Environmental assessment of Heavy Metals in Sedi - ments of Tigris, Euphrates, Shatt Al-Arab rivers and northern west of Arabian Gulf.

The most prevalent environmental contaminants found in sediments that suggest the presence of effluents from both home and industrial sources are thought to be heavy metals. The aim of this study was to assess the accumulation of heavy metals at surface sediment samples that were collected in order to measure the amounts of Cu, Zn, Pb, Cd, and Fe., to re-evaluate the environmental conditions and concentration of the analyzed elements in the sediment to detect any pollution of heavy metals in the studied area by using contamination factors (CF), Enrichment Factor (EF) and geo accumulation index (I-geo). To ascertain the connection between the sediment’s total organic carbon (TOC) level and heavy metal pollution, measurements were taken in addition of it. Using the inductively coupled plasma atomic emission spectrometer, studies were conducted., The mean values of the element in the sediments ranged as: Cu (13.45 μg/g at location 2 to 32.44 μg/g at location 9), Zn (20.76 μg/g at location 1 to 42.49 μg/g at location 10), Pb (9.78 μg/g at location 2 to 30.04 μg/g at location 9 and 10), Cd (7.89 μg/g at location 2 to 18.72 μg/g at location 7) and Fe (459.89 μg/g at location 1 to 833.83 μg/g at location 7) dry weight. The geochemical results show that the distribution and concentration of the heavy metals in the studied sediments is within the average concentration given for the FAO/WHO reported, and the sediment of the studied area is still free from pollution, except Pb and Cd in some local areas, which shows higher concentrations than those reported for world sediments.


Introduction
Heavy metals are persistent, non-degradable, and have the potential to bioaccumulate in the environment, making heavy metal pollution a major worldwide issue.[1].
Sediment contamination occurs when heavy metals accumulate in sediment from both natural and anthropogenic sources.A report has shown that heavy metal concentrations in sediment have been increasing over time [2].Heavy metals are released into the aquatic environment through natural geological and erosion processes [3].Rainwater that falls on the soil's surface can dissolve or suspend these metals, which are found in rocks and sediments.They can also be carried by wind as suspended particulates from one place to another through the atmosphere.Another naturally occurring cause of heavy metal contamination is volcanic activity, which can produce acid rain that is laden with harmful substances among other pollutants.Excessive trace metal concentrations in rivers, lakes, and seas are also a result of natural occurrences including leaching, weathering of rocks, and volcanic eruptions.[4].In addition to natural sources, industrial processes contribute significantly to environmental heavy metal pollution.These industries include, among others, the manufacture of gasoline, oil refineries, iron and steel factories, copper, glass, aluminum, tanner facilities, fertilizers, and pesticides.[5].1300 (2024) 012026 IOP Publishing doi:10.1088/1755-1315/1300/1/012026 2 These activities release heavy metals into the environment, leading to contamination of water sources, soil, and air.Therefore, it is crucial to regulate and monitor the discharge of these pollutants to minimize their impact on the environment and human health [6].
Some of the most important pollutants in the aquatic environment are heavy metals.The sediment particles settle down to the bottom of the water body and play a crucial role in returning these pollutants back to water systems, as noted by [7].However, the sediment and its component elements show the type and amount of pollution when these pollutants are reintroduced into the water column either by mixing or by passing via the food chain.This information can provide evidence of the quality of the sediment and the nature of its source.Once heavy metals enter rivers, they rapidly accumulate within the sediment, reaching notably higher concentrations in the sediment compared to the surrounding aquatic environment of the river system [8].
Heavy metals concentration in rivers is influenced by various factors, such as temperature, salinity, pH, and surface area of organic and mineral components in the river [9].Heavy metals can exist in various forms in the aquatic environment, including dissolved substances, suspended particles, benthic sediments, and crystalline particles in the minerals that make up river sediments [10].Sediments are considered a more reliable indicator of heavy metal contamination as they accumulate these substances over time.Clay minerals are particularly effective at adsorbing heavy metals in the sedimentation environment, and therefore, sediments with particles smaller than 2 microns are of particular interest since they tend to have high concentrations of heavy metals [11].
The aim of the present study was to determine the levels of Cu, Zn, Pb, Cd, and Fe in sediment samples and to reassess the current environmental situation of the research area by evaluating the levels of heavy metal pollution.The level of heavy metal pollution in the sediment was assessed using geoaccumulation index (I-geo), enrichment factor (EF), and contamination factors (CF).

Materials and Methods
Ten samples of sediment were taken from various locations, including the Tigris River at location 1, the Euphrates River at location 2, the Shatt Al-Arab at  In this study, heavy metal analysis was performed on the sediment's <63 µm fraction, which, after drying and grinding, was separated by sieve.The amounts of heavy metals in the sediment samples were ascertained by applying the procedure outlined in reference [12].In particular, each sample was treated to a mixture of concentrated HCl and HNO3 (1:1), which was then evaporated to almost dryness on a hotplate at 80 °C.Next, HF (1:1) and concentrated HCLO4 were mixed together and the mixture was heated until it was almost dry.After adding 20 milliliters of 0.5 HCL, the mixture was allowed to cool for ten minutes before being transferred into a 25 milliliter plastic volumetric flask.After doing this twice, all of the supernatants were mixed and stored in advance of a Pye-Unicam Atomic Absorption trace metal analysis.
The sediment samples were subjected to grain size analysis using the method outlined in reference [13].Additionally, the Total Organic Carbon (TOC) content in the sediment samples was determined by following the exothermic heating and oxidation procedure with chromic acid, as described in reference [14].In this method, 0.3 g of the dry, ground sample was used for the analysis.
The following formula was used to determine the degree of contamination represented by the contamination factor (CF) [15]: CF= (metal content into the soil) / (metal content in the natural reference soil).Four categories were used to categorize the contamination factors [16].When CF < 1, low contamination factors are indicated.One can designate mild contamination factors as 1< CF <3, large contamination factors as 3 < CF < 6, and very high contamination values as CF > 6.
The Enrichment Factor (EF) has the following definition, according [17]: EF = (M/Fe sample)/ (M/Fe background) In this case, (M/Fe) background is the ratio of metals to Fe concentration in a background, and (M/Fe) sample is the ratio of metals to Fe concentration in a sample.The following numbers represent the levels of enrichment: EF <1 indicates no enrichment, EF = 1-3 minor enrichment, EF = 3-5 moderate enrichment, EF = 5-10 moderate to severe enrichment, EF = 10-25 severe enrichment, EF 25-50 very severe enrichment.
According to [18], the geo accumulation index I-geo values were determined for several metals in the format described below: I-geo = log2 (Cn / 1.5 Bn) Whereas the observed concentration of element n in the soil is denoted by Cn, whereas the geo accumulation background for element n is represented by Bn, which can be obtained from the average shale value reported by [19] or directly measured in the precivilization soil of the region.If the background sample, is I-geo <1 basically unpolluted, then the sample is 1-2 unpolluted to moderately polluted, 2-3 moderately polluted to polluted.3-4 heavily polluted, 4-5 strongly to severely polluted, and >5 extremely polluted.

Result and Discussion
The element's mean values in the sediments ranged as: Cu (13.45 µg/g at location 2 to 32.44 µg/g at location 9), Zn (20.76 µg/g at location 1 to 42.49 µg/g at location 10), Pb (9.78 µg/g at location 2 to 30.04 µg/g at location 9 and10), Cd (7.89 µg/g at location 2 to 18.72 µg/g at location 7) and Fe (459.89µg/g at location 1 to 833.83 µg/g at location 7) dry weight (Table 1 It can be observed that the locations 1,2,3 and 4 located on the Tigris and Euphrates rivers and north of the Shatt al-Arab show lower concentrations of heavy metal pollutants compared to those locations in the southern part of the Shatt al-Arab.This is attributed to the fact that pollutants are transported by river waters and eventually settle.The upstream sources of these pollutants can lead to their transfer to downstream areas over time as they flow, where they accumulate in the sediments. Copper (Cu) is a metal that is commonly used in water pipes.Because of corrosion and improper disposal of its scrap, Cu can enter the environment either directly or indirectly through sewage sludge and wastewater treatment plant effluent.[20].
The study's results showed that the concentration of zinc (Zn) in the stations increased due to transportation, fuel combustion, and the impacts of human activity such as fishing boats.This increase could be a result of factors such as the abundant presence of silt and sand sediments in the area, its proximity to an untreated wastewater treatment facility, its closeness to landfill regions, and various other influencing factors [21].
According to reference [22], the high concentrations of Pb found in the sediment samples are likely due to nearby transportation activities, such as boat traffic, which can release lead particles into the air and water through the combustion of gasoline.This can result in a foggy suspension that spreads throughout the environment and contributes to increased pollution levels.The Khor region is significant because it is located to commercial and oil ports, such as Khor Al-Zubair and Um Qaser, where commercial and oil goods are loaded and unloaded.The primary causes of cadmium pollution in the environment are both natural and anthropogenic processes such rock erosion, wind, rain, agriculture, burning coal and oil, incineration of waste, and industrial waste.[23] so these sources could be effected on the pollution by cadmium such as in location 6,7 and 8.
The elevated levels of iron (Fe) concentration stemmed from the abundant natural presence of iron in the Earth's crust.Furthermore, the sustainable practices of fishing vessels and human activities played a role, particularly in the buildup of iron residues and the introduction of iron oxides into the river, which carries them along [24].
An additional noteworthy observation in the sediment samples was a rise in the percentage of clay particles, which are known to facilitate element absorption, compared to other sites.The high concentration of silt and sand sediments in the area, the close vicinity to a wastewater treatment facility that receives untreated water, and the close proximity to landfill zones are a few possible explanations for this increase.Reference [25] provides further insights into these factors.The Al-Ashar, Abu-Alkasib, and Al-Fao stations are experiencing continuous contamination, which is mostly being caused by the dumping of untreated sewage and industrial waste.The situation for the people living in these cities has been made worse by the growing urban population and urbanization.However, the transportation of manure discharges, land runoff, street runoff, and industrial and municipal wastewater-all of which contribute to river pollution-through urban rivers is essential.[26, 27, 28, and 29].
Table (  Table 3. Enrichment Factor (EF) of heavy metal in sediment of study area.
The present study's (I-geo) index of trace metals generally refers to basically unpolluted levels of Cu, Zn, Pb, and Fe.CD, on the other hand, was severely to severely contaminated.Total Organic Carbon (TOC%) analysis (Table 5 and Fig. 3) reveals high values 1.65 at location 6 and lower values 0.22 at location 10.Metals are released into the environment by humans through a variety of operations, including mining, smelting, burning fossil fuels, and disposing of industrial waste.Metals are released into the environment as a result of these operations.Large ships that have sunk at various Shatt al-Arab locations have also had an impact on the sediment's rising heavy element concentrations.

Locations
The transportation of metal loads mostly occurs through water, either in a dissolved state or as particulate matter.The majority of these metals eventually find their way into the sea through river flow or runoff from land.Moreover, rainwater plays a crucial role in carrying certain metals, notably Cadmium (Cd), Copper (Cu), Zinc (Zn), and especially Lead (Pb), from the atmosphere to the sea.This process adds to the metal pollution in aquatic environments, further impacting marine ecosystems and coastal regions.Appropriate measures are essential to manage and mitigate the harmful effects of metal pollution on the environment and marine life [29].
Regular Monitoring and Assessment, Reduce Emissions and Sources, Waste Management, Effluent Treatment, Educate and Raise Awareness, Phasing Out Hazardous Materials and Support research into more effective and sustainable pollution control technologies, all of these will Managing and mitigating the impact of heavy metal pollution.
Upon comparing our data with that presented in Table (6), we observed that our results fall within the range of values reported in other studies conducted in the region.

Conclusion
The results showed that, with the exception of a comparatively low percentage of Cd, the heavy metal concentrations in the sediment samples were considerable.They were done as follows in order: Fe > Zn > Cu > Pb > Co > Cd.
Increased levels of specific heavy metal concentrations in the sediments at the down of the river due to transport of these from upstream to downstream area.
Elevated concentrations of heavy metals were detected at Al-Ashar and Abu-Alkasib, with additional findings of heightened levels at Khor Al Zubair and Al Faw.The presence of heavy metals in sediment pollution is presumed to originate from diverse sources, including urban waste, oil refineries, industrial effluents, runoff from land, and boating activities.This study can serve as a foundational investigation for future research projects.

Figure 2 .
Figure 2. Mean concentrations of Heavy metals in different locations in sediment of study area.

Figure 3 .
Figure 3. TOC% in the sediment of study area.

Table 1 .
(a) Concentrations of Heavy metals in sediment samples (µg/g dry weight) at study area.

Table 1 .
(b) Concentrations of Heavy metals in sediment samples (µg/g dry weight) at study area.
2) displayed the contamination factors (CF) values.The sediment under investigation revealed the following contamination factors: Cu (0.22 -0.54), Zn (0.29 -0.60), Pb (0.69 -2.14), Cd (52.62-124.80),and Fe (0.008 -0.01).The low contamination factors in Cu, Zn, and Fe were generally referred to as the heavy metal contamination factors in the current study.Pb and Cd were found to have moderate and high levels of contamination, respectively.

Table 3
displayed the values of the enrichment factors (EF).It is reported that Cu (25.73-56.55),Zn(32.68-62.96),Pb(80.18-224.46),Cd(5940.36-10735.33),andFe (1) were the enrichment factors in the sediment under investigation.The minor enrichment factors in Fe were generally referred to as the enrichment factors of heavy metals in the current investigation.Zn, Pb, and Cd enrichment factors were extremely severe, whereas Cu was very severe.

Table 2 .
Contamination Factor (CF) of heavy metal in sediment of study area.

Table 4 .
Geo accumulation (I-geo) index of heavy metal in sediment of study area.

Table 5 .
TOC% in the sediment of study area.

Table 6 .
The current study's heavy metal concentrations (µg/g) in the sediment sample were compared to those of other earlier investigations.