According to the authors of this literature review, there are no innate differences in the potential environmental impact of GM crops compared with non-GM varieties. Crucial questions remain, however, as to what constitutes a "significant", and more importantly, an "acceptable" effect on the environment. Such questions are being asked about GM crops that have not previously been asked about varieties developed by so-called conventional methods.

Altered biodiversity, increased crop pervasiveness, and the effect of toxins such as Bt in soil and water systems are considered, as well as the impact of "free" transgenic DNA in the environment. The authors suggest a case-by-case approach for making decisions about the commercial cultivation of GM crops; the impact of gene transfer from a GM crop to a wild plant relative or other ecosystems will depend on the nature of the gene, as well as the local ecology.

The authors conclude that to minimise the environmental impact of GM crops or new agricultural practices associated with their commercial cultivation, the timing and expression of plant transgenes should be more specific. A wider range of pest resistance mechanisms is also needed to reduce the selective pressure on the pest population. In acknowledging that new and more creative ways of managing crops may be needed, the authors call for incentives that will require GM crops to be combined with other agricultural practices that promote crop and wildlife diversity, as well as soil fertility.

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