Neodymium trinitrate

Endpoint summary

Description of key information

Skin irritation/corrosion:
A weight-of-evidence approach is used for this endpoint (sequential testing strategy).
Based on the determination of the pH (2.07) and the acidic reserve (0.224), neodymium trinitrate was considered not to be corrosive (Rhodia Operations, 2012). This test was scored K2.
A K1 in vitro skin corrosion test in an EPISKIN reconstructed human epidermis model was performed according to OECD Guideline 431 and EU Method B.40 (Warren, 2013). Neodymium trinitrate was considered to be non-corrosive to the skin. 
A K1 in vitro skin irritation test in an EPISKIN reconstructed human epidermis model was performed according to OECD Guideline 439 and EU Method B.46 (Warren, 2013). Neodymium trinitrate was considered to be non-irritating to the skin.
Finally, a K1 acute dermal irritation study in New Zealand White rabbits was performed according to OECD Guideline 404, Commission Regulation (EC) NO 440/2008, B.4 and OPPTS Guideline 870.2500 and in compliance with GLP (Matting, 2014). Neodynium trinitrate was considered not to be irritating.
Eye irritation:
Based on the data of a study performed according to a method similar to OECD Guideline 405 study, the product containing 75% lanthanum nitrate and 25% neodymium trinitrate was considered to be extremely irritant to unwashed and washed eyes respectively, when instilled as received, undiluted (Guillot, 1980) and was used as an analogue for neodymium trinitrate.

Key value for chemical safety assessment

Skin irritation / corrosion

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not irritating)

Eye irritation

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (irritating)

Respiratory irritation

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

Skin irritation/corrosion:

Four studies are used in a 'Weight-of-Evidence' approach: one K2 test (Rhodia Operations, 2012), two K1 in vitro studies (Warren, 2013) and one K1 acute dermal irritation study (Matting 2014).

The pH-value of a 10% neodymium trinitrate solution was determined electrochemically at 20°C with a calibrated pH-meter in order to evaluate its irritant/corrosive potential (Rhodia Operations, 2012).

The pH-value was 2.07 and was used for deciding whether or not it was necessary to determine the acid reserve. The acid reserve of the 10% solution was determined via titration using a 1 mol/L NaOH solution. Based on an acidic reserve of 0.224 and pH of 2.07, the calculation for corrosivity was 2.051 which is higher than -0.5. Therefore the substance was considered to be non-corrosive.

An in vitro skin corrosion test in an EPISKIN reconstructed human epidermis model was performed according to OECD Guideline 431 and EU Method B.40 (Warren, 2013). Duplicate tissues were treated with 20 mg of the solid test item for exposure periods of 3, 60 and 240 minutes. At the end of the exposure period the test item was rinsed from each tissue before each tissue was taken for loading in a MTT solution (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide solution). After MTT loading a total biopsy of each epidermis was made and placed into micro tubes containing acidified isopropanol for extraction of formazan crystals out of the MTT-loaded tissues. At the end of the formazan extraction period each tube was mixed thoroughly and duplicate 200 µL samples were transferred to the appropriate wells of a pre-labelled 96-well plate. The optical density (OD) was measured at 540 nm (OD540). Data were presented in the form of percentage viability (MTT reduction in the test item treated tissues relative to negative control tissues). The relative mean viability of the test item treated tissues after the 240 minutes exposure was 105.1% (>= 35, relative mean tissue viability percentage of the negative control criteria). Neodymium trinitrate was considered to be non-corrosive to the skin.

An in vitro skin irritation test in an EPISKIN reconstructed human epidermis model was performed according to OECD Guideline 439 and EU Method B.46 (Warren, 2013). Ten mg of ground-up test substance was applied to tissues moistened with 5 µL sterile distilled water for 15 minutes. EPISKIN tissues were exposed in triplicate to test item, positive control and negative control. At the end of the exposure period each tissue was rinsed before incubating for 42 hours. At the end of the post-exposure incubation period each tissue was taken for MTT-loading. The maintenance medium from beneath each tissue was taken for MTT-loading. The maintenance medium from beneath each tissue was transferred to pre-labeled micro tubes and stored in a freezer for possible inflammatory mediator determination. After MTT loading a total biopsy of each epidermis was made and placed into micro tubes containing acidified isopropanol for extraction of formazan crystals out of the MTT-loaded tissues. At the end of the formazan extraction period each tube was mixed thoroughly and duplicate 200 µL samples were transferred to the appropriate wells of a pre-labeled 96-well plate. The optical density was measured at 540 nm. Data were presented in the form of percentage viability (MTT reduction in the test item treated tissues relative to negative control tissues). The relative mean viability of the test item treated tissues was 105.3% after the 15 -minute exposure period (>50% relative mean tissue viability percentage of negative control). Neodymium trinitrate was considered to be non-irritating to the skin.

Following a sequential testing strategy for the assessment of the irritant/corrosive properties of neodymium trinitrate, an in vivo acute dermal irritation study was performed (Matting, 2014) with neodymium trinitrate (hydrated form) in New Zealand White rabbits. The study was performed according to the OECD Guidelines for Testing of Chemicals No. 404, Commission Regulation (EC) No 440/2008, B.4, OPPTS Guideline 870.2500 and Good Laboratory Practice. Parameters monitored during this study included mortality, body weight measurements and clinical observations. The irritancy of the test item was evaluated according to the Draize scoring method. The animals were treated by topical semi-occlusive application of 0.5 g to the intact shaved flank of 3 young adult New Zealand White rabbits. Sufficient water to damp the material was used to ensure good contact with the skin. The untreated skin of each animal served as control. The duration of treatment was 4 hours. The scoring of skin reactions for erythema and oedema was performed 1, 24, 48 and 72 hours after removal of the dressing. The primary irritation index was calculated by totalling the mean cumulative scores at 24, 48 and 72 hours and then dividing by the number of data points using values from intact and abraded skin. Additional general examinations were performed daily. There was no mortality during the observation period. There was no test item related effect on body weight. At observation 1, 24, 48 and 72 hours after patch removal, there were no observed clinical signs noted on the skin of the treated animals. As no signs of irritation were observed at 72 hours after patch removal, the study was terminated after 72 hours observation. The animals' individual mean scores (considering readings at 24, 48 and 72 hours after patch removal) for erythema and oedema were 0.00, 0.00 and 0.00, respectively. The primary irritation index (considering readings at 24, 48 and 72 hours after patch removal) was calculated as 0.00.

In conclusion, the evaluation of the results of the abovementioned studies in a 'weight-of-evidence' approach demonstrates that neodymium trinitrate is not a dermal irritant/corrosive substance.

One supportive study is also included in this endpoint. Guillot (1980) investigated the in vivo skin irritation potential of a mixture containing 75% lanthanum nitrate and 25% neodymium nitrate in a study performed according to a method equivalent to OECD Guideline 404 in New Zealand White rabbits. After 24 hours exposure to 0.5 mL of the substance using a occlusive wrap, skin irritation (edema and erythema) was scored at 25 and 72 hours after application of the test substance. Based on the scoring system used in the study (mean value of the abraded skin obervations and intact skin observations), the product containing 75% lanthanum nitrate and 25% neodymium nitrate can be considered as a mild primary skin irritant when applied as received. Based on the criteria of the CLP Regulation, the mixture would not be classified as a skin irritant, assuming that the effects are reversible within 14 days and are not increased after 72h. However some deficiences were observed in the test.

Although the substance tested was a mixture instead of neodymium trinitrate pure, the response obtained is such that it meets the criteria for non-classification. Therefore, this study is used to support the non-classification of neodymium trinitrate for skin irritation/corrosion.

In addition two studies have been disregarded:

In the first study, Dunn (1980) investigated the in vivo skin corrosion potential of a substance containing 70% praseodymium nitrate and 30% neodymium nitrate in a study performed according to a method equivalent to procedure specified in Title 49, Code of Federal Regulation articles 173.240, Appendix A in New Zealand White rabbits. Patches were removed after 4 hours and scored for destruction or irreversible alteration of the skin. The test sites were again observed at 24 and 48 hours. The study conclusion was that the test item was not corrosive. However, due to the lack of a scoring system, no conclusion could be drawn on the skin corrosion potential of the mixture or its constituents to drive classification.

Bradshaw (2013) performed an in vivo acute dermal irritation study in rabbits with neodymium trinitrate (hydrated form). In this test, the substance was applied in a semi-occlusive dressing at three locations on the back of one rabbit for respectively 3 min, 1 hour and 4 hours of exposure and for 4 hours in one site of a second animal. Although no deviations were reported in the study, differences in the reversibility/irreversibility of the skin reactions were observed between animals after the same exposure period, with no apparent reason for these differences. However, other reliable experimental data available on this substance showed that neodymium trinitrate is neither irritant nor corrosivefor the skin:

- Measurement of the pH of a 10% w/w aqueous preparation (Bradshaw, 2013): pH value of 4.0 immediately and after 10 minutes.

- Episkin study according to OECD 431(Warren, 2013): non corrosive

- Episkin study according to OECD 439 (Warren, 2013): non irritant

In addition, reliable experimental data from other 'heavy' rare earth nitrates show that these nitrate salts are not irritant/corrosive to the skin:

- Cerium trinitrate: not irritant to skin in rabbits (Shapiro, 1990 and Gonnet, 1980)

- Lanthanum trinitrate: not irritant to skin in rabbits (Bradshaw, 2013)

Based on all the abovementioned information ('weight-of-evidence' approach), it can be concluded that the results of the study of Bradshaw (2013) are not conclusive but equivocal and that there is sufficient evidence to disregarded the study.

Eye irritation:

No GLP study evaluating the eye irritation/corrosion potential of the pure neodymium trinitrate is available. However one study has been identified (Guillot, 1980), where four rabbits were instilled 0.1 g of a mixture of 75% lanthanum nitrate and 25% neodymium nitrate, in the left eye. This study was performed according to a method similar to the OECD 405 guideline. The eyes were examined at 1 hour and 1, 2, 3, 4 and 7 days after instillation. The calculated index of ocular irritation for unwashed eye was 97.75 at day 7. Based on the scoring of Draize and Kay and Calandra, the substance was judged to be extremely irritating. Other effects observed: iris scores increasing from 1 to 2 after 7 days in 3 of 4 animals and no pupil reflex; reduced pupil reflex from day 3 onwards; myosis after 1 hour in 1 animal and after day 1 in all animals, whitish moisture on the eyelids.

Although the substance tested was a mixture instead of neodymium trinitrate pure, the response obtained is such that it meets the criteria for classification. Thus, this study is considered sufficient to cover this endpoint. Therefore, it is proposed to classify neodymium trinitrate for eye damage in a worst case approach, assuming that observed effects are not reversible.

Justification for selection of skin irritation / corrosion endpoint:
No test is selected as the endpoint is covered by 'Weight-of-evidence' approach.

Justification for selection of eye irritation endpoint:
There is only one study available for this endpoint. This study is performed on mixture of lanthanum trinitrate with neodymium trinitrate in which lanthanum trinitrate was the main component (75%). Although the substance tested was a mixture instead of neodymium trinitrate pure, the response obtained was such that it meets the criteria for classification. As such, this study is considered sufficient to cover this endpoint. Therefore, it is proposed to classify neodymium trinitrate for eye damage as a worst case, assuming that observed effects are not reversible.

Effects on eye irritation: corrosive

Justification for classification or non-classification

Based on the results of the available data (weight-of-evidence approach) and the criteria of the DSD and CLP Regulation, neodymium trinitrate should not be classified for skin irritation.

Based on the criteria of the DSD Regulation, neodymium trinitrate is classified as R41 and as Eye Dam 1 H318 based on the severe effects that have been observed in the available study with the read-across mixture of 75% lanthanum nitrate and 25% neodymium nitrate and the criteria of the CLP Regulation.