Baseline toxicity

As a conclusion one can say that the distinction of islands of specific activity from within a sea of baseline toxicity, with each island representing a local chemical biological mechanism domain, is still a challenge to be solved by scientists working both experimentally and computationally. 

Oherg, T. (2004) A QSAR for baseline toxicity validation, domain of application, and prediction. Chem. Res. Toxicol.,... 

Lipnick, R.L. (1993) Baseline toxicity QSAR models a means to assess mechanism of toxicity for aquatic organisms and mammals, in... 

Sorption II Partitioning to Living Media -Bioaccumulation and Baseline Toxicity... 

Quantitative Structure-Activity Relationships (QSARs) for Baseline Toxicity... 

Let us now evaluate how we can assess the baseline toxicity of organic chemicals in a quantitative way. We have already mentioned that certain membrane functions may be disrupted if a chemical occupies a certain volume fraction of that membrane. This means that for two compounds of the same size, we would anticipate that when they are present at equal concentrations in the membrane they would exert the same effect. Furthermore, since the majority of chemicals of interest to us do not differ in size by more than a factor of 3 to 4 (compare molar volumes in Chapter 5, e.g., Fig. 5.2), the membrane concentration required for any compound to cause a narcotic effect will be in the same order of magnitude. Therefore, we may expect that the concentration of a compound required in an environmental medium (e.g., water, air) to cause a narcotic effect in an organism should be inversely proportional to the tendency of the compound to accumulate from that medium into biological membranes. 

What is meant by the terms baseline toxicity or narcosis Why is this type of toxicity relevant in the environment ... 

You are interested in the well-being of Ampelisca abdita, living in a harbor whose sediments are contaminated with 4-nonylphenol. You remember that the lethal volume fraction of narcotic chemicals in membranes is about 0.01 L compound L I lipid. If the sediment contains 2% organic carbon by weight, and the amphipod is assumed to accumulate body burdens up to equilibrium with the sediments on which it lives, what sediment concentration of 4-nonylphenol should be deemed acceptable with respect to baseline toxicity Assume a log ,lipsw = 5.5 for 4-nonylphenol. Use Eq. 9-26c (alkylated and chlorinated benzenes ) for estimating Kioc. Compare your result with the findings of Fay et al. (2000), who observed a die-off of half the amphipods when they were exposed to about 0.16 g 4-nonylphenol - kg-1 sediment. 

Non polar narcotics Compounds causing baseline toxicity, i.e., reversible state of arrested activity of protoplasmic structures (Bradbury et al., 1989). Volume 1(8). 

Leslie, H.A., J.L.M. Hermens, and M.H.S. Kraak. 2004. Baseline toxicity of a chlorobenzene mixture and total body residues measured and estimated with solid-phase microextraction. Environ. Toxicol. Chem. 23 2017-2021. 

Two protocols are presented, the first for baseline toxicity, and the second for groups of compounds with the same assumed primary mode of action. The protocols are more broadly explained in De Zwart and Posthuma (2005). Example spreadsheet calculations can be found in Box 5.2. 

Method A Unspecific Modes of Action (Baseline Toxicity)... 

FIGURE 5.2 Schematized presentation of the mixed-model approach for assemblage-level extrapolation. Note A similar approach is followed for species-level mixed-model extrapolation. The system can be simplified by assuming response addition for all extrapolations except the baseline toxicity assessment (approach of Hamers et al. [1996], yielding combi-PAF). The system can also be more complex when predictions for compound class effects are made for different species groups. 

---