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Aflatoxin Movement in Soil¹

ABSTRACT

Crops contaminated with > 20 µg kg^–1 aflatoxin cannot be transported across state lines. Contaminated preharvest crops are often disposed of by plowing the crop into the soil, thereby creating the potential for aflatoxin contamination of groundwater. The objective of this study was thus to determine the leaching and adsorption potential of aflatoxin in soils.

Leaching and adsorption studies were conducted with a silt loam, clay loam, sandy loam, and silty clay loam soil. Soil columns were utilized in the leaching experiment. The length of the column and the volume of soil used were 30.54 cm and 1234 cm³, respectively. A total of 2.5 mg aflatoxin B₁ was applied to the soil surface and the column was leached with 1 L of water under saturated conditions for 24 h. The results demonstrate that aflatoxin B₁ or its derivatives, aflatoxin B² and G², were retained within the upper 20 cm of all soil types. Between 80 and 92% of the total amount of aflatoxin applied was retained in the upper 2.5 cm of the soil columns. No aflatoxin was found in the leachate from any of the soils.

Freundlichs isotherm was used to establish adsorption coefficients for the soils by the slurry technique. The concentrations of aflatoxin used to establish the constants were 0.1, 1.0, 5.0, and 10 mg L^–1. The resulting adsorption coefficients were 238, 76, 46, and 17 mg kg^–1 for the silty clay loam, silt loam, clay loam, and sandy loam, respectively. As a result of the two experiments, aflatoxin contamination of groundwater would not be expected to occur unless the soils were extremely sandy or shallow.

Key Words: adsorption • groundwater contamination • mycotoxin

¹ Scientific Article no. A-3831 and Contribution no. 6811 of the Maryland Agric. Exp. Stn., Dep. of Agron., Univ. of Maryland, College Park, MD 20742.

² Graduate research assistant and assistant professor, Dep. of Agron., Univ. of Maryland.

Received for publication May 14, 1984.