Phytoremediation of pesticide-contaminated soils

Screening tests of rhizosphere soils from 15 plant species were conducted to determine their ability to mineralize two common herbicide contaminants, atrazine and metolachlor. Mineralization of 14C-atrazine or 14C-metolachlor, applied at 50 ug/g each, was monitored. Kochia rhizosphere soil exhibited the greatest mineralization of 14C-atrazine, with 62.1% mineralized after 36 days. Other rhizosphere soils that exhibited the ability to mineralize high concentrations of atrazine included musk thistle, catnip, foxtail barley, witchgrass, and lambsquarters. None of the rhizosphere soils tested exhibited a positive response for 14C-metolachlor mineralization. Additional radiotracer studies were conducted to determine appropriate endpoints for atrazine and metolachlor degradation. Mineralization of atrazine was considerable after 36 days, while mineralization of metolachlor was minimal. Extractable metolachlor was significantly less, however, in kochia rhizospheric soils compared to nonvegetated soil. A comparison of the influence of kochia and rape on persistence of atropine in a herbicide-contaminated soil was studied by monitoring the degradation of 14C-atrazine in vegetated and nonvegetated soils. The percentage of extractable atrazine for kochia vegetated soils was significantly less than from nonvegetated soil, while the percentage of extractable atrazine from rape vegetated soils was not significantly different from either the kochia-vegetated soils or nonvegetated soils. Combustion of plants revealed that 11% of the applied 14C was taken up by kochia, whereas less than 1% was taken up by rape plants. This research indicates that the use of plants in remediating soils looks promising.