Studies On The Toxic Effects Of Mercury, Copper And Cadmium To Three Economic Marine Macroalgae

Heavy metals pollution is becoming more serious in marine environment due to industrial activities, and the effects of heavy metals on algae have been paid much attention. In this paper, the toxic effects of treatments with different mercury (Hg2+), copper (Cu2+) and cadmium (Cd2+) concentrations on relative growth rate (RGR), the contents of photosynthetic pigments, the optimal quantum yield (Fv/Fm), photosynthesis, the activities of supereoxide dismutase (SOD), catalase (CAT) and nitrate reductase (NR) and the content of malondialdehyde (MDA) in three economic marine macroalgae, Gracilaria lemaneiformis, Hizikia fusiformis and Porphyra haitanensis, were investigated, in an effort to evaluate the toxic effects of heavy metals pollution in marine on macroalgae. The main results are as follows:The threshold concentrations of heavy metals that could markedly inhibit the growth of G. lemaneiformis were 0.02 mg·L-1 Hg2+, 0.05 mg·L-1 Cu2+ or 4 mg·L-1Cd2+, respectively. With the increasing concentrations of Hg2+, Cu2+ or Cd2+, Fv/Fm and photosynthetic O2 evolution rate of G. lemaneiformis were depressed gradually, while MDA content was increased gradually. The contents of photosynthetic pigments (Chl a, Car, PE and PC) of G. lemaneiformis were decreased after an initial increase under Hg2+ or Cu2+ stress, while they were increased at high Cd2+ concentrations. The activities of two antioxidative enzymes (SOD and CAT) in G. lemaneiformis were increased under Hg2+, Cu2+ or Cd2+ stress, while the activity of NR was significantly inhibited at high concentrations of these three heavy metal ions. The order of toxicity of these three heavy metal ions to G. lemaneiformis was Hg2+>Cu2+>Cd2+. G. lemaneiformis possessed certain ability to tolerate lower Cu2+ or Cd2+ concentrations.The threshold concentrations of heavy metals that could markedly inhibit the growth of H. fusiformis were 0.04 mg·L-1 Hg2+, 0.05 mg·L-1 Cu2+ or 4 mg·L-1 Cd2+, respectively. With the increasing concentrations of Hg2+, Cu2+ or Cd2+, Fv/Fm and photosynthetic O2 evolution rate of H. fusiformis were depressed gradually, while MDA content was increased gradually. The contents of photosynthetic pigments (Chl a and Car) of H. fusiformis were decreased after an initial increase under Hg2+ or Cu2+ stress, while they were increased at high Cd2+ concentrations. The activities of SOD and CAT in H. fusiformis were increased with lower Hg2+, Cu2+ or Cd2+ concentrations, but they were reduced with higher Hg2+, Cu2+ or Cd2+ concentrations. The activity of NR was significantly effected by heavy metal ions exposure. It was increased at low concentrations of Cu2+ or Cd2+, but it was reduced under Hg2+ stress or at high Cu2+ or Cd2+ concentrations. The order of toxicity of three heavy metal ions to H. fusiformis was Hg2+>Cu2+>Cd2+. H. fusiformis possessed certain ability to tolerate lower Hg2+, Cu2+ or Cd2+ concentrations.The threshold concentrations of heavy metals that could markedly inhibit the growth of P. haitanensis were 0.04 mg·L-1 Hg2+, 0.10 mg·L-1 Cu2+ or 4 mg·L-1 Cd2+, respectively. With the increasing concentrations of Hg2+, Cu2+ or Cd2+, Fv/Fm and photosynthetic O2 evolution rate of P. haitanensis were depressed gradually, while MDA content was increased gradually. The contents of photosynthetic pigments (Chl a, Car, PE and PC) of P. haitanensis were decreased at high Hg2+ concentrations, and they were increased with lower but reduced with higher concentrations of Cu2+. The contents of PE and PC were firstly increased, and then were sharply declined with increasing concentrations of Cd2+. The contents of Chl a and Car were sharply decreased at 10 mg·L-1 Cd2+. The activity of SOD of P. haitanensis was increased under Hg2+ or Cu2+ stress, and it was increased firstly and then was dropped under Cd2+ stress. CAT activity was increased under Hg2+ stress, while it was firstly increased but was sharply declined with increasing Cu2+ or Cd2+ stress. The NR activity was activated and increased at low concentrations of Hg2+, Cu2+ or Cd2+, but it was markedly inhibited at high concentrations of these three heavy metal ions. The order of toxicity of three heavy metal ions to P. haitanensis, from most toxic to least toxic, was Hg2+>Cu2+>Cd2+. P. haitanensis possessed certain ability to tolerate lower Hg2+, Cu2+ or Cd2+ concentrations.It is found in the experiment result that the order of macroalgae to tolerate Hg2+ was P. haitanensis≈H. fusiformis > G. lemaneiformis, and to Cu2+ was P. haitanensis > H. fusiformis≈G. lemaneiformis. The toxicity of Cd2+ was approximately the same among all the three macroalgae.