The organochlorine pesticide Lindane is the gamma-isomer of hexachlorocyclohexane (HCH). Technical grade Lindane contains a mixture of HCH isomers which include not only gamma-HCH, but also large amounts of predominantly alpha-, beta- and delta-HCH. The physical properties and persistence of each isomer differ because of the different chlorine atom orientations on each molecule (axial or equatorial). However, all four isomers are considered toxic and recalcitrant worldwide pollutants. Biodegradation of HCH has been studied in soil, slurry and culture media but very little information exists on in situ bioremediation of the different isomers including Lindane itself, at full scale. Several soil microorganisms capable of degrading, and utilizing HCH as a carbon source, have been reported. In selected bacterial strains, the genes encoding the enzymes involved in the initial degradation of Lindane have been cloned, sequenced, expressed and the gene products characterized. HCH is biodegradable under both oxic and anoxic conditions, although mineralization is generally observed only in oxic systems. As is found for most organic compounds, HCH degradation in soil occurs at moderate temperatures and at near neutral pH. HCH biodegradation in soil has been reported at both low and high (saturated) moisture contents. Soil texture and organic matter appear to influence degradation presumably by sorption mechanisms and impact on moisture retention, bacterial growth and pH. Most studies report on the biodegradation of relatively low (< 500 mg/kg) concentrations of HCH in soil. Information on the effects of inorganic nutrients, organic carbon sources or other soil amendments is scattered and inconclusive. More in-depth assessments of amendment effects and evaluation of bioremediation protocols, on a large scale, using soil with high HCH concentrations, are needed.

Biodegradation of hexachlorocyclohexane (HCH) by microorganisms.

Aims: To study the comparative effect of diesel addition and simulated bioremediation on the microbial community in three different soil types.



Methods and Results: Three different soils were amended with diesel and bioremediation treatment simulated by addition of nutrients. The progress of bioremediation, and the effect on the indigenous microbial communities, was monitored using microbiological techniques. These included basal respiration, sole carbon source utilization patterns using both a commercially-available substrate set and a set designed to highlight changes in hydrocarbon-utilizing bacteria, and phospholipid fatty acid (PLFA) profiling. The development of active hydrocarbon-degrading communities was indicated by the disappearance of diesel, increases in soil respiration and biomass, and large changes in the sole carbon source utilization patterns and PLFA profiles compared with control soils. However, comparison of the relative community structure of the three soils using PLFA profiling showed that there was no tendency for the community structure of the three different soil types to converge as a result of contamination. In fact, they became more dissimilar as a result. Changes in the sole carbon source utilization patterns using the commercially-available set of carbon sources indicated the same result as shown by PLFA profiling. The specially selected set of carbon sources yielded no additional information compared with the commercially-available set.



Conclusions: Diesel contamination does not result in the development of similar community profiles in different soil types.



Significance and Impact of the Study: The results suggest that different soils have different inherent microbial potential to degrade hydrocarbons, a finding that should be taken into account in impact and risk assessments. Following the development of the microbial community and its recovery is a useful and sensitive way of monitoring the impact and recovery of oil-contaminated soils.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-2672.2002.01528.x

Microbial communities in different soil types do not converge after diesel contamination

Determination of total petroleum hydrocarbons and heavy metals in soils within the vicinity of facilities handling refined petroleum products in Lagos metropolis.

Net environmental benefits are gains in value of environmental services or other ecological properties attained by remediation or ecological restoration minus the value of adverse environmental effects caused by those actions. Net environmental benefit analysis (NEBA) is a methodology for comparing and ranking net environmental benefits associated with multiple management alternatives. A NEBA for chemically contaminated sites typically involves comparison of several management alternatives: (1) leaving contamination in place; (2) physically, chemically, or biologically remediating the site through traditional means; (3) improving ecological value through onsite and offsite restoration alternatives that do not directly focus on removal of chemical contamination; or (4) a combination of those alternatives. NEBA involves activities that are common to remedial alternatives analysis for state regulations and the Comprehensive Environmental Response, Compensation, and Liability Act, post-closure and corrective action permits under the Resource Conservation and Recovery Act, evaluation of generic types of response actions pertinent to the Oil Pollution Act, and land management actions that are negotiated with regulatory agencies in flexible regulatory environments (i.e., valuing environmental services or other ecological properties, assessing adverse impacts, and evaluating remediation or restoration options). This article presents a high-level framework for NEBA at contaminated sites with subframeworks for natural attenuation (the contaminated reference state), remediation, and ecological restoration alternatives. Primary information gaps related to NEBA include nonmonetary valuation methods, exposure–response models for all stressors, the temporal dynamics of ecological recovery, and optimal strategies for ecological restoration.

/pdf/a-framework-for-net-environmental-benefit-analysis-for-4mt5c7vatd.pdf

A Framework for Net Environmental Benefit Analysis for Remediation or Restoration of Contaminated Sites

Ecorisk evaluation and treatability potential of soils contaminated with petroleum hydrocarbon-based fuels.

Biodegradation of petroleum contaminants is an effective and generally inexpensive approach for reducing their concentrations in soils. However, little information is available on the toxicological status of contaminated soils and the fate of target hydrocarbons following bioremediation. Four texturally distinct soils were contaminated with diesel fuel and bioremediated in microcosms at 22°C, with moisture contents of 85% of soil water holding capacity, and nitrogen (N) and/or phosphorus (P) nutrient amendments. The progress of bioremediation was monitored using chemical and toxicological analyses. Soil toxicity was measured using five short-term bioassays: seed germination, red blood cell hemolysis, solid-phase Microtox, SOS-chromotest, and Toxi-chromotest. Reductions in target compound concentration were not always predictive of reductions in soil toxicity. Conflicting trends were indicated by the toxicity test results. For example, total petroleum hydrocarbon analysis revealed decreased hydrocarbon concentrations in all four soils following bioremediation but seed germination and seedling emergence data indicated increased soil toxicity. In contrast, the Microtox test data indicated decreased toxicity in two of the four soils. These results suggest that measurements of target contaminant concentrations should be complemented with several different soil toxicity bioassays, particularly when evaluating the ability of bioremediation to reduce the adverse effects of contaminants in soil. © 1998 John Wiley & Sons, Inc. Environ Toxicol Water Qual 13: 117–126, 1998

Cecily A. Flemming

Papers

Comparison of toxicity detected by five bioassays during bioremediation of diesel fuel-spiked soils