Accumulation, Bioavailability, and Health Risk of Heavy Metals in Some Plants Obtained from Abu-Ghraib Land, Baghdad, Iraq

Abstract


Introduction
In agriculture, the concentration of trace elements (TEs) such as Manganese (Mn), Chromium (Cr), Nickel (Ni), Vanadium (V), Zinc (Zn), Copper (Cu), Lead (Pb), Cobalt (Co), Molybdenum (Mo), Arsenic (As), Cadmium (Cd), Uranium (U), Selenium (Se), and Thorium (Th) often reflect the availability of those elements in the air and the various media (such as water, nutrient solution, and soil) used for plant cultivation (Khathi et al., 2016).The presence of these elements in plants can affect diverse fundamental biological processes, such as ionic competition and interaction, deficiency and toxicity, metabolic processes, transport within plants, speciation and concentration, and uptake (absorption) (Matejkovič et al., 2014).Some TEs, particularly heavy metals of Cu, Fe, Mn, Mo, and Zn, play a key role in plant metabolisms and are constituents of several enzymes (Arif et al., 2016).The elevated levels of heavy metals are attributed to serious diseases (such as lung and kidney cancers).
These can enter the food chain from aquatic and agricultural ecosystems and indirectly threaten human health (Bradney et al., 2019).
Many studies have indicated the accumulation of different TEs in various plant species.In a study conducted by Hassoun (2018), the average concentrations of heavy metals in imported vegetables were as follows: Fe > Zn > Cu > Ni > Co > Cd > Pb, while the concentrations of Cr, Fe, Cu, Zn, Cd, and lead in vegetables were locally produced, including tomatoes, lettuce, onions, potatoes, and carrots, rose to 1. 2075, 165.995, 37.2275, 43.775, 6.0375, and 1.48 mg/kg, respectively.Also, Hasan and Jeber (2016) reported that the mean values of lead concentrations in different plants, including peppermint, leek, cress, and celery, obtained from farms in Abu-Gruaib were high and concerning, ranging between 0.2813 and 1.4803 mg/kg.Another study reported high average concentrations of Zn in cress (67.73 mg/kg in samples: N7, N8, N9), basil (52.53 mg/kg in samples: N4, N5, N6), and arugula and celery (38.9 and 29.3mg/kg in samples: N7, N8, N9).The values of the Transfer Factor (TF) were also high in cress (0.729>TF), followed by basil (0.612>TF), arugula (0.511>TF), and celery (0.395>TF), indicating a high risk of TEs uptake by these plants.The study also reported concerning values of the total hazard quotient (THQ) in children (THQ>1 in samples: N4, N5, N7, N8, N9, N10) and adults (THQ>1 in samples: N5, N8, N9) indicating the high exposure and consumption TEs by the study participants (Al-Jumaily and Al-Berzanje, 2020).The geo-accumulation of heavy metals in marl collected from Kirkuk and Diyala, Iraq, was also concerning where the health risk index of Ni, Cu, and Cr, among other elements, in consuming children and adult participants was high (>1), indicating their elevated environmental hazards and potential causality of serious diseases (Ali & Naser, 2021).TEs were also found in high concentrations in tree leaves and walnuts, indicating a possible tendency of hyperaccumulation of those elements, acceding to the permissible reference value indicated by the Food and Agriculture Organization (FAO) and the World Health Organization (WHO) (Cervantes-Trejo et al., 2018).Such literature shows the extended presence of TEs in high concentration in most consumed nutrients in human daily life, which, on the other hand, necessitates further inspection of their levels in different regions of Iraq, especially after wars, immature industrial development, air pollutants, and the lack of efficient waste management.
The Abu-Ghraib agricultural land is a part of the lower Mesopotamian Plain of Holocene deposits, mainly belonging to the Euphrates River's flood plain, with only a relatively narrow strip in the east containing sediments from the Tigris River.The soil of the area has a rich history of being formed from calcareous alluvium.This region has a subtropical, hot, and dry environment.It has two distinct seasons separated by brief interludes (Mohammed et al., 2014;Muhaimeed et al., 2014;Papadakis, 1975).
Abu-Ghraib's agricultural production is challenged by several reasons, including poor soil quality, conversion of farmland to non-agricultural uses, and a lack of available water (Muhaimeed et al., 2014).However, this land is still suitable for the cultivation of different crops (Yaqub et al., 2021).
Aim of the study the presence of major oxides and heavy metals (As, Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, Se, Th, U, V, and Zn) in plants from Abu-Ghraib land, Baghdad, Iraq, is examined.The measurements included reporting the concentration of TEs in 18 vegetable samples of carrot, onion, eggplant, cucumber, and okra collected at different seasons.Besides, the study evaluates the daily intake of TEs and reports the total hazard quotient (THQ) among children and adult participants from the same region.

Location of the Study Area
The studied area is a part of the Abu-Ghraib City, covering approximately 90,000 hectares.Specifically, the study area is located at a distance of 20 km to the west of Baghdad and lies between longitudes (44⁰ 01' and 44⁰ 15' E) and latitudes (33⁰ 06' and 33⁰ 25' N), and the farms of used plants are annotated as in (Fig. 1).

Geology of the Study Area
The soil of the study area has a rich background of calcareous alluvium.The soil is permeable, and a system of irrigation and drainage has been built to support its long-term development.The area is nearly flat, with some meso-relief generated by an old irrigation system (Mohammed et al., 2014).The issue of soil salinity, however, persists.Water from the Euphrates and Tigris is used extensively for irrigation in the study area.However, the Euphrates River provides irrigation for a much larger acreage of study area than the Tigris River (Mohammed et al., 2014).

Collection of Samples
Eighteen plant samples of vegetables were collected in plastic bags.These samples were collected in three periods, including December 2021 and January 2022 for the harvest of carrots (N=3), July 2022 for the harvest of eggplant (N=4), cucumber (N=3), and okra (N=4), and February 2023 for the harvest of onions (N=4).Samples were tested using an X-Ray Fluorescence Instrument (XRF).at the Iraqi-German Laboratory, Department of Geology, University of Baghdad.The distribution of plant samples is annotated in Figs. 2 and 3.The exact coordinates of the vegetable plant sampling sites are presented in Table 1.

Preparation of Samples
Five duplicates of each sample and blanks were digested for the preparation phase.Dry ashing and wet digestion were the two methods used for the digestion.In a muffle furnace, samples were burned in a silicon capsule for 5 hours at 480  C. Remnants were then placed in a Teflon capsule with 5ml of hydrofluoric acid (HF) to solubilize the elements.The residue was filtered into a 100-ml volumetric flask and dried on a hot plate.The pH was then corrected using purified water, following a published protocol (Hussein, 2018).X-Ray Fluorescence Instrument (XRF) was then used to identify the presence and concentration of TEs (As, Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, Se, Th, U, V, and Zn).

Health Risk Assessment of Heavy Metals
Because of their ability to accumulate in soil and plants, heavy metals from natural and human sources seriously threaten environmental quality.However, this is one of the most critical ecological concerns due to food safety concerns and associated health hazards (Cui et al., 2004).The constants that were used to calculate the total hazard quotient (THQ) of metals in plants are listed in Table (2).3).Daily intake of metal (DIM) in mg/kg per day of metals was calculated using Eq. ( 1).
Where C is the concentration of heavy metals, EF is the exposure frequency, ED is the exposure duration, BWaverage is the body weight average, Taverage is the time average, and CF is the conversion factor.THQ values exceeding the value of 1.0 indicate a high risk of TEs on health.

Statistical Analysis
Microsoft Excel 365 was used for descriptive statistics and data visualization.IBM SPSS Statistics 26 was used to perform advanced analyses, including regression and hypothesis testing, to extract technical insights from the collected data.

Sample Distribution
In this study, 18 samples of plants were selected to study (Table 4 & Fig .4).

Health Risk Assessment of TEs
Heavy metals from natural and anthropogenic sources accumulate in soil and plants and therefore represent important environmental contamination problems.To assess the potential health hazards associated with a given pollutant, it is crucial to accurately determine the extent of exposure by identifying the pathways by which the target organisms encounter the pollutant.There exist multiple avenues by which humans may be exposed to various substances, with the food chain being identified as the primary conduit of significance.The estimation of daily metal intake was conducted based on the average intake of vegetables among adults and children.However, food safety issues and adverse health risks make this one of the most serious environmental issues (Yu-Jing, et al., 2004).
Among the studied vegetables, the highest Daily Intake of Metals (DIM) and target hazard quotients (THQ) values for both adults and children were observed in Cr in carrots, with DIM values of 4,093.70 and 5,226.20 mg/kg per day, and THQ values of 5.93145 and 18.61387, respectively.Mn exhibited the highest DIM and THQ values in cucumbers for adults and children.In eggplants, DIM values were highest for Mn (2,314.53 and 2,954.84mg/kg per day), while Cr had the highest THQ values at 0.89823 and 2.81878 for adults and children, respectively.Similarly, in okra, Cr displayed the highest DIM (859.78 and 1,097.63mg/kg per day) and THQ values of 1.24575 and 3.90937 for adults and children, respectively.Onions exhibited the highest DIM values in Mn (915.67 and 1,168.99mg/kg per day), and the highest THQ values for adults were associated with Cr (0.45912) (Table 6; Fig. 5).

Discussion
Vegetable consumption is a major route of human heavy metal poisoning.Many biological and metabolic systems in the human body may be disrupted by chronic exposure to hazardous levels of heavy metals in diet (Mengistu, 2021).Our result showed that the majority of TEs were observed in carrots, whereas other TEs showed a descending trend in the following order: Zn> Cr> V> Ni> Cu> Mn> Pb> Mo> Co> As> Cd> U> Se.
In agreement with our results, Mafuyai et al. (2019) reported that all of the metals investigated (Pb, Cu, Cd, Zn, Cr, Fe, Mn, and As) had greater quantities in the carrots that were analyzed from the sampled farms.However, the total hazard quotient (HQ) of these TEs indicated that their levels are not of high risk for health, except Cr, which was higher in all plant samples, making all these vegetables safe with no threat to human health except for Cr.
In this study, the highest concentration of Fe was in carrots, followed by onion, cucumber, and eggplant, and the lowest in okra.In a study conducted by Hassoon (2018), the Fe in imported vegetables to Baghdad had the maximal values in lettuce samples (411.625 mg/kg) as Fe largely accumulates in plant leaves (Gupta et al., 2008).The result showed that the mean concentration of Fe in carrots was lower than the Fe concentrations reported by Hassoon (2018), which was 8.64 mg/kg in carrot (roots).Hassoon (2018) also reported that the Co in imported vegetables to Baghdad had similar concentrations in tomato and onion, about 3.1 mg/kg, and about 3.09 mg/kg in lettuce, potatoes, carrots, and turnips.Interestingly, Co concentrations in local vegetables were similar to those recorded in imported types (3.1 mg/kg) but lower in local potatoes (2.8375 mg/kg).
Cr is a crucial element for insulin activity and DNA transcription, and an intake below 0.02 mg/day could reduce cellular insulin response (Makanjuola et al., 2019).According to our results, Cr was higher in adults and children for all plant samples.Hassoon (2018) reported that the Cr in imported vegetables was present at slightly similar values in almost all collected samples except with turnips, which had the highest concentration (1.7475 mg/kg).Another study by Mutune et al., (2014) in an industrial area found that Cr concentrations were between 1.19 and 1.24 mg/kg for spinach and spider plants, respectively.Chrome plate corrosion in vehicle motors may be the reason for the increased emissions of Cr (Essa and Al-jibury, 2017).High absorption rates of heavy metals by plants can lead to high storage of heavy metals in their tissues, increasing the risk among consuming individuals, especially children.Ingesting these heavy metal-contaminated foods over lengthy periods may increase that risk and hugely impact individuals' lives (Gupta et al., 2010).The absorption and transport of metals in plants may account for the diversity in metal concentrations (Sultana et al., 2015).Metals may be ingested by vegetables from the soil or through exposure to polluted air (Bahiru, 2021).
The study revealed that the dietary intake (DI) of heavy metals in children exceeded that of adults.The findings presented in this study were found to be incongruous with the results reported in prior research conducted by Zheng et al. (2007);Liu et al. (2011), andSatpathy et al. (2014).This observation is incongruent with the fact that adults tend to consume a comparatively larger number of vegetables in comparison to children.The FAO and WHO have established specific thresholds for the daily consumption of certain heavy metals, which are referred to as the Provisional Tolerable Daily Intake (PTDI) (FAO, 1999).
According to the study conducted by Mutter (2016) in Baghdad city (at Al-Taji, north of Baghdad and Al-Rashid, south of Baghdad), the major elements (Ca, K, and Mn) and trace elements (Fe, Cu, Pb, Sr, and Zn) in six plant samples (lettuce, bean, apples, potato, cabbage, and pear) were analyzed and found to be within acceptable ranges when compared to concentrations in neighboring countries and International Atomic Energy Agency (IAEU) standards.Precision represents the degree to which repeated measurements show the same results, also called reproducibility or repeatability (Maxwell, 1968).Precision is usually expressed in terms of the deviation of a set of results from the arithmetic mean of the set.However, it sounds reasonable to assume otherwise (Stoodley et al., 1980).Precision (P) is expressed as the coefficient and calculated using Eq. ( 1).
P is presented at a 95% confidence interval.The XRF precision was evaluated using 3 samples to ensure the high detectability of the XRF instrument towards TEs (Table 7).The permissible limit of TEs is ≤ 25.

Conclusions
The issue of metal contamination in ecosystems has gained growing global attention.Eighteen plant samples of vegetables from different farms in Abu-Ghraib, Baghdad, Iraq, including carrot, onion, eggplant, cucumber, and okra, were evaluated for the presence of TEs.Our findings indicated that the distribution of TEs differed based on the type of plant.The results of XRF indicated that the highest concentrations of As, Cr, Mo, Cu, Ni, Pb, Se, V, and Zn were in carrot, while eggplant exhibited the highest concentration of Mn and U.The total hazard quotient (THQ) of these TEs indicated that their levels did not cause a risk for health, except for Cr (HQ >1), which was high in all plant samples.Our findings highlight the importance of continued monitoring and regulations to preserve public health and ecosystem integrity.In a broader sense, legal authorities should require farmers to conduct soil evaluations for heavy metals.This can help identify high-absorbability plant species and avoid their cultivation in that specific farm to facilitate better public health practices and avoid the impact of a polluted environment on local consumers.

Fig . 4 .
Fig .4.Images of soil and plant sample collection from Abu-Gruaib farms.

Table 1 .
Coordinates of the vegetable plant sampling sites

Table 2 .
The constants that were used to calculate the THQ.RfD) values are used to calculate the THQs of the TEs in Plants (Table

Table 3 .
The reference dose (RfD) values are used to calculate the THQs.

Table 4 .
The selected plant species in this study with scientific name and number of samples (N).

Table 5 .
Concentration of TEs in plant samples (ppm).

Table 6 .
DMIs, DMIs, and HQs of Carrot in this study.

Table 7 .
Precision values (95% confidence interval) of the presence of elements in soil.