Finally a consideration for the possibility of a cumulative or synergistic effect that may occur as a result of a number of these adverse effects being realised within a single LMO or due to a number of LMOs being present in close proximity within the likely potential receiving environment should be evaluated within the risk assessment.

Resistance development – The extensive use of herbicides and insect resistant LM crops has the potential to result in the emergence of resistant weeds and insects. Similar breakdowns have routinely occurred with conventional crops and pesticides. Several weed species have developed resistance to specific herbicides which are extensively used in combination with herbicide-resistant LM crops. Insect-resistant Bt-crops similarly could lead to the emergence of Bt-resistant insects (FAO, 2004).

The extent of the adverse effect and possible consequences of the insurgence of resistant weeds and insects should be thoroughly considered in a risk assessment. Some regulatory frameworks require that risk management strategies are identified in order lower the risk of resistance development.