Dibismuth trioxide

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

0.1 mg/L

Assessment factor:

1 000

PNEC freshwater (intermittent releases):

1 mg/L

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0.01 mg/L

Assessment factor:

10 000

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

17.5 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

45 709 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

4 571 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

67.6 mg/kg soil dw

Extrapolation method:

equilibrium partitioning method

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

PNEC oral

PNEC value:

33.3 mg/kg food

Assessment factor:

30

Additional information

Read-across approach

In the assessment of the ecotoxicity of Bi and Bi compounds, a read-across approach is followed based on all information available for inorganic Bi compounds. This grouping of bismuth compounds for estimating their properties is based on the assumption that properties are likely to be similar or follow a similar pattern as a result of the presence of the common bismuth ion. For most metal-containing compounds, it is indeed the potentially bioavailable metal ion that is liberated (in greater or lesser amounts) upon contact with water that is the moiety of toxicological concern.

This assumption can be considered valid when

i) differences in solubility among Bi compounds do not affect the results for ecotoxicity,

ii) ecotoxicity is only affected by the bismuth-ion and not by the counter ions, and

iii) after emission to the environment, the various Bi compounds do not show differences in speciation of bismuth in the environment or differences in speciation do not affect toxicity

In assessing the ecotoxicity of metals it is assumed that toxicity is not controlled by the total concentration of a metal, but by the bioavailable form. No evidence is available on the bioavailable form of bismuth, but for metals, this bioavailable form is generally accepted to be the free metal-ion in solution. In the absence of speciation data and as a conservative approximation, it can also be assumed that the total soluble bismuth pool is bioavailable. Bismuth subnitrate was selected as a worst-case test substance in a read-across approach among inorganic Bi substances because it shows the highest solubility in a standard OECD 105 and EEC A.6 solubility test (solubility in deionised water >600 mg Bi/L according to the flask method). However, solubility was limited under the relevant conditions for the aquatic toxicity assays and all tests were therefore based on the water-accommodated fraction of after seven days equilibration prior to the start of the toxicity assays, according to the guidance on transformation dissolution of metals and metal compounds (OECD, 2001). This resulted in dissolved Bi concentrations <0.05 mg BI/L and all toxicity results are expressed based on total initial loadings of elemental Bi.

The ecotoxicity results selected for read-across among bismuth substances are all based on bismuth subnitrate (Bi₅O(OH)₉(NO₃)₄), dibismuth trioxide or bismuth metal powder. There is no concern on toxicity of the other constituents of Bi subnitrate (OH^- and NO₃^-).

Very limited information is available on the chemistry of Bi in the environment. Bismuth can exist under the following oxidation states: 0, +III and +V. No information on measured Bi-speciation in water is available, and it will be assumed that Bi³⁺ is the dominant species under the prevalent environmental conditions. A Pourbaix diagram, showing the oxidation state and major species of bismuth as a function of pH and reduction potential indeed predicts that trivalent Bi is dominant under conditions commonly found in oxic fresh waters, i.e., pH between 5 and 9; redox potential [Eh] between 0.5 and 1 V. It is assumed that upon dissolution of bismuth substances, the environmental conditions control the (redox) speciation of bismuth in water, soil and sediment, regardless of the Bi compound added.

Based on this information, it was concluded that all conditions stated above are met. Therefore, all toxicity data based on bismuth subnitrate were used as a worst-case scenario in a read-across approach for other inorganic Bi compounds. Results are all expressed based on total elemental bismuth concentrations.

Conclusion on classification

Acute and chronic reference values for environmental classification are based on standard test as laid down in Council Regulation (EC) No 440/2008 on “test methods pursuant to Regulation (EC) No 1907/2006 of the European Parliament and of the Council on the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH)”

For dibismuth trioxide, no Acute 1/Chronic 1, 2, 3 classification category under CLP is warranted as there was no acute toxicity observed to fish, invertebrates and algae up to >100 mg Bi/L, equivalent to >111 mg Bi₂O₃/L, nor chronic toxicity to the alga Pseudokirchneriella subcapitata (NOEC ≥100 mg Bi/L). All tests were based on the water-accommodated fraction of bismuth subnitrate (Bi₅O(OH)₉(NO₃)₄) after seven days equilibration prior to the start of the toxicity assays, according to the guidance on transformation dissolution of metals and metal compounds (OECD, 2001). Bismuth subnitrate was selected as a worst-case test substance in a read-across approach among inorganic Bi substances because it shows the highest solubility in a standard OECD 105 and EEC A.6 solubility test.

Although no chronic data are available for daphnids and fish, the remaining Chronic 4 classification category under CLP can be removed based on the following arguments:

• No significant acute toxicity was noted for daphnids and fish at a concentration of 100 mg Bi/L, equivalent to 111 mg Bi₂O₃/L, that is 111 times higher than the chronic threshold concentration level (1 mg/L). This observation strongly suggests that no chronic effects below 1 mg Bi₂O₃ are expected for fish and invertebrates.

• No significant chronic effects are noted for the alga Pseudokirchneriella subcapitata, at a concentration of 100 mg Bi/L, equivalent to 111 mg Bi₂O₃/L.

Therefore, there is no need for an environmental classification of dibismuth trioxide.