Once the adverse effects have been identified the development of scientifically plausible risk scenarios through which these adverse effects can lead to consequences on the assessment end points and/ or protection goals.

A risk scenario may be defined as a theoretical sequence of events with an associated probability and consequence. In the context of risk assessment of LMOs, a risk scenario may be explained as a scientifically supportable chain of events through which the LMO might have an adverse effect on an assessment endpoint.

A well defined risk scenario should be scientifically plausible and allow the assessor to identify information that is necessary for the assessment of risks.

Although some risk scenarios may appear as obvious (e.g. potential for insect resistant plants to affect insect herbivore populations), it is always useful to identify the risk scenarios fully.

Clear and well-defined risk scenarios can also contribute to the transparency of a risk assessment because they allow others to consider whether or not the subsequent steps of the risk assessment have been adequately performed and facilitate the consideration of possible strategies to manage the identified risks.

A common challenge in generating a well-defined risk scenario is to choose representative species that would be exposed to the LMO. This is why an exposure assessment should be considered when selecting assessment endpoints.

When establishing risk scenarios several considerations may be taken into account. These may include:

1. gene flow followed by undesired introgression of the transgene in species of interest;
2. toxicity to non-target organisms;
3. allergenicity;
4. tri-trophic interactions and indirect effects; and
5. resistance development.

The following paragraphs explain some of these considerations in more detail: