Bioassays invertebrate tests

We have addressed the topic of metal bioavailability and metal toxicity in environmental samples. Traditionally, metal availability is investigated using a chemical approach. Afterwards, the concept of Water Effect Ratio (WER) was proposed by the U.S. EPA and employed bioassays (e.g., fish and invertebrate tests) to assess metal bioavailability and toxicity. In the HMBC approach discussed in this review, we have made use of a bacterial assay that is specific for metal toxicity to achieve this goal. This is only a preliminary survey of the potential applications of the HMBC concept. Some preliminary results on the use of MetPLATE for the fractionation of HMBC to obtain information on the factor(s) that control metal bioavailability in environmental samples were also presented. Using MetPLATE eliminates or diminishes the confounding factor represented by the presence of organic toxicants in a given sample. Further work is needed to refine the fractionation scheme. 

Invertebrate species have been widely used in toxicity studies of pesticides [61]. Zooplankton play a key role in the food chain because they occupy a central position. Therefore, their responses to natural and anthropogenic stresses are intimately linked with other food predator organisms. The most widely accepted bioassays employ species such as Ceriodaphnia dubia, Daphnia magna, Artemia salina, or Thamnocephalus platyurus [62-64]. D. magna has been used for many years as a standard aquatic test species and formally endorsed by the major international organizations such as the EEC, OECD, and ASTM [65-67]. Its choice is mainly because it represents the zooplankton community and is a species of worldwide occurrence. In addition, it has a greater sensitivity to toxicants, particularly pesticides, compared with other aquatic species [61,68] (Table 1). 

Anderson, B.G. Aquatic invertebrates in tolerance investigations from Aristotle to Naumann. In Aquatic Invertebrate Bioassays Buikema, A.L. Jr., Caims, J. Jr., Eds. American Society for Testing and Materials Philadelphia, PA, 1980 Vol. 3, 3-35. 

Bioassays appeared to fit the bill to perform this service to monitor chemical contamination. They have been around for a while. Until relatively recently, however, they remained in the realm of the laboratory. Only over the last two decades have they found a niche in testing for toxic chemicals in water and sediment, but not yet specifically as a tool for routine water quality monitoring. As Small-scale Freshwater Toxicity Investigations, Volumes 1 and 2 amply demonstrates, the science has now come of age. Assays based on bacteria, microscopic or multi-cellular algae, protozoa, invertebrates and vertebrates (freshwater fish cell cultures) are discussed in... 

Some alternative ecotoxicological bioassays are available for environmental monitoring, and amongst these the tests based on invertebrates such us Daphnia magna (ISO, 1996), microalgae, such as Skeletonema costatum (ISO, 1995) and Selenastrum capricornotum (EPA, 1982), the marine bacteria Vibrio fischeri and Photobacterium phosphoreum (ISO, 1998) are well established. These tests use standardized organisms, and are available from a number of commercial companies. 

These are tests that are established within the academic community as monitors of chemical exposure and chemical effect. Unlike the procedures discussed in section 6.2, standards do not exist for these tests. Development instead can be tracked via a series of scientific papers. Some methods are long established in soil ecology and ecotoxicology. Examples include invertebrate bioassays, soil enzyme assays and litterbags. In contrast, a number of methods, such as bait lamina and some biochemical assays (e.g. lysosomal membrane stability), have been developed more recently but have passed quickly into widespread use. 

For environmental testing, bioassays provide an integrated picture of the overall toxicity of pore water, sediment elutriate or sediment from a contaminated site. Various aquatic organisms, such as vertebrates, invertebrates, protozoa, algae, macrophytes and bacteria are used to test environmental samples. The idea behind these toxicity tests is that the test organisms will react in a predictable way to various types of environmental contaminants. 

Screening tests for the trichothecene mycotoxins are generally simple and rapid but, with the exception of the immunochemical methods, are nonspecific. A number of bioassay systems have been used for the identification of trichothecene mycotoxins.73 Although most of these systems are very simple, they are not specific, their sensitivity is generally relatively low compared to other methods, and they require that the laboratory maintain vertebrates, invertebrates, plants, or cell cultures. Thin-layer chromatography (TLC) is one of the simplest and earliest analytical methods developed for myco-toxin analysis. Detection limits for trichothecene mycotoxins by TLC is 0.2 to 5 ppm (0.2 to 5 pg/ mL). Therefore, extracts from biomedical samples would have to be concentrated 10- to 1,000-fold to screen for trichothecene mycotoxins. 

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