Narcosis base-line toxicity

It is well known that the effects of narcosis type chemicals are completely concentration additive [92, 134-136]. Intrinsically, these chemicals are equally toxic. In other words body burdens at a certain effect are the same for all compounds within this toxicological class . The differences in aqueous effect concentrations of chemicals with base-line toxicity are only due to differences in... 

In view of the early observations of Meyer and Overton on the relationship of tadpole narcosis to hydrophobicity, and later the modern version of aquatic toxicity by Hansch and Dunn/ " it is not surprising that simple narcosis is the main component of base-line toxicity and can be delineated by a single parameter, log P with a slope close to unity. When a certain structural class of potential toxicants such as anilines or acrylates, fit to a line with the same slope as alkanes, but with a greater intercept, the excess toxicity of this structural feature can be expressed quantitatively. Alternatively, if the toxicity of a variety of structures is plotted against log P, those appearing above the background line clearly exhibit this excess toxicity. 

In a qualitative manner, the NBP test can be applied to select those compounds that have an enhanced toxicity compared to their unspecific toxicity based on a narcosis mechanism. The mode of toxic action xDf many aquatic pollutants, including aromatic and aliphatic chlorohydrocarbons, is based on this mechanism and aquatic toxicity is well correlated with (Mermens 1986 Lipnick and Dunn 1983 Veith et al. 1983 Konemann 1981). This kind of unspecific toxicity can be characterized by minimal or base line toxicity. 

Class I, represented by relatively unreactive chemicals with a nonspecific mode of action and they represent the base-line toxicity or nonpolar narcosis or simple narcosis (Bradbury et al., 2003 Hermens Verhaar, 1995). Narcosis is a reversible state of kept activity of protoplasmic structures, which is a result of exposure to the xenobiotic. Also the terms narcosis and general anaesthesia are used as equivalently in the circumstance of intact organisms. It presumed that, when the xenobiotic blood concentration is at equilibrium with the aqueous exposure concentration the aqueous concentrations of narcotic chemicals are proportional to the concentrations at the site of action (Bradbury et al., 2003). In the class I of chemicals we found aliphatic and aromatic (halogenated hydrocarbons) (Hermens Verhaar, 1995). 

Irrespective of whether there is one or several modes of toxic action for the outliers in the data sets, it appears the sum of sigma constants can improve the QSAR based on log P for aliphatic ketones, esters, alcohols, and nitriles in fathead minnows. If this observation holds true for a wide variety of chemicals in these classes, it should be useful in predictive equations as presented here or in identifying outliers to be treated separately from toxicants acting by base line narcosis (Veith et al. 1985). 

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