The Toxic Effects Of 2, 2', 4, 4'-tetrabrominated Biphenyl Ether (BDE-47) On Four Species Of Marine Microalgae

Polybrominated diphenyl ethers (PBDEs) are a group of new type persistent organic pollutants with significant ecological risk. PBDEs are a class of brominated flame retardants (BFRs) and used in a wide variety of consumer products. With increasing concentrations of PBDEs in marine environment, the impacts of PBDEs on the marine environment are drawing both international and local researchers' wide attentions. Reports show that PBDEs have acute toxicity effects on marine organisms. However, acute toxicity effects on marine microalgae have not been reported yet. Marine microalgae are primary producers in marine ecosystems, composition and changes of marine microalgae can affect the entire marine ecosystem structures and functions. Marine microalgae have large surface area and, thus, are very sensitive to changes in the external environment. The changes of physiological and biochemical characteristics of marine microalgae can reflect marine environmental quality, so they are the best bioindicator to indicate marine environmental pollution degree.In this research, the congener BDE-47 with a high concentration in marine organisms is chosen to conduct acute toxicity testing in marine microalgae. First, the acute toxic effects of BDE-47 on four species of marine microalgae (Chlorella autotrophica, Chaetoceros muelleri, Heterosigam akashiwo and Skeletonema costatum) are studied through the growth curve of microalgae. Then, the effect of different BDE-47 concentrations on the activities of antioxidant enzyme including superoxide dismutase (SOD) and catalase (CAT) and chlorophyll fluorescence parameters of four species of marine microalgae are studied. Response characters of antioxidant defense systems are also explored. The main concludions are listed as follows:(1) The median effect concentrations (EC₅₀) of BDE-47 on four marine microalgae are 0.79,1.52,1.99 and 2.25μg·L-1respectively. The results indicate that BDE-47 is highly toxic. The sensitivity of four species of marine microalgae to BDE-47 is in the order of Chlorella autotrophica> Chaetoceros muelleri > Skeletonema costatum > Heterosigam akashiwo.(2) In the concentration range of 0.1μg·L^-1～2.5μg·L^-1, both SOD and CAT of four species of microalgae are enhanced to alleviate oxidative damages to marine microalgae, but enzyme activities are increased in different extent. Compared with Heterosigam akashiwo and Skeletonema costatum, CAT and SOD of Chlorella autotrophica and Chaetoceros muelleri are more sensitive to BDE-47. The sensitivity of two enzymes of four species of marine microalgae to BDE-47 is in the order of Chlorella autotrophica> Chaetoceros muelleri > Skeletonema costatum > Heterosigam akashiwo. Therefore, the changes of SOD and CAT of Chlorella autotrophica can be used as sensitive biomarkers at the molecule level of the stress of BDE -47.(3) In this research, no significant inhibition of maximal photochemical efficiency of PSâ…¡(Fv/Fm) of Chlorella autotrophica and Heterosigam akashiwo is determined between treatment group and control group, which indicates the concentration(range from 0.1～2.5μg·L^-1) of BDE -47 doesn`t lead the damage to PSâ…¡reaction center. Chlorophyll fluorescence parameters(PSâ…¡potential fluorescence efficiency(Fv/Fo), actual photochemical efficiency of PSâ…¡(φPSâ…¡) go down after an initial obvious rise, but isn`t inhibited significantly compared with control group except Chlorella autotrophica exposed to BDE-47 for 96 hours under concentration of 2.5μg·L^-1, which demonstrates that Chlorella autotrophica and Heterosigam akashiwo has a certain degree of adaptability to BDE-47 and Heterosigam akashiwo is more tolerant than Chlorella autotrophica. Photochemical quenching (qP) of Chlorella autotrophica and Heterosigam akashiwo isn`t inhibited after exposed to BDE-47. After exposed to BDE-47 for 48 hours, qP of treatment group of Heterosigam akashiwo is significantly higher than control group, indicating Heterosigam akashiwo is more tolerant than Chlorella autotrophica.(4) Compared percentage change in chlorophyll fluorescence parameters exposed to different BDE-47 concentrations with percentage change in antioxidant enzyme activities exposed to different BDE-47 concentrations between Chlorella autotrophica and Heterosigam akashiwo, we can find CAT has a significant response to BDE-47 stress at most of time, its activity is far greater than the rate of change of chlorophyll fluorescence parameters and SOD. Therefore, CAT is the best biomarker to indicate marine environmental pollution degree.All above results show that responses of marine microalgae to BDE-47 stress are complicated physiological and biochemical processes. Chlorella autotrophica is the best biological indicator to indicate marine environmental pollution degree compared with other three marine microalgae, and the activity of CAT of Chlorella autotrophica is the best biomarker to indicate marine environmental pollution degree.