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چکیده
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Abstract The removing of heavy metals from the environment is one of the most important issues of scientist. It was determined that the high concentrations of these elements are toxic and can have negative impact on environmental resources and living organisms. Phytoremediation can use as a type of green technology which plants can absorb and accumulate pollutants and heavy metals in their tissues and purification contaminated environments. The current study was conducted from August 2022 to January 2023 on The Shat-Al-Kufa, which is one of the two branches of the Euphrates River in Najaf governorate. Two main sites were identified which consist the beginning of the river in the city of Kufa (upstream) and the other site at the end of river from the governorate (downstream). Also, the aim of study was found out the possible pollution levels of the studied area's water and sediments. The study included two main measurements which were physical and chemical properties of water such as temperature, pH, electrical conductivity (EC), total dissolved substances (TDS), total suspended solid (TSS), permeability, dissolved oxygen (DO), biological oxygen demand (BOD), total hardness (TH), NO3, PO4, total organic carbon percentage (TOC%), soil texture. In addition, the concentrations of some heavy elements like cadmium, lead and nickel were measured in water, sediments and species of Ceratophyllum demersum L. and Potamogeton pectinatus L. and Hydrilla verticillate (L.f.) Royle to found out the ability of plants to accumulate the heavy metals inside their tissues and purifications environments. The results of the current study showed that the water temperature ranged between 12.7-34.5°C which reason for this change depend on climatic changes. The pH value in the study area was between 6.4 and 9, and in addition, the second station showed a higher pH compared to the other station because this station was closer to the sewage treatment plant and the city of Kufa. The light transmission in all of study area was between 48-150 cm so that in the first site was higher compared to the second site because the width of the river and the water flow in the first site are lower. The Electrical Conductivity (EC) recorded, total dissolved substances (TDS) and total suspended solid (TSS) were between 1160-1940 micro-Siemens\cm, 630-960 mg\l and 5-120 mg\l, respectively and high values were recorded at all stations of the second site compared to the first site because of slow movement of water helped to deposit suspended solids and increase it. The dissolved oxygen (DO) values ranged from 3.6-11.8 mg\l Dissolved oxygen values did not appear during the study period. The values of BOD5 ranged from 0.4-7.6 mg\l so that at times it exceeded the limit. Also, the total hardness (TH) recorded high values ranging from 370-720 mg\L. The No3 concentrations were between 0.245-3.269 mg\l and did not show significant variations at the study sites because these nutrients are in running water that occur in thermal application and will mix during the movement of running water. The PO4 values ranged from 0.016-10.292 mg/l and these concentrations are considered good, as the water is considered nutrient – poor if it ranges from (0.3-1 mg/l) and the high and low concentrations of phosphate in particular and nutrients in general in the water are related to the activities of agricultural lands near the river. Total organic carbon percentage (TOC%) values were close in the first and second stations and ranged between 0- 0.4% because the presence of total organic carbon (TOC%) depends on the presence of heavy elements accumulated in the tissues of dead plants that were exposed to them during their lifetime. Also, concentrations of heavy metals like cadmium, lead and nickel elements in the dissolved form were (0.033, 0.065, 0.003 µg/l), respectively while their rates in the particulate form were (6.048, 0.65, 0.028 mg/g), respectively. As concentrations of these elements like cadmium, lead and nickel elements in the sediments measured (11.931, 3.434, 0.741 mg/g), respectively, where high values were recorded at the study stations especially at the second site in the end of the river, the high and low concentrations in all stations are associated with the inefficiency of heavy water discharge stations in the treatment and removal of pollutants. It was determined that Ceratophyllum demersum accumulated large amounts of cadmium and nickl while the Hydrilla verticillate had a high ability to accumulated nickel inside its tissues compared to other aquatic plants. It turned out that the concentrations of heavy elements inside the plant are higher than in the water and aquatic plants can be way to decrease pollutants in water.
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