Toxicants toxic effect criteria

Effect criterion by which toxicity is estimated (e.g., mortality, growth, reproduction). Volume 1(3,10). 

Toxicity data are scaled into dimensionless hazard units, preferably based on bio-available concentrations. A hazard unit is defined as the concentration where the effect criterion (e.g., NOEC) is exceeded for 50% of all species tested, that is, the median of the toxicity data of the whole data set, IHJJ = NOECj / NOEC, for i = 1 to n compounds and for / = I to m species, with HU/ = the scaled NOECs in dimensionless hazard units (mg-L 1 / rng-E ), and NOEC, = the median NOEC for substance i. The SSDs for each compound are obtained by fitting a log-logistic or log-normal model to the log toxicity data in hazard units. For the log-normal... 

The evaluation of different chemicals involves identification of potential active agents and the mechanisms by which they present their toxic effect, prediction of effective pharmaceutical cytotoxicity for treatment of patients with cancer, evaluation of the activity range of the studied compound, identification of a target cell population and of the toxic concentration range, and the relation between pharmaceutical concentration and exposure period to reach a desired activity. The chosen assay system should provide a reproducible dose-response curve with low variability over a concentration range that includes in vivo exposure. In addition, the selected response criterion should present a linear relationship with cell number, and the information obtained with a dose-response curve should be related to the in vivo effect of the same active agent or drug. 

Effect criterion The type of effect observed in a toxicity test (e.g., immobility). 

Sensitivity is a criterion that is used in the choice of a test species. The sensitivity of the species in Table 3 relative to one another as well as to indigenous flora and fauna in the ecosystem is a matter of contention. There is no single test species and no group of test species consistently most sensitive to toxicants or most reliable for extrapolation to all other organisms. Most toxic effects reported for a variety of test substances have been species-specific. Therefore, acute toxicity tests are conducted first with a variety of freshwater and marine test species to determine the most sensitive plant and animal. These sensitive species then are used in all subsequent chronic testing. 

Selenium may be a problem in the freshwater environment 5 pg/1 is the criterion for protection of aquatic life at chronic exposure and modifications of this criterion have been proposed recently [90]. A similar situation apparently does not exist in the marine environment. Selenium is a relatively abundant trace element in the marine environment and seems to counteract the toxic effects of mercury. 

If there is enough relevant information, it is possible to incorporate these interactions between toxicant effects and water qnality characteristics into water quality criteria. In the United States, for example, the criterion maximum concentration and the criterion continuous concentration are sometimes expressed as explicit functions of certain water qnality characteristics. In the case of NH3, for example, toxicity has been shown to be negatively correlated with pH and, below 20-25°C, with temperatnre. The EPA water qnality criteria for NH3 therefore are expressed in terms of mathematical eqnations that relate the criterion maximum and criterion continnons concentrations of NH3 to temperature and pH (EPA, 1986). 

The biological gradient (dose—response) criterion can also be readily answered in the affirmative. Two points in appraising the enumerated toxic effects are that (1) the persistence of the dose—response relationships span relatively wide exposure ranges in many cases, e.g., neurotoxicity. 

As noted, the main criterion for any cosmetic ingredient should be medical safety (free of allergances, sensitizers and irritants and impurities that have systemic toxic effects). These ingredients should be suitable for producing stable emulsions that can deliver the functional benefit and the aesthetic characteristics. The main components of an emulsion are the water and oil phases and the emulsifier. Several water-soluble ingredients may be incorporated in the aqueous phase and oil-soluble ingredients in the oil phase. Thus, the water phase may contain... 

For prediction of toxic consequences, two common approaches are the use of either a specific toxic concentration or a toxic dose criterion. Toxic dose is determined as toxic gas concentration for the duration of exposure to determine an effect based on specified probit models (Chapter 4). 

For this safety criterion, we consider the fact that as the velocity decreases with increasing distance from the surface of the tank, it will reach some critical velocity, at which the induced movement of air will be insufficient to overcome the effects of crossdrafts or the buoyancy velocity At this point, we must ensure that the concentration is at, or below, some critical allowable concentration, Qfj,. The values of the critical concentration and velocity will depend (tn particular circumstances, but it is worth noting that must be at least equal to I g in order to overcome the effects of buoyancy, and the appropriate value will depend on the crossdrafts, which typically vary between 0.05 m to 0.5 in s F For the sake of providing examples, we have chosen to be the maximum of the buoyancy velocity and the typical cross-draft velocity. For the critical concentration we have chosen two values, C = 0.05 and C = 0.10. The actual value used by a designer would depend on the toxicity of the contaminant in question. 

In the meantime, we believe that the best prediction of the toxicity of an ionic liquid of type [cation] [anion] can be derived from the often well known toxicity data for the salts [cation]Cl and Na[anion]. Since almost all chemistry in nature takes place in aqueous media, the ions of the ionic liquid can be assumed to be present in dissociated form. Therefore, a reliable prediction of ionic liquids HSE data should be possible from a combination of the loiown effects of the alkali metal and chloride salts. Already from these, very preliminary, studies, it is clear that HSE considerations will be an important criterion in selection and exclusion of specific ionic liquid candidates for future large-scale, technical applications. 

The information used for dose selection usually comes from subchronic toxicity studies, but other information about the pharmacological effects of a drug and its metabolism and pharmacokinetics may also be considered. The maximum recommended human dose (MRHD) of the drug may be an additional criterion, if this is known when the carcinogenicity studies are being designed. 

Toxicity tests are necessary tools to evaluate the concentration and duration of exposure of a chemical required to produce certain adverse effects. Molecular processes directly affected by the exposure to the chemical agent are the most liable criterions. Nevertheless, these effects are difficult to detect in aquatic toxicology because the processes are generally not well understood [72], Alternatively, other end points which fulfil the necessary requirements, namely the need to be unequivocal, relevant, easy to observe, describe and measure, biologically significant and repeatable, are used. These include measures of mortality, which is frequently employed in the early evaluation of the toxicity of a pollutant in acute toxicity tests. This criterion allows comparison of toxicity exerted by chemical agents with very different mechanisms of action. 

A Dutch smdy (Wilschut et al. 1998, as reviewed in Vermeire et al. 1999) has evaluated route-to-route extrapolation on the basis of absorption or acute toxicity data. Data were collected primarily on dermal and inhalation repeated dose toxicity. An extrapolation factor, defined as the factor that is applied in route-to-route extrapolation to account for differences in the expression of systemic toxicity between exposure routes, was determined for each substance by using data on absorption and acute toxicity data. As experimental data on absorption often were not available, default values for absorption were also used to determine an extrapolation factor. Despite a rather large overall database, relatively few data could be used for the evaluation and the selection criteria were modified in order to include data that initially were considered less suitable for data analysis interspecies extrapolation based on caloric demands was introduced, and a factor of 3 was applied in case a LOAEL instead of a NOAEL was available. The choice of NOAELs for different exposure routes known for a substance suitable for analysis was based primarily on the same effect, but this criterion could not be maintained. 

The evaluation of dose-response relationships is a critical component of hazard characterization (OECD, 1989 ECETOC, 1992 US , 1997a IPCS, 1999). Evidence for a dose-response relationship is an important criterion in establishing a toxic reproductive effect. It includes the evaluation of data from both human and laboratory animal studies. Because quantitative data on human dose-response relationships are infrequently available, the dose-response evaluation is usually based on the assessment of data from tests performed using laboratory animals. However, if data are available in humans with a sufficient range of doses, dose-response relationships in humans can also be evaluated. 

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