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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
Review of available and potential test methods
Limitations of the current trigger pathway
Alternatives ?
Assessing effects of pesticides onthe breakdown of organic matter
“ 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)
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
Tests relevant to OM breakdown ?
Litter bag
Minicontainer
Cotton-strip assay
Isotopes
Bait lamina
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)
Minicontainer
Similar to litter bag, but smaller PVC containers
Principle:
Duration: 2 - 6 months
Cotton strip assay
Measurement of cellulose decompositionPrinciple:
Factors measured:
Comments: Fungi may increase tensile strength
Loss of tensile strength of cottonstrips buried in soil
15N, 14C, 13C Isotopes
Detection of isotopes from labelled OMwhich is mixed directly into soil
Principle:
Comments: Mainly applied in laboratory studies
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
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
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…
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
• 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
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
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
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 ?
• 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
• 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
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
Could functional lower or middle tier tests be used to predict OM breakdown ?
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
Simultaneous multi-substrate assays for predicting OM breakdown ?
Microbial community profiling
using Biolog analyses
Catabolic Response Profile - CRP
Possible approaches
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
Biolog CRP
Enzyme activity profiles
for test and control soils
Catabolic activity profiles
for test and control soils
Risk assessment scheme ?
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 !
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 !