Microbial and photodegradation of aflatoxin B1 in two contrasting soils

In a 28-days experiment, we investigated the dissipation of aflatoxin B1 (AFB1) (0.5-500 μg kg −1 ) by microbial (MD) and photodegradation (PD) in two contrasting soils (sandy loam and clay). Sterile incubation in darkness served as control (C). AFB1 was degraded in all scenarios according to simple first-order kinetics with 50% dissipation times of 20 - 32 (PD), 19 - 48 (MD), and 56 - 65 days (C), respectively. Dissipation rates were significantly lower (p<0.001) in the clay soil, likely due to photoquenching and strong binding of AFB1 by clay minerals and humic substances. In the sandy loam, dissipation rate of MD decreased in function of initial AFB1 concentration, probably due to toxic effects on degrading microbes. In contrast, in the clay soil the dissipation rate increased with increasing concentration up to 250 μg kg −1 , followed by a sharp decrease at 500 μg kg −1 , indicating an effect of soil texture on the bioavailability of AFB1 to soil microbes. AFB2a was identified as a transformation product in all scenarios. These results confirm the function of soil for AFB1 degradation, which is modulated by abiotic and biotic processes, soil characteristics and initial AFB1 concentration.