| Cadmium (chemical formula Cd) is commonly found in the natural environment, continuing transffering and recycling. As the increase of human's activities for exploitating, smelting, processing and commercial manufacturing with cadmium, more and more cadmium continuously entered into atmosphere, water, soil and resulted in serious environmental pollution. Cadmium is not an essential element for life, but a completely useless and harmful heavy metals to life. Cadmium got a very low threshold of toxity, could cause cadmium poisoning at a low level. With a half-life up to 19-30 years, if accumulated, very little Cadmimus could be excreted. Cadmium could destroy almost all systems of biosystem seriously, for example, the circulatory system, digestive system, nervous system, motor system, endocrine system, reproductive system, urinary tract system.In 1973, the FAO/WHO listed cadmium as the third food contaminants which needed to be studied priority in the world, only followed by aflatoxin and arsenic. Then, cadmium was listed as the first globally dangerous goods by UNEP (United Nations Environment Programme) in 1984. As cadmium could damage DNA, interference DNA repair; accelerate the cellular proliferation, case distortion, cancerition and mutation of the body, result in tumorous, the International Union Against Cancer (IARC) concluded cadmium was Class IIA carcinogen in 1987, and amended it to IA-level carcinogen in 1993.Accompaning with the rapid development of China's industrial and agricultural, the water, soil, air in China had been polluted by cadmium at different degrees, and the pollution became worse in recent years, malignant cadmium pollution occurred at times. So, studying and controlling cadmium pollution is an emergency.This study selected juvenile southern catfish (Silurus meridionalis Chen) which artificial propagation and breeding in our laboratory to experiment from April 2009 to August 2009, using two Cd-exposure methods——acute injection and chronic immersion, to observe the effects of cadmium on southern catfish's index of blood's physiology(such as the red blood cell (RBC) number, white blood cell (WBC) number, hemoglobin (Hb) concentration, WBC types), index of blood's histochemistry(such as blood cell glycogen, blood cell peroxidase (POX)), and the effects on growth and development, organizational structure and haematopoietic function of liver and kidney.The results of acute cadmium exposure experiment showed that, on 1stday, as the osmotic pressure increased in vivo of southern catfish in Cadmium-exposured group, a lot of water in the environment entered into those fishes'body, casing a significant increase of the fishes'body weight. RBC number, WBC number, Hb content significantly decreased, blood cells'glycogen and POX content declined, but there's no change of the parameters mentioned above in the control group. The changes of WBC types were similar between the Cd-exposured group and the control group:the proportion of lymphocytes declined while the propotion of monocytes, neutrophils and thrombosis proportion increased, but the changes in control group were lower than Cd-exposured group. On 3rdday in Cd-exposured group, the body weight declined, had no significant difference with the control group; RBC number, WBC number, Hb content increased, but still significantly lower than the control group; blood cell's glycogen, POX content and proportion of lymphocytes continued declining; the propotion of neutrophils decreased, but was still significantly higher than control group. On 7thday in Cd-exposured group, the body weight continued declining, and significantly lower than control group; RBC number and Hb content continued rising, the RBC number had no significant difference with the control group, but Hb content remains significantly lower than it; glycogen content of blood cells got a rebound, but the POX content and proportion of lymphocytes continued declining; the proportion of neutrophils changed a little, still significantly higher than control group; Liver and kidney was damaged:the cell boundary blurred, and there're deformation and shrinkage happened to the cells'the nucleus deformated, diminutied, even disappeared.The results of chronic cadmium exposure showed that Cd2+could significantly inhibited the growth and development of southern catfish in Cd-exposured group, causing slowly growth and weight gain. From 7thday, the body weight of Cd-exposured groups were always significantly lower than control group, and the body weight increased along with the decrease of the concentration of the Cd2+, that is,50μg/L Group>500μg/L Group>5mg/L group. The results showed that Cd2+ could significantly affect blood cells. On 1stday, the RBC numbers of Cd-exposured groups were all significantly higher than control group, but on 7thday, the RBC number in 500μg/L and 5mg/L Cd-exposured group remained significantly higher than control group, but the there was no significant difference between 50μg/L Cd-exposured group and control group. After 14th day, there was no longer significant difference of those parameters mentioned above between Cd-exposured groups and control group. The effect of Cd2+on southern catfish showed up in the early stage of experiment, on 1stday, the WBC number of 5mg/L Cd-exposured group got significantly lower than control group. While on 7thday, 14thday and 21stday, the WBC number of 500μg/L and 5mg/L Cd-exposured group were all significantly lower than control group, from 28thday, the WBC number of all Cd-exposured group were all significantly lower than control group. Hb content changed the same as RBC number:except that the Hb content of all Cd-exposured groups were significantly higher than control group on 1stday, there were no significant difference between Cd-exposured groups and control group. Changes of WBC types mainly reflected on the variation in proportion of lymphocyte and thrombocyte:the proportion of lymphocyte was decreased along with the extension of the experiment and the increase of concentration of Cd2+, while the change proportion of thrombocyte was on the opposite side. The results showed that, Liver and kidney of Cd-exposured groups were hevealy damaged. The liver became atrophy and diminution, porta hepatic and hepatic sinusoid swelled, there was hyperemia in tela; the color of cells darken, cytoplasm reduced, nucleus cracked and disappeared, cells turned to vacuolization, the volume of the cells was significantly smaller than before. In kidney, the renal tubule and renal glomerulus got atrophy; nucleus deformed, condensed, deflected, even disappeared; there was hevealy deformation, atrophy and vacuolization in cells.The experimental results mentioned above showed that:cadmium could inhibit the growth and development of southern catfish, damage its haematogenetic organs, such as liver and kidney; the haematological parameters of southern catfish would regularly changed at a certain degree on different level of Cd or Cd2+, those parameters can be used to detected if there're cadmium poisoning occurred to southern catfish and the degree of cadmium poisoning.
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