Lower fumonisin mycotoxin levels in the grain of Bt corn grown in the United States in 2000-2002.

Fumonisins were monitored in corn grain collected from Bt hybrids grown in 107 locations across the United States in 2000-2002. Bt corn hybrids contain the Cry1Ab protein from Bacillus thuringiensis that controls European corn borers and other stalk-boring pests. Fumonisin levels were frequently lower in grain from Bt hybrids grown in field trials under conditions of natural (FACT trials) or manual insect infestation (university trials). Over three years of FACT trials, there were 126/210 comparisons when fumonisin levels in grain from control hybrids were >2 ppm, exceeding U.S. FDA guidance levels of 2 ppm for human food. Grain from Bt hybrids was at or below 2 ppm of fumonisins for 58 of the 126 comparisons. The use of Bt hybrids can increase the percentage of corn grain that would be suitable for use in food and feed.

Determination of total fumonisins in corn by competitive direct enzyme-linked immunosorbent assay: collaborative study.

Fumonisins-mycotoxins produced by some Fusarium species-have been shown to be the causative agent of diseases in horses and other domesticated animals as well as possible carcinogens in humans. A collaborative study was conducted to evaluate the effectiveness of a competitive direct enzyme-linked immunosorbent assay (CD-ELISA) for the determination of total fumonisins (B1, B2, and B3) in corn. The test portion was extracted with methanol-water (7 + 3), filtered, diluted, and tested on the CD-ELISA. Naturally and artificially contaminated corn test portions were sent to 13 collaborators in the United States. Naturally contaminated field test portions were prepared at 3 different levels. Artificially contaminated test portions were spiked at 1.0, 3.0, and 5.0 mg/kg total fumonisins (B1, B2, and B3). Average recoveries of total fumonisins were 120, 100, and 90%, respectively. The relative standard deviations for repeatability ranged from 13.3 to 23.3% and the relative standard deviations for reproducibility ranged from 15.8 to 30.3% across all levels tested. HORRAT values, calculated for each individual sample, ranged from 1.24 to 1.94. This method demonstrated acceptable intra- and interlaboratory precision at the levels tested.

Comparison of Fumonisin Concentrations in Kernels of Transgenic Bt Maize Hybrids and Nontransgenic Hybrids.

Maize hybrids genetically engineered with genes from the bacterium Bacillus thuringiensis (Bt maize) express CryIA(b) and other Cry proteins that are toxic to certain insects, particularly the European corn borer (Ostrinia nubilalis). Maize kernel feeding by O. nubilalis often leads to infection by fungi in the genus Fusarium, including the fumonisin-producing species F. verticillioides and F. proliferatum. In field experiments in 1995, 1996, and 1997, transgenic maize hybrids and near-isogenic, nontransgenic hybrids were manually infested with neonatal European corn borer larvae. Manual infestation increased Fusarium ear rot severity and fumonisin concentrations in kernels of nontransgenic hybrids. Transgenic hybrids with kernel expression of CryIA(b) consistently experienced less insect feeding on kernels and less Fusarium ear rot than their nontransgenic counterparts. In manually infested treatments, these hybrids also exhibited lower concentrations of fumonisins in kernels compared with their nontransgenic counterparts. In manually infested treatments in 1995, mean fumonisin B1 concentrations were 8.8 µg/g in the nontransgenic hybrid and 6.7 or 3.0 µg/g in transgenic hybrids. In 1996, mean fumonisin B1 concentrations in manually infested treatments were 4.9 µg/g (range 2.3 to 8.8) for nontransgenic and 1.2 µg/g (range 1.0 to 1.3) for transgenic hybrids with kernel expression. Mean total fumonisin concentrations (fumonisin B1 + B2 + B3) were 7.0 µg/g (range 3.0 to 12.2) for nontransgenic and 1.7 µg/g (range 1.5 to 1.9) for transgenic hybrids with kernel expression. In 1997, mean fumonisin B1 concentrations in manually infested treatments were 11.8 µg/g (range 7.6 to 17.3) for nontransgenic and 1.3 µg/g (range 0.8 to 2.2) for transgenic hybrids with kernel expression of CryIA(b) or Cry9C. Mean total fumonisin concentrations were 16.5 µg/g (range 10.7 to 24.0) for nontransgenic and 2.1 µg/g (range 1.5 to 3.1) for transgenic hybrids with kernel expression. Transgenic hybrids that do not express CryIA(b) or Cry9C in kernels did not consistently have fumonisin concentrations different from the nontransgenic hybrids. Higher fumonisin concentrations in nontransgenic hybrids were associated with high European corn borer populations during the early reproductive stages of the maize plants. These results indicate that under some conditions, genetic engineering of maize for insect resistance may enhance its safety for animal and human consumption.

Methods for Detection and Quantitation of Fumonisins in Corn, Cereal Products and Animal Excreta.

Fumonisins are a group of naturally occurring mycotoxins produced by strains of several different mating populations of Gibberella fujikori ( Fusarium section Liseola ). Fumonisins have been shown experimentally to be the causative agent of equine leukoencephalomalacia (ELEM), porcine pulmonary edema (PPE) syndrome, and to produce liver cancer in rats. Epidemiological evidence also indicates a possible correlation between the fumonisins and human esophageal cancer. The analytical method of choice for most samples has been high performance liquid chromatography (HPLC) using fluorescence detection. The present work describes the baseline resolution using an isocratic mobile phase of the o-phthalaldehyde (OPA) derivatives of fumonisin B1 (FB1), fumonisin B2 (FB2) and fumonisin B3 (FB3). The separation of the hydrolyzed forms of FB1, partially hydrolyzed FB1 (PHFB1) and fully hydrolyzed FB1 (HFB1) is also described. Results of analyses of com from 1992 crop year in both Iowa (mean = 0.05 µg/g, N = 80) and Pennsylvania (mean = 0.37 µg/g, N = 91) were significantly lower than mean levels reported for 1988, 1989, 1990 and 1991. Significant levels of FB1 were found in commercially prepared rat (2 µg/g) and horse (37 µg/g) feed. Levels of FB1, (0.05 to 1.2 µg/g) found in corn meal purchased from local groceries indicated a possible source of low level exposure of humans to fumonisins. The simultaneous isocratic separation of FB1, FB2, FB3 and the hydrolysis products of FB1, PHFB1 and HFB1from fecal samples indicated a possible difference in metabolism of FB1 in ruminants and nonruminants. In ruminants, the hydrolyzed forms of FB1 composed a significant (60 to 90%) portion of the total FB1 concentration found in the feces. In nonruminants, the parent compound, FB1, was the dominant (90%) species present. Both ruminants and nonruminants showed limited excretion of FB1 in their urine (<1 to 7% total FB1 in excreta).