Reduction of the bioavailability of 20 mu g/kg aflatoxin in trout feed containing clay

The absorption, metabolism, and excretion of dietary aflatoxin B-1 (AFB(1)) by trout given different diets were compared. Fish were fed one of two die ts: an AFB(1) contaminated basal diet or the contaminated basal diet with 2 % sodium bentonite. Urine, feces, and gill excretions were collected and an alyzed separately over a 7-day test period. On completion of the feeding tr ials, the fish were euthanized for chemical analysis of body fluids and maj or organs. Total organ loads as low as 0.05 ng AFB(1) were quantified throu gh the use of tritium (H-3) labeled AFB(1) coupled with chloroform/methanol extraction, oxygen bomb combustion and liquid scintillation counting of sa mples. Results demonstrated that 2% dietary bentonite supplementation block ed intestinal absorption of dietary aflatoxin, reducing liver and kidney af latoxin loads by at least 80 +/- 10%, and increasing the amount of AFB(1) f ound in the feces about 470 +/- 20%, compared to control fish not fed bento nite. AFB(1) or metabolite concentrations in urine increased daily for 6 da ys for both groups, but were always significantly lower in the bentonite-fe d group. On average, insoluble aflatoxin metabolites accounted for 40%-60% of the total aflatoxin load in tissues, indicating a high percentage conver sion to an adduct that binds to protein (or other materials in the tissues) and is not extracted by solvents. All data indicate that 2% bentonite cont ained in trout diets contaminated with 20 mu g/kg AFB(1) significantly redu ces the amount of AFB(1) absorbed from the digestive system following inges tion of contaminated diets. (C) 2000 Elsevier Science B.V. All rights reser ved.