Modelling of vapour intrusion into a building impacted by a fuel spill in Antarctica.

A new vapour intrusion contaminant transport model was designed specifically to allow an assessment of the impact of a hydrocarbon fuel spill on air quality in cold region buildings. The model is applied to a recent situation in Antarctica, where a diesel spill impacted the construction of a new building. For the first time, this model allows consideration of the diffusive resistance of different vapour barrier to the transport of hydrocarbons into the building and an assessment of the effectiveness of different products. Site specific indoor air criteria are derived. Five scenarios are modelled at field temperatures: (1) build on current contaminated site; (2) excavate contaminated soil, backfill with clean soil and assess impact of residual contamination; (3) excavate and backfill with remediated (biopile) soil; (4) backfill with remediated soil and assess impact of residual contamination; (5) backfill with remediated soil and assess impact of a potential future fuel spill. Two different vapour barriers, a co-extruded ethylene vinyl alcohol (EVOH) geomembrane (VB1) and a linear low-density (LLDPE) geomembrane (VB2), are investigated for each scenario and compared to a base case with no vapour barrier, providing quantifiable evidence of the benefit of installing an engineered vapour barrier Contaminant concentrations were below regulatory limits for Scenarios (2-5) with VB1 and air exchange in the building. For all scenarios, the EVOH geomembrane (VB1) was consistently superior at reducing vapour transport into the building indoor air space over the LLDPE geomembrane (VB2) and no vapour barrier. The risk mitigation measures developed for this contaminated Antarctic site may be relevant for other buildings in cold regions.

Novel Culturing Techniques Select for Heterotrophs and Hydrocarbon Degraders in a Subantarctic Soil.

The soil substrate membrane system (SSMS) is a novel micro-culturing technique targeted at terrestrial soil systems. We applied the SSMS to pristine and diesel fuel spiked polar soils, along with traditional solid media culturing and culture independent 454 tag pyrosequencing to elucidate the effects of diesel fuel on the soil community. The SSMS enriched for up to 76% of the total soil diversity within high diesel fuel concentration soils, in contrast to only 26% of the total diversity for the control soils. The majority of organisms originally recovered with the SSMS were lost in the transfer to solid media, with all 300 isolates belonging to Proteobacteria, Firmicutes, Actinobacteria or Bacteroidetes, the four phyla most frequently associated with soil culturing efforts. The soils spiked with high diesel fuel concentrations exhibited reduced species richness, diversity and a selection towards heterotrophs and hydrocarbon degraders in comparison to the control soils. Based on these observations and the unusually high level of overlap in microbial taxa observed between methods, we suggest the SSMS holds potential to exploit hydrocarbon degraders and other targets within simplified bacterial systems, yet is inadequate for soil ecology and ecotoxicology studies where identifying rare oligotrophic species is paramount.

On site remediation of a fuel spill and soil reuse in Antarctica.

The first large-scale remediation of fuel contamination in Antarctica treated 10000L of diesel dispersed in 1700t of soil, and demonstrated the efficacy of on-site bioremediation. The project progressed through initial site assessment and natural attenuation, passive groundwater management, then active remediation and the managed reuse of soil. Monitoring natural attenuation for the first 12years showed contaminant levels in surface soil remained elevated, averaging 5000mg/kg. By contrast, in five years of active remediation (excavation and biopile treatment) contaminant levels decreased by a factor of four. Chemical indicators showed hydrocarbon loss was apportioned to both biodegradation and evaporative processes. Hydrocarbon degradation rates were assessed against biopile soil temperatures, showing a phase of rapid degradation (first 100days above soil temperature threshold of 0°C) followed by slower degradation (beyond 100days above threshold). The biopiles operated successfully within constraints typical of harsh climates and remote sites, including limitations on resources, no external energy inputs and short field seasons. Non-native microorganisms (e.g. inoculations) and other organic materials (e.g. bulking agents) are prohibited in Antarctica making this cold region more challenging for remediation than the Arctic. Biopile operations included an initial fertiliser application, biannual mechanical turning of the soil and minimal leachate recirculation. The biopiles are a practical approach to remediate large quantities of contaminated soil in the Antarctic and already 370t have been reused in a building foundation. The findings presented demonstrate that bioremediation is a viable strategy for Antarctica and other cold regions. Operators can potentially use the modelled relationship between days above 0°C (threshold temperature) and the change in degradation rates to estimate how long it would take to remediate other sites using the biopile technology with similar soil and contaminant types.

Evaluation of a permeable reactive barrier to capture and degrade hydrocarbon contaminants.

A permeable reactive barrier (PRB) was installed during 2005/2006 to intercept, capture and degrade a fuel spill at the Main Power House, Casey Station, Antarctica. Here, evaluation of the performance of the PRB is conducted via interpretation of total petroleum hydrocarbon (TPH) concentrations, degradation indices and most probable number (MPN) counts of total heterotroph and fuel degrading microbial populations. Results indicate that locations which contained the lowest TPH concentrations also exhibited the highest levels of degradation and numbers of fuel degrading microbes, based on the degradation indices and MPN methods selected. This provides insights to the most appropriate reactive materials for use in PRB's in cold and nutrient-limited environments.

Fate and transport of petroleum hydrocarbons in engineered biopiles in polar regions.

A dynamic multi-media model that includes temperature-dependency for partitioning and degradation was developed to predict the behaviour of petroleum hydrocarbons during biopiling at low temperature. The activation energy (Ea) for degradation was derived by fitting the Arrhenius equation to hydrocarbon concentrations from temperature-controlled soil mesocosms contaminated with crude oil and diesel. The model was then applied to field-scale biopiles containing soil contaminated with diesel and kerosene at Casey Station, Antarctica. Temporal changes of total petroleum hydrocarbons (TPH) concentrations were very well described and predictions for individual hydrocarbon fractions were generally acceptable (disparity between measured and predicted concentrations was less than a factor two for most fractions). Biodegradation was predicted to be the dominant loss mechanism for all but the lightest aliphatic fractions, for which volatilisation was most important. Summertime losses were significant, resulting in TPH concentrations which were about 25% of initial concentrations just 1 year after the start of treatment. This contrasts with the slow rates often reported for hydrocarbons in situ and suggests that relatively simple remediation techniques can be effective even in Antarctica.

Hydraulic performance of a permeable reactive barrier at Casey Station, Antarctica.

A permeable bio-reactive barrier (PRB) was installed at Casey Station, Antarctica in 2005/06 to intercept, capture and degrade petroleum hydrocarbons from a decade old fuel spill. A funnel and gate configuration was selected and implemented. The reactive gate was split into five separate cells to enable the testing of five different treatment combinations. Although different treatment materials were used in each cell, each treatment combination contained the following reactive zones: a zone for the controlled release of nutrients to enhance degradation, a zone for hydrocarbon capture and enhanced degradation, and a zone to capture excess nutrients. The materials selected for each of these zones had other requirements, these included; not having any adverse impact on the environment, being permeable enough to capture the entire catchment flow, and having sufficient residence time to fully capture migrating hydrocarbons. Over a five year period the performance of the PRB was extensively monitored and evaluated for nutrient concentration, fuel retention and permeability. At the end of the five year test period the material located within the reactive gate was excavated, total petroleum hydrocarbon concentrations present on the material determined and particle size analysis conducted. This work found that although maintaining media reactivity is obviously important, the most critical aspect of PRB performance is preserving the permeability of the barrier itself, in this case by maintaining appropriate particle size distribution. This is particularly important when PRBs are installed in regions that are subject to freeze thaw processes that may result in particle disintegration over time.

The rate of removal and the compositional changes of diesel in Antarctic marine sediment.

Diesels and lubricants used at research stations can persist in terrestrial and marine sediments for decades, but knowledge of their effects on the surrounding environments is limited. In a 5 year in situ investigation, marine sediment spiked with Special Antarctic Blend (SAB) diesel was placed on the seabed of O'Brien Bay near Casey Station, Antarctica and sampled after 5, 56, 65, 104 and 260 weeks. The rates and possible mechanisms of removal of the diesel from the marine sediments are presented here. The hydrocarbons within the spiked sediment were removed at an overall rate of 4.7mg total petroleum hydrocarbons kg(-1) sediment week(-1), or 245mgkg(-1)year(-1), although seasonal variation was evident. The concentration of total petroleum hydrocarbons fell markedly from 2020±340mgkg(-1) to 800±190mgkg(-1), but after 5 years the spiked sediment was still contaminated relative to natural organic matter (160±170mgkg(-1)). Specific compounds in SAB diesel preferentially decreased in concentration, but not as would be expected if biodegradation was the sole mechanism responsible. Naphthalene was removed more readily than n-alkanes, suggesting that aqueous dissolution played a major role in the reduction of SAB diesel. 1,3,5,7-Teramethyladamantane and 1,3-dimethyladamantane were the most recalcitrant isomers in the spiked marine sediment. Dissolution of aromatic compounds from marine sediment increases the availability of more soluble, aromatic compounds in the water column. This could increase the area of contamination and potentially broaden the region impacted by ecotoxicological effects from shallow sediment dwelling fauna, as noted during biodegradation, to shallow (<19m) water dwelling fauna.

Sediment profile characterisation at contaminated and reference locations in the Windmill Islands, East Antarctica.

Sediment profiles for pH, Eh, 28 elements, water and organic content are presented here for human impacted and reference locations in the Windmill Islands, East Antarctica. Variations in element concentrations are observed with increasing depth, especially at Brown Bay where the impact of past human activities is most pronounced in the top 10 cm. Spatial differences were observed between sediment profiles at reference and impacted locations and were largely explained by Pb variability in the top 5 cm. Median element concentrations from surface, middle and bottom regions of the sediment profile were compared to composite sample medians (no depth stratigraphy) for 11 elements at O'Brien Bay (reference) and Brown Bay (impacted). Pronounced differences were observed for Brown Bay, particularly surface and middle sections, implying that composite samples dilute the near surface anthropogenic signal by mixing with deeper uncontaminated sediment.

Lead isotopic signatures in Antarctic marine sediment cores: a comparison between 1M HCl partial extraction and HF total digestion pre-treatments for discerning anthropogenic inputs.

Sensitive analytical techniques are typically required when dealing with samples from Antarctica as even low concentrations of contaminants can have detrimental environmental effects. Magnetic Sector ICP-MS is an ideal technique for environmental assessment as it offers high sensitivity, multi-element capability and the opportunity to determine isotope ratios. Here we consider the Pb isotope record of five marine sediment cores collected from three sites in the Windmill Islands area of East Antarctica: Brown Bay adjacent to the current Australian station Casey, Wilkes near the abandoned US/Australian Station and McGrady Cove lying midway between the two. Two sediment pre-treatment approaches were considered, namely partial extraction with 1M HCl and total dissolution involving HF. Lead isotope ratio measurements made following sediment partial extraction provided a more sensitive indication of Pb contamination than either Pb concentrations alone (irrespective of sample pre-treatment method) or isotope ratios made after HF digestion, offering greater opportunity for discrimination between impacted and natural/geogenic samples and sites. Over 90% of the easily extractable Pb from sediments near Casey was anthropogenic in origin, consisting of Pb from major Australian deposits. At Wilkes impact from discarded batteries with a unique isotopic signature was found to be a key source of Pb contamination to the marine environment with ~70-80% of Pb being anthropogenic in origin. The country and source of origin of these batteries remain unknown. Little evidence was found suggesting contamination at Wilkes by Pb originating from the major US source, Missouri. No definitive assessment could be made regarding Pb impact at McGrady Cove as the collected sediment core was of insufficient depth. Although Pb isotope ratio signatures may indicate anthropogenic input, spatial concentration gradients at nearby Brown Bay suggest contamination at McGrady Cove is unlikely. We recommend Pb isotopic analysis following 1M HCl partial extraction pre-treatment as a powerful and sensitive method for tracing Pb contamination in marine sediments.

Multiple Pb sources in marine sediments near the Australian Antarctic Station, Casey.

An extensive Pb isotope ratio survey of approximately 100 marine sediment samples from near Casey Station, East Antarctica has been undertaken. Sediment surface grabs and cores were collected over nine years between 1997-2006 and, following HF total digestion, were analysed by magnetic sector ICP-MS. Fifty-two reference samples ([Pb] range 5-26 mg kg(-1)) from 6 non-impacted locations displayed a broad range of Pb isotope ratios representative of the natural background geology of the region ((208)Pb/(204)Pb ratios of 37.5-40; (206)Pb/(204)Pb ratios of 17-19). Potentially impacted sediments from Brown Bay (n=27, [Pb] range 18-215 mg kg(-1)), adjacent to the current and former Australian Stations at Casey (and the associated Thala Valley tip site) showed contamination by Pb characteristic of Broken Hill and Mt Isa Australian deposits ((208)Pb/(204)Pb and (206)Pb/(204)Pb values of 35.5-36 and 16.0-16.1, respectively). The nearby abandoned Wilkes Station was previously manned by both US (1957-59) and Australian (1959-69) expeditioners. Adjacent marine sediment samples (n=24, [Pb] range 13-40 mg kg(-1)) displayed Pb isotopic signatures suggesting anthropogenic input from multiple sources. On a three-isotope diagram Wilkes sediments were found to display Pb ratios lying intermediate between Missouri (US), Broken Hill/Mt Isa (Australia)/Idaho (US), and natural geogenic Pb end members. Discarded Pb batteries, paint samples and fuel spills were all considered in this work as possible point sources of Pb contamination to the local environment. Batteries are thought to be the dominant source.

Characterisation of the dilute HCl extraction method for the identification of metal contamination in Antarctic marine sediments.

A regional survey of potential contaminants in marine or estuarine sediments is often one of the first steps in a post-disturbance environmental impact assessment. Of the many different chemical extraction or digestion procedures that have been proposed to quantify metal contamination, partial acid extractions are probably the best overall compromise between selectivity, sensitivity, precision, cost and expediency. The extent to which measured metal concentrations relate to the anthropogenic fraction that is bioavailable is contentious, but is one of the desired outcomes of an assessment or prediction of biological impact. As part of a regional survey of metal contamination associated with Australia's past waste management activities in Antarctica, we wanted to identify an acid type and extraction protocol that would allow a reasonable definition of the anthropogenic bioavailable fraction for a large number of samples. From a kinetic study of the 1 M HCl extraction of two Certified Reference Materials (MESS-2 and PACS-2) and two Antarctic marine sediments, we concluded that a 4 h extraction time allows the equilibrium dissolution of relatively labile metal contaminants, but does not favour the extraction of natural geogenic metals. In a regional survey of 88 marine samples from the Casey Station area of East Antarctica, the 4 h extraction procedure correlated best with biological data, and most clearly identified those sediments thought to be contaminated by runoff from abandoned waste disposal sites. Most importantly the 4 h extraction provided better definition of the low to moderately contaminated locations by picking up small differences in anthropogenic metal concentrations. For the purposes of inter-regional comparison, we recommend a 4 h 1 M HCl acid extraction as a standard method for assessing metal contamination in Antarctica.