Aflatoxin decomposition in various soils

Abstract

The persistence of aflatoxin in the soil environment could potentially result in a number of adverse environmental consequences. To determine the persistence of aflatoxin in soil, 14C-labeled aflatoxin B1, was added to silt loam, sandy loam, and silty clay loam soils and the subsequent release of 14CO2 was determined. After 120 days of incubation, 8.1% of the original aflatoxin added to the silt loam soil was released as CO2. Aflatoxin decomposition in the sandy loam soil proceeded more quickly than the other two soils for the first 20 days of incubation. After this time, the decomposition rate declined and by the end of the study, 4.9% of the aflatoxin was released as CO2. Aflatoxin decomposition proceeded most slowly in the silty clay loam soil. Only 1.4% of aflatoxin added to the soil was released as CO2 after 120 days incubation. To determine whether aflatoxin was bound to the silty clay loam soil, aflatoxin B1 was added to this soil and incubated for 20 days. The soil was periodically extracted and the aflatoxin species present were determined using thin layer chromatographic (TLC) procedures. After one day of incubation, the degradation products, aflatoxins B2 and G2, were observed. It was also found that much of the aflatoxin extracted from the soil was not mobile with the TLC solvent system used. This indicated that a conjugate may have formed and thus may be responsible for the lack of aflatoxin decomposition.

Aspergillus flavus aflatoxin occurrence and expression of aflatoxin biosynthesis genes in soil

“…No. of Aspergillus flavus propagules (log cfuÁ(g soil) -1 ) study is one of the first to demonstrate the rapid degradation of AFB1 in soil, as compared with previous work (Angle 1986) using 14 C-radiolabelled AFB1, which showed that there is minimal mineralization of this important mycotoxin in soil. Even considering that our study was conducted in vitro under favorable conditions (i.e., temperature and soil water content) for microbial growth and AFB1 degradation, the detection of AFB1 in soil approximately 5 months after corn harvest suggests that in the warm conditions of the Mississippi Delta, corn debris gradually releases AFB1 into the soil, prolonging the time span of aflatoxin contamination.…”

“…However, little is known on the occurrence and fate of aflatoxin in soil. Radiological assays conducted to assess the fate of aflatoxin B1 (AFB1) in soil indicated that a low level of mineralization of AFB1 to CO 2 was observed, with less than 1%-8% mineralized in 120 days (Angle 1986). Not surprisingly, several microorganisms have the potential to degrade aflatoxins (Ciegler et al 1966), especially bacteria, e.g., Flavobacterium (Line and Brackett 1995) and Mycobacterium (Hormisch et al 2004).…”

Solvent-dependent transformation of aflatoxin B1 in soil

“…These results suggest that previous studies (Angle and Wagner 1980;Goldberg and Angle 1985;Bean et al 1986;Angle 1986) describing adsorption, mineralization rates, and leeching of AFB 1 in soil lacked sufficient selectivity to correctly identify the transformation products. Since the soils used in those studies were mostly acidic, and methanol was the solvent vehicle, the transformation products may have been the methoxy aflatoxins rather than AFB 2 and AFG 2 as reported.…”

Ecotoxicological Effects of Aflatoxins on Earthworms under Different Temperature and Moisture Conditions

“…Studies from the early 1980s found that AFB 1 does not persist in the soil for long as soil microbes degrade it into less toxic metabolites (AFB 2 and AFG 1 and AFG 2 ) in a relatively short period. Later studies found that AFB 1 may persist in soil for up to 120 days [14] when adsorbed to the soil binding sites. Once bound to the soil binding sites, AFB 1 is mostly resistant to microbial degradation [14].…”