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Assessing effects of pesticides onthe breakdown of organic matter
Geoff FramptonSusan JonesUniversity of Southampton, UK
Thomas KnackerJoerg RoembkeBernhard FoersterECT Oekotoxikologie, Germany
Juliane FilserHolger MebesUniversity of Bremen, Germany
Funded by
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Review of available and potential test methods
Limitations of the current trigger pathway
Alternatives ?
Assessing effects of pesticides onthe breakdown of organic matter
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“ An assessment of effects on breakdown oforganic matter is required …”
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)
based on chemical persistence data (DT90 field)
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Test for pesticide impact on OM breakdown:
• exposure in soil is likely, and
• risk to soil microflora, earthworms, or
other soil fauna (e.g. Collembola)
DT90 100 to 365 days
Test requiredIF…
DT90 < 100 days Test not required
DT90 > 365 days Test required
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Tests relevant to OM breakdown ?
Litter bag
Minicontainer
Cotton-strip assay
Isotopes
Bait lamina
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Litter bags
OM (e.g. straw) enclosed in gauze bagsPrinciple:
Duration:
Factors measured:
Exposure of OM: On soil surface or buried
Comments:
Typically 6-12 months
Mesh size and exposure crucial for realism
Litter mass loss (rate)
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Minicontainer
Similar to litter bag, but smaller PVC containers
Principle:
Duration: 2 - 6 months
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Cotton strip assay
Measurement of cellulose decompositionPrinciple:
Factors measured:
Comments: Fungi may increase tensile strength
Loss of tensile strength of cottonstrips buried in soil
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15N, 14C, 13C Isotopes
Detection of isotopes from labelled OMwhich is mixed directly into soil
Principle:
Comments: Mainly applied in laboratory studies
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Bait-lamina method
Detects feeding activity of soil organismsPrinciple:
Factors measured:
Duration:
OM bait removed from small (1mm diam.)holes in PVC strips inserted into soil
1-4 weeks
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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
Assessment criteria
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Litter bag
Mini-container
Cottonstrip Isotopes
Bait-lamina
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
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Litter bag is the most appropriatemethod at present for assessingeffects of pesticides on OMbreakdown
Conclusion…
But…
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Relevant only to early (microbially-mediated) stages of OM breakdown
Limitations of the litter-bag method
Acceptability of effects on mass loss are unclear
Realistic simulation of exposure for repeat-application chemicals is difficult
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• Relevant only to early mass loss phase of OM breakdown; does not assess later mineralisation
Limitations of the litter-bag method
Acceptability of effects on mass loss are unclear
Realistic simulation of exposure for repeat-application chemicals is difficult
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Relevant only to early (microbially-mediated) stages of OM breakdown
Limitations of the litter-bag method
• Acceptability of effects on mass loss are unclear
Realistic simulation of exposure for repeat-application chemicals is difficult
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Relevant only to early (microbially-mediated) stages of OM breakdown
Limitations of the litter-bag method
Acceptability of effects on mass loss are unclear
• Realistic simulation of exposure for repeat-application chemicals is difficult
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Limitations of the overall RA scheme
relevance to OM breakdownunclear
representativeness of testspecies unproven
functional redundancy andecological complexity
Are soil fauna tests appropriate as a trigger for the OM breakdown test ?
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• relevance to OM breakdownunclear
representativeness of testspecies unproven
Limitations of the overall RA scheme
Are soil fauna tests appropriate as a trigger for the OM breakdown test ?
functional redundancy andecological complexity
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• relevance to OM breakdownunclear
• representativeness of testspecies unproven
Limitations of the overall RA scheme
Are soil fauna tests appropriate as a trigger for the OM breakdown test ?
functional redundancy andecological complexity
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Are soil fauna tests appropriate as a trigger for the OM breakdown test ?
• relevance to OM breakdownunclear
• representativeness of testspecies unproven
• functional redundancy andecological complexity
Limitations of the overall RA scheme
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Could functional lower or middle tier tests be used to predict OM breakdown ?
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Existing tests related to system function
FURTHER TESTS :
Nitrification
Soil respiration
Soil enzymes
TIER I TESTS :
N transformation
C mineralization
?
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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
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Simultaneous multi-substrate assays for predicting OM breakdown ?
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Microbial community profiling
using Biolog analyses
Catabolic Response Profile - CRP
Possible approaches
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Biolog CRP
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
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Biolog CRP
Enzyme activity profiles
for test and control soils
Catabolic activity profiles
for test and control soils
Risk assessment scheme ?
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Standard methods available, homogeneous substrates
Substrate profile could be customised for OM processing
Rapid results
Biolog / CRP - pros
consBiolog 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 !
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The litter-bag method is the most appropriate…
Concluding remarks
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 !