The potential for biotransformation of weathered hydrocarbon residues in soils collected from two commercial oil refinery sites (Soil A and B) was studied in microcosm experiments. Soil A has previously been subjected to on-site bioremediation and it was believed that no further degradation was possible while soil B has not been subjected to any treatment. A number of amendment strategies including bioaugmentation with hydrocarbon degrader, biostimulation with nutrients and soil grinding, were applied to the microcosms as putative biodegradation improvement strategies. The hydrocarbon concentrations in each amendment group were monitored throughout 112 days incubation. Microcosms treated with biostimulation (BS) and biostimulation/bioaugmentation (BS + BA) showed the most significant reductions in the aliphatic and aromatic hydrocarbon fractions. However, soil grinding was shown to reduce the effectiveness of a nutrient treatment on the extent of biotransformation by up to 25% and 20% for the aliphatic and aromatic hydrocarbon fractions, respectively. This is likely due to the disruption to the indigenous microbial community in the soil caused by grinding. Further, ecotoxicological responses (mustard seed germination and Microtox assays) showed that a reduction of total petroleum hydrocarbon (TPH) concentration in soil was not directly correlable to reduction in toxicity; thus monitoring TPH alone is not sufficient for assessing the environmental risk of a contaminated site after remediation.

A sequential ultrasonic extraction method for contaminated soils with weathered hydrocarbons is presented. The method covers the determination of total petroleum hydrocarbons between nC 8 and nC 40, and subranges of hydrocarbons including diesel range organic compounds, kerosene range organic compounds, and mineral oil range organic compounds in soils. Further modifications to the carbon banding may be made as requested for risk assessment. These include a series of ranges known as Texas banding (from the Texas Risk Reduction Program) as well as separation of the aliphatic and aromatic fractions. The method can be routinely used for measuring hydrocarbons down to 10 mg kg (-1) in soil. Lower limits can be achieved by employing a suitable solvent concentration step following extraction; however, this would result in increased cycle time. Detection limits may vary for individual carbon ranges calculated on the percentage of the full range they cover. With an extraction efficiency and recovery between >or=95 and 99%, this method can be easily positioned as a good alternative to Soxhlet extraction and shows a good potential for implementation as a standard method potentially providing further insight to the contaminated land sector.

We provide a primer and critical review of the characterization, risk assessment, and bioremediation of weathered hydrocarbons. Historically the remediation of soil contaminated with petroleum hydrocarbons has been expressed in terms of reductions in total petroleum hydrocarbon (TPH) load rather than reductions in risk. 199 Downloaded by [Uppsala universitetsbibliotek] at 09:55 04 October 2014 200 K. J. Brassington et al. There are several techniques by which petroleum hydrocarbons in soils can be characterized. Method development is often driven by the objectives of published risk assessment frameworks. Some frameworks stipulate analysis of a wide range of petroleum hydrocarbons; for example, the United Kingdom (UK) approach suggests compounds from EC 5 to EC 70 be examined. Methods for the extraction of petroleum hydrocarbons from soil samples have been reviewed extensively in the open literature. Although various extraction and analytical methods are available for petroleum hydrocarbons, their results suffer from inter-method variation, with gas chromatography methods being used widely. Currently, the implications for risk assessment are uncertain. Bioremediation works well for remediating soils contaminated with petroleum hydrocarbons. As a result, the optimization of environmental conditions is imperative. For petroleum hydrocarbons in soil, international regulatory guidance on the management of risks from contaminated sites is now emerging.There is also growing support for the move toward compound-specific risk-based approaches for the assessment of hydrocarbon-contaminated land.

The effects of soil characteristics and oil types as well as the efficacy of two fertilizer formulations and three bioaugmentation packages in improving the bioremediation of oil-contaminated soils were assessed as a means of ex situ treatment selection and optimization through seven laboratory microcosm studies. The influence of bioremediation on leaching of oil from the soil was also investigated. The studies demonstrated the benefits ofbiostimulation to overcome nutrient limitation, as most of the soils were nutrient depleted. The application of both liquid and pelleted slow-release N and P fertilizers increased both the hydrocarbon biodegradation rates (by a factor of 1.4 to 2.9) and the percentage of hydrocarbon mass degraded (by > 30% after 12 weeks and 80% after 37 weeks), when compared with the unamended soils. Slow-release fertilizers can be particularly useful when multiple liquid applications are not practical or cost-effective. Bioaugmentation products containing inoculum plus fertilizer also increased biodegradation by 20% to 37% compared with unamended biotic controls; however, there was no clear evidence of additional benefits due to the inocula, compared with fertilizer alone. Therefore biostimulation is seen as the most cost-effective bioremediation strategy for contaminated soils with the levels of crude oil and refined products used in this study. However, site-specific considerations remain essential for establishing the treatability of oil-contaminated soils.

No abstract

Weathered petroleum hydrocarbons are highly complex and important soil contaminants, which, despite 40 years of petroleum research, are still not sufficiently understood or appropriately characterized for informing contaminated land risk assessments. Improved insights into biotransformation of these contaminants and their residual toxicity are essential for improving risk assessments, bioremediation strategies, and effective regeneration of previously contaminated land. The remediation of land contaminated with weathered hydrocarbons has long been limited by inappropriate analytical methodology, the absence from risk assessment frameworks, reduced stakeholder confidence, lack of ecotoxicological analysis in risk assessments, and a distinct paucity of information regarding weathered hydrocarbon toxicity, distribution, transport, and availability in the environment. Recent research has resulted in the development of a robust analytical method for identification of hydrocarbon residues (weathered hydrocarbons) which are the principal source of the organic carcinogens or suspected carcinogens that drive quantitative risk assessment (e.g., benzo[a]pyrene), development of a tool kit for contaminated sites incorporating ecotoxicological consideration, and an improved understanding of weathered hydrocarbon toxicity and biotransformation chemistry. However, knowledge gaps still remain, and additional implications for bioremediation practitioners have been identified concerning remedial methodology at previously remediated sites.

No abstract