Assessing and modifying China bentonites for aflatoxin adsorption

Bentonites have been used to reduce or to diminish the toxicity of aflatoxins to animals and humans. Due to bentonites' large variations in mineral composition, and the dominant mineral smectite can differ in interlayer cation composition, charge density, charge origin, bentonites demonstrated more than ten fold of differences in aflatoxin adsorption capacity. To maximize the efficiency of local bentonites for aflatoxin detoxification, modifications of bentonites are often needed. The objectives of this study are to asses and to modify selected bentonites from China for aflatoxin detoxification. Thirteen Chinese bentonites were collected and evaluated for montmorillonite contents. A 6-fold difference in aflatoxin B-1 (AfB(1)) adsorption capacity among these 13 natural bentonites were observed. Six bentonites, representing the low-, medium-, and high-adsorption for AfB(1), were selected for detailed assessment and modification. The clay fractions of the bentonites (Na-saturated) were harvested and exposed to the following three treatments: (1) Ca saturation (Ca_) (2) Mg saturation and heating (Mg_Heat), (3) Mg saturation and heating then Ca saturation (Mg_Heat_Ca), respectively. These three treatments enhanced the AfB(1) adsorption capacity of the six bentonites and the relative efficiency of the treatments follows the order of Mg_Heat_Ca > Mg_Heat > Ca_ in most of the six bentonites. Calcium saturation or heating can improve the clays' adsorption affinity and capacity for AfB(1) mainly because of the reduction of cation exchange capacity (CEC). This assumption was confirmed by the change of CEC and single-point AfB(1) adsorption capacity of bulk bentonites before and after heating. Our adsorption data suggest that some Chinese bentonites are generally suitable for AfB(1) adsorption, and high selectivity can be achieved by optimizing their charge density. Similar approach should be applicable to other local bentonites worldwide.