MICROBIAL RESPONSE TO REPEATED APPLICATIONS OF LOW CONCENTRATIONS OF PENTACHLOROPHENOL IN AN ALFISOL UNDER PASTURE

Columns of an Alfisol under permanent pasture were polluted by repeate d additions of pentachlorophenol (PCP) (7 mg l(-1)) to levels of 102 a nd 510 mg Kg(-1), to simulate a dynamic diffuse pollution. PCP was rap idly sorbed to the soil organic matter, and was only slightly degraded . Measurements of soil microbial biomass-C revealed a 25% decrease in total biomass-C caused by both leaching and PCP toxicity. Microbial bi omass-C measurements performed on soil fractions showed that only micr oorganisms located in the outer compartment of the aggregates were aff ected. Microorganisms protected by soil micro-aggregates were not affe cted, suggesting that they were not in contact with PCP, which was thu s unavailable for biodegradation. Three gram negative bacterial strain s (Si, C3 and C2), able to use PCP as a sole carbon and energy source, were isolated after 0, 1 and 3 months of PCP enrichment respectively, and were identified as Pseudomonas (Si) and Acinetobacter (C3 and C2) . In liquid degradation tests, the strains C2 and C3 degraded 60% of P CP within 26 days whereas the Pseudomonas degraded only 25%. A specifi c immuno-labeling of the three strains permitted to show that repeated PCP additions to soil had a positive, negative or absence of effect o n the populations C2, C3 and Si respectively. (C) 1997 Elsevier Scienc e Ltd.