Toxic effects classification

Fig. 1. Schematic representation showing the basis for classification of toxic effects into local and systemic by single or repeated exposures.

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. 

The following additional descriptive terms are also useful for the classification of toxic effects. 

PEL Pg pmol PHS PMR ppb ppm ppt REL RfD RTECS sec SCE SIC SIR SMR STEL STORET TLV TSCA TRI TRS TWA u.s. UF yr WHO wk permissible exposure limit picogram picomole Public Health Service proportionate mortality ratio parts per billion parts per million parts per trillion recommended exposure limit Reference Dose Registry of Toxic Effects of Chemical Substances second sister chromatid exchange Standard Industrial Classification Standardized incidence ratio standard mortality ratio short term exposure limit STORAGE and RETRIEVAL threshold limit value Toxic Substances Control Act Toxics Release Inventory total reduced sulfur time-weighted average United States uncertainty factor year World Health Organization week... 

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. 

But the output of the model has to be carefully evaluated according to the law. For instance, some regulations address chemicals according to property categories, such as carcinogenic or not, toxic for aquatic organism, etc. The purpose can be classification and labeling. In other cases, a continuous dose is necessary, e.g., the aquatic toxicity (toward fish, for instance) has to be compared with an exposure value to assess if there will be a toxic effect in fish for the environmental concentration that may occur. This is the case of risk assessment. Thus, we can have... 

The lARC classifications for the carcinogenic risk from exposure to some laboratory solvents (and other selected reagents) are summarised in Table 11.9. Other toxic effects for classes of solvents categorised by functional group are given in Table 11.10. 

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