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Decomposition of Aflatoxin in Soil¹

ABSTRACT

Corn infected by Aspergillus flavus and A. parasiticus is frequently contaminated with aflatoxin. If the contamination exceeds 20 ppb, the corn is considered unfit for animal consumption and is often plowed into the soil. This study was undertaken to determine the fate of aflatoxin in the soil. Aflatoxin B₁ was added to soil at a rate of 10,000 ppb. The soil was periodically extracted with acetone, and the quantity and species of aflatoxins were determined using thin-layer chromatographic procedures. The rate of decomposition was also monitored by adding ¹⁴C-aflatoxin to the soil and periodically measuring the evolution of ¹⁴CO₂.

Aflatoxin B₁ was observed to be rapidly reduced to aflatoxin B₂ when added to the soil. The speed of this reaction suggests a chemical mechanism. The resulting aflatoxin B₂ decomposed at a much slower rate, declining to a level where it could no longer be detected at 77 days. Aflatoxin G₂ was also detected 2 days after the addition of aflatoxin B₁ to the soil. Its concentration remained, however, well below that of the other aflatoxins observed. Aflatoxin G₂ reached a maximum concentration at 14 days after the addition of aflatoxin B₁ to the soil and was no longer detectable at 49 days. Microbial decomposition of ¹⁴C-aflatoxin B₁, as measured by CO₂ evolution, accounted for 14% of added ¹⁴C in 112 days of incubation. When wheat straw or sugar was added to the soil, the amount of aflatoxin C liberated as CO₂ was less.

¹ Contribution from the Department of Agronomy, Missouri Agric. Exp. Stn. Missouri Journal Series no. 8519. Approved by the Director.

² Graduate Research Assistant and Professor of Agronomy. respectively, University of Missouri-Columbia.

Received for publication April 8, 1980. Accepted for publication June 16, 1980.