Environmental Safety of Genetically Engineered Crops

Environmental Biosafety Issues Associated with Genetically Engineered Crops

21 Environmental Biosafety Issues Associated with Genetically Engineered Crops Cholani Weebadde and Karim M. Maredia Biotechnological tools allow the transfer of DNA between distantly related species. These techniques have facilitated the engineering of novel traits into crops, including insect resistance, herbicide tolerance, virus resistance and nutritional enhancement. The most widely deployed genetically engineered (GE) crops today contain insect resistance and herbicide tolerance, with farmers in over 25 countries growing these crops (James 2008). Many other traits are in the pipeline, such as tolerance to drought and cold and increases in the ability to use soil nitrogen (Grumet et al., this volume). Many of these target traits have been difficult or impossible to develop using conventional crop improvement techniques. Among the key considerations that must be weighed in the release of GE crops is whether they pose an unacceptable risk to the environment and human safety. These concerns have been recognized in many countries and have led to the establishment of regulatory policies and decision-­ making bodies. In this chapter we provide an introduction to the ecological concerns that have been raised with respect to GE crops and describe how those risks can be assessed. Environmental Issues and Concerns Associated with GE Crops Concerns about the potential environmental impacts of GE crops and approaches to evaluate these concerns have been discussed by many authors, including excellent reviews by Conner et al. (2003), Dale et al. (2002), Hancock (2003), Nickson (2008), and Snow et al. (2005). These concerns are briefly outlined here. Environmental concerns consider both natural ecosystems and agroecosystems, and primarily center around the possibility that production of GE crops might reduce the biodiversity of organisms living in or near areas where they are grown. The potential negative environmental impacts associated with transgenic crops can be grouped into the following four broad areas: (1) weediness and invasiveness, (2) gene flow, (3) nontarget effects, and (4) pest resistance. 22| Cholani Weebadde and Karim M. Maredia Weediness and Invasiveness One of the potential concerns about GE crops is that they will become agricultural weeds or invade natural habitats (Hancock, this volume). The term weediness is best applied to a species’ competiveness in agricultural fields, while invasiveness relates to how effectively a species competes in natural environments. The concern is that traits introduced by genetic engineering might increase the reproductive success or fitness of the crop and thereby increase its competitive ability. For example, if a crop was engineered for tolerance to a particular herbicide, it would be more difficult to control as a “volunteer” in subsequent plantings. Alternatively, a crop engineered for salt tolerance may be able to invade previously inaccessible environments and outcompete other wild species. It should be noted, however, that the competitive ability of a plant is a function of many characteristics regulated by numerous genes acting in concert, and most crops have been so domesticated that they have difficulty surviving in the wild (Hancock et al. 1996; Hancock and Hokanson 2003). Genes controlling traits such as reproductive effort, seed size, dormancy, germination rate, ripening periods, and fruit and seed dehiscence all act in concert to determine relative competitiveness in different environments (Hancock 2003; Keeler 1989; Baker 1974). The potential impact of any given transgene will depend on competitive characteristics of the crop or recipient population, the specific environment into which it is introduced, and fitness traits conferred by the introduced gene. Gene Flow The possibility that transgenes may be transferred via pollen “escape” to wild or weedy relatives growing nearby is often cited as a potential risk of GE crops. Gene flow between crops and their close wild relatives is a well-­ documented natural phenomenon (Ellstrand et al. 1999). Several kinds of gene flow from GE crops to relatives are possible, including (1) gene/ pollen flow from GE crops to conventionally bred crops, (2) gene/pollen flow from GE crops to landraces and (3) gene/pollen flow from GE crops to wild relatives (Hancock, this volume; Hancock and Halsey, this volume). In the first case, there is concern that seeds and fruit of organic or conventionally grown crops will acquire transgenes from nearby GE crops. Levels of gene flow can be controlled by isolation distances, but at present, laws do restrict how close GE crops can be planted to organic ones. In the second case, pollen flow is expected to occur wherever GE crops and landraces are grown in close proximity. If farmers choose to keep the hybrids, the landraces could be dramatically altered. However, landraces are rarely static...