Pesticide Registration Toolkit

Operator exposure modelling and local risk assessment

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 Tolerable Systemic Dose (TSD) (The TSD is equivalent the Acceptable Operator Exposure Level used in agricultural operator risk assessment)

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.

Generic operator exposure models for public health pesticides have been developed by the WHO Pesticide Evaluation Scheme (WHOPES). These models are used by WHOPES when evaluating the efficacy and safety of insecticides for vector control. They can also be used, and adapted to local situations, by national registration authorities.

Models

WHOPES has developed generic risk assessment models for various public health pesticide application scenarios. These models include both operator risk assessment as well as residential or bystander risk assessment. In this section, only operator risk assessment is discussed.

The following risk assessment models are available:

• Indoor and outdoor space spraying (exposure if mixing, loading and spraying the insecticide, and cleaning/maintenance of the spray equipment)

• Indoor residual spraying (exposure if mixing, loading and spraying the insecticide, and cleaning/maintenance of the spray equipment)

• Laviciding (exposure if mixing, loading and spraying the insecticide, and cleaning/maintenance of the spray equipment)

• Insecticide treated nets (exposure if treating nets with insecticides or professional net dipping)

• Aircraft disinsection (cabin crew exposure during spraying, and ground personnel exposure in sprayed aircraft)

Data required

The following data are generally used for an operator risk assessment using a WHOPES exposure model:

  • Acceptable Daily Intake (ADI) and (if relevant) Acute Reference Dose (ARfD)
  • If no ADI and/or ARfD are available: the No Observed Adverse Effect Level (NOEAL)
  • For insecticide treated nets: fraction of pesticide released in a wash; target concentration of the insecticide in the net; actual size of the net; concentration of insecticide in the dipping solution.
  • For indoor residual spraying: concentration of the a.i.in the formulation and the spray solution; additional data needed if the pesticide is volatile.
  • For space spraying: concentration of the a.i.in the formulation and the spray solution; dermal absorption percentage.
  • For larviciding: concentration of the a.i.in the formulation and the spray solution; dermal absorption percentage; target concentration of a.i. per unit area of surfaces)
  • For aircraft insectization: concentration of the a.i. in the formulation and the spray solution;
  • For other parameters used in the models, default values are provided which, however, can be locally adjusted.


Procedures

  1. Download the risk assessment spreadsheet (if available)
  2. Obtain the input data to run the model from the registration application dossier or, if absent, from reputable alternative sources.
  3. Establish or calculate the Tolerable Systemic Dose (TSD), and if relevant the Acute Tolerable Systemic Dose (TSDac)
  4. Calculate the exposure levels through all relevant exposure routes
  5. Calculate the total exposure
  6. Calculate risk ratios (total exposure/TSD)

This Assessment Summary Table 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 TSD. When it is higher, there are possible health risks and the planned use of the insecticide may not be acceptable..
If the risk may be unacceptable, one can assess whether any risk mitigation measures (e.g. reduced formulation concentration, (additional) personal protective equipment, or engineering controls) 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.