[en] In first experiments the reduction sequence of Pu starting with Pu(VI) was studied in presence of hydroquinone (HQ) and fulvic acid (FA) as reducing compounds at various pH values between pH 1 and 7. The Pu species were monitored by UV-Vis spectroscopy and liquid-liquid extraction. Pu(V) and (VI) are not stable in aqueous solutions containing hydroquinone and fulvic acid (FA) at pH 1 to 7. With 200 mg/L FA the reduction of Pu(VI) to Pu(V) is fast and complete after 30 minutes at pH 3. Compared to the reduction reaction at similar concentration of HQ, the FA reduction is slower. We also observed that Pu(VI) is unstable in solutions devoid of FA at pH values > 3, but that the rate is much slower than in presence of FA and HQ. Pu(V) in same solutions is converted to Pu(IV), the most stable oxidation state in aqueous solutions containing FA at pH 3 - 7 (relevant for natural aquifers). Reduction of Pu(IV) to Pu(III) was found only at pH values < 5 for HQ and < 3 for FA. The reactions were also monitored by Eh measurements. The present studies showed that a correlation between Eh values and thermodynamic calculations might be a capable tool for modelling redox reactions between Pu ions and hydroquinone or hydroquinone-like compounds like FA. It cannot be excluded that Pu(III) is more stable in solutions containing organic compounds with lower redox potential than the GoHy-573-FA batch used in the present studies