Hydrocarbons in surface sediments and bivalves from Shatt Al-Arab and its rivers, Southern Iraq

Oil & Chemical Pollution 7 (1990) 17-28

Hydrocarbons in Surface Sediments and Bivalves from Shatt AI-Arab and its Rivers, Southern Iraq

Nadia A1-Mudaffar, Issam N. O. Fawzi & Tariq A1-Edanee Department of Environmental Chemistry, Marine Science Center, Basrah University, Basrah, Iraq (Received 22 August 1989; accepted 22 January 1990)

ABSTRACT Levels of aliphatic hydrocarbons within the boiling range of alkanes n-C14 to n-C34 were determined in samples of surface sediments and in two bivalve species, Unio tigridis and Pseudodontopsis euphraticus (Unionidae),from seven locations in the lower reaches of the rivers Tigris and Euphrates, and the upper Shatt Al-Arab. These levels, and data derived from them, indicate only slight pollution, mostly by degraded hydrocarbons arisingfrom anthropogenic sources. The Shatt AI-Arab samples were most contaminated and those from the river Tigris the least contaminated.

1 INTRODUCTION In this paper, we report the results of a survey i n t e n d e d to determine the present levels of h y d r o c a r b o n pollution in the most i m p o r t a n t national waterway o f Iraq. The two m a i n rivers, the Tigris a n d Euphrates, r u n from n o r t h to south a n d join together north of the city of Basrah to form a short c o m m o n river/estuary, the Shatt A1-Arab (Fig. 1), which discharges about 5 × 109 m 3 of nutrient-rich water a n n u a l l y into the h e a d of the A r a b i a n Gulf. This water is well oxygenated; its temperature varies from about 15 o C in winter to over 30 oC in summer. D o u a b u l & A1-Saad (1985) estimated that about 48 tonnes of oil residues is transported to the G u l f every year. H y d r o c a r b o n s m a y enter the river system at low levels from 17 Oil & Chemical Pollution 0269-8579/90/$03.50© 1990 Elsevier Science Publishers Ltd, England. Printed in Ireland.

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domestic and industrial effluents, agricultural run-off, navigation and transportation, and also from atmospheric fall-out. The study was carried out by examining the accumulation of petroleum residues in surface sediments and also in unionid bivalves, as indicator species. Pollution of aquatic systems by oil has already been extensively investigated. Saturated hydrocarbons are generally analysed by gas chromatography to establish the extent of pollution quantitatively and to resolve interfering biogenic hydrocarbons, which afford additional information on natural processes (Readman et al., 1986). Molluscs are being used increasingly by many researchers as indicators of local levels of pollution from hydrocarbons, pesticides and other substances (Goldberg et al., 1978; National Academy of Sciences USA, 1980; Farrington et al., 1982 and Risebrough et al., 1983). In Shatt A1-Arab, representatives of the Unionidae (fresh-water mussels) are widely

Hydrocarbons in surfaee sediments and bivalves

19

distributed and locally abundant. They therefore seem to be appropriate indicator organisms in a situation where there have been no previous detailed studies. The only relevant work which we are aware of, which gives detailed analyses of aliphatic and aromatic hydrocarbons in the same general area, is that ofAnderlini etal. (1981) on the Mollusca of the coastal waters of Kuwait. The lack of data on petroleum residues in the bivalves or other invertebrates and in sediments from the inland waters of southern Iraq prevents us from reaching any conclusions as to whether levels have declined, as might be expected, during the eight years of reduced industrial and navigational activity brought about by the recent war in this area.

2 MATERIALS AND METHODS Samples of surface sediments and two species of Unionidae (Mollusca Bivalvia), Unio tigridis and Pseudodontopsis euphraticus, were collected from a series of stations along the lower Tigris and Euphrates rivers and the Shatt-A1-Arab during the period June to August 1987; the sites are marked on Fig. 1. After collection, the samples were wrapped in aluminium foil, stored in a cool-box and frozen immediately upon return to the laboratory. The flesh of each bivalve was homogenized in a high-speed electric blender and an aliquot of between 10 and 15 g (weighed to the nearest 0.01 g) was taken for extraction. Anhydrous sodium sulphate amounting to 50 g was added and mixed well. Next the sample was extracted twice under dichloromethane using an orbital shaker. The extracts were combined, concentrated by boiling, and aliphatic hydrocarbons separated by running through a column of silica gel above alumina following the procedure described by McLeod et al. (1985). Samples of 30-35 g of sediment were similarly treated. Dry weights for tissue and sediment were determined after heating in an oven at 120 °C for about 24 hours to constant weight. Details of the bivalve samples are given in Table 1. The extracted aliphatic hydrocarbon fractions (F1) from both the bivalve flesh and sediments were determined using a Perkin-Elmer Sigma 300 gas chromatograph equipped with a capillary inlet system and flame ionization detector (FID); injection of F1 samples was splitless, using volumes of 4 or 5 pl; the inlet temperature was 280 °C and the inlet was kept in the splitless mode for one minute after injection. The extracts were analysed with a 50 m fused silica column, using helium as the carrier gas. After an initial temperature of 40 oC, held for one minute, the oven was programmed to rise at 10 ° per minute to 100°C and at 5 ° per

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minute to 310 °C; the detector temperature was 320 0C. Concentrations of n-alkane were quantified from the ratio of the area of each identified peak to that of the internal standard (triphenyl ethylene). The area of the unresolved complex mixture (which forms a 'hump' in the base-line of the chromatogram) was determined by planimetry, and its total concentration was estimated by again using the ratio of its area to that of the internal standard peak. 3 RESULTS AND DISCUSSION The concentration of total aliphatic hydrocarbons (TAH), normal alkanes (n-alk), unresolved complex mixture (UCM) and the pristane : phytane ratio (Pr/Ph) for the seven sediment-sampling locations and the two bivalve species are given in Table 2. Shatt N-Arab sediments show the highest TAH values, whilst those from stations on the Euphrates have slightly higher concentrations than from the Tigris. The sediments give similar chromatograms (Fig. 2) which provide indications of the relative importance of anthropogenic versus biogenic hydrocarbon inputs. Apart from some enhancement of the n-C17 and pristane concentrations (Fig. 3) which can be attributed to biological sources, particularly phyto- and zooplankton (Farrington & Tripp, 1977; Sleeter et al., 1980; Shaw et al., 1985), no predominance of homologues with an odd carbon number was noted in any of the samples. Sleeter et al. (1980) expressed this as the Carbon Preference Index (CPI), based on the ratio between odd-carbon and even-carbon compounds. In living organisms n-alkanes often exhibit a preponderance of odd-numbered homologues over evennumbered ones but, here, the ratio lies reasonably near to unity (Tables 2 & 3), similar to the findings of the above workers for harbour sediments chronically polluted by petroleum around Bermuda. Phytane, which is present in crude oils but is not found in most biota, was nearly always detected in the sediment samples, although in concentrations lower than n-C18 and often quite a bit less than pristane or n-Cl7. Sediments from stations 2, 3 and 4 show a higher concentration of phytane than of pristane. The distribution of phytane and of the UCM, which are also indicative of degraded or chronic oil pollution (Thompson & Eglinton, 1978) are, together with a Pr/Ph ratio near unity in many stations, features indicating an anthropogenic source. Contamination of the sediment by recent inputs of non-degraded petroleum, however, is shown to be very small by the low concentrations of resolved hydrocarbons and the presence of a UCM signal in all chromatograms. The Marine Oil Pollution Index (MOPI) developed by Payne and fellow

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present together with a marked UCM, confirming the inclusion of petrogenic hydrocarbons. Total aliphatic hydrocarbon concentrations in P. euphraticus and U. tigridis range from 48.45 to 483.1 ng g-1 dry weight, more than 90% of which forms an unresolved complex mixture. Both pristane and phytane were detected, along with a homologous series ofn-alkanes. The calculated M O P I ranges from 1.2 to 3.0 (Table 3), indicate a biogenic or low-level petrogenic hydrocarbon burden.

4 CONCLUSIONS These preliminary data suggest that the sediments and bivalves of southern Iraqi waterways are relatively unpolluted. The similarity in the respective spectra of such hydrocarbons as are present indicates that the nature a n d levels of invertebrate contamination result from a dynamic equilibrium arising from the non-selective direct uptake of polluted particulate elements from the surrounding sediments. The traces of pollutant hydrocarbons detected probably originate from sewage discharges a n d u r b a n run-off, as the vast majority appear to be degraded rather than fresh. In addition to the low level of waterborne hydrocarbons, dust fallout (which was estimated in a R O P M E report of 1987 to a m o u n t to 6.90 g m -2 annually over southern parts of Iraq) can carry measurable quantities of pollutants to the Arabian Gulf, via Shatt A1Arab or directly. Hauser & Pattison (1972) detected an unresolved complex mixture of hydrocarbons in urban air particulate samples similar to that found by us in these sediments. The possible impact of such fallout u p o n the northern Arabian Gulf is currently being investigated.

REFERENCES Anderlini, V. C., A1-Harmi, L., De Lappe, B. W., Risebrough, R. W., Walker, W., Simoneit, B. R. & Newton, A. S. (1981). Distribution of hydrocarbons in the oyster, Pinctada margaritifera, along the coast of Kuwait. Mar. Poll. Bull., 12, 57-62. Douabul, A. A. Z. & A1-Saad, H. T. (1985). Seasonal variations ofoil residues in water of Shatt A1-Arab river, Iraq. Water, Air & Soil Poll., 24, 237-46. Farrington, J. W. & Tripp, B. W. (1977). Hydrocarbons in Western North Atlantic surface sediments. Geoehim. Cosmochim. Acta, 41, 1627-41. Farrington, J. W., Davis, A. C., Frew, N. M. & Rabin, K. S. (1982). No. 2 fuel oil compounds in Mytilus edulis. Retention and release after an oil spill. Mar. Biol., 66, 15-26.

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Nadia Al-Mudaffar, Issam, N. O. Fawzi, Tariq Al-Edanee

Goldberg, E. D., Bowen, V. T., Farrington, J. W., Harvey, G., Martine, J. H., Parker, P. L., Risebrough, R. W., Robertson, W., Schneider, E. & Gamble, E. (1978). The Mussel Watch. Environ. Conservation, 5, 101-25. Hausser, T. R. & Pattison, J. N. (1972). Analysis of aliphatic fraction of air particulate matter. Envir. Sci. Tech., 6, 549-55. McLeod, W. D., Jr., Brown, D. W., Friedman, A. J., Burrows, D., Maynes, O., Pearce, R. W., Wigren, C. A. & Bogar, R. G. (1985). Extractable toxic organic compounds. National Marine Fisheries Service, Northwest and Alaska Fisheries Center, Envir. Conser. Divis., 2725 Montlake Boulevard East, Seattle, Washington 98112 (2nd edition). National Academy of Science, U.S.A. (1980). The international mussel watch. NAS, Washington, D.C., 248 pp. Payne, J. R., Clayton, J. R., Jr., Phillips, C. R., Lambach, J. L. & Farmer, G. H. (1985). Marine Oil Pollution Index. Oil & Petrochem. Pollut., 2, 173-91. Readman, J. W., Mantoura, R. F. C., Llewellyn, C. A., Preston, M. R. & Reeves, A. D. (1986). The use of pollutant and biogenic markers as source discriminants of organic inputs to estuarine sediments. Intern. J. Environ. Anal. Chem., 27, 29-54. Regional Organization for the Protection of the Marine Environment (1987). Dust fallout in the northern part of the ROPME sea area. ROPME/GC-5/005. P.O. Box 26388, 13124 SAFAT, Kuwait. Risebrough, R. W., Delappe, B. W., Walker II, W., Simoneit, B. R. T., Grimalt, J., Albaiges, J., Regueiro, J. A., Inolla, A. B. & Fernandez, M. M. (1983). Application of the mussel watch concept in studies of the distribution of the hydrocarbons in the coastal zone of the Ebro delta. Mar. Poll. Bull., 14, 181-7. Shaw, D. G., Hogan, T. E. & McIntosh, D. J. (1985). Hydrocarbons in the sediments of Port Valdez, Alaska. Consequences of five years permitted discharge. Estuar. Coast. Shelf Sci., 21, 131-44. Sleeter, T. D., Butler, N. J. & Barbash, J. E. (1980). Hydrocarbons in the sediments of the Bermuda region: Lagoonal to abyssal depths. In Petroleum in the Marine Environment, ed. L. Petrakis & F. T. Weiss. Advances in Chemistry Series 185.American Chemical Society, Washington, DC, pp. 267-88. Thompson, S. & Eglinton, G. (1978). Composition and sources of pollutant hydrocarbons in the Severn estuary. Mar. Pollut. Bull., 9, 133-6.