Speciation of arsenic in a thermoacidophilic iron-oxidizing archaeon, Acidianus brierleyi, and its culture medium by inductively coupled plasma-optical emission spectroscopy combined with flow injection pretreatment using an anion-exchange mini-column.
The thermoacidophilic iron-oxidizing archaeon Acidianus brierleyi is a microorganism that could be useful in the removal of inorganic As from wastewater, because it simultaneously oxidizes As(III) and Fe(II) to As(V) and Fe(III) in an acidic culture medium, resulting in the immobilization of As(V) as FeAsO₄. To investigate the oxidation mechanism, speciation of the As species in both the cells and its culture media is an important issue. Here we describe the successive determination of As(III), As(V), and total As in A. brierleyi and its culture medium via a facile method based on inductively coupled plasma-optical emission spectroscopy (ICP-OES) with a flow injection pretreatment system using a mini-column packed with an anion-exchange resin. The flow-injection pretreatment system consisted of a syringe pump, a selection valve, and a switching valve, which were controlled by a personal computer. Sample solutions with the pH adjusted to 5 were flowed into the mini-column to retain the anionic As(V), whereas As(III) was introduced into ICP-OES with no adsorption on the mini-column due to its electrically neutral form. An acidic solution (1 M HNO₃) was then flowed into the mini-column to elute As(V) followed by ICP-OES measurement. The same sample was also subjected to ICP-OES without being passed through the mini-column in order to determine the total amounts of As(III) and As(V). The method was verified by comparing the results of the total As with the sum of As(III) and As(V). The calibration curves showed good linearity with limits of detection of 158, 86, and 211 ppb for As(III), As(V), and total As, respectively. The method was successfully applicable to the determination of the As species contained in the pellets of A. brierleyi and their culture media. The results suggested that the oxidation of As(III) was influenced by the presence of Fe(II) in the culture medium, i.e., Fe(II) enhanced the oxidation of As(III) in A. brierleyi. In addition, we found that no soluble As species was contained in the cell pellets and more than 60% of the As(III) in the culture medium was oxidized by A. brierleyi after a 6-day incubation.
Department of Chemistry, Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushimanaka, Okayama 700-8530, Japan.
Naoki
N
Higashidani
Department of Chemistry, Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushimanaka, Okayama 700-8530, Japan. Electronic address: kaneta@okayama-u.ac.jp.
Takashi
T
Kaneta
Department of Chemistry, Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushimanaka, Okayama 700-8530, Japan.
Nobuyuki
N
Takeyasu
Okayama University, 1-1-1 Tsushimanaka, Okayama 700-8530, Japan.
Shoji
S
Motomizu
Department of Earth Resources Engineering, Graduate School of Engineering, Kyushu University, 744 Motooka, Fukuoka 819-0395, Japan.
Naoko
N
Okibe
Department of Earth Resources Engineering, Graduate School of Engineering, Kyushu University, 744 Motooka, Fukuoka 819-0395, Japan.
Keiko
K
Sasaki
D041541:Acidianus / Q000737:chemistry* / Q000378:metabolism; D000837:Anion Exchange Resins / Q000737:chemistry*; D001105:Archaea / Q000737:chemistry / Q000378:metabolism; D001151:Arsenic / Q000032:analysis*; D003470:Culture Media / Q000032:analysis* / Q000378:metabolism; D017022:Flow Injection Analysis / Q000379:methods; D007501:Iron / Q000032:analysis* / Q000378:metabolism; D013057:Spectrum Analysis / Q000379:methods
D000837:Anion Exchange Resins; D003470:Culture Media; D007501:Iron; D001151:Arsenic
Acidianus brierleyi; Arsenic; Flow injection pretreatment; Inductively coupled plasma–optical emission spectroscopy; Speciation; Thermoacidophilic iron-oxidizing archaeon