Bioassays species selection

Most commonly, bioassays for the evaluation of the acute toxic effects of pesticides are based on single aquatic species selected to be representative of a range of taxonomic and functional groups, i.e., bacteria, algae, invertebrates or fish [ 53,54]. Generally, toxicity evaluation using a single species is the alternative of choice rather than the use of multiple species, because extrapolation of effects to an ecosystem is more difficult and can often lead to incorrect conclusions. 

Janackovic, R, V. Tesevic, P.D. Marin, et al. 2008. Brine shrimp lethality bioassay of selected Centaurea L. species (Asteraceae). Arch. Biol. Sci. 60(4) 681-685. 

A sharp distinction must be drawn between bioassay methods used to screen for potentially herbicidal molecules and those used to study allelopathy. If one is interested only in identifying potential herbicides, standardized bioassays using selected crop and weed species under specified protocols are highly appropriate. Such assays are also useful in gauging the relative phytotoxicity of compounds. They are not adequate, however, for demonstration of allelopathy ... 

Parasitic hymenoptera hold promise in integrated pest management schemes, because they parasitize many economically important insect pests in a species-and stage-selective manner. The pheromones and kairomones of the parasitic hymenoptera have been studied for a long time, and there are many examples where there is evidence of chemical mediation of parasitoid behavior. This review emphasizes work done since the last major reviews [11, 12, 42] and, where it is available, on the primary bioassay-guided chemical identification of the semiochemical (Fig. 2 and Tables 3 and 4). 

The selection of suitable single species and protocols is not a trivial task and may be dependent on various factors. Some of these include simplicity, low cost, or modest material and equipment demand. However, a higher sensitivity than other species to toxicants may be decisive in this choice in order to serve as warning systems. Table 1 shows the sensitivity in terms of effective concentration (EC50), which is the toxicity endpoint for the organisms (bacteria, crustaceans, algae, and fish) selected for the toxicity bioassays. These toxicity bioassays are usually classified according to the test species involved. 

The ideal species for carcinogenicity bioassays should absorb, metabolize, and excrete the compound under study exactly as humans do. Unfortunately, because of the small number of species that meet the other criteria for selection, there is limited practical utility to this important scientific concept, as applied to carcinogenicity studies. 

The bioassay technique was developed to reduce the uncertainties associated with the use of native vegetation or cultivated crops. Plants can be started under controlled conditions and exposed under standardized conditions. Species and cultivars can be selected for oxidant sensitivity and symptom characteristics. The two studies just noted were the most closely controlled. Similar work has not been repeated. However, many investigators have grown plants under known cultural conditions and then transplanted them to field sites where they received special care. These plants can then be read for foliar symptoms throughout a given period, and the symptoms related to oxidant concentrations. The lack of apparent correlation in the two early studies could be due to the lack of specificity for the monitored oxidants, the presence of different concentrations of interacting oxidants at different times, or variations in cultural conditions between exposure times. 

Dourson et al. (1996) noted that if data are only available from one chronic study on which to base the estimation of a sub-threshold dose, the question could be asked whether data from chronic studies in other species or data from different types of bioassays (e.g., reproductive or developmental toxicity) would yield lower NOAELs. The uncertainty related to this issue must therefore be addressed and, according to the authors, the default approach to address this uncertainty is to apply a 3- or 10-fold UF, based on the assumption that the critical effect can be discovered in a reasonably small selection of toxicity studies. With a reference to some analyses performed within this area, the authors suggested the use of a UF to account for missing bioassays however, the quantification of this UF was considered to require additional work. 

Possibly, the most extensive screening of NPs ever undertaken was conducted by the US National Cancer Institute, starting In i960. Over two decades, 114,000 extracts from 35,000 plant samples (from over 12,000 species) were screened but less than 1% showed selective anticancer potential. One assumes each sample must have contained tens or hundreds of NPs so the hit rate was really much lower. However, the bioassays used have a very questionable relationship to any functional significance of endogenous NPs because plants do not form cancers in the manner that animals do (see Chapter 8). 

Table 2. Bioassay testing conditions and reference methods for the selected species. 

It has to be noted that this review was undertaken to illustrate the large number of bioassays that have been used for waste assessment (45 different species and more than 45 tests if different test methods dedicated for each species are taken in account) and to give some general remarks on the 37 different test batteries presented in Table 2. Although a selected test battery is proposed in Section 5.4, a unique test battery cannot be recommended because each waste is specific in its composition and may thus require the use of a particular test battery. 

A total of 45 different species were employed, but authors did not always specify their choice of species. Ideally, bioassays should have some basic characteristics, as defined by Giesy and Hoke (1989). An adequate battery of bioassays needs in principle to measure various types (acute, chronic, genotoxic) and levels (lethal, sublethal) of ecotoxicity, without any redundancy, with test species belonging to different trophic levels or characterized by different ecological and biological traits (Ducrot et al., 2005). Another important aspect in the selection of bioassays for a test... 

Various organisms were selected to address the effects of diterpenes on different organizational structures and sensitivities. Alternative, small-scale aquatic toxicity tests known as microbiotests were used. These tests are independent of the culturing of live organisms and based on immobilized or dormant (cryptobiotic) stages of aquatic species set free or hatched when needed. The following bioassays for freshwater supplied by Creasel, Deinze, Belgium were applied ... 

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