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ORIGINAL ARTICLE
Year : 2013  |  Volume : 36  |  Issue : 1  |  Page : 20-26  

The status of natural radioactivity and heavy metals pollution on soil at Assiut Zone in Central Upper-Egypt


1 Department of Physics, Faculty of Sciences, Al-Azhar University, Assiut Branch, Egypt
2 Egyptian Environmental Affairs Agency, Assiut Branch, Egypt

Date of Web Publication21-Nov-2013

Correspondence Address:
Mohamed Amin Uosif
Department of Physics, Faculty of Sciences, Al-Azhar University, Assiut Branch
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0972-0464.121819

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  Abstract 

Context: To examine the status of the environmental quality of the soils in Assiut zone in central Upper-Egypt, investigation was carried out to determine the concentration of natural radionuclides (radium [ 226 Ra], thorium [ 232 Th] and 40 K) and the contents of eight heavy metals (Cd, Pb, Ni, Fe, Mn, Cr, Cu, and Zn). Materials and Methods: The measurements of concentration of natural radionuclides were carried out by using the gamma spectrometry (NaI (Tl); 3× 3"). Results: The results indicate that the soil samples' radioactivity concentrations of 226 Ra, 232 Th, and 40 K were ranging from 10.4 ± 0.5 to 19 ± 1 Bq/kg; 6 ± 0.3-21 ± 3 Bq/kg and 103.6 ± 5-221 ± 10 Bq/kg respectively. The typical radiation doses (D o ), the external hazard index (H ex ) and annual effective dose rate values for the corresponding samples were also estimated. The concentration of heavy metals was measured by using the atomic absorption spectrometry method. Data were analyzed by using the statistical methods. The representative H ex values for the corresponding samples were also estimated. Generally, heavy metals and major elements concentration of the sediments were found decrease in sequence of Fe > Mg > pb > Zn > Cr > Cu > Ni > Cd. In some locations, the concentration for the investigated heavy metals exceeds the permissible limits recommended by the Canadian Environmental Quality Guidelines. The highest concentration of the most heavy metals (Cd, Pb, Ni, Cr, and Zn) was found in Arab Al-Madabegh region; the sewage irrigated zone. Whereas, the lowest ones was found in the not irrigated lands, which considered as a reference point of analyses. Conclusion: The maximum admitted concentrations of toxic heavy elements in the sensitive areas revealed to be exceed from three to thirty times than the non-irrigated zone.

Keywords: Natural radionuclides, soil toxic heavy metals, radiological implications and NaI(Tl) gamma ray spectrometry


How to cite this article:
Uosif MA, Issa SA, Abuel-Fadl KY, Taha MA, Mostafa A M. The status of natural radioactivity and heavy metals pollution on soil at Assiut Zone in Central Upper-Egypt. Radiat Prot Environ 2013;36:20-6

How to cite this URL:
Uosif MA, Issa SA, Abuel-Fadl KY, Taha MA, Mostafa A M. The status of natural radioactivity and heavy metals pollution on soil at Assiut Zone in Central Upper-Egypt. Radiat Prot Environ [serial online] 2013 [cited 2020 Jul 7];36:20-6. Available from: http://www.rpe.org.in/text.asp?2013/36/1/20/121819


  Introduction Top


One of the main characteristics of soil is that it contains natural radionuclides and heavy metals. It is well-known that radionuclides in the uranium ( 238 U) and thorium ( 232 Th) decay chains do present in varying degrees of concentration in the earth's crust. The product in decay chain of uranium ( 238 U) are radium ( 226 Ra), radon( 222 Rn) and bismuth ( 214 Bi), while the other radionuclides, such as actinium ( 228 Ac), bismuth ( 212 Bi), and lead ( 212 Pb) do occur in the decay chain of the thorium element ( 232 Th). In addition, the radionuclide - 40 K is also present in the earth's crust.

Heavy metal contamination of soil results from anthropogenic activities such as mining, smelting procedures, and agriculture as well as natural activities. Chemical and metallurgical industries are the most important sources of heavy metals in the environment. [1] Heavy metals are generally and naturally found at very low concentrations, while elevated concentrations are commonly associated with the pollution from human activities. The role of trace elements in the soil is increasingly becoming an issue of global concern at private and governmental levels, especially, as soil constitutes a crucial component of the rural and urban environments, and can be considered as a very important "ecological crossroad" in the landscape. [2] One of the most limiting factors for land disposal and use of sewage wastewater for agriculture is the presence of heavy metals, [3] which depends on the type and degree of wastewater treatments. With repeated applications of wastewater, heavy metals could accumulate to toxic levels for plant and soil organisms. [4]

The toxicity and bioavailability of heavy metals depends on their total concentrations and their chemicals forms in the soil. The total concentrations of heavy metals may provide a little indication of their specific bioavailability and mobility. [5] All trace elements are toxic to living organisms at excessive concentration, but some are essential for normal healthy growth and reproduction by plants and animals at low however, critical concentrations. The essential trace elements include Co, Cr, Cu, Mn, Mo, Ni, Se, and Zn while Ag, As, Ba, Cd, Hg, Pb, Sb, and Th have no known essential function but cause toxicity above certain tolerance level. Deficiencies in these essential elements or micronutrients can lead to disease and even death of the plant or animal. The most important heavy metals with regards to potential hazards and the occurrence in contaminated soils [6] are As, Cd, Cr, Hg, Pb, and Zn. Monitoring the endangerment of soil with heavy metals is of interest due to their influence on groundwater and surface water [7] and also on plants, [8] animals and humans. [9]

The present study examines the concentrations and distribution of the natural radioactivity and heavy metals in order to evaluate the current state of the environmental quality in the soils of Al-Arbaeen, Arab Al-Madabegh, Ezbat Al-Geish and Manqabad zones. The ultimate aim is to assess the impact of human activities and sewage wastewater on the soils of this environment. The farms nearest this area were irrigated only from the effluent wastewater. Hence, it considered as the most polluted area in Assiut and classified as an environmental disaster area (with 57992 people). Samples are collected and examined primarily to determine their physicochemical and radiological properties. This section outlines the more important factors, which should be considered when devising a sampling program for soil and related material.


  Materials and Methods Top


Study area

[Figure 1] shows the four different areas in the northern west Assiut town near to Arab Al-Madabegh region where there is a sewage wastewater treatment station and other non-point pollution sources are located [Figure 1].
Figure 1: Location map of the studied areas in assiut

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The soil samples were collected from locations where the ground is not sliding and the probability of alluvial deposits is small. Three replicates of analyses were undertaken from 30 cm to 60 cm depth intervals [Table 1], avoiding the surface contaminants, using hand auger soil samples from each site and put in polyethylene containers. Hence, the investigation includes 24 sub-samples for each determination for further qualitative characterization should ensure a precise estimate of the physicochemical parameters concentration.
Table 1: Name and locations of the four study areas

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  Experimental Procedure and Methods Top


Sampling preparation for natural radioactivity determination

The samples were dried in an oven at about110°C, The samples were crushed, homogenized, and sieved through a 200 mesh, which is the optimum size enriched in heavy minerals. The samples were weighed and transferred to polyethylene bottles of 350 cm 3 volume. The beakers were completely sealed for four weeks to reach a secular equilibrium, where the rate of decay of the progeny becomes equal to that of the parent ( 226 Ra and 232 Th) (American Society for Testing Materials 1983 and 1986) [10],[11] within the volume and the progeny will also remain in the sample.

Instrumentation and calibration

Activity measurements were performed by gamma ray spectrometer, employing a scintillation detector (3″× 3″). It is hermetically sealed assembly, which includes a NaI (Tl) crystal, coupled to personal computer-multi channel analyzer PC-MCA Canberra Accuspec. To reduce the gamma ray background, a cylindrical lead shield (100 mm thick) with a fixed bottom and a movable cover shielded the detector. The lead shield contained an inner concentric cylinder of copper (0.3 mm thick) in order to absorb X-rays generated in the lead. In order to determine the background distribution in the environment around the detector, an empty sealed beaker was counted in the same manner and in the same geometry as the samples. The measurement time of activity or background was 43200 s. The background spectra were used to correct the net peak area of the gamma rays of measured isotopes. A dedicated software program (Genie, 2000). [12]

The 226Ra radionuclide was estimated from the 609.3 keV (46.1%) γ-peak of 214 Bi, 351.9 keV (36.7%), 1120.3 keV (15%), 1728.6 keV (3.05%) and 1764 keV (15.9%) γ-peak of 214 Pb. The 186 keV photon peak of 226 Ra was not used because of the interfering peak of 235 U with energy of 185.7 keV. 232Th radionuclide was estimated from the 911.2 keV (29%) γ-peak of 228Ac and 238.6 keV (43.6%) γ-peak of 212 Pb. 40K radionuclide was estimated using 1,461 keV (10.7%) γ-peak from 40 K itself. The below detectable limitwere 25.2 Bq/kgfor 40 K, 6.5 Bq/kgfor 226 Ra and 5.7 Bq/kg for 232 Th. All procedures were described in previous publications. [13]

Heavy metals analysis

Doubly distilled water (De-ionized) free from metals was used throughout the work. Analysis is undertaken on sieved air-dried samples of the fine-earth (<2 mm) fraction and the results corrected for moisture content. Heavy metals are extracted from the soil samples (1 g) by using method 3050 B in Test Methods for Evaluating Solid Waste Physical/Chemical Methods (U.S. Environmental Protection Agency Solid Waste-846) (EPA SW-846), 1996. This procedure breaks down most of the organic matter present and extracts all the heavy metals. After digestion total Cd, Pb, Cu, Ni, Cr, Mn, Zn, Fe were measured in soil samples using the Shimadzu AA-6800 atomic absorption spectrophotometer.

Statistical analysis

All values from chemical analyses were presented as mean ± SD and the statistical analyses were carried out using the Statistical Software. [14] Normality of distribution of dependent and independent variables was tested using the Kolmogorov-Smirnov test [15] at P < 0.05 level of significance. Statistical significance of differences at P < 0.05 level between the means were subjected to one-way ANOVA.


  Results and Discussion Top


Radioactivity

Activity concentrations of 226 Ra, 232 Th and 40 K in controlled samples of were listed in [Table 2].
Table 2: The activity concentration of 226Ra and 232Th series and 40K in (Bq/kg) of the studied samples

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The obtained results in [Table 2], and illustrated in [Figure 2], show that the minimum values of the measured specific gamma ray activities (Bq/kg) in different soil samples at depth 30 cm from Ezbat Al-Geish (non-irrigated) are (10.4 ± 0.5), (6 ± 0.3) and (111 ± 6) due to 226 Ra, 232 Th and 40 K respectively while the maximum values from Arab Al-Madabegh (Sewage Irrigated) samples are (18.8 ± 1), (18.8 ± 2) and (221 ± 10) due to 226 Ra, 232 Th, and 40 K respectively.
Figure 2: The activity concentration of radium and thorium series and 40K (in Bq/kg) of the samples studied

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In the other side at 60 cm depth, the arithmetic mean activities concentrations (Bq/kg) ranged from (12 ± 0.6) Manqabad Mixed (Clean and Sewage) samples to (19 ± 1) Arab Al-Madabegh (Sewage Irrigated) for 226 Ra. For 232 Th the mean activities concentrations (Bq/kg) varied from (8.2 ± 0.5) Ezbat Al-Geish (Non-Irrigated)) to (21 ± 3) Arab Al-Madabegh (Sewage Irrigated)), while for 40 K it is ranged from (103 ± 5) Manqabad Mixed (Clean and Sewage) to (200.7 ± 10) Arab Al-Madabegh (Sewage Irrigated). The activity concentration of 40 K in soil is an order of magnitude higher than that of 226 Ra or 232 Th.

The results obtained showed that the maximum contaminant level are in the range of the activity concentrations of 238 U, 232 Th and 40 K in Bq/kg in different soil available in other countries in the world United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR 2000) [16] are given in [Table 3].
Table 3: Natural radionuclide content in soil from UNSCEAR 2000 survey of natural radiation exposures

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In its first assessment of representative concentrations of these radionuclides in soil, in the (UNSCEAR 1982) [17] the Committee suggested the values of 370, 25 and 25 Bq/kg for 40 K, 226 Ra and 232 Th respectively. On the basis of the higher levels reported for China and the United States, the Committee revised the values for both 238 U and 232 Th to 40 Bq/kgin the (UNSCEAR, 1993). [18]

Derivation of the radiation hazard indices

The gamma radiation doses (in outdoor air D o) for the population living in the areas under study is due to the sediments content of radionuclides, which can be estimated by employing a half-infinite source of a homogenous distribution and by considering only the contribution from the natural radionuclides in the samples. The convenient formula [19] is given as:



Where D is the calculated dose rate (in nGy/h), T is the outdoor occupancy time (0.2 × 24 h × 365.25 d ≈ 1753 h/y), and F is the conversion factor (0.7 × 10 -6 SvG/y). The experimental results of Annual Effective Dose Rate are presented in [Table 4], column (4 and 7). From the results it is clear that the average total annual dose (based on the samples of this study) is 27.7 μSv/y. This value is about 6.72% of the 1.0 mSv/yrecommended by the International Commission on Radiological Protection (ICRP-60) [21] as the maximum annual dose to members of the public.
Table 4: The dose rate (nGy/h), external Hex (nGy/h) and annual effective dose equivalent (μSv/year) of the studied samples

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Basic approaches to radiation protection are consistent all over the world. The ICRP-60 (1990) [21] recommends that any exposure above the natural background radiation should be kept As Low As Reasonably Achievable (ALARA) but below the individual dose limits, which for radiation workers averaged over 5 years is 100 mSv and for members of the general public is 1 mSv/y. These dose limits have been established on the prudent approach by assuming that there is no threshold dose below, which there would be no effect. This means that any additional dose will cause a proportional increase in the chance of a health effect.

Chemistry

The concentration of the selected eight heavy metals (mg/kg) (e.g., Cd, Pb, Fe, Mn, Cu, Zn, Ni, and Cr) in investigated samples (at 30 and 60 cm depth) are summarized in [Table 5]a and b respectively. From such table it was found that the highest concentrations of most heavy metals were recorded in the sewage irrigated soil samples collected from Arab Al-Madabegh region and the lowest ones were detected in the non-irrigated samples collected from Ezbat Al-Geish region. A significant, P < 0.05 compared to non-irrigated site reflecting a high correlation were observed between the concentrations of the selected heavy metals in soil samples.
Table 5:

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According to the present results, the levels of the analyzed heavy metals in soil exhibited different patterns of the heavy metal accumulation some above and other under the permissible limits admitted by the Canadian Environmental Quality Guidelines in most areas. The average concentration of the heavy metals in the soil samples ranged from it's the lowest value in non-irrigated region to it's the highest value in sewage irrigated region. The average concentrations of cadmium and lead were higher than the permissible limits in Arab Al-Madabegh region while other heavy elements level was within the permissible limits.

Cluster analysis was applied on the present results to find out the similarity in heavy metals concentration in the different sampling sites. According to surface (30 cm) (A) and down (60 cm) (B) soil cluster analysis, the sampling sites were divided into two groups [Figure 3]. The first group included Al-Arbaeen and Ezbat Al-Geish, the second group included Arab Al-Madabegh and Manqabad.
Figure 3: Surface (30 cm) (a) and down (60 cm) (b) soil cluster analysis

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The contamination of soil by heavy metals is of important concern especially in many industrialized countries because of their toxicity, persistence, and bioaccumulative nature. Soil samples collected from Arab Al-Madabegh site (as expected) displayed the highest metal content. This result confirm the previous studies of many authors [22] who reported that such sites polluted because it receives huge amounts of sewage, industrial, and agricultural wastes.

The concentrations of the selected heavy metals present are dependent on the anthropogenic input into lands. This would disrupt a sinusoidal curve pattern. The maximum level of the most heavy metals was detected in the sewage irrigated lands which represent the bad effect on its environment. In addition, to anthropogenic inputs, metals may also come from natural erosion. [23] Fine grain particles in soil usually act as effective collectors and carriers of dissolved metals from the water column to the soil and thus elevate concentration of heavy metals in soil.

According to present results, the metal levels in down soils profile were higher than those in the surface one. This study has confirmed that soils are important hosts for toxic metals. It has been shown that soil permit the detection of the heavy metals that may be either absent or present in low concentration in the water column.


  Conclusions Top


The conclusion of our study can be summarized in the following points:

  1. The obtained results showed that the maximum natural activity levels are in the range of the activity concentrations of 238 U, 232 Th and 40 K in Bq/kg in different soil available in other countries in the world (UNSCEAR 2000).
  2. The presence of studied heavy metals was determined in most of the investigated areas. Some exceeding at the alert level was identified in the sensitive areas (sewage irrigated areas).
  3. The results of the study can lead to an image of the historical pollution, determining the concentration of several elements, according to the depths in the soil.
  4. Different correlation rapports were identified in different areas. The maximum correlation was found with high significant (P < 0.01) in Arab Al-Madabegh area. The greatest excess for cadmium and lead was registered in Arab Al-Madabegh area that exceed 2-20 times than the permissible limits. Excepting the rent areas, the heavy metal concentration ranges within normal limits.
  5. The presence of the heavy metals detected in both soil profiles allows us to conclude that the pollution was produced a long time ago and the pollutant activities in the investigated areas are still present.


Acknowledgment

This work was carried out using the nuclear analytical facilities at the Physics Department, Faculty of Sciences, Al-Azhar University, Assiut, Egypt and chemical analytical facilities at Egyptian Environmental Affairs Agency, Assiut Branch, Egypt.

 
  References Top

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21.International Commission on Radiological Protection. ICRP-60, Radiation Protection: Recommendations methods. Part 1. Monoenergetic sources of natural radionuclides in the ground, GSF-B2/90 of the International Commission on Radiological Protection. Oxford: Pergamon Preis; 1990.  Back to cited text no. 21
    
22.Osman AG, Abd El Reheem AM, Abuel-Fadl KY, GadEl-Rab AG. Enzymatic and histopathologic biomarkers as indicators of aquatic pollution in fishes. Nat Sci 2010;2:1302.  Back to cited text no. 22
    
23.O`leary C, Breen J. Seasonal variation of heavy metals in Mytilus edulis, Fucus vesiculosus and sediment from the Shannon Estuary. Biol Environ Proc R Irish Acad 1998;98B:153.  Back to cited text no. 23
    


    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]



 

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