Acute Dermal Toxicity test. OECD 402: 2017;

EPA (Environmental Protection Agency) OPPTS 870.1200:1998 (Office of Prevention, Pesticides and Toxic Substances, USA).

Test with the Certificate of Good Laboratory Practices (GLPs).

This test provides information on the health risks of short-term dermal exposure to a test chemical. The purpose of the OECD 402 procedure is to provide information on the hazardous properties of the product to be tested and to allow the classification of the substance based on its acute toxicity according to the Globally Harmonized System of Classification and Labeling of Chemicals (GHS, for its acronym in English).

The animals of choice for this study are young adult female rats. The test product is applied to the skin of experimental animals of the same sex, using one dose per group, consisting of one animal in the preliminary test, and two animals in the main study. To determine the acute dermal toxicity of a product, the animals are exposed to the test product for 24 hours in a stepwise procedure, where depending on the results, different doses (50 mg/kg, 200 mg/kg, 1,000 mg/kg and 2,000 mg/kg) are administered are observed for at least 14 days.

To minimize the use of animals and optimize the design of the experiment, a preliminary study is carried out to determine the initial concentration to be used in the main study. When there is insufficient information about the product to be tested, it is recommended to start with an initial dose of 200 mg/kg. If there is prior information on the chemical, other starting doses can be selected (50 mg/kg, 1,000 mg/kg or 2,000 mg/kg). For the preliminary study, one animal per test dose is assayed with the initial dose (200 mg/kg or other). According to the results obtained, groups of an animal will be inoculated with a lower or higher dose, until the concentration that is expected to produce clear signs of toxicity without causing serious toxic effects or mortality is selected. If the lower dose causes toxicity, the substance will be directly classified as GHS Category 1. If not, the main study should be carried out with two more animals to confirm the result obtained.

For the main study, two animals are dosed with the dose obtained by the preliminary study. Depending on the results obtained, lower or higher doses (50 mg/kg, 200 mg/kg, 1.000 mg/kg and 2.000 mg/kg) may be dosed in groups of two other animals. The test process continues until the dose causing toxicity or no more than one death is identified in the group of animals tested, when no effects are observed at the highest concentration, or when deaths occur at the lowest concentration, facts that allow to classify the products within the GHS categories 1, 2, 3, 4, 5 or not classified.

In both studies, the animals are observed after application of the product, intermittently during the 24 hours of exposure. Subsequently, the product is eliminated, and the animals are observed daily until at least the 14 mandatory observation days have elapsed. However, the duration of observation is not fixed, but must be determined by the nature and time of appearance of clinical signs and the length of the recovery period. A minimum period of 48 hours should be maintained between tests with different dose levels, until the survival of the animals previously exposed to the product is verified. In addition to the GHS category, any alteration observed in the animals and their behavior must be reported. The animals that die or are euthanized during the study, and the surviving animals that are euthanized at the end of the study, undergo a general necropsy and all the macroscopic alterations observed are reported, which can be completed with histopathology observations if necessary.

Test substances should be kept in contact with the skin with a porous gauze dressing and non-irritating tape for a 24-hour exposure period. When solids are analyzed, which can be pulverized if necessary, the test substance should be moistened sufficiently, preferably with water or, where appropriate, with a suitable vehicle to ensure good contact with the skin. When using a vehicle (other than water), the influence of the vehicle on the penetration of the test substance into the skin must be taken into account. Liquid tests chemical are generally used undiluted.

If the sample sent requires the use of a vehicle other than water for its administration, the test will have an extraordinary cost.