Naphthenic acids

Endpoint summary

Description of key information

Two in vivo skin sensitization studies have been published in the paper of Yamano et al. 2006 i.e. a local lymph node assay (LLNA) and a guinea pig maximization test (GPMT). The LLNA turned out to be not conclusive due to co-occurring skin irritation whereas the GPMT gave positive results for the skin sensitizing properties of naphthenic acid. The results were further supported by QSAR information that was generated with the VEGA tool, showing that almost all molecules in Naphthenic acids were predicted sensitisers.

Although there were 3 endpoints with Weight of Evidence value, the Guinea pig maximization test was considered most relevant for classification.

Key value for chemical safety assessment

Skin sensitisation

Link to relevant study records

Reference

Endpoint:

skin sensitisation: in vivo (non-LLNA)

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Although the information is only available as a published peer reviewed article which does not mention GLP compliance of the studies enough details are provided to adequately interprete the obtained data.

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 406 (Skin Sensitisation)

Deviations:

yes

Remarks:

The most inmportant deviation is the number of animals per group. In this test 5 in stead of the recommended minimum of 10 animals have been used; non-reporting of the performance of the positive control is deviating from the guideline.

Principles of method if other than guideline:

Although no guideline was followed the methods and results are well described allowing a detailed interpretation of the results.
The most important deviation is the number of animals per group. In this test 5 instead of the recommended minimum of 10 animals have been used. Next to this also the non-reporting of the performance of the positive control is deviating from the guideline.

GLP compliance:

not specified

Type of study:

guinea pig maximisation test

Justification for non-LLNA method:

The Murine Local Lymph Node Assay (LLNA) is the first-choice method for in vivo testing according to the REACH Regulation. However, this reliable guinea pig maximisation test was performed before entry into force of the REACH Regulation.

Specific details on test material used for the study:

Chemical obtained from Wako Pure Chemical Industries (Osaka Japan)
Next to naphthenic acid also cobalt naphthenate, copper naphthenate and zinc napthtenate have been investigated using the Guinea pig maximization test.

Species:

guinea pig

Strain:

Hartley

Sex:

female

Route:

epicutaneous, open

Vehicle:

other:

Concentration / amount:

1%, 25% as induction; 0.5% as challenge dose

Route:

epicutaneous, open

Vehicle:

other:

Concentration / amount:

1%, 25% as induction; 0.5% as challenge dose

No. of animals per dose:

5

Details on study design:

6-week-old female Hartley guinea pigs from Japan SLC (Shizuoka, Japan) were used The GPMT was performed as described previously in the literature 5 animals were used for each sensitization group (CuN, CoN, ZnN and Ν A) The first induction dose was set at 1%, while the second induction dose was 25%. 2 weeks after the second induction, 0.1 ml aliquots of the 7 chemicals in vehicles (0.5% in petroleum ether for CuN, CoN. ZnN and NA, 1% in ethanol for C0CI2. CuCL and ZnCU) were applied to a shaved area of the fiank for challenge all at once. 2 D after the challenge, each site was scored according to the criteria of Sato et al. (*). 1 week later, CoN-sensitized animals were further challenged with various concentrations of CoN and C0CI2 for a dose-response study.
* Sato Y. Katsumura Y. Ichikawa H. Kobayashi T. Kozuka T. Morikawa F. Ohta S. A modilied tcchnique of guinea pig testing to identify delayed hypersensitivity allergens. Contact Dermatitis 1981: 7: 225 237.

Positive control substance(s):

not specified

Positive control results:

Not reported

Key result

Reading:

1st reading

Hours after challenge:

48

Group:

negative control

Dose level:

0

No. with + reactions:

0

Total no. in group:

5

Clinical observations:

Reading: 1st reading. . Hours after challenge: 48.0. Group: negative control. Dose level: 0. No with. + reactions: 0.0. Total no. in groups: 5.0.

Remarks on result:

other: Reading: 1st reading. . Hours after challenge: 48.0. Group: negative control. Dose level: 0. No with. + reactions: 0.0. Total no. in groups: 5.0.

Reading:

1st reading

Hours after challenge:

48

Group:

test chemical

Dose level:

0.5%

No. with + reactions:

4

Total no. in group:

5

Clinical observations:

Reading: 1st reading. . Hours after challenge: 48.0. Group: test group. Dose level: 0.5%. No with. + reactions: 4.0. Total no. in groups: 5.0.

Remarks on result:

other: Reading: 1st reading. . Hours after challenge: 48.0. Group: test group. Dose level: 0.5%. No with. + reactions: 4.0. Total no. in groups: 5.0.

Reading:

1st reading

Group:

positive control

Remarks on result:

not measured/tested

Interpretation of results:

Category 1A (indication of significant skin sensitising potential) based on GHS criteria

Conclusions:

Althought there are only a limited numer of animals used per group the sensitizing properties of this substance were clearly positive.

Executive summary:

A GPMT test in 6-week-old female Hartley guinea pigs was performed with Natphenic acids and salts (copper, zin and cobalt naphthenate). The first induction dose was set at 1%, while the second induction dose was 25%. Two weeks after the second induction, 0.1 ml aliquots of the 7 chemicals in vehicles (0.5% in petroleum ether for CuN, CoN. ZnN and NA) were applied to a shaved area of the fiank for challenge. Each site was scored 48 hours after challenge. Napthenic acid resulted in 4/5 animals with clear reactions at 48 hours, therefore it is considered to be sensitizing for skin.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (sensitising)

Additional information:

Both data from published experimental studies and QSAR prediction for sensitisation were used in a Weight of Evidence approach:

- A Guinea pig maximisation test (GPMT) test in 6-week-old female Hartley guinea pigs was performed with Naphthenic acids and salts (copper, zinc and cobalt naphthenate) (Yamano et al, 2006). The first induction dose was set at 1%, while the second induction dose was 25%. Two weeks after the second induction, 0.1 ml aliquots of the 7 chemicals in vehicles (0.5% in petroleum ether for CuN, CoN. ZnN and NA) were applied to a shaved area of the flank for challenge. Each site was scored 48 hours after challenge. Naphthenic acid resulted in 4/5 animals with clear reactions at 48 hours, therefore it is considered to be sensitizing for skin.

- In an LLNA test, 6- to 8-week-old female mice were exposed to Naphthenic acids and salts (copper, zinc and cobalt naphthenate ) in a petroleum ether and olive oil (4 : 1) through application to the dorsum of both ears for 3 consecutive days (Yamano et al, 2006). On the 5° & 6° day, 4, 5- bromo-7-deoxyuridine (BrdU) was administered intraperitoneally to each mousse to measure the LLNA stimulation index. At the time of lymph node excision, the thickness of the ears was measured at the edge of the right pinna. There was an increase of the stimulation index, which was accompanied with an increase in the irritation index, therefore the results are not conclusive about the sensitizing properties of naphthenic acid under the conditions of the LLNA test, however a positive reaction is not excluded.

- Finally, skin sensitisation was predicted using the VEGA QSAR sensitisation model which is an extension of the original CAESAR model. Since naphthenic acids do not have a fixed composition, the prediction was performed on a broad selection of different possible structures in accordance with the substance identification. As can be seen from the results, almost all of the molecules in Naphthenic acids were indicated to be sensitisers. Only two molecules were indicated to be a non-sensitiser with a low applicability domain index (ADI). Most molecules fell in the applicability domain (with ADI >=0.8) and thus the prediction can be assumed to be reliable.
Although there were 3 endpoints with Weight of Evidence value, the Guinea pig maximization test was considered most relevant for classification.

Respiratory sensitisation

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

One reliable study indicated skin sensitising properties for naphthenic acid, which was further supported by QSAR prediction of almost all components. Therefore the substance is classified as Skin. sens 1 under Regulation 1272/2008 (CLP).