Pesticide Registration Toolkit

Existing WHO risk assessment.


The WHO Pesticide Evaluation Scheme (WHOPES) conducts assessments of the safety and efficacy of pesticides used in public health pest management. The WHOPES Working Group advises WHO on these aspects for individual pesticides.
The WHOPES Working Group will use the generic risk assessment models developed by WHO to assess the risks of the pesticides it evaluates, under global, worst case, expected use conditions. (See the Toolkit Assessment page on operator exposure models for public health). A short summary of the risk assessment for a given product is published in the Working Group reports, which provide the main assumptions and conclusions of the assessment.  
The existing WHOPES risk assessment is reviewed and a comparison is made between pesticide use situation described for the other country with the local situation. On the basis of this comparison, the registrar then evaluates whether the risk in the local situation is similar, higher or lower than in the other country. 
This extrapolation is based on the principle that the human toxicity of a pesticide is relatively similar, irrespective of the country or situation in which the pesticide is being used. Differences in operator risk are then determined mainly by differences in the level of exposure. The assessment therefore provides a qualification, and where possible quantification, of the difference in exposure between a situation for which a thorough and reliable risk assessment exists, and the situation for the pesticide under review.
Bridging can only be done for products containing the same active ingredient (technical material). If the manufacturing source of the technical materials is different, whenever possible, equivalence between the two technical materials should be established.
The more similar the pesticide use situation (e.g. application equipment and conditions, PPE, technical capacity of the user) the easier bridging is likely to be. When the differences in use situations are greater, bridging may be more complicated or even impossible.
Note that the assumption that human toxicity of the pesticide is similar, irrespective of the country in which it is used, may not always be true. In certain cases, persons may be more, or less, susceptible to adverse effects caused by pesticides; see the section on General hazard assessment, for more information.

Data required

The following data are generally used for bridging operator risk assessments.
  • The WHOPES Working Group report for the pesticide of interest
  • Information on the proposed directions for use of the pesticide to be registered: e.g. application rate and frequency, application equipment.
  • Information on local pesticide application practices for the uses under review: e.g. work rate, duration of application per day, number of applications per year, personal protective equipment and possible other protective measures.


  1. Go to the WHOPES Safety and Effectiveness page.
  2. The most recent Working Group report is published on this page. For older ones, click the link to Reports of the previous WHOPES Working Group meetings (full list).
  3. After opening the report, the risk assessment is summarized in the chapter Safety Assessment.
  4. Compare the application details for which the WHOPES risk assessment was conducted with the directions for use and application practices in the local situation.
  5. Assess whether the risk in the local situation is likely to be lower, similar or higher than in the WHOPES assessment.

Interpretation of the outcome

In principle, the WHOPES Working Group assesses operator risks under global, worst case, expected use conditions. This should normally cover the use conditions in the local situation your country.
However, if operator risk is likely to be higher in the local situation when compared to the WHOPES assessment, the registration authority may conduct its local risk assessment, using the WHOPES exposure models, but with local input parameters.