| With the rapid development of nuclear power industry,the nuclear power is becoming more and more important in China's energy production and supply.The safety operation of the coastal nuclear power plant and marine radioactive pollution caused by serious accident of the nuclear power plant have attracted a growing and wide concern.137Cs,one of the main artificial radionuclides in liquid effluents,can be enriched and accumulated by algae and and is regarded as an important environmental monitoring indicator.At present,the effects of radionuclides on algae are mainly focused on the concentration,few studies on the effects of radionuclides is reported on the growth,photosynthesis,physiology and biochemistry of algae.In this paper,the change of morphology,growth rate,chlorophyll fluorescence characteristics,soluble protein content and antioxidant system enzymes and the concentration of 137Cs were investigated in marine planktonic algae Phaeodactylum tricornutum treated under exposure of 1000 Bq/L and 10000 Bq/L 137Cs radiation.These findings could provide scientific data support for understandin g the ionizing radiation damage and and nuclide concentration.The main results were included as follow:?1?Physiological response of algal cells to 137Cs stress:There was no significant difference in morphology,growth rate and chlorophyll fluorescence characteristics between the treatment group and the control group under the exposure of 137Cs.The average growth rate of P.tricornutum in the 137Cs treatment group with radioactive 1000 Bq/L specific activity,CsCl control group and blank group were 0.600/d,0.600/d and 0.610/d,respevtively,and the average growth rate of P.tricornutum in the 137Cs treatment group with radioactive 10000 Bq/L specific activity,CsCl control group and blank group were 0.373/d,0.354/d and 0.371/d,respectively.Compared with the stable isotope control group and blank group,the difference among the groups was not significant?P>0.05?.The value of Fo,Fv and Fm increased with the culture time under 1000 Bq/L 137Cs exposure.The ratio of Fv/Fm and Fv/Fo,NPQ and QY tended to be stable after a slight incease,respectively;Qp tended to decrease before it stabilized.The value of Fo,Fv and Fm increased with the culture time under 10000 Bq/L 137Cs exposure.Fv/Fm,Fv/Fo and QY increased followed by a slow decline.QY and Fv/Fm were basically within the range of 0.40.6.In the early stage of the experiment,NPQ decreased and then it was in a fluctuating state,while the overall change was not dramatic.Qp tended to decrease before it stabilized.There was no significant difference in the soluble protein,MDA,SOD,POD and GSH-PX among the treatment group,the control group and the blank group.The content of soluble protein and MDA did not change significantly during the culture time,and the soluble protein was basically stable within the range of 47×10-10 nmol/cell.MDA was about 10-8 nmol/cell,and there was no significant difference between the groups.The SOD activity decreased from 10-6 to 10-8within the culture time.GSH-PX activity decreased from 10-5 units to 10-6 units.The POD activity was maintained at 10-8 units during the culture time.Although the measured parameters showed different trends within the culture time.?2?Concentration of 137Cs in algal cells:the radioactive activity of 137Cs in algal increased gradually and reached equilibrium after 48 hours under the exposure of 10000 Bq/L 137Cs.The maximum radioactive activity was?15.721±1.518?Bq/g?wet?and?145.951±5.305?Bq/g?dry?,respectively.The concentration coefficient was 1.701±0.158?fresh?.Compared with Prorocentrum,a single-cell plankton-alga,the concentration coefficient of P.tricornutum was 73%?wet?of Prorocentrum,and the concentration capacity was weaker than that of Prorocentrum.To evaluation of the effects of radiation on algae,biological radiation impact assessment was conducted by ERICA,considering some parameters change such as the nuclide activity of water and biological concentration.The results showed that the radiation dose of P.tricornutum was about 9.04?Gy/h under the exposure 10000 Bq/L137Cs,lower than the radiation dose limit?10?Gy/h?set by the EU for aquatic organisms.The specific activities of 137Cs involved in the experiment?1000 Bq/L and 10000 Bq/L?were within the radiation dose limits set by the EU. |
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