(Received 25 January 2001). The adsorption of aflatoxin B1 (AFB1) by cation-exchanged clinoptilolite zeolitic tuff and montmorillonite was investigated at 37 ºC ...
J.Serb.Chem.Soc. 66(8)555–561(2001) JSCS – 2885
UDC 541.183.1:553.67:632.4 aflatoxin B1 Original scientific paper
The effect of exchangeable cations in clinoptilolite and montmorillonite on the adsorption of aflatoxin B1 MAGDALENA TOMA[EVI]-^ANOVI]*, ALEKSANDRA DAKOVI], VESNA MARKOVI] and DRAGAN STOJ[I]1 Institute for Technology of Nuclear and Other Mineral Raw Materials, P. O. Box 390, YU-11001, Belgrade and 1VMA - Institute for Hygiene, YU-11000, Belgrade, Yugoslavia (Received 25 January 2001) The adsorption of aflatoxin B1 (AFB1) by cation-exchanged clinoptilolite zeolitic tuff and montmorillonite was investigated at 37 ºC and pH 3.8 from an aqueous electrolyte having a composition similar to that of gastric juices of animals. Both minerals were exchanged from the natural form to the sodium form and then to the Cu2+, Zn2+ and Co2+-rich forms. The cation exchange was different for the different cations, but in all cases the exchanges were larger on montmorillonite than on clinoptilolite. The degree of exchange on montmorillonite was 76 % for copper (from a total of CEC 0.95 meq/g, Cu2+ –0.73 meq/g) and 85 % for zinc and cobalt. Under the same conditions (concentration, temperature, pH, contact time), the degree of exchange on zeolitic tuff was 12 % for Cu2+ (from a total CEC of 1.46 meq/g, Cu2+ –0.17 meq/g), 8 % for Zn2+ and 10 % for Co2+. Both groups of mineral adsorbents showed high AFB1 chemisorption indexes (ca). For the montmorillonite forms, ca ranged from 0.75 for the Cu-exchanged montmorillonite to 0.89 for the natural Ca-form, 0.90 for the Zn-exchanged form and 0.93 for the Co-exchanged montmorillonite. The adsorption of AFB1 on the different exchanged forms of clinoptilolite gave similar values of ca for the Cu and Ca forms (0.90) and values of 0.94 and 0.95 for the Zn- and Co-exchanged form. The impact of the mineral adsorbents on the reduction of essential nutrients present in animal feed (Cu, Zn, Mn and Co) showed that the Ca-rich montmorillonite had a higher capability for the reduction of the microelements than the Ca-rich clinoptilolite. Keywords: clinoptilolite, montmorillonite, cation exchange, adsorption, aflatoxins. INTRODUCTION
Aflatoxins comprise a diverse group of pervasive, naturally occurring, fungal elaborated poisons that have been strongly implicated in animal diseases. Aflatoxin B1 (AFB1) is the most toxic and cancerogenic of the aflatoxins.1 Phillips et al.2–4 and Toma{evi}-^anovi} et al.5 have shown that certain natural aluminosilicates (bentonite and zeolite) may be used, in animal diets, to prevent signs of * Author for correspondence.
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certain mycotoxicoces. These mineral materials bind aflatoxins, forming highly stable complexes. Hydration of the exchangeable cations creates a hydrophilic environment on the surface of zeolites and on the surface and in the interlayer region of montmorillonite. This parameter has an influence on the adsorption of different organic molecules, including mycotoxins, on zeolite and montmorillonite particles and on the stability of the adsorbed complexes.4,6,7 A proposed mechanism of aflatoxin chemisorption by mineral adsorbents involves the rapid formation of a complex between a ligand and the mineral.8 Although these mineral adsorbents are added to animal rations to prevent the negative effects of aflatoxins, their impact on other components of the feed (vitamins, aminoacids, and microelements) is not well known. Chung and Baker9 reported effects of montmorillonite on phosphorous and Chung et al.10 on Zn, Mn, vitamin A and riboflavin. They noted no reductive effects on phosphorous, Mn, vitamin A, and only a slight reduction in Zn utilization. The addition of 0.2–0.5 % clinoptilolite to basal diets did not impair the utilization of tryptophane, phenylalanine, vitamin A, D and E.11 The in vitro adsorption of vitamin B6 on different mineral adsorbents showed that the Ca and H form of clinoptilolite adsorbed this vitamin to about 20 %. On the contrary, vitamin B6 was tightly bound to hydrate sodium calcium aluminosilicate (HSCAS)-mineral adsorbent based on montmorillonite (98 %).12 The objective of the present study was to evaluate the affinity of different cation-exhanged forms of clinoptilolite and montmorillonite for aflatoxin B1 in vitro. In addition, the impact of natural Ca-rich clinoptilolite and Ca-rich montmorillonite on essential microelements (Cu, Zn, Co and Mn) present in animal feed were examined. EXPERIMENTAL Preparation of the different forms of the adsorbents The natural zeolite sample used in this study was a clinoptilolite-rich tuff from the Zlatokop deposit (Vranjska Banja, Yugoslavia). From X-ray diffraction analysis, the content of clinoptilolite was ³ 90 %. The chemical composition of this sample was as follows (wt. %): SiO2 – 64.21, Al2O3 – 11.48, Fe2O3 – 0.88, CaO – 4.55, MgO – 1.45, Na2O – 1.71, K2O – 1.29, L.I. – 14.0. The cation exchange capacity (CEC) was 1.46 meq/g. The sample was crushed and sieved, and the fraction
