Soil Sciences Research Articles Research Articles: Soil Sciences !~i~ !~i i~! ~ !~i ~i ~ ~i Aliphatic Hydrocarbons in an Oil-Contaminated Soil Carbon Economy During Microbiological Decontamination 1Michael L. Wibbe, 2Michael M. Blanke 1CLAYTEX CONSULTING GmbH, Giersbergstr., D-50126 Bergheim, Germany Hnstitut fiir Obstbau der Universit~it, Auf dem Hfigel 6, D-53121 Bonn, Germany Corresponding address: Dr. M. Blanke Abstract Microbial decontamination of hydrocarbon-polluted soil was paralleled with soil respiration measurements. About 1,500 tons of a loamy top soil were found to be contaminated with ap- proximately 2000 mg/kg of aliphatic hydrocarbons, mainly oleic (C 18:1 ) and linoleic acid (C 18:2) found in the vicinity of a lino- leum manufacturing and then a car dewaxing plant. The con- taminated soil was analysed for dry matter, pH, dehydrogenase activity, electrical conductivity and nutrient content viz. nitrate, phosphorus and potassium, as well as a number of indigenous microbes. The soil was low in salt and nutrients. This paper describes the procedure and measures to decontaminate this bulk soil on site from approx. 2,000 to 500 mg of aliphatic hydro- carbons/kg dry matter by use of a nutrient emulsion, indigenous micro-organisms and aeration over 13 months. This 75% re- duction in aliphatic hydrocarbons resulted in a concomitant carbon efflux, measured as soil respiration, and was used to calculate carbon fluxes. Keywords: Biodegradation; (de-)contamination; hydrocarbons; micro-organisms; PAHs; PCBs; pollution; polychlorinated bi- phenyls (PCBs); polycyclic aromatic hydrocarbons (PAHs); res- piration; soil 1 Introduction Potycyclic aromatic hydrocarbons (PAHs) as components of petroleum and derived products are environmental pollut- ants because of their carcinogenicity (AKHLAQ, 1997). Soil contamination by such xenobiotic chemicals has become a serious global problem, not only because it reduces the value of land for recreational use and habitation, but also because these chemicals are potential sources of water pollution. The effects of environmental disasters, such as those in Alaska, Kuwait or Russia have produced a worldwide increase in the awareness of land hydrocarbon pollution and subsequent requirements for large-scale soil decontamination. Xenobiotic compounds such as hydrocarbons may persist in soil because the physical or chemical environment is un- suitable for degradation. These constraints can include in- appropriate soil pH, low levels of mineral nutrients and oxy- gen deprivation. In soils where the appropriate indigenous bacterial strains are present, bioremediation may consist of optimising soil conditions such as modifying pH, nutrient amendment and aeration, a process sometimes referred to as biostimulation (ELLIS, 1992). However, the biological ac- tivity of the soil microbes during decontamination is not completely understood. There is no indication how the mi- crobial breakdown of hydrocarbons affects soil activity viz. respiration, carbon turnover and carbon balance and whether these factors could be used for in situ monitoring of the sig- moidal rate of degradation (LOTTER, HEERENKLAGEa n d STEGMANtq, 1993). Monitoring of environmental conditions and soil respiration could be used to determine those situa- tions which favour indigenous microbes. Hence, the objec- tive of the present work was to monitor soil respiration as a measure of microbial activity during hydrocarbon degrada- tion. Therefore, a time course study related to hydrocarbon concentration was established to examine whether soil res- piration and the resulting carbon balance could be used as a bio-indicator for microbial decontamination. The work was conducted as part of an industrial project in Germany on a soil affected by the demolition of a linoleum manufacturing and the subsequent establishment of a car dewaxing plant. 2 Experimental 2.1 Soil and treatment The topsoil requiring decontamination comprised a pleisto- cene loess and loess-loam with a predominant silt fraction. The soil was from the environs of an old linoleum manufac- turing plant in Bedburg, near Cologne, Germany (Rheinische Linoleum Betriebe) which had partially been converted into a car de-waxing planL It was heavily mono-contaminated with an average of 2,000 mg hydrocarbons per kg soil dry matter. The hydrocarbons consisted of polar and non-polar aliphatic molecules and mainly oleic (C18"1) and linoleic acid (C18:2). There was no polycyclic aromatic hydrocarbon (PAH) or polychlorinated biphenyl (PCB) contamination. 2 ESPR - Environ. Sci. & Pollut. Res. 6 (1) 2 - 6 (1999) 9 ecomed publishers, D-86899 Landsberg, Germany