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METHOD 1120

DERMAL CORROSION

1.0 SCOPE AND APPLICATION

1.1 The dermal corrosion assay system is an in vitro test method which determines the

corrosive potential of a substance toward human skin. The method is simple, rapid, accurate, and

may be applied to both solids, liquids and emulsions. The liquids may be aqueous or non-aqueous.

Solids can be water-soluble or non-soluble. The samples may be pure chemicals, dilutions,

formulations, or waste. No prior treatment of the sample is required. This method may be used to

meet certain regulatory applications, e.g., DOT corrosivity measurement for Packing Groups, but is

not required for determining if a waste passes or fails the characteristic of corrosivity per the RCRA

definition.

1.2 This method is applicable to a limited number of materials, specifically: Acids, inorganic

and organic; acid derivatives (anhydride, halo acids, salts, etc.), inorganic and organic; acyl halides;

alkylamines and polyalkylamines; bases, inorganic and organic; chlorosilanes; and metal halides and

oxyhalides.

2.0 SUMMARY OF METHOD

2.1 The assay system is an in vitro test method which is composed of two components, a

synthetic macromolecular biobarrier and a Chemical Detection System (CDS). Test samples are

applied on top of the macromolecular biobarrier. Corrosive samples are able to disrupt the

macromolecular structure of the biobarrier. A color change in the CDS, located beneath the

biobarrier, is detected visually and indicates that the test sample has altered the biobarrier

sufficiently to allow its passage through the full thickness of the biobarrier. The time it takes a

sample to disrupt the biobarrier is inversely proportional to the degree of corrosivity of the sample -

the longer it takes to observe a color change, the less corrosive the substance is. Noncorrosive

samples do not disrupt the biobarrier, or disrupt the biobarrier after a predetermined time period (see

Section 2.4). 

Corrosive samples may be placed into three different classes of corrosivity, established by the

time required for the sample to break through the biobarrier. These classes are called Packing

Groups by the U.S. Department of Transportation (DOT). Packing Groups are assigned according

to the degree of danger presented by the corrosive material; Packing Group I indicates great danger;

Packing Group II, medium danger; Packing Group III, minor danger. For consistency, these same

definitions are used for this test method and are referred to as Group I, Group II, and Group III.

2.2 Prior to performing the assay, samples are pre-qualified to establish their compatibility

with the assay system. The sample is placed in a small amount of CDS fluid. If any detectable

change occurs in the CDS, the sample is qualified and can be analyzed by the test. If a sample is

non-qualified, it is incompatible with the CDS and must be tested by another method. 

2.3 Test samples are classified into categories by the screening test which is supplied with

the assay kit. The category that a sample is assigned to will determine how the Groups will be

assigned. Test samples are classified by pH changes produced in two well-defined buffers - one

designed to buffer acids and another that buffers bases. These buffers are supplied as part of the

screening test. Four different categories are defined as follows:
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2.3.1 Category A1 substances produce a large change in pH when they are added to

the acid buffer. This change in pH is indicated by a strong color change of the acid buffer

solution.

2.3.2 Category B1 substances produce a large change in pH when they are added to

the base buffer. This change in pH is indicated by a strong color change of the base buffer

solution.

2.3.3 Category A2 substances produce little or no pH changes when added to the acid

buffer, and therefore, little or no color change in the buffer solution is observed.

2.3.4 Category B2 substances produce little or no pH changes when added to the base

buffer, and therefore, little or no color change in the buffer solution is observed.

2.4 Groups are assigned in the assay system by taking into account the category that is

assigned to a sample by the screening test, and the time it takes to detect a color change in the CDS

in the assay. Category A1 and B1 samples are assigned to Group I if a color change is observed

between zero and three minutes, to Group II if a color change is observed after three minutes and

up to one hour, and to Group III if a color change is observed after one hour and up to four hours.

If no color change occurs in four hours, the chemical is classified as Noncorrosive. 

Category A2 and B2 samples are assigned to Group I if a color change is observed between

zero and three minutes, to Group II if a color change is observed after three minutes and up to 30

minutes, and to Group III if a color change is observed after 30 minutes and up to 60 minutes. If no

color change occurs in 60 minutes, the chemical is classified as Noncorrosive.

3.0 INTERFERENCES

3.1 The test is not subject to interference from color, turbidity, colloidal matter or high salinity.

3.2 The Pre-qualification Test, the Screening Test and the Assay must be performed at room

temperature. The samples must also be at room temperature (17- 25EC).

4.0 APPARATUS AND MATERIALS

4.1 Corrositex Assay Kit (InVitro International, 16632 Millikan Avenue, Irvine, CA 92714).

The following three items are supplied in the Corrositex Assay Kit:

4.1.1 Four racks holding seven vials with black caps.

4.1.2 One tray of 24 membrane discs.

4.1.3 Four data sheets (color charts).

4.2 Combination hot plate/stir plate or equivalent - able to heat to 75EC. Stirring speed

should be adjustable.

4.3 Digital thermometer - able to read to 75EC.

4.4 Timers (6) - able to measure hours, minutes and seconds.
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4.5 Repeat pipettor - this pipet is different than the pipet specified in Section 4.12. Delivers

200 μL repeatedly, without refilling between individual deliveries. 

4.6 2.5 mL combitip for repeat pipettor.

4.7 Lab Industries or equivalent sample pipettor - a positive displacement pipettor useful

when pipetting viscous samples.

4.8 Pipet tips for Lab Industries, or equivalent, pipettor.

4.9 Test tubes

4.10 Balance - capable of weighing 100 mg accurately.

4.11 Spatula - capable of transferring 0.1 - 0.5 g. 

4.12 Pipets - microliter, with disposable tips. Should be able to measure 100 μL accurately.

4.13 Tweezers.

4.14 Permanent marker pens.

4.15 Plastic wrap.

5.0 REAGENTS

5.1 All reagents listed below are provided in the Corrositex Assay Kit except for the positive

and negative controls mentioned in Section 5.7. The Corrositex Assay Kit is available from InVitro

International, 16632 Millikan Avenue, Irvine, CA 92714.

5.2 Chemical Detection System (CDS).

5.3 Screening test buffer solutions.

5.4 Confirmation Test Solution. 

5.5 One gram of the biobarrier matrix and a microstir bar.

5.6 10 mL of biobarrier diluent.

5.7 Positive and negative controls, if desired, for GLP purposes. 

6.0 SAMPLE COLLECTION, PRESERVATION, AND HANDLING

6.1 Appropriate precautions should be taken for handling potentially corrosive substances

such as wearing gloves and having proper eye protection.

6.2 Samples should be analyzed as soon as possible after collection. 
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7.0 PROCEDURE

7.1 Follow the established laboratory procedures for working with hazardous test samples.

Wear lab coat, gloves and safety glasses when working with any potentially corrosive material. 

7.2 Pre-Qualification Test

7.2.1 Add 100 mg or 150 μL of sample to 1.0 mL of CDS in duplicate test tubes.

7.2.1.1 Sample qualifies if there is a color reaction within 5 minutes: proceed

with assay.

7.2.1.2 If no reaction is observed, the sample is non-qualified. Seek other

methods to determine corrosivity.

7.3 Screening Test

7.3.1 Liquid samples

7.3.1.1 Add 150 μL of sample to Test Tubes A and B. Cap the test tubes and

shake vigorously for 10 seconds. Read the color change of the mixture within one

minute. If the sample is immiscible in the solution, wait one minute and then read the

color change at the interface.

7.3.1.2 Assign the category. If an intense color change (similar to the Category

1 color chart) is observed in Tube A or Tube B, assign the sample to Category 1. If a

less intense color change (similar to the Category 2 color chart) is observed in either

Tube A or Tube B, assign the sample to Category 2 . If no color change is observed in

either Tube A or Tube B, proceed to the next step.

7.3.1.3 Confirm test. Add two drops of the Confirm reagent to Tube B. Cap the

test tube and shake vigorously for 5 seconds. The color of the solution will match one

of the colors shown in the accompanying color chart, confirming that the sample is

Category 2 material.

7.3.2 Solid samples

7.3.2.1 Add 100 mg of sample to Test Tubes A and B. Cap the test tubes and

shake vigorously for one minute. Wait another minute and read the color change of the

mixture. If the sample is insoluble in the solution, allow the mixture to settle and read the

color change at the interface of the solution and the solid.

7.3.2.2 Assign the category. If an intense color change (similar to the Category

1 color chart) is observed in either Tube A or Tube B, assign the sample to Category 1.

If a less intense color change (similar to the Category 2 color chart) is observed in either

Tube A or Tube B, assign the sample to Category 2. If no color change is observed in

either Tube A or Tube B, proceed to the next step.

7.3.2.3 Confirm test. Add two drops of the Confirm reagent to Tube B. Cap the

test tube and shake vigorously for 5 seconds. The color of the solution will match one

of the colors shown in the accompanying color chart, confirming that the sample is

Category 2 material.
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7.4 Assay

7.4.1 Biobarrier preparation

7.4.1.1 Biobarrier matrix preparation - must be completed at least two hours

prior to running assay.

7.4.1.2 Place scintillation vial containing biobarrier matrix powder on the hot

plate pad. Begin spinning the stir bar before adding the diluent.

7.4.1.3 Add the entire contents of the biobarrier diluent vial slowly and

constantly to the vial of biobarrier matrix powder. Make sure that the stir bar is turning

while adding the diluent. The stir bar should be turning rapidly, but not so fast that the

solution foams.

7.4.1.4 Turn the heat on low; monitor the temperature of the solution as it is

warming. Gradually increase the heat as necessary to warm the solution to 68EC (±1EC)

to solubilize the matrix. This may take approximately 20 minutes. DO NOT allow the

temperature to exceed 70EC.

7.4.1.5 While the solution is warming, remove the tray of 24 membrane discs

from the refrigerator. Remove the tray lid.

7.4.1.6 After the biobarrier matrix solution reaches 68EC and has been

completely solubilized, turn off the heat and move the vial toward the edge of the heat

pad to keep it warm while aliquotting into the membrane discs.

7.4.1.7 Dispense solubilized solution into membrane discs. Using the repeat

pipettor, set to dispense 200 μL. Slowly fill the pipette tip with biobarrier solution,

avoiding air bubbles. Dispense one aliquot back into the biobarrier vial to ensure proper

subsequent volume delivery. Wipe the tip before dispensing each aliquot. Dispense 200

μL into each disc, ensuring that the entire membrane is covered and no air bubbles have

formed. Any air bubbles in the gel will alter the results of the test, therefore the disc

cannot be used.

7.4.1.8 Label the lid with the date, time, lot number, and initials of the technician

preparing the biobarrier. Wrap the filled tray evenly with plastic wrap; do not bunch up

the plastic wrap underneath the plate.

7.4.1.9 Store the tray at 2 - 8EC for at least two hours before beginning any

testing. The biobarrier is stable for seven days if wrapped and stored at 2 - 8EC.

7.4.2 Running the assay.

7.4.2.1 On the data sheet, complete the lot number, date, time, name of

technician, name of chemical, whether it is solid or liquid, and pH of a 10% solution

diluted in water or appropriate solvent. 

7.4.2.2 When ready to test, remove one tray of seven pre-filled black-capped

scintillation vials from the kit box.
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7.4.2.3 Remove the tray of 24 membrane discs from the refrigerator. Place on

a tray of ice. 

7.4.2.4 Place disc into first scintillation vial. Do not allow the discs to be in

contact with the CDS for longer than two minutes before applying the test sample.

Within two minutes, add 500 μL (using the Lab Industries pipettor, or equivalent) or 500

mg (using spatula or tweezers) of test sample to disc. Start timer the instant the sample

is added. 

Note: Do not cap the vials while test is in progress due to potential pressure

build-up.

7.4.2.5 Watch the vial for three minutes, ensuring that the color reaction is not

missed if it is a Group I sample. Changes in the CDS may include various color changes,

flaking or precipitation. 

7.4.2.6 Add three more discs and samples to vials, staggering each start time

so that the most accurate reaction times are recorded.

7.4.2.7 Allow assay to run until color or physical reaction occurs. Category 1

samples should be checked for reactions at 3 minutes, 1 hour and 4 hours. Category 2

samples should be checked for reactions at 3, 30 and 60 minutes.

7.4.2.8 At the first indication of the presence of a chemical reaction in the CDS,

there will be a color change produced beneath the bottom-center of each biobarrier disc.

As soon as a reaction is observed, immediately record net time of each vial on the data

sheet.

7.4.2.9 Run positive and negative controls in the other two vials, if desired, for

GLP purposes.

7.4.3 Assignment of Groups.

7.4.3.1 Category 1 samples are assigned to Group I if a color change is

observed between zero and three minutes, to Group II if a color change is observed after

three minutes and up to one hour, and to Group III if a color change is observed after one

hour and up to four hours. If no color change occurs in four hours, the chemical is

classified as Noncorrosive. 

7.4.3.2 Category 2 samples are assigned to Group I if a color change is

observed between zero and three minutes, to Group II if a color change is observed after

three minutes and up to 30 minutes, and to Group III if a color change is observed after

30 minutes and up to 60 minutes. If no color change occurs in 60 minutes, the chemical

is classified as Noncorrosive.

8.0 QUALITY CONTROL

8.1 Samples should be analyzed in quadruplicate. The test may be analyzed in duplicate if

a simple screening of corrosives and noncorrosives is all that is required. However, it is

recommended that for greater accuracy, samples be analyzed in quadruplicate. It is suggested that

positive and negative controls be analyzed to conform with GLP. 
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9.0 METHOD PERFORMANCE

9.1 Interlaboratory and intralaboratory studies were conducted with five different laboratories.

Ten different chemicals were tested with six replicates. The data are presented in Table 1.

9.2 More than 200 data points have been collected at InVitro International for six reference

samples. Statistical analysis of this data shows the standard deviation for ethylenediamine and ferric

chloride is about 5% of their respective assay times, and about 10% for maleic anhydride, sodium

hydroxide, and dicyclohexylamine. The standard deviation for sulfuric acid approaches 18% of its

assay time, but when taken into account that the mean assay time is less than 1 minute, a standard

deviation of 0.13 minutes is actually a reflection of the difficulty of measuring such brief time periods.

9.3 The Corrositex assay has been used by more than 300 laboratories to test approximately

4,000 test materials in its first phase of utilization in industry. Diverse chemicals and formulations

which include liquids, solids, insolubles and immiscibles have been studied from many major

industries including petrochemical, agrochemical, surfactant, textile, paper and pulp, electroplating

and water treatment. Examples of dermal corrosion values compared to pH for selected compounds

are shown in Table 2.

9.4 Data results from 1,050 samples that have been tested using the assay system were

complied and compared with in vivo data. Ninety-two percent of the samples (965 samples) passed

the Pre-qualification Test and were then analyzed in the screening test and the assay. Assay was

found to be highly concordant with corrosive/noncorrosive in vivo results. Of 406 corrosive samples

with in vivo data, 377 (93%) were correctly identified as corrosive by assay. Of 296 noncorrosive

samples with in vivo data, 83% were identified as noncorrosives, demonstrating the ability of this in

vitro method to correctly identify corrosives and noncorrosives. Assay was also shown to accurately

predict Packing Groups. Six hundred out of 702 samples (85.5%) were placed in the same Packing

Group as that indicated by in vivo testing. Only 38 test samples out of 702 samples that had in vivo

data were found to underestimate (5.4%). Of these 38 samples, 28 were distinct samples and the

remainder were samples that had been tested in more than one laboratory. When taking this

information into account, the percent of underestimation decreased to about 4%.

10.0 REFERENCES

1. Code of Federal Regulations, Transportation Title 49, Hazardous Materials Table, Section

172.101 (1991).

2. Code of Federal Regulations, Transportation Title 49, Method of Testing Corrosion to the Skin,

Part 173, Appendix A (1991).

3. Schlesselman, J.J. (1973) Planning a Longitudinal Study: I. Sample Size Determination. J.

Chron. Dis. 26, 553-560. 

4. ASTM Standards on Precision and Bias for Various Applications, “Standard Practice for

Conducting an Interlaboratory Study to Determine the Precision of a Test Method”; ASTM:

Philadelphia, PA, 1992; E 691-92.

5. Gordon, V.C., Harvell, J., and Maibach, H. (1994). Dermal Corrosion, The Corrositex System,

A DOT Accepted Method to Predict Corrosivity of Test Materials. In Vitro Toxicology. Ed. Mary

Ann Liebert, 1994.
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TABLE 1

LABORATORY DATA

Dichloroacetyl chloride

Laboratory Results (minutes) Deviation

Mean of 6 Test Standard Deviation Relative Standard

1 3.30 0.59 17.88%

2 2.99 0.30 10.03%

3 3.88 0.47 12.11%

4 2.50 0.26 10.40%

5 3.30 0.28 8.48%

Formic acid

Laboratory Results (minutes) Deviation

Mean of 6 Test Standard Deviation Relative Standard

1 6.32 0.51 8.07%

2 5.08 0.46 9.06%

3 5.18 0.77 14.86%

4 4.82 0.29 6.02%

5 4.02 0.29 7.21%

Dichloroacetic acid

Laboratory Results (minutes) Deviation

Mean of 6 Test Standard Deviation Relative Standard

1 6.92 0.32 4.62%

2 5.21 0.25 4.80%

3 6.32 0.98 15.51%

4 5.78 0.26 4.50%

5 5.65 0.46 8.14%

Chloroacetic acid

Laboratory Results (minutes) Deviation

Mean of 6 Test Standard Deviation Relative Standard

1 5.46 0.36 6.59%

2 7.83 0.00 0.00%

3 4.95 0.35 7.07%

4 6.91 0.94 13.60%

5 4.95 0.34 6.87%
TABLE 1 (continued)

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Dodecyltrichlorosilane

Laboratory Results (minutes) Deviation

Mean of 6 Test Standard Deviation Relative Standard

1 10.78 0.05 0.46%

2 11.59 0.36 3.11%

3 11.22 0.82 7.31%

4 11.96 0.56 4.68%

5 10.98 0.29 2.64%

Ammonium hydrogen sulfate

Laboratory Results (minutes) Deviation

Mean of 6 Test Standard Deviation Relative Standard

1 10.47 0.56 5.35%

2 9.02 0.33 3.66%

3 13.82 1.0 7.24%

4 11.17 0.93 8.33%

5 7.88 0.26 3.30%

Ethylenediamine

Laboratory Results (minutes) Deviation

Mean of 6 Test Standard Deviation Relative Standard

1 17.24 0.38 2.20%

2 21.33 0.53 2.48%

3 26.12 1.30 4.98%

4 20.76 0.19 0.92%

5 22.48 1.40 6.23%

Aluminum chloride

Laboratory Results (minutes) Deviation

Mean of 6 Test Standard Deviation Relative Standard

1 11.91 0.41 3.44%

2 21.33 0.53 2.48%

3 26.12 1.30 4.98%

4 20.76 0.19 0.92%

5 22.48 1.40 6.23%
TABLE 1 (continued)

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Acetic acid

Laboratory Results (minutes) Deviation

Mean of 6 Test Standard Deviation Relative Standard

1 28.52 0.87 3.05%

2 27.00 0.00 0.00%

3 34.98 0.22 0.63%

4 36.30 0.41 1.13%

5 29.67 0.62 2.09%

Dicyclohexylamine

Laboratory Results (minutes) Deviation

Mean of 6 Test Standard Deviation Relative Standard

1 181.73 0.47 0.26%

2 168.83 9.11 5.40%

3 210.70 7.68 3.64%

4 159.04 7.58 4.77%

5 126.75 0.62 0.49%
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TABLE 2. EXAMPLES OF DERMAL CORROSION VALUES FOR SELECTED COMPOUNDS

Compound Name Concentration pH Time

 (weight %) (minutes)

1

Acetic acid 99+ 0.00 29.31

Aluminum chloride pure 2.92 16.50

Ammonium hydroxide 10.00 12.37 5.41

Bromoacetic acid 55.60 0.93 9.17

Butylamine 40.00 12.96 >240

Citric acid 20.00 1.28 47.65

1,2-Diaminopropane 99+ 12.06 21.67

Dichloroacetic acid 3.10 0.98 37.63

Dicyclohexylamine 99.00 9.57 210.00

Diethylamine 98.00 13.86 5.89

Diethylene triamine 99.00 12.01 34.00

Ethanolamine 99+ 11.82 21.68

Ferric chloride 98.00 3.00 21.30

Formic acid 33.90 0.62 >240

Hydrochloric acid 35.00 0.00 5.80

Hexanoic acid 99.00 3.00 149.00

Maleic acid 99.00 1.30 15.55

Mercaptoacetic acid 15.10 1.60 42.09

Nitric acid 90.00 0.00 0.57

Phosphoric acid 85.00 0.00 15.00

Potassium hydroxide pellets 14.00 6.82

Propionic acid 99+ 0.35 34.59

Sodium hydroxide pellets 13.81 14.67

Sodium metasilicate 20.00 13.28 17.17

Sulfuric acid 15.00 0.00 11.48

Thiophosphoryl chloride 98.00 5.81 10.13

Tributylamine 99+ 10.70 >240

Trichlorotoluene 99.00 3.32 >240

Triethanolamine 60.00 11.02 41.03

Triphosphoryl chloride 98.00 5.80 10.25

 pH of a 10% solution of the compound in water. 1
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METHOD 1120

DERMAL CORROSION