Dissipation
of Insecticidal Cry1Ac Protein and Its
Toxicity to Nontarget Aquatic Organisms
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Abstract
The
widespread cultivation of <i>Bacillus thuringiensis</i> crops
has raised public concerns on their risk to nontarget organisms.
Persistence of Cry1Ac protein in soil, sediment and water and its
toxicity to nontarget aquatic organisms were determined. The dissipation
of Cry1Ac toxin was well described using first order kinetics, with
the half-lives (DT<sub>50</sub>) ranging from 0.8 to 3.2, 2.1 to 7.6
and 11.0 to 15.8 d in soil, sediment and water, respectively. Microbial
degradation played a key role in the dissipation of Cry1Ac toxin and
high temperature accelerated the processes. Cry1Ac toxin was more
toxic to the midge <i>Chironomus dilutus</i> than the amphipod <i>Hyalella azteca</i>, with the median lethal concentration (LC<sub>50</sub>) of <i>C. dilutus</i> being 155 ng/g dry weight
and 201 ng/mL in 10-d sediment and 4-d water bioassays, respectively.
While Cry1Ac toxin showed toxicity to the midges, risk of <i>Bt</i> proteins to aquatic nontarget organisms was limited because
their environmentally relevant concentrations were much lower than
the LC<sub>50</sub>s