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 !