Urea amendment decouples nitrification in hydrocarbon contaminated Antarctic soil.

Hydrocarbon contaminated soils resulting from human activities pose a risk to the natural environment, including in the Arctic and Antarctic. Engineered biopiles constructed at Casey Station, Antarctica, have proven to be an effective strategy for remediating hydrocarbon contaminated soils, with active ex-situ remediation resulting in significant reductions in hydrocarbons, even in the extreme Antarctic climate. However, the use of urea-based fertilisers, whilst providing a nitrogen source for bioremediation, has also altered the natural soil chemistry leading to increases in pH, ammonium and nitrite. Monitoring of the urea amended biopiles identified rising levels of nitrite to be of particular interest, which misaligns with the long term goal of reducing contaminant levels and returning soil communities to a 'healthy' state. Here, we combine amplicon sequencing, microfluidic qPCR on field samples and laboratory soil microcosms to assess the impact of persistent nitrite accumulation (up to 60 months) on nitrifier abundances observed within the Antarctic biopiles. Differential inhibition of ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) Nitrobacter and Nitrospira in the cold, urea treated, alkaline soils (pH 8.1) was associated with extensive nitrite accumulation (76 ± 57 mg N/kg at 60 months). When the ratio of Nitrospira:AOB dropped below ∼1:1, Nitrobacter was completely inhibited or absent from the biopiles, and nitrite accumulated. Laboratory soil microcosms (incubated at 7 °C and 15 °C for 9 weeks) reproduced the pattern of nitrite accumulation in urea fertilized soil at the lower temperature, consistent with our longer-term observations from the Antarctic biopiles, and with other temperature-controlled microcosm studies. Diammonium phosphate amended soil did not exhibit nitrite accumulation, and could be a suitable alternative biostimulant to avoid excessive nitrite build-up.

Microbial community analysis of biopiles in Antarctica provides evidence of successful hydrocarbon biodegradation and initial soil ecosystem recovery.

Microorganisms comprise the bulk of biodiversity and biomass in Antarctic terrestrial ecosystems. To effectively protect and manage the Antarctic environment from anthropogenic impacts including contamination, the response and recovery of microbial communities should be included in soil remediation efficacy and environmental risk assessments. This is the first investigation into the microbial dynamics associated with large scale bioremediation of hydrocarbon contaminated soil in Antarctica. Over five years of active management, two significant shifts in the microbial community were observed. The initial shift at 12-24 months was significantly correlated with the highest hydrocarbon degradation rates, increased microbial loads, and significant increases in alkB gene abundances. ANCOM analysis identified bacterial genera most likely responsible for the bulk of degradation including Alkanindiges, Arthrobacter, Dietzia and Rhodococcus. The second microbial community shift occurring from 36 to 60 months was associated with further reductions in hydrocarbons and a recovery of amoA nitrification genes, but also increasing pH, accumulation of nitrite and a reduction of oligotrophic bacterial species. Over time, the addition of inorganic fertilisers altered the soil chemistry and led to a disruption of the nitrogen cycle, most likely decoupling ammonia oxidisers from nitrite oxidisers, resulting in nitrite accumulation. The results from this study provide key insights to the long-term management of hydrocarbon bioremediation in Antarctic soils.

Using an expert judgment response matrix to assess the risk of groundwater discharges from remediated fuel spill sites to the marine environment at sub-Antarctic Macquarie Island, Australia.

This study assesses toxicity of groundwater from remediated fuel spill sites, as the final phase of an environmental risk assessment of contaminated sites at sub-Antarctic Macquarie Island, Tasmania, Australia. To complement previous terrestrial ecotoxicological research, we determine risk to marine environments from residual biodegraded hydrocarbon contaminants in groundwater discharges. Direct toxicity assessments were conducted on 7 composite groundwater test solutions, adjusted to ambient seawater salinity. Eleven native marine invertebrates (from varied taxa: gastropods, bivalves, flatworms, amphipods, copepods, isopods) were exposed and observed for up to 21 d. Lethal time estimates (LT10, LT50) showed sensitivity was time dependent (LT10s = 4-15 d) and variable between species. Three species showed no response to any test solution, and most species did not respond for up to 5 d. Data were interpreted using an expert judgment response matrix with multiple lines of evidence to predict risk. No consistent patterns in the relative toxicity of test solutions, based on polar or nonpolar hydrocarbon concentrations, were identified. Although toxicity was observed in some species, this was only under worst-case conditions of undiluted, continuous, extended exposure. Natural dynamics of the site, including low groundwater discharge rates, high rainfall, and a highly energetic receiving environment, ensure groundwater is rapidly diluted and dispersed. In this context, and based on site conditions at the time of testing, these toxicity assessments provide robust evidence that residual contamination in groundwater at remediated sites at Macquarie Island is unlikely to represent a risk to the adjacent marine communities tested. Integr Environ Assess Manag 2021;17:785-801. © 2020 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Applying microbial indicators of hydrocarbon toxicity to contaminated sites undergoing bioremediation on subantarctic Macquarie Island.

Microorganisms are useful biological indicators of toxicity and play a key role in the functioning of healthy soils. In this study, we investigated the residual toxicity of hydrocarbons in aged contaminated soils and determined the extent of microbial community recovery during in-situ bioremediation at subantarctic Macquarie Island. Previously identified microbial indicators of hydrocarbon toxicity were used to understand interactions between hydrocarbon concentrations, soil physicochemical parameters and the microbial community. Despite the complexity of the field sites, which included active fuel storage areas with high levels of soil heterogeneity, multiple spill events and variable fuel sources, we observed consistent microbial community traits associated with exposure to high concentrations of hydrocarbons. These included; reductions in alpha diversity, inhibition of nitrification potential and a reduction in the ratio of oligotrophic to copiotrophic species. These observed responses and the sensitivity of microbial communities in the field, were comparable to sensitivity estimates obtained in a previous lab-based mesocosm study with hydrocarbon spiked soils. This study provides a valuable and often missing link between the quite disparate conditions of controlled lab-based spiking experiments and the complexity presented by 'real-world' contaminated field sites.

Characterization of polar metabolites and evaluation of their potential toxicity in hydrocarbon contaminated Antarctic soil elutriates.

Hydrocarbon polar metabolites are gaining interest from industry and the remediation community due to their ubiquity and uncertainty around their toxicity. In this study, we used headspace-gas chromatography/mass spectrometry (HS-GC/MS) to characterize polar metabolites present in elutriates derived from uncontaminated, freshly hydrocarbon contaminated and partially remediated Antarctic soils. Elutriates represent the bioavailable fraction and may be used as a proxy for leachate runoff in environmental risk assessments. Control and contaminated soil elutriates were analysed for the presence of 12 aldehydes and two ketones, which cover a broad spectrum of metabolites, ranging from nC2 - nC12 carbon chain length. A total of nine aldehydes were detected in the soil elutriates. Types of aldehydes present in uncontaminated and hydrocarbon contaminated elutriates were similar. Among the polar metabolites measured in elutriates, acetaldehyde was most abundant in partially remediated soils. Microtox assays were used to determine the potential toxicity of elutriates. In addition, three aldehydes that were present at the highest concentrations in the contaminated and partially remediated soil elutriates (acetaldehyde, octanal and undecanal) were tested as single compounds. Contaminated soil elutriates tested were found to be toxic, with partially remediated elutriates less toxic than freshly contaminated elutriates. None of the three aldehydes tested separately were toxic at levels at which they were measured in elutriates. We infer that high levels of acetaldehyde in partially remediated soil due to hydrocarbon degradation highlight the potential of this metabolite as a useful chemical marker for hydrocarbon degradation under certain conditions. Microtox was sensitive to metabolites and provided a useful initial screening tool for elutriates.

Ecosystem effects and the management of petroleum-contaminated soils on subantarctic islands.

Human activity in the Polar Regions has resulted in petroleum contamination of soils. In this context, subantarctic islands are a unique management challenge for climatic, biological and logistical reasons. In this review we identify the main abiotic factors affecting petroleum-contaminated soils in the subantarctic environment, the primary effects of such contamination on biota, and lessons learned with regards to remediation techniques in this region. The sensitivity of biota to contamination depends on organism life stage, on soil properties, and on the degree of contaminant weathering. Initial studies using species endemic to subantarctic islands suggest that for fresh diesel fuel, sensitivities may range between 103 and 20 000 mg total petroleum hydrocarbons (TPH) kg -1 soil. Diesel that has undergone a short period of weathering is generally more toxic, with sensitivities ranging between 52 and 13 000 mg TPH kg-1 soil for an earthworm and a grass respectively (based on EC20 and IC50 values). A sufficient body of data from which to develop remediation targets for existing spills in the region does not yet exist for the region, but there has been a recent increase in research attention to address this data gap. A range of remediation methods have also now been trialled, and techniques such as in-ground aeration and nutrient addition have achieved some success. Passive management techniques such as permeable reactive barriers and phytoremediation are in preliminary stages of investigation for the region and show promise, not least because they cause less collateral disturbance than other methods.

Permeable bio-reactive barriers to address petroleum hydrocarbon contamination at subantarctic Macquarie Island.

A reliance on diesel generated power and a history of imperfect fuel management have created a legacy of petroleum hydrocarbon contamination at subantarctic Macquarie Island. Increasing environmental awareness and advances in contaminant characterisation and remediation technology have fostered an impetus to reduce the environmental risk associated with legacy sites. A funnel and gate permeable bio-reactive barrier (PRB) was installed in 2014 to address the migration of Special Antarctic Blend diesel from a spill that occurred in 2002, as well as older spills and residual contaminants in the soil at the Main Power House. The PRB gate comprised of granular activated carbon and natural clinoptilolite zeolite. Petroleum hydrocarbons migrating in the soil water were successfully captured on the reactive materials, with concentrations at the outflow of the barrier recorded as being below reporting limits. The nutrient and iron concentrations delivered to the barrier demonstrated high temporal variability with significant iron precipitation observed across the bed. The surface of the granular activated carbon was largely free from cell attachment while natural zeolite demonstrated patchy biofilm formation after 15 months following PRB installation. This study illustrates the importance of informed material selection at field scale to ensure that adsorption and biodegradation processes are utilised to manage the environmental risk associated with petroleum hydrocarbon spills. This study reports the first installation of a permeable bio-reactive barrier in the subantarctic.