EFFECT OF INOCULANT DENSITY, FORMULATION, DISPERSION AND SOIL NUTRIENT AMENDMENT ON THE REMOVAL OF CARBOFURAN RESIDUES FROM CONTAMINATED SOIL

Our study was aimed at investigating some factors affecting the use of a carbofuran-degrading bacterium as an inoculant to remove carbofuran residues from contaminated soil. Soil samples inoculated with a liqui d cell suspension of strain C28 to give an initial density ranging fro m 10(3) to 10(7) cfu g(-1) (dry weight of soil) significantly improved pesticide removal. When the soil was inoculated with a granular formu lation of strain C28 to give theoretical cell densities of 5 x 10(3), 5 x 10(4) and 5 x 10(5) cfu g(-1) (dry wt of soil), a significant incr ease in the rate of carbofuran degradation, as compared to uninoculate d samples, was seen only for the highest inoculum size. The rate of ca rbofuran degradation in non-inoculated samples was significantly reduc ed by chloroform fumigation, but inoculation of natural and chloroform -fumigated soil with equivalent cell densities of strain C28 in both l iquid and granular formulation led to a significant increase in the ra te of carbofuran breakdown. The effect of soil glucose amendment on pe sticide degradation by strain C28, in a liquid or solid formulation, d epended on the concentration of the sugar and on inoculant density. A low concentration of glucose significantly reduced the lag phase befor e pesticide degradation by a low density inoculant. A high concentrati on, however, led to a significant reduction of the degradation rate fo r all inoculum sizes. Mixing the soil after inoculation was essential to obtain rapid degradation of the pesticide. When theoretically-equiv alent cell densities were introduced in 0.1 and 1 g of microgranules, no significant difference in the rate of pesticide degradation was obs erved in these experiments. (C) 1997 Elsevier Science Ltd.