Naphthenic acids, bismuth salts

Short-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Endpoint:

short-term toxicity to aquatic invertebrates

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Study period:

2010

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Justification for type of information:

REPORTING FORMAT FOR THE ANALOGUE APPROACH

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
The substance naphthenic acids, bismuth salts is manufactured from bismuth oxide/hydroxide and 3 equivalents of naphthenic acids, resulting in the bismuth tri-naphthenate. Thus, in order to assess acute toxicity to invertebrates, results for bismuth 3+ cations were assessed as well as data for naphthenic acids, the two potential hydrolysis products of the substance. The undissociated substance is considered uncritical, as its molecular mass of ~850 Dalton makes it unlikely that such compounds efficiently pass biological membranes. Thus, the acute aquatic toxicity on naphthenic acids bismuth salts will be dominated by its ions, derived from hydrolysis.

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
The source compound naphthenic acids is the starting material for the manufacturing of naphthenic acids, bismuth salts. Naphthenic acids do contain mainly hydrocarbon acids with a carbon range from 10 - 15 (other naphthenic acids may have wider ranges), with a variable number of cyclics contained (n = 0, 1, 2 and rarely 3). To a minor extent also aliphatics may be present as "impurities".
The naphthenic acids are reacted in a slight excess of >3 equivalents of naphthenic acids with bismuth oxide to derive naphthenic acids, bismuth salts with a slight excess of naphthenic acids, the target substance. Thus, the starting compound for the synthesis of the target compound is actually the source substance. Whereas the bismuth oxide used has a purity of 99% by weight typically, the naphthenic acids, being a UVCB-type substance, are of 100% purity, by definition.
The second source substance used here is bismuth hydroxy nitrate oxide, a soluble form of bismuth compounds, suitable to achieve high Bi3+ concentrations in aqueous systems.
Thus, the two source compounds naphthenic acids (as surrogate for naphthenate anions) and bismuth hydroxy nitrate oxide (as surrogate for bismuth cations) are ideal surrogates for assessing the acute toxicity to invertebrates.

3. ANALOGUE APPROACH JUSTIFICATION
Although the two source substances are different in respect of properties compared to the target substance, the read-across is justified, as the source substance bismuth hydroxy nitrate oxide allows to achieve excessively high bismuth concentration in aqueous systems compared to the target substance (water solubility of < 0.036 mg/L) and still no EC50 was observed at 137 mg/L. The second source substance naphthenic acids allows to assess the anionic hydrolysis product of the target substance, and for naphthenic acids an EC50 of ~20 mg/L (based on dissolved fraction) was found. Thus, it can be concluded, that both results of the two source substances do consider a worst-case approach with respect to the target substance, especially considering the very low water solubility of the target substance.

4. DATA MATRIX
The source substance bismuth hydroxy nitrate oxide was found being uncritical to daphnia and an EC50 (48 h) of > 137 mg/L was found, equivalent to more than 463 mmol/L. Thus, determining for the toxicity towards invertebrates will be any naphthenic acid anions formed upon hydrolysis of the target substance. Considering an EC50 (48 h, daphnia magna) of ~20 mg/L naphthenic acids determined in an acute daphnia toxicity study, this result was re-calculated to approx. 88 mmol/L (calculated based on an average of C14, 1-ring naphthenic acid as average value) and considering the 3:1 molar ratio of naphthenic acid and bismuth in the target substance (on average estimated as Bi(O2C13H24)3) as well as the molecular average mass of 850 Dalton, the calculated theoretical EC50 is derived as 25 mg/L for naphthenic acids, bismuth salts. This value is almost three orders of magnitude above the value for water solubility (determined as < 0.036 mg/L – see study on water solubility), and in consequence, it is expected that naphthenic acids, bismuth salts are not acutely toxic to invertebrates.

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

read-across source

Qualifier:

according to guideline

Guideline:

OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)

Duration:

48 h

Dose descriptor:

EC50

Effect conc.:

> 463 mmol/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mobility

Remarks on result:

other: value for Bi(OH)(NO3)O

Duration:

48 h

Dose descriptor:

EC50

Effect conc.:

ca. 88.3 mmol/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat. (dissolved fraction)

Basis for effect:

mobility

Remarks on result:

other: value for naphthenic acids

Duration:

48 h

Dose descriptor:

EC50

Effect conc.:

ca. 25 mg/L

Nominal / measured:

estimated

Conc. based on:

test mat.

Basis for effect:

mobility

Remarks on result:

other: estimated EC50 for naphthenic acids, bismuth salts

Validity criteria fulfilled:

yes

Conclusions:

For naphthenic acids, bismuth salts an EC50 to invertebrates, such as daphnia magna, of approx. 25 mg/L is estimated based on data from naphthenic acids, considered relevant for the acute invertebrates toxicity. Soluble bismuth compounds such as Bi(OH)(NO3)O have been tested and were found being non-toxic to invertebrates. Therefore, the inorganic moiety is considered uncritical for acute toxicity to invertebrates.

Description of key information

The source substance bismuth hydroxy nitrate oxide was found being uncritical to daphnia and an EC50 (48 h) of > 137 mg/L was found, equivalent to more than 463 mmol Bi/L. Thus, determining for the toxicity towards invertebrates will be any naphthenic acid anions formed upon hydrolysis of the target substance. Considering an EC50 (48 h, daphnia magna) of ~20 mg/L naphthenic acids determined in an acute daphnia toxicity study, this result was re-calculated to approx. 88 mmol/L (calculated based on an average of C14, 1-ring naphthenic acid as average value) and considering the 3:1 molar ratio of naphthenic acid and bismuth in the target substance (on average estimated as Bi(O2C13H24)3) as well as the molecular average mass of 850 Dalton, the calculated theoretical EC50 is derived as 25 mg/L. This value is almost three orders of magnitude above the value for water solubility (determined as < 0.036 mg/L – see study on water solubility), and in consequence, it is expected that naphthenic acids, bismuth salts is not acutely toxic to invertebrates.

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Effect concentration:

25 mg/L