Geometric dilution series

If a preliminary dilution step is deemed necessary before the geometric dilution series, as recommended in the case of heavily polluted wastewater, the preliminary dilution step, for example, should be 1 64 or 1 128. If it is necessary to obtain LC0 values for determining the pT-value, then the geometric dilution series with the factor of 1 2 must be followed through from the first dilution step. This is required in the fish test according to DEV L31 (1989) (Section 5.3). The same is required for other quantal tests like the Daphnia test, where 9 of 10 animals must survive. 

Table 2. Geometric dilution series, pT-values andpT-indices for wastewater effluents. The pT-values of receiving surface waters and of final effluents from wastewater treatment plants determined thus far are marked by the sign +.

The pT-values of geometric dilution series are always integers, and the resulting pT-value of 11.6, as in this example, is ultimately reported as a pT-value of 12. Hence, by convention, calculated pT-values, determined from the relationship between concentration and effect, are always rounded-up to integers. 

The pT-values obtained without calculation from the standard pT-method are also listed in Table 3. As explained previously (Section 5.4), pT-values of each geometric dilution series are rounded up to whole numbers from IC 19 values. 

Figure 1. Multiple bioassay examination of porewater and elutriate of sediment core sample AS 3" collected from the River Saar. The pT-scale is based on a geometric dilution series with the factor 2 (Krebs, 1999).

The sensory evaluation differentiates between the stimulation threshold (a just detectable level where a perceptible but not yet definable deviation of the sample from the standard is observed) and the recognition threshold, a level where the odor is identifiable or creates odor problems (a no longer tolerable quality deterioration caused by a definite off odor and/or taste). The difference between a perceptible and identifiable level is usually only one to two steps of a geometric dilution series. Therefore, only undifferentiated odor and taste thresholds are given in Table 13-6, because of the very different sensitivities of individual testers. The perceptible (stimulation) levels of a less sensitive tester can overlap with the identifiable (recognition) level of another more sensitive tester. 

For semiquantitative gelation method, the geometric mean of the endotoxin concentration = antilog (Xe//), where Xe is the sum of the log endpoint concentrations of the dilution series used, and/ is the number of replicate test tubes. 

Variations of resistance with frequency can also be caused by electrode polarization. A conductance cell can be represented in a simplified way as resistance and capacitance in series, the latter being the double layer capacitance at the electrodes. Only if this capacitance is sufficiently large will the measured resistance be independent of frequency. To accomplish this, electrodes are often covered with platinum black 2>. This is generally unsuitable in nonaqueous solvent studies because of possible catalysis of chemical reactions and because of adsorption problems encountered with dilute solutions required for useful data. The equivalent circuit for a conductance cell is also complicated by impedances due to faradaic processes and the geometric capacity of the cell 2>3( . 

The point of change is determined for every series of dilution evaluated. It is defined as the geometric mean of the dilution of the last negative and the first positive answer. The arithmetical mean and its standard deviation are calculated from the logarithms of the points of change. 

Geometric means the dilution at which the response changes from no perception to perception has to be determined for each test series, After that the geometric means of the so defined dilution has to be calculated. 

To determine the endotoxin concentration of solution A, calculate the endpoint concentration for each replicate series of dilution factor by X. The endotoxin concentration in the sample is the geometric mean of the endotoxin concentration of the replicates. 

Specific exposure concentrations for effluent dilution are often evenly spaced in a linear or geometric series (e.g., 100%, 50%, 25%, 12.5%, and 6.25% effluent). Replicate exposures are required, with test vessels arranged in the incubator in a randomized block design. At the end of the test, statistical calculations of NOECs for survival and reproduction or growth are typically performed as a multiple comparison procedure of effluent-treated groups. The induced effects of effluent pollutants on growth or reproduction and on survival may or may not be equal, suggesting information on the relative... 

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