Mineralization performance of Rhodococcus chlorophenolicus strain PCP-1 in contaminated soil simulating on site conditions

Abstract

Mineralization of pentachlorophenol (PCP) was studied in non-sterile soil using Rhodococcus chlorophenolicus strain PCP-1. The effect of the inoculum size, concentration of PCP and soil moisture on mineralization of PCP was investigated in two different types of soil. Non-sterile peaty and sandy soils, containing from 30 to 600 mg of PCP kg − soil dry wt were inoculated to a density of from 500 to 10 8 R. chlorophenolicus cells g −1 soil. A mass balance of PCP-carbon and -chloride in the inoculated soils was made after exposure for 200 days. The products from PCP-mineralized carbon and released chloride were related to the degraded PCP in highly-contaminated soils. The degree of mineralization of PCP responded positively to an increase in the numbers of R. chlorophenolicus cells. The mineralizing capacity per inoculant cell was higher (40 fg PCP day −1) in soil with 350 and 600mg PCP kg −1 dry wt than in soil with 30mg PCP kg −1 dry wt (4fg PCP day −1). The mineralization was similar in soil with a high content of organic matter (30%) to that in mineral soil (1% organic matter). The rate of degradation of PCP by indigenous soil microbes in sand and in peat was equivalent to 0.3 and 1 mg PCP kg −1 dry wt month −1, respectively. This indicates that unforced bioremediation would require years for completion, even at a low concentration of PCP pollution. The results also show that more than 10 7 active R. chlorophenolicus cells should be applied g −1 soil to ensure effective mineralization of PCP in the soil.