Regional and Seasonal Variation of Polycyclic Aromatic Hydrocarbons in Water and Mollusca at Quarna North of Shatt AL-Arab River

Abstract Distribution and seasonal variations and sources of of the sixteen polycyclic aromatic hydrocarbons (PAHs) was studied in surface water and and fuor species of molluscs (Theodoxus Jordani, Melanoides taberculata Melanopsis nodosa, Bellamya bengalensis ) from three stations at Al-Quarna in Shatt Al Arab river during the low tide period from September, 2018 to March, 2019 . Liquid-liquid extraction was used for water samples, while PAHs in molluscs were extracted using Soxhlet Extraction and finally analyzed by means of gas chromatography. physical and chemical parameter were measured such as . Water Temperature range from (13°C to 39°C), Dissolved oxygen range from (6.5 mg/l to 3.84 mg/l),PH range from (8.15-7.17) and Electrical conductivity (2.59 ms/cm4.75 ms/cm). Results of PAHs in water samples was ranged from (1.4754ng / l) during summer in the first station to (3.4215ng / l) during winter at the third station. While the total PAHs in molluscs range from 0.876 ng/g dry weight in the T.jordani in station 1during summer to 9.093 ng/g dry weight in the B.bengalensis during winter . The Highest concentration of PAHs in the four species were arranged as fellow :Bellamya bengalensis ˃ Melanopsis nodosa ˃ Melanoides taberculata ˃ Theodoxus Jordani. When we compares the concentration TPHs in water and molluscs with other study it allies within these concentration.

molluscs tissues were placed in a pre-extracted cellulose thimble and soxhlet extracted with 150 ml methanol : benzene (1 : 1 ratio) for 24 -hours. The extract was then transferred into a storage flask. The sample was further extracted with a fresh solvent. The combined extracts were reduced in volume to ca 10 ml in a rotary vacuum evaporator. They were then saponified for 2 -hours with a solution of 4 N KOH in 1: 1 methanol: benzene. After extraction of the unsaponified matter with hexane, The sample is taken from the rotator and then placed on a chromatography column that contains the activated silicagel (2% deactivated alumina) to remove the fatty acid residue and a layer of anhydrous sodium sulphate to absorb the water, if any, (50) ml of benzene to obtain the aromatic fraction that evaporates to the extent of dehydration and then dissolved in (5) ml of hexane for the purpose of measuring the total concentration of aromatic hydrocarbons.
The procedure used by (22) was employed to determine the fat content of molluscs samples. Three grams of each freeze-dried sample was soxhlet extracted with a 2 : 1 mixture of petroleum ether and acetone for 24-hours. The extracts were reduced in volume in a rotary vacuum evaporator, and subsequently reduced to exactly 1 ml. Ten µl of the concentrated extracts were taken by a Hamilton syringe and weighted after evaporation of the solvent.

Results and Discussion: Environmental parameters
The hydrological condition of the Shatt Al-Arab River basin is affected by several factors including conditions at the upper reaches of the Tigris and Euphrates rivers, the status of advancing flood tides from the Arabian Gulf, seepage of saline ground water into the basin, as well as the impact of climate conditions prevailing in the region on discharge rates and the payload of the river (23).
The basic statistical seasonal variations for the water quality parameters are summarized in Table 1 and illustrated in Figure 2,3 ,4 and 5. Temperature is a high-fluctuations environmental factor, which consider important parameter which regulated the biogeochemical processes in ecosystem (24).Temperature affects the solubility and, consequently, the availability of gases such as oxygen in water (25). it also affects the toxicity of some chemicals in water systems as well as the sensitivity of living organisms to toxic substances (26). In this study, the variability in temperature values at the study locations may have resulted from the weather condition at the time of study (13°C to 39°C).
Shatt Al-Arab river has high values of dissolved oxygen due to continuous diffusion , mixing , and the role of phytoplankton , and occurrence of different aquatic plants,The dissolved oxygen is essential for aquatic life, as it is needed to keep organisms alive.The DO content of water is influenced by the sources, raw water temperature and chemical or biological processes taking place in the aquatic system (27) .Our results showed that the DO concentrations range from (6.5 mg/l to 3.84 mg/l).
pH is an important factor to describing the chemical processes state in water, PH mean is a measure the concentration of hydrogen ion (H+ ) in water (28) The pH results show seasonal differences but for all. Stations fall within the acceptable range of (8. 15-7.17); the average values tend to be slightly alkaline during the study period which is consistent with previous studies made on aquatic ecosystems in Southern Iraq (27,29). The pH is an important parameter that determines the suitability of water for different purposes.
EC estimates the amount of total solids or amount of total dissolved ions in water. The EC of water generally increases as the levels of dissolved pollutants and salinity increases (30). In this study, EC showed clear seasonal differences (4.75 ms/cm -2.59 ms/cm).

PAH concentration
PAHs do not usually exist as separate entities in environmental media; they are often regarded as a mixture and the total concentration of their mixture is often used to describe their distribution (31). 16 PAHs recommended by the (US EPA) were investigated, The results of the chromatographic gas system showed that concentrations ranged from (1.4754ng / l) in the summer in the first station to (3.4215ng / l) in winter at the third station(table 2,3,4 and Fig.6). The results showed that the total concentrations of PAHs introduced into the environment are higher in winter than in summer This is confirmed by (22) and (32) explained that the increase in the total concentration of PAHs in autumn and winter is due to the fact that aromatic compounds entering the environment are higher in autumn and winter due to the increase in fuel and wood burning, which is used in heating during the winter. As well as the low rate of evaporation of PAHs in the winter and reduce the effectiveness of various microorganisms in the degradation of these compounds with low temperatures (33). While low concentrations in the spring and summer are due to the warm climate of Iraq in summer, where high temperatures cause PAHs to evaporate from water (34) .High temperatures also encourage microorganisms to break down these compounds, especially low molecular weights (35) The process of oxidation is due to the long period of solar brightness and also because of the intensity of solar radiation (33). Generally, the high molecular weight (HMW) PAHs with ≥4 rings was predominant in the rivers samples . This may be attributed to their low solubility in water, less volatility due to their molecular size and higher persistence in aqueous environment when compared to the low molecular weight (LMW) PAHs (36). The major source of HMW PAHs can be linked to anthropogenic activities ( 37). HMW PAHs are more persistent than LMW PAHs in the environment due to their increased resistance to oxidation, reduction and vapourisation as molecular weight increases (38). LMW PAHs such as naphthalene and fluorene have more significant acute toxicity to aquatic organisms than HMW PAHs but are non-carcinogenic (31). Some HMW PAHs such as benzo[a]pyrene and benzo[b] fluoranthene are carcinogenic and mutagenic to a wide variety of organisms including fish, birds and mammals ( 39).

Summer season Autumn season
Winter season Spring season (Fig.6

) :Chromatograms of PAHs compounds in water samples of the studied stations during the season
While the concentration in molluscs varied from 3.672 ng /g at the third station in the summer to 7.257ng / g at the first station in the winter in the M.nodosa and from 0.876 ng/g in the summer at the first station to 3.506ng/g in the third station in the winter in the T.jordani and from 1.778ng / g at the third station in the summer to 5.924ng / g at the second station in the winter in the M.tuberculata and from 4.07 ng/g in the summer at the second station to9.093 ng/g at the second station in the winter (table 6, The current results showed that the concentrations of PAHs in the water column were lower than those in the

Summer season Autumn season
Winter season Spring season (Fig.7)

Summer season Autumn season
Winter season Spring season (Fig.8)

Summer season Autumn season
Winter season Spring season (Fig.9)

Conclusion:
Water and 4 species of Mollusca have some concentrations of Polycyclic Aromatic hydrocarbons. The Highest concentration of PAHs in the four species were arranged as fellow :Bellamya bengalensis ˃ Melanopsis nodosa ˃ Melanoides taberculata ˃ Theodoxus Jordani. The sources of PAHs came from many sources, and there is seasonal variations of PAHs in the water due to many factor such as Temperature, photooxidation and bacterial degradation.