Re-inoculation of autoclaved soil as a non-sterile treatment for xenobiotic sorption and biodegradation studies

Autoclaved soil is commonly used for the study of xenobiotic sorption and a s an abiotic control in biodegradation experiments. Autoclaving has been re ported to alter soil physico-chemical and xenobiotic sorption characteristi cs such that comparison of autoclaved with non-autoclaved treatments in soi l aging and bioavailability studies may yield misleading results. Experimen ts could be improved by using autoclaved soil re-inoculated with indigenous microorganisms as an additional or alternative non-sterile treatment for c omparison with the sterile, autoclaved control. We examined the effect of a utoclaving (3 x 1 h, 121 degrees C, 103.5 KPa) on the physico-chemical prop erties of a silt loam soil (pH 7.2, 2.3% organic carbon) and the establishm ent of indigenous microorganisms reintroduced after autoclaving. Sterilisat ion by autoclaving significantly (p less than or equal to 0.05) decreased p H (0.6 of a unit) and increased concentrations of water-soluble organic car bon (WSOC; nontreated = 75 mg kg(-1); autoclaved = 1526 mg kg(-1)). The ini tial first-order rate of C-14-2,4-dichloro-UL-phenol (2,4-DCP) adsorption t o non-treated, autoclaved and re-inoculated soil was rapid (K-1 = 16.8-24.4 h(-1)) followed by a slower linear phase (K-2) In comparison with autoclav ed soil (0.038% day(-1)), K-2 values were higher for re-inoculated (0.095% day(-1)) and nontreated (0.181% day(-1)) soil. This was attributed to a bio logical process. The Freundlich adsorption coefficient (K-t) for autoclaved soil was significantly (p less than or equal to 0.05) higher than for re-i noculated or non-treated soil, increased adsorption was attributed to autoc laving-induced changes to soil pH and solution composition. Glucose-induced respiration of autoclaved soil after re-inoculation was initially twice th at in the non-treated control, but it decreased to control levels by day 4. This reduction corresponded to a depletion of WSOC. 2, I-DCP mineralisatio n experiments revealed that the inoculum of nonsterile soil (0.5 g) contain ed 2,4-DCP-degrading microorganisms capable of survival in autoclaved soil. The lag phase before detection of significant 2,4-DCP mineralisation was r educed (from 7 days to less than or equal to 3 days) by pre-incubation of r e-inoculated soils for 7 and 14 days before 2,4-DCP addition. This was attr ibuted to the preferential utilisation of WSOC prior to the onset of 2,4-DC P mineralisation. Cumulative (CO2)-C-14 evolved after 21 days was significa ntly lower (p less than or equal to 0.05) from non-treated soil (25.3%) tha n re-inoculated soils (ca. 45%). Experiments investigating sorption-biodegr adation interactions of xenobiotics in soil require the physico-chemical pr operties of sterile and non-sterile treatments to be as comparable as possi ble. For fundamental studies, we suggest using re-inoculated autoclaved soi l as an additional or alternative non-sterile treatment. (C) 1999 Elsevier Science B.V.