| The study was conducted to investigate whether dietary supplementation of zeolites can alleviate the toxic effects of cadmium (Cd) on carps (Cyprinus carpio). The effects of dietary zeolite supplementation on the heavy metal accumulation in different tissues, plasma indexes and liver metallothionein in carps with water Cd exposure were determined. The study was divided into three parts:Trial1was conducted to determine the effects of zeolite dose, temperature and time on Cd adsorption in simulated intestinal envirionment of carps. A3×3×5factorial arrangement of treatments was used in trial. The temperature were16℃,24℃and32℃, the zeolite dosage were0.05g,0.1g and0.15g, the time were0.5h,1h,2h,4h and8h. The results showed that the zeolite adsorption of Cd increased with increased zeolite dose, temperature and time. The adsorption rate was fast from2to4h; after then it slowed down. Besides, the dosage, temperature and time had a significant effect (P<0.001) on Cd adsorption rate, and there was a significant interaction (P<0.001) between every two factors, while the interaction among three factors was not significant (P>0.05).Trial2was conducted to study the effect of dietary zeolite supplementation on heavy metal contents in different tissues of carps with water Cd exposure. A total of540carps with average weight of (25.6±2.3) g were randomly divided into6treatments, each of which had6replicates with15fish per replicate, The treatments were:1(C),2(Z):The content of Cd in the water were0μg/L, fed basal diet and4%zeolite of diet respectively;3(Cdl):the exposure concentration of Cd was5μg/L, fed common diet;4(ZCdl):the exposure concentration of Cd was5μg/L, fed4%zeolite of diet;5(Cd2):the exposure concentration of Cd was50μg/L, fed common diet;5(ZCd2):the exposure concentration of Cd was50μg/L, fed4%zeolite of diet. The experiment lasted for30d. The results showed that compared with the non-exposure groups, the longer the exposure period, the higher the level of the Cd accumulation in the gill, hepatopancreas and kidney. Kidney had the highest accumulation of Cd ion, followed by the hepatopancreas and gills. In addition, experimental time and the concentration of Cd did not affect the amount of Cd sediment in the muscle of carps, only trace amounts of Cd (0.02-0.04mg/kg) were detected in the muscle. Zeolite did not have any effect on Cd accumulation in tissues, all water exposure of Cd caused high concentrations in different tissue (except muscle), and the accumulation in50μg/L Cd exposure groups was significantly higher than that in5μg/L Cd exposure groups (P<0.05). There was no interaction between zeolite and Cd concentration on Cd accumulation in tissues (P>0.05). The zinc, iron and copper contents in hepatopancreas had no significant difference (,P>0.05) in the whole trial. Zeolite and Cd did not have any effect on the amount of zinc, iron sediment in the kidney of carps. The copper content in50μg Cd/L exposure groups increased and significantly higher than that in non-exposure and5μg Cd/L exposure groups (P<0.05) in the kidney of carps at12,18and30d, however, the copper content in the kidney of carps was not affected by zeolite (P>0.05). Zinc and iron contents in the gill of carps in the exposure groups were significantly lower than non-exposure group (P<0.05) at30d, and zeolite had no effect (P>0.05) on zinc, iron accumulation in gill of carps; zinc, iron and copper accumulation in the50μg Cd/L exposure groups reduced significantly in the muscle at6d (P<0.05), while zeolite had no effect (P>0.05) on zinc, iron and copper contents in the muscle.Trial3was aimed to study the effect of zeolite on plasma indexes and liver metallothionein in carps with water Cd exposure. Treatments were the same as in Trial2. The results showed that the different concentrations of Cd did not affect the plasma SOD activity and MDA content; GOT activity in50μg Cd/L exposure groups was significantly higher than that in non-exposure and5μg Cd/L exposure groups (P<0.05) at30d; there was no significant difference between non-exposure and5μg Cd/L exposure groups(P>0.05). Plasma calcium in the exposure groups tended to be lower compared to non-exposure groups, plasma calcium was significantly lower (P<0.05) in50μg Cd/L exposure groups at18and30d; the plasma phosphorus content in the exposure groups were significantly lower than that in non-exposure groups (P<0.05) at12,18and30d, and plasma phosphorus did not differ among the exposure groups (.P>0.05); zeolite had no significant effect on the plasma parameters (P>0.05). The zeolite and the concentration of Cd did not exist interactions. At3,6,12and18d, MT content was not significantly different (P<0.05) in the hepatopancreas among groups. However, at30d, MT content in50μg Cd/L exposure groups was significantly higher than that in non-exposure and5μg Cd/L exposure groups (P<0.05) in hepatopancreas; zeolite had no effect (P>0.05) on MT levels in the hepatopancreas during the whole trial period; there was no interaction between zeolite and Cd concentration. |
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