Maleic acid

Endpoint summary

Description of key information

Maleic acid was tested as corrosive in an in vitro corrosion study conducted according to OECD 435. Additional data is supporting the irritation potential of the target substance (Sax, 1989; Smith, 1993 and Britz, 1979). Data from an in vivo skin irritation study showed, that the structural analogue Maleic anhydride can also be considered as corrosive to the skin.

Based on available data from maleic acid and from the structural analogue Maleic anhydride, the target substance is considered to be severely irritating to the eyes and to have the potential of causing serious damage to the eyes.

Key value for chemical safety assessment

Skin irritation / corrosion

Link to relevant study records

Reference

Endpoint:

skin corrosion: in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2015 to 2015-04-14

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 435 (In Vitro Membrane Barrier Test Method for Skin Corrosion)

Deviations:

yes

Remarks:

Different batches of the negative and positive control substances then indicated in the protocol were used. The fact that different batches were used (but with the same purity) has no effect on the study results.

GLP compliance:

yes (incl. QA statement)

Species:

other: in vitro: Corrositex® test system

Amount / concentration applied:

Maleic acid was applied (approximately 500 mg), directly on top of the bio-barrier. During weighing was the test substance protected from light by wrapping the glassware in tin foil.

Duration of treatment / exposure:

Corrositex® penetration response time (minutes)

Timescale Category 1: 0 to 3 min. (Cat 1A); > 3 to 60 min.(Cat 1B); > 60 to 240 min. (Cat 1C); > 240 min. (Non-corrosive)
Timescale Category 2: 0 to 3 min. (Cat 1A); > 3 to 30 min. (CAT 1B); > 30 to 60 min. (CAT 1C); > 60 min. (Non-corrosive)

Details on study design:

Test system
Corrositex® is a test system that is composed of two components, a hydrated collagen matrix (bio-barrier) on a supporting filter membrane and CDS, an underlying aqueous solution of two pH indicator dyes.

The Corrositex® kit contained:
- Bio-barrier matrix.
- Bio-barrier diluent.
- Vials with Chemical Detection System (= CDS).
- Membrane discs.
- Compatibility test tubes.
- Timescale categorize test tubes with buffer A and B.
- Confirm reagent.

The batch number of the kit used for the experiment was CT051214
Rationale
Recommended test system in international guideline (OECD 435).

Source
InVitro International Inc., Irvin CA, USA.
The bio-barrier diluent (10 ml) was added to the bio-barrier matrix powder (1 gram) which contained a micro stir bar. This was stirred and heated slowly to 68°C in a water bath container. After preparation the matrix was stored refrigerated.

The day before testing the matrix was solubilized by heating it for 3-4 minutes at 60 °C. The membrane discs (at room temperature) were filled with 200 µl solubilised bio-barrier matrix. The entire membrane was covered with matrix and care was taken to avoid air bubbles.

The bio-barrier was prepared the day before testing and stored in the refrigerator until use.

All tests were performed at room temperature. The samples were at room temperature when applied.

Prior to performing the membrane barrier penetration study, Maleic acid was evaluated for the compatibility with the CDS. Maleic acid (102 mg) was added to the compatibility test tubes filled with CDS fluid. The tube was shaken to dissolve solids. In case the test substance was immiscible, the vial was shaken and the colour change was read at the interface after 1 minute.

If the CDS solution detected a colour or consistency change within 5 minutes, the test substance was tested for corrosivity using the Corrositex® kit. In case the CDS solution detected no colour or consistency change the membrane barrier penetration study was not performed with Corrositex®.
Maleic acid was classified into one of the two timescale categories.

This category determined how the penetration response time (if one occurs) was interpreted. The two different penetration response timescales were based on the acid or alkali reserve of the chemical. Maleic acid, 109 and 114 mg, was added to buffers A and B, respectively, shaken vigorously for
10 seconds and after 1 minute the colour change was read on the chart. In case the test substance was immiscible, the colour change was read at the interface after another minute. Buffer A detected weak or strong acids and buffer B detected strong or weak bases. In case no colour change was observed in both buffers a conformation test was performed. Two drops of confirm reagent were added to buffer B. The tube was shaken vigorously for 5 seconds and the colour of the solution was read on the chart confirming that the substance is a timescale category 2 substance.

The test was performed on a total of 4 membrane discs with bio-barrier matrix together with a negative and positive control. A disc was placed on a vial with CDS fluid. The test substance (526, 503, 518 and 504 mg) was applied on top of the matrix within two minutes after the disc was placed on the CDS fluid. One disc was exposed to 500 µl citric acid (10%, negative control) and one disc was exposed to 510 mg of the positive control sodium hydroxide. The test substance and controls were evenly distributed. Each vial was at least monitored for the first 5 minutes and 5 minutes before and after each packing cut-off time. The time of a change in the CDS fluid was recorded. Changes in the CDS may be colour changes (red, orange or lightening) and flaking or precipitation. The elapsed time between application and penetration of the membrane was determined.

Irritation / corrosion parameter:

penetration time (in minutes)

Run / experiment:

mean

Value:

25

Vehicle controls validity:

not examined

Negative controls validity:

valid

Positive controls validity:

valid

Remarks on result:

positive indication of irritation

Other effects / acceptance of results:

Maleic acid was evaluated for the compatibility with the CDS. Because a colour change (to pink/red) was observed after 1-minute, Maleic acid was compatible with the Corrositex® test system.
Maleic acid was classified into one of the two timescale categories. The timescale category test showed that Maleic acid is a timescale 1 substance (after one-minute tube A showed a colour change into pink). After 5 minutes the colour was pink-red. Since there appeared a colour change after 1 minute, the addition of the confirm reagent to tube B was not performed.
The membrane barrier test was performed and the elapsed time between the application of Maleic acid and controls and penetration through the membrane was recorded. The individual penetration times are presented in APPENDIX 2.
Since Maleic acid was a timescale 1 test substance and showed a mean penetration time of 25 minutes, based on this test Maleic acid would be classified as Skin Corrosive 1B (CLP) and UN packing group II (= GHS 1B). The negative control citric acid (10%) showed a mean penetration time of >60 minutes (actual penetration time 95 minutes) and was therefore non-corrosive. The positive control sodium hydroxide (as it is) showed a mean penetration time of 22 minutes and was therefore classified as UN packing group II (= GSH 1B). It was therefore concluded that the test system functioned properly.

Interpretation of results:

Category 1B (corrosive) based on GHS criteria

Conclusions:

It is concluded that this test is valid and that Maleic acid would be classified as Skin Corrosive 1B (CLP) and UN packing group II (= GHS 1B) in the Corrositex® assay under the experimental conditions described in this report.

Executive summary:

This report describes the ability of Maleic acid to pass through a bio-barrier and to elicit a colour change in the underlying liquid chemical detection system. The study procedures described in this report were based on the most recent OECD guideline OECD 435. Maleic acid was a white solid with a purity of 100.1%. The test substance compatibility test showed that Maleic acid was compatible with the chemical detection system. Based on the acid reserve, Maleic acid was classified as a timescale 1 compound. Maleic acid was applied directly (approximately 500 mg) on top of the bio-barrier matrix. The elapsed time between application and penetration was determined by monitoring changes in the chemical detection system.  The penetration time of Maleic acid was 25 minutes. Since Maleic acid was a timescale 1 test substance and showed a mean penetration time of 25 minutes, based on this test Maleic acid would be classified as Skin Corrosive 1B (CLP) and UN packing group II (= GHS 1B). The negative control citric acid (10%) showed a mean penetration time of >60 minutes (actual penetration time 95 minutes) and was therefore non-corrosive. The positive control sodium hydroxide (as it is) showed a mean penetration time of 22 minutes and was therefore classified as UN packing group II (=GSH 1B). It was therefore concluded that the test system functioned properly. Finally, it is concluded that this test is valid and that Maleic acid would be classified as Skin Corrosive 1B (CLP) and UN packing group II (= GHS 1B) in the Corrositex® assay under the experimental conditions described in this report.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (corrosive)

Eye irritation

Link to relevant study records

Reference

Endpoint:

eye irritation: in vivo

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

no data

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with national standard methods

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 405 (Acute Eye Irritation / Corrosion)

Deviations:

yes

Remarks:

3 rabbits/sec, study terminated after 48 hrs

GLP compliance:

yes

Species:

rabbit

Strain:

New Zealand White

Details on test animals or tissues and environmental conditions:

The rabbits used in this study weighed 2.27 to 2.79 kg. Room temperature was maintained at an average temperature and relative humidity of 23 °C and 54%, respectively.

Vehicle:

unchanged (no vehicle)

Controls:

yes, concurrent no treatment

Amount / concentration applied:

TEST MATERIAL
- Amount(s) applied: 0.1 g

Observation period (in vivo):

48 hours p.a.

Number of animals or in vitro replicates:

3/sex

Details on study design:

Test substance was administered undiluted at a dose of 0.1 g to the eyes of rabbits (three/sex). The treated eye of each rabbit was examined 1, 24, and 48 hours following test article administration. According to the study protocol, treated eyes were to be examined a minimum of 72 hours after dosing. However, due to signs of severe ocular irritation, the study was terminated following the 48-hour examination.

Irritation parameter:

cornea opacity score

Basis:

animal: 1-6

Time point:

24/48 h

Score:

3.8

Max. score:

4

Reversibility:

not reversible

Remarks on result:

other: Due to the severity of the effects the 72-hour time point was not assessed anymore

Irritation parameter:

iris score

Basis:

animal: 1-6

Time point:

24/48 h

Score:

2

Max. score:

2

Reversibility:

not reversible

Remarks on result:

other: Due to the severity of the effects the 72-hour time point was not assessed anymore

Irritation parameter:

chemosis score

Basis:

animal: 1-6

Time point:

24/48 h

Score:

4

Max. score:

4

Reversibility:

not reversible

Remarks on result:

other: Due to the severity of the effects the 72-hour time point was not assessed anymore

Irritation parameter:

conjunctivae score

Basis:

animal: 1-6

Time point:

24/48 h

Score:

2.5

Max. score:

4

Reversibility:

not reversible

Remarks on result:

other: Due to the severity of the effects the 72-hour time point was not assessed anymore

Irritation parameter:

cornea opacity score

Basis:

animal: 1-6

Time point:

72 h

Remarks on result:

not measured/tested

Irritation parameter:

iris score

Basis:

animal: 1-6

Time point:

72 h

Remarks on result:

not measured/tested

Irritation parameter:

conjunctivae score

Basis:

animal: 1-6

Time point:

72 h

Remarks on result:

not measured/tested

Irritation parameter:

chemosis score

Basis:

animal: 1-6

Time point:

72 h

Remarks on result:

not measured/tested

Irritant / corrosive response data:

No deaths occurred during the study. The maximum eye irritation score was 106.7 (out of a maximum of 110). The study was terminated at 48 hours post dosing due to severe occular irritation. Also due to the corrosivity of maleic anhydride shown in the skin irritation study, the risk of severe damage to eyes is considered implicit (GHS Cat.1).

Interpretation of results:

Category 1 (irreversible effects on the eye) based on GHS criteria

Conclusions:

The maximum eye irritation score was 106.7 (out of a maximum of 110). The study was terminated at the 48-hour postdosing timepoint due to signs of severe ocular irritations.

Executive summary:

Test substance was administered undiluted at a dose of 0.1 g to the eyes of rabbits (three/sex). The treated eye of each rabbit was examined 1, 24, and 48 hours following test article administration. According to the study protocol, treated eyes were to be examined a minimum of 72 hours after dosing. However, due to signs of severe ocular irritation, the study was terminated following the 48-hour examination.

No deaths occurred during the study. The maximum eye irritation score was 106.7 (out of a maximum of 110). The study was terminated at the 48-hour postdosing timepoint. The test substance was considered as highly irritating to the eyes of rabbits and classification as H318 is warranted in accordance to CLP regulation 1272/2008.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (irreversible damage)

Respiratory irritation

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

Supporting studies conducted with Maleic acid showed the irritating potential to the skin of rabbits and of humans.

Moreover, based on the results from an in vitro skin corrosion study conducted in accordance with OECD 435, the target substance can be considered to be corrosive.

In addition, available data from the structural analogue Maleic anhydride showed that the test item was severely irritating to the skin of rabbits after application of 0.5 g to the skin for 4 hours. The mean irritation scores for erythema and oedema ranged from 3.67 to 4.00 throughout the 7-day observation period (Chevron Chemical Company, 1976). Maleic anhydride hydrolyses under test conditions. As a result it is believed that maleic acid and its sodium salt were the test materials investigated in this study.

Maleic anhydride is severely irritating to the eyes of rabbits. In one study with maleic anhydride the mean conjunctival erythema scores at 24 and 48 hours were 2.0 and 3.0, respectively. The mean conjunctival chemosis scores at 24 and 48 hours were 4.0 and 4.0, respectively. The corneal opacity scores at 24 and 48 hours were 3.8 and 3.8, respectively. The iridial lesions scores at 24 and 48 hours were 2.0 and 2.0, respectively. The study was terminated at the 48-hour postdosing timepoint. Maleic anhydride hydrolyses under test conditions. As a result it is believed that maleic acid and its sodium salt were the test materials investigated in this study.

In a supporting study with maleic acid doses of 100 mg or application of 1% concentration of maleic acid for 2 minutes resulted in moderate to severe eye irritation, in another study application of a 10 % solution for 30 seconds resulted in permanent opacity of the cornea of rabbits.

Justification for classification or non-classification

Based on the results from an in vitro skin corrosion study (OECD 435) and from an in vivo skin irritation study conducted with the structural analogue Maleic anhydride, the target substance does warrant classification for skin corrosion (Skin Corr 1B, H314). Moreover, based on the results from the structural analogue Maleic anhydride, the target substance can be considered to be severely irritating to the eye (H318).