Occurrence, leaching, and degradation of Cry1Ab protein from transgenic maize detritus in agricultural streams

- Bt maize with Cry1Ab protein enters aquatic ecosystems, but fates are understudied.
- Examined occurrence, leaching, and degradation of Cry1Ab in agricultural streams
- Cry1Ab protein concentration in streams and tile drains was 3-60 ng/L.
- 99% of Cry1Ab leached from submerged Bt maize leaves into water over 70 d.
- Cry1Ab protein degraded rapidly in microcosms with water-column microorganisms.
- Cry1Ab may be pseudo-persistent at watershed scales due to multiple input pathways.

The insecticidal Cry1Ab protein expressed by transgenic (Bt) maize can enter adjacent water bodies via multiple pathways, but its fate in stream ecosystems is not as well studied as in terrestrial systems. In this study, we used a combination of field sampling and laboratory experiments to examine the occurrence, leaching, and degradation of soluble Cry1Ab protein derived from Bt maize in agricultural streams. We surveyed 11 agricultural streams in northwestern Indiana, USA, on 6 dates that encompassed the growing season, crop harvest, and snowmelt/spring flooding, and detected Cry1Ab protein in the water column and in flowing subsurface tile drains at concentrations of 3-60 ng/L. In a series of laboratory experiments, submerged Bt maize leaves leached Cry1Ab into stream water with 1% of the protein remaining in leaves after 70 d. Laboratory experiments suggested that dissolved Cry1Ab protein degraded rapidly in microcosms containing water-column microorganisms, and light did not enhance breakdown by stimulating assimilatory uptake of the protein by autotrophs. The common detection of Cry1Ab protein in streams sampled across an agricultural landscape, combined with laboratory studies showing rapid leaching and degradation, suggests that Cry1Ab may be pseudo-persistent at the watershed scale due to the multiple input pathways from the surrounding terrestrial environment.

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