Critical toxicity value

Table 19 List of estimated exposure values (EEV), critical toxicity values (CTV) and RQs for SCCPs...

The RfD is derived from the NOAEL (or LOAEL) for the critical toxic effect by consistent application of uncertainty factors (UFs) and a modifying factor (ME). The uncertainty factors generally consist of multiples of 10 (although values less than 10 are sometimes used), with each factor representing a specific area of uncertainty inherent in the extrapolation from the available data. The bases for application of different uncertainty factors are explained below. 

Since the publication of the third edition, additional data have been critically reviewed. New or additional data included in this edition are bioconcentration factors, aquatic mammalian toxicity values, degradation rates, corresponding half-lives in various environmental compartments, ionization potentials, aqueous solubility of miscellaneous compounds, Henry s law constants, biological, chemical, and theoretical oxygen demand values for various organic compounds. Five additional tables have been added Test Method Number Index, Dielectric Values of Earth Materials and Fluids, Lowest Odor Threshold Concentrations of Organic Compoimds in Water, and Lowest Threshold Concentrations of Organic Compounds in Water. 

The amount of alkalinity that is necessary to leach from the soil can be estimated from the ratio of base cations to aluminum, (Ca + Mg)/Al, assuming a critical threshold value for biological effects at 1 1. (Above a ratio of (Ca -I-Mg)/Al = 1 roots are assumed to be protected from aluminum toxicity and Mg deficiency.) Then, based on gibbsite solubility and a minimum required... 

One way of improving SFE efficiency is by using a more suitable SF to extract the target analyte. Unfortunately, the choice of fluids other than CO, is restricted by the desire to have reasonable critical parameter values and costs, chemical inertness, low toxicity and little environmental impact. The use of supercritical N2O has proved to increase the extraction efficiency for high-molecular weight PAHs and chlorinated dibenzo-p-dioxins from fly ash and sediment [52]. This extractant, however, does not always improve the extraction efficiency [53] also, it can be explosive in the presence of reactive organics. Other polar fluids such as CHCIF, (Freon-22) have exhibited increased efficiency in the extraction of nitrated and non-nitrated PAHs from particulate matter in diesel exhaust [54]. Freon-22 has also been found to allow significantly fast and effective extraction of... 

As discussed earlier, nitroaromatic compounds introduced into soil can undergo rapid transformation to the amino-nitro intermediates. Frequent co-occurrence of TNT, TNB, DNTs, and ADNTs in soils of contaminated sites or in experimentally contaminated soil treatments precluded investigators from partitioning the effects of the parent materials and their transformation products on soil microorganisms [7,12,17], As a result, the established toxicity values for TNT reported in previous studies should not be accepted unequivocally. Additional studies will be required to definitively resolve the toxicity of individual nitroaromatic EMs to the soil microbial community and to critical processes in the soil ecosystem regulated by this community. 

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