Environmental fate and effects of Bacillus thuringiensis (Bt) proteins from transgenic crops: a review.

This paper reviews the scientific literature addressing the environmental fate and nontarget effects of the Cry protein toxins from Bacillus thuringiensis (Bt), specifically resulting from their expression in transgenic crops. Published literature on analytical methodologies for the detection and quantification of the Cry proteins in environmental matrices is also reviewed, with discussion of the adequacy of the techniques for determining the persistence and mobility of the Bt proteins. In general, assessment of the nontarget effects of Bt protein toxins indicates that there is a low level of hazard to most groups of nontarget organisms, although some investigations are of limited ecological relevance. Some published reports on the persistence of the proteins in soil show short half-lives, whereas others show low-level residues lasting for many months. Improvements in analytical methods will allow a more complete understanding of the fate and significance of Bt proteins in the environment.

Effect of prairie grass on the dissipation, movement, and bioavailability of selected herbicides in prepared soil columns.

Phytoremediation of pesticide-contaminated sites using a prairie grass mixture (big bluestem, yellow indiangrass, and switch grass) has been suggested as a low-cost in situ remediation strategy. In this study, the proposed phytoremediation technique was applied to artificially prepared soil columns that were fortified with high concentrations of four herbicides (atrazine, alachlor, metolachlor, and pendimethalin). The fate and toxicity of the herbicides were compared with results from soil columns lacking vegetation. After either 150 or 240 d of phytoremediation, soils were watered with 7.5 cm of water, and leachate was collected. Columns were then divided into three sections (top, middle, bottom). For each section of the column, chemical analysis (ethyl acetate and water extractions), earthworm accumulation tests, and lettuce seedling growth tests were performed. The leachate was chemically analyzed and tested for chronic toxicity to algae. Atrazine and alachlor degraded rapidly in the column, and the total amount recoverable was less than 2% of applied. After 250 d, vegetation reduced the total recoverable amounts of metolachlor and pendimethalin by 78 and 39%, respectively. Metolachlor was the only compound found in leachate, and the amounts recovered were reduced 5- to 20-fold by vegetation. Vegetation decreased the bioavailability of pendimethalin as measured by 8-d, earthworm bioaccumulation factors (BAFs) and lettuce seedling growth assays. Decreases in mobility and bioavailability indicate that this technique may stabilize pesticide residues in addition to increasing dissipation rates.

Acute toxicity and cholinesterase inhibition in larval and early juvenile walleye exposed to chlorpyrifos.

Application of organophosphorus (OP) insecticides to agricultural fields during the spring often overlaps the period of spawning, egg incubation, and larval stages of fish species such as walleye (Stizostedion vitreum). Because life stage can affect uptake, distribution, and effects of contaminants, our objective was to identify the most sensitive life stage of walleye tochlorpyrifos, a broad-spectrum OP insecticide. Prolarvae (yolk sac, endogenous feeding stage) were least sensitive to chlorpyrifos (median lethal concentration [LC50] = 225-316 microg/L), and postlarvae I (oil globule, exogenous feeding stage) were less sensitive (LC50 = 24-29 microg/L) than postlarvae II (oil globule absent; LC50 = 12-13 microg/L). The differences in sensitivity of the larval stages coincide with stages of gill development. Gill filaments were absent until the end of the prolarval stage, and development of secondary lamellae did not occur until the end of the postlarval I stage. Juvenile fish were less sensitive than postlarval stages, but did not differ significantly among the juvenile ages tested. The LC50s ranged from 37 to 45 microg/L for 30- and 90-d-old juvenile walleye, respectively. Larval walleye survived when cholinesterase (ChE) activity was inhibited by as much as 90%; however, 60- and 90-d-old juvenile walleye did not survive when ChE activity was inhibited more than 71%.