Biotransformation Of Arsenic By Microcystis Aer?ginosa Under Different Environmental Conditions

The algal bloom caused by eutrophication of waters is one of the hot spots in the study of global ecological environment,and cyanobacteria bloom is the main form of algal bloom in china.The biological toxicity of arsenic depends largely on the chemical speciation of arsenic,the inorganic arsenic more toxic than organic arsenic and trivalent arsenic more poisonous than pentavalent arsenic.As one of the main products of water eutrophication,cyanobacteria is also an indispensable primary producer.Arsenic is one of the most common pollutants in the natural water body,and it is of great significance to study the biotransformation of arsenic and its influencing factors.In this study,the dominant species of cyanobacteria--Microcystis aer?ginosa was used to study the absorption and transformation of arsenic under different environmental conditions by controlling the pH,N/P and arsenic concentrations respectively.The main conclusions of this paper are summarized as follows:(1)When initial pH is 6,Microcystis aer?ginosa absorbed more arsenic,the content of arsenic in algae reaching up to 8.97mg/kg.With the increase of pH,the absorption of arsenic in Microcystis aer?ginosa decreased.In the suitable range of pH(8.0-9.5)for the growth of Microcystis aer?ginosa,Microcystis aer?ginosa showed more effective methylation of arsenic.In the experimental groups of pH=8 and pH=9,trivalent arsenic,pentavalent arsenic and two methylation arsenic in Microcystic aer?ginosa were detected.(2)High concentration of phosphate can reduce the absorption of arsenic in Microcystis aer?ginosa,because of the competition between phosphate and arsenic.When the ratio of N/P was 4:1,the absorption of arsenic by Microcystis aer?ginosa was the most among the experimental groups.With the decrease of the ratio of nitrogen to phosphorus,the absorption of arsenic by Microcystis aer?ginosa decreased gradually.When the ratios of nitrogen and phosphorus were 4:1 and 2:1 respectively,trivalent arsenic,pentavalent arsenic and two methylation arsenic was detected in Microcystis aer?ginosa,but no organic arsenic was detected in the other two experimental groups with low nitrogen to phosphorus ratios.When nitrogen phosphorus ratio was 1:1,only pentavalent arsenic and trivalent arsenic was detected in algae;when nitrogen phosphorus ratio was 1:2,only the pentavalent arsenic was detected in algae.(3)The absorption of arsenic by Microcystis aer?ginosa increased with arsenic concentration at preliminary stage,but the content of arsenic in algae cells tended to decrease with the increase of arsenic concentration later.When the initial arsenate concentration was 50?g/L,the arsenic content of the algae was 5.42mg/kg after 14 days.When the initial concentration of arsenate increased from 50?g/L to 100?g/L,the absorption of arsenic by Microcystis aer?ginosa increased by 2.11mg/kg.Only in the experimental group which the arsenic concentration was 100?g/L,methyl arsenic was detected.The results showed that high arsenate concentration could promote the transformation of As(?)into As(?),and As(?)into DMA which was excreted by Microcystis aer?ginosa.