Bioaccessibility and Distribution of Heavy Metals in Particles from a Dust Storm in Iraq

The issue of dust storms in Iraq is one of the issues that has caused Iraq to suffer economic and health losses and requires immediate attention. Nine of Iraq’s most important cities provided the collected samples. Atomic spectrometry was used to analyze dust samples for heavy metals such as lead, zinc, cadmium, nickel, copper, and chromium. The analysis was based on the particle size of the dust samples. The SBET was utilized for the goal of determining the scope of the threat posed by all of these elements of the dust storm and the impact they have on the health of humans. The results showed that Basra had the highest value of relative bioaccessibility of zinc (73.87%) in dust particle size (200 μm), whereas Samawah had the lowest value for cadmium (0.90%). Both values were based on the dust particle size. The relative bioaccessibility of cadmium was found to be at its highest in Najaf (85.80%) in dust particle 63 μm, whereas the relative bioaccessibility of lead was found to be at its lowest in Diwaniyah (0.28%). In addition, the findings demonstrated that the relative bioaccessibility of zinc was maximum in Amarah at a particle size of 75 μm (89.56%). The value distributions were sorted where there was high contamination of heavy metals during a dust storm from dark blue to yellow. With Kirkuk city having the highest concentration of Cr in size particle 75, the spatial distribution of Cu was notably distinct from other areas in Baghdad and Basra, where it was highest in particle sizes 63 and 200 μm. This study is important in order to determine the amount of human health damage and to control dust storms in Iraq.


Introduction
The climatic changes in the Middle East including Iraq are considered among the worst and most dangerous environmental phases the world is going through, which led to severe drought and the expansion of desertification in those regions.Climate changes included a lack of rainfall and high temperatures, as well as high levels of salinity in agricultural lands, which led to the deterioration of farm crops and their transformation into desert areas [1].The most prevalent and important indication of urban pollutants, which are harmful to both human health and the ecology of the environment, is dust.Iraq and other Middle Eastern regions have experienced numerous issues with air quality, notably in relation to sandstorms.Heavy metallic elements created by the refinement of petroleum fuels, power plants, pollution from automobiles, dwellings, and other sources are frequently found in dust in the atmosphere [2,3].Arsenic, cadmium, chromium, lead, and mercury are examples of elements with a high level of toxicity that have the potential to accumulate in human tissue and eventually have an effect on public 1259 (2023) 012040 IOP Publishing doi:10.1088/1755-1315/1259/1/012040 2 health.Other examples are chromium and lead.The mining industry, metal foundries and smelters, and several other types of metal-based industrial processes are the primary sources of heavy metals [4,5].Research conducted by Iraq's Ministry of Environment suggests that the number of sandstorms that occur in that country may increase over the course of the next ten years [6,7].In addition to this, the occurrence of sandstorms in Iraq, namely in the middle and southern portions of the country, has been progressively increasing over the past few years.Moreover, [2] claimed it may even spread to countries that are nearby, such as Kuwait and Saudi Arabia.Because of this, it is vital to determine the levels of heavy metals that come from sandstorms as well as the geographic origins of these metals in order to control them and raise awareness about the threat that these poisons pose to human health.As stated by [8], the bioaccessibility of metals in the digestive tract is a crucial factor in determining the extent to which the body is able to absorb heavy metals once they have been consumed.Due to the fact that heavy metals that enter the human body are not entirely absorbed, it is essential to evaluate the bioaccessibility of heavy metals in vitro in addition to the total concentration of heavy metals that are consumed [9][10][11][12].Limited studies have investigated the bioaccessibility of heavy metals in dust particles in Middle Eastern countries.As a result, the study aimed to ascertain the total and bioaccessibility of heavy metals in dust particle size as well as the geographical distribution of heavy metals in dust from the northernmost to the southernmost regions of Iraq.

Study Area
The Western Desert constitutes the largest part of the geographical area of Iraq and its coverage area is about 104,000 Km 2 .The Western Desert area extends from the Euphrates River in the north to the Iraqi-Jordanian and Saudi borders in the west and south [2].The climate in Iraq is hot and dry during the summer months, with temperatures that can reach up to 50 degrees Celsius in July and August.The winters are mild, with temperatures ranging from 1 to 11 degrees Celsius in November, December, and February [3].The research was conducted in five cities across Iraq, beginning in Kirkuk (S1) and ending in Basra (S9).The other cities were Baghdad (S2), Kut (S3), Hillah (S4), Diwaniyah (S5), Najaf (S6), Samawah (S7), and Amarah (S8) Fig 1.

Sample Collections and Analysis
The sandy dust was collected based on [6], From nine sites, sandy dust samples were collected in May and June 2022.Samples were dried at room temperature, and then each sandy dust sample was sieved individually through 63, 75, and 200-μm stainless steel meshes.The samples were conducted for total heavy metals using the method developed by [5], and the bioaccessibility of heavy metals was determined using the simplified bioaccessibility extraction test (SBET) by [13].The concentrations of total and bioaccessibility of heavy metals were measured using an atomic absorption spectrophotometer (SHIMADZU AA-7000).

Geostatistical Analysis
ArcGIS software (Version 10.7.1, ESRI, Inc., Redlands, California, United States) was utilized in order to apply the inverse distance weighting (IDW) interpolation to the concentrations of heavy metals that were found in the sandy dust storm from the north to the south of Iraq.One of the methods of interpolation that is utilized on a regular basis is known as the inverse distance weighted (IDW) approach.It is used to predict values for any unmeasured site by examining the values in the neighborhood of the anticipated place [14].This can be done by looking at the values in the area surrounding the projected location.

Total and Bioaccessibility of Heavy Metal in Sandstorm
Total heavy metal value in five cities (Kirkuk, Baghdad, Kut, Samawah, and Basrs) has been reported [15].The study indicates concentrations of heavy metal found in sandstorms in Iraq (Table 4).This study measured not only the total metal concentrations but also the oral bioaccessibility of heavy metals in dust storm of Iraq.According to [16][17][18][19][20][21], the findings of SBET can show the quantity of pollutants that can be absorbed by the ingestion of soils and other comparable media.From this perspective, the significance of bioaccessibility is demonstrated in the current health assessment of heavy metals, where bioaccessibility of heavy metals is of greater interest than their total concentrations in dust, which is defined as the chemical fraction that can be used for metabolism Six metals (Cd, Zn, Ni, Cu, Cr, and Pb) were recorded at 9 sites in Iraq, moving from north to south, using a geographic information system (GIS)-based chemometric technique to examine the spatial distribution patterns of heavy metals in dust storms and find spatial trends.The geographic distribution of heavy metals in the dust storms can be mapped using IDW.Because the IDW can forecast the values of the elements as well as the qualities in the dust storms based on the data entered between any two known places, it was used to predict the values of heavy metals in dust stroms of the research area Fig 2. This interpolation method performs better with evenly spaced out points [20].In addition, compared to other tools, the IDW is simpler to use in the program and not required for pre-modelling and individual assumptions [19].IDW is divided into classes that range in value by color from minimum to highest Fig 2.
The value distributions were sorted where there was high contamination of heavy metals during a dust storm from dark blue to yellow.With Kirkuk city having the highest concentration of Cr in size particle 75 μm, the spatial distribution of Cu was notably distinct from other areas in Baghdad and Basra, where it was highest in particle sizes 63 and 200.The 75-μm-sized hotspot with significant Cr concentrations was also found in Baghdad, Samawah, and Baghdad cities.Additionally, significant Cd levels were found in Baghdad's size particle 75 μm.Additionally, Najaf and Kut have elevated Cd concentrations in the size particle ranges between 75 and 63.Zn had a similar spatial distribution, and Kirkuk City's high value zones for particles 200, 75, and 63 μm were fairly large.Through spatial analysis, the distribution of metals in sand dust storms could be clearly shown.In Basra city, the Sandy dust storm had greater concentrations of Pb in all particle sizes.Therefore, the northern to southern regions of Iraq have the highest concentrations of heavy metals in dust storms.The variation in the concentrations of heavy metals in different parts of Iraq has had a significant impact on the dust storm, which could endanger humans, animals, and plants due to the buildup of these toxins in tissues.This will unavoidably have an impact on human health both now and in the future.The presence of industrial plants and car exhaust could have an impact on soil pollution, and excessive use of pesticides and fertilizers for plants could have an impact on the increase of metals in soils, which will turn into dust when the climate conditions are right.

Conclusion
The purpose of this study was to determine the amounts of six different metals in the dust storms that occurred over Iraq, from the north to the south.According to the findings, Basra had the highest value of relative bioaccessibility of zinc (73.87%) in dust particle size (200 μm), whereas Samawah had the lowest value for cadmium (0.90%).Both values were based on the dust particle size.Both of these values were determined by the size of the dust particles.It was discovered that the relative bioaccessibility of lead was at its lowest in Diwaniyah (0.28%), whereas the relative bioaccessibility of cadmium was found to be at its highest in Najaf (85.80%) in dust particle 63 μm.In addition, the results showed that the relative bioaccessibility of zinc was at its highest in Amarah at a particle size of 75 μm (89.56%), as evidenced by the data.Geographic information system (GIS) represented by IDW found the spatial distribution of Kirkuk city having the highest concentration of Cr in size particle 75 μm, and the spatial distribution of Cu was notably distinct from other areas in Baghdad and Basra, where it was highest in particle sizes 63 and 200 μm.In addition to Baghdad and Samawah, the city of Baghdad contained the 75-μm -sized hotspot that contained large amounts of Cr.

Figure 1 .
Figure 1.Iraq map and sampling collection.

Figure 2 .
Figure 2. Distributions of heavy metals in dust storm based on size particles.

Table 1 .
[12]t al. (2011)tudy, the bioaccessibility of heavy metals in a dust storm was found to range from (0.90%) for cadmium to (73.87%) for zinc for particles of size 200 μm Table(1).Lead (Pb) bioaccessibility varied among the study sites, with the highest value (67.203%) at the Samawah site and the lowest value (9.72%) at the Baghdad site for particles of size 200 μm.The highest relative bioaccessibility of Cd (85.80%) is found in Najaf in size particle (63 μm) Table(2), where the high bioaccessibility of cadmium in this region may be a result of the increased use of phosphate fertilizers and manure that introduce cadmium into these compounds.Cadmium bioaccessibility for the current study is close to the range of Cd bioaccessibility (53.3 to 76.9%) reported by[12], in Chinese street dust, it is also close to the bioaccessibility of Cd (74.5%%) reported byHu et al. (2011)in street dust of Nanjing, China.It was also close to the relative bioaccessibility of Pb reported by[8], in dust from the indoor.Bioaccessibility of Cr varied considerably among dust samples.In samples of dust with a particulate size of 75 μm, the bioaccessible Cr ranged from 5.78 to 53.14%, whereas the bioaccessible Zn ranged from 5.82 to 89.56% Table(3).The Najaf site recorded the highest relative bioaccessibility of Cu (55.55%), and the Samawah site recorded the highest relative bioavailability of Ni in the dust (53.80%) in size particle 75 μm.The results of the study showed that the highest relative bioaccessibility of Cr (71.32%) was in the dust of Kirkuk site, while the lowest relative bioaccessibility (14.61%) was in the dust of Diwaniyah site in dust particle size 63 μm.Several conditions of the in vitro digestion tests (e.g., pH, composition of the gastric and intestinal solution, ratio of samples to solution, temperature, and duration of simulated digestion) varied between studies, resulting in disparate estimates of the bioaccessibility of heavy metals[12].The relative bioaccessible (%) and bioaccessible (mg/kg) of the heavy metals for the study samples of size 200 μm. [22]].

Table 2 .
The relative bioaccessible (%) and bioaccessible (mg/kg) of the heavy metals for the study samples of size 63 μm.

Table 3 .
The relative bioaccessible (%) and bioaccessible (mg/kg) of the heavy metals for the study samples of size 75 μm.

Table 4 .
Concentrations (mg/kg) of six metals in various fraction sizes of sand dust storms in Iraq.