Interpretation Response #14-0008

A limit test is used when the test article is known or expected to be virtually non-toxic, i.e., eliciting a toxic response only above the regulatory limit concentration. In a limit test, a single group of three males and three females is exposed to the test article at a limit concentration. Information about the toxicity of the test material can be gained from knowledge about similar tested compounds or similar tested mixtures or products, taking into consideration the identity and percentage of components known to be of toxicological significance. In those situations where there is little or no information about its toxicity, or the test material is expected to be toxic, the main test should be performed.

The selection of limit concentrations usually depends on regulatory requirements. When the GHS Classification System is used, the limit concentrations for gases, vapours, and aerosols are 20,000 ppm, 20 mg/L, and 5 mg/L, respectively (or the maximum attainable concentration). It can be technically challenging to generate limit concentrations of some test articles, especially as vapours and aerosols. When testing aerosols, the primary goal should be to achieve a respirable particle size (MMAD of 1-4 µm). This is possible with most test articles at a concentration of 2 mg/L. Aerosol testing at greater than 2 mg/L should only be attempted if a respirable particle size can be achieved (see GD 39). GHS discourages testing in excess of a limit concentration for animal welfare reasons (3). The limit concentration should only be exceeded when there is a compelling reason, such as a direct relevance to the protection of human health, and the reason must be explained in the study report. In the case of potentially explosive test articles, care should be taken to avoid conditions favourable for an explosion. To avoid an unnecessary use of animals, a test run should be conducted prior to the limit test to ensure that the chamber conditions for a limit test can be achieved.

If mortality or moribundity is observed at the limit concentration, the results of the limit test can serve as a sighting study for further testing at other concentrations (see main study). If a test article's physical or chemical properties make it impossible to attain a limit concentration, the maximum attainable concentration should be tested. If less than 50% lethality occurs at the maximum attainable concentration, no further testing is necessary. The study report should contain an explanation and supportive data for why the limit concentration could not be attained. If the maximum attainable concentration of a vapour does not elicit toxicity, it may be necessary to generate the test article as a liquid aerosol.

The "maximum attainable concentration" is the greatest amount of test material that can be suspended and maintained in the air in an inhalation chamber to test for acute inhalation toxicity in conformance with the methods prescribed in OECD Guideline 403.

A2: Under § 173.22 of the HMR it is a shipper's responsibility to properly classify a hazardous material. This Office does not generally perform that function. However, based on the test results provided in the MSDS, it is the opinion of this Office that the material does not meet the LC50 criteria for acute inhalation toxicity.

The HMR defines a poisonous material in § 173.132 as a material, other than a gas, that is known to be toxic to humans because it falls within one of the following categories when tested on laboratory animals: oral toxicity, dermal toxicity, and inhalation toxicity. Included in the definition under §173.132(a)(1)(iii) for inhalation toxicity, if a dust or mist has an LC50 of not more than 4 mg/L then it meets the Division 6.1 criteria. If the MSDS for Halamid® you provided is accurate and the "maximum attainable concentration" of 0.275 mg/L is not toxic, it is the opinion of this Office that this material would not meet the definition of a Division 6.1 material in addition to any other hazard class the material might meet. As such, the description "UN3263, Corrosive solid, basic, organic, n.o.s. (Sodium p-toluenesulfonchloramide), 8, PG III" is appropriate.

I trust this satisfies your inquiry. Please contact us if we can be of further assistance.