Estimates of thresholds

The platform includes different decision trees for the following endpoints the estimation of Threshold of Toxicological Concern (TTC), aquatic modes of action [44], skin and eye irritation and corrosion, mutagenicity and carcinogenicity [45], in vivo micronucleus assay, identification of Michael Acceptors and biodegradation potential [46]. 

The results published in 120) should have been analyzed exactly from this viewpoint. The work 120) presents interesting comparative data on the estimation of threshold voltages U, xon, xoff for homopolymers XIII-XVI and for a series of copolymers with varying spacer length... 

For most chemicals that induce deterministic effects, the nominal threshold in humans or animals has been estimated based on NOAELs or LOAELs. However, the benchmark dose method should provide more reliable estimates of thresholds (see Section 3.2.1.2.7). Therefore, whenever the nominal threshold in humans for an important chemical in waste that induces deterministic effects has been estimated based on NOAELs or LOAELs, NCRP believes that the data should be re-evaluated using the benchmark dose method to promote greater consistency in classifying waste. As in the case of chemicals that induce stochastic effects discussed in the previous section, NCRP believes that uncertainties in the data beyond those incorporated in the benchmark dose method should be taken into account, if need be, in setting allowable exposures, rather than in an estimate of the nominal threshold. 

B2 Estimation of Threshold Current Density of GaN-Based VCSELs... 

FIGURE 10.24 Tensile strength of SBR vulcanizates versus degree of crosslinking, represented by Ve. (From Bueche and Dudek (1963).) Broken curve author s estimate of threshold strength under nondissipative conditions. 

Threshold limit value (TLV) not estabUshed by ACGIH. Value given is an estimate of a comparable iadex based on limited or incomplete toxicity testing made by chemical producers. 

As the production methods of MWCNTs is very efficient [8] (see Chaps. 2 and 12), it is an advantage to implement a filling procedure after the synthesis. A promising approach to fill CNT cavities, could exploit the capillary properties that have been revealed by Ajayan and lijima [9]. Subsequent studies by Dujardin et al.[10] allowed the estimations of a surface tension threshold in order to select materials that are good candidates to wet and fill CNTs. 

This same sensitivity can, however, be misleading. Even minor radical routes to a particular reaction product could give rise to intense polarized n.m.r. signals which could obscure the normal monotonic increase of the signal due to product formed by a non-radical route. This problem can be overcome in some cases by estimation of the spectral enhancement factor. Again, it is not possible to justify a firm, threshold value, but as a useful rule of thumb when enhancements fall below about 100 then the possibility of an important alternative non-radical route to the same product should be carefully investigated. 

Many publications use an absolute measure that denotes water security, frequently referring to an index that identifies a threshold of 1,700 CM per capita per year of renewable water, based on estimates of water requirements in the household, agricultural, industrial, and energy sectors as well as the needs of the enviromnent. Countries whose renewable water supplies cannot sustain this figure experience water stress. When supply falls below 1,000 m per capita per year, a country is said to experience water scarcity, and below 500 m per capita per year, absolute scarcity. However, these terms are easy to misinterpret, because they do not take into account possibilities for trade in agricultural products, efficiency of water use in agriculture, and other variables, and thus obscure the primacy of economic demand rather than physical need in determining water use [3-5]. 

Basically, there are four major types of measures that are used in taste intensity measurements (a) threshold measures or estimates of the physical level at which the sensation of sweetness begins, (b) equal-sweetness matches between a sugar and other sweeteners, (c) category or rating scales, and (d) ratio scales. Each method has found its adherents and uses, and each possesses specific advantages and defects that indicate its use for one application, but contraindicate its use for another. These methods and their applications have been critically analyzed and reviewed, " " and it is, therefore, superfluous to deal with the topic here. 

Janke D (1987) Use of salicylate to estimate the threshold inducer level for de novo synthesis of the phenoldegrading enzymes in Pseudomonas putida strain H. J Basic Microbiol 27 83-89. 

The availablility of an estimate of the conditional cdf F CzjCN)) at each nodal joint x allows an assessment of the risks a(x) or p(x) of making wrong decisions. Consider the contour map of a particular estimate p (x), x (see Figure 3a). Suppose that the threshold value 500 has been selected to declare any sub-area of A hazardous. The contour line 500 on Figure 3 delineates the zones which are candidates for cleaning. Within these zones, the probability that the concentration is actually under 500, i.e. the risk a(x) of cleaning unduly, can also be mapped ... 

In the United States, the threshold mercury concentration for commercial sale of fish is determined by the Food and Drag Administration, whereas consumption advice for recreational (noncommercial) fish is developed by individual states and tribes. Mercury data collected for development of fish-consumption advisories are typically from analyses of filets (axial muscle tissue, with or without skin) for total mercury, with concentrations expressed on a wet-weight basis. Analysis of filets for total mercury yields a valid estimate of MeHg concentration (Grieb et al. 1990 Bloom 1992), whether the analyzed sample consists of a large filet or a small mass of tissue obtained with a biopsy needle (Cizdziel et al. 2002 Baker et al. 2004). 

If linear (dose) models without thresholds are to be used for carcinogen (or other) risk assessment, estimation of exposure at specified levels becomes irrelevant to risk assessment or, at least, its use is nonintuitive. For example, a carcinogen risk analysis may be based on a linear, nonthreshold health effects model. The total health risk would thus be proportional to the long-term exposure summed for all affected people for the identified period, and exposure of many people at low concentrations would be equivalent to exposure of a few to high concentrations. The atmospheric dispersion that reduces concentrations would also lead to exposure of more people therefore, increments... 

This model does not allow for a threshold effect, and thus may overstate the risk at low doses. It tends to yield higher estimates of human risk than the other models discussed below. 

Although several data sets could be used to derive AEGL-3 values, the 1-h exposure data from the mouse study by Peterson and Bhattacharyya (1985) provided the most sound basis and were selected to derive AEGL-3 values. Due to the steep concentration-response curve for arsine, the 15-ppm exposure (where there was no lethality) was considered an estimate of the lethality threshold. An uncertainty factor of 30-fold was applied to account for interspecies extrapolation (10-fold) and intraspecies variability (3-fold) (see Section 6.3). 

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