Solvent-dependent transformation of aflatoxin B1 in soil

Abstract

To date, all studies of aflatoxin B1 (AFB1) transformation in soil or in purified mineral systems have identified aflatoxins B2 (AFB2) and G2 (AFG2) as the primary transformation products. However, identification in these studies was made using thin layer chromatography which has relatively low resolution, and these studies did not identify a viable mechanism by which such transformations would occur. Further, the use of methanol as the solvent delivery vehicle in these studies may have contributed to formation of artifactual transformation products. In this study, we investigated the role of the solvent vehicle in the transformation of AFB1 in soil. To do this, we spiked soils with AFB1 dissolved in water (93:7, water/methanol) or methanol and used HPLC-UV and HPLC-MS to identify the transformation products. Contrasting previous published reports, we did not detect AFB2 or AFG2. In an aqueous-soil environment, we identified aflatoxin B2a (AFB2a) as the single major transformation product. We propose that AFB2a is formed from hydrolysis of AFB1 with the soil acting as an acid catalyst. Alternatively, when methanol was used, we identified methoxy aflatoxin species likely formed via acid-catalyzed addition of methanol to AFB1. These results suggest that where soil moisture is adequate, AFB1 is hydrolyzed to AFB2a and that reactive organic solvents should be avoided when replicating natural conditions to study the fate of AFB1 in soil.

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Acknowledgements

The authors express their gratitude for the editing and insightful comments provided by Mary Starr and Weiwei Li in contributing to this manuscript.

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Correspondence to James M. Starr.

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The research described in this document was conducted in whole at The University of Iowa in the Department of Preventive Medicine and Environmental Health in Iowa City, Iowa. The research was funded wholly through a grant from The University of Iowa Center for Health Effects of Environmental Contamination.

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Starr, J.M., Rushing, B.R. & Selim, M.I. Solvent-dependent transformation of aflatoxin B1 in soil. Mycotoxin Res 33, 197–205 (2017). https://doi.org/10.1007/s12550-017-0278-x

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Keywords

  • Aflatoxin B1
  • Aflatoxin B2a
  • Soil
  • Transformation
  • Breakdown
  • Mycotoxin