Nondestructive analysis of dumpsite soil and vegetable for elemental composition

In this study, dumpsite soils and vegetables were analyzed for total elemental composition using a 5SDH Tandem Pelletron accelerator available at Centre for Energy Research and Development, Obafemi Awolowo University Ile-Ife. The results at a 2.5 MeV energy revealed the presence of elements: Cu, Cr, Ni,Al, Si, P, S,Cl, K, Ca, Ti, Mn, Fe, Zn, Rb, Sr, Y, Zr and Pb in the dump site soil, with the exception of Cu, Cr,Ni, Zr and Y; other elements with Mg in addition were found in the vegetables around the dump site soil, majority of the elements were at lesser concentrations. However, there was a sharp difference in the concentrations of Mg, Ca and K being present at higher concentrations in the vegetables than in the soil. The result showed no significant difference in the concentration of elements analyzed on each site with the control site, both in the vegetable and the soil samples at 95 and 99% confidence interval. The analysis of variance (ANOVA) for the soil and vegetable samples also confirmed no significant differences. The relationship among the sites was determined in either direction (positive and negative, 2-tailed analysis) using correlation coefficient, the R values among sites were all above 0.5 in vegetable and > 0.9 in the dumpsite soil, showing that all sites were well related depicting common components. Fe, Zn and Pb were within the range of concentration of metals in plant but were higher than the permissible limit of International Organization (WHO/FAO, 2007; EU, 2006). High concentrations coupled with high standard deviation values of some elements suggest influence of anthropogenic activities.


INTRODUCTION
Open dump disposal system of waste has been on for a long time in developing countries with its associated risk.The increase in urbanization and industrialization increases waste generation at homes, in industries and market places with little consideration of its impact on environmental health.Since waste sorting and separation are uncommonly practiced, anything that has lost its value is deposited at dump sites, from home, municipal and small scale workshops (Odia et al., 2008).The constituents of these wastes include scraps from mechanic workshops, household materials such as, papers, food wastes and many more.Open dump site is believed to be rich in organic fertilizer as a result of decayed and composted organic materials that enrich soil fertility (Ogunyemi et al., 2003).The random deposition of these wastes, consequently leads to adjacent lands getting enriched in elemental composition and salts of such wastes (Lawan et al., 2012).Studies on municipal waste have shown that heavy metals concentration ranges were high and that waste sites can accumulate heavy metals in the soil at toxic level hence the risk of vegetable grown in the areas getting contaminated with heavy metals and consequently endangering the human health (Purves, 1973;Carlson, 1976).
Amaranthus spinosus is a common vegetable that grows naturally on soil but appears leafy and greenish on and around dumpsite.Grubben and Denton (2004) considered it as valued food in Africa.Due to the greenish and leafy nature of the vegetable (Amaranthus spinosus) around the dump site, many people living below poverty line collect this vegetable for food and sales for economic gain with or without the full implications on the people's health.
Particle-induced X-ray emission or proton-induced Xray (PIXE) is a technique used in determining elemental make-up of a material or sample.It is based on the ionization of the sample atoms by the incidence of a particle beam; when a material is exposed to an ion beam, atomic interactions occur that give off electromagnetic radiation that is characteristic of the elements present in the sample (Joansson et al., 1970).It analyzes solids down to 10 −4 g and 1 ml of liquids.It is multi elemental and analyzes elements in samples simultaneously.It is a routine analytical technique employed by chemists, physicists, geologists, archaeologists and art conservators.Vegetables (especially Amaranthus spinosus) consumed in many areas within Ile-Ife metropolis have their sources attached to dumpsites, hence the need to identify the major heavy metals present at various dumpsites, ascertain their levels of concentration in vegetables which could have resulted from the up-take from the soil and to know the contamination level and health risk of direct consumption of vegetables grown on these dumpsites.

Collection of samples and pre-treatment
Soil and vegetable samples were collected from three different major dumpsites around Ile-Ife and the fourth one that serves as the control site was not a dump site.Each site was divided into four parts, soil samples were taken to a depth of 0 to 20 cm soil level from each quadrant, and vegetables were also collected likewise.Soil and vegetable samples from each quadrant were mixed together to form composite samples that adequately represent each site.This was so because wastes were concentrated on some part than the others.The vegetable samples were rinsed separately with water to remove dust and sand particles and later rinsed with distilled water.The rinsed vegetable and the soil samples were air dried for several days in an aerated cupboard to prevent cross contamination.The air-dried soil and vegetable samples were oven dried for 2 to3 min at 103 to105°C to remove moisture content until  1.The Google Earth search (Figure 1) was used to locate the grid of the sampling site.

Samples preparation and methods
The dried samples were ground in agate mortar and mixed with 10% by weight of ultra pure graphite powder and prepared into thick pellets of 11 mm diameter without binder.
The PIXE experiments were performed using 2.5 MeV proton beam obtained from CERD ion beam analysis (IBA) facility.The facility is centered on a NEC 5SDH 1.7 MV Pelletron Accelerator, equipped with a radiofrequency charge exchange ion source.The end-station consists of an Aluminium chamber of about 150 cm diameter and 180cm height.It has four ports and a window.Port 1 at 165° is for the RBS detector, port 2 at 135° is for PIXE detector, port 3 at 30° is for the ERDA detector, the window at 0° is for observing the beam position and the size, while port 4 at 270° is for PIGE.The chamber has a turbo pump and a variable beam collimator to regulate beam size, and an isolation value.The measurements were carried out with a beam spot of 4mm in diameter and a low beam current of 3 to 6 nA, depositing a charge of 0.5 µC on target.The irradiation was for 10 to 20 m, a Canberra Si(Li) detector Model ESLX 30-150, beryllium thickness of 25µm, with full width half maximum (FWHW) of 150 eV at 5.9 keV, with the associated pulse processing electronics, and a Canberra Genie 2000(3.1)MCA card interfaced to a PC were used for the X-rays data acquisition.With respect to the beam director, the sample's normal was located at 0° and the Si(LI) detector at 45°.

Analytical validation
The PIXE set-up was calibrated using some pure element standards and the National Institute of Standards and Technology (NIST) geological standard, NBS278.The accuracy of the method was studied by analyzing the Certified Reference Material.Apple Leaves (NIST 1515) and (IAEA-SOIL7) were used for the determination of the H-value which was subsequently used for analyzing the soil and vegetable samples and to assure the accuracy of the experimental procedure (Tables 2 and 3).

Statistical analysis
Statistical Package for the Social Sciences (SPSS, version 16.0, Inc., Chicago, USA) was used for data analysis.The significant differences between groups were compared using analysis of independent t-test and analysis of variance at probability level of 95 and 99% confidence level.Correlation coefficient was performed on the data to test the relationship among the elements and factor analysis was carried out to classify the element into groups for possible identification of its sources.

RESULTS AND DISCUSSION
Tables 2 and 3 showed the result of the method validation for sample analysis, the observed values were comparable with the expected values and adjudged good for precision and accuracy of the work.Tables 4 and 5 were the mean and standard deviation of the elements analyzed, the result showed no significant difference in the concentration of elements analyzed both in the vegetable and the soil samples at 95 and 99% confidence interval.The analysis of variance both for the soil and vegetables samples also confirmed no significant differences.The relationship among the sites was determined in either direction (positive and negative, 2-tailed) using correlation coefficient, the r-values among sites were all above 0.5 in vegetable and >0.9 in the dumpsite soil, showing that all the sites were well related.Fe, Zn and Pb were within the range of concentration of metals in plants as stipulated in Opaluwa et al. (2012); but were higher than the permissible limit of Standard organizations as stipulated by the WHO/FAO (2007) and EU (2006).
High concentrations coupled with high standard deviation values of some elements suggest influence of anthropogenic activities (Manta, 2012).This showed that the control soil site in this study probably bear some imprint of anthropogenic activities or occurrence of diffuse pollution and do not reflect purely natural conditions.Dhrubajyoti et al. (2011) carried out similar work on municipal waste soil with EDXRF and similar pattern was observed.Mineral elements such as Fe, Ca, K were higher than other elements (Cr, Mn, Ni, Cu, Zn, Rb, Sr, Zr, and Pb) analyzed.However, the work of Opaluwa et al. (2012) carried out on dumpsite soil of Nassarawa State Nigeria, using AAS showed relatively low concentration compared with this work.Considering the concentration of elements in unpolluted soil of Italy (Palumbo et al., 2000) and calculation based on world scale range (Fergusson, 1990) shown in Table 5, all the soil sites were polluted except site A that was not polluted with Cu.
Multivariate statistical procedures were used to identify the pattern in the data sets of these elements in the soil and the vegetable found on them.Cluster analysis of the vegetable data gave two groups with three distinct clusters (Figure 2) which was complemented by principal component analysis (Figure 3) (all loading taken into consideration), with three components extracted for distribution of the elements and possible interpretation in relation to the sources of the elements in the vegetable.Factor I consisting of Al, Si, Ti, Zn, S and Ca (cluster I) contributed 9.097 with 60.65% variance, these are likely to be from soil natural materials.
Factor II associated with factor III and made of P, Cl, Rb and Sr (cluster II) with contribution of 3.692 and 24.616% variance, these elements could possibly be from the waste dumped on the soil and picked by vegetables.Factor III contributed 2.210 with 14.734% variance and was loaded mainly with Mn and Rb with Mg, K having a low positive loading value.Fe and Pb were negative meaning that they were not fulfilling same mission with Mn, Rb, Mg and K that has positive value in factor III but were in the same cluster, therefore, Pb and Fe are likely to be from the waste because of their positive values in factor II.These elements with positive component values (Mn, Mg and K) in factor III that clustered with Pb and Fe in the cluster III were majorly mineral elements.The vegetable is likely to derive these nutrients from the wastes and formed its mineral components.This is likely to have accounted for the association of cluster II and III; they were likely from the same source.
The principal component graph of factor I and II which are the main contributor showed clearly that the elements are from the lithogenic waste (upper part), mineral constituents of the vegetable (lower Part) taken from the    (Palumbo et al., 2000).** Mean ranges calculated to the world scale (Fergusson, 1990).D: Control site; BDL: Below detection limit.--------+---------+---------+---------+--------- polluted soil with Pb from aerial deposition.An explorative hierarchical cluster analysis performed on the dumpsite soil data set (Figure 4), showed two main groups of elements clustered at three levels of similarity as shown in Figure 5, discriminating Mn, Zn, S, Y, P, Ca, Fe, Al and Cu (Group I) from Cl, Zr, Ni, Cr, Pb, Rb, Sr and Si (Group II).These two groups discriminated the elements into natural origin-elements from the parent material and other soil-forming factors that may have added or removed some elements from the soil.Group II could be classified as elements from the waste in association with elements from anthropogenic activities with some natural elements from the soil.This result is consistent with elemental relationships indicating that the elements in Factor I (Figure 4) do not correlate with Al and Si (Figure 3), meaning that they are not from alumino-silicate phases of the soil and as such, not from the natural origin and possibly from the waste and anthropic inputs.Factor II has its major elements from the natural sources and weathering processes with changes that would have occurred as a result of the wastes.Al correlated with Ca (0.5) and positively correlated with Fe (0.4) as shown in Table 6; these pointed to the parent rock to likely be from CaO, Al 2 O 3 ,Fe 2 O 3 (Manta et al., 2002).Factor III consists of Ti, K, Y, P, S and Ca.It is likely to be a combination of elements released from agricultural wastes with remnants of fertilizers such as NPK and CaO together with P 2 O 5 soil components.Plant ability to take up chemical elements from growth media is evaluated by a ratio of element concentration in plants to element concentration in soils and is called Biological Absorption Coefficient (BAC), Index of Bioaccumulation (IBA), or Transfer Factors (TF).Some elements are more susceptible to phytoavailability than others.

Al
In this study, elements such as P, S, Cl, K, Ca, Sr, Mg were phytoavailable in the vegetable than the soil.These are essential elements in relation to photosynthesis and normal growth of the plants.Trace elements (TEs) concentrations in plants are highly associated with the chemical composition of growth media.Plant responses to TEs in soils depend on several factors; however some general trends expressed by plant/soil, Transfer Factor (TF) can be presented as generalized values: 10: Cd, 1: B, Br, Cs, Rb, 10 −1 : Ag, Co, Cu, Ge, Hg, Mo, Pb, Sr, Te, Zn, 10 −2 : Be, As, Li, F, I, Mn, Ni, Sb and 10 −3 : Ba, Bi, Ga, Fe, Se, V, Tl, Zr (Kabata-Pendias, 2011).
The transfer factor of elements were calculated and shown in Table 7; it was found that TF were not within the range provided as normal above.The TF of Al and Si (<0.1) mg/kg; P and Ca < 2.50 mg/kg, S and K were <15.00 mg/kg, while Cl and K were < 20.00 mg/kg.Only Rb and Fe in the control site were within the normal range of TF among the elements analyzed.Ernst (2007) reported that Asian herbal medicinal plants sampled from polluted soils, have elevated contents of TE mainly of Hg, Pb, and As.Therefore, the main source of the elevated concentration in the vegetable could be the polluted soil, comprising lithogenic elements, inherited from mother material and wastes that both form the growth media and probably atmospheric deposition.
Animals including humans generally get exposed to elemental toxicity through food contaminants as the case of this study.Opaluwa et al. (2012) and Epstein (1965) gave the normal range of elements in plants, only the concentrations of Fe in the vegetables fulfilled this condition.Others deviated and well above the stipulated values (Table 4).The tolerable/ permissive values for metals in food as given by WHO/FAO (2007) was fulfilled only in Zn(Sites A,B,C) and was above the value in site D. Heavy metals have health implication in human because they bioaccumulate and are not biodegradable in the body, and the rate of excretion differ from individuals.The tolerable limits of transition elements were not provided.
In this study, heavy metals such as Pb, Al, Zn were above the WHO tolerable limits in food.Lead is a neurotoxic metal, in adults, lead poisoning can cause poor muscle coordination, nerve damage to the sense organs and nerves controlling the body, increased blood pressure, hearing and vision impairment, reproductive problems (e.g., decreased sperm count), retarded fetal development even at relatively low exposure levels.In children, lead poisoning can cause damage to the brain and nervous system, behavioral problems, anemia, liver and kidney damage, hearing loss,hyperactivity, developmental delays, in extreme cases, death.Although the effects of lead exposure are a potential concern for all humans, young children (less than seven years old) are most at risk (Reagan and Silbergeld, 1989).
As for many food components, the intake of metal ions can be a double edged sword.Both their excesses and deficiencies can cause diseases.Redox-Active Metal   (2007).The elements in the soil were inflated by the waste deposition on the soil and other anthropogenic sources, changes in soil formation play important roles in interrelationship of the elements and its discrimination.The uptake of these elements by Amaranthus spinosis caused increases in the metal levels above acceptable limits in the vegetable.This is because the concentrations of metals in the dumpsites were higher than the international permissive limits in soil.Redox active metals such as Fe, Zn, Mn, Al are capable of catalyzing oxidative stress processes, thereby causing chronic inflammatory diseases, cancer, Alzheimer's disease and premature ageing.

Figure 1 .
Figure 1.Imagery of the sampling site.Source: Google Earth Search.

Figure 3 .
Figure 3. Principal component analysis of the vegetable.

Figure 4 .
Figure 4. Cluster analysis of elements in the soil.

Figure 5 .
Figure 5. Principal component analysis of soil.

Table 1 .
The grid location of the sample sites.

Table 2 .
The result of the analysis of Apple leaves (NIST 1515).

Table 3 .
Result of analysis of soil reference material, International Atomic Energy Agency (IAEA-SOIL7).

Table 5 .
Concentration of elements in the dumpsite soil (mg/kg).
* Mean values of different natural soils of Sicily

Table 6 .
Correlation table of soil elements.

Table 7 .
Transfer factor of elements from soil to vegetable.