Tuesday, November 6, 2007
227-5
Layer Charge of Clays and Aflatoxin Adsorption.
Aflatoxins are toxic fungal metabolites produced by Aspergillus flavus and other fungi. Human and animal cancers and death can result from aflatoxin ingestion. Grain crops, such as corn and peanuts, are frequently contaminated with aflatoxins due to fungal infestations before or after harvest. Clay minerals when added to animal feeds have been shown to effectively bind aflatoxins and reduce aflatoxicosis. Aflatoxin binding to clays must occur during digestion because dry clays are mixed with dry feeds. The Langmuir-like form of aflatoxin adsorption isotherms suggest that aflatoxins adsorb to the clay surface. Clay products that effectively bind aflatoxins and reduce aflatoxicosis generally have low to intermediate layer charge. This suggests that layer charge affects aflatoxin adsorption by clays. N-alkylammonium exchange indicated that the commercial feed additive, Novasil plus, is a low-charge montmorillonite comparable in charge to the CMS reference montmorillonite, SWy-2. Animal feeding studies have shown that Novasil plus prevents or reduces aflatoxicosis. Adsorption isotherms of aflatoxin B1 (AfB1) indicated that SWy-2 adsorbed AfB1 as effectively as Novasil plus, but high-charge CMS reference montmorillonite, SAz-1, was much less effective. AfB1 adsorption by natural expandable clays was as follows: hectorite > SWy-2 = Novasil plus > SAz-1 >> vermiculite. Reduced-charge SAz-1 montmorillonite samples were synthesized by Li exchange and heat treatment. The reduced-charge SAz clays adsorbed AfB1 more effectively than SAz-1 in proportion to the charge reduction. Low-charge expandable clays more effectively adsorb AfB1 and would likely be more effective feed additives to reduce aflatoxicosis.
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