Pesticide Registration Toolkit

Operator exposure models and local risk assessment

Relevant documents
Assessment Summary Table for Operator risk models 
summary of the main exposure scenarios and the assumptions of the EFSA Calculator 

Principle

This assessment evaluates the risk of the formulated product for pesticide operators using exposure models. Using an appropriate exposure scenario, exposure of operators to a pesticide is being estimated by a model and the outcome is compared with the acceptable operator exposure level (AOEL).

An exposure scenario is a description of the situation where the operator is exposed to the pesticide. It typically includes: the type of application equipment used, pesticide formulation, application rate, work rate, level of personal protection, etc.

Operator exposure models have been developed mainly for European and North American pesticide application situations, but not (yet) for developing countries. However, by choosing the appropriate exposure scenarios, existing models can be used to obtain an initial indication of occupational exposure to a pesticide and assess the risk to the operator.

Models

Several operator exposure models are available, though some are more up-to-date and reliable than others. The following models describe a wide range of exposure scenarios and are based relatively recent data.

1. The European Food Safety Authority (EFSA) Calculator was published in 2014 and contains two operator exposure models: 1) the Agricultural Operator Exposure Model (AOEM), which covers mixing, loading and spraying of liquid pesticides and 2) the US Pesticide Handler Exposure Database (PHED), for the application of granules. A summary of the main exposure scenarios and the assumptions  underlying the Summary EFSA Calculator is provided.

The EFSA Calculator replaces various older European exposure models such as the UK Predictive Operator Exposure Model (POEM) and the German Operator Exposure Model.

The EFSA Calculator can be downloaded here

Further details about the operator risk assessment approach applied in the European Union are described in an EFSA guidance document.
 

2. The CropLife OPEX Tool is mainly based on the US EPA Occupational Pesticide Handler Exposure Data. Certain scenarios for handheld application have been used from the German Model. A summary of the main exposure scenarios and the assumptions underlying the CropLife model is provided here.

The CropLife OPEX Tool can be downloaded here. A summary manual for using the tool is provided on the first page of the spreadsheet.

The above mentioned models are different with regard to the exposure scenarios which they cover, the underlying exposure studies which are at the basis of the models, the degree of protection provided by personal protective equipment, and some of the default assumptions on absorption of the pesticide into the body. In some cases, it may be useful to run the same scenario in more than one model.

Data required

The following data are generally used for an operator risk assessment using an exposure model.

  • Acceptable Operator Exposure Level (AOEL) (In the EFSA Calculator, the AOEL is referred to as the “Reference value non acutely toxic active substance” (RVNAS))
  • (in the CropLife OPEX Tool) No Observed Adverse Effect Level (NOAEL)
  • Crop type
  • Type of application and application equipment
  • Type of pesticide formulation
  • Maximum application rate (kg of a.i. per ha)
  • (in some cases) Volume application rate (L of spray solution per ha)
  • (if available) Dermal absorption factor
  • Type of personal protective equipment available/required


Procedures

  1. Describe the operator exposure scenario(s) applicable to the pesticide to be evaluated
  2. In the exposure models, choose the exposure scenario(s) which most closely approache(s) the situation that you wish to evaluate. If appropriate scenarios appear in more models, run the assessment with all these models.
  3. Obtain the input data to run the model from the registration application dossier or, if absent, from reputable alternative sources.
  4. Run the model(s)
  5. If provided by the model, note the estimated total systemic exposure (mg a.i./kg bw/day)
  6. Note the AOEL.
  7. Calculate or note the exposure as % of the AOEL.

This Assessment Summary Table for Operator risk models  can be used to summarize the data.

 

Interpretation of the outcome

The risk of the application is considered acceptable for the operator when the predicted exposure level is lower than the AOEL. Most of the models listed above show the total systemic exposure to the pesticide as a percentage of the AOEL, and exposure < 100% AOEL is considered acceptable.

If the risk is unacceptable, one can assess whether any risk mitigation measures (e.g. using personal protective equipment or engineering control) can be applied to reach an acceptable operator risk. If risk mitigation measures are required, one should also evaluate whether they are feasible and realistic under the local conditions of use of the pesticide.

Alternatively, if the risk is unacceptable, higher tier risk assessments may be done, such as: using measured pesticide absorption rates rather than the default ones provided in the model; using exposure levels that have been measured under local pesticide use conditions rather than the model estimates