Carbon transformations by indigenous microbes in four hydrocarbon-contaminated soils under static remediation conditions

We sought to learn about the transformations of hydrocarbons and limitation s to bioremediation in four hydrocarbon-contaminated soils. Two soils were contaminated with creosote and two with petroleum. We incubated them either with or without added N, P, K and S. We monitored CO2 evolution, and resid ual dichloromethane-extractable organic C (DEO-C) after 10 wk. Indigenous p opulations were active in all soils. A single-component first-order model f it the CO2 respiration rate data, yielding estimates of potentially mineral izable C (C-o), and specific decay rate, k. The ratio C: DEO was lower in h eavier textured and strongly aggregated soils compared with the more poorly aggregated sandy soils. Low respiration rates in the more clayey soils wer e related to low C-o rather than to k for the available C. In the highly am ended soils the loss of total C approximated the production of CO2-C while the loss of DEO-C was greater than the evolution of CO2-C. We conclude: 1) Under circumstances such as hydrocarbon contaminants with long exposure to the soil, static systems may be sufficient for metabolism of available cont aminants by indigenous microorganisms. 2) Increases in clay content and sta bility of aggregates, together with biotreatment to remove hydrocarbons may reduce bioavailability of residual contamination. 3) In soils with high cl ay content, contaminant transformations or attenuation without production o f CO2 may be substantial.