Soil Dynamics of Cr(VI) and Responses of Portulaca Oleracea Grown in a Cr(VI)-Spiked Soil under Different Nitrogen Fertilization Regimes

Abstract The reduction potential of the highly toxic Cr(VI) to the inert Cr(III) in an alkaline soil was studied during a 50-day experiment with Portulacaoleracea grown in pots. We aimed at assessing whether our test species can be a phytoremediation candidate for Cr(VI)-contaminated soils. We measured the Cr(VI) reduction rate in soil, determined the Cr(VI) and Cr(III) concentrations in aerial and root P. oleracea tissues, calculated the Transfer coefficient (TC=metal in plant over metal in soil) and the Translocation factor (TF=metal in aerial biomass over metal in roots) in order to assess Cr(VI) uptake and distribution in plant tissues, while we also studied the effect of added nitrogen in the studied parameters. We added five different Cr(VI) levels,reaching 148.6 mg Cr(VI) kg-1soil and also had two N levels (equivalent to 0 and 200kg ha-1). The results indicated that Cr in plant tissues was mainly found in its reduced form (Cr(III)) and only a minor fraction of Cr was detected in its oxidized form (Cr(VI)). The main remediation mechanism was found to be that of the naturally occurring Cr(VI) reduction that effectively produced Cr(III), followed by the uptake of Cr(VI) from our test plants. We also found that Cr(VI) in P. oleracea tissues was mainly found in roots and relatively low Cr(VI) concentrations were found in the above ground tissues. We concluded that P. oleraceais a tolerant plant species, especially if assisted with a sufficient level of N fertilization, although it failed to approach the threshold of being categorized as an accumulator species.However, before reaching more conclusive suggestionsabout P. oleracea as a potential phytoremediation species, further investigation is necessary.