Presence of Cr(III) in glomalin related protein fraction in a Cr polluted soil

GIL CARDEZA ML; FERRI A; CORNEJO RIVAS P; GÓMEZ E

Workshop; II Workshop Latinoamericano sobre PGPR; 2014

Industrial development has helped to improve human?s quality of life during the last decades. However, the lack of knowledge for appropriate industrial waste handling and final disposal has contributed to soil and water contamination.  Chromium is used in several industrial processes (i.e. leather tanning, alloy and stainless steel production). Chemistry of Cr is quite complex; Cr is found in soils in two oxidation states, Cr(III) and Cr(VI). Cr(III) is non-toxic and not readily absorbed by plants; in contrast, Cr(VI) is highly toxic; it is a Class A carcinogen by inhalation and an acute irritating agent to living cells. Phytoremediation, which uses higher plants and the associated soil microbes as decontaminating agents, is a less expensive, long-lasting and eco-friendly strategy to decontaminate PTE polluted soils. Arbuscular mycorrhizal fungi (AMF), which develop mutualistic associations with the roots of most terrestrial plants, allow plant a greater absorption of nutrients and water due to an increase in soil exploration area. In this sense, it is worth exploring AMF in relation to their potential for improving phytoextraction and/or phytostabilization. Materials and methods Cr soil distribution was studied in rhizosphere soils from Ricinus communis and Conium maculatm and bare soil (BS) from an industrial and urban area in Morón, Provincia de Buenos Aires, Argentina. Total Cr, Cr(VI) and Cr(III) concentrations were determined in 3 soil fractions: total, extractable (0.5 M EDTA for Cr(III) and 10 mM phosphate buffer pH = 7.2 for Cr(VI)) and associated to total-glomalin-related protein (T-GRSP). Moreover, total Cr in plant tissues and presence of AMF in roots were determined. Total Cr was determined by atomic absorption spectrophotometry; Cr(VI) by diphenylcarbazide photometric method and AMF structures by observation of stained roots under a light microscope at 400X magnification. Results BS had the highest total Cr and total Cr(VI) concentrations. Total Cr(VI) concentration from both rhizosphere soils did not differ from the allowed value for residential area in Argentina (8 µg Cr(VI) g-1 soil), while total Cr(VI) in BS was 1.8 times higher. Total Cr concentration in all the soils was higher than the allowed value (250 µg Cr g-1 soil). Extractable and associated to T-GRSP Cr(VI) concentrations were below the detection limit. Cr(III) bound to T-GRSP was the highest in the BS. In both plant species, total Cr was higher in root than in shoot and both species presented arbuscular mycorrhizal fungi (AMF). Conclusion As far as we know, this is the first study that reports the presence of Cr in T-GRSP fraction of soil organic matter. These findings are in agreement with a long term effect of glomalin in sequestrating Cr and suggest that Cr mycorrhizostabilization could be a predominant mechanism used by R. communis and C. maculatum to diminish Cr soil concentration. Nevertheles, further research is needed to clarify the contribution of native AMF isolated from R. communis and C. maculatum rhizosphere to the Cr phytoremediation process.