The FAO Pesticide Registration Toolkit refers to bridging when an existing risk assessment conducted by a reputable body (generally a pesticide registration authority or an international organization) is reviewed and then compared to a local situation; subsequently, a conclusion is drawn about the risk in the local situation.

The existing risk assessment is referred to as the “reference assessment”, which is “bridged” to the conditions of use in a second country or region, the “local situation”.

Bridging does not require a full-fledged assessment of toxicity data and detailed local exposure estimations. Rather, it makes optimal use of work conducted by reputable evaluators elsewhere (often with more resources). But bridging does require good knowledge of the principles and procedures of risk assessment, to be able to interpret the reference risk assessment and assess its relevance to the local situation under review.

In some cases, a bridging assessment provides clear, unequivocal conclusions about the risk of a pesticide in a local situation and no further local assessments are needed. In other cases, conclusions are less clear, but the bridging assessment can focus the local risk assessment on specific issues of concern and as a result still facilitate the overall risk assessment. Sometimes bridging will not be possible; e.g. if the pesticide product deviates too much from the reference product or the exposure conditions between the two situations cannot be compared.

Conducting human health or environmental risk assessments of a pesticide requires considerable resources from a pesticide registration authority. Appropriate toxicological and environmental data need to be available; local estimates of exposure have to be made, either through an appropriate model or with other means; and staff needs to be trained in conducting the risk assessment and its interpretation. Such resources and tools may not always be available at the registration authority.

On the other hand, pesticide registration authorities or other reputable institutions with more resources may already have conducted risk assessments of the same pesticide. It could well be possible to use an existing assessment conducted elsewhere to draw conclusions about the risks of the pesticide in another country. In other words, it may not be necessary to “reinvent the wheel”.

Bridging of risk assessments is therefore one of several approaches for rationalizing the use of limited resources at the pesticide registration authority (see the Registration Strategies module)

The general principles and procedures of bridging are described in this guidance document.

The International Code of Conduct on Pesticide Management defines the hazard as

The risk of a pesticide is defined as

where exposure is the concentration or amount of a pesticide that reaches a target organism.

So in a risk assessment, we need to evaluate the hazard (e.g. toxicity) of a pesticide and the level of exposure. Data on hazard will determine the acceptable exposure level of humans or non-target organisms in the environment; the exposure assessment will show whether this acceptable level will be exceeded or not (Figure 1).

The same principle is applicable both to the assessment of risks to human health as well as to the environment.

Figure 1.  Principles of risk assessment

The basis of bridging is that we compare an existing risk assessment (the reference risk assessment) with – generally – an application for (re-)registration of the same or a similar pesticide in another country (the local situation under review). 

To be able to apply bridging, the reference risk assessment should provide a description of the hazard of the pesticide, the evaluated exposure level(s) and the resulting risk. It should also include a conclusion regarding the acceptability of that risk in the reference country (see section 3, step 2).

Bridging can be conducted if the pesticide active ingredient (a.i.) in the reference assessment is the same or similar to the one in the local situation. Ideally, the active ingredients are identical, i.e. manufactured by the same company through the same manufacturing process. However, active ingredients that are equivalent or otherwise substantially similar can also be bridged (see section 3, step 4).

Bridging is easier if the type and composition pesticide formulations are similar, but products with different a.i. concentrations in the formulated product or which have different formulation types can often also be bridged (see section 3, step 4).

It may be more obvious to conduct bridging if the exposure conditions and exposure levels in the local situation are similar to the reference assessment. However, this is not imperative and in many cases bridging is also possible if exposure is quite different (see section 3, step 6).

Bridging is essentially a comparative risk evaluation method. The outcome of a bridging assessment indicates whether the local risk is likely
to be lower, similar or higher than in the reference situation. If the institution that conducted the reference assessment also drew a conclusion about the acceptability of the evaluated risk, bridging can often lead to a conclusion about the risk in the local situation.

In some cases, however, no firm conclusion can be drawn about risk in the local situation. Bridging is then not feasible and the registration authority will need to conduct a different type of risk assessment. This is further described in section 3, steps 8 and 9.

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