Fitorremediación de suelo contaminado con cromo hexavalente empleando las especies Portulacaria afra y Cynodon dactylon

Abstract

This research work presents a feasible biotechnological proposal to address a priority environmental problem such as soil contamination by hexavalent chromium (Cr(VI)), which is highly toxic. Phytoremediation is a treatment that provides the opportunity to identify plant species that are capable of remediating soils and is based on an economical and passive technology driven by solar energy, in contrast to traditional physicochemical treatments, which are expensive, alter soil properties and promote secondary contamination. The phytoremediation capacity of Cr(VI) of a contaminated industrial soil was evaluated using the plant species Portulacaria afra (P. afra) and Cynodon dactylon (C.dactylon) during 192 days of treatment. The initial concentration of total Cr in the soil was 5782.06 ± 258.3 mg/kg (2683.01 ± 38.2 mg/kg Cr(VI)). Chromium concentration in roots and shoots was monitored from total Cr. Bioconcentration (BCF) and translocation factors (TF) were calculated with final concentrations of Cr: 0.87 and 0.02 for P. afra; 1.66 and 0.01 for C. dactylon. Both species accumulated Cr mainly in the roots, thus, they are suitable for phytostabilization processes. The maximum phytoremediation capacity of Cr(VI) was observed in C. dactylon with a removal efficiency of 98.41%, obtaining a similar value with P. afra (98.12%). Using P. afra, the treatment was driven by the reduction of Cr(VI) to Cr(III), and with C. dactylon, by simultaneous reduction and root absorption. The participation of two strains of indigenous microorganisms from the contaminated soil in the reduction of Cr(VI) was evidenced. The isolates were identified as Bacillus sp. And Aspergillus sp. And were inoculated in reactors at different Cr(VI) concentrations (50, 100 and 200 ppm). The highest reduction rates were observed with the Aspergillus sp. strain, obtaining 99.96% (50 ppm), 97.28% (100 ppm) and 54.39% (200 ppm) at the end of the experiment. The reduction rates using the Bacillus sp. strain were lower: 44.75% (50 ppm), 26.89% (100 ppm) and 27.79% (200 ppm). The Cr(VI) concentration in the soil at the end of treatment using both plant species was lower than the limits established by Mexican regulations for agricultural, domestic, commercial and industrial soils. This study represents a great contribution to the application of phytoremediation in contaminated soils with Cr(VI) by increasing its scope and complementing the catalog of species used for restoration purposes.