Toxic units

Toxicity is also frequentiy expressed as toxicity units (TU), which is 100 divided by the toxicity measured ... 

Bacillus thuringiensis produces a variety of organic compounds which are toxic to the larvae of certain susceptible insect hosts. Among the toxic entities are proteinaceous crystals, probably three soluble toxins, and certain enzymes. The protein material is the major toxin active in killing lepidopterous larvae. The protein is formed by the cells apparently in close synchrony with sporulation, and its nature is a constant function of bacterial strain. The mode of action of the protein is under study. The sequence of events in the pathology observed is probably solubilization of the crystal (enzymatic or physical)—>liberation of toxic unit—>alteration of permeability of larval gut wall— change in hemolymph pH—>invasion of hemolymph by spores or vegetative cells of the bacterium. 

These experimental toxicity values were compared with the theoretical toxicity units calculated for each sample and organism from the pesticide concentrations measured in the samples and their toxicity (50% effective concentration, EC50) towards the corresponding test organisms [12]. This comparison, which is illustrated in Fig. 6, gives an estimation of the extent to which the pesticides measured contribute to the observed experimental toxicity as well as about their relative contribution to it. 

Toxicity indicators, 23 112-114 Toxicity inhalation tests, 10 660 Toxicity studies acute, 25 217 chronic, 25 218 short-term repeated, 25 217 subchronic, 25 217-218 Toxicity units (TU), 25 887 Toxic materials, 21 833-836... 

The humic/organic matter coatings of different solid phases (i. e., SPm /SP0M), such as soils, sediments, suspended solids, colloids, and biocolloids/biosolids, interact with organic pollutants in aqueous systems in various ways. Adsorption is an important interaction mode. The reversibility and/or irreversibility of the adsorption processes is of major importance. The question whether the bound residues of pollutants are to be considered definitely inactivated has been the focus of extensive research. This question was posed as follows. Have the adsorbed pollutants become common components incorporated into the humic polymer coating of solid phases (i. e., being absorbed), or are they only momentarily inactivated in reversibly bound forms thus representing a possible source of pollution by a time-delayed release of toxic units ... 

In quantifying the joint actions of PAHs in mixtures, for instance, the concept of toxic unit (TU) is used. It is defined as... 

In summary, the different joint effect models of multicomponent pollutant mixtures (i.e., the toxic unit, additive and mixture toxicity indices) were presented. Using such models to analyze the joint effect of a group of toxic and carcinogenic organic compounds such as polycyclic aromatic hydrocarbons will be presented and evaluated in Sect. 3.2. 

Locate the two points on the graph that are separated by the vertical 50% mortality line and read the LC50 at the intersect of the two lines. Expression and interpretation of the toxicity data of wastewaters all median toxicity values are converted into toxic units (TU), that is, the inverse of the LC/EC50 expressed in %, according to the formula TU = [l/L(E)C5o] x 100. 

Toxicity data analysis [calculation percent of inhibition (%l), calculation LID10, calculation toxicity units (TU=(1/LIDio)x100)]... 

This toxicity unit reflects the total toxicity of all toxic substances in the sample. 

All test results are expressed as threshold values (LOECs), and subsequently transformed to toxic units (TUs). The entire scheme results in a total number of 10 TUs per effluent. The results are put through the following calculation to produce the PEEP index. 

In Ireland, compliance with toxicity limits for selected industries is ascertained by annual or biannual test on representative samples of effluent. The test species most commonly used is the rainbow trout (Salmo gairdneri). Control authorities normally require results from 96-hour tests. The toxicity values are expressed as the minimum acceptable proportion of effluent (as a percentage) in a test resulting in 50% fish mortality after 96 hours of exposure. The toxic units (TU) are defined as the maximum number of times an effluent may be diluted to produce the test criteria (TU = 100/96-hour LC50, with LC50 expressed as the percentage of effluent in the test) (Fig. 5). 

In order to encourage the optimum selection of sites for new industries, it is recommended that receiving waters at all times must provide a minimum of 20 dilutions in the immediate vicinity of the discharge for each toxic unit discharged. How measurements, mixing and dispersion studies are therefore a necessary addition to monitoring toxicity limits of effluents [12]. 

Level of toxicity Toxic unit Multiplying coefficient... 

Poirier, D.G. Westlake, G.P. Abemethy, S.G. Daphnia magna Acute Lethalithy Toxicity Test Protocol Ontario Ministry of Environment, Aquatic Toxicity Unit, Water Res. Br. Rexbale, Ontario, Canada, 1988. 

A toxicity unit (TU) approach was used to identify pesticides potentially responsible for observed toxicity. 

Rogers, H.R., 2002. Assessment of PAH contamination in estuarine sediments using the equilibrium partitioning-toxic unit approach. Sci. Total. Environ. 290, 139-155. 

So that toxic effects of all bioassays could be later integrated in the PEEP scale formula (Section 5.5), TC values were again transformed into toxic unit (TU) values by means of the following formula (Sprague and Ramsay, 1965) ... 

Once toxic units are calculated for all bioassays, they are integrated in the toxic print portion of the PEEP formula, which is multiplied by effluent flow datum (Q = 3213 m3/h). The product of toxic print and flow yields the toxic loading of the effluent. The resulting PEEP index value of 5.8 is then simply the log10 of the calculated effluent sample toxic loading (plus 1). The value of 1 , inserted into the PEEP formula just ahead of the toxic print, insures that the inferior scale of the PEEP index will commence at 0 for effluents which are non toxic (i.e., those where toxicity responses are absent for all of the bioassays and which yield a ETz value = 0). 

Figure 1. Evolution of effluent toxicity in France from 1974 to 1993 in terms of actual (discharged toxic units) and avoided (treated toxic units) toxic loading reaching surface waters.

Linking toxicity and chemical data can be useful in the early stages of a TRE, but may be most valuable when the TIE treatments implicate a particular substance(s) as the cause of toxicity. A common approach is the use of Toxic Units (TUs). Lethal TUs express the degree of effluent toxicity, or the concentration of substance, as a fraction of the LC50. Similarly, sublethal TUs are expressed as a fraction of the IC25 or IC50 (Environment Canada, 1999). TUs are dimensionless, and allow for normalization of LC50 data. The TU can be used to predict toxicity of an effluent based on the measured toxicant concentrations. 

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