Bioremediation is considered an appropriate technology for decontamination of polluted natural environments. The successful application of bioremediation depends on appropriate hydrocarbon-degrading microorganisms and environmental conditions in situ. Las Heras is a place located in northwest Santa Cruz (Patagonia, Argentina) with a very intensive activity of oil industry. In this region the conditions most likely to limit hydrocarbon degradation include cold and fluctuating temperatures, low moisture contents, low nutrient levels and alkaline pH. In this work we describe three representative cases of biostimulation treatments (nutrients and water addition) applied to soils with different pollution states: Case A (1680 m3) exhibited high values of total petroleum hydrocarbons (TPH 33510 mg/kg); Case B (480 m3) showed high values of total petroleum hydrocarbons (TPH 27754 mg/kg) and polyaromatic hydrocarbons (PAH 1.64 mg/l in lixiviate); and Case C (1680 m3) exhibited high PAH values (PAH 1.94 mg/l in lixiviate). The controlled addition of nitrogen and phosphorous sources and water increased bacterial counts of soil in all cases and resulted in a significant elimination of hydrocarbons: 32 % TPH in Case A after 7 months of treatment (from May to December 2005); 39 % TPH and 88 % PAH in Case B after 5 months (from October 2005 to February 2006) and 90 % of PAH after 3 months of treatment (from May 2005 to July 2005) were removed. In addition, we performed a comparative evaluation of natural attenuation, biostimulation and bioaugmentation (inoculation of bacterial strains) for bioremediation of PAH-contaminated soil in situ. Both, biostimulation and bioaugmentation promoted significant degradation (> 90 %) of PAH after 6 weeks of treatment, whereas attenuation resulted in a reduced degradation rate (67 %). In conclusion, this study suggests that autochthonous bacterial communities from semiarid soils in Patagonia have the potential to degrade hydrocarbons after amelioration of unfavorable environmental conditions.
Las Heras is a place located in northwest Santa Cruz province (Patagonia, Argentina) with a very intensive activity of the oil industry. Crude oil spills have occurred at many sites in the region, and there is a need to remediate contaminated soil. Biodegradation by natural populations of microorganisms represents one of the primary mechanisms for eliminating hydrocarbon pollutants from the environment [1, 2]. However, the successful application of bioremediation depends on appropriate hydrocarbon-degrading microorganisms and environmental conditions in situ . The persistence of old spilled hydrocarbons in this region suggests that the rate of natural degradation is very slow under the environmental conditions of semiarid soil. Several conditions may limit hydrocarbon degradation by natural populations of microorganisms in this area, including cold and fluctuating temperatures (between -20° C in winter to 37° C in summer), strong winds (up to 120 km/h), low moisture and low nutrient contents in soil (principally the nitrogen and phosphorous sources) and alkaline pH. Low temperatures and desiccation normally reduce microbial metabolism and the nutrient availability can influence the rate and extent of degradation in contaminated soils. These conditions represent a challenge to the classic in situ bioremediation procedures, which were developed for more temperate climates. One of the primary benefits of in situ bioremediation is that the procedure does not require excavation, although it involves minimal site disruption, so site disturbance is much less. This should make in situ bioremediation cost-competitive since the bulk of the transportation and excavation cost has been significantly reduced or nullified . In addition, this procedure is friendly to the environment.
Some studies have examined biodegradation of hydrocarbon-polluted soil in cold environments, such as Artic and Antartic soils. Mohn et al.  demonstrated that on-site bioremediation of fuel-contaminated soil at Artic tundra sites is feasible. On the other hand, other authors demonstrated that indigenous microbial communities of Antartic soils are able to degrade petroleum hydrocarbons after the adequate management of the bioremediation procedure [6, 7]. All these studies indicate the potential for in situ bioremediation of hydrocarbon-contaminated soils at sites with extreme environmental conditions.