Sorption Of Aflatoxin B₁by Minerals And Particle-Sized Soils

Aflatoxins are naturally occurring mycotoxins that are produced by many species of Aspergillus, a fungus, the most notable ones being Aspergillus flavus and Aspergillus parasiticus. They can be identified as the Aflatoxin Bi, B2, Gi, G2, M1, M2, and Qi. The Aflatoxin B1, classified as first-degree carcinogen by WHO, is considered most carcinogenic substances known among these toxins. The native habitat of Aspergillus is in soil, decaying vegetation, hay, and grains undergoing microbiological deterioration, and it invades all types of organic substrates whenever conditions are favorable for its growth. It is thus that the toxin can be usually found in the milk of animals, soil, agricultural products, and feeds. It causes the great harm to human and animal health, and enormous economic losses.The study explores the interfacial behavior between a model mycotoxin, Aflatoxin Bi and solil by using the batch experiment and spectroscopic analysis. Three mainly scientific probloms are discussed:1) Sorption of Aflatoxin Bi by mineral(montmorillonite)2) Contribution of particle-sized soils to Aflatoxin Bi immobilization.3) The mechanism is then discussed. Obtained results are shown as follows:(1) Sorption of a typical biogenic toxin aflatoxin Bi on montmorillonite modified by low-molecular-weight humic acids (<3500Da). The montmorillonite rapidly adsorbed the aflatoxin Bi until the maximal capacity, and then the adsorbed aflatoxin Bi slowly released into solution and reached the sorption equilibrium state after12h. The sorption isotherm of aflatoxin Bi by montmorillonite could be well described by Langmiur model, while the sorption isotherm by humic acid-modified montmorillonite fitted well the Freundlich model. The amounts of aflatoxin adsorbed by humic acid-modified montmorillonite were obviously higher than those by pure montmorillonite. The enhancement was attributed to (1) the more adsorption sites due to the surface collapse of crystal layers induced by organic acids, and (2) the partitioning of aflatoxin B1by humic acids on mineral surface. In addition, the adsorption amounts of aflatoxin Bi by montmorillonite and modified montmorillonite increased with the increase in pH, and increasing amount for the modified montmorillonite was high as compared to pure montmorillonite at same basic condition, This attributed to the release of humic acids from the modified montmorillonite with the high pH values in solution. This indicates that increasing pH values resulted in the enhanced hydrophilic property and the release of the organic acids presented in modified montmorillonite, and more sorption sites on the modified montmorillonite were available for aflatoxin B1.(2) Yellow-brown soils were dissolved in water and fractionated down to four scales by sieving, sedimentation and centrifugation:the50～250μm fine sand, the5～50μm silt, the1～5μm fine silt and the0.1～1μm colloid fraction. Sorption of Aflatoxin B1(AFB1) by four particle-sized soils was investigated to explore the effect of pH value, dissolve organic matter(DOM), and complex metal ions. AFB1sorption isotherms by four particle-sized soils could be well described by linear sorption models. Sorption of AFB1on silt was slightly decreased with the increase of pH value, while others were independent with pH change. Both DOM and complex metal ions inhibited the sorption of AFB1on the four particle-sized soils. The addition of DOM from0to400mg·L-1caused the Kd values decreased683.6、809.1、1350.9、3785.4L·kg-1respectively. Complex metal ions (Zn2+or Cu2+) of10mmol·L-1also decreased the Kd significantly (46.8%～84.7%) and Cu2+displayed stronger inhibition of AFB1sorption on particle-sized soils. Based on the analysis, a variety of factors such as soil pH, DOM and existence of complex metal ions that may affect the interaction between AFB1and soil particles were revealed and would provide an important theoretical basis for AFB1migration and transformation in soil environment.(3) Removal of organic matters from four particle-sized soils causes that decreasing sorption capacity. The Kd values of AFB1by4particle-sized soils decreased80.3%、95.4%、83.1%、91.4%, respectively. As the solubility of AFB1in organic matters of the4particle-sized soils(Som) were much higher than that of soil minerals(SM), sorption of AFB1by soil particles were as a result of partitioning into soil organic matters and adsorptions, but partitioning was the main mechanism. Sorption of AFB1by Na+-saturated and Ca2+-saturated soils were much lower than soils without any treatments. The Kd values of AFB1by Na+-saturated soils decreased to31.3～70.0%, while that of Ca2+-saturated soils decreased to10.6～33.5%. Exchangeable cations played an important role during adsorption, but not the limiting factor.