Polycyclic Aromatic Hydrocarbons (PAHs) in water of Al-Kahlaa River in Missan Province, Iraq

The present study was performed to have knowledge of Polycyclic Aromatic Hydrocarbons pollution status in water. The samples were collected during two seasons (winter and summer 2012 ,2013) from four different stations) Al-Magideh, Treatment unit, Al-Husaichi and Al-Zubair) distributed along Al-Kahlaa River in Missan province, in addition to reference station lies on the Tigris river before 25 Km from entering to Amara city. The concentrations of PAHs were determined in by using capillary Gas Chromatography. Results of the present study revealed that the total concentrations of PAHs in dissolved fraction ranged from 0.739 ng.l -1 in Reference station to 1.974 ng.l-1 in Treatment unit during winter, and from 0.300 ng.l-1 in Reference station to 1.125 ng.l-1 in Treatment unit during summer, while in the particulate fraction they varied from 0.79 ng.g-1 dry weight in Reference station to 24.42 ng.g-1 dry weight in Treatment unit during winter, and from 4.369 ng.g-1 dry weight in Reference station to 10.545 ng.g-1 dry weight in Al-Husaich during summer. It had been noticed that there were a predominance of high molecular weight PAHs on low molecular weight, while BaA/(BaA+Chr) ratio in water ranged from 0.218 to 0.804. InP/(InP+BghiP) ratio ranged between 0 and 0.578, where as Fl/Py ratio ranged between 0.150 and 2, this give an indication of the origin of PAHs compounds in water which were mainly pyrogenic and few from them petrogenic.


Introduction
Pollution of the rivers water in Iraq is considered as important problem that must treated and controlled it, so not being complicated in future, such as what occurred in other industrial countries which have high population density (Al-Sayegh and Taka, 2002).Now a days, Petrochemical industries are considered as one of the most important basic industries all over the world.Although these industries have too many benefits for our life, the pollution caused by Petrochemical industries have been a cause for concern and major challenges to save the environment against their adverse impacts.These impacts not only affect the biological characters of the ecosystem but also can affect the water resource quality and threat human health (Esmaeli-Sari, 2002;Rooney, 2005).
Controlling such pollution problems in the aquatic environment is very complex because of the large number of input sources and their geographic dispersions.Contrary to popular views, evidences were accumulated to buttress the fact that these compounds mixes with water and penetrates to the under lying sediments (Patin, 1999).The chemical composition of each crude oil and petroleum products vary significantly, and can have diverse effects on different living organisms within the same ecosystem (Overton et al., 1994).These differences in toxic effects are attributed to qualitative compositional differences in the various products, in addition to concentration differences of the chemical constituents (Albert, 1995;Sverdrup, 2003).
Polycyclic Aromatic Hydrocarbons (PAHs) may reach aquatic environments from industrial and domestic sewage effluents, exhaust of gasoline and diesel combustion engines, surface run off from land, deposition of airborne particulates, and especially from spillage of petroleum and petroleum products into water bodies (Prahl et al., 1984).The majority of PAHs enter aquatic environments remain close to sites of deposition, suggesting that rivers near centers of human populations are the primary repositories of aquatic PAHs (Neff, 1979).In water, PAHs may either disperse into the water column or evaporate or become incorporated into bottom sediments or concentrate in aquatic biota or affected by biodegradation and chemical oxidation (Suess, 1976).
In the aquatic ecosystems, most PAHs are associated with the particulate fraction of PAHs due to their hydrophobic properties giving rise to the accumulation in the sediments (Perra et al., 2009;Qiu et al., 2009).This study is the first of its kind in Al-Kahlaa River which provides a necessary information on the pollution of this region by Polycyclic Aromatic Hydrocarbons (PAHs) and aim to determine the concentrations, seasonal and spatial variations in addition to the sources of these compounds in water.

Collection and extraction of dissolved and particulate fractions of these compounds in water samples
The samples were collected during two seasons (winter and summer 2012, 2013) from four different stations) Al -Magideh, Treatment unit, Al-Husaichi and Al-Zubair) distributed along Al-Kahlaa River in Missan province, in addition to reference station lies on the Tigris River before 25 Km from entering to Amara city as shown in (Fig. 1).The samples of water were suction filtered as soon as possible (within 5 h) through pre-weighted 0.45 µm pore size whatman glass fiber filter (GFF) pre-ignited at 450ºC.Materials passing through the filter were considered as dissolved fraction and the retained as particulate fraction, then the CCl4 was added to the dissolved fraction until the arrival to the lab for analysis, whereas particulate fraction was dried and wrapped in aluminum foil and transferred to the laboratory in ice packed and kept in freezer prior to analysis .
The hydrocarbons were extracted from dissolved fraction following the procedure of UNEP (1989 ).While from particulate fractions following a method of Goutex and Saliot (1980).The concentrations of PAHs in samples were determined by using capillary Gas Chromatography.Simple thermometer with range from 0 to 100 O C graduated at 0.2 O C was used to measure water temperature.

Evaluation indices of oil pollution
Many parameters have to be analyzed in order to evaluate the probable origin of Polycyclic Aromatic Hydrocarbons (pyrogenic or petrogenic).These are as follows : A. Ratio of Low Molecular Weight (LMW-PAHs) to High Molecular Weight (HMW-PAHs).Values more than one indicate petrogenic sources from crude oil and their derivatives and values less than one are pyrogenic sources (Vrana et al., 2001).

Results and Discussion
Total PAHs concentrations as dissolved fraction ranged from 0.739 to 1.974 ng.l -1 and 0.300 to 1.125 ng.l -1 , where as in particulate fraction ranged from 5.796 to 24.42 ng.g -1 d.w and 4.639 to 10.545 ng.g -1 d.w during winter and summer, respectively (Tables 1,2,3 and 4).The highest and the lowest mean concentrations of PAHs in both dissolved and particulate fractions were observed in winter and summer, respectively.This may be attributed to the climatic condition that affect photo-oxidation, volatilization and high degradation during summer (Mohammed et al., 2009).PAHs dissolved in the water column will probably degrade rapidly through photo-oxidation and degrade most rapidly at elevated temperatures and dissolved oxygen and at higher incidences of solar radiation (Suess, 1976).Intensive solar radiation is a characteristics of weather feature in Iraq coupled with relatively high water temperature during summer (Table 5) leading to high evaporation rate and increase biodegradation processes by microorganisms (Al-Edanee et al., 1990).Photo degradation is an important degradation pathway in aquatic ecosystems for high molecular weight PAHs (Suess, 1976).Photo-oxidation can chemically transform PAHs, and the resulting products may be more toxic and carcinogenic than the parent compounds (NRCC, 1983).
Evaporation process plays an important role in the removal of low molecular weight PAHs from aquatic ecosystems.Also PAHs are subjected to biodegradation by various microorganisms such as fungi, bacteria, and certain algae that are suspended in the water column (Gibson, 1976).Microbial degradation of PAHs is one of the main processes responsible for removing these compounds from water column.Biodegradation of PAHs depends on such factors like type of ring fusion and the number of aromatic rings (Wild et al., 1991).Whereas the highest values during winter may be attributed to the lower rates of photooxidation and microbial degradation of PAHs during winter leading to relatively higher PAH concentrations compared with summer, in addition to increase hydrocarbon compound input to aquatic environment with run off and increase for use fuel in heating during winter (Al-Khatib, 2008).
Results of the present study revealed that the total concentrations of PAH compounds were in the particulate fraction more than dissolved fraction along the period of study, this due to the tendency of PAHs to adsorb on to solid materials inaquatic ecosystems and because of their hydrophobic nature and low water solubility (Sloof et al., 1989).
The association of PAHs with the solid objects depends on their molecular weight.In addition to that PAHs adsorbed to water suspended matters are more resistant to photo-degradation (McGinnes and Snoeyink,1974).Other researchers, however, found that PAHs attached to particulate matter are more susceptible to photolysis than PAHs in solution (Neff, 1979;Moore and Ramamoorthy, 1984).
In this study HMW-PAHs were more than LMW-PAHs in both dissolved and particulate fractions in all stations along the period of study, this may be attributed to the molecular weight.(Bakhtiari, 2009;Obayori and Salam, 2010).In addition to that the low molecular weight PAHs such as naphthalene has the highest vapor pressure of PAHs, therefore volatilization in aquatic ecosystems is probably the most important removal mechanism for these compounds (Southworth, 1979).
As an individual of PAHs in dissolved fraction Benzo(a)pyrene form the greater values ranged from 0.326 to 1.365 and from 0.123 to 1.125 during winter and summer, respectively while in particulate fraction benzo(a)pyrene also form the greater values 15.134 and 4.162 in Treatment unit and Al-Zubair stations, respectively.Acenaphthene and benzo(b+k)fluornanthene compound form the higher values 2.051 and 4.316 in Al-Magidehand Al-Husaichi stations during winter, respectively Alsobenzo(a)pyrene compound form greater values 1.606, 3.791 and 1.789 in Treatment unit, Al-Husaichi and Al-Zubair stations, respectively and Benzo(ghi)perylene form the higher values 1.390 in Al-Magideh station during summer.Benzo(a)pyrene levels and other individual of HMW-PAHs like total PAHs, were higher in winter than summer probably due to increase hydrocarbon compounds input to aquatic environment with run off because much of the PAHs released into the atmosphere and eventually reach the soil and these PAHs may be washed off by rain to reach the aquatic environment, in addition to that the increase in the use of fuel in heating during Winter (Lee and Grant, 1981;Al-Khatib,2008 ).
To determine the origins of PAHs as dissolved and particulate fractions according to the following ratios.The ratio of LMW-PAHs to HMW-PAHs (LMW/HMW) had been used to distinguish between petrogenic (>1 values) and pyrogenic (<1 values) origins.The ratios LMW-PAHs/HMW-PAHs were less than one in all stations during winter and summer except in Al-Magideh station was more than one during winter.Petrogenic and natural organic matter sources of PAHs were dominated by low molecular weight PAHs, while combustion derived PAHs are predominantly of high molecular weight (Neff, 1979).The results indicate that the origin of these compounds in dissolved fraction were pyrogenic except in Al-Magideh station was petrogenic.In addition to that BaA/(BaA+Chr) ratioranged from 0.218 to 0.552 and 0.243 to 0.368 in dissolved fraction and from 0.31 to 0.46  (Guo et al., 2007).Fl/py ratio in dissolved fraction ranged from 0.23 to 1.204, while in particulate fraction from 0.150 to 1.923 during winter and summer respectively.The Fl/pyratio >1 indicates pyrogenic source and values <1 attributed to petrogenic source (Qiu et al., 2009).The results indicate that the origins of PAHs in dissolved and particulate fractions were pyrogenic from combustion sources and few of them petrogenic which come from petroleum contaminations by sewage effluents and industrial wastes which usually contained measurable levels of PAHs (Al-Khatib,2008).

Conclusion
Results of the present study revealed that the higher concentrations of PAHs were recorded in winter, where as the lower in summer.The total concentrations of PAHs were in the particulate fraction more than dissolved, also high molecular weight of PAHs were more than low molecular weight in both dissolved and particulate.According to the ratios of LMW-PAHs/HMW-PAHs, BaA/(BaA+Chr), InP/(InP+BghiP) and Fl/pythe sources of PAHs were mainly pyrogenic and few are petrogenicin these water.
Figure 1.Map of Al-Kahlaa River showing the position of stations

Table 1 .
Levels of PAHs (ng.l -1 ) in dissolved fraction during winter

Table 2 .
Levels of PAHs (ng.l -1 ) in dissolved fraction during summer

Table 3 .
Levels of PAHs (ng.g -1 ) in particulate fraction during winter

Table 4 .
Levels of PAHs (ng.g -1 ) in particulate fraction during summer

Table 5 .
Mean of water temperature( O C) during winter and summer in all stations .33 to 0.80 in particulate fraction during winter and summer, respectively BaA/(BaA+Chr) ratio <0.20 indicates petroleum source, values between 0.20 and 0.35 either petroleum or combustion sources, and values >0.35 combustion source .Also InP/(InP+BghiP) ratio in particulate fraction was more than 0.20.InP/(InP+BghiP) ratio <0.20 indicates petroleum source, values between 0.20 and 0.50 either petroleum or combustion sources and values >0.50 combustion source