The Concentration and Origin of Total Petroleum Hydrocarbons (TPHs) in Coastal Sediments of the Kharg Island in the Persian Gulf

Persian Gulf is a water body at the margin of Indian ocean which makes way to Oman Sea and Indian Ocean through the Strait of Hormuz with the minimum width of 56 km. Specific condition of the Persian Gulf such as high evaporation, high salinity, aqueous species diversity, fisheries value and especially oil sources of the area, which have extra importance in the world, have made it a sensitive and strategic area. Marine environment of the Persian Gulf suffers severely from oil pollution. Oil extraction and transportation together with the effluent dischrges from the coastal cities and oil refinneries are among the major sources of oil pollution in the Gulf. Kharg Island is a coral anticline in the Persian Gulf located within 28 km of the southern coasts of Iran. This island has a length of approximately 8 km and a width of approximately 4 to 5 km. The coastal environment of the Kharg Island is rich with corals. The corals are the host to many types of local fishes of the Persian Gulf. Kharg Island contains the most important and also the biggest crude oil export terminal of Iran. More than 90% of Iranin oil exportation is conducted through the island. In addition, many other oil related activities including storing and filtering of the crude oil are performing in the island. Hosting extensive oil related activites during the past 50 years has subjected the marine and coastal environment of Kharg Island to huge amount of oil discharges from different sources icluding Oil Tanker accidents, leakages at the oil term inals, discharge of oily effluents from crude oil stores and oil refineres. However, surprisingly, there are only a few studies conducted on the oil pollution around the island. In this paper, the oil pollution and its origin in the near shore coastal sediments of the Kharg Island are examined and discussed. This is conducted by using the analysis of the concentration of hydrocarbones in the sediment samples collected early 2012 from 11 points around the island. Near shore sediment samples were collected at 11 points around the Island. The stations were selected in a way that they cover the whole parts of the island's coastline. The samples were also more concentrated near the oil terminals. All of the samples were taken near the coastline at knee deep water points in low tide condition. About 200 to 300 grams of wet sediments were taken from the top 5 centimeter of surface sediment and was poured into boron silicate vial which was washed by washer material, hot water, acetone solution and distilled water and had a lid of polyethylene. The collected samples were packed and protected for transferring to laboratory using the USEPA-sw-846 standard method. The standard method of American Association of Environmental Protection (USEPA-SW 846#3540C) named SOXHLET has been used for preparation of the samples and extraction of petroleum hydrocarbons from them. The samples were passed through a 63 micron sieve (<63) before the lab analysis. A gas chromatography device (GC-FID) Model VARRIAN was used to determine the concentration of Total Petroleum hydrocarbons (TPH) and aliphatic compositions in the sediment samples. In addition, the concentration of petroleum normal alkanes with different numbers of carbons (n-c 10, n-c 35) was measured. Concentrations of total petroleum hydrocarbons (TPH) in surface sediments TPH concentrations are represented by a diagram in surface sediment samples collected along the coastlines of the Kharg Island. The concentrations varied from a very low amount of 1 􀂗g/g to very high amount of 5624 􀂗g/g. The highest TPH concentrations were observed at stations 2, 3 and 4, at 5624, 1660 and 4186 􀂗g/g, repectively. These stations were located on the eastern coast of the island near the T shape quay, next to the major crude oil export terminal. The results indicate that the leakage from the loading activities have highly polluted the coastal area around the T shape quay. Stations 9 and 10, where are located near Azarpod Jetty on the west side of the island, have relatively high TPH concentration, 141 and 75 􀂗g/g, respectively. The oil pollution in this area is resulted from the oil leakage in Azarbad oil terminal and also tanker incidents. The lowest amount of TPH concentration was observed in stations 1, 7, 8 and 11 up to <1, <1, 2 and 32 􀂗g/g, respectively. Station 1 was located in the south of the T shape quay and is somehow close to this oil terminal. However, considering the dominant direction of the wind waves on the eastern coast, the sediments in the position of this station were not affected from the oil discharges near the T shape quay. Staions 7 and 8 positioned on the northern part of the island are far from the oil pollution sources near the oil terminals and were not affected from these sources. TPH concentrations at stations 5 and 6 were 78 and 232 􀂗g/g, repectively. The concentrations in these stations are much less in comparison with the station 2, 3 and 4 adjacent to the T shape oil terminal. However, the T shape quay seems to be the source for the oil content of the sediments at these stations as well. Commendatore and Esteves (2007) dividedc oastal areas into three categories from the view point of oil hydrocarbon rate: low concentration (􀂗g/g < 10), low to average (10-100 􀂗g/g) and average to high (100-1000 􀂗g/g). Readman et al, (2002) considered the sediments with concentration above 100 􀂗g/g as polluted. Tolosa et al, (2004) considered the sediments with concentration above 500 􀂗g/g as severe polluted and the ones with concentration less than 10 􀂗g/g as non-polluted. Regarding to the above criteria the sediments on the eastern part of the Kharg Island adjacent to the T shape quay can be considered as highly polluted. The polluted area extends to the north of the T shape quay along the east coast to the positions of stations 5 and 6. On the west coast of the Island the polluted area are limited to the vicinity of the Azarpad Jetty. Apart from the above mentioned areas, the shallow water sediments around the rest of the Kharg Island in most of the west coast and in the north and south of the Island can be considered as not polluted. The origin of aliphatic hydrocarbons (AHC) in Kharg Island sediments Hydrocarbons in sediments might be originated from fossil petroleum origin resulted from human activities or originated from biological activities of Algae, Planktons, Bacteria, marine animals and terrestrial vascular plants. In this part, the origin of hydrocarbons in studied region was determined through developing a set of present indices and the position ofo bservance pollutants in each of the stations. In Kharg Islandby regarding to oil activities in this area, crude oil is considered as the first oil pollutant. Relative abundance of normal alkanes with different numbers of carbons or predominance of the specified alkane in sediments can be the index of certain types of oil hydrocarbons presence in sediment samples. Therefore, the presence of 18 carbons normal alkane (n- C18) in sediment samples shows the oil origin of observed hydrocarbons (Clarke and Finely., 1973). Odd carbons normal alkanes with low number of carbon atoms such as 17 carbon normal alkane (n-C17) is identified as the index of phytoplankton hydrocarbons presence (Tolosa et al., 2004). Normal alkanes with odd numbers of carbon 27, 29 and 31 (n-C31, n-C29 and n-C27) are introduced as the index of plant waxes presence with land organic plant origin (Tulloch, 1976). N-C16 index, which is equal to n-alkanes/n-C16, is the number less than 15 for polluted samples by fossil petroleum and the number more than 50 for polluted samples by biological hydrocarbons (Clarke and Finely., 1973). Carbon priority index (CPI) is defined such as equation (1) with Boehm and Requejo in1986: CPI= 2(C27+C29)/ C26 + (2C28) + C30 (1) The CPI index is about 1 for petroleum hydrocarbons, while it varies from 3 to 6 for vascular plants and fornon-polluted sediments by fossil oils (Colombo et al., 1989). The other index is the Odd/Even index, which is the ratio of odd numbers of carbon atoms to even numbers. This ratio varies about 1 for petroleum, while for plant waxes; alkanes with odd chain are 8 to 10 times more than alkanes with even carbon chain. In some diagrams we show normal alkanes concentration profiles with different numbers of carbon atoms in stations of the study area. As these profiles show, in stations numbers 2, 3 and 4, which are eastern dock of island (T shape quay) and in stations 8 and 9, which are on the proximity of western jetty (Azarpod jetty), 18 carbons with normal alkane has the most rate in compositions and this shows the presence of oil hydrocarbons. At stations number 7 and 10, 17 carbons with normal alkane has the most rate and these rates show the presence of phytoplankton hydrocarbons in these stations. At stations 1, 5, 6 and 11 by increasing the distance from oil docks placed on island, the rate of n-C17 concentration is more than n-C18 and this indicates that in these stations present hydrocarbon in the sediment has biological origin. By regarding to insignificant concentration of earth alkanes (n-C27, n-C29 and n-C31) in general profile of normal alkanes, there are no hydrocarbons with land vascular and organic plants in surface sediments of the study area. Because of the plant poverty in Kharg Island, lack of presence of terrestrial plants hydrocarbons is observed. The range of n-C16 index, in sediments of this region is 6.36 to 332.4. This rate in stations 2, 3, 4, 5, 8 and 9 are less than 15 and typical of the polluted sediments of this region from petroleum. However, this rate is more than 50 in other stations (stations 1, 6, 7, 10 and 11), this means the pollution of sediments in these regions is from the type of biological hydrocarbons. The other index is “CPI” which is between 0.75 and 5.7, and from its results in stations 2, 3, 4 and 10, we can find out that in all the point near the oil quays of Kharg Island, there are oil sources in coastal sediments. In other stations, the rates of these indices show that their hydrocarbons have biological origins. Some stations including stations number 1, 5, 6, 7, 8 and 11 have not oil pollutions. Evaluation of observing hydrocarbons concentrations based on ratio of alkans with odd carbon numbers to evens shows that this ratio varies in a range from 0.8 to 7.36. These rates are equal to one in stations No. 2, 3, 4, 5, 8 and 9.In other stations including 1, 6, 7, 10, 11 this quantity is more and there are high concentrations of old normal alkanes which suggests that there are biological sources with plant waxes for hydrocarbons. Therefore, general position of observed hydrocarbons in sediments of Kharg Island coastline suggests that there are fossil oil origins in the proximity of oil jetties in which high oil activities are performing and there are biological and natural origins in other stations of the island. The pollution of the sediments in the studied area from the total petroleum hydrocarbons (TPH) was investigated by oil hydrocarbons analysis in coastline sediments of Kharg Island and also by comparative analysis of these concentrations with the present guidelines and standards. The results of the studies based on the total petroleum hydrocarbons concentration indicate the high pollution in some stations and very low to average pollution in other stations from oil activities resources. At stations near to the eastern and western docks (particularly near T shape quay), this rate is high and by getting away from oil terminals, this rate is reduceing.In northern and southern regions of island, this rate also reaches to the minimum. Using the relative indices, it has been shown that the observed hydrocarbons in studied sediments have natural phytoplankton origin in farther points from jetties; in addition to havingoil origin in most of the east and west stations and near the oil terminals.