Risk estimate by USDA-APHIS

General Information
Two concerns have been identified by USDA-APHIS (2008) that need to be addressed through the regulation process: 1) the persistence risk (weediness) of the recipient plant species, and 2) the potential harm or damage of the engineered trait. Primary and secondary factors are considered in estimating the potential risks posed by the cultivation of GM crops. The primary risk factors include: 1) the ability of the unmodified recipient plant species to persist in the wild, 2) the potential of the engineered trait to cause harm, injury, or damage. The secondary risk factors include: 1) how the recipient plant is commonly used (e.g., as a food or feed crop); 2) the impact of the engineered trait on the fitness of the GE plant, and 3) the degree of uncertainty associated with the trait and its possible impacts.

Based upon these factors, all plants have been sorted into four groups, listed in order of the likelihood that they will persist: Low, Moderate, High and Severe (Table 1). Engineered traits also have been grouped into four categories and listed in order of increasing potential hazard: Low, Moderate, High and Severe (Table 2)

Table 1
Table 1: Descriptors of crop plants species based on their risk of persistence (USDA-APHIS, 2008)
Persistence Risk of the crop species

  • Plant species with low persistence ranking include crops plants that are unlikely to persist in the environment without human intervention, and that have no inter-fertile wild relatives in the intended environment of release.
  • Plant species with moderate persistence ranking are crop plants known to be weakly persistent in the environment without human intervention, or have inter-fertile wild relatives in the intended environment of release.
  • Plant species with high persistence ranking are crop plants known to be strongly persistent in the environment without human intervention, or have inter-fertile wild relatives which are aggressive colonizers.
  • Plant species with severe persistence ranking are crop plants listed as noxious weeds or are known to be similarly aggressive in their ability to colonize and persist in the environment without human intervention.

Table 2
Table 2: Descriptors of engineered traits based on their potential hazard (USDA-APHIS, 2008)

Engineered traits with low hazard potential: This category includes 1) any new proteins or substances produced that are unlikely to be toxic or otherwise cause serious harm to humans, vertebrate animals, or invertebrate organisms upon consumption or contact with the plant or plant parts; 2) traits that don’t result in any morphological changes which could cause mechanical injury or damage; and, 3) traits with introduced sequences that have not been found to result in plant disease, and do not confer increased disease susceptibility.

Examples include marker genes that do not pose a food or feed safety concern, and viral genes where it is demonstrated that no protein is produced.

Engineered traits with moderate hazard potential: This category includes: 1) any new proteins or substances that are unlikely to be toxic or otherwise cause serious harm to humans or vertebrate animals upon consumption of or contact with the plant or plant parts or 2) traits that confer novel resistance to herbicides or 3) traits that have novel ability to cause mechanical injury or damage, or 4) traits that produce proteins or substances that are associated with plant disease, but are not prevalent in the area of release, or that confer an increased susceptibility to disease.

Examples include expression of new CRY proteins, known mechanisms of herbicide tolerance (e.g., CP4-EPSPS, which confers glyphosate tolerance), and production of viral movement proteins.

Engineered traits with high hazard potential: This category includes: 1) any new proteins or substances produced that may be toxic or to otherwise cause serious harm to humans or vertebrate animals, upon consumption of or contact with the plant or plant parts or 2) traits that produce an infectious entity which can cause disease in plants.

Examples include mercury hyper-accumulators or production of some pharmaceutical compounds.

Engineered traits with severe hazard potential: This category includes any new proteins or substances produced are known or likely to be highly toxic or fatal to humans or vertebrate animals, upon consumption of or contact with the plant or plant parts.

The values for persistence risk of the crop plant and the potential harm of the engineered trait have been combined to determine tiered categories that represent an initial estimation of levels of potential risks.

Table 3
Table 3: Categorization based upon persistence risk of the recipient plant species and potential harm or damage of the engineered trait (based on USDA-APHIS)

Persistence ranking of the
recipient plant species		 Potential Harm or Damage of Engineered Trait
Low Moderate High Severe
Low Category A Category A Category C Category D
Moderate Category A Category B Category C Category D
High Category D Category B Category C Category D
Severe Category B Category D Category D Category D

This categorical system gives practical and simple estimators of risks levels. Different permits (A, B, C, D) have been assigned to the defined categories: Permit A for category A, Permit B for category B, etc. As an example, Permit A will be issued to an event such as “Bt corn expressing Bt toxin” that poses negligible risk as the plant (corn/maize), is unlikely to persist in the environment and the protein expressed by the engineered trait (Bt toxin) has been evaluated and proved no harmful. At the opposite extreme is any event involving a federally listed noxious weed or a trait expressing a protein toxic to vertebrates. This would fall into Permit D.