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Skin Corrosion: rat Transcutaneous Electrical Resistance (TER) test

The ability of a chemical or mixture to cause skin corrosion can be predicted through assessing transcutaneous electrical resistance of rat skin and by assessing the penetration of a dye through the skin.

The results and full reports of this test method will be soon available on TSAR, the Tracking System for Alternative methods towards Regulatory acceptance.

Skin corrosion

[collapsed]According to most international (regulatory) guidance, skin corrosion refers to chemically induced corrosion of dermal tissue and specifically full thickness destruction (necrosis) of skin tissue.

In some cases corrosion refers to any irreversible alterations caused to the skin.

Determining skin corrosion potential is important from the perspective of safe handling, packing and safe transport of chemicals.[/collapse]

Rat Transcutaneous Electrical Resistance (TER) test

[collapsed]The assay is based on determining the effects of a chemical on the electrical resistance of rat skin (i.e. TER).

A second endpoint is the ability of a dye to penetrate through rat skin following exposure to a chemical.

The test can be used to identify potential corrosive chemicals or mixtures. It can also be used to identify chemicals that are non-corrosive when used in combination with other methods.

Evidence indicates that TER measurements are predictive of severe cutaneous effects in vivo.

The (later) addition of the dye to the test reduces false positives.[/collapse]

Animal testing replacement

[collapsed]The method has been scientifically validated and has received regulatory approval as a replacement for in vivo skin corrosively tests, such as the Draize rabbit skin test.

However, the method is still based on the use of rat skin and the method still involves sacrifice of the animals to obtain skin in the required state. While the method reduces the need for testing on live animals and therefore substantially reduces suffering, it clearly still involves animals.[/collapse]

Validation study

[collapsed]Both a prevalidation and validation study have previously been conducted in relation to the TER method. The results of these have been published in peer-reviewed journals. The prevalidation study aimed to provide an initial assessment of validity/predictive capacity of the TER method. The subsequent validation study then aimed to confirm results. Both studies were coordinated by EURL ECVAM.[/collapse]

Validation study outcomes

[collapsed]The prevalidation study showed that the TER method had high sensitivity but relatively low specificity (i.e. too many false positives). The subsequent validation study (with the modifications to reduce false-positives) demonstrated wide applicability to a range of chemicals and could distinguish between non-corrosives and corrosives. Reproducibility was also high between laboratories.[/collapse]

EURL ECVAM recommendations

[collapsed]The conclusions of the validation study were that the TER method should be considered scientifically validated and that it should be considered for regulatory acceptance.

ESAC subsequently agreed with the conclusion. Since then, the method has been included in various pieces of legislation and an OECD test guideline (No 404) has been issued.[/collapse]