Potential of natural attenuation processes in environmental contamination by petroleum hydrocarbons

Once released in the environment, petroleum hydrocarbons can be long-term sources of contamination. The main advantage of bioremediation compared to conventional remediation treatments is its reduced cost. Natural attenuation is the passive bioremediation approach that relies on natural processes to reduce contamination. This study provides insight into the natural attenuation processes in groundwater in the alluvial deposits of the Zapadna Morava River (the site of historical contamination by kerosene in Vitanovac, Kraljevo, Serbia). Monitoring was performed in the direction of groundwater flow, downgradient from the source of contamination. Groundwater samples were analyzed for the following parameters: total petroleum hydrocarbons (TPH), O-2, NO3-, Mn, Fe and SO42-. TPH concentrations declined in groundwater across the site, and were accompanied by increasing concentrations of electron acceptors (O-2, NO3-, SO42-) and decreasing concentrations of metabolic products of biodegradation (Mn, Fe). The observed trends provide strong evidence of the activity of different biodegradation mechanisms at this site (aerobic respiration, nitrate reduction, reduction of manganese (IV), reduction of iron (III) and sulfate reduction). The results obtained confirm the natural occurrence of aerobic and anaerobic biodegradation mechanisms in this phreatic aquifer contaminated by petroleum hydrocarbons 20 years ago. However, use of natural attenuation as a cost-effective remediation alternative depends on its capacity to ensure protection of public health, safety and the environment.