Antarctic Science 11 (4): 427-429 (1999) 0 British Antarctic Survey Printed in the United ... ofthe long-term fate ofpetroleum hydrocarbons in the Antarctic.
Antarctic Science 11 (4): 427-429 (1999) 0 British Antarctic Survey Printed in the United Kingdom
Petroleum hydrocarbons ten years after spillage at a helipad in Bunger Hills, East Antarctica D.B. GORE1*, A.T. REVILL2s3andD. GUILLE3 'Department of Physical Geography, Macquarre CJniversrQ,NSW 2109, Australia *dgore@laurel ocs mq edu au 'CSIRO Division of Marine Research, GPO Box 1538, Hobart, TAS 7001, Australia 'Antarctic CRC, University of Tasmania, Hobart, TAS 7001, Australra
Abstract: Surface and subsurface sediments from a helipad in Bunger Hills were collected ten years after accidental contamination with a small quantity (probably < 10 litres) of petroleum products. The contaminants are dominated by Jet A2 synthetic lubricating oil which exhibits no evidence of degradation or environmental mobility. In contrast, Jet A 1 turbine kerosene is less abundant at the surface than at 20 cm depth. There is no evidence for biodegradation of the Jet A 1 in the subsurface sample, suggesting that kerosene is environmentally mobile in the surface sediments. Received 12 March 1998, accepted 9 September 1999
Key words: hydrocarbon degradation, pollution Introduction
Methods
The relatively recent interest in understanding and minimizing human impacts in Antarctica means that there is little known ofthe long-term fate ofpetroleum hydrocarbons in the Antarctic environment. To date, studies have concentrated on inputs to the marine environment from station runoff and shipping (e.g. Karl 1989, Pople et al. 1990, Epply 1992, Kennicutt et a1 1992a, 1992b, Green & Nichols 1995) while a few have monitored the fate of light diesel spills on land (e.g. Green 1992, Keny 1993, Green & Nichols 1995). Green (1992) argued that evaporation of diesel could be important over times as short as 30 days in summer, while Keny (1 993) found that up to 50% of diesel in an artificial 'spill' was lost over one year. However, little is known of the longevity of petroleum hydrocarbon contaminants in the Antarctic over periods of more than a year. Surface and subsurface sediments from a helipad at Edgeworth David Station, Bunger Hills, East Antarctica, were collected opportunistically ten years after accidental contamination with a small quantity (probably < 10 litres) of petroleum products. Edgeworth David (Fig. 1) was first occupied during the 1985/86 summer, and again during the 1995196 summer. During the first summer, three small turbine aircraft were refuelled and serviced on three helipads for six weeks. Emergency repairs to one aircraft required stripping down a motor and transmission (Ledingham 1985) although it was not recorded on which helipad this occurred. During the 1995/96 summer, old petroleum spills were observed at two ofthe helipads with a third, smaller spill close to the third helipad. This presented an opportunity to investigate, albeit in a very limited way, the fate ofapetroleum spill one decade after its occurrence.
The largest helipad with the most conspicuous spill (Fig. 1) was mapped and trenched during February 1996. The surface area of the spill was 2.2 mz and the total volume measured at 0.3 m3. The 'wetting front' between the spill and surrounding clean sediment was distinct in Trench A, and it was there that
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sediments were samples at the surface and at 20 cm depth (Fig. 2). The helicopters used Mobil Jet A1 (turbine kerosene) as fuel, and three types of lubricating oils for hydraulics, transmission and turbine. Jet A 1 is compositionally similar to a light diesel in which the predominant n-alkane in C, The hydraulic and transmission oils were mineral oils characterized by the presence ofhopanes and steranes (Peters & Moldowan 1993)superimposedon a broad Unresolved Complex Mixture (UCM). The turbine oil was Mobil Jet A2, which is a synthetic lubricating oil composed of aliphatic esters. The contaminants, and reference samples of Mobil Jet A1 and Jet A2, were characterized and quantified using GC and GC-MS (analytical details and chromatographs are available at
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www.es.mq.edu.au/physgeog/gore/bhspill. htm or by post from the first author). Results and discussion
Total Petroleum Hydrocarbon (TPH) measurements indicated surface contamination of 4580 kg-I dry sediment, declining to 4070 mg kg-I at 20 cm depth. These concentrations are within the ranges documented for heavily impacted sites at other Antarctic and sub-Antarctic research stations (e.g. Cripps 1992, Kennicutt et a1 1992a, Deprez et af. 1994, Green & Nichols 1995). Jet A1 exhibited ann-alkane distribution from
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n-C, to n-C,,, with a maximum at n-C,, (with trace n-alkanes to n-C,,). JetA2 exhibited resolvable peaks in the range n-Cz0 to n-C,, (confirmed from GC-MS as aliphatic esters) with a maximum at n-C,,, and with no discernible UCM that would characterize mineral lubricating oils (Gough & Rowland 1990). The surface and subsurface samples were dominated by compounds that ranged from n-C,, to n-C,,. The subsurface sample exhibited a compositionally minor group ofcompounds that ranged from n-C,, to n-C,,, with a maximum at n-C,,, while the surface sample exhibited a trace of a group of compounds with a maximum at n-C,,. As the contamination occurred at a helipad, likely contaminants were restricted to a small group of petroleum products. Comparisons of the GC chromatograms of the reference and field samples indicated clearly that the dominant contaminant was Jet A2, and it was slightly more abundant at the surface than the subsurface. This is consistent with surface-spilled turbine lubricating oil migrating downwards into the porous sandy sediment. Theminor components ofthe surface and subsurface sample between n-C,, and n-C,,, most likely belong to Jet A1 turbine kerosene. Only a vestige remains of the JetA1 in the surface sample. However, a comparison of the reference Jet A1 sample andthe subsurface sample indicates that there has been a loss ofthe lighter, more volatile n-alkanes from n-C, to n-C, , , leaving the sample enriched in the n-C,2-,4fraction. This fractionation, and the increase in Jet A1 with depth in the sediment, contrasts strongly with the Jet A2 component of the contamination which is not fractionated and decreases in concentration with depth. Reasons forthese contrasts must lie with the contrasting physical characteristics ofthe Jet A1 and Jet A2, that result in fractionation and preferential transport of the Jet A 1 away from the spill surface (either downwards in the sediment, or downslope), or biodegradation or evaporation of Jet A1 at the surface. Three physical differences between Jet A1 and JetA2 might have resulted in fractionation and preferential transport of the Jet A1 away from the surface of the spill. Firstly, Jet A1 has a higher vapour pressure (> 0.1 mmHg @ 25°C) and would evaporatefasterthan Jet A2 (
