Barium fluoride

Endpoint summary

Description of key information

Acute toxic effects of barium and fluoride released from BaF2 are relevant for the aquatic hazard assessment of Barium fluoride. Reliable acute and chronic toxicity data of barium and fluoride are available for three trophic levels: algae, invertebrates and fish. Based on these available results it may conservatively be assumed that the toxicological moiety for the short- and long-term aquatic toxicity of BaF2 is barium.

Additional information

Read across approach:

No aquatic toxicity studies with barium fluoride are availabe. In the aquatic environment, barium fluoride will dissociate into barium and fluoride ions. Therefore the aquatic toxicity of barium fluoride may reasonably be considered to be determined by the availability of Ba2+ cations and F- anions. Comprehensive data on aquatic toxicity are available for barium chloride and sodium fluoride. Both barium chloride and sodium fluoride are highly soluble with ca. 375 g/L and 40 g/L, respectively at neutral pH, whereas barium fluoride has a solubility of 1.6 g/L. Hence, any read across from barium chloride and sodium fluoride to BaF2 is inherently conservative and therefore the available data from studies with barium chloride and sodium fluoride are given as indication of the aquatic toxicity of barium fluoride.

Barium

For the assessment of the environmental fate and behaviour of barium substances, a read-across approach is applied based on all information available for inorganic barium compounds. This is based on the common assumption that after emission of metal compounds into the environment, the moiety of toxicological concern is the potentially bioavailable metal ion (i.e., Ba2+). The dissolution of barium substances in the environment and corresponding dissolved Ba levels are controlled by the solubility of barite (BaSO4) and witherite (BaCO3), two naturally occurring barium minerals (Ball and Nordstrom 1991; Menzie et al, 2008). The solubility of barium compounds increases as solution pH decreases (US EPA, 1985a). However, the concentration of dissolved Ba cations in freshwater is rather low– unless solutions are strongly undersaturated with respect to barite and witherite. In solutions, undersatured in barite and wiltherite, barium occurs largely as free Barium cations. Barium cations are not readily oxidized or reduced and do not bind strongly to most inorganic ligands or organic matter. Thus, the barium ion is stable under the pH-Eh range of natural systems, and in the dissolved state, the divalent barium cation is the predominant form in soil, sediments and water.

In sum, transport, fate, and toxicity of barium in the aquatic compartment are largely controlled by the solubility of barium minerals, specifically barium sulfate. The barium cation is the moiety of toxicological concern, and thus the hazard assessment is based on barium ions.

Fluoride

The available studies for fluoride were performed with sodium fluoride (NaF). The concentration of free fluoride ions in the environment is strongly dependent on the presence of other inorganic mineral species. In the presence of phosphate and calcium, insoluble fluoride salts are formed, a large part of which are transferred to sediment.  Under aqueous conditions where phosphate and calcium levels are relatively high, there will be virtually no free fluoride in the water. The EU RAR notes a clear relationship between the aquatic toxicity of sodium fluoride and water hardness. Tests performed in soft water (<50 mg CaCO3/L) showed greater toxicity than those performed in hard water (>50 mg CaCO3/L) due to the precipitation of fluoride as CaF2. All endpoints are expressed in terms of concentrations of the fluoride ion (F-).

References:

- Canadian Council of Ministers of the Environment (2013) Canadian Soil Quality Guidelines for the protection of environmental and human health: Barium.

- US EPA (1985a) Health advisory — barium. Washington, DC, US Environmental Protection Agency, Office of Drinking Water.

- US EPA (1984) Health effects assessment for barium, Cincinnati, Ohio, US Environmental Protection Agency, Office of Health and Environmental Assessment, Environmental Criteria and Assessment Office (Prepared for the Office of Emergency and Remedial Responsible, Washington, DC) (EPA 540/1-86-021).

Fluoride - acute toxicity data:

For fluoride several studies performed with sodium fluoride in different aquatic species are available. The table below provides an overview of reliable toxicity data of fluoride. Reported values are expressed as fluoride concentrations. 

Table. Overview of reliable acute toxicity data of fluoride

	Parameter	Endpoint	Value (mg F/L)	Reference
Oncorhynchus mykiss	mortality	96h-LC50	51	EU-RAR 2001
Benthic trichoptera larvae	mortality/immobility	96h-EC50	26	EU-RAR 2001
Scenedesmus sp.	growth rate	72h-ErC50	43	EU-RAR 2001

Reliable acute data for fluoride are available for three trophic levels: algae, invertebrates, and fish. The lowest effect value is the 96h-EC50 of 26 mg F/L for benthic trichoptera larvae, corresponding to 120 mg BaF2/L.

Barium - acute toxicity data:

The table below provides an overview of reliable toxicity data of barium substances. Reported values are based on barium concentrations. 

Table. Overview of reliable acute toxicity data of barium applied in hazard assessment

Species	Parameter	Endpoint	Value (mg Ba/L)	Reference
Danio rerio	mortality	96h-LC50	> 97.5 > 3.5 (dissolved)	Egeler and Kiefer, 2010
Daphnia magna	mortality/immobility	48h-LC50	14.5	Biesinger and Christensen, 1972
Pseudokirchneriella subcapitata	growth rate	72h-ErC50	> 30.1 >1,15 (dissolved)	Egeler and Kiefer, 2010

Reliable acute data were available for three trophic levels: algae, invertebrates, fish. The lowest effect value (based on dissolved barium in the test medium) is a 72h-ErC50 of > 1.15 mg Ba/L, corresponding to > 1.47 mg BaF2/L, for growth reduction in algae.

It should be noted that the outcome of fish and algae tests, when expressed as dissolved barium concentrations resulted in effect levels that are > 3.50 mg Ba/L and > 1.15 mg Ba/L, respectively, whereas these levels are approximately a factor of ~30 higher when expressed as total barium, i.e. > 97.5 mg/L and > 30.1 mg/L of total Ba, respectively.

The low recovery of dissolved barium in the algae and fish study may be explained with the precipitation of barium sulfate. Thus, the Chemical Safety Assessment is based on the dissolved barium concentration.

Fluoride - chronic toxicity data:

Reliable studies on chronic toxicity of fluoride to the aquatic environment are available for three trophic levels: algae, invertebrates and fish. The toxicity tests were performed with sodium fluoride as test substance.

Table.Overview of reliable chronic toxicity data of fluoride applied in hazard assessment   

Species	Parameter	Endpoint	Value (mg F/L)	Reference
Oncorhynchus mykiss	mortality	21d-NOEC	4	EU-RAR 2001
Pseudokirchneriella subcapitata	growth rate	7d-NOECr	50	EU-RAR 2001
Daphnia magna	reproduction	21d-NOEC	8.9 (arithmetic mean of two tests)	EU-RAR 2001

The lowest effect value is the 21d-NOEC of 4 mg F/L for  Oncorhynchus mykiss, corresponding to 18.5 mg BaF2/L.

Barium - chronic toxicity data:

Reliable studies on chronic toxicity of barium to the aquatic environment are available for three trophic levels: algae, invertebrates and fish. The toxicity tests were performed with barium dichloride dihydrate as test substance.

Table.Overview of reliable chronic toxicity data of barium applied in hazard assessment   

Species	Parameter	Endpoint	Value (mg Ba/L)	Reference
Danio rerio	mortality	33d-NOEC	≥ 40.3 ≥ 1.26 (dissolved)	Gilberg, 2014
Pseudokirchneriella subcapitata	growth rate	72h-NOECr	≥ 30.1 ≥1.15 (dissolved)	Egeler and Kiefer, 2010
Daphnia magna	reproduction	21d-NOEC	2.9	Biesinger and Christensen, 1972

- A chronic fish study according to OECD 210 (Gilberg, 2014) was performed withDanio rerio. A NOEC of ≥ 40.3 mg/L total barium was derived, corresponding to a NOEC of ≥ 51.4 mg/L total BaF2. Further, the NOEC of ≥ 1.26 mg/L dissolved barium corresponds to a NOEC of ≥ 1.61 mg BaF2/L. The low recovery of dissolved barium in the study may be explained with the precipitation of barium sulfate. Thus, the Chemical Safety Assessment is based on dissolved barium.

-In the study of growth inhibition of the algae speciesPseudokirchneriella subcapitataperformed by Egeler and Kiefer (2010), all significant effect levels (acute and chronic) were≥ 30.1 mg total Ba/L and≥1.15mg dissolved Ba/L. Thus, the 72-h NOEC is≥30.1 mg total Ba/L and≥1.15 mg dissolved Ba/L corresponding to a 72-h NOEC of≥38.4 mg total BaF2/L and≥1.47 mg dissolved BaF2/L, respectively.

- The study on the chronic toxicity of barium to invertebrates (Biesinger and Christensen, 1972) reports a calculated NOEC forDaphnia magna(i.e., EC16/2) of 2.9 mg Ba/L (nominal) corresponding to 3.7 mg BaF2/L.