Classification of Toxicity Tests

Classification of toxicity tests in environmental toxicology. Generally the two parameters that are involved are the length of the test relative to the test organism and the species composition of the test system. 

Multispecies toxicity tests, as their name implies, involve the inclusion of two or more organisms and are usually designed so that the organisms interact. The effects of a toxicant upon various aspects of population dynamics 

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Figure 1 Classification of toxicity tests in environmental toxicology.

The nature of a toxic effect and the probabiUty of its occurring are often related to the number of exposures. The classification of toxic effects, and descriptions of toxicology tests, may be dictated by the number of exposures that eUcit toxic effects. The following terms are convenient in this respect. 

Level 2 Classification of Toxicity Samples identified as dissimilar to matched control samples can be fitted to a series of mathematical models that define the multivariate boundaries for known classes of toxicity (Figures 5.4 and 5.5) [6,7,12,63]. Therefore, biofluid or tissue samples from experimental animals treated with novel drugs can be tested to ascertain if the drug induces biochemical effects that would infer a particular site or mechanism of toxicity. 

DIPHOTERINE solutions, including practical experience using these decontaminating agents. These products are classified as a medical device (class Ila). They have undergone a variety of toxicity tests. Taken together, the classification, the reported toxicity tests, and case reports show that the products can be considered safe to use. 

The importance of hydrolysis potential, ie, whether moisture or water is present, is illustrated by the following example. In the normal dermal toxicity test, namely dry product on dry animal skin, sodium borohydride was found to be nontoxic under the classification of the Federal Hazardous Substances Act. Furthermore, it was not a skin sensitizer. But on moist skin, severe irritation and bums resulted. 

Famphur is considered a Class II toxic compound to the Japanese quail (Cotumix japonica) according to the classification of Hill and Camardese (1986). Class II compounds (very toxic) kill 50% of the test organisms on diets containing 40 to 200 mg chemical/kg ration for 5 days followed by a 3-day observation. By comparison, the 50% kill in other classes (in mg/kg diet) is <40 in Class I (highly toxic), >200 to 1000 in Class III (moderately toxic), >1000 to <5000 in Class IV (slightly toxic), and >5000 in Class V (practically nontoxic) (Hill and Camardese 1986). Smith (1987) rates famphur as a Class I toxic compound, as judged by results of dietary tests with mallards. 

A Guidance Document on Acute Inhalation Toxicity Testing is being developed and presently exists as a draft (OECD 2004b). The document recommends the Acute Toxic Class (ATC) Method with a group size of three animals per sex, if the objective of the test is solely related to hazard classification. Limits for particle-size distribution of aerosolized test substances are suggested. The preferred mode of exposure is the nose-only, head-only, or head/nose-only exposure technique, because this mode of exposure minimizes exposure or uptake by noninhalation routes. 

All these standard tests have the water solubility of the toxic materials or impurities or extractables as a provision of the test strategy. In the case of PFCLs, this can result in an incorrect classification. Therefore, the test design has to be adjusted to the special behaviours of PFCLs. 

Due to the specificity of toxicogenomic signatures, compounds may be classified based on common genes (or pathways) disrupted. In developmental toxicity testing, approaches may be used for classification between (1) toxic and nontoxic exposures and/or (2) classes of chemical compounds. To date, most classification studies have been conducted in alternative developmental systems (i.e. stem cells, zebrafish, whole embryo culture) due to the size of material and experimental groups needed. In a series of studies by... 

More in-depth behavioral tests are required if dose-related toxicant effects are noted in screening tests. These tests may also be required as part of more selective toxicological screening, such as for developmental neurotoxicity. Focused tests of neuromotor function and activity, sensory functions, memory, attention, and motivation help to identify sites of toxicant-mediated lesioning, aid in the classification of neurotoxicants, and may suggest mechanisms of action. Some of these tests, like the schedule-controlled operant behavior tests for cognitive function, require animal training and extensive operator interaction with the animals. 

Our scrutiny of publications identified in the literature search has enabled us to uncover the various ways in which laboratory toxicity tests have been applied, many of which are small-scale in nature. We have assembled papers based on their application affinities and classified them into specific sections, as shown in Figure 1. This classification scheme essentially comprises the structure of this chapter and each section is subsequently commented hereafter. 

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