Abstract
To inform the ecological risk assessment (ERA) of a transgenic crop with multiple insecticidal traits combined by conventional breeding (breeding stack), a comparative field study is customarily conducted to compare transgenic protein concentrations in a breeding stack to those in corresponding component single events used in the breeding process. This study tests the hypothesis that transgenic protein expression will not significantly increase due to stacking, such that existing margins of exposure erode to unacceptable levels. Corroboration of this hypothesis allows for the use of existing non-target organism (NTO) effects tests results, where doses were based on the estimated environmental concentrations determined for a component single event. Results from over 20 studies comparing expression profiles of insecticidal proteins produced by commercial events in various combinations of conventionally-bred stacks were examined to evaluate applying previously determined no-observed-effect concentrations (NOECs) to stack ERAs. This paper presents a large number of tests corroborating the hypothesis of no significant increase in insecticidal protein expression due to combination by conventional breeding, and much of the variation in protein expression is likely attributed to genetic and environmental factors. All transgenic protein concentrations were well within conservative margins between exposure and corresponding NOEC. This work supports the conclusion that protein expression data generated for single events and the conservative manner for setting NTO effects test concentrations allows for the transportability of existing NOECs to the ERA of conventionally-bred stacks, and that future tests of the stated hypothesis are no longer critically informative for ERA on breeding stacks.
Highlights
Insect pests in agricultural fields can cause immense damage to crops, lowering yields and decreasing grower income
The objective of this work was to examine the results from multiple studies conducted to compare transgenic protein concentrations between several stacks and component single events, and to examine how the observed statistically significant increases in expression levels relate to no-observed-effect concentrations (NOECs)
The conclusion of the studies examined collectively in this paper is that the transgenic protein concentrations were generally similar between the stack and the corresponding component single event, indicating a lack of interaction that increases the production of the transgenic insecticidal proteins due to combination of the traits by conventional breeding
Summary
Insect pests in agricultural fields can cause immense damage to crops, lowering yields and decreasing grower income. Transgenic crops that have been engineered to express genes encoding proteins that are toxic to specific insect pests have been labeled as plant incorporated protectants (PIP) by the United States Environmental Protection Agency (US EPA) (Matten et al 2012). These PIPs provide benefits to growers as protection to optimize yield and benefits to the environment, as they may reduce the need for and localize the application of insecticides (Carpenter et al 2002; Brookes and Barfoot 2017a, b). Because these proteins have toxic activity to insect pests, it is important to evaluate the risk that these proteins may affect non-target organisms (NTOs) due to cultivation of transgenic crops in the environment (Carpenter et al 2002; Romeis et al 2008)
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