Atrazine and simazine degradation in Pennisetum rhizosphere

The ability of rhizosphere of four plant species to promote the degradation of charcoal-fixed atrazine and simazine in cement blocks of a long-term contaminated soil when mixed with a normal soil at 1:1 ratio was tested. Of the four selected plants viz., rye grass (Lolium perenne), tall fescue (Festuca arundinacae), Pennisetum (Pennisetum clandestinum) and a spring onion (Allium sp.) used in this study, only P. clandestinum was able to survive in herbicide contaminated soil while other plants died within few days after germination/transplanting. Both atrazine and simazine were degraded at a faster rate in contaminated soil planted to P. clandestinum than in unplanted soil. Within 80 days, nearly 45% and 52% of atrazine and simazine, respectively, were degraded in soil planted to P. clandestinum while only 22% and 20% of the respective herbicide were degraded in the unplanted soil. During 80-day experimental period, both microbial biomass and soil dehydrogenase activity were significantly increased (7-fold) in soil planted to P. clandestinum over that in unplanted soil. The suspension of contaminated rhizosphere soil, planted to P. clandestinum exhibited an exceptional capability to degrade both atrazine (300 microg) and simazine (50 microg) in a mineral salts medium over that of non-rhizosphere soil suspension. Results indicate that P. clandestinum, a C4 plant, may be useful for remediation of soils contaminated with atrazine and simazine.