Metallic nutrients in enset (Ensete Ventricosum) corm and soil sample from some West Shoa Zone, Oromia Regional State, Ethiopia

The aim of this study was to investigate the essential and non-essential metals concentration in corm of Ensete ventricosum and soil samples from some West Showa Zone. Ca and Mg were determined complecometric titration method, K and Na were analyzed using Flame Absorption Emission spectroscopy and the other metals with fl ame atomic absorption spectroscopy after appropriate quality control measures were undertaken to verify and maintain the quality of the data generated. The optimized wet digestion method for corm and soil analysis was found effective for all of the minerals and as it was evaluated through the recovery experiment, a good percentage recovery 95% (Fe concentration in corm) to 112% (Pb concentration in soil) was obtained for the minerals identifi ed. The results of this study showed that the average the metallic nutrient concentrations of elements in the soil sample were ranged in order of decreasing in (mg.kg-1) 3521.11(K) >3497.85(Mg) > 3461.59(Fe) > 3294.93(Ca) >1096.89(Na) > (93.99(Mn) >16.74(Zn) > 3.77(Cu) > 0.26(Cd) but, the concentration of Pb was not detected and the metallic nutrient concentrations of elements in the corm were ranged in order of decreasing in (mg.kg-1) 16425.13(Ca) >13813.33(K) > 1323.55(Mg) > 1131.11(Na) > 76.78(Fe) > 16.16(Zn) >2.77(Cu) >1.94(Mn) but, Cd and Pb were not detected. The nutrient concentrations of the metals were also compared with recommended maximum permissible limits and some international reports; and found to be in a good agreement indicating no exposure risk of using the corm of Ensete ventricosum under the current situation. Statistical test of signifi cance using ANOVA revealed that there were signifi cant differences (P<0.05) between the values of metals in the corm and soil samples obtained from all the sampling sites except Zn concentration for corm and Ca concentration in soil) is not found. Research Article Metallic nutrients in enset (Ensete Ventricosum) corm and soil sample from some West Shoa Zone, Oromia Regional State, Ethiopia Teressa Bedada* and Alemayehu Abebaw Department of Chemistry, College of Natural and Computational Sciences Ambo University, P.O. Box 19, Ambo, Ethiopia Received: 02 January, 2021 Accepted: 19 February, 2021 Published: 22 February, 2021 *Corresponding author: Teressa Bedada, Department of Chemistry, College of Natural and Computational Sciences Ambo University, P.O. Box 19, Ambo, Ethiopia, E-mail:


Introduction
Root and tuber crops are widely cultivated in southern Ethiopia, which are supporting a considerable portion of the country's population as source of food. Prominent among these are potato (Solanum tuberosum L.), sweet potato (Ipomoea batatas L.), Enset (E. ventricosum), Godere (Colacasia esculanta L.), Yams (Dioscorea spp.), Ethiopian dinch (Coleus parvifl orus), koteharrie (Diaspora bulbiferous) and Anchote (Coccinia abyssinica). Among these, Enset, Anchote and some yams are endemic to Ethiopia [1]. Enset based farming systems play an important role in food security in Ethiopia [2] and Ensete ventricosum is one of the indigenous root crops widely cultivated in the Central, South and South Western parts of Ethiopia, but recurrent droughts have led to the expansion of Enset cultivation to other parts of the country [3,4].
Ensete ventricosum parts contained high percent of water (85 to 90%), which is benefi cial when used as fodder during dry periods. Corm of Ensete ventricosum contained 17 of 20 amino acids. Leaves had 13% protein, among the highest available in Ethiopia, 20% crude fi bre and 10% sugar. The pseudostem the main food source, was rich in 80% of soluble carbohydrates and 65% of starch, but has low protein content 4% [5].
Eating the right foods is an important part of maintaining a healthy lifestyle. A single day's intake of nutrients may affect the body's organs only slightly but over years and decades the effects of unhealthy diet compounds into disease, shortened Citation: Bedada

Description of the study areas
The study was conducted in Oromia National Regional State, West Shoa administrative zone. It was found between lifespan, and a less active lower productive life. The nutrients that we intake today will become part of us tomorrow. The nature and composition of what we eat as determines our future, Enset as a food would have its own infl uential impact on millions of peoples in Ethiopia. The corm of Enset has rich in essential nutrients and low in non-essential nutrients [6].
The human body requires a number of nutrition to preserve a good health that nutrition accumulated in different parts of plants (FAO, 2004). Thus plants are intermediate reservoirs through which trace elements from soil and partly from water and air, transfer to man and animal (Rogan, et al. 2009).
The content of heavy metals is one of the criteria for the use of plant material as food or traditional medicines. Hence determination of mineral compositions in food and medicinal plant is essential for understanding their nutritive importance and health risk [7].
However, no literature report was found on comparative determination the concentration of essential and non-essential metals in corm of Ensete ventricosum with its supporting soil samples. Therefore, the aim of this study to compare the essential and non-essential metals concentration in corm of Ensete ventricosum and soil environment from some different locations of West Shoa Zone, Oromia Regional State, Ethiopia by using fl ame atomic absorption spectroscopy and fl ame emission atomic spectroscopy.

Sample collection and protocol
The corm of Ensete ventricosum sample was collected in January, 2016 from the three agricultural areas with its supporting soil. Each sample was collected purposely from four different sub-sites (farm lands) to provide replicate samples. From the three agricultural areas corm can be prepared according to the traditional method. The edible designated plant out of the land was cut into three parts for the separation of pseudostem and Corm with knife ( Figure 2). The soil sample was collected from the surface 15cm-25cm depth of the same four sampling areas of Enset by spade. Finally three corm and soil samples one from each stated areas were collected and put into clean cooled.

Sample preparation
Corm and soil samples were collected from each sub-sites (kebeles) were air dried for three days to remove moisture and all clods and clumps. The samples were grinded with a mortar and pestle and then sieved through a 2mm mesh sieve. The four sub-samples were mixed equal proportion together to form a composite sample that represents each sampling areas. The powdered two samples were placed in pre-cleaned screw capped polyethylene container and stored in desiccators containing calcium chloride to keep to constant dry weight till digestion [8].
Optimization of digestion procedure for corm and soil samples 0.5g of air dried and homogenized corm and soil samples were transferred into a 250mL round bottomed fl ask. To this was added 3.5ml a mixture of HNO 3 (69-72%) and HClO 4 (70%) with a volume ratio of 2:1.5 for corm and 4.5ml a mixture of HNO 3 (69-72%), HClO 4 (70%) and H 2 O 2 (30%) with a volume ratio of 2:1.5:1 for soil. The mixture were digested on a micro Kjeldahl digestion apparatus by setting the temperature 210 and 230 for 1:45hr and 2:30hr respectively. Then, after the digested solution were allowed to cool for 20min without dismantling the condenser from the fl ask and for 10min after removing the condenser. To the cooled solution 25ml of distilled water was added to dissolve the precipitate formed on cooling and to minimize dissolution of fi lter paper by the digest residue while fi ltering with Whatman fi lter paper. The round bottom fl ask was rinsed subsequently with 5ml distilled water until the total volume reached around 45ml. To this fi nal solution, 1% lanthanum nitrate solution was added and the solution was fi lled to the mark 50ml with distilled water. The digested samples were kept in the refrigerator, until the level of all the metals in the sample solutions were determined by FAAS and FAES. and accuracy was calculated by this equation [9].

Spike sample
Unspike sample

Instrument Detection Limit (IDL)
Instrument Detection Limits (IDLs) was estimated by taking seven replicate measurements of the calibration blank (Distilled water). The IDL is calculated to the concentration equal to three times the standard deviation of seven replicate measurements of blank [10].
Where, S b is standard deviation of blank (n = 7) and IDL is Instrument detection limit.

Method Detection Limit (MDL)
Method detection Limit is the minimum concentration of analyze that can be identifi ed measured and reported with 99% confi dence that the analyze concentration is greater than zero. MDL was based up on seven replicate measurements of a series of calibration blanks (reagent blank) that are carried through the entire sample preparation scheme [11]. The MDL was calculated by: MDL = S×T-test Where, S is standard deviation of the replicated analysis with n-1 degree of freedom, t = 3.71 (T-test value for a 99% of confi dence level for six degrees of freedom).

Method Quantifi cation Limit (MQL)
Method quantifi cation limit was obtained from analysis of seven reagents blanks which were digested in the same digestion procedure as actual samples. The method quantifi cation limit was calculated by multiplying standard deviation of the reagent blank by ten plus the mean of the reagent blank signals [11]. It can be calculated by: is standard deviation of the blank.

Method blank
The method blank accounts for contamination that may occur during sample preparation and analysis. These could arise from the reagents, the glassware or the laboratory environment [8]. Sucrose was used as matrix since there was no other plant and clear soil that can serve as the matrix for the corm and soil samples. The blank which was prepared from the sucrose and any reagents used for the digestion was taken through the entire measurement procedure to detect contamination from reagents, sample handling, and the entire measurement process [12].

Matrix spike
Matrix Spike (MS) is portion of a sample spiked with known concentration(s) of target analyte(s). The spiking occurs prior to sample preparation and analysis. The purpose of a matrix spike sample is to determine whether the sample matrix contributes bias to the analytical results [13]. In this study, Matrix spike was prepared for each sample item by spiking aliquots of 0.5g of each corm and soil samples with 2.5ml standards mixture solution giving concentrations of 1.0mgL -1 for K, Zn, Cd and Pb; 2.0mgL -1 for Na, Cu, Fe and Mn. They were all carried through the same digestion and analysis steps as an unspiked sample (

Transfer factor of metals from soil to Ensete Ventricosum
Transfer factor is the ratio of the concentration of metals in a plant to the concentration of metals in soil. Transfer factor for each metals was computed based on the method Harrison and Chirgawi (1989) as described by [14] according to the following formula.

Statistical analysis
Analysis of variance (ANOVA) and F-test at p<0.05 are used to examine statically signifi cant differences in the mean concentrations of metals among groups of soil and corm of E. Ventricosum. A probability level of p<0.05 is considered statistically signifi cant. All statistical analysis was done by Microsoft Offi ce Excel 2007 was used for data analysis and SPSS Version 16.0 Software Window was used for Analysis of variance (ANOVA) and correlation between metals in corm and soil samples [11].

Instrument detection, method detection and quantifi cation limits
As indicated Table 2 the method detection values ranged from 0.08mgkg -1 (Cd in soil) to 2.441mg.kg -1 (Zn in corm) and the MQL values lied in range from 0.3mg.kg -1 (Pd in Corm) 4.21 mgkg -1 (Mn in corm). The results revealed the both MDL and MQL values were greater than the IDL; hence, the results of the analysis could be reliable.

Calibration
The Calibration curves for the various concentrations were ranged between 0.9969 and 0.9999, which were all greater than the required limit (0.995) for trace element analysis. This showed that there was good correlation (relationship) between concentration and absorbance indicating good calibration of instrument (Table 2).

Method precision and accuracy
As it can be indicated Table 3, The mean percent recovery values ranged between 94.85% Fe in soil to 109% (Cu in corm), all lied in the acceptable range (80-120%) for metal analysis [12]. This showed that the analytical method provided results in the required level of accuracy. The RSD values of recovery was ranged between 0.05% (Mn in corm) to 12.22% (K in corm), all lied under the required limit ≤15% [15].

Laboratory control samples result
The percent recovery values of LCS measurements lied  in the range 94.0% (Na in soil) to 113.6% (Zn in bulla) and their relative standard deviations 0.09 (Cu in soil) to 11.37 (Cd in soil), and all the values were found under standard control limits 80-120% for LCS recovery, and ≤15% for RSD [15].
This showed that the method used for the study has provided the required level of accuracy and precision throughout the analytical process.  (Table 4).

Metal concentration in soil used for Enset (Ensete ventricosum) cultivated
The analyzed K concentration of the soil sample was ranged from 3403.33 to 3710mgkg -1 . The highest K concentration was observed in the Dire Enchini and the lowest in the Jeldu, Which is found within the permissible level 1000 to 30000mgkg -1 of K in soil (EPA, 2002). The values of concentration of K in this study greater than with the one reported by Wodaje and Alemayehu [16], which was ranged from 1980 to 6065mgkg -1 .    (Table   6).

Metal levels in corm of E. Ventricosum
The mean concentrations K was the second most accumulated corm next to calcium. The values of K concentration in corm sample was studied areas ranged from 12050.00 to 15013.33mgkg -1 . The highest K concentration was observed in the Jibat corm and lowest in the Jeldu corm, which is below the permissible limit of K concentration in plant dry matter was ranged from 15% [18]. While, as have compared the concentration of K in corm in this study less than in corm with the one reported by Ayalew, et al. [6] around welkete, which was ranged from 14100 to 32200 mg.kg -1 .
The analyzed sodium concentration of Corm was ranged from 1023.33 to 1326.67mgkg -1 . The lowest Na concentration was observed in Jeldu and highest in Jibat, This concentration was below the WHO recommendation on sodium maximum consumption for adults, which is 2 g sodium/day (WHO, 2012).
The analytical data of Mg concentration in corm of Enset was ranged from 1268.67 to 1370 mgkg -1 . The highest Mg concentration was observed in the Jibat and lowest in the Jeldu, which is below the maximum allowed concentration of Mg 0.1 to 0.4% in dry matter of plant FAO [18]. The mean concentration of Mg in corm of Enset in this study less than in corm with the one reported by Ayalew, et al. [6] around welkete, which was ranged from 24900 to 26900 mgkg -1 .
The average concentration of Calcium in corm was studied areas ranged from 15912.22 to 16875.78mgkg -1 . When compared the concentration of Ca, was observed highest in the Jibat lowest in the Jeldu. This concentration found within the range of the maximum permissible limit of Ca in plant dry matter was ranged from 15% [18]. While, as have compared the amount of Ca in corm of Enset in this study within the same range with the one reported by Ayalew, et al. [6] around welkete, which was ranged from 36100 to 39100 mg.kg -1 .
The concentration of iron was analyzed in corm of Enset sample was ranged from 53.67 to 62.0mgkg -1 . The lowest Fe concentration was observed in the Jibat Corm whereas highest in the Jeldu Corm. This concentration is found within the maximum permissible limit of iron ranged between 50 to 250mg.kg -1 in plant dry matter [18]. When, as have compared concentration of Fe in this study almost similar concentration in corm with the one reported by Ayalew, et al. [6], which was ranged from 18.2 to 54.4mgkg -1 .
The Concentration of Manganese in Corm of Enset was found between 1.13 to 2.40mg.k -1 , which was found below the FAO [18] maximum permissible limit of 20 to 300mg.kg -1 . When as compared the manganese concentration in Corm from the three sites the lowest Mn concentration was observed in the Jeldu corm but, the highest in the Dire Enchini Corm and the concentration of Mn in Corm of Enset in this study slightly less than with the one reported by Ayalew, et al. [6], around welkete,which was ranged from ND to 5.61μgg -1 and 2.0 to 5.0μg -1 .
The Concentration of Zn accumulated in corm next to iron among of micro nutrients from the study areas, which was ranged from 15.43 to 17.43mgkg -1 . While, the lowest Zn concentration is observed in the Jibat and the highest in the Dire Enchini, Which was found below the maximum permissible limit of Zn set FAO [18], was ranged from 50 to 250mgkg -1 in plant dry matter. The concentration of Zn in this study with the one reported by Ayalew, et al. [6], which was ranged from 2 11.9 to 42.3mgkg -1 .  The mean concentrations of Cadmium and lead were not detected in corm sample ,those were below the acceptable concentration for food stuff which is around 1ppm [19][20][21][22], indicating no exposure risk to Cd and pb. The lowest level of Cd which can cause yield reduction is 5-30ppm [19][20][21][22] Table 7.

Transfer factor of metals from soil to E. ventricosum
The transfer factor of metals from soil to E. ventricosum, Ca, K, Na, Mg and Cu concentration were more accumulated. When as compared the transfer factor among the different metals, Ca, K, Cu, Na and Zn concentration showed the maximum transfer factor value (Table 8)