VERTIMAR-2005
Symposium on Marine Accidental Oil Spills
Inorganic elements in the Prestige fuel-oil spill,could they contaminate the sediments?
RicardoPrego, AntonioCobelo-GarcíaandJuanSantos-Echeandía
Instituto de Investigaciones Marinas (CSIC), Vigo, Spain.
Marine Biogeochemistry Research Group, Instituto de Investigaciones Marinas (CSIC). Vigo, Spain.
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ABSTRACT: Nineteen inorganic elements present in the heavy fuel oil spilled by the Prestige tanker has been quantified, and only Mo, Ni, Se and V seems to represent a potential contaminant danger for the Galician coastal sediments. In the LaxeRia sediments, located in the middle of the most affected area, these four elements were analyzed one year before and after the oil spill accident. Contamination factors, based on background concentrations normalized with respect to aluminum, did not indicate metal contamination in the sediments of most part of the ria. However, a certain contamination by Mo, Ni and V was found in the area of the Corme Inlet
1. INTRODUCTION
The residual fuel oils, since they are composed by the less-volatile matter of the crude, are richer in metals(Reid, 1973): for example, vanadium and nickel compounds, which are low in volatility, do not distil into the first petroleum fractions. However, no attention has been paid to the potential metal contamination from oil spills (e.g. heavy fuels tanker accidents in December 1999: Erika in the French Coast; in April 2001: Baltic Carrier in the Danish Coast), being the exception the Arabian Gulf where the sediment status of chronic oil-pollution due to some trace metals was surveyed (Fowler et al., 1993) after the 1.7 Tg spilled to the Gulf from the Kuwait oil terminals in 1991. Recently, the Prestige tanker shipwreck, transporting high sulphur (2.58% taken from Crown Resources information) residual fuel oil (type 6, UK classification), caused a widespread contamination of the Galician coast during three consecutive events.
The Coast of Death the area most intensively impacted by the residual fuel oil spilt during a first event when the tanker breakage provoked a spill that four days later impacted 190 km of littoral between Finisterre Cape and Coruña Ria; a second event when the Prestige broke in two and sunk at 130 miles westwards off Finisterre Cape; and also, to a lesser extent, on a third event taking place until February 15th 2003, when the tanker sunk was sealed. Therefore, the aim of this study is to review which are the potentially contaminant elements present in the fuel oil and their possible presence in the sediments of the Laxe Ria, located in the middle of the Coast of Death, that were analyzed before and after the oil spill.
2. Material and Methods
Surface sediment samples were taken from the R/V Mytilus using a box corer at eight stations in the LaxeRia. The first sampling campaign was carried out on 20-21 July 2001 and the second on 23-24 September 2003, approximately one year before and after of the Prestige shipwreck, in order to compare both sediment data. Also, seventeen samples of emulsified fuel were collected in the Coast of Death littoral and shore waters from 19th November 2002 to 3rd February 2003, and one sample from the original cargo of the tanker was also analized. Fuel samples were kept in hermetically-closed polyethylene vials and preserved at -20ºC.
In the on-shore lab, sediments were oven-dried at 40ºC and sieved through 2 mm nylon meshes. Then, were digested in duplicate in Teflon bombs using a microwave oven (Milestone MLS 1200 Mega) following the EPA 3052 guideline and a certified reference material (PACS-2) was used to check the accuracy of the analytical procedure. Moreover, three subsamples of each fuel oil were digested following the the standard Milestone digestion procedures for oil samples. The determination of arsenic, selenium and metals was carried out by means of ETAAS using a Varian 220 apparatus equipped with Zeeman background correction and FAAS using a Varian 220-FS apparatus.
3. RESULTS AND DISCUSSION
The relative proportions of heteroelements in a crude oil vary with the source; around twenty metals could be presents from the indigenous crude oil, and tend to be accumulated in the black, viscous distillation-tower bottoms. This constitutes a heavy fuel rich in ash (0.051% for Prestige fuel taken from Crown Resources information) where nineteen element have been identified in the fuel deposited on the littoral rocks and beaches (Table 1). The potentially contaminant elements can be identified if the typical coastal concentrations are considered (Prego & Cobelo-Garcia, 2003). Thus, Mo, Ni, Se and V are higher than sediment values (Table 1), and therefore the potential contamination should be considered; moreover, for As and Cu is low (Table 1) since they are close to the sediment ranges.
The next step will be to investigate the presence of these elements in the surface sediments of LaxeRia. Mo, Ni, Se and V concentrations can be then normalised using Al (Hanson et al., 1993). Therefore, enrichment factor (EF) is defined according to: EF = [Me]2003 / [Me]Al where [Me]2003 is the metal concentration measured in 2003 and [Me]Al is the background level obtained from the 2001 sediment data as Me:Al relationship. According to the Hakanson (1980) criteria, results indicate that at those sites the sediments were not contaminated by the oil deposited in the ria (EF<3). Nevertheless, a certain contamination (3<EF<6) of sediment was detected in the Corme Inlet where Mo, Ni and V were 4-5 times higher than in 2001.
Table 1. Presence of inorganic elements in the fuel oil spilled from the Prestige Tanker and their potential influence on the coastal sediment.
Emulsioned fuel range / Prestige cargo fuel / Coastal sediment / Potential sediment contamination1000 g g-1 / g g-1 / g g-1
Al / 264.9 / 10,700 - 102,400 / null
Si / 27.9 / 70,000 - 300,000 / ---
Ca / 48.6 / 29,000 / ---
Fe / 11.3 / 15,000 – 33,000 / null
Mg / 26.5 / 21,000 / ---
Ti / ? / 3,000 - 3,900 / null
100 g g-1
Ni / 96.5 / 7 - 38 / should be considered
V / 381.8 / 60 - 94 / should be considered
10 g g-1
Mn / ? / 240 - 600 / null
Mo / 3.00 / 1.5 - 1.8 / should be considered
Zn / 4.79 / 50 - 136 / null
1 g g-1
As / 1.19 / 1.5 - 10.0 / low
Co / 0.31 / 4 - 13 / null
Cr / 0.54 / 12 - 76 / null
Cu / 2.74 / 5 - 35 / low
Se / 0.34 / 0.04 - 0.08 / should be considered
< 0.1 g g-1
Cd / 0.98 / 0.01 - 0.20 / low
Hg / ? / 0.02 - 0.03 / null
Pb / 0.41 / 16 - 78 / null
Sn / ? / 2.5 - 3.5 / null
Acknowledgements
The authors would like to thank Captain J.Alonso, the crew of the R/V Mytilus and Prof. J. Mora (USC) for their kind cooperation during sampling; Dr.M.Maestro (UDC) and Ms. A. Labandeira (IIM) for the AAS analysis. This work is a contribution to the CICYT projects ‘Hydrodynamic and hydrochemistry of AnllonsRiver – Laxe Ria System’ (ref. HID99-0699) and ‘Historical evolution of the anthropogenic influence in the AnllonsBasin, Anllons Estuary and LaxeRia’ (ref. REN2002-04629-C03).
REFERENCES
Hanson, P.J., Evans, D.W., Colby, D.R. & Zdanowicz, V.S. 1993. Assessment of elemental contamination in estuarine and coastal environments based on geochemical and statistical modeling of sediments. Marine Environmental Research, 36, 237-266.
Fowler, S.W., Readman, J.W., Oregioni, B., Villeneuve, J.-P. & McKay, K. (1993). Petroleum hydrocarbons and trace metals in nearshoreGulf sediments and biota before and after the 1991 war: An assessment of temporal and spatial trends. Marine Pollution Bulletin, 27: 171-182.
Hakanson, L. (1980). An ecological risk index for aquatic pollution control. A sedimentological approach. Water Research, 14: 975-100.
Prego, R. & Cobelo-García, (2003). A. 20th Century overview of Heavy Metals in the Galician Rias (NW Iberian Peninsula). Environmental Pollution, 121: 425-452.
Reid, W.T. (1973). Heat generation, transport and storage. In: Perry, R.H.; Chilton, C.H., eds. Chemical Engineers’ Handbook, Section 9. McGraw-Hill, Auckland.