The Reproductive Toxicity On The Rotifer Brachionus Plicatilis Induced By BDE-47 And Studies On The Effective Mechanism Based On Antioxidant Defense System Changes

Polybrominated diphenyl ethers are new kinds of persistent organic pollutants (POPs), which are ubiquitous in marine environments and marine biota worldwide and are known to have noxiously ecological impacts on marine ecosystem. Rotifer, Branchionus plicatilis, are useful as models in ecotoxicology. Marine zooplanktons are the key loop of the material cycle and energy fluid in marine ecosystems and have been suggested to be the entrance for PBDEs into marine environments and it might be the start point of bio-concentration and biological transfer. Therefore,2,2’,4,4’-tetrabromodiphenyl ether (BDE-47), a low brominated Tetra-BDE, which is widely distributed in marine ecosystem, was chosen to investigate its reproductive toxicity on marine invertebrate zooplankter Branchionus plicatilis from different levels and the possible mechanism on base of antioxidant defense system changes were studied under controlled laboratory conditions.The main methods and results are as follows: 1 The two indexes, namely the egg production per animal and the egg production rate (EPR) of the population, were examined by anatomical lens and A life table was established by calculations.The results indicated that:Low concentration of BDE-47 (0.008 mg L-1) had little effect on female’s individual egg production and population’s egg production rate (EPR) during the experimental course except that at 72h after exposure, while obvious inhibition (P<0.05) was observed when being exposed to medium concentrations (0.08 mg L-1) at 48h and 72h exposure as compared to the control. BDE-47 at high concentration of 0.8 mg L"’had the most severely reproductive inhibition throughout the whole experiment course as compared to the control group (P<0.05) in a time and concentration-dependent manner. Life table was set up and results indicated that BDE-47 at high concentration of 0.8 mg L’1 prolonged the generation time while the low and medium concentrations shortened the generation time. Meanwhile, BDE-47 at medium concentration of 0.08 mg L-1 significantly decreased the life expectancy and the net reproductive rate (P<0.05). The high concentration of BDE-47 (0.8 mg L-1) also decreased the net reproductive rate and intrinsic rate of increase significantly (P<0.05).2 Further analysis on ultra-structure of ovary by transmission electron telescope (TEM) showed that BDE-47 exposure(0.008mg L-1,0.08mg L-1) made the vitellarium wrinkled, the nucleus deformed and the electron density of lipid decreased, inferring the ovary of B.plicatilis be severely damaged.3 Reactive oxygen species (ROS) production was labeled with DCFH-DA,and the treated samples were observed with a fluorescence microscope. The fluorescence value was detected with a microplate reader. The following four antioxidant system components, which are closely related to the glutathione detoxification cycle, were selected for analysis of their activities:glutathione peroxidase (GPx), glutathione S-transferases (GST), glutathione reductase (GR) and glutathione-SH (GSH). A bivariate Pearson’s correlation analysis of the enzyme activities and ROS levels was performed to identify the sensitive index of oxidative stress induced by BDE-47.The possibly effective mechanism was studied on base of antioxidant enzyme systems changes, and the ROS level and activities of three antioxidant enzymes closely relating to the detoxification of organic pollutant:glutathione peroxidase (GPx), gultathione S-transferases (GST)、glutathione reductase (GR) and gultathione-SH (GSH) were estimated. BDE-47 stress elevated ROS level in B. plicatilis in a concentration-related manner. Meanwhile, the GST activity was induced significantly at low treated group (0.008 mg L-1) but was inhibited exposuring to the highest concentration(0.8 mg L-1). Meanwhile, GPx activity and GSH content occurred significant decreased of all tested groups. On the contrary, GR activity was induced under exposure to the BDE-47, but the significant effects began to occur at the medium concentration tested (0.08 mg L-1).Among the studied enzymes, GPx、GST and GSH seemed to be the most responsive index for oxidative stress. The correlation among different antioxidant enzymes suggests that glutathione-related antioxidant enzymes are able to detoxify ROS and play an important role in preventing the disruption of the antioxidant/pro-oxidant balance in the organism.The main conclusion is as follows:1 Reproductive toxicity experiments indicate that:BDE-47 exerted reproductive inhibition effects in a time-and concentration-dependent manner. Additionally, we also found that the net reproductive rate is a sensitive parameter for indicating the effect of BDE-47 on reproductive toxicity in B. Plicatilis.2 BDE-47 exposure damaged the ultrastructure of B. plicatilis:the vitellarium became wrinkled, and the nuclear structure was disordered with compact spots of dense chromatin, indicating that the ovary was seriously damaged. It lead to the decline of individual reproductive ability, reflecting on the population level.3 BDE-47 exposure elevates the ROS level in B. plicatilis in a concentration-related manner, indicating the occurrence of oxidation; The increased level of ROS interfere with the organism detoxification and altered the activities of the glutathione-related enzyme; GST、 GPx and GSH appeared to be more sensitive to oxidative stress than GR; Oxidative stress interferes with detoxification and anti-stress oxidative defenses, leading to physiological disorders, causing adverse effects on the reproductive ability of B. Plicatilis.4 The obtained results comprehensively indicated that BDE-47 causes reproductive toxicity in B. plicatilis and that the ROS-mediated pathway is responsible for the observed toxicity.In summary, our study provide relatively complete assessment on the reproductive toxicity of BDE-47 exposure throughout population, individual, issue and physiological levels and explored the possible mechanism fundamentally and it may provide useful theoretical foundation for evaluation of PBDEs ecotoxicological effects.