Mesocosm tests

The Community-Level Aquatic Systems Studies Interpretation Studies (CLASSIC) guidance document, which deals with the interpretation of results of microcosm and mesocosm tests in the risk assessment procedure of pesticides, recommends that regulatory model ecosystem experiments be conducted in spring to midsummer (Giddings et al. 2002). On the basis of the limited number of model ecosystem experiments described above, it seems that threshold concentrations for effects observed in early-season studies are reasonably predictive for threshold concentrations later in the season. Above these threshold concentrations, however, the intensity and duration of the responses (direct and indirect effects) may vary during different periods of the year. Consequently, the extrapolation of NOECcommunity values from one season to another seems to be possible with lower uncertainty than hazard estimates of higher concentrations in which both direct and indirect effects are involved. 

It appears from the above that microcosm and/or mesocosm tests are limited by the constraints of experimentation, in that usually only a limited number of recovery scenarios can be investigated. Consequently, modeling approaches may provide an alternative tool for investigating likely recovery rates under a range of conditions. Generic models, like the logistic growth mode (for example, see Barnthouse 2004) and life history and individual-based (meta)population models, which also may be spatially explicit, provide mathematical frameworks that offer the opportunity to explore the recovery potential of individual populations. For an overview of these life history and individual-based models, see Bartell et al. (2003) and Pastorok et al. (2003). 

Mesocosm no-effect data on a rapidly dissipating compound such as a pyrethroid insecticide may not be suitable for a chronic EQS applied to a river. Furthermore, most existing micro- and mesocosm studies are inappropriate for EQS derivation if fish are the most sensitive species because fish have generally been excluded from such tests. There is consequently a need for evidence-based decision making for interpretation of nonstandard mesocosm studies. Microcosm and mesocosm tests can, however, be used directly for EQS derivation if algae, macrophytes, and invertebrates are appropriately represented in the test systems and if they concern substances subject to transient exposure. They are then directly applicable for the derivation of M AC-EQSs. For this purpose, the NOEAEC can be used as it represents the highest initial concentration that causes no ecologically relevant effects. 

Ecological effects data may come from a variety of sources. Relevant sources of information include field observations (e.g., fish or bird kills, changes in aquatic community structure), field tests (e.g., microcosm or mesocosm tests), laboratory tests (e.g., single species or microcosm tests), and chemical structure-activity relationships. Available information on ecological effects can help focus the assessment on specific stressors and on ecological components that should be evaluated. 

Microcosm/Mesocosm Testing with Aquatic Organisms... 

The differential sensitivity of aquatic species to surfactants (as illustrated in the toxicity ranges table) can lead to misinterpretations of the overall ecotoxicity of surfactants. Recent novel approaches have used small-scale ecosystems which are surveyed for the effects on a broader range of aqnatic organisms. This stategy, called mesocosm testing, has been nsed for a C12-13AE65 surfactant, and tests produced a mesocosm NOEC of 0.28 mg [29]. 

In the quest for better methods of establishing the environmental safety (or otherwise) of chemicals, interest has grown in the use of microcosms and meso-cosms—artificial systems in which the effects of chemicals on populations and communities can be tested in a controlled way, with replication of treatments. Mesocosms have been defined as bounded and partially enclosed outdoor units that closely resemble the natural environment, especially the aquatic environment (Crossland 1994). Microcosms are smaller and less complex multispecies systems. They are less comparable with the real world than are mesocosms. Experimental ponds and model streams are examples of mesocosms (for examples, see Caquet et al. 2000, Giddings et al. 2001, and Solomon et al. 2001). The effects of chemicals at the levels of population and community can be tested in mesocosms, although the extent to which such effects can be related to events in the natural environment is questionable. Although mesocosms have been developed by both industrial... 

Another issue is the development and refinement of the testing protocols used in mesocosms. Mesocosms could have a more important role in environmental risk assessment if the data coming from them could be better interpreted. The use of biomarker assays to establish toxic effects and, where necessary, relate them to effects produced by chemicals in the field, might be a way forward. The issues raised in this section will be returned to in Chapter 17, after consideration of the individual examples given in Part 2. 

In a similar way, an integrated biomarker approach has a role when carrying out experiments in mesocosms. Under these controlled conditions, behavioral effects of neurotoxic pollutants, acting singly or in combination, can be monitored and compared with data on predator-prey relationships and effects at the population level. The employment of mechanistic biomarker assays can facilitate comparisons between results obtained in mesocosms and other data obtained in the field or in laboratory tests. Here is one way of attempting to answer the difficult question— how comparable are mesocosms to the real world ... 

The relationship between biomarker responses and effects at the population level can be tested in both field experiments and more controlled experiments in mesocosms. It may be possible to define thresholds for biomarker assays performed on indicator species, above which population effects have been shown to occur. Indicator species may be either free living or deployed. The advantage of the latter is... 

An approach that has gained attention recently is the use of model ecosystems microcosms, mesocosms, and macrocosms for testing chemicals (Chapter 4,... 

Section 4.5). Of these, mesocosms have stimulated the greatest interest. In these, replicated and controlled tests can be carried out to establish the effects of chemicals upon the structure and function of the (artihcial) communities they contain. The major problem is relating effects produced in mesocosms to events in the real world (see Crossland 1994). Nevertheless, it can be argued that mesocosms do incorporate certain relationships (e.g., predator/prey) and processes (e.g., carbon cycle) that are found in the outside world, and they test the effects of chemicals on these. Once again, the judicious use of biomarker assays during the course of mesocosm studies may help to relate effects of chemicals measured by them with similar effects in the natural environment. 

Krabbeiihoft DP, Orem W, Aiken G, Gilmour CG. 2004. Unraveling the complexities of mercury methylation in the Everglades the use of mesocosms to test the effects of new mercury, sulfate, and organic carbon. Proc 7th Int Conf Mercury Pollut, RMZ-MG, 51(l-3) June2004. 

Webber, E.C., W.G. Deutsch, D.R. Bayne, and W.C. Seesock. 1992. Ecosystem-level testing of a synthetic pyrethroid insecticide in aquatic mesocosms. Environ. Toxicol. Chem. 11 87-105. 

However, the effect of a harmful compound should be studied with respect to the community level, not only for the organism tested. Tests with several species are realized in microcosm and mesocosm studies. Mesocosms are larger with respect to both the species number and the species diversity and are often performed outdoors and under natural conditions. 

Kraft mill using 100% chlorine dioxide New and old wood pulp bleaching employing various bleach sequences Coastal fish community Mesocosm and fish biomarker tests High levels of mortality and low embryo quality Elemental chlorine containing bleach sequence, CEHDED was the most toxic Sandstrom, 1994 [25] Tana et ah, 1994 [26]... 

Tana, J. Rosemarin, A. Lehtinee, K.-J. Hardig, J. Grahn, O. Landner, L. Assessing impacts on Baltic coastal ecosystems with mesocosm and hsh biomarker tests a comparison of new and old pulp bleaching technologies. Sci. Total. Environ. 1994, 145, 213-214. 

Laboratory toxicity tests have been developed and conducted over the past decades to demonstrate adverse effects that chemicals can have on biological systems. Along with other complementary tools of ecotoxicology available to measure (potential or real) effects on aquatic biota (e.g., microcosm, mesocosm and field study approaches with assessment of a variety of structural and/or functional parameters), they have been, and continue to be, useful to indicate exposure-effect relationships of toxicants under defined, controlled and reproducible conditions (Adams, 2003). 

In most cases, limited information is available regarding the toxic effects of chemicals. Empirical guidelines are then used in an attempt to protect most of the aquatic ecosystem s biota. The regulation of chemicals, for instance, generally uses safety factors from 10 to 1000 depending on the number of species tested. Mesocosm studies or comparisons with real field situations are accepted with lower safety factors on a case by case basis, since these studies reduce the uncertainty linked to the relevance of laboratory models in terms of site-specific data. 

WASTOXHAS was developed for assessing leaching hazardous impact of wastes in laboratory and field situations. It is a part of a tiered approach (Fig. 1). It assumes that classical batch leaching tests (see for example Sahuquillo et al., 2003), followed by application of relevant bioassays, have been initially undertaken for i) deciding to continue ecotoxic hazard assessment and ii) selecting adequate and sensitive bioassays. It can be eventually followed by a more complex and elaborate hazard assessment scheme based on microcosms or mesocosms. ... 

Single species tests and tests using bioassay batteries are called lower-tier tests.19 But in order to carry out a more stringent examination of the complex interactions between potentially toxic chemical compounds and organisms inhabiting specific ecosystems, experiments are sometimes carried out in microcosms and mesocosms the literature describes these as higher-tier tests.19... 

Surface water estimated t/2 = 9.9-32 d in surface waters at various locations in case of a first order reduction process t/2 = 3-30 d in rivers, t,/2 = 30-300 d in lakes and ground waters (Zoeteman et al. 1980) t,/2 = 25 d in spring at 8-16°C, 14 d in summer at 20-22°C and 12 d in winter at 3-7°C when volatilization dominates, and t/2 = 12.1 d and 12.0 d for experiments with and without HgCl2 as poison respectively in September 9-15 in marine mesocosm (Wakeham et al. 1983) t,/2 = 4320-8640 h, based on aerobic river die-away test data (Mudder 1981 quoted, Howard et al. 1991) and saltwater sample grab data (Jensen Rosenberg 1975 quoted, Howard et al. 1991) calculated t/2 = 10 d and 32 d concentration reduction between sampling points on the Rhine River and a lake in the Rhine basin, respectively (Zoeteman et al. 1980 quoted, Howard 1990) t,/2(aerobic) = 180 d, t/2(anaerobic) = 98 d in natural waters (Capel Larson 1995). 

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