Evidence of perchlorate (CIO4-) reduction in plant tissues (poplar tree) using radio-labeled 36CIO4-

Phytoremediation of perchlorate (ClO4-) by poplar trees Populus deltoidex nigra was investigated using small cuttings growing in hydroponic Hoagland solution and plant tissue cultures, consisting of spherical photosynthetic cell aggregates (i.e. nodules) developing in Murashige and Skoog culture medium. Both plants and nodules were grown under a 16 h/8 h photoperiod cycle and under sterile conditions. Degradation experiments, performed by the incubation of pregrown plants and nodules in the presence of Cl-36 radio-iabeled ClO4- (25 mg L-1), showed a reduction of the initial ClO4- concentration in the solution of about 50% after 30 d of incubation. Analysis of the distribution of radioactivity in different plant fractions indicated that 27.4% of the total was translocated to the leaves, while 66.9% remained in the solution. Very little radioactivity (less than 3.0%) was detected in the other parts of the plants. 32.0% of the radioactivity recovered in the solution was shown to consist of Cl-36(-) and 68.0% of nontransformed (ClO4-)-Cl-36. The radioactivity recovered in the leaf extracts was distributed as chloride (Cl-36(-)) (1.6% of the total), chlorite ((ClO2-)-Cl-36) (2.4%), chlorate ((ClO3-)-Cl-36) (4.8%), nontransformed (ClO4-)-Cl-36 (21.6%), and an unidentified organic compound (1.4%). The radioactivity recovered in the solution containing submerged nodules consisted of Cl-36(-) (6.4% of the total), (ClO3-)-Cl-36 (1.3%), and nontransformed (ClO4-)-Cl-36 (51.5%). Radioactivity detected in the nodule extracts was distributed as Cl-36(-) (2.0% of the total), (ClO2-)-Cl-36 (5.2%), (ClO3-)-Cl-36 (6.4%), (ClO4-)-Cl-36 (22.7%), and an unidentified organic compound (0.5%). These results provide evidence of perchlorate reduction inside poplar tree tissues. (ClO4-)-Cl-36 is partially reduced to (ClO3-)-Cl-36, (ClO2-)-Cl-36, and Cl-36(-).