"As part of their studies, they presented evidence that Fe(II)-EDTA is not oxidized abiotically by nitrite and therefore concluded that all oxidized Fe(II) must originate from direct enzymatic activity. However, the absence of Fe(II)-EDTA oxidation by nitrite in their work differed from the results of other studies that have shown chemical oxidation of Fe(II)-EDTA by nitrite and NO (Zang et al., 1988; Van Der Maas et al., 2004; Kumaraswamy et al., 2006). It should be noted that some of these other studies measured Fe(II) concentrations with ferrozine as the colorimetric agent (Stookey, 1970) to follow Fe(II)-EDTA oxidation, while others used phenanthroline as the colorimetric complexant (Tamura et al., 1974). "
"However, the chemical control with nitrite/ [Fe(II)EDTA] 2À clearly gave a spontaneous reaction, forming [Fe(II)EDTA Á NO] 2À complex. A similar reaction was observed by Maas et al.  in their study of nitrite dependent [Fe(II)EDTA] 2À oxidation with mixed cultures. Previous studies on denitrificationdependent iron oxidation by Straub et al.  and Benz et al.  also had discussed how nitrite might chemically react with ferrous iron (ferrous iron was supplied as ferrous sulfate in bicarbonate buffered medium in these studies) in the absence of cells. "
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