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Soil

In general Annex II environmental fate data relates to the behaviour of the active substance and its metabolites.  The data requirements specify data on degradation in soil and partitioning between soil and water must be submitted (eg to allow understanding of degradation in soil and also to determine the likely partitioning between soil and water).

Annex III environmental fate data generally relates to the calculation of predicted environmental concentrations (PEC's) in all relevant compartments.  The Annex II data on fate and behaviour in soil significantly affect the magnitude of the PEC values in the different compartments of soil, groundwater, surface water and sediment.

General information on soil exposure can be found in the following documents: 'Soil Persistence Models and EU Registration' (29.2.97)' and the Guidance document on Persistence in Soil (9188/VI/97 rev. 8, 12.07.2000.

Aged Soil Sorption

Proceedings of a Workshop on Aged Sorption of Pesticides in Soil

The proceedings of a workshop on aged sorption of pesticides in soil held in York on 27th – 28th April 2010 are available in Proceedings of Aged Sorption of Pesticides Workshop).

Draft guidance document on generation and use of aged soil adsorption parameters for pesticides

Following Defra-sponsored research and development work, CRD have recently submitted a draft guidance document on generation and use of aged soil adsorption parameters for pesticides for scrutiny by the PPR Panel of EFSA. For the sake of transparency and information purposes, CRD has placed this draft guidance on the website: Guidance on how aged sorption studies for pesticides should be conducted, analysed and used in regulatory assessments {30.07/.2012}.

CRD recommends that the draft guidance is NOT used for registration purposes until after the PPR Panel scrutiny and until the guidance document has been 'noted' by the EU Standing Committee on the Food Chain and Animal Health (SCFCAH). If Applicants wish to use the guidance as part of a regulatory submission, it is strongly recommended that they discuss this first with the appropriate regulatory authority.

Active substance PECsoil calculations (for EU, Zonal and UK specific authorisation requests)

Guidance on the calculation of PECsoil is given in the executive summary of the FOCUS document 'Guidance Document on Estimating Persistence and Degradation Kinetics from Environmental Fate Studies on Pesticides in EU Registration' (Sanco/10058/2005, version 2.0, June 2006) and the 'Guidance Document on Persistence in Soil' (9188/VI/97 rev.8, 12.07.2000).

PECsoil should be calculated with the realistic worst case DT50.  In many cases this will be longest field dissipation DT50.  Calculations should use the proposed GAP for dose, number of applications and application interval (using the shortest interval where a range is specified).  Suitable crop interception values should be chosen as suggested on Page 23 of Generic Guidance for FOCUS Groundwater Scenarios Version 1.1, April 2002).

Where PECsoil has to be calculated for multiple applications with different doses for different timings eg due to different interception values at each application or differing application intervals, CRD have produced a simple Excel spreadsheet 'PEC Soil' which can be downloaded "as is".

Where field dissipation DT90 is ≥ 1 year, active substance accumulation must also be calculated.  CRD have produced a simple Excel spreadsheet 'PEC Soil' spreadsheet which can be downloaded "as is".

Metabolite PECsoil calculations (for EU, Zonal and UK specific authorisation requests)

PECsoil for metabolites may be calculated using the same spreadsheets as specified above, but the principles are slightly more complex.  The application rate input into the spreadsheet should be based on the application of the parent compound adjusted for formation percentage.  This is normally the highest percentage seen in the studies.  Where appropriate field studies are available, it is preferable to use the percentage formed in these studies*.

*Where metabolite concentrations are reported as % AR or parent equivalents adjust parent dose for the molecular weight of the metabolite. eg
Parent molecular weight = 350.            Metabolite molecular weight = 300.
Molecular weight correction factor = 300/350 = 0.857
Maximum formation in laboratory study was 60% AR (ie 0.6)
Application rate of parent is 1000 g/ha,
'Application rate' of metabolite = 1000 x 0.6 x 0.857 = 514.2 g/ha.

*Occasionally actual concentration of metabolite is reported instead of %AR or parent equivalent, in which case there is no need to adjust for molecular weight difference
For example:

Peak concentration of parent in field dissipation study was 3 mg/kg.
Peak concentration of metabolite in same study was 1.5 mg/kg.
Application rate of parent is 1000 g/ha,
'Application rate' of metabolite = 1000 x (1.5/3) = 500 g/ha.

In the case of multiple applications, the pattern of formation and decline of metabolites becomes more uncertain, and particularly where the peak concentration occurs.  Thus, at the first tier, the rate of application for the metabolite should be calculated as described above, but on the basis of a single application of the maximum total dose of the active substance.  This is the same as assuming there is no degradation of the metabolite between applications, and whilst being a worst case, removes much of the uncertainty.

If accumulation of a metabolite is a concern, the 'PEC Soil' spreadsheet can be used in a similar way to that used for calculation for active substances.  If the GAP uses multiple applications per crop, it is suggested that the application rate of the metabolite is based on the maximum total dose of the active substance per crop per year.

Formulation PECsoil calculations (for EU, Zonal and UK specific authorisation requests)

This is required when the ecotoxicological soil exposure is driven by the formulation, rather than the active substance.  The formulation PECsoil is always based on a single application (even for multiple application GAPs) using the simple Excel spreadsheet 'PEC Soil' spreadsheet which can be downloaded "as is".

The single application selected is always the application which gives the greatest soil loading which is generally, but not always, the highest application rate and lowest (worst case) crop interception.  For liquid formulations, the volume applied is converted to mass applied using formulation density (or specific gravity).  For solid formulations, no adjustment is necessary.  Note application rate used in the Excel spreadsheet must be in g/ha, therefore the initial formulation rate used must in in mls/ha or g/ha). 

Additional information: soil exposure from treated growing media.  CRD are aware that material such as spent compost/growing media can be applied to land at a nominal maximum rate of 50 tonnes/ha (consistent with the Code of Good Agricultural Practice).  The potential for contamination of land from residues within treated growing media must be addressed for products which may be used, for example, ornamental plant production.

Generally, the active substance concentration in the growing media may be converted into a rate per hectare using the assumptions in The Use and Disposal of Growing Media report from March 2001. Applicants should consider this report and include first tier calculations for products which can be used in situation where treated growing media may be disposed on agricultural land.
Updated 2017-01-27