Accidental Oil Spills

Unfortunately, local hydrocarbon pollution incidents have occurred in Antarctica (e.g. Jouventin et al. 1984; Cripps 1992b), and there are many reports of oiled or killed seabirds (e.g. Williams 1984; Croxall 1987). In general, the most significant oil spills have been caused by shipwrecks, collisions or accidents during bunker fuel transfer. Cripps and Shears (1997), for instance, studied the fate of 1,000 l of an accidentally spilled diesel fuel at

Faraday Station. Total PAH concentrations in seawater reached 222 |g l-1 the day after the spill, and decreased to background values within 1 week. However, the worst incident in Antarctica was the sinking of the Argentine supply ship Bahia Paraiso on 28 January 1989. The shipwreck occurred at Arthur Harbor near Anvers Island, about 2 km from the small scientific US Palmer Station. The release of about 550 m3 of diesel fuel, together with the Exxon Valdez oil spill in Prince William Sound (Alaska) the same year, for the first time focused international attention on the possible environmental risk of human activities in polar environments. The US National Science Foundation undertook significant efforts to contain environmental pollution, and sponsored a Quick Response Team for environmental monitoring of the area affected by the grounding of Bahia Paraiso (Kennicutt et al. 1990). Within 4 days of the accident, 100 km2 of sea surface was covered by an oil slick. Kennicutt et al. (1991,1995) and Kennicutt and Sweet (1992) described and quantified the extent and duration of the environmental impact, which was compared to the low-level, long-term impact of Palmer Station. Over the first weeks, all intertidal areas within a few kilometres of the wreck were contaminated and populations of intertidal limpet Nacella concinna were reduced by 50 %. Owing to the volatility of fuel and the generally high hydrodynamic energy of the marine environment, contaminated beaches were cleansed within days or weeks of the main phase of spillage; nevertheless, high concentrations of total PAHs (about 400 |g kg-1 dry wt.) were detected on the beaches, and the intertidal environment was occasionally re-oiled or freshly oiled for about one year after the spill. As occasional releases from the wreck, calm weather conditions and marine currents enhanced the accumulation of hydrocarbons in relatively low-energy areas, beach sediment samples collected in 1991 showed unusually high PAH contamination with respect to those in 1990. However, PAH contamination in subtidal sediments from Arthur Harbor, except those within a few metres of the ship, was mainly attributed to other local inputs such as shipping, boating and station activities. After two years, in most intertidal zones affected by the spill, PAH concentrations in N. concinna tissues had decreased to values at or near the detection limit of the analytical method. An example of this temporal decrease is shown in Fig. 43, which reports average concentrations of total PAHs (Kennicutt et al. 1990; Kennicutt and Sweet 1992) for limpets, collected between February 1989 and April 1991 at different distances from the Bahia Paraiso wreckage.

McDonald et al. (1992) measured PAH concentrations in fish collected at Arthur Harbor and from remote sites of the Antarctic Peninsula. In general, higher total PAH values were detected in the stomach contents and liver of Notothenia coriiceps neglecta caught near the Bahia Paraiso wreck. Amphi-pods and the limpet N. concinna were the dominant identifiable materials in the stomach contents of fish, and phenanthrenes and dibenzothiophenes were the most abundant PAHs. Naphthalene was the major PAH in liver and mus-

Fig. 43. Indicative temporal trends (1988-1991) of total PAH concentrations (pgkg-1 dry wt.; mean±SD) in composite tissues of the limpet Nacella concinna at different distances from the Bahia Paraiso wreckage. (Data from Kennicut et al. 1990, 1992)

Fig. 43. Indicative temporal trends (1988-1991) of total PAH concentrations (pgkg-1 dry wt.; mean±SD) in composite tissues of the limpet Nacella concinna at different distances from the Bahia Paraiso wreckage. (Data from Kennicut et al. 1990, 1992)

cle tissue, suggesting a preferential bioaccumulation of more water-soluble PAHs. Total PAH concentrations in the stomach contents and muscle tissues of N. coriiceps neglecta captured near Palmer Station were significantly lower than those in fish caught near the wreck. The average content of naphthalene and phenanthrene in the bile of fish collected near Bahia Paraiso, Palmer Station and Low Island (a control site) was 69,000 and 9,000, 51,000 and 6,000, and 38,000 and 5,000 ng g-1 wet wt. respectively, with large standard deviations and considerable overlap of values. However, through gas chromatography with mass spectrometric detection (GC/MS), the metabolites of phenan-threnes and dibenzothiophenes were detected in the bile of some fish collected near the wreck and at Palmer Station, but not in samples from control sites. Likewise, hepatic EROD activity (ethoxyresorufin-O-deethylase, a biomarker of fish exposure to PAHs and to planar-halogenated and structurally similar compounds) was low to undetectable in N. coriiceps neglecta from remote sites of the Antarctic Peninsula, whereas values were variable in samples captured near the Bahia Paraiso wreck (30±29 pmol min-1 mg-1), and highest (121±54 pmol min-1 mg-1) near the pier at Palmer Station (Kennicutt et al. 1995).

The spill occurred at the middle to end of the seabird breeding season and potentially affected about 40,000 individuals (Kennicutt et al. 1990). The earliest evidence of the lethal exposure of seabirds to oil was recorded on 1 February 1989, when several dead, oiled Adelie penguins and blue-eyed shags were found in Biscoe Bay, adjacent to Palmer Station. Documented mortality from fouling and toxicity, in the 3-week period after the spill, was estimated to be less than 300 individuals. The direct effects of oil were not apparent in surface-feeding birds, although many of them fed on krill and limpets killed by the oil. However, mortality may have been higher due to other concomitant factors such as severe weather conditions, the efficiency of scavengers and predators, and the abandonment of breeding colonies during the period of seasonal dispersal of chicks. The effects of oil on reproduction were observed in blue-eyed shag nestlings which died of toxicity and abandonment. Mortality was exacerbated by the natural disappearance of prey. During the oil spill the local population of south polar skua (Cathar-acta maccormicki) suffered complete reproductive failure. As very few skuas (adults or chicks) died from direct contact with oil, it was hypothesised that sublethal oiling of adults temporarily reduced parental guarding (parents neglected their territories while cleansing themselves after feeding in slicks, thereby favouring the predation of chicks by other skuas; Eppley and Rubega 1989). However, other ornithologists working in the same region suggested that there was no relationship between the reproductive failure of skuas and the oil spill (Trivelpiece et al. 1990). In regions with extreme climatic and environmental conditions, natural events such as storms or food shortages in critical periods of the breeding season may occasionally result in reproductive failure. Without a better understanding of the natural variability of skua populations in the region, it is impossible to clear the controversy (e.g. Barinaga 1990; A. Anderson 1991) over the possible indirect effects of oil on seabird reproductive failure.

The impact of oil pollution on the metabolism of natural microbial communities is poorly understood. Crude oil contains thousands of hydrocarbons and related compounds, and these compounds can enhance (Bunch 1987), reduce (Griffiths et al. 1981) or have no effect (Carman et al. 1996) on the total abundance of sedimentary bacteria. It is well known that microorganisms play a critical role in the breakdown of hydrocarbons. Microbiological studies at Arthur Harbor showed that local densities of hydrocarbon-oxidising bacteria and degradation rates were extremely low (<100 g n-C16 cm3 sediment year1) when compared with those in temperate regions (Kennicutt et al. 1990). On different sub-Antarctic intertidal beaches (Kerguelen Archipelago), Delille and Delille (2000) found that less than 5 % of the total number of saprophytic bacteria consists of hydrocarbon-degrading microorganisms, but there are differences of one order of magnitude in the original richness of different sites. It has been suggested (Atlas 1991) that an initially high number of oil-degrading bacteria may indicate previous histories of oil contamination and/or chronic contamination. In the 3-year period following the Exxon Valdes oil spill in Alaska, for instance, Braddock et al. (1995) found significantly higher numbers of hydrocarbon-degrading microorganisms at sites affected by the oil slick (from 3.6x103 to 5.5X105 bacteria ml1) than at reference sites (<102 bacteria ml1). Delille and Delille (2000) performed oil-contamination experiments at nine intertidal beaches of the Kerguelen Archipelago; hydrocarbon-degrading microorganisms at some sites increased by several orders of magnitude within a few days, but no obvious effects were detected at two other sites. After 3 months of contamination, there was still a strong heterogeneity in the biodégradation capacity of different sites. It was hypothesised that this heterogeneity was due not only to differences in the grain size of sediments and in the availability of organic matter and nutrients, but also to previous contamination of some beaches by human activities, such as a whaling station operating at Port Jeanne d'Arc for more than 50 years.

George (2002) studied seasonal variations of anionic surfactant SDS (sodium dodecyl sulphate) biodegradation in Antarctic coastal waters at Rothera Station (Adelaide Island). He found that the half-lives of SDS in Antarctic coastal waters were generally far higher (160-460 h) than in temperate waters. Despite small seawater temperature differences (up to 2.45 °C), the persistence of surfactants in mid-winter was twice that measured in midsummer. As at sites with higher hydrocarbon biodegradation capabilities, acclimatisation was taking place at the marine site receiving grey wastewater from the station. A large population of SDS-degrading bacteria developed in polluted waters during the summer months, and SDS half-lives were about 80 h shorter than in pristine Antarctic waters.

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