Assessing and Limiting Contamination of the Seed Supply by Bt Toxins

EPA Grant Number: F07F21023
Title: Assessing and Limiting Contamination of the Seed Supply by Bt Toxins
Investigators: Heuberger, Shannon
Institution: University of Arizona
EPA Project Officer: Michaud, Jayne
Project Period: January 1, 2007 through January 1, 2010
RFA: STAR Graduate Fellowships (2007) RFA Text |  Recipients Lists
Research Category: Biology/Life Sciences , Academic Fellowships , Fellowship - Entomology


Genetically engineered cotton that produces toxins from Bacillus thuringiensis (Bt) is widely used for insect control. Contamination of conventional cotton varieties by gene flow from Bt cotton varieties was revealed in a preliminary study. Such contamination results in liabilities for organic farmers, complicates removal of genetically engineered plants from the environment if unanticipated problems arise, and could negatively impact programs designed to delay insect resistance to Bt toxins. The mode by which Bt cotton has entered the seed supply of conventional cotton is unknown, but possibilities include pollen-mediated gene flow (outcrossing), contamination through volunteer plants or human error. Objectives of this project are to 1) quantify Bt contamination in the non-Bt cotton seed supply, 2) evaluate pollen flow, emergence of volunteer plants, and human error as potential sources of contamination, and 3) use simulation models to predict future contamination levels and test strategies for minimizing contamination.


Bags of conventional cotton seed will be screened for Bt toxin using enzyme-linked immunosorbent assay (ELISA) to determine a baseline level of contamination. Fifteen non-Bt cotton seed production fields throughout Arizona will be monitored in each of the three years of study, with data collected on emergence of volunteer plants, pollinator abundance, distance from Bt cotton fields, agronomic practices, and contamination level of produced cotton seed at the end of the season. A greenhouse study will be used to closely examine the effects of pollinator abundances, pre-existing contamination levels, and herbivory on changes in contamination rate. Finally, computer simulation modeling will be used to explore the effects of examined variables on future contamination rates.

Expected Results:

Low rates of contamination in seed bags are expected (i.e., 0-1%), based on results from preliminary study. The highest rates of Bt-outcrossed cotton plants will likely occur in fields with high pre-existing Bt contamination levels, proximity to Bt cotton fields, and high pollinator activity. Results from this study will be useful for seed producers and policy makers in designing methods that reduce contamination of conventional crops by genetically modified organisms.

Supplemental Keywords:

Bacillus thuringiensis crops, contamination, gene flow, cotton, transgenic, modeling,

Progress and Final Reports:

  • 2007
  • 2008
  • Final