Tracking the source of Bacillus thuringiensis Cry1Ab endotoxin in the environment

The application of Bacillus thuringiensis (Bt) and the growing of genetically-modified crops are currently practised to control infestations of crop-eating insects. The increasing use of these biopesticides could lead to an increase in Cry1Ab endotoxin in both terrestrial and aquatic environments. The aim of this study was to quantify levels of Cry1Ab endotoxin and locate its source in the environment. Agricultural soils and surface waters were spiked with crystals (biopesticide-Dipel®) or with pure Bt-corn endotoxin. Cry1Ab concentrations were then determined with immunoassays. Additionally, surface water, soils and sediments were sampled in an area sprayed with Bt kurstaki and at a site where genetically-modified corn expressing Cry1Ab is grown. Isotopic analysis was performed on the endotoxin from Bt and Bt corn to characterize the proportions of 13C/12C and 15N/14N. The results showed that Bt-corn endotoxin is degraded more rapidly in water than in soils (t1/2: 4 and 9 days, respectively), while crystals appeared to be more resilient, as expected. The isotopic patterns of 13C and 15N in Bt-corn endotoxin differed markedly from Bt, making it possible to track the source of Cry1Ab in the environment. Preliminary field surveys indicate that Cry1Ab is fairly uncommon in aquatic environments, being found only at trace concentrations when it is detected.