Water Quality and Radionuclides Content Assessment of the Al-Najaf Sea: Case Study

The Al-Najaf state is witnessing an increased economic development and attracting more investments that require the development of new areas and exploring new water resources. This study evaluates the quality of 12 surface water samples and groundwater from 12 wells for irrigation according to the salinity and sodicity hazards based on electrical conductivity (EC) and sodium adsorption ratio (SAR). In addition, the concentrations of radionuclides, which include Thorium (232Th), Uranium (238U), Potassium (40K) and Cesium (137Cs) were tested in four soil samples in the study area. It was found that the average values of pH, total hardness, Na, Ca, Mg, K, Cl, SO4, NO3 for groundwater and surface water were 8 and 6, 2287 and 4006 mg/L, 1140 and 1232 mg/L, 378 and 637 mg/L, 327 and 587 mg/L, 2 and 2 mg/L, 989 and 2007 mg/L, 1149 and 1325 mg/L, as well as 2 and 2 mg/L, respectively. From salinity and sodicity hazards analysis, the groundwater had EC of 5242 μS/cm and SAR of 61, whereas surface water had EC of 6253 μS/cm and SAR of 50. Furthermore, the concentrations of radionuclides, i.e. 232Th, 238U, 40K and 137Cs in the soil samples were found to be 11.02, 34.12, 544.45, and 1.6 Bq/kg, respectively. The concentrations of radionuclides were within the worldwide baseline, expect for 40K. The study concluded that both water sources are classified as very high salinity and sodium water (class C4-S4), and it cannot be used for irrigation, only suitable for the salt tolerant crops.


INTRODUCTION
Water is an essential resource for humans' consumption and irrigation. Due to increased urbanization and human population, agricultural and industrial expansions demand more water. Furthermore, the water supply is affected by the water characteristic, which is caused by anthropogenic activities including city expansion, industrial and agricultural growth, and natural processes like precipitation quantity, weather condition, and residue transport (Bouaroudj et al., 2019). Poor quality of irrigation water has adverse effects on crop production and its quality, as well as the public health of farmers and consumers who are directly involved with irrigation water. The water quality impact assessment is measured by the irrigation water effect on soil and crops. Monitoring the irrigation water quality is therefore essential to improve crop yield and soil condition under good management practices. Thus, special management practices are needed to overcome poor Water Quality and Radionuclides Content Assessment of the Al-Najaf Sea: Case Study water and soil quality in order to increase crop production and yield (Etteieb et al., 2017).
It was found that the primary drawbacks in irrigation water and soil are salinity, ion toxicity, and sodicity. The amount of soluble salts concentration in irrigation water that may affect crops is referred to as salinity. Toxicity indicates the crucial levels of chloride (Cl -), boron (B 3+ ), sodium (Na + ) and certain trace elements, which have a negative effect on plant growth. Sodicity refers to the deterioration of soil structure due the presence of sodium in excess, which can reduce water diffusion to the soil (Zaman et al., 2018b). In this regard, the United Nations Food and Agriculture Organization (FAO) has set the permissible limits of several quality indicators for water to be suitable for irrigation (Ayers & Westcot, 1985).
On the basis of the US Salinity Laboratory Staff (USSLS) (US Salinity Laboratory Staff, 1954) report, the data on electrical conductivity (EC) and sodium adsorption ratio (SAR) can be linked to a classification diagram of sixteen classes (C1-C4 and S1-S4) for the purpose of examining the suitability of water for irrigation. However, this classification diagram is only valid for EC below 2250 μS/cm. Since higher values of salinity is generally observed in the irrigation waters, Shahid SA and Mahmoudi H (2014) has modified the USSLS classification diagram to provide the water salinity at higher values equal to 30 000 µS/cm.
In Iraq, high demand for food security requires the development of new agricultural areas and new irrigation water resources. Unfortunately, most of the lands surrounding fresh surface water (the Tigris and Euphrates rivers) are used; thus, there is a need to develop new agricultural lands nearby to utilize alternative water resources such as lakes and marshes. Recently, the Al-Najaf state has been witnessing an increased economic development and attracting more investments. In this regard, several projects have been initiated in the Al-Najaf Sea area due to its strategic location and available resources. The Al-Najaf Sea is noted as one the essential wetlands which is located in the southwestern part of Iraq. Concurrently, the interest to the Al-Najaf Sea has increased in order to benefit from its surface water and groundwater sources. Consequently, it is important to identify the quality and suitability of the surface water and groundwater for irrigation and other consumption demands in this area. However, there are very limited reliable studies comprising the full assessment of the Al-Najaf Sea water resources quality, as well as radioactive elements in soil.
Thus, the intentions of this investigation were to examine the groundwater and surface water of the Al-Najaf Sea for its quality, and to evaluate their utilization for irrigation based on sodium adsorption ratio (SAR) and electrical conductivity (EC). Concurrently, the study aimed to determine the concentrations of radionuclides including Thorium ( 232 Th), Uranium ( 238 U), Potassium ( 40 K) and Cesium ( 137 Cs) in the soil samples.

Study Area
The study area is the Al-Najaf Sea (Bahr Al-Najaf), located west of the Al-Najaf Governorate between longitudes 32°00'39.6"N & 44°13'53.2"E, as shown in Figure 1. The Al-Najaf Sea is considered one of the key depression wetlands in Iraq that is located in the lower parts of Iraq, in a region called the Middle Euphrates to the west of the Euphrates River, and 2 km west of the Al-Najaf city. Geologically, the Al-Najaf sea area is located within the boundaries of the Al-Salman subzone including the stable shelf. The exposed rocks are sedimentary rocks of the upper Quaternary and Cretaceous period. The area increases steadily from northeast to southwest 50 m every 10-15 km, whereas, it declines gradually from the southwest and west to the north east and north.
Currently, its lowland is filled with water due to the surface runoff during winter via wadies, effluents from industries, agriculture lands and fish farms via marshes, and flow of groundwater to the surface via wells. The area of study is characterized by some wades that discharge stormwater from the west and south-west to the east and northeast directions which is associated with the declined route of the regional topography. Additionally, the groundwater in the area is recharged from other depressions nearby and also from declined underground channels from Euphrates. The climate in the area is commonly sub-arid to arid with an average of humidity of 41%, wind speed of 10 km/hr, evaporation of 3483 mm/year, precipitation of 1.3 mm/year and temperature of 24°C.

Sampling and experimental work
Twelve groundwater samples were frequently taken from twelve wells at 20 m depth, twelve surface water samples were frequently taken from the Al-Najaf Sea, and three soil samples were taken from the surrounding area. The water samples were collected monthly for examination from March 2019 to February 2020 to cover all four seasons, and only average values of 12 months were reported. In order to assess the quality of the ground and surface waters in the Al-Najaf Sea, the chemical characteristics were tested, including pH, EC, TH, Na + , Ca +2 , Mg +2 , K + , Cl -, SO 4 -2 and NO 3 . The soil samples were also tested to determine the concentrations of radionuclides like 232 Th, 238 U, 40 K and 137 Cs.

Water quality evaluation
Many techniques have been applied for the quality criteria examination of irrigation water. In this study, the quality of irrigation water in the study area was examined by using the US Salinity Laboratory Staff (USSLS) classification (US Salinity Laboratory Staff, 1954). In this classification diagram, salinity and sodicity hazards are considered by incorporating the data on electrical conductivity (EC) and sodium adsorption ratio (SAR). The SAR is defined by the following equation (1) to measure the relative concentration of sodium ions (Na) to calcium ions (Ca) and magnesium ions (Mg).

SAR =
According to the USSLS classification (US Salinity Laboratory Staff, 1954), the irrigation water sodicity can be categorized based on SAR, i.e. low hazard (SAR<10), medium hazard (10-18), high hazard (18-26) and very high hazard (>26). On the basis of the diagram of the USSLS classification, irrigation water is classified into four types C1, C2, C3 and C4 based on salinity hazard and S1, S2, S3, and S4 based on sodium hazard. However, the USSLS classification [5] diagram is only valid for EC below 2250 μS/cm. Since the value of water salinity is generally observed in the irrigation waters is higher than 2250 µS/cm, thus, Shahid SA and Mahmoudi H (2014) modified the USSLS classification diagram to accommodate higher water salinity values up to 30000 µS/cm. In addition, the total hardness (TH) of water (expressed as CaCO 3 ) can be computed by Eq. (2).

Characteristic of surface water and groundwater
The water samples from 12 wells and 12 locations around the Al-Najaf Sea were tested for chemical characteristics, and the results are listed in Table 1, and compared with the permissible  (Ayers & Westcot, 1985).
pH. For groundwater, the water pH was varied from 6.8 to 8.3 (moderately alkaline) within the permissible limits. The alkaline level of groundwater reflects relatively higher concentrations of bicarbonates, indicating a limestone and gypsum aquifers in the area of the Al-Najaf Sea. In contrast, the surface water pH ranged from 5.1 to 6.8 (moderately acidic) with 75% of the samples slightly below the permissible limits. This might be due to anthropogenic activities like fish farming and use of nutrients, breakdown of organic substances, and high surface water temperature. The irrigation water with poor pH values can cause the potting material to become too acidic which then can restrict the plant root growth, leading to rapid breakdown of fertilizers, and nutrients deficiency caused by excessive rinsing of phosphorus, potassium, magnesium, aluminum and iron (Zhao et al., 2013). On the other hand, a pH value of less than 6 occurs so often in nature that is considered as neutral. However, since the soil can alter the water pH and majority of crops have pH tolerance at a wide range of water pH [3], thus the pH of irrigation water is not a reliable parameter for water quality.
Total hardness (TH). Water hardness (expressed as CaCO 3 ) shows the presence of metallic cations (Ca 2+ and Mg 2+ ), and it can be calculated using Eq. (2). The TH showed that both water sources are very hard according to total hardness classification of water by US Environmental Protection Agency (US EPA) (1986), as listed in Table 2. High levels of TH do not cause health risk; however, it is considered as an undesirable feature in water. The observed high TH in both  water sources is related to the main soil types in the area investigated, where limestone and gypsum are the most dominant formations. Cations content. Sodium (Na + ), calcium (Ca 2+ ), magnesium (Mg 2+ ) and potassium (K + ) are the primary soluble mineral cation salts. Figure 2 shows the total ionic content fraction (%) for both water sources. For groundwater and surface water, the concentrations of Na, Ca, Mg, and K were in the following ranges: 1000-1300 mg/L and 852-1512 mg/L, 303-591 mg/L and 445-796 mg/L, 132-400 mg/L and 451-700 mg/L, and 1.9-2.6 mg/L 1-3.8 mg/L, respectively. For both water sources, Na + was the most dominating cation, compared to a moderate content of Ca and Mg and trace level of K. Na was the most dominant soluble cation, followed by a moderate content of Ca and Mg, and trace level of K. The percentage of samples exceeding the permissible limits for groundwater were Na + (100%), Ca 2+ (33%), Mg 2+ (100%) and K + (0%); while for surface water were Na + (100%), Ca 2+ (41%), Mg 2+ (100%) and K + (0%).
When sodium levels become excessive, compared to Ca and Ma proportion, soils are called sodic. High Na content increases soil swelling and aggregate breakdown due to clay soil dispersion, thus causing soil structure degradation and water penetration problems. In contrast, the soil can be easily tilled with easily permeable granular structure when both Ca and Ma are predominantly cations adsorbed onto the soil medium. Additionally, excessive absorption of Na concentration by plants is toxic, which appears in the form of leaf damage (Zaman et al., 2018b).
For both water sources, all of the Cl content was above the permissible limit, showing high a very high Cl concentration > 106 mg/L, which is classified as a serious problem. High Cl concentration in surface water may be due to the dissolution of gypsum soil and industrial effluent discharge in the area. High Cl content is alarming and considered as a major factor effecting the growth and yield of the crops. At low concentrations, Cl is an important element for plant growth, but at high concentration may be toxic. Even moderately tolerant plants are harmed by the Cl concentrations between 140 and 350 mg/L. These  The NO 3 concentrations were low (<30 mg/L) for both water sources, and classified in the class 'no problem' according to FAO (Ayers & Westcot, 1985). NO 3 is generally a product of fertilizer application, if high nitrate and bicarbonate are present, a disruption of the absorption process of iron (Fe) and other nutrients in crops may occur (Shahabi et al., 2005).

Salinity and sodicity hazards of surface and ground waters
Salinity and sodicity are important water quality parameters for the environmental values of water resources (including potential beneficial uses). In order to examine the quality of irrigation water, the USSLS classification (US Salinity Laboratory Staff, 1954) has taken into account the salinity and sodicity hazards coupled with electrical conductivity (EC) and sodium adsorption ratio (SAR) data. The EC and SAR values for both water resources compared with the permissible limits by FAO (Ayers & Westcot, 1985) are shown in Table 3, and water quality evaluation according to the USSLS classification (US Salinity Laboratory Staff, 1954) is shown in Figure 3.
Sodium adsorption ratio (SAR). The calculated values based on equation (1) were in the range (59-71) and (39-57) for groundwater and surface water, respectively. All SAR values exceeded the permissible limits by FAO (Ayers & Westcot, 1985). Relatively high concentration of Na to the concentrations of Ca and Mg results in higher SAR. While Na directly contributes towards the total salinity content and possible toxicity to vulnerable plants, its high concentration effect on the soil physical properties is a major issue. Continuous irrigation with high SAR may impress the soil permeability, leading to an infiltration problem. The excessive amounts of colloidally adsorbed Na break down the soil physical structure, leading to rigid and dense soil when it is dry and gradually becomes impenetrable to water infiltration. It is important to note that when sandy soils are irrigated with high SAR water, it is not easily depraved as compared to other type of soils [3].
According to the USSLS classification (US Salinity Laboratory Staff, 1954) showed in Figure 3, both water sources are classified as very high salinity and sodium water (class C4-S4). C4 indicated that this water is suitable for irrigation of salt tolerant crops. High rates of salinity decrease the growth of plants and makes water adsorption via plant roots difficult. This is due to high osmotic water pressure resulting from high water soluble ions at plant roots. In order to ensure the substantial leaching , it is essential to have penetrable soils and adequate drainage. S4 showed that this water is unacceptable for the irrigation purposes, but acceptable at medium or low salinity. In this study, sodicity class S4 irrigation water is still possible to be used where the soil water solution contains high Ca or it can be applied to irrigate gypsum soil (Bouaroudj et al., 2019).
Electrical conductivity (EC). EC is used to show the overall soluble salts concentration which may indicate salinity hazard in irrigation water.
The key element for soluble mineral salts are anions (chloride (Cl -), sulfate (SO4 2-), bicarbonate (HCO 3 -), carbonate (CO 3 2-), and nitrate (NO 3 -)) and cations (sodium (Na + ), calcium (Ca 2+ ), magnesium (Mg 2+ ), potassium (K + )) (Zaman et al., 2018a). It was found out from Table 3 that EC recorded a very high value of more than 3000 µS/cm for both types of water, representing a "serious problem" class for the irrigation water. In comparison, the surface water had higher concentration of EC than the groundwater, suggesting that the groundwater in the Al-Najaf Sea area is less harmful to be used for irrigation. High saline contents in surface water might be due to the evaporation of water. Moreover, both water sources are considered moderately saline water according to the saline water classification by FAO (Rhoades, 1992), as tabulated in Table 4. Although soil may contain water, high EC concentration can make accessible water for plants is less. High concentration of EC makes plants unable to compete for water with other ions in the soil solution. As the EC concentration rises significantly, unusable plant water in the soil solution can be noticed, since plants only absorb pure water from the soil (Bauder et al., 2011). According to the EC results, both water sources are mostly suitable for irrigation of medium and salt tolerance crops. A comparison can be made to the reported data (Ghalib et al., 2019), as shown in Table 5.

Radionuclides content
The sources of radionuclides are natural background radiation and anthropogenic. Due to the ionizing radiations emission from different sources, soils may contain natural radionuclides like Thorium ( 232 Th), Uranium ( 238 U) and Potassium ( 40 K), and substantially man-made radionuclides  Th was similar. This might be due to the type of surrounding mineral, chemical structure of the rock, groundwater flowrate, and ions holding in soil (Jadiyappa, 2018).
In the soil samples from the Salah Aldeen State (north-west of Baghdad) in Iraq, a study by Shaker M. Al-Jobori et al. (2013) reported that the concentration of Th 232 , U 238 , K 40 and Cs 137 were 15.83, 56.28, 323.61 and 4.43 Bq/kg. The concentrations of Th 232 , U 238 and Cs 137 were slightly higher that these reported in this study, while the concentrations K 40 were lower. The main variation in the Cs 137 concentration is due to the changes in the soil structure by the human activity. 137 Cs is bound in the soil surface layers, washed away and redeployed into ecosystem. 137 Cs was found in the environment mostly as a result of the nuclear weapons activities and the Chernobyl nuclear plant accident in 1986. (Jadiyappa, 2018). The concentration of Cs 137 is expected to be less towards the southern hemisphere, which was also proven by this study as the Al-Najaf Sea area (South-west of Baghdad) is south of Salah Aldeen State.
From 1990 to 2000, Iraq has recorded increased birth defects from 3. In comparison, the levels of 238 U and 232 Th were much higher than these reported in our study. Such health defects might be associated with people's exposure to uranium. Uranium is found at changing low concentration in soil, food, water, and air. The people who consume the yields farmed in contaminated soil and live nearby hazardous locations may suffer a stronger exposure  According to the "soil-plant-animal-human" chain, plants are the main recipients of radioactive contamination to the food chain, where plant root systems absorb the radionuclides from the soil, resulting in ingestion exposure. The absorption of radionuclides from the soil by plant roots depends not only on the physiology of plant roots but also on processes in the soil (UNSCEAR, 2000). High concentrations of radionuclides may gradually accumulate in the food chain, causing health hazards and may lead to serious diseases like cancer in human being. However, the values of radionuclides in this study are still within the acceptable limit and no contamination may occur.

CONCLUSION
The quality of groundwater and surface water of the Al-Najaf Sea has been successfully evaluated. The available water resources can support the development of the area to some extent, and supply water of low quality. Total hardness showed that both water sources are very hard due to the main soil types of limestone and gypsum in the area. High content of anions (Cl and SO 4 ) compared to cations (Na, Ca, and Mg) characterized both water sources, whereas the magnitude of ions in groundwater were in the order of SO 4 > Na > Cl > Ca > Mg, and in surface water they were in the order of Cl > SO 4 > Na > Ca > Mg. According to the USSLS classification, the evaluation of salinity and sodicity hazards based on EC and SAR indicated that both water sources are classified as very high salinity and sodium water (class C4-S4). The groundwater had lower salinity and higher sodicity compared to surface water. However, both water sources are considered highly saline and mostly suitable for the irrigation of salt tolerant crops. Regarding the radionuclide content in the soils of the Al-Najaf Sea, the average concentrations of 232 Th, 238 U, 40 K and 137 Cs area were 11.02, 34.12, 544.45, and 1.6 Bq/kg, respectively. The measured values were within the worldwide average baseline, except for 40 K. However, the radionuclide content does not present any health hazards at this level.