Atrazine and phenanthrene degradation in grass rhizosphere soil

Organic contaminants often disappear more quickly from planted than from no n-planted soils. Five grass species (Sudan grass, ryegrass, tall fescue, cr ested wheatgrass and switch grass) were grown in soils without (Phase I) or with (Phase II) prior atrazine (ATR) and phenanthrene (PHE) amendment to s tudy the degradation of these compounds by rhizosphere microorganisms. In s uspensions of soil without prior chemical exposure, no significant loss of ATR was observed after 16 days incubation. The most probable number (MPN) o f ATR-degrading bacteria in the soils was below detection. Phenanthrene deg radation was observed in suspensions inoculated with all soils, but the rat es of degradation were not significantly different among them. The number o f PHE-degrading bacteria was similar in planted and nonplanted soils (10(5) cells g(-1) soil) except the number in tall fescue soil was significantly higher than in non-planted soil. In the Phase II study, both compounds were mineralized whether or not soils had been conditioned with ATR or PHE. Pri or amendment with either ATR or PHE significantly reduced the acclimation p eriod preceding the onset of mineralization. However, enumeration procedure s detected ATR-degrading bacteria only in ATR-amended soils. Prior exposure to PHE did not alter the number of PHE-degrading bacteria significantly. ( C) 2001 Elsevier Science Ltd. All rights reserved.