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Soil assessment for pesticide registration in Great Britain and Northern Ireland

When applying for pesticide registration in Great Britain and Northern Ireland, you must provide a soil assessment for the pesticide active substance and any of its metabolites which are formed in soil. Data must show the rate of degradation of the compound in soil and the formation of degradation products, including metabolites. You must identify and quantify metabolites in line with the data requirements set under Regulation No. 1107/2009 (GB/NI). Active substance data requirements are set under Regulation No. 283/2013 (GB/NI) and plant protection product (PPP) data requirements are set under Regulation No. 284/2013 (GB/NI)

PECsoil values of the active substance are always required for active substance approvals and plant protection product (PPP) authorisation. PECsoil values are sometimes required for metabolites and the product formulation. The recommended HSE methods are described below.

For product evaluations, the use of a 'Risk Envelope' approach may be appropriate.  Care should be taken if the risk envelope product has any form of mitigation or assumes crop rotation. Details on the suitability of risk envelopes can be found at Risk envelope suitability for pesticide registration in Great Britain and Northern Ireland.

Active substance standard PECsoil calculations

You must calculate PECsoil values for each active substance within a pesticide product. 

Selecting endpoints

Calculate PECsoil values using the realistic worst-case best fit DT50/90 values. This should be the longest non-normalised DT50/90 values derived from field dissipation studies.  In the absence of field data, normalise laboratory data to 20°C if the studies were conducted at a temperature greater than 20°C using the Arrhenius and Walker converter from Environmental fate models: Excel calculator tools. Do not normalise laboratory DT50/90 values for moisture.

Use the worst-case use pattern for PECsoil calculations. This is normally the highest application rate (units in g a.s./ha) with the lowest crop interception. Accepted crop interception values are provided in the FOCUS Generic Guidance for Tier 1-Groundwater v2.2 (2014) report. Use the shortest timing interval when modelling multiple applications.

The default parameters of 5cm for soil depth and 1.5 g/cm3 for soil density are suitable for most crop types and situations. For specific use patterns where incorporation will occur immediately at the time of application, a 20 cm soil depth may be justified for PECsoil calculations for the first year of applications.

Method

You can use either the HSE PECsoil calculator from Environmental fate models: Excel calculator tools or the ESCAPE v2.0 model. The HSE PECsoil calculator is recommended when the substance DT50 value is derived from SFO kinetics. The ESCAPE model can be used for substances with endpoints derived from biphasic kinetics (for example DFOP or HS).

Presentation of results

Present the actual PECsoil values and the time weighted average (TWA) values for the time period 0-100 days. PECsoil values should be reported in mg/kg. For use patterns with multiple applications, the maximum initial PECsoil value should be reported for both a single application and multiple applications.

Active substance accumulation PECsoil calculations

You must calculate PECsoil accumulation values for active substances with a DT90 value greater than 1 year. Do not use FOMC kinetics for long term accumulation calculations even if it provides the best fit. Use the 'PECsoil accumulation' tab in the PECsoil calculator from Environmental fate models: Excel calculator tools .

Report the maximum peak PECsoil value and the corresponding steady state concentration.  Also report the year when the maximum peak PECsoil is predicted to occur.

Use a tillage depth of 5 cm for all annual and perennial crops for first tier accumulation calculations. A refinement of 20 cm tillage depth may be used for specific crops that undergo soil disturbance at harvest, for example root crops.

Crop type Depth to use for PECsoil initial Depth to use for PECsoil accumulation Example
Perennial crops 5 cm 5 cm Orchards, soft fruits, vines, hops
Any crops where incorporation occurs at the time of application 20 cm 20 cm Incorporation immediately following application is specified on label or authorisation documents
Root crops which will involve ploughing at harvest 5 cm 20 cm Potatoes, beets, carrots, turnips etc
Arable crops 5 cm 5 cm This should be the standard first tier for all other annual field crops

The PECsoil calculator can account for use patterns with different crop rotation patterns. For example, a crop with a specific use pattern for applications every other year will be defined as '1 year in 2'.

Metabolite standard PECsoil calculations

You must calculate PECsoil values for all major metabolites for active substance approvals. A major metabolite is a metabolite observed ≥ 10% AR, or ≥ 5% AR on two consecutive occasions, or still increasing over the duration of the study and at > 5% at study termination.

For PPP authorisations, only PECsoil values for ecotoxicologically relevant metabolites are required. The PECsoil calculator from Environmental fate models: Excel calculator tools can be used.

Calculate metabolite PECsoil values based on a single application to reduce uncertainty over the pattern of formation and decline between applications. Adjust the maximum total parent application rate to give a pseudo metabolite application rate. For example, if the worst-case use pattern is for 2 applications of 500 g a.s./ha, then the total parent application rate is 1000g a.s/ha. This value is then adjusted for the difference in molecular weight and the maximum peak formation of the metabolite (not the formation fraction), as detailed in the example below:

Example 1 - metabolite pseudo application rate if the data come from lab studies:

If metabolite concentrations are reported as % AR, then you must adjust the parent application rate for the molecular weight of the metabolite.

Parent molecular weight = 350g/mol
Metabolite molecular weight = 300g/mol
Molecular weight correction factor = 300/350 = 0.857
Maximum formation, expressed as a fraction = 0.6 (based on the maximum mean of replicates, 60% AR)
Application rate of parent = 1000 g a.s./ha

'Pseudo application rate' of metabolite = parent total dose x MW correction factor x maximum formation
= 1000 x 0.6 x 0.857 = 514.2 g/ha.

Example 2 - metabolite pseudo application rate if the data come from field studies:

If metabolite concentrations are reported in mg/kg, then you simply adjust the parent application rate using the ratio of the levels of parent and metabolite observed.

Peak concentration of parent in field dissipation study = 3 mg/kg
Peak concentration of metabolite in same study = 1.5 mg/kg
Application rate of parent = 1000 g/ha

'Pseudo application rate' of metabolite = parent total dose x ratio parent : metabolite observed = 1000 x (1.5/3) = 500 g/ha.

The pseudo application rate of the metabolite is then used to calculate an initial PECsoil value. The same minimum crop interception value that was used in the parent calculations must be used.

PECsoil values calculated over time or Time Weighted Average (TWA) values are not normally required for metabolites. If these values are calculated, then the worst-case metabolite soil DT50 should be used.

Metabolite accumulation PECsoil calculations

You should only calculate PECsoil accumulation values for ecotoxicologically relevant metabolites with DT90 values greater than 1 year. Calculate a pseudo metabolite application rate using the method described above and put this into the accumulation tab in the PECsoil calculator from Environmental fate models: Excel calculator tools.

Formulation PECsoil calculations

Calculate an initial PECsoil value for a single application of the product formulation. The application rate needs to be entered in g/ha. If the product application rate is given in ml/ha, multiply this by the formulation density to calculate the equivalent application rate in g/ha.

For example, if 1.5 L is the highest application rate for an individual dose, and the formulation density is 1.120 g/ml (cm3), the equivalent dose in g/ha is: 1500 ml/ha x 1.120 g/ml =1680 g/ha.

Enter the equivalent product application rate as a single application into the PECsoil calculator from Environmental fate models: Excel calculator tools . Use the minimum crop interception. DT50 values are not required for the formulation.

For products formulated as solids, the application rate does not need to be adjusted for the formulation density.

Updated 2021-01-19