| Nonylphenol (NP) is a nonionic surfactant, which is widely used in the industries of paper-making, rubber, plastics and cleanser, being intimate to our daily life. However, nonylphenol is a kind of endocrine disrupting chemicals, which can cause adverse effects to organisms. Therefore, understanding of its negative ecological effects has important realistic meanings to ecology protection and health maintenance of human beings. This study was designed to evaluate acute and chronic toxicities of NP to hybrid tilapia {Oreochromis Niloticus x O. Aureus) and determine NP accumulation in the fish tissues after chronic exposure.Acute test used semi-static method with an experimental period of 96 h. In the experiment, groups of 10 randomly selected fish were exposed to the different treatments including NP concentrations at 150.0, 225.0, 337.5, 506.3, and 759.4μg/L, and blank and ethanol controls. There were two parallels in each treatment. Immediately at the end of the experiment or immediately after death of the last three fish, three fish from each treatment were randomly collected for counting of micronucleus and abnormal nuclei, and evaluating of histological lesions. Chronic test also used semi-static method with an experimental period of 20 w. In chronic test, groups of 20 randomly selected fish were were exposed to the different treatments including NP concentrations at 0.265, 0.529, 2.646, 5.292, and 26.46μg/L determined by LC50 from acute test, and blank and ethanol controls. There were three parallels for each treatment. In 4w, 8w, 12w, 16w and 20w, three fish were randomly collected from each treatment for counting of micronucleus and abnormal nuclei, and evaluating of histological lesions. Also immediately after chronic test in 20 w, three fish from three parallels of each treatment were randomly collected for detecting of NP in the tissue. The extraction method of NP from fish tissues and chromatographic detection method of NP were all optimized before the formal detection of NP in the experimental fish.The results from the acute test showed that mortality of experimental fish increased with the increasing of NP concentrations. LC50 of experimental fish exposed for 24, 48, 72, and 96h, were 413.4, 351.5, 311.2 and 264.6μg/L, respectively. Therefore, NP is a virulent poison to the hybridtilapia. The kinds of abnormal nuclei in the blood cells of experimental fish included small nucleus, cleavage of nucleolus, concave nucleolus and double nuclei. Micronucleus and abnormal nuclei rates in the blood cells were significantly higher from the fish exposed to NP than those from the controls. Histological observation also showed that there were great pathological changes in the tissues of gill, kidney, spleen, and liver from the fish exposed to NP. By NP treatment, the tilapias showed a proliferation of epithelial cells in the gillbrachial leaflets, a connection of gillbrachial leaflets, or a connection of gill filaments. The kidney lesions included an atrophy of capillary blood vessels in glomerulus and hydropic degeneration with epithelial cells of renal tubules and haemorrhage in the tissue. In the spleen, amyloidosis and fibrosis degeneration and massive eosinophilic materials were observed. Liver lesions were characterized by hydropic and fatty degeneration, accompanied by haemorrhages in the central veins.The results from the chronic test showed that micronucleus and abnormal nuclei rates of blood red cells were also significantly higher from the fish treated by NP than those from the controls. Moreover, micronucleus rate significantly increased with extending of exposure time and increasing of NP concentration, indicating a significant time and dosage dependent. Although abnormal nuclei rate showed a significant time-effect, it did not increase but decrease in some cases with high NP concentration and long exposure time. In the chronic test, NP exposure also exhibited a great pathological damage to the gill, kidney, spleen and liver of tilapia. Compared to the results in acute test, however, lesion in chronic test was much slighter in the gill, but more serious observed in the kidney and spleen and liver, where massive necrotic areas were all found except for the symptoms observed in acute test.In 20 w of chronic test, NP was found in the fish tissues from every NP treatment with an average bio-concentration factor of 2961.6. This finding indicated that the hybrid tilapia could accumulate NP at a high rate. Moreover, a significant positive correlation was found between the NP concentration in the fish tissue and those in the experimental treatments. The concentrations of NP in the chronic test ranged from 0.265 |ig/L to 26.46 ug/L, equal to the NP concentrations in the natural rivers with intensive pollution. Because NP concentration as low as 0.265 ug/Lshowed genetic toxicology and pathological damage to tilapia in the present study, NP level in some intensive rivers would be enough to cause serious effects to their aquatic organisms. If the pollution transfer to human begins by food chain, it would be very harmful to human health.
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