecal

faecal

faecal

faecal

Irritation

no

no

no

no

Granulometry

> 44 µm and < 0.8 mm

 D10 = 0.183 µm

D50 = 0.250 µm

D90 = 0.533 µm

D10 = 32 µmD50 = 76 µmD90 = 141 µm

< 2 µm

Table 1: Comparison between Zr and Hf compounds parameters

 

In addition, acute oral toxicity studies have been performed with Hf and HfO2 to support this read across approach. These two tests confirms the non-toxic effect of Hf and HfO2 after oral administration to rats at the dose level of 2000 mg/kg bw. These results are exactly the same as for Zr and ZrO2.

 

Threshold values

In this section, data from all end-points are examined and analyzed in order to determine for which it is relevant and possible to establish a DNEL value. The method followed is that proposed in the guidance for the implementation of REACH (Chapter R.8: Characterisation of dose (concentration) -response for human health, November 2012).

1.   Oral toxicity

Not considered for workers

2.   Inhalation toxicity

 

a.   Acute exposure

 

No relevant data available because of the corrosive effect of HfCl4.

 

b.   Repeated exposure

 

Two reliable studies were available for ZrO2, as a read across compound for HfO2: a 30 day repeated dose inhalation test in dog, rabbit and rat and a 60 day repeated dose toxicity test in cat, dog, guinea pig, rabbit and rat. No effects were reported in any of the species studied after inhalation of ZrO2 dust. NOAEC > 75 mg Zr/m3air in the 30 day study and NOAEC > 11 mg Zr/m3air in the 60 day study.

 

An occupational value for hafnium of 0.5 mg/m3was drawn up in 1987, but no document is available that could explain how this value was elaborated. Moreover, this occupational value was set for several countries; it is not a European Occupational Value and is only recommended, not indicative or binding value. Lastly, and as developed throughout this REACh dossier, no human health effect was observed in any of the tests realized with Hf compounds (or Zr compounds used as read across) by any of the routes and with any of the doses tested.

That is why the threshold values chosen as relevant ones, are those of HCl released during the HfCl4 process when in contact with humidity of air. These values of concern were communicated by the HCl consortium and are European OELs:

- Short Term Exposure Limit (STEL) (15 min): 10 ppm (15 mg/m3)  

- Time Weighted Average (TWA) (8h): 5 ppm (8 mg/ m3

 

The STEL is then considered as threshold value to cover peak exposure of HCl during the manufacturing process or uses (short exposure duration tasks as cleaning, sampling or maintenance).

This value of 15 mg/m3is chosen for acute local effect risk characterization.

And the TWA at 8 mg/m3value and is then chosen to cover repeated exposure of HCl during manufacture or uses.

 

3.   Dermal toxicity

 

On the basis of column 2 of annex VIII, in addition to the oral route, for substances other than gases, the information mentioned under acute toxicity sections shall be provided for at least one other route. The choice for the second route will depend on the nature of the substance and the likely route of human exposure. Based on the properties of the substance (inorganic corrosive chemical), the dermal route of exposure is not considered to be relevant, compared to inhalation one.

 

4. Irritation / sensibilisation

No dose descriptor can be set for the corrosive / irritant effects (as HfCl4 and HCl are classified for corrosive effects).

A qualitative approach, based on the part E of the ECHA technical guidance document on chemical safety report (part E.3.4.2) is followed. The general approach when no DNEL for an endpoint is available aims at reducing/avoiding contact with the substance. However, implementation of risk management measures (RMMs) and operational conditions (OCs) needs to be proportional to the degree of concern for the health hazard presented by the substance. The purpose of this qualitative approach is to minimize the exposure considering the level of risk related to the hazard properties of the substance (indicated by R-phrases). 

According to this guidance document, HfCl4 and HCl, with the R-phrase R34 (causes burns), which relates to strong corrosive effects, are allocated to the high hazard category on the basis that exposure to such corrosive substances should be strictly contained.

Because no systemic effects were seen in any of the studies registered for HfO2 (or ZrO2 as read across) or HCl (no DNEL for systemic effect), this qualitative assessment was performed for acute and repeated exposure by cutaneous/ eye route, only for local effects.

 

 

5. Genetic toxicity

 

Tests in bacterial systems are not appropriate for metal due to a lack of sensitivity related to either probable mechanism of action or lack of metal uptake. The high prevalence of false negatives for metal compounds might suggest that mutagenesis essay with mammalian cells, as opposed to bacterial cells, would be preferred starting point.

 

But, as HfCl4 is not stable and degrades instantaneously, testing for genotoxicity in general is not possible. The substance needs to be estimated considering the toxicity of its degradation products. HfOCl2 and HfO2, by read across with ZrOCl2 and ZrO2 are considered as not hazardous substances and are not classified at all for human health effects. ZrO2 was especially testedin vitrowith bacteria and mammalian cells and all tests were negative for genotoxicity (Ames, mouse lymphoma assay, chromosomic aberration and comet assay).

HCl is not classified for genotoxicity too and then no threshold value was linked to genotoxicity.

 

 

6.   Reprotoxicity

 

HfCl4 is not stable and degrades instantaneously; the toxicity to the reproduction is thus not relevant for HfCl4 and needs to be estimated considering the toxicity of its degradation products, that is to say HCl and HfOCl2/ HfO2.

Concerning HfO2, based on the same behavior and toxicological effects, and their very low systemic absorption, a read across with Zr/ZrO2 is performed.

Overall, the available repeated dose toxicity data indicate that Zr is a metal with an extremely poor potential for causing long-term toxicity. Further, the available results do not suspect Zr of being toxic for reproduction, as no long-term effects on reproductive organs have been observed in any of the available studies.

A testing proposal according to OECD 414 was judged relevant by ECHA. Once the results of the ZrO2 test are available, an update of the HfCl4 dossier will be made.

On the other side, HCl was not classified for reprotoxicity.

In conclusion, no threshold value was linked to reprotoxicity.

 

7.   Carcinogenicity

 

No data was found for carcinogenicity potential of hafnium compounds.

General Population - Hazard via inhalation route

Systemic effects

Long term exposure
Hazard assessment conclusion:
no hazard identified
Acute/short term exposure
Hazard assessment conclusion:
no hazard identified
DNEL related information

Local effects

Long term exposure
Hazard assessment conclusion:
no hazard identified
Acute/short term exposure
Hazard assessment conclusion:
no hazard identified
DNEL related information

General Population - Hazard via dermal route

Systemic effects

Long term exposure
Hazard assessment conclusion:
no hazard identified
Acute/short term exposure
Hazard assessment conclusion:
no hazard identified
DNEL related information

Local effects

Long term exposure
Hazard assessment conclusion:
no hazard identified
Acute/short term exposure
Hazard assessment conclusion:
no hazard identified

General Population - Hazard via oral route

Systemic effects

Long term exposure
Hazard assessment conclusion:
no hazard identified
Acute/short term exposure
Hazard assessment conclusion:
no hazard identified
DNEL related information

General Population - Hazard for the eyes

Local effects

Hazard assessment conclusion:
no hazard identified

Additional information - General Population

The general population; consumers as professionals, is not a relevant population for deriving DNEL as workers only, in industrial plants for manufacture or use of HfCl4 are potentally in contact with the substance or degradation products.