Naphthenic acids, bismuth salts

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

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

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

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. Inorganic components such as bismuth cations cannot be biodegraded by definition and thus, the concept of biodegradability is only applicable to the anionic moiety of the substance, i.e. the naphthenic acids. Naphthenic acids have been investigated for biodegradability, and thus these data are used for assessing the biodegradability of the organic moiety of the substance.

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.

3. ANALOGUE APPROACH JUSTIFICATION
Not applicable, as the source substance fully characterizes the organic moiety of the target substance, which is the corresponding bismuth salt. The target substance is expected to slowly hydrolyse to insoluble bismuth hydroxide, altering to bismuth oxide again in biota, whereas the organic parts (the source substance) upon hydrolysis becomes biodegraded as shown by the data on the source substance.

4. DATA MATRIX
The source substance was analysed in two modifications, namely the naphthenic acids with a carbon range of C8 – C20 and their corresponding sodium salts. Both did not differ significantly with respect to biodegradation in that they both achieved 60% biodegradability within 22 and 17 days, respectively.
The target compound was analysed for the carbon distribution and found being mainly in the range of C10 – C15 with small amounts of higher carbon numbers present that were not quantified. Thus, the chain length distribution of the target compound is fully within the range of the source carbon chain distribution.

Reason / purpose for cross-reference:

read-across source

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 310 (Ready Biodegradability - CO2 in Sealed Vessels (Headspace Test)

Deviations:

yes

Remarks:

no information regarding a reference substance and enrichment culture based on process affected waters

Parameter:

% degradation (inorg. C analysis)

Remarks:

and CO2 in the headspace have been analysed

Value:

ca. 60

Sampling time:

22 d

Remarks on result:

other: According to a graph shown in the article the CO2 emitted in viable cultures reaches 60% after about 22 days in the case of the Kodak naphthenic acid sodium salt

Parameter:

% degradation (inorg. C analysis)

Remarks:

and CO2 in the headspace have been analysed

Value:

ca. 60

Sampling time:

17 d

Remarks on result:

other: In the case of the Merichem 60% CO2 is reached after 17 days.

Validity criteria fulfilled:

yes

Interpretation of results:

inherently biodegradable

Conclusions:

This work showed that two commercial naphthenic acids preparations (one a naphthenic acid and the other one naphthenic acids sodium salts) can be biodegraded extensively under laboratory conditions, using aerated cultures with an abundant supply of inorganic nutrients including phosphorus and fixed nitrogen.
Upon degradation the GC-MS fingerprints are changed dramatically. The napththenic acids concentration was decreased to level approaching zero by day 14.
In conclusion, it is expected that the organic moiety of naphthenic acids bismuth salts, similar to the sodium salts and their free acids, will degrade rapidly in biota.

Executive summary:

This work showed that two commercial naphtenic acids preparations can be biodegraded extensively under laboratory conditions, using aerated cultures with an abundant supply of inorganic nutrients including phosphorus and fixed nitrogen. Upon degradation the GC-MS fingerprints are changed dramatically. The napththenic acids concentration was decreased to level approaching zero by day 14. Decomposition products of the nathphthenic acid include palmitic acid and stearic acid. Further the decrease in toxicity upon aerobic degradation has also been shown.

Description of key information

This work showed that two commercial NAs preparation can be biodegraded extensively under laboratory conditions, using aerated cultures with an abundant supply of inorganic nutrients including phosphorus and fixed nitrogen. Upon degradation the GC-MS fingerprints are changed dramatically. The naphthenic acids concentration was decreased to level approaching zero by day 14. In conclusion, it is expected that the organic moiety of naphthenic acids bismuth salts, similar to the sodium salts and their free acids, will degrade rapidly in biota.

Key value for chemical safety assessment

Biodegradation in water:

inherently biodegradable

Type of water:

freshwater