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In this study sodium dithionite (NaS 2 O 4 ) and sodium borohydride (NaBH 4 ) were employed as reducing agents for the synthesis of nanosized iron-based particles. The particles formed using NaBH 4 (denoted nFe(BH 4 )) principally contained (as expected) Fe(0) according to XAS and XRD analyses while the particles synthesized using NaS 2 O 4 , (denoted nFe(S 2 O 4 )) were dominated by the mixed Fe(II)/Fe(III) mineral magnetite (Fe 3 O 4 ) though with possible presence of Fe(0). The ability of both particles to reduce trichloroethylene (TCE) under analogous conditions demonstrated remarkable differences with nFe(BH 4 ) resulting in complete reduction of 1.5 mM of TCE in 2 h while nFe(S 2 O 4 ) were unable to effect complete reduction of TCE in 120 h. Moreover, acetylene was the major reaction product formed in the presence of nFe(S 2 O 4 ) while the major reaction product formed following reaction with nFe(BH 4 ) was ethylene, which was further reduced to ethane as the reaction proceeded. Considering that effective Pd reduction to Pd(0) requires the presence of Fe(0), this is consistent with our finding that Fe(0) is not the dominant phase formed when employing dithionite as a reducing agent under the conditions employed in this study. [ABSTRACT FROM AUTHOR]