Normes OEPP EPPO Standards · Normes OEPP EPPO Standards Environmental risk assessment scheme for plant ... phytosanitaires pour l’environnement a été mis au point par un Groupe

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Blackwell Publishing Ltd.Oxford, UKEPPBulletin OEPP/EPPO Bulletin1365-2338OEPP/EPPO, 200333Original ArticleEPPO StandardsEnvironmental risk asessment for plant protection products

Organisation Européenne et Méditerranéenne pour la Protection des PlantesEuropean and Mediterranean Plant Protection Organization

Normes OEPP EPPO Standards

Environmental risk assessment scheme for plant protection products Système pour l’évaluation du risque des produitsphytosanitaires pour l’environnement

PP 3/3 (revised)PP 3/13

Organisation Européenne et Méditerranéenne pour la Protection des Plantes1, rue Le Nôtre, 75016 Paris, France

148 Environmental risk assessment of plant protection products

© 2003 OEPP/EPPO,


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Approval

EPPO Standards are approved by EPPO Council. The date of approvalappears in each individual standard.

Review

EPPO Standards are subject to periodic review and amendment. Thenext review date for this set of EPPO Standards is decided by the EPPOWorking Party on Plant Protection Products

Amendment record

Amendments will be issued as necessary, numbered and dated. The datesof amendment appear in each individual standard (as appropriate).

Distribution

The EPPO Standards making up the EPPO/Council of Europedecision-making scheme for the environmental risk assessment ofplant protection products are distributed by the EPPO Secretariat to allEPPO member governments. Copies are available to any interested personunder particular conditions upon request to the EPPO Secretariat.

Scope

The EPPO Standards making up the EPPO/Council of Europedecision-making scheme for the environmental risk assessment of plantprotection products are intended to be used by National PlantProtection Organizations or equivalent national authorities, in theircapacity as bodies responsible for the registration of plant protectionproducts, including an evaluation of the environmental risks arisingfrom their use.

Outline of requirements

The decision-making scheme for the environmental risk assessment ofplant protection products was developed by a joint Panel of EPPO andthe Council of Europe and provides guidelines on how to assess thepotential impact of a particular plant protection product on variousdifferent elements of the environment, each element being presented asa separate standard. The assessment scheme is for use by agrochemicalcompanies and by regulatory authorities, and aims to:

1

guide assessors on the questions that should be addressed, and thedata that may need to be requested from registrants;

2

provide information on the test methods and approaches that aresuitable in each case;

3

indicate how the data should be interpreted in a consistent manner,involving expert judgement where appropriate;

4

produce a reliable assessment of environmental risk, as a suitable aidto risk management (though the assessment scheme will not provideall the information needed for decisions on the acceptability of plantprotection products).The Standards in the scheme provide a set of flexible procedures that

can be adapted for use in various ways according to the priorities indifferent countries, yet retain the consistency of a common framework.They are not based on a series of fixed, automatic ‘triggers’ for testingrequirements, but are able to take full account of the particular featuresof each plant protection product, and to make use of expert judgementwhen necessary.

Approbation

Les Normes OEPP sont approuvées par le Conseil de l’OEPP. La dated’approbation figure dans chaque norme individuelle.

Révision

Les Normes OEPP sont sujettes à des révisions et des amendementspériodiques. La prochaine date de révision de cette série de Normes OEPPest décidée par le Groupe de travail sur les produits phytosanitaires.

Enregistrement des amendements

Des amendements sont préparés si nécessaires, numérotés et datés. Lesdates de révision figurent (si nécessaire) dans chaque norme individuelle.

Distribution

Les Normes OEPP composant le système de décision OEPP/Conseil del’Europe pour l’évaluation du risque des produits phytosanitaires pourl’environnement sont distribuées par le Secrétariat de l’OEPP à tous lesEtats membres de l’OEPP. Des copies sont disponibles, sous certainesconditions, auprès du Secrétariat de l’OEPP pour toute personne intéressée.

Champ d’application

Les Normes de l’OEPP composant le système de décision OEPP/Conseilde l’Europe pour l’évaluation du risque des produits phytosanitairespour l’environnement sont destinées aux Organisations Nationales deProtection des Végétaux, en leur qualité d’autorités responsables del’homologation des produits phytosanitaires, qui comporte une évalu-ation des risques pour l’environnement liés à l’utilisation de ces produits,et aux firmes agrochimiques demandant l’homologation de leurs produits.

Vue d’ensemble

Le système de décision pour l’évaluation du risque des produitsphytosanitaires pour l’environnement a été mis au point par un Grouped’experts conjoint OEPP et Conseil de l’Europe. Il donne desrecommandations sur la manière d’évaluer l’impact potentiel d’unproduit phytosanitaire donné sur diverses composantes de l’environ-nement, chacun de ces composantes étant traitée dans une normedistincte. Le système d’évaluation a pour objectif de:

1

guider les responsables des évaluations sur les questions à aborder etsur les données que les demandeurs de l’homologation peuvent avoirà fournir;

2

donner des informations sur les méthodes d’essai et les approchesappropriées dans chaque cas;

3

montrer comment interpréter les données d’une manière cohérente,en ayant recours au jugement d’experts lorsque cela s’impose;

4

permettre une évaluation fiable du risque pour l’environnement,pouvant faciliter la gestion du risque (même si le système d’évalua-tion ne fournira cependant pas toutes les informations nécessairespour décider de l’acceptabilité des produits phytosanitaires).Les Normes OEPP qui composent le système présentent une série de

procédures souples qui peuvent être adaptées et utilisées de différentesmanières dans différents pays, tout en conservant la cohérence d’un cadrecommun. Elles ne reposent pas sur une série de seuils fixes définissantautomatiquement la nécessité de conduire des essais, mais permettent detenir compte de l’ensemble des caractéristiques particulières de chaqueproduit phytosanitaire et de recourir au jugement d’experts lorsque celas’impose.

EPPO Standards 149

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Normes OEPP déjà existantes dans cette série

Les 10 premières Normes de ce système ont initialement été publiéesdans le


en 1993/1994:OEPP/EPPO (1993) Système pour l’évaluation des effets non inten-

tionnels des produits phytosanitaires sur l’environnement. Chapitres1–6, 8 & 10.


23

, 1–165.OEPP/EPPO (1994) Système pour l’évaluation des effets non intent-

ionnels des produits phytosanitaires sur l’environnement. Chapitres7, 9 & 11.


24

, 1–87.Entre 1994 et 2002, ces textes ont d’abord été reformatés sous forme

de Normes OEPP, pour former la série PP 3. Ces Normes ont ensuiteété mises à jour pour tenir compte des évolutions dans ce domaine etdeux Normes supplémentaires ont été approuvées. Les chapitres 7 et 8ont été combinés. Un premier groupe de ces Normes nouvelles etrévisées a été publié comme suit:

PP 3/1 (2) Chapter 1: Introduction.


33

,103–112

PP 3/2 (2) Chapter 2: Guidance on identifying aspects of environmentalconcern.


33

, 113–114PP 3/9 (2) Chapter 9: Non-target terrestrial arthropods.


33

, 131–140PP 3/10 (2) Chapter 10: Honeybees.


33

,141–146

PP 3/12 (1) Chapter 3: Air.


33

, 115–130.

Les Normes publiées ici complètent la série. Bien que la série originalede Normes ait été publiée sous forme bilingue, en anglais et en français,la présente série n’est publiée qu’en anglais. Les nouvelles versionsfrançaises de ces Normes seront publiées ultérieurement. Les anciennesversions, anglaises et françaises, des Normes de cette série sont retirées.

Existing EPPO Standards in this series

The first 10 Standards in the scheme were originally published in


in 1993/1994:OEPP/EPPO (1993) Decision-making scheme for the environmental

risk assessment of plant protection products. Chapters 1–6, 8 & 10.


23

, 1–165.OEPP/EPPO (1994) Decision-making scheme for the environmental

risk assessment of plant protection products. Chapters 7, 9 & 11.


24

, 1–87.Over the period from 1994 to 2002, these texts were first reformatted

as EPPO Standards, to constitute Series PP 3. All the Standards werethen updated to take account of new developments and two additionalStandards were approved. Chapters 7 and 8 were combined. A first setof these new and revised standards was published as follows:

PP 3/1 (2) Chapter 1: Introduction.


33

,103–112

PP 3/2 (2) Chapter 2: Guidance on identifying aspects of environmentalconcern.


33

, 113–114PP 3/9 (2) Chapter 9: Non-target terrestrial arthropods.


33

, 131–140PP 3/10 (2) Chapter 10: Honeybees.


33

,141–146

PP 3/12 (1) Chapter 3: Air.


33

, 115–130.

The present set completes the Series. Although the original set ofStandards was published bilingually in English and French, the presentset is now published only in English. The new French versions of theseStandards will be published at a later date. The corresponding old Eng-lish and French versions of the Standards in this set are withdrawn.

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151

Blackwell Publishing Ltd.

European and Mediterranean Plant Protection Organization PP 3/3(2)Organisation Européenne et Méditerranéenne pour la Protection des Plantes

Environmental risk assessment scheme for plant protection products

Chapter 4: Soil

Specific scope

This standard provides a process for assessing the exposurepresented by a given plant protection product to soil.

Specific approval and amendment

First approved in 1992-09.Edited as an EPPO standard in 1998.Revised in 2002-09.

Introduction

Plant protection products can reach the soil in target areas bydirect application to the soil surface or by run-off from treatedcrop surfaces, but can also contaminate non-target areas such asgroundwater, surface water and soils adjacent to treated fields.This contamination can occur by transfer from treated areas viathe air (spray drift, volatilization and deposition), by leachingand by run-off. The purpose of this subscheme is to estimate ordetermine concentrations in soil, as one essential part of everyenvironmental risk assessment. The behaviour of a plantprotection product in the plough layer of the soil determines itspossible dispersion in the environment, especially towards air,surface water and groundwater.

This subscheme determines the concentration of a plantprotection product in the surface horizon (plough layer) of soilas a function of time (Ct), as well as concentrations beyond thetreated (target) area due to run-off and leaching. It does notcover estimation or determination of concentrations in non-targetsoil caused by transport via the air (spray drift, volatilization).The data on predicted and/or determined soil concentrations, inconjunction with ecotoxicity data, is used to assess the risk tovarious soil organisms, higher plants and surface water organismswithin other subschemes. In a separate section more detail isgiven on the relationships with the other subschemes.

In most cases, the plough layer is aerobic but in other cases(e.g. paddy rice cultures) anaerobic conditions exist within theplough layer. This subscheme is mainly intended to assess fateand behaviour in aerobic soils but can also be used to assess fateand behaviour for anaerobic soil conditions.

The residues considered are the active substance(s) of theproduct and any transformation products occurring inappreciable quantities and likely to be relevant. Figure 1presents the general structure of this subscheme on soil.

Relationship with other subschemes

The subscheme on soil is intended to provide input onpossible environmental concentrations to the following sub-schemes (resulting from the field use of a plant protectionproduct).

Groundwater (Chapter 5)

The subscheme on groundwater focuses on the estimation orcalculation of predicted environmental concentrations in uppergroundwater. Data on the rate of transformation and adsorptionin topsoil is taken from Module B of the present subscheme.The same data is used in the groundwater scheme to estimate theconcentrations discharged via drains for input into the surfacewater scheme.

Surface water and sediment (Chapter 6)

The subscheme on surface water and sediment is used toestimate or calculate predicted environmental concentrations insurface water and sediment, resulting from the differentpathways of entry. One of these pathways is run-off from thesoil of the treated field. This run-off is calculated in Module Cof the present subscheme.

Soil organisms and functions (Chapter 8)

The subscheme on soil organisms and functions covers theassessment of possible adverse effects due to the use of plant

Fig. 1 Schematic presentation of the structure of the subscheme on soil, also indicating the other subschemes to which output is delivered.

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protection products within the treated fields (target areas).Such assessments are based on predicted concentrations in topsoil.These concentrations, either initial or as a function of time afterapplication, are calculated within Module A of this subscheme.

Non-target higher plants (Chapter 12)

The subscheme on non-target higher plants is used to assessadverse effects beyond the edge of a treated field, due to the useof plant protection products within the field. Within thesubscheme on higher plants, different routes of exposure aredistinguished. One deals with run-off. This run-off is calculatedwithin the present subscheme on soil.

Processes in the soil environment

Within the soil environment, different processes are involved inthe dissipation and distribution of plant protection products.The processes covered by this subscheme on soil aretransformation and run-off. The subscheme also provides basicdata for the assessment of leaching to groundwater. Otherprocesses such as wind erosion, plant uptake, photochemicaltransformation (on soil and crop surfaces) and wash-off arenot considered for the following reasons:

•

Wind erosion is relevant only in exceptional cases. It is atpresent considered to be too complex to calculate, althoughprogress in this area is expected.

•

Plant uptake, by either leaves (wet or dry) or roots, is coveredby the subscheme on non-target higher plants.

•

The contribution of photochemical transformations to theoverall dissipation of a plant protection product is covered bythe data on dissipation of residues from crops and soils.

•

Wash-off is a process whose quantitative importance cannotcurrently be assessed because of lack of information.

Entrance to the different modules of this subscheme on soil

This subscheme includes separate modules on prediction ofconcentrations in the topsoil (Fig. 2), leaching to groundwater(Fig. 3) and run-off (Fig. 4). In general, all three modules shouldbe entered for each separate assessment but, in some cases,answering the first question of a module will indicate thatfurther assessment within that module is not necessary. Wherepossible, transformation products should also be considered ineach module. The module on the prediction of concentrationsin topsoil (Module A) explicitly includes them but the othersdo not. Interception by the crop is relevant to all three modules.Wash-off is not included for the reasons given above.

Exposure assessment scheme

Details of the product and its pattern of use

1

Take from Chapter 2 the basic information on theproduct and its pattern of use. The active substance is

considered in all cases, and transformation products whererelevant.

go to 2

Indoor treatments

Applications made indoors are not expected to expose fieldsoils significantly to plant protection products. Volatilematerials formed in glasshouses may be released duringventilation and may contaminate non-target areas or soils butsuch situations are covered by the subscheme on Air.

2

Is the treatment conducted indoors (for definition of indoorssee Note 1)?

If yes this subscheme is of no relevanceIf no go to 3

MODULE A: Determination of exposure concentration Ct in topsoil

This module presents the principles and necessary steps usedfor the estimation and determination of Ct. Exposure con-centrations considered in this module can be initial con-centrations after single applications, total concentrations afterrepeated applications, time-weighted average concentrations,etc., depending on the use pattern of a particular product and thetype of input needed in the respective effects chapters.

Possibility of exposure of soil

3

Can the product reach the soil (see Note 2)?

If yes go to 4If no this subscheme is of no relevance

Interception

The crop intercepts plant protection products applied to anagricultural field, as long they are not applied to bare soil.Interception depends on a number of factors, such as formu-lation type, application technique, type of crop, crop stage,and cropping system. Interception may be either small, e.g.in open crops in early growth stages, or substantial, e.g.in a full-grown potato crop. When interception is low, soildeposition at the time of application is high. When inter-ception is high, soil deposition at the time of application islow.

4

Is the plant protection product applied to bare soil (Note 3)?

If yes go to 7If no go to 5

5

Is the plant protection product applied to cropped fields (seeNote 4)?


6

Determine the interception factor (f

I

) (see Note 5).

go to 7

Exposure estimation in topsoil

7

Estimate the exposure concentration in topsoil relevantfor the respective use pattern of the plant protection product(see Note 6). Transfer the outcome to Module B and to

Environmental risk assessment scheme for plant protection products 153

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Fig. 2 Simplified diagram of the subscheme for evaluation of the risk of a plant protection product for soil: Module A (risk of exposure of topsoil).

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Fig. 3 Simplified diagram of the subscheme for evaluation of the risk of a plant protection product for soil: Module B (risk of leaching to groundwater).


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Fig. 4 Simplified diagram of the subscheme for evaluation of the risk of a plant protection product for soil: Module A (risk of run-off).

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Module C (run-off) and also to Chapter 8 (Soil organisms andfunctions).

Where the level of concern is exceeded in that chapter, theexposure assessment is repeated at the next tier (Step 8) and amore exact value provided in respect of that subscheme. Is thelevel of concern exceeded?

If yes go to 8If no exposure of topsoil acceptable

go to 9

Field experiments

Concentrations in the plough layer can be obtained fromboth laboratory and field studies. Laboratory data is normallyalways available, but field studies are generally performed onlywhen indicated by laboratory results. Field data is consideredto represent realistic use situations, whereas concentrationsderived from laboratory data are taken as estimates.

8

Perform an appropriate number of dissipation rate studies insoil under field conditions to determine actual concentrationsin topsoil (see Note 7). Transfer the outcome to Chapter 8(Soil organisms and functions). Is the level of concernexceeded?

If yes

risk from exposure of topsoilIf no

exposure of topsoil acceptablego to 9

9

Transfer outcome of Module A to Module B (leaching togroundwater)

go to 10

MODULE B: Leaching to groundwater

This module provides data for input to Chapter 5 (Groundwater).

Rate of transformation in soil

The transformation rate in soil (DT50, DT90), under eitheraerobic or anaerobic conditions, is determined by laboratorytests. The values of the DT50 or DT90 are used to decide whetheradditional field tests should be performed. Agricultural practicedetermines whether transformation rates for aerobic or anaerobicconditions, or both, are needed to run the subscheme.

10

Perform a transformation pathway study, using one orseveral soils, on the active substance(s) of the product (see Note8) under aerobic and/or anaerobic conditions in the laboratoryto obtain information whether relevant transformation productscan be formed in soil which should be included in the exposureassessment of this subscheme.

go to 1111

Perform an appropriate number of transformation ratestudies in the laboratory to derive DT50

lab

or DT90

lab

values(see Note 9).

go to 12

Mobility in soil

Mobility of the active substance(s) and relevant metabolites insoil depends primarily on the adsorption partition coefficientK

d

, determined by adsorption/desorption studies.

12

Determine the partition coefficient K

d

in the laboratory in anappropriate number of different soils showing a range of organicmatter content and pH (see Note 10). Transfer data obtained in

Steps 10 and 11 to Chapter 5 (Groundwater). Where the levelof concern is exceeded in that chapter, the exposure assessmentis repeated at the next tier (Step 12) and more exact valuesprovided in respect of that subscheme. Is the level of concernexceeded?

If yes go to 13If no leaching to groundwater acceptable

go to 15

Field experiments

13

Perform an appropriate number of dissipation rate studies inthe field and determine DT50

field

or DT90

field

values (see Note11). This information can also be obtained from Step 8 in thissubscheme. Transfer data to Chapter 5 (Groundwater). Is thelevel of concern exceeded?

If yes go to 14If no

leaching to groundwater acceptablego to 15

Additional experiments

In some cases when the level of concern is exceeded in groundwaterafter Step 12, additional experiments under field conditions, suchas lysimeter studies or field leaching studies, may be conducted.

14

Perform field lysimeter experiments or field leaching studiesfollowing the recommended use pattern of the plant protectionproduct (see Note 12). Transfer outcome of experiments to Chapter5 (Groundwater). Is the level of concern exceeded in that chapter?

If yes

risk of leaching to groundwaterIf no

leaching to groundwater acceptablego to 15

15

Transfer outcome of Module A to Module C (run-off)

go to 16

MODULE C: Estimation of run-off

16

Is run-off in the region of concern considered to be arelevant way of transport of applied plant protection productsbeyond the edge of the treated field (target area) (see Note 13)?

If yes go to 17If no this module is of no relevance

go to 2617

Define a scenario for run-off which can be considered to repre-sent a realistic worst case for the region of concern. The scenarioshould include at least the following elements (see Note 14):a realistic rainfall event from many-year meteorological datasets; a realistic soil slope; the soil type, with respect to textureand organic matter content; the time assumed to elapsebetween application and the run-off event; soil cover atapplication.

go to 1818

Take the distance(s) of concern beyond the edge of the fieldfrom the other subschemes which demand input because of run-off (see Note 15).

go to 1919

Is a simple approach to run-off, not related to the substance,sufficient for this stage of assessment (see Note 16)?



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Simple approach not related to the substance

20

Using expert judgement, estimate the percentage of thedose applied to the field that will be transported as a result ofrun-off beyond the edge of the field.

go to 2121

Calculate the concentration in the upper soil layer beyondthe edge of the field (see Note 17). Transfer outcome to Chapter6 (Surface water and sediment), Chapter 8 (Soil organisms andfunctions) and Chapter 12 (Non-target higher plants). Is thelevel of concern exceeded in those chapters?

If yes go to 22If no

risk of run-off acceptable

Approach related to the substance

22

Take from the scenario the period between application andthe run-off event (time lag) (see Note 18).

go to 2323

Calculate from the defined scenario the fraction of the doseapplied, F

DOSE

, that is still present at the time of the run-off event,based on the DT50

lab

or DT50

field

and the time elapsed be-tween application and the run-off event (see Note 19).

go to 2424

Derive the K

oc

for adsorption to soil from the data set (seeNote 10).

go to 2525

Take from Module A (determination of exposure concen-tration in topsoil) the initial concentration (Ci) and correct thisconcentration for F

DOSE

(see Note 20).

go to 2626

Calculate the run-off that will pass the edge of the field (seeNote 21).

go to 2727

Calculate the concentration of the substance in the top layerof the soil beyond the edge of the field (see Note 17). Transferoutcome to Chapter 6 (Surface water and sediment), Chapter 8(Soil organisms and functions) and Chapter 12 (Non-targethigher terrestrial plants). Is the level of concern exceeded inthose chapters?

If yes

risk from run-offIf no

risk from run-off acceptablego to 28

Acceptability of exposure

28

Where exposure concentrations, estimated or determinedaccording to the Modules of this subscheme on soil andtransferred to other subschemes (i.e. Soil organisms and func-tions, Groundwater, Surface water and sediments), do not exceedthe levels of concern in those subschemes, such exposurelevels can be considered acceptable.

Are all exposure levels acceptable?

If yes go to 30If some levels of concern have been exceeded go to 29

Sensitivity

29

Certain of the risk assessments conducted in thesubschemes on Groundwater, Surface water and sediment, Soilorganisms and functions, and Non-target higher terrestrial

plants have exceeded the level of concern and risks havetherefore been identified. It may in these cases be useful toexamine sensitivity, since it is possible that errors inmeasurements, or variations in conditions of use (e.g. soil type,climate, agricultural practice), may alter the conclusions. Insuch cases, some of the assessments in the present subschememay be repeated using values that represent realistic extremesof variation. The necessity for such repeated assessment isindicated by the results of the risk assessments conducted inother subschemes.

go to 30

Risk management

30

If the product cannot reach the soil, there is no exposure andthus negligible risk to soil organisms. The same applies to therisk for groundwater and surface water via the soil, unless someother pathways exist. This conclusion should be passed on tosubschemes on Groundwater, Surface water and sediment andSoil organisms and functions.

Where data has been transferred to other subschemes, therisk management under those subschemes will, to a greater orlesser extent, require consideration of restrictions on usedirectly concerning the entry, transformation, mobility and per-sistence of the plant protection product in the soil.

Explanatory notes

Note 1

For the purposes of this subscheme, applications in glasshousesand for protection of stored products are considered as indoortreatments. It is very unlikely that field soils can be significantlycontaminated by such uses. Release of volatile materials fromglasshouses during ventilation is covered by the subscheme on air.

Note 2 Possibility of exposure

When the product is applied in the field, soil will normallybe exposed, except in certain specific situations, e.g. whenprecautions are taken to prevent contact with the soil (pots orcontainers are placed on sheeting) or when the crop is notcultured in soil, but on other substrates.

Note 3

Pre-emergence herbicides and soil sterilants are products whichare mainly applied to bare soil.

Note 4

Examples of products applied to cropped fields are as follows:

•

post-emergence herbicides

•

soil insecticides or nematicides

•

foliar insecticides or fungicidesSoil insecticides and nematicides are often also applied to

bare soil.

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Note 5 Crop interception

Interception factors (f

I

) can be measured in field studies ondissipation from the field. Mostly, however, they have to betaken from the literature, where two types of information can beobtained. The first comes from reviews on field data. Forexample, Linders

et al

. (2000) present a review of data fromGermany, Netherlands and USA which includes a large tablewith proposed interception factors. The second comes fromstudies on the correlation between ground coverage and soildeposition (Becker

et al

., 1999). Although measured data onthe crop and the product applied is considered to be the mostvaluable, interception factors taken from the literature areusually adequate. Ideally, the crop and its growth stage at thetime of application should be specified. If such data is notavailable, data for similar crops may be adequate. For moreinformation, see Report of the FOCUS Groundwater ScenariosWorkgroup (FOCUS, 2000).

Note 6 Exposure estimation in topsoil

Estimation of exposure concentrations in topsoil is based onthe recommended use pattern of a plant protection product.The following types of exposure concentrations may beneeded to assess the risk to soil organisms and functions inChapter 8:

•

initial concentration C

i

•

time-weighted average concentration TWAC

•

concentration C

t

at time t after application

•

plateau concentration after repeated applications.Estimation of initial concentrations C

i

is based on theassumption of instantaneous, homogeneous distribution of theproduct in a layer of soil with a certain depth and of a certainbulk density. The following formula can be used calculate suchestimates (OECD 2002a):

C

i

= A · (1

−

f

I

) · 106/ l · 104 · d

in which:Ci = initial concentration in soil (mg kg−1 soil)A = application rate (kg ha−1)fI = fraction intercepted by the crop (dimensionless)l = thickness of soil layer (m)d = bulk density of soil (kg m−3).Normally, initial exposure concentrations Ci are compared withacute effects.

The time-weighted average concentration TWAC is the averageconcentration during a period of time after the last applicationand covers the decline of the concentration during that period.Information on the rate of decline is taken from the studiesdetermining the transformation rate in soil under laboratoryconditions (Step 10). The time period depends on the soilorganism of concern and should be the same as the duration ofthe respective toxicity test. Normally, TWAC concentrationsare compared with chronic effects. They can be calculatedusing the following formula:

TWAC (mg kg−1) = Ci · (DT50/(t · ln 2) · [1 − exp(−t · ln 2/DT50)].

The concentration Ct represents the concentration in theplough layer at time t after each application. It can be estimatedfrom the transformation rates in laboratory soils (Step 10) orfrom field dissipation studies (Step 12).

Ct = Ci · exp − (ln 2/DT50) · t

in which:Ct = concentration in soil at time t (mg kg−1 soil)Ci = initial concentration in soil (mg kg−1 soil).

Ct can be used to determine the concentration in topsoil atharvest which might be of interest not only with regard to potent-ial adverse effects on soil organisms but also before plantinga succeeding crop in the same or the next growing season.

In situations where multiple applications are made (constantapplication rate, constant interval between applications, linearfirst-order transformation), the system eventually reaches asteady state where concentrations fluctuate between a maximumlevel, when an application has just been made (the upper plateauconcentration), and a minimum level just before the nextapplication is made (the lower plateau concentration).

This lower plateau concentration can be calculated by thefollowing equation (Hill et al., 1955).

in which:Rlow = the lower plateau concentration, i.e. the residue at theend of the nth applicationX = the proportion of the applied dose remaining after the firstapplicationA = the amount applied at each applicationn = the number of applications.

The equation for the upper plateau concentration is:

Note 7 Exposure concentrations in field situations

Field dissipation experiments can be triggered by effects onsoil organisms and functions (Chapter 8) and/or by trans-formation rates obtained in laboratory studies as required inStep 10 of Module B ‘Leaching to groundwater’ (see Note11). Such field dissipation experiments should be conductedby following the use recommendations for the plant pro-tection product under consideration. Application rates shouldcorrespond with the maximum rates recommended for eithersoil type or crop species. Soil samples should be taken atappropriate time intervals down to a depth sufficient toaccount for the distribution of the substance in the soil pro-file. Samples should be analysed for the active substance(s)and for relevant transformation products. Exposure (residue)concentrations (e.g. mg kg−1) obtained are compared with

RA X X

Xlow

n

=⋅ ⋅ −

− ( )1

1

RA X

Xhigh

n

=⋅ −

−( )1

1


© 2003 OEPP/EPPO, Bulletin OEPP/EPPO Bulletin 33, 151–162

effect concentrations for soil organisms and functions inChapter 8.

Guidelines for conducting field dissipation studies have beenpublished, for example by BBA (1986a), SETAC (1995) andEPA (1982).

Note 8 Transformation pathway

For most uses, aerobic conditions will normally dominate inagricultural soils but in some cases (e.g. paddy rice) anaerobicconditions will be more relevant. Laboratory studies on thetransformation pathway in aerobic and anaerobic soils arerequired by many national registration authorities. National(e.g. EPA, 1982; BBA, 1986a; Dutch Commission for Regis-tration of Pesticides, 1995) and international guidelines (SETAC,1995; OECD, 2002a) exist which give guidance on how toconduct such experiments under controlled laboratory condi-tions. Important experimental parameters in transformationpathway studies under aerobic conditions are initial concen-tration of the chemical, soil moisture content, soil temperatureand soil microbial activity. Soils are analysed for unchangedactive substance, transformation products (including CO2)and soil-bound (non-extractable) residues at several times duringthe test.

The results of the transformation pathway study are also usedto identify relevant transformation products which should beincluded in this exposure assessment. Major transformationproducts are those which are formed in amounts of 10% ormore of the applied dose at any time during the test.

Note 9 Transformation rate

The transformation rate in soil is relevant for two reasons. First,it determines the need for field studies (see Note 11). Secondly,it enables the calculation of levels of substances in soil as afunction of time after application to the soil. For informationon test guidelines, see Note 8. The order of transformation isof major influence on the values for DT50 and DT90, i.e.time needed for the dissipation of 50% and 90%, respectively,of the active substance, at defined conditions of incubation.A simple starting point is often the assumption of first-orderkinetics. A simple rule of thumb is that first-order kineticsmay be valid when the DT90 is approximately three times theDT50. A minimum correlation coefficient may be set to decideon the validity of first-order kinetics, e.g. r2 > 0.7. Due to lossof microbial activity of the soil on incubation, which may occurafter approximately three months, a biphasic approachoften appears to be valid. This means that both the first andthe second part of transformation can be described with first-order kinetics, but with different rate constants. The pointof transition in rate constants is called the ‘hinge point’, whichoccurs mostly between 50 and 150 days after the start ofthe incubation. Computer software exists to establish theexistence of such a hinge point. In other cases, other ordersof kinetics may be valid and, there also, computer softwareexists.

Transformation rates depend on the incubation temperature.As a general rule, the DT50 increases two or three times whentemperature is lowered by 10 °C. The Arrhenius equation, orany empirical relation of this kind, can be used to normalizeresults to other temperatures, as long as the temperature doesnot deviate too much from the test temperature. As most activesubstances and their transformation products are transformed toa large extent by microbial activity, it can be assumed that suchnormalization is possible between approximately 4 and 30 °Cfor mesophilic microbial populations. The use of a factor of 2.2(recommended by FOCUS) is often considered acceptable inthe EU for extrapolating DT50 values from 20 °C to 10 °C. Formore information, see EU, 2000).

Note 10 Adsorption coefficient Kd

The adsorption coefficient Kd is a determining factor formobility in soil. Within this subscheme, it is used to predictconcentrations in the plough layer with simulation models.These models, using the DT50 for transformation in soil and theKd for mobility in soil, provide concentrations as a functionof time in the plough layer. Kd values can be derived fromcolumn leaching studies and adsorption/desorption tests. Forconducting column leaching studies, national (e.g. EPA, 1982;BBA, 1986b; Dutch Commission for Registration of Pesticides,1995) and international test guidelines (SETAC, 1995; OECD,2002b) can be used. Several national (EPA, 1982; DutchCommission for Registration of Pesticides, 1995) and inter-national test guidelines (SETAC, 1995; OECD, 2000a) alsoexist for adsorption/desorption studies. From column studies,Kd values can be calculated, using, for example, the followingequation:

in which:Xp = penetration depth of the substance (cm)WL = water layer put on top of the column (cm)θ = moisture content of the soil column during percolation (–)ρ = bulk density of the soil within the soil column (g cm−3)Kd = partition coefficient between soil matrix and water(cm3 g−1).

If no specific values can be derived from the report of the test,default values for the moisture content of the soil column dur-ing percolation, θ, of 0.4 and the bulk density of the soil withinthe soil column, ρ, of 1.5 may be used, unless these values areconsidered unrealistic for the type of soil used in the test. Thepenetration depth is defined as the distance below which 50%of the substance recovered in both the percolate and the soil col-umn after leaching is found.

In general, substances are adsorbed to the organic matterfraction in the soil matrix. Therefore, normalization to KOM valuesis often performed:

KOM = Kd/fOM

XWL

Kpd

=+ ⋅θ ρ

160 Soil


in which:KOM = adsorption (partition) coefficient between organicmatter in the soil matrix and waterfOM = fraction organic matter in the soil matrix.

Another means of normalization is towards the fraction oforganic carbon in the soil matrix, which leads to KOC values:

KOC = Kd/fOC

in which:KOC = adsorption (partition) coefficient between organiccarbon in the soil matrix and waterfOC = fraction organic carbon in the soil matrix.

The most commonly used relation between KOM and KOC isthe following (Scheffer & Schachtschabel, 1975):

KOC = KOM × 1.724

Note 11 Field studies triggered by transformation rate in the laboratory

Laboratory studies on transformation in soil may indicatepersistence of a substance. In the field, however, persistencemay be less than would be expected from the laboratorytest, due to other processes involved in the field. Processes, suchas leaching to the subsurface of soil, plant uptake andphotochemical transformation, which are normally excluded instandard laboratory tests, can result in faster dissipation fromthe plough layer than expected from the laboratory results.Trigger values on the DT50lab have been set by the EuropeanUnion, within its data requirements. In fact two triggers aregiven, one of 60 days and one of 90 days. The trigger of 90 daysis relevant for northern European countries, because of theircolder climate and is related to DT50lab values at 10 °C. Thetrigger of 60 days is valid for the rest of the EU countries withmore moderate climates and is related to DT50lab values at20 °C.

As the DT50lab is temperature-dependent, available DT50values should be normalized to an appropriate temperaturebefore applying the trigger. This can be done by means of theArrhenius equation (FOCUS, 1997) but, in that case, tests atdifferent temperatures should be available. The default valuefor the Arrhenius activation energy is taken to be 54 kJ mol−1.

Field dissipation/transformation experiments should be car-ried out in representative agricultural use areas of a plant pro-tection product. Such studies should follow the instructionsgiven in available guidelines (e.g. EPA, 1982; BBA, 1986a;SETAC, 1995).

Note 12 Lysimeter experiments/field leaching studies

Monolith lysimeters can be used to study the fate and behaviourof plant protection products in an undisturbed soil profile underoutdoor conditions. They allow for monitoring of the volumeof leaching/drainage water as well as the concentrations of achemical and its transformation products. An outstanding feature

of monolith lysimeters therefore is the capability to monitormass fluxes of water and chemicals. In addition, the distribu-tion of the chemical and its transformation products betweenthe soil and crops can be determined, along with their transfor-mation rates. Instructions for conducting such studies are givenin OECD guidance document no. 22 (OECD, 2000b). Altern-atively, field leaching studies can be carried out where soillayers and groundwater are analysed for active substance(s)and for relevant transformation products (see also Chapter 5Groundwater).

Note 13 Necessity to assess run-off

Run-off is a process where rainwater flows from a sloped fieldas a result of exceeding the infiltration capacity of the soil.Storm events, with high amounts of precipitation within a shortperiod of time, may result in high concentrations of residues ofplant protection products reaching non-target areas. In flatareas, run-off is of little relevance. When plant protectionproducts are applied to soil with a texture whose infiltrationcapacity will never be exceeded by the amounts of precipitationduring realistic storm events in the region of concern, then run-offwill also be of little relevance. This might be the case for gravelly,coarse, sandy soils (Klöppel et al., 1994). Run-off depends ona number of characteristics of the field. It also depends to someextent on the use of land, such as crop cover, tillage, etc., andthus agricultural practice may be such that run-off beyond theedge of the field is effectively prevented. Run-off is of norelevance for indoor applications of plant protection products.

Run-off can be divided into two distinct processes. The firstdeals with water running from the field, carrying residues ofplant protection products with it. The second involves erosionwhere the top layer of the soil is washed off and trans-ported. Erosion is considered to be the result of bad soilmanagement and, as such, this process is not included within thissubscheme.

Note 14 Run-off scenario

In primary tiers of assessment, it is necessary to define ascenario to enable calculations on run-off. Such a scenario mayapproach the realistic worst case in order to try to avoidproblems with run-off arising after registration. Within arealistic scenario, different parameters are set so that thescenario finally reflects a realistic system that could be found inthe field. This is important, as it should allow a check in the fieldof theoretical assessments. The following parameters that willinfluence the outcome of the calculations are relevant forestablishing a scenario.• slope: slope is expressed in percentages. A slope of 3% means

that, on every 100 m in the horizontal direction, the surfacewill be elevated by 3 m.

• soil texture: soil texture influences the infiltration capacity ofthe soil.

• precipitation: data on precipitation gathered for long timeperiods (a few decades) can be used to derive a figure for the



amount of precipitation that might fall during an extremestorm event in the region of concern.

• time lag: the period between application of the plant protectionproduct and the storm event is called the time lag. A farmerwill not apply a product when he might expect it to be flushedaway by a storm event. Based on good agricultural practice,it is therefore reasonable to allow for a time lag. During thistime lag, part of the applied product will degrade in soil.

• soil cover: more plant protection product will be transportedfrom a field as a result of run-off when a higher fraction of theapplied dose reaches the soil. The soil cover at applicationgoverns this. Run-off will be greatest for fallow land and low-est in dense crops.The definition of a realistic worst case deals with a level of

probability. Often, it is translated into an overall 90th percentileprobability. If a scenario depends on only two parameters, Aand B, and if both parameters are set to the 90th percentile, thenthis would result in an overall 99th percentile probability.Instead, the probability of parameter A could be set at the 70thor 80th percentile, which, together with a 70th or 80th percen-tile for parameter B, would result in an overall 90th percentileprobability. So, in the typical case, the rainfall event should bechosen in such a way that, in combination with the soil slope,soil texture, time lag and soil cover, an overall 90th percentileprobability of the scenario is created.

‘Realistic’ could also be defined more qualitatively, namelyin a situation in which all relevant parameters are set in thedirection of worst case but the combination can actually befound in the field within the region of concern. For more detailssee also the Report of the FOCUS Groundwater ScenariosWorkgroup (FOCUS, 2000).

Note 15 Distance(s) of concern beyond the edge of the field

Within the subscheme on surface water, it is necessary toestimate the exposure concentration in surface water (PECwater)in a chosen ditch adjacent to the treated field. Such a ditchnormally has limited dimensions with respect to width of thewater surface, width of slopes, as well as its distance fromthe edge of the field. The distance from the edge of the field tothe midpoint of the water surface will mostly be in the order ofa few metres. Run-off, not entering adjacent surface waters, butadjacent fields (or any other soil surface) will lead to the highestconcentrations immediately beyond the edge of the field. Itseems appropriate therefore for a realistic worst-case scenariofor run-off to adjacent soil surfaces, to set the distance beyondthe edge of the field to a few metres, analogous to a situationwith run-off to adjacent surface waters.

Note 16 Simple non-substance-related approach

In a non-substance-related approach, no differentiation is madebetween substances in calculating run-off. For first guesses,this might be appropriate. Such an approach may be basedon conservative assumptions, based on expert judgement, that

run-off will lead to concentrations in the soil beyond the edgeof the field corresponding to a certain percentage of the doseapplied in the field. Within the EU, such approaches are pro-posed by the FOCUS working group on surface waterscenarios.

In an extended review of run-off data, Burgoa & Wauchope(1995) found that total run-off losses are generally proportionalto the amounts applied and are typically 0.5% or less. Evenunder worst-case conditions, run-off losses are usually less than5% of applied amounts.

Note 17 Calculation of the concentration in the upper layer of the off-field soil

From the percentage of the dose applied to the field which endsup beyond the edge of the field as a result of run-off, and assuminghomogenization in the top 5-cm layer and a bulk density ofthe soil of 1500 kg m−3, the concentration in the upper layer ofthe soil beyond the edge of the field can be calculated using theformula presented in Note 6 for estimation of Ci.

Note 18 Time lag

The time lag, i.e. the period between application of the plantprotection product and the storm event, allows the product todegrade to some extent. Within the European Pesticide HazardInformation and Decision Support System (EUPHIDS) 1996, itis considered unlikely that run-off will occur earlier than 3 daysafter application because farmers will listen to the weatherforecast and will avoid the application of plant protectionproducts if heavy rainfall is announced. The EU FOCUSworking group on surface water scenarios is presently pro-posing 4 days.

Note 19 Calculation of the dose left in the soil after the time lag

In order to obtain FDOSE, two approaches are possible. The firstis to use the DT50lab (obtained from laboratory data), with first-order kinetics during the time elapsed between application ofthe plant protection product and the rain event (t in days):

The second is to use the DT50field (obtained from field data) ina similar way:

Note 20 Application rate

The application rate or dose of the plant protection product isthe one proposed in the use recommendations. It should becorrected for degradation/dissipation between the application

FC

CeDOSE

o

DT tlab= = −( / )*ln2 50

FC

CeDOSE

o

DT tfield= = −( / )*ln2 50

162 Soil


and the rain event. This can be done by means of the followingequation:

doserun-off = doseproposed * FDOSE

It should be borne in mind that the dose for different proposeduses can differ.

Note 21 Calculation of run-off

Several tools are available to calculate run-off. For simplecalculations, the European Pesticide Hazard Information andDecision Support System (EUPHIDS) can be used. ThisEUPHIDS was prepared by the National Institute of PublicHealth and the Environment (RIVM, Netherlands), FreeUniversity of Amsterdam, Fraunhofer Institute for Environ-mental Chemistry and Ecotoxicology (Germany) and the Interna-tional Centre for Pesticide Safety (ICPS, Italy) and is availableon a CD-ROM (Beinat & van den Berg, 1996). The run-off partof EUPHIDS is based on experiments by Klöppel et al. (1994).

There are also more advanced tools available, in particularthe simulation models SWAT, PELMO and PRZM3. See alsothe report of the Surface Water Scenario Working Group(FOCUS, 2001).

ReferencesBBA (1986a) Richtlinie für die amtliche Prüfung von Pflanzenschutzmitteln,

Teil IV, 4.1. Verbleib von Pflanzenschutzmitteln im Boden – Abbau,Umwandlung und Metabolismus. Biologische Bundesanstalt, Braunsch-weig (DE) (in German).

BBA (1986b) Richtlinie für die amtliche Prüfung von Pflanzenschutzmitteln,Teil IV, 4.2. Versicherungs-verhalten von Pflanzenschutzmitteln. Biolo-gische Bundesanstalt, Braunschweig (DE) (in German).

Becker FA, Klein AW, Winkler R, Jung B, Bleiholder H & Schmider F(1999) [The degree of ground coverage by arable crops as a help in esti-mating the amount of spray solution intercepted by the plants.]. Nachrich-tenblatt des Deutschen Pflanzenschutzdienstes 51, 237–242 (in German).

Beinat E & van den Berg R (1996) EUPHIDS, a Decision Support Systemfor the Admission of Pesticides. RIVM report no. 712405002. RIVM,Bilthoven (NL).

Burgoa B & Wauchope RD (1995) Pesticides in run-off and surface waters.In: Progress in Pesticide Biochemistry and Toxicology, Vol. 9. Environ-mental Behaviour of Agrochemicals (Ed. Roberts, TR & Kearney, PC).Wiley, London (GB).

Dutch Commission for Registration of Pesticides (1995) Application forRegistration of a Pesticide. Section G: Behaviour of the Product and itsMetabolites in Soil, Water and Air. Dutch Commission for Registration ofPesticides, Wageningen (NL).

EPA (1982) Pesticide Assessment Guidelines, Subdivision N. Chemistry:Environmental Fate. US Environmental Protection Agency, Washington(US).

EU (2000) EU Guidance Document on Persistence in Soil. (9188/VI/97Rev8, 12/07/2000). EU Commission, Brussels (BE).

FOCUS (1997) Soil Persistence Models and EU Registration. Soil Model-ling Working Group, EC Document 7617/VI/ 96. EU Commission, Brussels(BE).

FOCUS (2000) FOCUS Groundwater Scenarios in the EU Review of ActiveSubstances. Report of the FOCUS Groundwater Scenarios Workgroup,EC Document Reference Sanco/321/2000 rev.2. EU Commission, Brussels(BE).

FOCUS (2001) FOCUS Surface Water Scenarios in the EU EvaluationProcess Under 91/414/EEC. Report of the FOCUS Working Group onSurface Water Scenarios, EC Document Reference SANCO/4802/2001-rev.0. EU Commission, Brussels (BE).

Hill GD, McGahen JW, Baker HM, Finnerty DW & Bingeman CW (1955)The fate of substituted urea herbicides in agricultural soils. AgronomyJournal 47, 93–104.

Klöppel H, Haider J & Kördel W (1994) Herbicides in surface runoff: a rainfallsimulation study on small plots in the field. Chemosphere 28, 649–662.

Linders J, Mensink H, Stephenson G, Wauchope D & Racke K (2000) Foliarinterception and retention values after pesticide application. A proposalfor standardized values for environmental risk assessment (IUPAC tech-nical report). Pure and Applied Chemistry 72, 2199–2218.

OECD (2000a) Guidelines for Testing of Chemicals No. 106: Adsorption–Desorption Using a Batch Equilibrium Method. OECD, Paris (FR).

OECD (2000b) Guidance Document No. 22: Performance of Outdoor Mon-olith Lysimeter Studies. OECD, Paris (FR).

OECD (2002a) Guidelines for Testing of Chemicals No. 307: Aerobic andAnaerobic Transformation in Soil. OECD, Paris (FR).

OECD (2002b) Guidelines for Testing of Chemicals (Draft): Leaching inSoil Columns. OECD, Paris (FR).

Scheffer F & Schachtschabel P (1975) Lehrbuch der Bodenkunde. F. EnkeVerlag, Stuttgart (DE).

SETAC (1995) Procedures for Assessing the Environmental Fate and Eco-toxicity of Pesticides (Ed. Lynch, MR). SETAC Press, Pensacola (US).

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