Assessment of heavy metals in sediments and water accumulated by effects shipwrecks in Shatt Al-Arab River, southern Iraq

In this study, the total concentration of seven heavy metals (Cd, Cu, Fe, Pb, Mn, Ni, and Zn) in sediment and water was taken to determine how much the environment is impacted by rising levels of heavy metals that are not naturally occurring in five stations representing the large shipwrecks in Shatt Al-Arab River in Basra South Iraq by using atomic absorption. The heavy metals concentration in the five sediment stations is ordered as follows: Fe>Mn>Ni>Zn>Cu>Cd> Pb. While, the heavy metals concentration in the five water stations is ordered as follows: Fe>Ni>Mn>Cu>Pb>Zn>Cd. The current results of the study indicate that the concentrations of Cd, Fe, and Pb (slightly contaminated) metals in water are higher than the Iraqi standards (Iraqi standards for drinking water) and international standards (WHO, U.S. EPA, E.U.). An increase in heavy metal concentrations is attributed to the raw materials from which sunken ships are made near stations and these ships being exposed to military bombardment. The level of pollution in the sediment was assessed by employing the Geo accumulation index (I-geo), Contamination factor (CF), and Enrichment factor (EF). The calculated results of I-geo indicate that Cd can be considered to be moderate – strongly polluted except S5 considered strong to extremely polluted. However, Cu, Fe, Pb, Mn, Ni, and Zn showed almost unpolluted levels across all stations. The CF values indicate that this environment is very highly contaminated with Cd, while CF values for Cu, Fe, Pb, and Mn display low contamination. while CF values for Ni are moderate contamination except for S1 is low contamination. The pollution level for Zn is S1and S5 is low contamination and S2,3,4 is moderate contamination. The EF values refer to Cd at S5 indicating extremely severe enrichment and other stations refer to severe enrichment and minor enrichment for Fe, Mn, Ni, and Zn. Copper (Cu) has minor enrichment at S2 but no enrichment at the other stations. Conversely, Lead (Pb) shows no enrichment at any of the stations.


Introduction
Shatt Al-Arab River originates in Al-Qurna, where the Tigris and Euphrates Rivers converge.It then flows southeastward and empties into the Arabian Gulf south of Faw.Throughout its history, the Shatt Al-Arab River has played a crucial role in the economic, social, and political 2 development of the region.Shatt Al-Arab, over the past 40 years, has experienced various types of changes, both natural and man-made.Moreover, the region surrounding Shatt Al-Arab has been marred by conflicts and wars, including the first Gulf War (1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987)(1988), the second Gulf War (1991), and the third war (2003).These wars have resulted in sunken ships, wrecks, and debris cluttering the river.Heavy metals are a group of elements that have a high weight and density they are introduced into the environment from both natural and anthropogenic origins.They are considered pollutants and can have negative effects on the environment.These elements cannot be broken down by natural processes when released into the environment.Some heavy metals, like Cadmium (Cd), have been shown to have toxic effects on organs in animals and can cause health issues in humans, such as respiratory and skin problems [1].In recent years, the increase in heavy metal concentrations has been due to human activities [2].Urban areas have both man-made sources of pollution (such as industrial and traffic emissions, coal combustion, waste incineration, and agricultural waste) and natural sources [3].Heavy metals are naturally present in water, sediments, plants, and animals, but can also be released into the environment through processes like rock weathering, soil leaching, forest fires, and other natural factors [4].These apparent and sunken shipwrecks and debris represent major environmental pollutants through their large size, interception of the river flow, their load, and the way they sank.This study aims to determine how much the environment is impacted by rising levels of heavy metals that are not naturally occurring in water and bottom sediments.

Location of study area
The Shatt al-Arab contains more than 100 sunken marine pieces, representing marine pieces or debris, and these marine pieces are submerged in water (completely or partially).Five stations were selected that represent the identified shipwrecks which has the most environmental impact, study area map was drawn by Arc GIS, figure 1.

Materials and Methods
The stations were selected and identified using previous information and the Sub-Bottom Profiling technique (SBP).SBP is an acoustic investigation method used to map the sub-bottom of a river cross-section where sound waves are emitted through a transducer or an array of transducers towards the riverbed using a specific frequency for the mapping and analysis of the geological features beneath the riverbed [5].Many shipwrecks were identified in the stream of the Shatt al-Arab River where these shipwrecks serve as barriers that trap and accumulate river sediments in their vicinity.Sediments and water were studied in this research to determine the impact of these shipwrecks on the selected stations.Water samples were gathered from five stations on 26 Jun 2022, with each station being below the water surface by a depth of 20 to 30 cm.Approximately 5 liters of water were collected directly into polyethylene containers for analysis of heavy metals.The samples were digested and then the concentrations of the elements were measured using a flame Atomic Absorption Spectrophotometer device [6].Water and sediment samples were analysis carried out in laboratories of the Marine Science Center (at Basrah University) and tests were carried out in Basrah oil company (laboratories of Naher Omer oil field).Sediment samples were obtained from each station using a Van Veen grab sampler, and the water was drained off before being preserved in polyethylene bags.Detailed information was recorded on the bag for each sample.The sediment samples were thoroughly mixed after removing the solid parts and then dried at a temperature between 60-70 degrees Celsius for 48 hours.They were then ground using a mortar and sieved through a 63-mesh sieve.The resulting sediment was stored in polyethylene containers.Heavy metal ions (including cadmium, copper, iron, lead, manganese, nickel, and zinc) were extracted from the sediment samples after digestion with acids.The levels of these elements were measured using an Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-OES) [7].
To prepare the samples, the sediment was washed multiple times with distilled water.Then, 5 ml of concentrated nitric acid was added to the sample and heated on a hot plate until nearly dry, followed by cooling.A mixture of concentrated hydrofluoric acid (HF) and concentrated chloric acid (HCIO4) in a 1:1 ratio was added to extract the heavy metals.This mixture was also heated on a hot plate until nearly dry.Then, 30 ml of 0.5N hydrochloric acid (HCl) was added to the sample and left on a hot plate to ensure incomplete digestion of the precipitate.The sample size was reduced to less than 25 ml, after which the volume was completed to 50 ml.The final solution was transferred to plastic bottles and labeled before measuring with the ICP-OES device [8].

Determination of geo accumulation index
The geo-accumulation index (I-geo) is a measure of the accumulation of different metals in sediment [9].It is calculated using the formula: Where Cn is the measured concentration of element n in the sediment and Bn is the geoaccumulation background for element n.The background value can be either directly measured in sediments from the area before human civilization or taken from the literature, specifically using the average shale value described by [10].The factor 1.5 is included to account for possible variations in the background values due to lithological variations [11].I-geo classify sediment pollution to 7 classes, table 1

Determination of Contamination factor (CF)
The current study utilized the contamination factor (CF) to assess the contamination status of sediment.CF was determined below the formula: Where Mc is the concentration of the metal, and Bc is the background concentration of the same metal.Based on the contamination factor, four categories of contamination were identified according to [12], table 2

Determination of enrichment factor (EF)
The magnitude of source material can be evaluated by comparing it to the abundance of species found in the Earth's crust [10].The enrichment factor (EF) is calculated using the following equation [13]: Where (CM / CFe) sample is the ratio of the concentration of a trace metal (CM) to that of iron (CFe) in the sediment sample, and (CM / CFe) Earth's crust is the same ratio in the Earth's crust.The reference value of iron (Fe) at 5.2% is chosen as the reference element due to its dominance in the Earth's crust and its immobility.Based on the calculated EF value, different levels of enrichment can be determined [14], table 3:

Heavy Metals concentration
To assess the concentration of metals in Shatt AL-Arab sediments near large marine wrecks, it is crucial to establish permissible levels for these metals.Anthropogenic sources can introduce heavy metals into the aquatic system, making it important to determine their distribution and concentrations in the sediments.This data can help identify the source of pollution in the aquatic systems [15].
According to the study's findings in table (4), the range of concentration in the five sediment stations include: Cd:(  Many studies have found similar results, indicating that there are no significant differences in total metal concentration among different stations.It is likely that the variation in concentrations is a result of the complex interactions between multiple factors that influence the levels of total metals.The outcome of the current study on sediments in the identified shipwrecks in the Shatt al-Arab corresponds with previous studies conducted in the same area table (5).

C: Station 5 Oriental
The contamination of water with heavy metals poses a significant environmental concern due to their long-lasting presence, toxic nature, and inability to degrade naturally [20].Heavy metals have an important role in aquatic ecosystems, with certain amounts being necessary for various organisms.However, human activities have led to elevated levels of these elements in water sources [21].The concentrations of heavy metals in the water in the current study were as follows table (6): According to the study's findings in table (6), the range of concentration in the five water stations include: Cd:( The current results of the study indicate that the concentrations of cadmium (Cd) and iron (Fe) metals in water are higher than the Iraqi standards (Iraqi standards for drinking water) [22] and international standards World Health Organization (WHO) [23], U. S. EPA (U. S. Environmental Protection Agency) [24], European Union (E.U.) [25].The concentration of lead (Pb) in water was higher than the standards of WHO and EU.The concentration of nickel was higher than the EU standards table (4).An increase in heavy metals concentrations is attributed to the raw materials from which shipwrecks are made, which affect the concentration of these materials.In addition to these ships being exposed to military bombardment.Differences can be noted in the ratios of distribution of heavy metals in sediments and water for each metal in all stations, as shown in figure 3.

Indices
The metal contamination levels in the sediment samples were evaluated using different indices such as the Geo-accumulation index (I-geo), Contamination Factor (CF), and Enrichment Factors (EF).To establish background values, data on the average heavy metal content in surface rocks worldwide were obtained from [10].

Geo-accumulation index
The calculated results of I-geo (table 8) indicate that Cd can be considered to be moderatestrongly polluted except S5 considered strong to extremely polluted.However, Cu, Fe, Pb, Mn, Ni, and Zn showed almost unpolluted levels of across all stations.

Contamination factor (CF)
Sediments have long been utilized as a way to gauge environmental conditions, particularly when it comes to detecting heavy metal pollution sources and monitoring the presence of contaminants.
The build-up of metals in sediments is heavily influenced by factors such as the composition of the sediment and the conditions governing the dissolution and precipitation processes [7].The contamination factor (CF) was employed in this study to evaluate the extent of metal contamination in the sediment.
In the heavy metals of sediments of the Shatt Al-Arab, the average CF values for various heavy metals follow the order: Cadmium (Cd) has the highest value, followed by Nickel (Ni), Zinc (Zn), Manganese (Mn), Iron (Fe), Copper (Cu), and Lead (Pb) (table 9).For all stations, the CF value for Cd is >6, indicating that this environment is very highly contaminated with Cd, while CF values for Cu, Fe, Pb, and Mn display low contamination.while CF values for Ni are moderate contamination except for S1 is low contamination.The pollution level for Zn is S1and S5 is low contamination and S2,3,4 is moderate contamination.

Enrichment factor (EF)
To estimate the abundance of metals in sediment samples, Enrichment Factors (EF) were utilized.EF was determined by comparing the concentration of each metal being tested with that of a reference metal [26].The commonly employed reference metals for this purpose are Mn, Al, and Fe, [27].In this research, iron was employed as a marker to distinguish between and anthropogenic components.This was based on the assumption that iron content in the earth's crust has not been significantly affected by human activities.Iron was chosen as the normalization element because its contribution mainly originates from natural sources (98%), [28] according to [29].

Acknowledgment
The research presented in this paper was conducted with support from the University of Basrah.The authors would like to express their gratitude to the Marine Science Center at Basrah University for their assistance.Additionally, the researchers would like to thank the laboratory management of the Naher Omer oil field for providing the required facilities and their assistance during laboratory analysis.

Figure 3 .
Figure 3. Distribution of heavy metals in sediments and water at each station for different metals, were: A: Cadmium, B: Copper, C: Iron, D: Lead, E: Manganese, F: Nickel, G: Zinc.

Table 2 .
. Contamination Factor Indicate (2) metals concentration is order follows: Fe>Mn>Ni>Zn>Cu>Cd> Pb.The Cadmium results indicate that the highest value of cadmium was in sediment at station 5 (7.11 μg/gm) which represents the sunken ship Oriental Star (cargo ship from Panama, 138 meters long and 19 meters wide).It was sunk in 1980 during the First Gulf War and is located north of Abu Floos port.The highest metals concentrations in the sediment of iron (Fe) (34800 μg/gm), lead (Pb) (1.09 μg/gm), manganese (Mn) (611 μg/gm), nickel (Ni) (153 μg/gm), and copper (Cu) (37 μg/gm) are found in station 3, which refers to the sunken Bolivar ship (a cargo ship from Panama, 100 meters long and 21 meters wide, that sink nearly Al-Maaqal port after bombed during the First Gulf War.An increase in the metal concentration in this station due to the materials that the ship was made and this ship was bombed with military ammunition.The highest concentrations of zinc and copper metals in sediment were at Station 2, which refers to a sunken ship in Al-Maaqal port called the Culf Hero, a ship from Panama, 150 meters long and 18.6 meters wide, that was bombed during the First Gulf War figure(2).

Table 5 .
Heavy metals concentrations in sediments (μ g/g) in the present study as compared with the other previous studies in Shatt Al-Arab A: Station 2 Gulf Hero B: Station 3 Bolivar

Table 6 .
Concentration of heavy metals in water in ppm unite (μg/l)

Table 8 .
I-geo for heavy metals sediment samples

Table 9 .
Contamination Factor (CF) for the sediments samples of the Shatt Al-Arab 10e average EF values for heavy metals in sediments are as follows: Cd>Ni>Zn>Mn>Fe>Cu>Pb, according to table10.Cadmium at S5 indicates extremely severe enrichment and other stations refer to severe enrichment.On the other hand, the EF values suggest that stations have only minor enrichment for Fe, Mn, Ni, and Zn.Copper (Cu) has minor enrichment at S2 but no enrichment at the other stations.Conversely, Lead (Pb) shows no enrichment at any of the stations.The levels of Cd, Fe, and Pb (slightly polluted) metals in water are exceeding both the Iraqi and global standards.The rise in heavy metal concentrations is believed to be a result of the materials used in the shipwrecks where stations, as well as these vessels being subjected to military attacks.2-The results of the I-geo analysis can be considered that the levels of Cd can be classified as moderate to strongly polluted, except station S5 which is considered to be strongly to extremely polluted.However, Cu, Fe, Pb, Mn, Ni, and Zn demonstrated nearly unpolluted levels at all stations.3-The CF values indicate that the presence of Cd in this environment is highly contaminated, while the contamination levels for Cu, Fe, Pb, and Mn are low.The CF values for Ni suggest moderate contamination levels, except station S1 which shows low contamination.As for Zn, station S1 and S5 display low contamination levels, while stations S2, S3, and S4 demonstrate moderate contamination levels.4-The EF values reveal that station S5 exhibits extremely severe enrichment of Cd, while the other stations show severe enrichment.Fe, Mn, Ni, and Zn exhibit minor enrichment at all stations.Copper (Cu) displays minor enrichment at S2, but no enrichment is observed at the other stations.In contrast, Lead (Pb) does not demonstrate any enrichment at any of the monitoring stations.
Table10.Enrichment Factor (CF) for the sediments samples of the Shatt Al-Arab