The Toxic Effects Of Tributyltin And Phenanthrene On Fish

Tributyltin (TBT) has been widely used as biocide in anti-fouling paints for ships and fishing gear in aquaculture. Polycyclic aromatic hydrocarbons (PAHs) are a group of products of incomplete combustion, which are widely distributed in the air and aquatic environments. Phenanthrene (Phe) is a representative environmental pollutant of PAHs. TBT and Phe in the contaminated environment can be cumulated in organisms via skin exposure and food intake, and bring obvious toxic effects. Fish as an important group of aquatic ecosystems, are the ideal test animals for studying the toxicity of environmental pollutants study.In order to study the toxic effects of TBT and Phe on fish, three experiments were carried out in this study. (1) Freshwater or seawater Japanese eels (Anguilla Japonica) were intraperitoneally injected with tributyltin chloride (TBTCl) at the dose of 0.5 mg/kg body weight (BW) or Phe (5 mg/kg BW) dissolved in corn oil once a week and for a total of five weeks. (2) Ovarian tissues from freshwater or seawater eels were incubated with TBTCl (100,200,300 nmol/L) or Phe (5,10,15μmol/L) solution in vitro for 4-18 hours; (3) Tilapia (Sarotherodon sp) were exposed to static water with Phe (50-400μg/L) for 14 days. The toxic effects of TBTCl and Phe on fish were evaluated based on the changes of hepatosomatic index (HSI), histopathology, steroid hormone levels, the hepatic antioxidant and metabolic enzymatic activity. The main results are as follows:1. Effects of TBTCl and Phe on HSI and the histological structure in eelsAfter the eel were exposed to TBTCl or Phe for five weeks via intraperitoneal injection, the HSI and gonadal microstructure were not affected. However, obvious histopathological changes appeared in livers and spleens: the hepatocytes became slightly hypertrophy, the cell membrane became fuzzy or disappeared, acidophilic grains decreased, cells became vacuolization, the karyons were jundied to the edge of the cells or disappeared. The erythrocytes and the splenic hemosiderosis number and area both increased in the spleen. Part tissue was necrose and dissolved until disappeared. These symptoms were aggravated with the exposure time, and more obvious in seawater eels than in freshwater eels.2. The effect of TBTCl and Phe on hepatic glutathione-s-transferase (GST) activityTBTCl induced the GST activity in seawater eels. After the 4th and 5th injection, GST activity was significantly increased. However, TBTCl had no obvious effects on GST activity in freshwater eels, and Phe also had no obvious effects on GST activity in eels3. Effects of TBTCl and Phe on plasma cortisol and estradiol levels in eelsTBTCl and Phe had no obvious effect on plasma estradiol levels, but affected the levels of plasma cortisol. This effect varied with the numbers of ip and environmental salinity (seawater or freshwater).After the 3rd injection with TBTCl or Phe significant increase in plasma cortisol levels was observed in freshwater eels but not in seawater eel. After the 1st injection with TBTCl, the plasma cortisol levels in freshwater eels were significantly higher than those in seawater eels, opposite results were observed in treatment with Phe.4. Effects of TBTCl and Phe estradiol production from the in vitro eel ovarian tissuesBoth TBTCl and Phe affected the estradiol production from the in vitro ovarian tissues.The effects of Phe varied with the incubation time and concentrations, as well as the source of ovarian tissues. TBTCl inhibited, while Phe increased, the production of estradiol.5. Effects of Phe on HSI, hepatic antioxidant and metabolic enzymatic activity in Tilapia(1) After the Tilapia were exposed to water with 50-400μg/L Phe for 4-14 days, HSI was significantly reduced in 400μg/L group for 14d exposure, was not affected in any other groups.(2) Phe induced the hepatic antioxidant enzymatic activity, and the effects varied with the exposed time and doses. The activity of hepatic catalase (CAT), glutathione peroxidase (GSH-Px), superoxide dismutase (SOD) was not affected after 4d exposure; that of CAT, GSH-Px, SOD activity in 100 and 400μg/L groups was significantly increased compared with that in controls after 8d exposure. When treated with Phe for 14d, the GSH-Px activity in 400μg/L group and CAT activity in all groups were significantly increased.(3) Phe had no effects on hepatic GST activity. However, it affected the activity of hepatic ethoxyresorufin-O-deethylase (EROD), and the effects varied with the exposed time and doses. The activity was increased at low dose (50μg/L) and short exposure time (4, 8d), and decreased at high doses (100, 400μg/L) and long time (14 d).The results show that both TBTCl and Phe had obvious toxicties on Japanese eel. Obvious histopathologic changes were observed in liver and spleen, the hepatic GST activity and plasma cortisol levels were affected. After the Tilapias were exposed to Phe, the activity of hepatic CAT, GSH-Px, SOD and EROD were obviously affected. The above histopathologic changes, physiological and biochemical indexes can be used as the biomarkers or indexes for evaluating the toxic effects of environmental pollutants such as tributyltin and phenanthrene. The results are of important academic significance for understanding the toxic mechanism of endocrine disruption, and can ccumulate data for using fish as an experimental animal to biomonitor the fresh water or marine environment. They can also provide scientific proof for the establishment or modification of environmental laws or rules, and are of far-reaching significance for protecting the aquatic resources and the health of human being.