Toxicity classification system

Both systems are based on the application of a battery of bioassays with short exposure time (1-3 days). The battery of bioassays is composed of test species belonging to different phylogenetic groups and is comprised of the following bioassays  

The principle of the classification systems is a one-step determination of the acute hazard of natural waters on non-diluted samples with the battery of bioassays. The classification system is based on two values  

Waters are ranked into one of five classes on the basis of the highest toxic response shown by at least one of the tests applied. After determination of the percentage effect (PE) obtained with each of the microbiotests, a weight score is calculated for each hazard class to indicate the quantitative importance (weight) of the toxicity in that class. This weight score is expressed as a percentage and ranges from 25% (only one test in the battery has reached the toxicity level of that class) to 93% (all tests but one have reached the toxicity level of that class). 

The weight scores for the effect results of each bioassays are calculated as follows  

The class weight score = X all test scores/n, where n = number of tests performed. The class weight score as a percentage = (class weight score)/(maximum class weight score) x 100. 

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Persoone, G., Marsalek, B., Blinova, I., Tordkne, A., Zarina, D., Manusadzianas, L., Nalecz-Jawecki, G., Tofan, L., Stepanova, N., Tothova, L. and Kolar, B. (2003) A practical and user-friendly toxicity classification system with microbiotests for natural waters and wastewaters, Environmental Toxicology 18 (6), 395-402. 

A toxicity classification system for wastes discharged into the aquatic environment... 

Toxicity Classification System for Effluents Discharged into the Aquatic Environment According to Persoone101... 

Persoone, G., B. Marsalek, I. Blinova, et al. 2003. A practical and user-friendly toxicity classification system with microbiotests for natural waters and wastewaters. Environ. Toxicol. 18 395-402. 

Table 7.2 presents a toxicity classification system based upon an LD50 single oral dose in rats. In applying this system to the drugs listed in Table 7.1 we can see that these drugs would be classified from almost nontoxic to highly toxic. However, it must be emphasized that caution should be exercised when using such classification systems to communicate risk information. 

The principle of the toxicity classification system for wastes discharged into the aquatic environment is a two-step determination and quantification of the acute toxicity of the liquid wastes or leachates with the battery of bioassays. In the first step the toxicity is determined on non-diluted samples, and in the second step the toxicity tests are performed on a dilution series of the samples with all bioassays for which more than 50% effect has been found in the non-diluted sample. 

The lanthanides are considered only slightly toxic in the Hodge-Stemer classification system and are safely handled with ordinary care (15). Inhalation of rare-earth vapors or dust should be avoided, and the skin washed thoroughly if it comes into contact with any dust or solution. 

The pneumatic classification system should be designed to handle ha2ardous dust (28). A ha2ardous dust is one which, when finely divided and suspended in air in the proper concentration, bums, produces violent explosions, or is sufficiently toxic to be injurious to personnel health (see Air pollution control methods Powders, handling). At the least, almost any dust can be irritating to personnel because of inhalation or skin or eye contact. Fully oxidi2ed and hydrated materials are generally considered safe. 

Broaden the application to cover reactive hazards resulting from process-specific conditions and combinations of chemicals. Additionally, broaden coverage of hazards from self-reactive chemicals. In expanding PSM coverage, use objective criteria. Consider criteria such as the North American Industry Classification System (NAICS), a reactive hazard classification system (e.g., based on heat of reaction or toxic gas evolution), incident history, or catastrophic potential. 

The traditional scheme is complicated by the fact that some antidepressants exhibit characteristics of more than one class. For example, clomipramine, a tricyclic antidepressant (TCA) with side effects and toxicity similar to other TCAs, works more like the selective serotonin reuptake inhibitors (SSRls). Similarly, venlafaxine and duloxetine, which are usually grouped with the atypical antidepressants, have a side effect and safety profile comparable to the SSRls. Although a classihcation system based on mechanism of action offers some advantage (see Table 3.7), even this scheme is limited by the fact that antidepressants that work in the same way may have widely divergent side effect and safety profiles. In the following discussion, the traditional classification system is adopted. Although fraught with problems and inconsistencies. 

OECD has published a document on a Harmonised integrated classification system for human health and environmental hazards of chemical substances and mixtures (OECD 2001b). Chapter 2.1 addresses a harmonized system for the classification of chemicals which cause acute toxicity, and Chapter 2.8 addresses the chemicals which cause specific target organ oriented systemic toxicity following a single exposure. 

In accordance with both the old and the new European classification system teratogenic effects constitute a health hazard but a separate classification for teratogenicity is not provided. Instead, teratogens are classified as developmental toxicants, with developmental toxicity falling within the hazard class of reproductive toxicity. 

The various national and international regulatory authorities have used different hazard classification systems in the past. In light of the importance of hazard classification, the Organisation for Economic Cooperation and Development (OECD) recently harmonized criteria for hazard classification for global use. For example, the five harmonized categories for acute oral toxicity (in mg/kg body weight) are 0-5, 5-50, 50-300, 300-2000, and 2000-5000. 

The system for classification and disposal of hazardous chemical waste developed by EPA under RCRA does not apply to all wastes that contain hazardous chemicals. For example, wastes that contain dioxins, polychlorinated biphenyls (PCBs), or asbestos are regulated under the Toxic Substances Control Act (TSCA). In addition, the current definition of hazardous waste in 40 CFR Part 261 specifically excludes many wastes that contain hazardous chemicals from regulation under RCRA, including certain wastes produced by extraction, beneficiation, and processing of various ores and minerals or exploration, development, and use of energy resources. Thus, the waste classification system is not comprehensive, because many potentially important wastes that contain hazardous chemicals are excluded, and it is not based primarily on considerations of risks posed by wastes, because the exclusions are based on the source of the waste rather than the potential risk. 

Some existing waste classification systems are quantitative. For example, the concentrations of radionuclides defining the different subclasses of low-level radioactive waste that is generally acceptable for near-surface disposal are clearly stated in the regulations (NRC, 1982a), as are the quantitative conditions defining ignitable, corrosive, reactive, and toxic hazardous chemical wastes (see Section 4.2.1.1). 

The waste classification system should be developed in recognition of the types of information that are available and likely to be obtainable, and it should be specified to maximize compatibility with available information consistent with maintaining the fundamental integrity of the system. Establishment of a risk-based waste classification system must begin with the existing classification systems and associated databases (e.g., toxicity of hazardous substances). These would be expanded and refined as needed. However, if the foundations of a risk-based waste classification system or its implementation involve radically new concepts or call for data that cannot feasibly be obtained, the effort will be for naught. A realistic waste classification system must use the existing base of concepts and data to achieve the desired result. 

As indicated by the current subclassifications of existing waste classes summarized above, a variety of waste properties could be used to develop meaningful subclassifications of broadly defined waste classes. These properties include, for example, waste volumes, levels of decay heat and external radiation, and the long-term persistence of the hazard posed by waste constituents. Subclassifications of waste classes also could be based on the presence of particular hazardous substances. However, if the broadly defined waste classes are based on risk, as in the classification system proposed in this Report, the intrinsic toxicity of hazardous substances normally would not provide a basis for subclassification, because this property already is accounted for in determining the basic classification of any waste. Examples of possible approaches to subclassifying the basic waste classes are discussed in the following paragraphs. 

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