Toxicity to non-target organisms – The potential for an introduced gene product to be toxic to organisms in the environment is typically addressed by controlled exposure in the environment or by direct toxicity testing, or by a combination of the two. Non-target organisms may include, for instance, herbivores, natural enemies (e.g. parasitoids and predators), pollinators and pollen feeders, soil ecosystems and weeds.
If toxicity testing is needed, it typically follows a sequential series of tiered tests. Early tier studies involve highly controlled laboratory environments where representative or surrogate test species are exposed to high concentrations of the gene product being studied (i.e. worst case exposures) to determine if there are any toxic effects. If toxic effects are observed in early tier tests or if unacceptable uncertainty exists, more realistic conditions representative of field-level exposures can be tested to determine the extent of the risk.
The gene products of the modified genetic elements in LMOs may be produced in very small quantities thus may be difficult to isolate in the amounts required for toxicity testing. If this is the case, and it is determined that toxicity tests are required, the risk assessor may consider results from tests using gene products obtained from alternate (surrogate) sources (e.g. bacterial expression systems or the organism from which the transgene was derived) provided that these gene products are chemically and functionally equivalent.
Allergenicity – Allergies are a type of adverse immunological response that affect individuals who are predisposed to certain types of substances (i.e. allergens). Allergens are often proteins or peptides.
In considering allergenicity caused by LMOs, it is important to take into account the exposure to proteins newly expressed by the LMO, including some variants of these proteins that may be produced uniquely by the LMO. As a consequence, some allergenicity studies must be carried out with proteins isolated from the LMO itself, and not obtained from alternate (surrogate) source such as a bacterial expression system).
It is also possible that allergens known to exist in the recipient or parental organism(s) are produced in higher amounts, for example by over-expression of the gene that encodes a protein that is known to be a common allergen.
Tri-trophic interactions and indirect effects – “Tri-trophic interaction” is an important concept in ecology and occurs when a change at one trophic level indirectly affects trophic levels which are more than one step away. Consideration of tri-trophic interactions and indirect effects may be relevant to biodiversity protection goals.
Observations and experimentation to identify such effects are challenging because of the complexity of ecological interactions, the difficulty of establishing causality between observed variation and treatment effects (e.g. the presence of the modified genetic element or its products), and natural variability in populations over time. Moreover, in a food chain (or food web), effects at the trophic levels may become observable only at a later stage.
Example – A tri-trophic interaction
“Suppose that there were a grassland where the major herbivore was a species of vole (n.b. a small rodent) which eats grass seeds and that this vole was able to reach population levels which allowed the vole to eat nearly all of the seeds. Further suppose that the main predator of this vole was a species of hawk and that this hawk was capable eating enough voles to reduce the voles population to nearly zero (at least to the point that voles could no longer eat very many of the seeds). So, if the population of hawks is high, the population of voles is low and the grass produces lots of seeds. However, if the population of hawks is low, the vole population will be high, and the grass will disperse few seeds.
Source: Abrahamson (website).
