Ring-testing and field-validation of a terrestrial model ecosystem (TME)--an instrument for testing potentially harmful substances: effects of carbendazim on soil microbial parameters.

The effects of carbendazim on substrate induced respiration (SIR), dehydrogenase activity (DHA), phosphatase activity and thymidine incorporation by bacteria were evaluated in an experiment with an open intact Terrestrial Model Ecosystem (TME) and in a simultaneous field-validation study. Experiments were performed on four different European soils in Germany, The Netherlands, United Kingdom and Portugal. Data analysis focused on (i) detecting differences between experiments, especially in control values, (ii) checking similarity in data variability at each treatment level between experiments and (iii) analysing the resemblance of response to the model chemical in both experiments. Results obtained showed that control values from TME experiments were similar to those obtained on the respective field site, in most of the comparisons made for SIR, DHA and thymidine incorporation. Phosphatase activity revealed more differences, but values of both experiments had the same order of magnitude. At least part of the variation could be explained from the correlation of the microbial parameters with soil moisture content. Comparisons on data variability also revealed the absence of significant differences between experiments in all parameters in most cases, indicating that TMEs were able to represent the spatial variability found in the field. Effects of carbendazim, when occurring, were observed at treatment levels exceeding the highest recommended application rate of 0.36 kg a.i./ha. Effects on SIR and DHA were observed early in time, but effects on phosphatase activity and thymidine incorporation rate were found 8 or 16 weeks after chemical application. These effects were mild, and rarely a 50% inhibition on any of these parameters was seen at carbendazim dosages up to 87.5 kg a.i./ha. The response to the model chemical in TMEs and field plots was similar in most cases. These results give promising prospects for the use of TMEs as an integrative tool in higher tier levels of different assessment schemes.