Aquatic test systems

Van Veld PA, Spain JC. 1983. Degradation of selected xenobiotic compounds in three types of aquatic test systems. Chemosphere 12 1291-1305. 

Besides the complexity of the biological system and the length of the test, there are more practical aspects to toxicity tests. In aquatic test systems the tests may be classified as static, static renewal, recirculating, or flow-through. 

In aquatic test systems, exposure is usually a whole-body exposure. That means that the toxicant can enter the organism through the skin, cell wall, respiratory system (gills, stomata), and ingestion. Occasionally, a toxicant is injected into an aquatic organism, but that is not usually the case in toxicity tests to screen for effects. Whole-body exposures are less common when dealing with terrestrial species. Often an amount of xenobiotic is injected into the musculature (intramuscular), peritoneum (intraperitoneal), or into a vein... 

What is whole-body aquatic test systems exposure ... 

Step 3 Determination of the material disintegration under relevant conditions (same as for Step 2) with a batch size of at least 2 litres (liquid) or 20 kg (solid) artificial or natural sediments should be included in aquatic test systems. 

In a continuous model river test system it can be shown that after passage through a sewage treatment plant ester sulfonates have no significant influence on the qualitative and quantitative composition of the biocenosis of a receiving water [113]. All the investigations into the environmental fate of a-sulfo fatty acid esters demonstrate that aquatic toxicity is alleviated by their fast ultimate biodegradability, which allows them to be classified as environmentally compatible. 

Paper mill whitewaters and effluents are rich in bisphenol A (BPA), which is used in great quantities for the production of epoxy resins and polycarbonate plastics. Its presence in effluents has been reported as a result of its use in the manufacture of thermal paper or due to migration from plastic containers at the high water temperatures of whitewaters [35]. This compound is preferably analysed by GC-MS. The levels encountered in paper mill effluents are between 28 and 72 pg/L [36,37]. Another study revealed levels up to 226 pg/L [33]. Special in vitro test systems and animal experiments have demonstrated a weak oestrogenicity for BPA. Since aquatic wildlife could be endangered by paper mill waste discharges at the concentration that BPA is found, its survey in paper mill effluents should be taken into consideration. 

Johnson, B.T. 1998, Microtox Toxicity Test System—New Developments and Applications. In Microscale Testing in Aquatic Toxicology Wells, P.G., Lee, K., Blaise, C., Eds CRC Press Washington, D.C. pp. 201-218. 

For nanomaterials this is especially true if the exposure scenarios used in the test system are not representative of those likely to be found in the field [91, 92]. For example, the degree of toxicity observed in aquatic invertebrates exposed to multi-walled nanotubes (MWNTs) in water and sediment was influenced by the functional groups on the MWNTs and their preparation for dispersal into the test systems [93]. As noted, even the concept of what constitutes nanomaterials is not fixed [87], so these emerging materials will likely require a rethinking of how their toxicity is assessed and the hazards and risks they might pose to ecosystems [90]. For more information on nanomaterials, including application of life-cycle concepts to their design, see Chapter 8. 

Along these lines, other test systems in combination with concentration methods were developed and applied. Although most chemicals have been introduced into the environment in ways that did not result in immediate effects on the environment, the total load of chemical pollutants has certainly contributed to observed changes in the structure and function of aquatic ecosystems. We now rely on aquatic toxicology to give reliable and proper information on the possible effects of man-made chemicals. This information enables the protection of aquatic ecosystems and, in particular, provides for the required scientific guidance in legislation and enforcement. 

When evaluating the influence of the time of year on responses of aquatic communities to chemical stress, it is convenient to make a distinction in threshold concentrations of direct toxic effects, and in the magnitude of effects that occur above these threshold concentrations. Only a limited number of (model) ecosystem experiments are available that allow a comparison of responses due to treatment with the same chemical in the same type of test system at different periods of the year. These studies indicate that, in freshwater communities, threshold concentrations for direct toxic effects may vary little with the season (within a factor of 2). At higher exposure concentrations, however, the intensity and duration of the responses (direct and indirect effects) may vary considerably between different periods of the year (Section 6.3.2). 

Spatial variability and ecotoxicological data extrapolation This section describes the current knowledge and available extrapolation tools with respect to the effect assessment of the same type of stressor in test systems of different sizes, in different types of aquatic ecosystem within a region, and in comparable ecosystems in different geographical regions. 

Experimental aquatic ecosystems have become widely used tools in ecotoxicology because they allow for a greater degree of control, replication, and repeatability than is achievable in natural ecosystems. The test systems in use vary from small indoor microcosms to large and complex outdoor experimental ecosystems. However, natural freshwater systems may also vary considerably in size and ecological complexity. Before addressing the spatial extrapolation of results of model ecosystem experiments that were conducted on different localities, the possible influence of the size and ecological complexity of test systems on responses to chemical stress will be discussed. 

A9.3.5.9.2 Polymers are typieally not available in aquatic systems. Dispersible polymers and other high molecular mass materials can perturb the test system and interfere with uptake of oxygen, and give rise to mechanical or secondary effects. These factors need to be taken into account when considering data from these substances. Many polymers behave like complex substances, however, having a significant low molecular mass fraction which can leach from the bulk pol)mier. This is considered further below. 

Microcosms are composed of large chambers, terreria, aquaria, or artificial pools aquatic mesocosms include artificially constructed ponds or streams, while terrestrial mesocosms are large containers filled with soil, plants, and (sometimes) leaf litter. Microcosms and mesocosms typically contain more than one species of test organism, are located outdoors (but may also be located indoors), and often contain sediment and/or vegetation. The rationale is to produce a test system with similarities to the natural environment, but is more controllable. End points examined may include acute toxicity, suble-thal effects, or community/population level effects. 

In the aquatic arena some of the biodegradation tests are done with volumes of less than a liter. Tests to evaluate community interaction conducted in a laboratory have test vessels ranging in size from 1-1 to 55-gal aquariums. Larger test systems can also be used outside the laboratory. A proposed outdoor aquatic microcosm proposal uses large tanks of approximately 800-1 capacities. Larger still are the pond mesocosms used for pesticide evaluations. These systems are designed to mimic farm ponds in size and morphology. 

Kersting, K. 1984. Development and use of an aquatic micro-ecosystem as a test system for toxic substances. Properties of an aquatic micro-ecosystem IV. Int. Rev. Hydrobiol. 69 567-607. 

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