Post-harvest treatments: Environmental fate considerations for pesticide registration in Great Britain and Northern Ireland

When you are applying for pesticide registration in Great Britain and Northern Ireland for active substances used post-harvest you must provide a consideration of potential environmental exposure routes.

Post-harvest pesticide treatment is defined as treatment of plants or plant products after harvest in an isolated space where no run-off is possible, for example in a warehouse, see Regulation EC 1107/2009.

Throughout the life cycle of the pesticide used as a post-harvest treatment, environmental exposure (relevant to 1107/2009) can occur during:

  • venting of the warehouse
  • planting out of treated crops
  • industrial processing of plants and plant materials
  • disposal of waste product

The calculations required depend upon the application type and routes of exposure and are detailed in the following sections.

If you require further guidance please contact HSE.

Exposure via air

Exposure to air should be considered in line with Pesticides in air: Considerations for exposure assessment (otherwise know as FOCUS air).

The FOCUS air report concludes that deposition after volatilisation from indoor uses (for example in glasshouses) is in general less than in the field.  Therefore, it may be possible to use an existing assessment of an outdoor use as a risk envelope to address emissions from the post-harvest indoor use.  For further information see Risk envelope suitability for pesticide registration in Great Britain and Northern Ireland.

Alternatively, FOCUS air recommends default deposition percentages of 0.05% for high and low application volume techniques, or 0.2% in the case of ultra-low volume techniques.  These default values can be applied irrespective of vapour pressure.  A refined approach may be possible considering vapour pressure and the triggers proposed by the FOCUS air report, noting that the triggers established for volatilisation from soil or plants may not be appropriate for specific post-harvest treatment methods. Refined approaches should be fully justified.

Seed potatoes

Where seed potatoes are treated in a warehouse prior to subsequent planting there is a need to calculate soil exposure.

Example calculation:

A measured or estimated residue level (in mg/kg) and planting rate (in kg/ha) are needed to calculate the soil loading:

Soil loading (mg/ha) = residue level (mg/kg) x planting rate (kg/ha)

You should provide justification for any planting densities used in your applications.

Active A has a measured residue level of 1.84 mg/kg potatoes and the planting rate for seed potatoes is 7.5 tonnes/ha.

The soil loading is therefore 1.84 x 7500 = 13800 mg/ha, equivalent to an application rate of 13.8 g active/ha.

Using the soil loading as a pseudo application rate the initial PECsoil can be calculated, where a soil density of 1.5 g/cm3; a soil mixing depth of 5 cm and crop interception of 0% are used within the PECsoil calculator in Environmental fate models: Excel calculator tools.

Industrial processing of plants and plant material

Prior to industrial processing, treated commodities such as apples and potatoes are often washed; the water is collected and may be discharged to a sewage treatment plant (STP) (there is more information - Emissions to STP) or directly discharged to surface water (there is more information - Exposure via direct discharge).

Emissions to STP

The assessment of environmental fate within an STP can be conducted using the SimpleTreat model.  To derive subsequent concentrations in receiving water you can use the equations from ECHA- Guidance on the biocidal product regulation- part B. HSE has developed a simple Excel calculation tool to implement the equations from the ECHA guidance along with information on fate within the STP derived from the SimpleTreat model (see STP_PEC_calculator).

The first step in quantifying the exposure is to determine the amount of a.s. discharged into the processing effluent. To conduct this calculation the Measured Residue Level (MRL) of the a.s., the percentage of residue lost to the effluent and the amount of the crop which is processed per day are required. With the exception of the MRL, these values are dependent upon the crop type, the table below contains suggested default values.

Crop Representative production plant Amount processed per day Residue lost to effluent
Potatoes Starch Production Plant 767 tonnes potatoes/ day (based upon 140000 tonnes/6 months) 10%
Apples Apple processing plant 500 tonnes apples/ day 5 % (water)


Active Substance MRL: 15mg/kg, Crop: Potatoes

767 tonnes of potatoes are processed per day. Considering an MRL of 15 mg/kg, the daily load of the a.s. into the processing water is calculated to be 11.505 kg a.s/day. It is estimated that 10% of the residue will be discharged into the processing effluent, this results in a daily discharge into the processing effluent of 1.150 kg a.s./day.  This value can be entered as the Elocalwater value in the STP PEC calculator.

Exposure via direct discharge

Exposure through direct discharge to surface water from industrial processing must also be considered. The calculations to determine the PECs are identical to exposure via an STP, except it is considered that 100% of the processing effluent enters surface water. Practically this is achieved by setting Fstp water to 1 within the STP PEC calculator.

In the UK, the discharge of trade effluent directly into surface water requires a permit under the Environmental Permitting Regulations. 

This is outside HSE’s remit, and following discussions with the Environment Agency, it has been agreed that the following phrase must be included on all product labels:

'The use of this product on [crop] may result in dilute pesticide waste that requires disposal. All dilute pesticide waste must be disposed of safely and legally to protect humans, wildlife and the environment, especially groundwater and surface water. Pesticide disposal advice is detailed in the ‘Code of Practice for Using Plant Protection Products’ (Section 5: Disposing of Pesticide Waste).'

This information is available in the Code of practice for using plant protection products.

Disposal of the product

For disposal of drip/drenching solutions the following restriction should be placed on the label and is required on the Notice.


Do not empty into drains. THIS MATERIAL AND ITS CONTAINER must be disposed of in a safe way.

Disposal of used dipping/drenching solution:

Please refer to the Code of Practice for the Safe Use of Pesticides on Farms and Holdings for guidance with regards to the disposal of used excess dipping/drenching solutions.

Spillage/drainage onto hard surfaces should be prevented from reaching drains.'


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Updated 2023-03-13