In this research, Microcystis aeruginosa 905 and arsenate were used to investigate the influence of arsenic on Microcystis aeruginosa and the arsenic speciation transformation. Cell density was observed by microscope in order to investigate the toxicity of the arsenate to the Microcystis aeruginosa. The speciation analysis method of HPLC-HG-AFS was applied to determinate the biotransformation of the Microcystis aeruginosa to the arsenate. The matched matrix was used in the speciation analysis method to eliminate the matrix effects of the algae broth.
The main results were summarized as follows:
(1) When intracellular and extracellular phosphorus of the Microcystis aeruginosa was absent, the effect of toxicity caused by the arsenate to the Microcystis aeruginosa was strong and rapid. The toxicity was enhanced evidently along with the increase of arsenate concentration and was reduced unobviously along with the increase of Microcystis aeruginosa biomass. When the arsenate entered into the cell by Pit system, it was deoxidized to arsenite rapidly, and then the arsenite was methylated toMMA and DMA slowly. MMA was the intermediate product, so As(III)、DMA、As(V) were found in the Microcystis aeruginosa broth finally.
(2) Under the conditions of low, moderate and high phosphorus concentration, the effect of toxicity caused by the arsenate to the Microcystis aeruginosa was weak and slow. The toxicity was enhanced unobviously upon the increase of arsenate concentration and reduced with the increase of Microcystis aeruginosa biomass. Here, the arsenate entered into the cell by Pst system and was deoxidized to arsenite that was methylated completely to DMA slowly, and only DMA、As(V) were found in the Microcystis aeruginosa broth. However, As(III)、DMA、As(V) were found under high phosphorus and arsenate concentration because large number of arsenate was deoxidized to arsenite which couldn’t be methylated completely.
(3) The influence of arsenate to Microcystis aeruginosa was affected by biological growth manner. It was the most obvious in the lag phase that the effect of arsenate to the Microcystis aeruginosa. The reasons were that the metabolism of Microcystis aeruginosa.was promoted and enzyme was high, and the adsorption and reduction of arsenate was rapid, which induced evident toxicity.
In conclusions, the entrance system of arsenate into the Microcystis aeruginosa was controlled by phosphate concentration, which decided the influence of the arsenate on growth of the Microcystis aeruginosa and the arsenic speciation transformation. Under low and moderate phosphorus concentration of broth that was equivalent to phosphorus of environment, the arsenate was translated into low toxic arsenic speciation. It was worth noting that the harm to the circumstance induced by the biotransformation of the Microcystis aeruginosa to the arsenate can not be enlarged.