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Assessing effects of pesticides on the breakdown of organic matter

Assessing effects of pesticides on the breakdown of organic matter. Geoff Frampton Susan Jones University of Southampton, UK Thomas Knacker Joerg Roembke Bernhard Foerster ECT Oekotoxikologie, Germany Juliane Filser Holger Mebes University of Bremen, Germany. Funded by.

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Assessing effects of pesticides on the breakdown of organic matter

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  1. Assessing effects of pesticides on the breakdown of organic matter Geoff Frampton Susan Jones University of Southampton, UK Thomas Knacker Joerg Roembke Bernhard Foerster ECT Oekotoxikologie, Germany Juliane Filser Holger Mebes University of Bremen, Germany Funded by

  2. Assessing effects of pesticides on the breakdown of organic matter Review of available and potential test methods Limitations of the current trigger pathway Alternatives ?

  3. Authorisations Directive 91 / 414 / EEC (as amended by 96 / 12 / EC) Annex III (Formulated products) Point 10.6.2 (Effects on other soil non-target organisms) “ An assessment of effects on breakdown of organic matter is required …” based on chemical persistence data (DT90 field)

  4. DT90 < 100 days Test not required DT90 100 to 365 days • exposurein soil is likely, and • riskto soil microflora, earthworms, or • other soil fauna (e.g. Collembola) Test required IF… DT90 > 365 days Test required Test for pesticide impact on OM breakdown:

  5. Tests relevant to OM breakdown ? Litter bag Minicontainer Cotton-strip assay Isotopes Bait lamina

  6. Litter bags Principle: OM (e.g. straw) enclosed in gauze bags Exposure of OM: On soil surface or buried Factors measured: Litter mass loss (rate) Duration: Typically 6-12 months Comments: Mesh size and exposure crucial for realism

  7. Minicontainer Principle: Similar to litter bag, but smaller PVC containers Duration: 2 - 6 months

  8. Cotton strip assay Principle: Measurement of cellulose decomposition Factors measured: Loss of tensile strength of cotton strips buried in soil Comments: Fungi may increase tensile strength

  9. 15N, 14C, 13C Isotopes Principle: Detection of isotopes from labelled OM which is mixed directly into soil Comments: Mainly applied in laboratory studies

  10. Bait-lamina method Principle: Detects feeding activity of soil organisms Factors measured: OM bait removed from small (1mm diam.) holes in PVC strips inserted into soil Duration: 1-4 weeks

  11. Assessment criteria 1. Relevance to RA scheme 2. Ecological relevance 3. Experience 4. Flexibility 5. Robustness 6. Practicability 7. Sensitivity 8. Data assessment 9. Reproducibility, repeatability 10. Standardisation, validation

  12. ? ? ? ? ? ? ? ? ? ? ? ? ? ? Litter bag Mini- container Cotton strip Bait- lamina Isotopes 1. Relevance to ERA 2. Ecological relevance 3. Experience 4. Flexibility 5. Robustness 6. Practicability 7. Sensitivity 8. Data assessment 9. Reproducibility, repeatability 10. Standardisation, validation

  13. Conclusion… Litter bag is the most appropriate method at present for assessing effects of pesticides on OM breakdown But…

  14. Limitations of the litter-bag method Relevant only to early (microbially-mediated) stages of OM breakdown Acceptability of effects on mass loss are unclear Realistic simulation of exposure for repeat-application chemicals is difficult

  15. Limitations of the litter-bag method • Relevant only to early mass loss phase of OM breakdown; does not assess later mineralisation Acceptability of effects on mass loss are unclear Realistic simulation of exposure for repeat-application chemicals is difficult

  16. Limitations of the litter-bag method Relevant only to early (microbially-mediated) stages of OM breakdown • Acceptability of effects on mass loss are unclear Realistic simulation of exposure for repeat-application chemicals is difficult

  17. Limitations of the litter-bag method Relevant only to early (microbially-mediated) stages of OM breakdown Acceptability of effects on mass loss are unclear • Realistic simulation of exposure for repeat-application chemicals is difficult

  18. Limitations of the overall RA scheme Are soil fauna tests appropriate as a trigger for the OM breakdown test ? relevance to OM breakdown unclear representativeness of test species unproven functional redundancy and ecological complexity

  19. Limitations of the overall RA scheme Are soil fauna tests appropriate as a trigger for the OM breakdown test ? • relevance to OM breakdown • unclear representativeness of test species unproven functional redundancy and ecological complexity

  20. Limitations of the overall RA scheme Are soil fauna tests appropriate as a trigger for the OM breakdown test ? • relevance to OM breakdown • unclear • representativeness of test • species unproven functional redundancy and ecological complexity

  21. Limitations of the overall RA scheme Are soil fauna tests appropriate as a trigger for the OM breakdown test ? • relevance to OM breakdown • unclear • representativeness of test • species unproven • functional redundancy and • ecological complexity

  22. Could functional lower or middle tier tests be used to predict OM breakdown ?

  23. Existing tests related to system function FURTHER TESTS : Nitrification Soil respiration Soil enzymes TIER I TESTS : N transformation C mineralization ?

  24. Enzymes as predictors of OM breakdown ? YES … Because some enzymes have clear roles in OM turnover YES … Because some enzymes (e.g. lignocellulases) are specific to the decomposer fauna BUT … Single enzyme tests are poor predictors of pesticide effects on soil processes

  25. Simultaneous multi-substrate assays for predicting OM breakdown ?

  26. Possible approaches Microbial community profiling using Biolog analyses Catabolic Response Profile - CRP

  27. Test and control soils added to range of enzyme substrates in microtiter plate Range of substrates added to test and control soils After 1 week incubation, enzyme activities in test and control soils determined colorimetrically Over 12h, substrate-induced respiration measured for all substrates CRP Biolog

  28. Enzyme activity profiles for test and control soils Catabolic activity profiles for test and control soils Risk assessment scheme ? CRP Biolog

  29. Standard methods available, homogeneous substrates Substrate profile could be customised for OM processing Rapid results cons Biolog is restricted to culturable microorganisms Predictive capability for OM processing requires clarification Refined method would require validation …these limitations are no worse than for the existing single-species tests ! Biolog / CRP - pros

  30. Concluding remarks The litter-bag method is the most appropriate… But it still has key limitations and uncertainties The OM breakdown trigger pathway for medium-persistence substances does not make ecological sense Could Biolog and / or CRP be more appropriate ‘middle-tier’ (functional) methods than the existing (structural) tests ? Thanks for listening !

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