Effect of Soil Physical and Chemical Parameters on Benzene Biodegradation in the Vadose Zone: Comparison of Cultivated and Urban Soils.

Vadose zone biodegradation processes are governed by a combination of various soil parameters, among which many are related to soil texture and land use. To evaluate applicability of bioremediation at a contaminated site, knowledge concerning how physical and chemical soil characteristics are affecting contaminant attenuation is needed. In this study bacterial abundance and activity in Danish soils was studied using total bacterial cell counts (DAPI staining) and batch experiments on aerobic biodegradation of benzene. The soils used varied in depth, soil texture, alkalinity, and land use. Biodegradation of benzene was described using zero order kinetics and compared with particle size distribution, soil pH, extractable macro and micro nutrients, and degree of previous contamination. Benzene was degraded at relatively high rates in all soils, illustrating abundance of gasoline degrading microorganisms across soil types and depths. In addition, results implied that total bacteria numbers and aerobic biodegradation rates generally were higher in fine textured and clayey soils than in sandy soils. These results illustrate a typical barrier to in-situ soil biophysical remediation technologies, as soil zones containing the highest microbial density often will be the least accessible for enhanced transport and distribution of nutrients and oxygen.