Influence Of Dissolved Organic Matter On The Arsenic Speciation And Availability To Algae

Arsenic is ubiquitous in the environment. Its speciation and transportion will determine its bioavailability, which is influenced by many kinds of factors, such as dissolved organic matter (DOM) and hydrous metal oxides. This paper studied the interaction between arsenic and dissolved organic maters, by an established HPLC-HG-AAS analytical method, combined with the analytical methods such as Ultraviolet-Visible Spectroscopy, Fluorescence Emission spectrum, three-dimensional excitation emission matrix fluorescence spectra. The influential factors such as pH value, lighting, microorganisms, temperature, and the originality of DOM were studied. The competitive adsorption of As and DOM onto amorphous hydrous ferric oxides was also studied. At last, the As bioavailability to algae was discussed preliminary.First, the interaction between arsenic and DOM was discussed, a kind of commercial humic acid (Sigma-Aldrich Company) and some natural DOM of different originality were chosen as the aim DOM, results showed that this kind of DOM can absorb As(V) and reduce it into As(III) partly. Several influential factors were also studied: Different pH values cause different arsenic speciation in DOM-As system. In neutral condition less arsenic is combined with DOM than acidic and basic conditions; Sunlight, microorganisms can inhibit the reduction of As(V) by DOM; lower temperature lead to weaker interaction between DOM and arsenic; the interaction between DOM and arsenic have a positive correlation with arsenic concentration; four DOM samples from different sources can interact with arsenic, both As(III) and As(V) can weaken the fluorescence intensity of DOM.Second, the competitive sorption of As and DOM onto hydrous ferric oxide (HFO) was studied, and the findings were as follows: HFO can strongly absorb As(III), DMA, MMA and As(V); DOM can combine with As(III) and As(V), it also can oxidize As(III) into As(V); besides, DOM can compete with arsenic to adsorb onto HFO and delay the attainment of sorption equilibrium and diminish the extent of sorption of both arsenate and arsenite. At last, the arsenic toxicity on the algae photosynthesis was studied by ToxY-PAM and Phyto-PAM. The results showed that As(III) and As(V) show no evident acute toxicity to photosynthesis of Chlorella vulgaris, As(III) and As(V) have different toxicity to different algae. For Chlorella vulgaris, As(III) and As(V) have no evident inhibition to its photosynthesis; for Microcystis aeruginosa, As(V) will decrease its photosynthesis activity; the presence of DOM can weaken the arsenic toxicity to Microcystis aeruginosa; higher arsenic concentration causes higher arsenic accumulation in algae. Compared with As(V), As(III) is accumulated more easily by Microcystis aeruginosa.