IIVS | Corrositex (OECD 435)
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Corrositex (OECD 435)

The Corrositex® assay is a standardized and quantitative in vitro test developed as a replacement for the dermal corrosivity rabbit test. The Corrositex kit, manufactured by In Vitro International (IVI), uses a proprietary biobarrier membrane to model the skin for evaluating the potential dermal corrosivity of a test material.

A test material is evaluated based on its penetration through the biobarrier membrane into a Chemical Detection System (CDS). The time required for the test material to break through the biobarrier and into the CDS is determined. A U.S. Department of Transportation (USDOT) packing group is assigned based on the break through time.

The Corrositex® assay is presently the only in vitro assay approved by the U.S. Department of Transportation for testing potential corrosive materials and assigning packing group categories.

Quick Facts

Assay Model: proprietary biobarrier membrane

Detection Agent: CDS (chemical detection system)

Endpoint: the time required for a corrosive material to break through the membrane

For more information about testing your materials using this assay, please see Applications. Specialized protocols may be prepared as requested through consultation with an IIVS Study Director.

Corrositex Assay: Components of the Corrositex Assay Kit as provided by In Vitro International.

Corrositex Assay: Components of the Corrositex Assay Kit as provided by In Vitro International.

Applications

Test Material Compatibility

The assay is compatible with both water soluble and insoluble formulations. Both solid and liquid test materials can be tested.

In order to be tested in the Corrositex® assay, test materials must cause an observable color change in the CDS. Additionally, the use of the Corrositex® assay to assign packing goups is limited to specific chemical classes, including acids, acid derivatives, acyl halides, (poly)alkylamines, bases, chlorosylanes, metal halides, and oxyhalides.

Validation/Regulatory Acceptance

  • The U.S. Department of Transportation (USDOT) accepts Corrositex® as a test to assign subcategories of corrosivity packing groups for labeling purposes according to the United Nations transport guidelines.
  • ECVAM has recommended its use as a stand-alone alternative to in vivo corrosivity tests when used in specific testing circumstances (i.e., as required by USDOT).
  • It is endorsed by NIEHS, NTP, and 13 federal agencies that support ICCVAM.
  • In 2006, OECD Test Guideline (TG 435) was adopted for the Corrositex®Assay.

Step-by-Step

  1. Qualification of Test Material
  2. Categorization
  3. Biobarrier Preparation
  4. Biobarrier Qualification with the Positive Control
  5. Dosing of the Test Material
  6. Determination of Packing Group
Step 1: Qualification of Test Material
Qualification screen

Qualification screen

Each test material is added to a vial containing the Chemical Detection System (CDS) to determine if the test material will qualify for testing. The CDS is a pH neutral solution that contains two pH indicator dyes. A color change can be detected when the pH of the CDS drops below 4.5 or rises above 8.5. Test materials must cause a color change in the CDS to be tested in this assay.

Step 2: Categorization

Once qualified, the test material is categorized to determine the appropriate timetable for Packing Group Assignment. The test material is added to two tubes. The resulting color change in each tube is compared to the color chart provided by In Vitro International. A category 1 test material will be evaluated for up to 4 hours; while a category 2 test material will be evaluated for up to 1 hour.

Categorization tubes
Categorization
Step 3: Biobarrier Preparation

After a test material has qualified for the Corrositex assay, biobarrier membranes are prepared. To prepare the biobarrier membranes, the biobarrier matrix powder is completely solubilized. The solubilized collagen matrix, composed of water and dissolved proteins, is then added to a membrane disc containing a porous cell membrane. Once prepared, the biobarrier membranes are refrigerated and used within seven days.

Biobarrier Preparation
Biobarrier Preparation
Biobarrier disc
Step 4: Biobarrier Qualification with the Positive Control

A biobarrier membrane is placed on top of a vial containing CDS. The positive control is then added onto the biobarrier membrane disc. The vial is continuously monitored until a color change (i.e. break through) has occurred. The break through time is then compared to the IIVS positive control historical data range. Following the acceptance of the positive control, the test materials can then be dosed.

Biobarrier Placement
Detection of color change
Step 5: Dosing of the Test Material

Each test material is tested in four replicate biobarrier membranes. The biobarrier membrane is placed onto a vial of CDS. The test material is added onto the biobarrier membrane disc. The vial is continuously monitored for the first ten minutes. If no color change occurs, this process is repeated an additional three times until the remaining biobarrier membranes are treated with the test material. The vials are observed until a color change (i.e. break through) occurs. When a color change occurs in each vial, the breakthrough times are recorded. Category 1 test materials are observed for a break through for up to four hours. Category 2 test materials are observed for up to one hour.

Corrositex Assay
Break through
Step 6: Determination of Packing Group
Break through

Break through

To determine the appropriate packing group for a test material, a mean break through time is calculated from the four replicates. Each test material is evaluated using the appropriate category on U.N. Packing Group Assignment Table. When a break through does not occur in the time alloted, the Packing Group of the test material is designated as non corrosive according the Corrositex protocol.

U.N. Packing Group Table