Las presiones vienen del norte

The fate of chemicals was examined in combinations of open and closed TME with homoge- nous soil (LICHTENSTEIN et al.1982, LICHTENSTEIN et al.1983). Some of the combined ap-

proaches represented very extensive studies, funded by national authorities. HEISE et al.

(1988) were instructed by the Federal Biological Office of Germany, the work of MIETH et al.

(1993) was funded by the German Federal Environment Agency, dealing with combinations of closed, disturbed and intact soil columns. It became obvious that these studies included a great variety of ecotoxicological, microclimatic, chemical, biological and ecological end- points; the combination of several different approaches should serve as an estimate of the rep- resentativeness of different environmental conditions, vegetation units or soil properties. ED-

WARDS et al.(1998) described very similar systems containing sieved soil and reduced fauna

and flora, as well as systems consisting of intact soil cores with diverse flora and fauna to assess the impact of chemicals more realistically. They proposed a battery of different func- tional and structural measurements and concluded the systems as suitable for use in a tiered approach to assess the risk of new pesticides. WEYERS &SCHUPHAN (1998) examined systems that were especially designed to calculate the variability of endpoints expressed as the coeffi- cient of variance in artificially composed closed and open model ‘ecosystems’ equipped with an artificially introduced combination of grass species, arthropods and microorganisms. They concluded that the apparently high variation could be lowered with more experience of the experimenters and that effect levels of 10-20 % could be observed in such systems. There was

Scope, aim and purpose of TME studies

less attention on field studies in this survey but some of the model ecosystem studies were accompanied by field studies or the results were compared to field studies. Some authors that used combinations of different TME approaches paid special attention to the question whether TME could predict the field or semi-field situation. Others only wanted to measure the degra- dation products which occurred to less extent in the laboratory than in the field (e.g. by photo- lytic reactions that could not occur in glass chambers that filter the UV-light, compare NASH

&BEALL 1980b). JACKSON & LEVIN (1979), JACKSON et al. (1979), TOLLE et al. (1983) or

KLOSKOWSKY et al.(1981) calibrated the results of experiments with open or closed TME by

a corresponding field study.Theyconcluded that TME could represent the field situation ap- propriately and would offer several of the following advantages compared to field studies. That is the contaminated soil could be controlled and separated, and therefore pollution of the environment could be avoided. The mass balance of the test item could be calculated more precisely. Relatively small systems would allow for a centralized testing of several ecosys- tems and would be cost-effective. Unfortunately, it seemed not to be possible to predict the long-term behaviour of chemicals. The pollutants were ranked in terms of the intensity of ob- served effects. A combination of open TME with sieved soil and intact soil cores compared to field studies was used to determine the survival of artificially released microorganisms in the environment. Intact soil cores provided better conditions for the survival of Pseudomonas aureofaciens than TME consisting of sieved and dried soil. The former systems maintained stable populations of microorganisms for up to three months use of intact TME (ANGLE et al.

1995). In the opinion of ANGLE et al., the intact TME may reflect the field situation sufficient- ly (these finding was later confirmed by further experiments of GAGLIARDI et al.(2001)with another species Pseudomonas chlororaphis. The extrapolation to the field situation may be restricted to studies on chemical fate, to single species systems or to very realistic approaches. However, often the soil structure was disturbed, the soil was maintained under laboratory conditions, and was therefore not comparable to normal outdoor circumstances, or there was only a small, isolated part of natural communities introduced in the experiments. This could lead to overemphasize the role of a few, less representative species or one could disregard the complex mutual interrelationships between biotic and abiotic factors. LAAKSO et al. (1995) conducted several ‘ecological’ experiments on the topic ‘community structuring factors’. Some of the above authors had to put their former results into perspective while repeating the experiments including more endpoints or more advanced set-ups and obtaining inconsisten- cies. For example, TOLLE et al.1983 found their TME very predictive in terms of trace ele-

Scope, aim and purpose of TME studies

30

et al. 1985), they detected only a poor accuracy in predicting plant responses in the field. However, they concluded that corrections on the experimental design would be necessary.

WILSON et al.(1987) obtained results that overestimated the biotransformation of bromoform

and carbon tetrachloride while the behaviour of tetrachloroethylene and hexachloroethane was simulated accurately using their TME approach. Following the authors conclusions, this was due to natural variability and poor replication. As mentioned by many authors, the natural variation of biological results has to be taken into account if one aims to conduct well- controlled and reproducible experiments.