J Sci Food Agric 1998, 77, 18È24

Trace Elements in Faba Bean Plant(Vicia faba L)and Soil as Determined by Atomic AbsorptionSpectroscopy and Ion Selective ElectrodeM N Rashed* and R M Awadallah

Chemistry Department, Faculty of Science, Aswan, Egypt

(Received 1 August 1995 ; revised version received 11 June 1997 ; accepted 23 July 1997)

Abstract : Trace (Ag, Au, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sr and Zn) and macro (Ca,K, Mg and Na) element concentrations were determined by atomic absorptionspectrophotometry, and chloride by an ion selective electrode, in di†erent partsof the faba bean (V icia faba L) plant. Leaf, stem, pod, pericarp, cotyledon, testaand seeds were all analysed as were soil samples taken from the immediate vicin-ity of the plant roots at depths of 10, 30 and 60 cm before and after planting thebean plant. The experiment was situated on the shores of the High Dam Lake inAswan (Egypt). The bean leaves showed the highest concentrations of Ca, Mg,Fe, Sr, Mn, Ni, Co, Pb and Cr while the seeds showed the highest concentrationsof Zn and Cu. The highest levels of trace elements in the soil were found at60 cm depth after planting which suggests the uptake of most trace elements bythe plant is from the 10È30 cm depth zone. Statistically there were signiÐcantcorrelations between trace element concentrations in the bean and soil samples.The levels of trace elements in the bean under study were not considered to betoxic for man or animal uses. 1998 SCI.(

J Sci Food Agric 77, 18È24 (1998)

Key words : bean soil trace element ; nutrient ; ion selective electrode ; toxicelement

INTRODUCTION

Trace elements are necessary for the healthy develop-ment of man, animals and plants. Their concentrationsin the plant di†er from part to part and from plant toplant, depending on the trace element levels in the soil.

Bean seeds are considered an important and essentialfood for man in developing countries. Trace elements inkidney beans (Awadallah et al 1986) and in beans(Sherif et al 1979) from Egypt have previously beendetermined using atomic absorption spectroscopic andneutron activation analysis techniques. Also, theresponse of kidney bean to concentration and thechemical form of Co, Zn and Pb in polluted soils, hasbeen reported (Xingu Xian 1989). The distribution oftrace elements in di†erent parts of plants and crops

* To whom correspondence should be addressed.

(leaves, stem, pericarp, cotyledon, pods, roots and seeds)as well as in the soil at depths of 10, 30 and 60 cm inthe shores of the High Dam Lake, have been reported(Rashed 1989 ; Awadallah and Rashed 1993).

After the creation of the High Dam Lake (South ofAswan, Egypt) (Fig 1), many studies have been done inthe lake mud (Moalla 1990 ; Awadallah et al 1994 ;Moalla et al 1995). Sediments (Sherif et al 1980, 1981 ;Hassouna 1989 ; Awadallah et al 1994) and in soil at thenew lands near the shores of the lake (REGWA 1978 ;Rashed 1989 ; 1992, 1994 ; Awadallah and Rashed 1993).

Our study aimed to examine the suitability of the soilat the new land near the shore of the High Dam Lake,for cultivation. We cultivated faba beans in this newland and analysed the di†erent parts of the bean plant(leaf, stem, pod, pericarp, cotyledon, testa and seed) tomonitor the distribution of trace element concentrationsin each part, and to determine if toxic levels for plant,

181998 SCI. J Sci Food Agric 0022È5142/98/$17.50. Printed in Great Britain(

T race elements in faba beans 19

Fig 1. Location map showing study area.

human or animals were achieved. We also determinedthe relationship between trace elements in the plant andthe uptake from di†erent soil depths.

EXPERIMENTAL

Faba bean (V icia faba L) plants were cultivated at theexperimental farm (at Kalabsha area Fig 1) on thewestern shore of the High Dam Lake in October 1991).This soil was new and used for the Ðrst time. Beanswere planted in basins (3] 5 m) in hills, the distancebetween hills being 30] 20 cm. Potassium nitrate wasused to fertilise the soil.

Sample collection

Ten sites on the experimental farm were selected, and 10samples of faba bean plants were collected from thecentre of each site in June 1992. The plants were cleanedto remove visible soil and then washed with tap waterand bidistilled water several times. The parts of thebean plants (leaf, stem, pod, pericarp, cotyledon, testaand seed) were separated from the plant, washed againwith bidistilled water and allowed to drain, then ovendried at 100¡C for 24 h. They were then ground in astainless-steel blender.

A 5 cm core of soil sample, close to where the beanwas planted, was collected by a stainless-steel samplerbefore planting the beans. Another 5 cm core of thesame soil after planting was collected from the imme-diate vicinity of the plant roots at depths of 10, 30 and60 cm. The representative samples of bulk soil fromeach depth were ground and powdered with the aid of amechanical agate mortar to 100 mesh. The powderedsamples of bean plant and the soil samples were storedin clean polyethylene bottles until analysis.

Sample preparation for AAS and measurement

Plant samplesTwo grams of each plant subsample was wet ashed in acovered TeÑon beaker using 20 ml of 1 : 1

acid mixture, followed by the addition ofHNO3/HClO43 drops of HF. This was heated to clear solution andcontinued until dryness. The cooled residue was dis-solved in 5 ml conc HCl and the liquor was made up to50 ml using bidistilled water.

Soil samplesOne gram of the Ðnely ground dried soil sample wasmixed with 20 ml (1 : 1) acid mixture andHCl/HNO3the content was heated until dryness. The residue wasextracted using 2 M HCl and brought to 50 ml withbidistilled water.

An SP 1900 Pye Unicam atomic absorption spectro-photometer (AAS) equipped with an airÈacetyleneburner was used. Ag, Au, Ca, Co, Cr, Cu, Fe, K, Mg,Mn, Na, Ni, Pb, Sr and Zn were determined using a PyeUnicam hollow cathode lamp at the recommended cur-rents and conditions. Ca, K, Mg and Na were measuredafter dilution, other elements were measured withoutdilution in the range of the element detection limits.

Sample preparation for ISE and measurements

Plant sampleOne gram of the dried powdered bean sample wasextracted by shaking with 1 M A single knownNaNO3 .addition technique was used to prevent the e†ect ofionic strength (Orion Research Inc 1976, 1982).

Soil sampleTen grams of soil sample was shaken with 100 ml freechloride deionised water for 30 min. The soilÈwatermixture was Ðltered o†. One ml of 5 M (ISENaNO3adjustor) was added to all standard and sample solu-tions to prevent a constant background ionic strength.Chloride ion-selective and double junction referenceelectrode were used in the measurements. Both standardand sample solutions were brought to the same tem-perature and stirred constantly during measurement toprevent any change in chloride electrode slope (Carisonand Keeney 1971 ; Orion Research Inc 1970, 1980).

20 M N Rashed, R M Awadallah

TABLE 1Trace element concentrations (ppm) in di†erent parts of bean plant samples from 10 sitesa

Elements Mean

a b c d e f g

Ag 0É012 0É003 0É004 0É00 0É008 0É003 0É002Au 0É17 0É05 0É04 0É036 0É00 0É006 0É007Ca(%) 7É6 1É66 1É53 1É71 0É68 0É90 0É65Cl 37É7 50 78 72 66 58 56Co 0É16 0É07 0É13 0É09 0É04 0É04 0É07Cr 0É035 0É035 0É045 0É035 0É01 0É025 0É005Cu 0É15 0É07 0É23 0É13 0É21 0É28 0É29Fe 22 9É5 33 10 7É5 7É5 9É5K 188 298 592 517 364 406 411Mg 208 59 77 80 38 41 48Mn 3É39 0É15 0É51 0É48 0É09 0É48 0É29Na 26 49É7 7É9 15É5 1É3 4É9 2É5Ni 0É19 0É04 0É10 0É07 0É09 0É09 0É13Pb 0É10 0É005 0É005 0É01 0É0 0É01 0É015Sr 2É98 1É04 0É38 0É49 0É05 0É14 0É06Zn 0É35 0É09 0É39 0É21 0É51 0É41 0É53

Elements SD

a b c d e f g

Ag 0É002 0É002 0É002 0É000 0É00 0É005 0É002Au 0É02 0É009 0É01 0É009 0É00 0É002 0É003Ca(%) 1É2 0É21 0É08 0É17 0É06 0É11 0É07Cl 3É8 25É4 6É1 3É6 5É1 4É7 5Co 0É02 0É008 0É02 0É008 0É007 0É008 0É011Cr 0É007 0É007 0É007 0É012 0É004 0É006 0É010Cu 0É02 0É04 0É008 0É02 0É032 0É018 0É01Fe 1É8 1É0 8É1 0É41 0É75 0É27 0É27K 11 5É7 5É9 9 23 6É1 17Mg 17 8É5 7É6 3 3É1 1É3 4É1Mn 0É37 0É37 0É09 0É05 0É023 0É038 0É02Na 5 3É1 2É3 3 2 1É3 0É6Ni 0É019 0É018 0É025 0É008 0É012 0É013 0É011Pb 0É033 0É007 0É02 0É008 0É00 0É004 0É005Sr 0É39 0É25 0É06 0É07 0É014 0É016 0É005Zn 0É00 0É15 0É12 0É24 0É07 0É02 0É08

Elements CV (%)

a b c d e f g

Ag 22É8 91 26 0É0 0É0 71 91Au 11É7 18 24 26 0É0 40 47Ca(%) 3É6 13 5É6 10 9É5 12 10Cl 10 50 7É8 5 17 8 9É7Co 13 10 18 9É5 17 19 17Cr 16 24 19 43 22 34 74Cu 12 43 3É8 18 14 6É8 3É6Fe 9É3 13 41 4 8É7 3É5 2É9K 5É6 2 1 1É7 6É2 1É5 4É2Mg 8É8 16 8É5 3É8 7É9 3 8É7Mn 12 23 18 11 22 8É4 6É2Na 14 6É8 21 21 26 30 23Ni 10 31 23 10 13 15 8É5Pb 38 70 43 49 0É0 38 50Sr 12 20 17 17 35 13 8É5Zn 22 64 27 49 14 6É3 6É9

a Abbreviations : a, leaves ; b, stems ; c, pods ; d, pericarp ; e, cotyledon ; f, testa ; g, seeds.

T race elements in faba beans 21

TABLE 2Trace elements concentrations (ppm) at di†erent depths of soil samples (n\ 10) before and after planting the

bean

Elements Before planting

Mean SD CV (%)

10 30 60 10 30 60 10 30 60

Ag 0É011 0É011 0É00 0É002 0É003 0É003 20 27 0É0Au 0É18 0É16 0É15 0É03 0É03 0É04 16 18 26Ca (%) 4É0 3É9 4É2 1É0 1É8 1É7 25 46 40Cl 0É5 1É0 3É0 0É02 0É05 0É04 4 5 1É3Co 0É29 0É25 0É21 0É02 0É03 0É05 6É8 12 23Cr 0É99 1É0 0É60 0É27 0É28 0É25 27 28 41Cu 0É54 0É25 0É21 0É10 0É19 0É12 18 76 57Fe 345 383 206 29 16 9 8É4 4É1 4É3K 30 21 24 2É1 3É6 2 7 17 8Mg 98 95 41 2É3 3É1 2É4 2É3 3É2 5É8Mn 4É5 6É9 1É7 0É15 0É13 0É14 3É3 1É8 8É2Na 3 2É6 1É7 1 1 1É2 33 38 70Ni 0É32 0É86 0É29 0É11 0É13 0É12 34 15 41Pb 0É29 0É28 0É10 0É03 0É02 0É05 10 7 50Sr 0É58 0É48 0É42 0É13 0É15 0É15 22 31 35Zn 1É8 2É2 1É47 0É30 0É28 0É25 16 12 17

Elements After planting

Mean SD CV (%)

10 30 60 10 30 60 10 30 60

Ag 0É01 0É01 0É0 0É0 0É0 0É0 0É0 0É0 0É0Au 0É17 0É16 0É15 0É03 0É06 0É06 22É2 39 41Ca (%) 4É9 3É6 4É1 2É6 0É84 1É5 53 23 36Cl 4É2 3É7 3É35 1É67 1É54 1É49 39 41 42Co 0É23 0É21 0É20 0É04 0É04 0É06 18 22 32Cr 0É67 0É84 0É55 0É13 0É21 0É14 20 25 25Cu 0É16 0É14 0É09 0É02 0É03 0É05 17 22 26Fe 249 211 208 16 50 55 6É4 23 26K 34É1 25É7 23É6 4É8 9 8É4 14 35 36Mg 55É9 43É3 39 7É9 14É2 15É8 14 32 40Mn 5É14 4É83 5É47 0É97 1É43 1É45 18 29 26Na 2É52 2É31 1É61 0É66 0É88 0É74 26 38 46Ni 0É49 0É54 0É40 0É11 0É13 0É09 22 25 24Pb 0É08 0É07 0É06 0É02 0É03 0É03 34 50 60Sr 0É46 0É42 0É43 0É10 0É13 0É26 23 31 60Zn 0É48 0É42 1É3 0É06 0É15 0É85 13 36 65

Data were statistically analysed using the analysis ofstandard deviation, coefficient of variance and corre-lation coefficient (Steel and Torrie 1980).

RESULTS

The data obtained from the chemical analysis of bean(leaf, stem, pod, pericarp, cotyledon, testa and seed)are given in Table 1, while the results of the chem-ical analysis of soil samples at depths of 10, 30 and

60 cm depths before and after planting are recorded inTable 2.

The results show that amongst all parts of the beanplant, leaves accumulated large concentrations of K, Ca,Mg, Fe, Sr, Mn, Ni, Co, Pb and Cr from the soil solu-tion. Stems show large concentrations of Na and Cl,which exists as NaCl Ñuid and regulate the osmoticpressure (Bowling 1976 ; Oser 1979 ; Yagodin 1982). K,Cl and Fe accumulate in pods, while Zn and Cu accu-mulated in the seed.

On analysis of the soil samples taken from depths of10, 30 and 60 cm, the data obtained before and after

22 M N Rashed, R M Awadallah

TABLE 3Coefficient of variance between 10, 30 and 60 cm soil depths for each element

concentrations (ppm) before and after planting of bean

Elements Before planting After planting

M SD CV (%) M SD CV (%)

Ag 0É007 0É006 85 0É006 0É005 83Au 0É16 0É01 6É2 0É16 0É01 6É2Ca(%) 4 0É15 3É7 4É2 0É65 15Cl 1É5 1É3 86 3É7 0É42 11Co 0É25 0É04 16 0É21 0É015 7Cr 0É86 0É22 25 0É68 0É14 20Cu 0É29 0É22 76 0É13 0É03 23Fe 311 93 30 223 23 10K 25 4É5 18 28 5É5 19Mg 78 32 41 46 8É7 3É7Mn 4É4 2É6 59 5É1 0É3 5É8Na 2É4 0É66 27 2É1 0É47 22Ni 0É49 0É32 65 0É47 0É07 14Pb 0É22 0É10 45 0É07 0É01 14Sr 0É49 0É08 16 0É43 0É02 4É6Zn 1É85 0É41 22 0É73 0É49 67

planting (Table 2) show that at 10 cm depth concentra-tions of Ag, Au, Cl, Co, Cr, Cu, Fe, Mg, Na, Pb, Sr andZn decreased after planting, while Ca, K, Mn and Niincreased, possibly as a result of using potassium nitratefertiliser which contains impurities of Ca, Mn and Ni(Turner and Olson 1976 ; Runger 1983). At a depth of30 cm, Cl and K increased after planting, while otherelements decreased. This decrease of element concentra-tions was statistically signiÐcant through CV(%) andSD determinations at depths of 10, 30 and 60 cm (Table3). At a depth of 60 cm there was no di†erence (exceptthe increase of Mn and Ni after planting).

After planting of bean, Ag, Au, Ca, Cl, Co, Ca, Mg,Na, Fe and Pb were present in large concentrations inthe soil at a depth of 10 cm than other depths, while adepth of 60 cm exhibited low concentrations of theseelements (except Zn and Mn). Soil at a depth of 30 cm

exhibited nearly the same levels of the element concen-trations as in the soil at a depth of 60 cm (except Crand Ni), suggested that the bean plants take most oftheir trace elements from the 10È30 cm soil zone.

Statistical analysis of the data

In the statistical analysis of the database in this study,correlation coefficient values of trace element concentra-tions distributed between the bean plant (p) and the soildepths 10, 30 and 60 cm and (Table 4)(S10 , S30 S60)show that highly signiÐcant and positive correlationcoefficients were found between for Cl, Co, Cr, K,p/S10Mg, Ni, Sr and Zn. Ag, Cr and Cl showed a positivecorrelation of While elements Ag, Cl, Cr and Mnp/S10 .showed a positive correlation of p/S60 .

TABLE 4Correlation coefficient values between trace elements in beans and soil at depths of 10, 30 and

60 cma

Ag Au Cr Cl Co Cr Cu Fe

P/S10 0É49 0É06 0É23 0É64 0É84 0É81 [0É48 [0É57P/S30 0É56 0É10 [0É30 0É56 [0É49 0É85 [0É05 [0É15P/S60 0É94 0É03 [0É30 0É69 0É25 0É85 [0É01 [0É91

K Mg Mn Na Ni Pb Sr Zn

P/S10 0É69 [0É57 [0É39 [0É12 0É73 [0É20 0É92 0É18P/S30 [0É01 [0É42 [0É09 [0É85 [0É48 [0É35 [0É46 [0É47P/S60 0É11 [0É69 0É68 [0É34 0É03 [0É72 0É09 [0É02

a Abbreviations : P, mean plant ; soil depth at 10, 30, 60 cm.S10 , S30 , S60 ,

T race elements in faba beans 23

On analysis of the coefficient of variance (CV(%)) oftrace element concentrations between 10, 30 and 60 cmsoil depths before and after planting bean (Table 3)show that CV(%) for Ag, Au, Cl, Co, Cr, Cu, Fe, Mg,Mn, Na, Ni, Pb and Sr decreases signiÐcantly afterplanting.

DISCUSSION

A previous study on trace elements in faba bean (seeds)from Egypt (Sherif et al 1979) has revealed that Cu andZn can be present in high concentrations and this isconÐrmed by results of this study. At the same experi-mental farm (near our study area), on the shore of theHigh Dam Lake, measurements in fenugreek and lupinshowed higher concentrations of K, Cl, Mg, Ni, Fe, Mn,Co, Au and Pb in leaves. The stems had higher concen-trations of Na and Cl, while seeds exhibited high con-centrations of Zn and Cu (Rashed 1989). In the samesoil (also near our study area), barley, millet and purs-lane were cultivated and the picture of trace elementsdistribution in these plants showed that the leavesexhibited higher concentrations of K, Mg, Cl, Mn, Na,Fe, Ni, Co, Pb, Ag and Zn than in other parts (Rashed1989). This soil contains Fe, Mg, K, Na, Mn, Cl, Cu,Co, Pb and Zn in low concentrations at the depth zoneof 10È30 cm (Rashed 1989).

Leaves of lemon trees on the south shore of the HighDam Lake exhibit higher concentrations of trace ele-ments than in the other parts of the tree. While the soilat a depth of 60 cm of the tree root contains the highestlevels of Ca, Mg, K, Zn, Cr, Sr, Co, Au and Pb. Soil at adepth of 10 cm exhibits high values of Mn, Cl and Ni,whereas soil at a depth of 30 cm possesses high levels ofFe, Mn, Na, Zn, Ni, Cr and Cu. These lemon treesabsorb their essential nutrient trace elements from alldepths (Awadallah and Rashed 1993).

Leaves represent the nutrient store for the plants, so,high concentration of the nutrient elements present inthe leaves of the plants (Stiles 1961 ; Oser 1979). Traceelements are essential for leaf growth, cell wall bonding(Ca and Mg), chlorophyll synthesis (Fe, Mg and Ca),vitamins and coenzymes (Fe, Co and Zn) colour, smelland taste (Mn, Fe, Co, Ni, Cu and Ag) and protein (Cuand Zn) (Stiles 1961).

The distribution of trace element concentrations indi†erent parts of a range of plants cultivated in thefarms around the High Dam Lake has revealed thatleaves of these plants (millet, barley, purslane and beet)exhibit the higher concentrations of K, Mg, Cl, Mn, Na,Fe, Ni, Co, Pb, Ag and Zn than in the other parts ofplant.

Concentration of the studied elements in the soil ofbean decreases after planting due to absorption of theseelements by bean roots from the surrounding soil solu-

tion and accumulates in the di†erent parts of the plant.The presence of Ca and K in higher concentrations at adepth of 10 cm after planting of bean is higher thanbefore (Bowling 1976 ; Deser 1979 ; Runger 1983) ;because of the use of nitrate fertiliser containing Ca andK (Runger 1983).

Measurements of soil in the Kalabsha farm on thebeach of the High Dam Lake reveal that the high levelsof trace element concentrations are present in the 10È30 cm depth zone (Rashed 1989). This was conÐrmed inthis study. This indicates that the bean plant takes mostof its need for trace elements from 10È30 cm as a resultof the shallow roots of the plant (Yagodin 1982).

Heavy metals such as Ag, As, Cu, Hg, Pb, Sb and Znare found to be enriched in the upper layer of the soil.Other trace elements were reported to be enriched inthe lower layer of the soil, where clay minerals and/orhydrous oxides accumulate, include Al, Fe, Ga, Mg, Ni,Se, Ti, V and Zr (Bowen 1979).

Trace elements in the soil depend on the soil forma-tion and the geology of the area (Hume 1934 ; Magnard1983). So, Kalabsha farm soil (in this study) di†ers inthe chemical composition from the other areas at theeastern side of the lake (Allaqi area) and Aswan city soilat the beach of the river Nile (Hume 1934 ; Rashed1992). The results of trace element analysis in soil of thisarea reveal that Kalabsha soil exhibits the highest levelsof K, Co, Cu, Zn and Ca concentrations (Rashed 1992,1994). In the same side of the lake at the south (AbuSimble), leaves of cultivated lemon trees contain higherlevels of Ag, Au, Cl, Ca, Co, Cr, Mg, Mn, Sr, Zn and Nithan in the other parts of the tree and the fruit. Soil at adepth of 60 cm contains lower levels of trace elements,indicating that a lemon tree takes most of its trace ele-ments from this depth as a results of the long roots ofthe tree (Awadallah and Rashed 1993). The di†erence oftrace element concentrations in the soil from one depthto another may be attributed to the geomorphologicaldi†erentiation and agrochemical properties (Shata1962).

Seeds of beans in this study contained high levels ofCu and Zn concentration. They are considered as agood source of proteins, since Zn and Cu are activatorsand coenzymes (Stiles 1961).

Trace elements play an essential biological role inplant and human metabolism. Cl is essential for plantgrowth, root formation, photosynthesis and fruiting(Oser 1979). K is an essential nutrient element and hasan important role in the synthesis of amino acids andproteins and mainly accumulates in the green leavesand activates enzymes of carbohydrate metabolism(Malik and Srivastava 1982). Ca, Mg and Fe are essen-tial nutrient elements for all living cells and play animportant role in photosynthesis and carbohydratemetabolism (Gibbs 1978 ; Bowling et al 1976 ; Malik andSrivastava 1982). Cr is essential for the chloroplastmembrane system (Oser 1979).

24 M N Rashed, R M Awadallah

The toxic doses of Co, Cr, Cu, Fe, Mn, Ni, Pb and Znto plants are 0É13, 0É5È10, 0É5È8, 10È200, 1È100, 0É5È2,3È20 and 60È400 ppm, respectively. The toxic levels forman are Co 500, Cr 200, Cu 250, Fe 200, Mg 10È20, Ni50, Pb 1 and Zn 150È600 mg day~1 (Bowen 1979). So,the levels of the studied trace elements for both plantand man are within the safety baseline levels.

In the statistical analysis of the database in this study,correlation coefficient values of trace element concentra-tions between plant and soil at depths of 10, 30 and60 cm revealed that Ag, Cl, Co, Cr, K, Mg, Mn, Fe, Znand Sr are essential trace elements for plants. The plantcan easily absorb these elements from the external soilsolution. However, Ag, Cl, Co, Cr, K, Mg, Ni, Zn andSr are easily absorbed from 10 cm, Ag, Cl and Cr from30 cm, and Ag, Cl, Cr and Mn from 60 cm and com-plexed with the high molecular weight cells. Experi-ments have shown that a major factor of inorganicnutrient uptake is the ratio of ions in the medium(Yagodin, 1984), and when the nutrient elements areabsorbed by the root, the diameter of ions in thehydrated state is a matter of importance. Accordinglyunivalent cations enter root cells at faster rate than bi-and multivalent ones (Yagodin 1984).

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