| In order to study the biotoxicity of QDs, this paper chooses Nile tilapia (Oreochromis niloticus) as the research object and employs techniques and methods of enzymology, hematology and histological to assess the biological safety of QDs. The paper includes three aspects:oxidative stress of QDs on liver, kidney and testis; the influence of microstructure of QDs the liver, kidney and testis, the influence of ultrastructure of QDs on testis; the rate of micronucleus and nuclear anomalies of red blood cells. This research sets four QDs concentrations treatments, namely 20nmol/L, 200mol/L,2000mol/L and 4000nmol/LQDs. Blank treatment, NaCl control treatment and Cd2+ control treatment are also included. Fishes are exposed to active substance by intraperitoneal infection and are analyzed on 1d,4d,7d,14d and 28d post treatment by making blood smears and testing the frequency of micronucleus and frequency of nuclear abnormality, determinating the total antioxidant capacity (T-AOC) level and malondialdehyde (MDA) content of liver, kidney, gonad and determinating microstructure of QDs the liver, kidney and testis, the ultrastructure of QDs on testis.Major results:The results of experiment on enzymology, hematology and histology show no significant difference with NaCl control treatment.Enzymology(1) Look from the dose effect:with the increase of QDs dose, these is no obvious dose effect relationship in the T-AOC level on 1-7 days liver and testis, while 2000 nmol/L QDs peaks and show significant difference with control group in three points (P＜0.01) and 4000 nmol/L QDs also peaks in kidney. SOD、CAT and GPX activity of each QDs group on 1d,7d arise the peak all the 2000 nmol/L QDs (P＜0.05). As the dose increases, MDA content of liver and testis generally shows a rise first followed by a decline, peaking around 2000 nmol/L QDs group(P＜0.01). However, the kidney MDA content rises with the increase of dose, peaking about 4000 nmol/L QDs group(P<0.01). There is no significant difference with each NaCl control group in the T-AOC, MDA content of each QDs group in the liver, kidney and testis in the 14-28 days. There is no significant difference with NaCl control group in LDH activity of each QDs group in testis, but Cd+ treatment group is lower than the minimum value of QDs group in the 1-28 days. The T-AOC level of liver, kidney and testis of Cd2+ treatment group higher than each QDs treatment group in 1-4 days,4-7 days and 1-14days; the MDA content of liver, kidney and testis higher than maximum value of each QDs treatment group during the whole experiment(except the 4 days in testis).(2) Look from the time effect:the T-AOC level of liver and kidney first rises and then decreases. On the whole,200nmol/L and 2000nmol/L treatment group got the maximum value in 7 days in liver, while 4000nmol/L treatment group get the maximum value in 7 days. In addition,2000nmol/L and 4000nmol/L treatment group both get the maximum value in 4 days in the testis. This shows that the strongest antioxidant capacity of fish is in 4-7days.On the whole, the SOD activity in liver first go down then rise then down, and all the 200nmol/L treatment group significant higher than NaCl treatment group (P<0.05); the CAT activity first go down then up and down after it get the maximum value on the whole; the GPX activity go up to 7days and then down after it get the maxmum value. Generally, the MDA content of each QDs treatment group in liver and testis first go up and then down and get the maximum value in 4 days(P< 0.05). In contrast, the MDA content of kidney presents the decline trend. The ACP activity of each QDs treatment group in testis first go up then decline in 1-7 days, but the Cd2+ treatment group Continue to decline in 1-28 days. The MDA content of liver, kideny and testis continue to rise in the Cd2+ treatment group, and higher than each maxmum value of QDs treatment group(except the 4 days in testis). The liver’s SOD, CAT and GPX activity continue to decline, and down the minimum value in 28 days.Hematology(1) The results showed that the frequency of micronucleus reach the maximum in 1 day, after that the trend decline. The micronucleus of Cd2+ control group reach the maximum in 14d days, One-way ANOVA analysis between each Cd2+ control group and NaCl control group showed significant difference from 1 day to 28days.(2) Convex and concave nucleoplasm of the red blood cell are the dominant types of abnormality. Pyknotis nucleus and unequal karyomitosis were induced by QDs in the treatment prophase.Histology(1) In the QDs treatment group, the liver damage constitutes partial Central venous bleeding, liver blood sinus congestion and partial liver cell volume increase.(2) In the QDs treatment group, the kidney damage comprises partial swelling in the glomerular, renal tubular epithelial cell swelling, congestion between renal tubules.(3) In the 4000 nmol/L QDs treatment group, the testis microstruture damage mainly is that partial base membrane dissolved and fracture, Leydig’s cells swelling and the number of support cells decreased;and ultrastructural damage mainly reflects that cytoplasmic mitochondria of spermatogonium swelling and appear water sample, the head plasma membrane of sperm loosen and swelling.Main research concludes:Enzymology(1) Liver:SOD,CAT and GPX activity showed that the sensitivity isn’t completely consistent.2000nmol/L QDs treatment group shows more sensitivity than 4000nmol/L QDs treatment group in oxidative stress and the most serious damage is in 4 days, but the liver’s T-AOC level increase and suppress or remove the excessive reactive oxygen species.(2)Kidney:4000nmol/L QDs treatment group shows the most sensitivity and QDs trigger the most serious damage in 4 days, but the kidney’s T-AOC level increase and suppress or remove the excessive reactive oxygen species.(3)Testis:QDs trigger the most serious damage in 4 days, but the testis’s T-AOC level increase and suppress or remove the excessive reactive oxygen species. The LDH activity is restrained mildly during the early period, and the ACP activity suffered from slightly negative effect which gradually recovers in anaphase.In conclusion, the result suggested that the shell of QDs and the surface modification group have negative effect on micronucleus, as time goes by, the fish can remove the negative effect step by step.(4)Every antioxidant enzymes are induced or inhibited in Cd2+treatment group in early days and the T-AOC level goes up. The fish cannot resist the excessive ROS induced by Cd+ treatment group, which causes oxidation-oxidation mechanism imbalanced finally.HematologyThe result suggests that the shell of QDs and the surface modification group have increased in micronucleus and nuclear anomalies. As time goes on, the fish can eliminate the genotoxicity reduced by QDs in 28 days.Histology(1) 2000nmol/L QDs treatment group has slight damage on the liver in 4 days while it has the same effect on kidney in 7 days. This shows that Nile tilapia may be the target organs of the quantum dots and the negative effect on the liver is larger.(2) Liver,kidney and testis of QDs treatment groups show no difference with NaCl control group in microstructure in 14days and 28days. It illustrates that the shell of QDs and the surface modification group have slightly negative effect on three organs in fish. Cd2+ treatment group have toxic effects on kidney, liver and gonad. As time goes on, the negative effect is enlarged and the damage slows in 28 days.In conclusion, Nile tilapia fish tends to be negatively affected by CdSe/ZnS QDs which brings stimulus damages to fish. Each index of fish returns to normal in 28 days and the negative effect on fish can be removed. However, whether the QDs exposure has toxicity or not to human and animals needs to be further researched. |
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