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DETERMINATION OF SOME TOXIC AND ESSENTIAL TRACE METALS IN SOME MEDICINAL AND EDIBLE PLANTS OF KARACHI CITY.

Byline: Mahwash Zahra Kirmani - E-mail: mahwash_kirmani@yahoo.com, Sheikh Mohiuddin, Farah Naz, Iftikhar Imam Naqvi and Erum Zahir

Abstract

Trace metals in eight different medicinal plants commonly available in Karachi namely Azadirachta indica (Neem), Syzygium aromaticum (Clove), Murraya koenigii (Curry Leaves), Trachyspermum ammi (Ajowan), Foeniculum vulgare (Fennal), Brassica oleracea (Cabbage), Brassica rapa (Turnip), and Pipper nigrum (Black pepper) have been quantitatively analyzed using Atomic Absorption Spectroscopy and Flame Photometry. A wet digestion procedure involving the use of H 2 SO 4 (95%) and H 2 O 2 (35%) has been adopted to digest medicinal plants. Nine heavy metals (Cd, Cr, Co, Cu, Fe, Pb, Mn, Ni, and Zn) and two alkali metals (K and Na) were chosen on the basis of their effects upon health. In general the order of concentration of toxic metals in medicinal plants was found to follow the order Pb greater than Ni greater than Cr greater than Co greater than Cd. Sodium and Potassium content was found to be very high in all the samples.

Concentration of sodium were recorded to be the highest in roots of Brassica rapa and Murraya koenigii i.e., more than 1000 ug/g. Potassium concentrations are around 9038 mg/g in Foeniculum vulgare. Plant samples of Trachyspermum ammi, leaves of Brassica rapa, and Foeniculum vulgare, Brassica oleracea (Cabbage), contained comparatively higher amounts of Fe i.e., greater than 100ug/g. Out of all toxic metals Lead is present at noticeable levels in all the samples that indicates higher soil pollution .Concentrations of Na, K and Mn and Cu are found to be very high in Brassica rapa roots as compared to its leaves while Fe levels are found to be high in leaves.

Keywords: Medicinal plants, Heavy metals, Pollution, Atomic Absorption Spectrophotometer.

INTRODUCTION

Medicinal plants are consumed worldwide for the treatment of several diseases and such plants are also an important source of raw material for pharmaceutical industries, summarized as shown in Table 1. In recent decades the use of herbal medicines has increased worldwide. This may be because of the fact that the side-effects of these materials are often lower than synthetic drugs apart from the higher costs of many conventional pharmaceutical formulations (Rates, 2000). Many medical herbs used in formulating these medicines can present a health risk due to the presence of toxic ingredients like heavy metals. The toxicity of heavy metals depends upon the chemical form of elements. Heavy metals are dangerous in the form of their cations and are highly toxic when bonded to the short chains of carbon atoms (Hussain, 2006).

Plants may absorb heavy metals from soil, water or air. Medicinal herbs may be easily contaminated during growing and processing. The ability of plants to selectively accumulate essential elements is different for different species and is subjected to certain geochemical characteristics depending on the type of soil (Bin et al., 2001). Usually soil is subjected to contamination through atmospheric deposition of heavy metals from point sources including metalliferous mining, smelting and different industrial activities. Some other sources of soilcontamination involve use of fertilizers, pesticides, ewage sludge and organic manures (Singh et al., 1997). Plants readily assimilate such elements through the roots. Metallic ions get dissolved in water and retained. Additional sources of these elements for plants are rainfall, atmospheric dusts and plant protection agents, which could be adsorbed through the leaf blades.

An important source of contamination, in vegetable crops, is considered to be the foliar uptake of atmospheric heavy metals emissions by the soil (Salim et al., 1993).

In general, most plants grow by absorbing nutrients from the soil. Their ability to do this depends on the nature of the soil. A soil contains some combination of sand, silt, clay, and organic matter. This combination depends on its location. Soil texture and its pH determine the extent to which nutrients are available to plants. The path taken by metal to transport into the plant is: soil greater than roots greater than stems greater than leaves. The minerals often accompanied by various organic molecules supplied by root cells get transported after being dissolved in the water. This mixture deposits into xylem and from there it moves up in the vessels and tracheids. Minerals enter the root by active transport into the epidermal cells and move towards other parts of plant.

The accumulation of metals in plants is associated swith nature of soil and climatic conditions. Bioavailability of metal in plant depends on active and passive transport processes, the response of plant to element, redox state of metal and its solubility and also on plant genotype.

Table 1. Importance of medicinal plants

Plant Specie###Common Name###Part Analyzed###Medicinal Properties

Azadirachta indica###Neem###Leaves###Its bark is a good bitter tonic, astringent, antiperiodic

###also used in skin diseases. .Its leaf extract is reputed

###to treat Malaria (Kulkarni, 1999; Badam, 1987).

Pipper nigrum###Black pepper###Berries###It is an aromatic carminative stimulant. It contains

###antioxidant constituents and possesses anti-

###inflammatory and antimicrobial properties

###(Purseglove, 1981).

Brassica rapa###Turnip###Leaves and###Its juice is used for Acne, Bronchitis, Constipation,

###Root###Gout, Infections, Intestinal Disorders and joint pain.

Syzygium###Clove###Dried Buds###It is used as antiseptic, mind and body stimulant, and

aromaticum###analgesic, antibacterial, carminative. It is also used in

###nausea and vomiting.

Trachyspermum###Ajowan###Seed###It is used as antispasmodic, stimulant, diuretic tonic

ammi###and for carminative purpose. It is also used in

###bronchitis, asthma and often constitutes an ingredient

###of cough mixture (Caius, 1986).

Foenicumlum###Fennal###Seed###It is considered as Stomachic, Carminative, Pectoral,

vulgare###Diuretic, Anti -inflammatory, and Stimulant.

Murraya koenigii###Curry Patta###Leaves and###It is used to cure eruptions and the bites of poisonous

###stem###animals, also used for curing dysentery, and the

###infusion of the washed leaves stops vomiting

Brassica oleracea###Cabbage###Leaves###It is effective in diabetes, obesity, uric acid and

###diseases often associated to the retention of liquids.

There are no guidelines to establish a permissible level of metals in herbs. By monitoring the level of metals in medicinal plants one can be able to indicate the level of nvironmental pollution in that area. Environmental pollution effects badly on plant growth and its genotype. The sources of environmental pollution are varied, Industries, metallurgical process, traffic fumes and also advanced life style play a vital role in this regards, which may cause serious health hazards such as renal failure, skin diseases, and liver damage.

The present study is concerned with the assessment of the metal content of some medicinally important herbs and plants. This study has been focused to estimate the concentrations of some toxic and essential metal ions in the plants namely Azadirachta indica, Syzygium aromaticum, Trachyspermum ammi, Foenicumlum vulgare, Brassica oleracea , Brassica rapa, and Pipper nigrum .Nine heavy metals (Cd, Cr, Co ,Cu Fe, Pb, Mn , Ni, Zn ) and two alkali metals (K and Na) have been chosen on the basis of their ability to cause health disorders.

MATERIALS AND METHODS

Samples of different herbs including Azadirachta indica (Neem), Syzygium aromaticum (Clove), Trachyspermum ammi (Ajowan), Foeniculum vulgare (Fennal), Brassica oleracea (Cabbage), Brassica rapa (Turnip), and Pipper nigrum (Black pepper), were bought from different markets of Karachi. These samples were transferred to plastic bags and brought to the Laboratory.

The samples were washed thoroughly with distilled water and rinsed with deionized water. Subsequently they were dried in oven in between 80-100 o C followed by grinding, using pistol mortar. The dried and grinded samples were then stored in clean, dried and decontaminated plastic bottles. About two grams grinded powder of each sample was transferred to a 100ml beaker. Subsequently, 32ml H 2 SO 4 (95%) was poured into it and the resulting mixture was heated to 200 o C. so that the water got eliminated. As a result of this the mixture attained a brown color.

It was followed by the addition of 8ml H2O 2 (35%) through a dropping funnel. As the reaction finished another 8ml H 2 O 2 (35%) was added. The mixture was heated again. The addition of H 2 O 2 had to be repeated at 200 o C temperature till the digested solution stayed clear (Application Bulletin Metrohm, Method No.114/1e). After cooling, the content was transferred to a 100ml volumetric flask and the final volume was made up using ultra pure water. These solutions were then stored in dry and clean plastic bottles. Triplicate analysis of each sample was undertaken and that Atomic Absorption Spectroscopy and flame Emission Spectroscopy were employed for this purpose. Atomic Absorption Spectrometer, Perkin Elmer model A-analyst 700 and Sherwood Flame Photometer were the two instruments used for this purpose.

RESULTS

In all eight plants namely Azadirachta indica (Neem), Syzygium aromaticum (Clove), Trachyspermum ammi (Ajowan), Foeniculum vulgare (Fennal), Brassica oleracea (Cabbage), Brassica rapa (Turnip), Murraya koenigii (Curry Patta) and Pipper nigrum (Black pepper) were investigated for their metal load. In this respect concentration levels of Cd, Cr, Co, Cu, Fe, Pb, Mn, Ni, Zn, K and Na in units of ug/g have been determined. The results of our investigation are being presented through Table 2. These results show that highest concentration of Iron was found to be greater than 100 ug/g in the plant samples of Trachyspermum ammi, Leaves of Brassica rapa, and Foeniculum vulgare, Brassica oleracea.

Highest concentration of Manganese was found to greater than 20 ug/g except in Brassica rapa ( roots and leaves). Level of Cadmium in all the plant samples is less than 0.5 ug/g. Roots of Brassica rapa was found to contain highest concentration of Sodium metal which is greater than 10 4 ug/g while Potassium was found to be the highest in Foeniculum vulgare. Roots of Brassica rapa and Murraya koenigii contained relatively higher concentrations of Copper than other plant samples. Foeniculum vulgare and Trachyspermum ammi contained almost same concentrations of Zinc. Chromium and Cobalt were less than 3.5 ug/g in all the samples. Concentrations of lead were recorded in between 9 - 25 ug/g.

DISCUSSION

Metals play a vital role as structural and functional components of protein and enzymes in cells. Each mineral plays a number of different functions in the body. The most important pathway of metals to transport into human is from soil to plant and from plant to human. Some metals such as Ca, Mg and Zn have been reported to be essential for human health, whereas others such as Pb, Cd and Al have been identified as toxic. Rests of the elements are not toxic to human unless they are present in high concentrations. The present study provides baseline data on trace metal concentration Cd, Cr, Co, Cu, Fe, Pb, Mn, Ni, Zn, K and Na in spices and medicinal plants commonly used for the treatment of different ailments.

Table 2. Concentration of metals mg/g dry wt +- Standard deviation

Plant Specie###Na###K###Fe###Mn###Cd###Pb###Ni###Cr###Co###Cu###Zn

Azadirachta###76.56###2295###20.91###20.91###0.041###12.35###3.726###1.704###1.126###23.14###34.89

indica###+-0.971###+-204.3###+-7.030###+-0.314###+-0.013###+-2.521###+-1.043###+-0.040###+-0.067###+-1.234###+-5.090

Pipper nigrum###269.4###1494###31.05###42.84###N.D###10.93###0.293###1.076###0.195###3.394###20.53

###+-1.597###+-89.20###+-1.774###+-2.465###+-1.672###+-0.196###+-0.008###+-0.086###+-0.028###+-2.557

Brassica rapa###2291###2019###189.3###N.D###0.495###21.36###5.255###3.219###0.866###12.54###32.64

Leaves###+-439.3###+-67.20###+-2.574###+-0.141###+-1.385###+-1.034###+-0.590###+-0.122###+-0.524###+-6.381

Brassica rapa greater than 10.4###45.55###60.90###6.860###0.457###9.515###5.480###1.932###0.752###112.3###17.15

Roots###+-1354###+-354.2###+-5.627###+-1.401###+-0.035###+-0.276###+-1.230###+-0.230###+-0.222###+-6.390###+-4.325

Syzygium###2409###16.18###60.03###57.30###0.090###9.727###0.699###0.961###0.654###3.240###4.940

aromaticum###+-81.60###+-135.6###+-0.785###+-6.826###+-0.062###+-1.112###+-0.082###+-0.109###+-0.040###+-0.261###+-1.228

Trachyspermum###8112###1920###194.9###40.89###0.227###13.99###0.129###0.267###1.837###7.618###53.7

ammi###+-144.7###+-64.50###+-3.960###+-2.170###+-0.088###+-0.798###+-0.039###+-0.006###+-0.187###+-0.301###+-1.706

Foenicumlum###69.61###9038###136.5###41.20###N.D###14.67###4.353###3.342###1.018###37.13###53.69

vulgare###+-0.532###+-571.0###+-7.927###+-1.264###+-0.917###+-0.032###+-0.124###+-0.183###+-1.220###+-1.465

Murraya###2783###23.17###89.08###34.57###0.263###24.02###3.436###N.D###1.634###117.09###12.77

koenigii###+-103.8###+-156.8###+-8.76###+-2.237###+-0.031###+-2.027###+-0.785###+-0.086###+-7.391###+-0.994

Brassica###2363###2519###101.3###18.49###0.160###14.22###9.230###1.506###0.738###5.133###11.54

oleracea###+-171.7###+-109.4###+-8.200###+-0.943###+-0.052###+-1.125###+-0.432###+-0.510###+-0.225###+-1.635###+-0.397

N.D Not Detectable

Table 3. Levels of metals in medicinal plants in previously published results from other parts of the world

Samples###Metals###Ref

Azadirachta indica###Lead 16.53 ; Cadmium 2.43 mg/g###Ghosh et. al., 2009

Pipper nigrum###Cu 9.1 +- 0.1, Zn 6.9 +- 0.1, Mn 244 +- 7, Fe 640 +- 7 mg/g###Lavilla et.al., 1999

Brassica rapa###Fe 8.8 +- 0. 01, Cu 1.1 +- 0.01, Mn 1.1 +- 0.01, Zn 4.1 +- 0.02, Cr 0.4 +-###Hashmi et.al., 2007

###0.00 mg/g

Syzygium aromaticum###Cu 5.6 +- 0.4, Zn 14.5 +- 0.6, Mn 939 +- 15, Fe 219 +- 7 mg/g###Lavilla et.al., 1999

Trachyspermum###Cu 14.4 +- 0.4, Zn 46.9 +- 1.1, Mn 123 +- 1, Fe 2486 +- 28###ppm###Lavilla et.al., 1999

Foeniculum vulgare###Zn 37.0 +- 2.4, Mn27.8 +- 0.4, Fe 224.8 +- 9.2, Cu 16.2 +- 0.4 mg Kg -1###Basgel and Erdemoglu, 2005

Murraya koenigii###Na(1710+-70) mg Kg -1 K%(1.78+-0.06), Mn%(67.15+-3.31)###Balaji et.al., 2000

Brassica oleracea###Fe 13.7 +- 0. 03, Cu 1.1 +- 0.00, Mn1.7 +- 0.00, Zn 3.8 +- 0.02, Cr 0.4 +-###Hashmi et.al., 2007

###0.00 mg/g

Previous literature shows that some metals have the same concentration pattern as that of our studies while other metals having much more concentrations like in Azadirachta indica where cadmium was reported to be 2.430ppm whereas in present studies it was found to be 0.041ppm as shown in Table 3. Concentration of metals is usually high in the roots as compared with leaves. In our study the same pattern seems to be followed. There was higher metal accumulation in roots than that of leaves and other parts of plant including fruit and seed.

Some of the metals contents found in Brassica rapa (root) were lower than that of its leaves which may be due to the fact that different parts even different leaves of the same plant may contain different proportion of same metals, depending upon age of plant and because of other factors.

There was higher metal accumulation in roots than that of leaves and other parts of plant including fruit and seed. Some of the metals contents found in Brassica rapa (root) were lower than that of its leaves which may be due to the fact that different parts even different leaves of the same plant may contain different proportion of same metals, depending upon age of plant and because of other factors.

Each element has its individual impact in the structural and functional integrity of the living cells and organisms. Results shown in Table 2 verify the presence of variable amounts of these metals in the medicinal plant samples. Iron is an essential element for growth of animals and plants. Its deficiency can hinder metabolism. Plant samples of Trachyspermum ammi, Leaves of Brassica rapa, and Foeniculum vulgare, Brassica oleracea, contained comparatively higher amounts of Fe, recorded to be as greater than 100 ug/g while the highest concentration found in the other analyzed samples was 89.08 mg/g. The concentration of iron in Brassica rapa was found in order of leaves greater than roots. This information is highly valuable in view of the recommended daily dietary intake of iron as 10-28 mg/day as shown in Table 4.

Copper levels greater than 100 ug/g are found in samples of Brassica rapa root and Murraya koenigii L. while Pipper nigrum, Syzygium aromaticum, Trachyspermum ammi and Brassica oleracea contained less than 10 ug/g. Copper is an essential enzymatic element. Such concentrations level of copper are necessary for normal biological activities of amino oxides and tyrosinase enzyme. Tyrosinase is the enzyme that is required for catalytic conversion of tyrosine to melanin, which is a vital pigment located beneath the skin, and thus protects the skin from dangerous radiations (Hashmi, D. R. et al., 2007). Copper normally finds its way into drinking water from copper pipes, as well as additives designed to control algal growth. Concentration of copper in our plant samples ranged from 0.195 to 1.837 mg/g whereas the daily dietary intake of 2-3 mg copper, reported in the study, is recommended for human adults as shown in Table 4.

Table 4. Daily needs or the world's daily average up-take of elements by a person weighing 70 kg (Mahan and Scott-Stump, 1996).

Element###Average Daily dietary intake

###(ADDIs) mg/day (Range)

Fe###15 (10-28)

Mn###2.8 (2-5)

Zn###15

Cu###2.5 (2-3)

Ni###0.025

Cr###0.05-0.2

Co###0.04

Pb###0.415

Cd###0.057

Sodium is a mineral element and an important part of the human body. It controls the volume of fluid in the body and helps maintain the acid-base level. A sodium level in the blood that is too low is dangerous and can cause seizures and coma. Very high sodium levels can lead to seizures and death. The highest concentration of sodium was recorded in Brassica rapa root which is more than 10000 ug/g. The concentration of other elements analyzed in the study decrease in the order Mn greater than Pb greater than Ni greater than Cr greater than Co greater than Cd.

The major source of Sodium uptake is the common salt which is used in cooking as well in widely used in industries and for dyeing purposes.

Manganese is one of the major minerals, which is related to the carbohydrate and fat metabolism. Our studies established that concentration of manganese is in the range of 34.57 ug/g to 57.30 ug/g in Murraya koenigii, Trachyspermum ammi, Foeniculum vulgare, Pipper nigrum and Syzygium aromaticum. The major sources of manganese in soil are fertilizers, sewage sludge and ferrous smelters. Highest concentration of manganese was recorded for Pipper nigrum. It is of the order of 42.84 ug/g.

Whereas the daily dietary intake of 2-5 mg manganese is considered to be suitable for human adults as shown in Table 4.

Zinc has been well known to be an important trace element as a cofactor for insulin. Highest concentrations of zinc were found to be as 53.69 ug/g and 53.74 ug/g in Foeniculum vulgare and Trachyspermum ammi respectively. Its lowest concentration was recorded in Syzygium aromaticum which was 4.94 ug/g. Whereas the recommended daily dietary intake of zinc stands at about 15 mg. Major sources of Zinc in atmosphere are due to its use in Zinc batteries and also its widely use in furniture industries.

Cadmium is toxic to human even at low concentrations. It is reported to cause osteomalacia (Shumacher et al., 1991). It badly affects the cardio vascular system and kidney functioning. Cadmium was not detected in Pipper nigrum and Foeniculum vulgare while in rest of our plant samples concentration of cadmium was recorded to be in the range of 0.041-0.495 mg/g as shown in Table 2. Highest concentration of cadmium was approximately similar in Brassica rapa leaves and roots i.e., 0.495 and 0.457 mg/g. Cadmium is used in batteries, pigments, fertilizers, detergents and it is also present in refined petroleum products.

Plant samples of Brassica rapa leaves and root had concentration exceeding the WHO limit i.e., greater than 0.3 ug/g reported for medicinal plants (Ghosh et al., 2009).

Lead has been shown to have toxic impact on a variety of metabolic processes essential to plant growth and development, including photosynthesis, transpiration, DNA synthesis, and mitotic activity (Wierzbicka, 1999). Sources of lead include metal smelting, pigments, lead battery manufacturing and lead contaminated petrol. In soil Lead tightly binds itself to organic soil particles which may decrease the mobility of lead in most soils and may reduce uptake by plants (Singh et al., 1997; Kumar et al, 1995; Cooper et al., 1999; Salim et al., 1993).

It has been suggested that the mobility of lead and copper is greater in sandy soils, which tend to lack organic matter, than in organic soils. Murraya koenigii. has been found to bear the highest concentration of lead i.e., 24.02 ug/g. Concentration of lead in Brassica rapa leaves is greater than that of Brassica rapa roots which may be due to high concentration of lead in air than in soil. All the plant samples other then Brassica rapa root and Syzygium aromaticum had concentration exceeding the WHO limit i.e., greater than 10.0 ug/g reported for medicinal plants (Ghosh et al., 2009), while daily need of lead for a person weighing 70 Kg is about 0.415 mg as shown in Table 4.

Nickel regulates the mineral metabolism, enzyme activity and several other metabolic processes in plants. It is used as a fungicide but it is well toxic to the germination of some seeds. It causes mitotic disturbances in root tips of some plants. High concentrations of nickel cause severe chlorosis and necrosis in plants and a host of other growth abnormalities and anatomical changes (Mishra and Kar, 1974).Generally Nickel and its salts do not affect the human body but in some cases it has been recorded to cause allergic problems as it comes in contact with moist skin. It also affects adversely the lungs and nasal cavities (Kumar et al., 1995).

According to our results concentration of Nickel in Trachyspermum ammi, Pipper nigrum , and Syzygium aromaticum is less than 1.0 mg/g while in other plant samples the order was Brassica oleracea greater than Brassica rapa (leaves and roots) greater than Foeniculum vulgare greater than Azadirachta indica greater than Murraya koenigii. Same level of Nickel was detected in Brassica rapa leaves and roots. This pattern shows the different rates of absorption of element in different plant species. Major sources of Nickel that bring it into the atmosphere involve Iron, steel and cement production and Fuel combustion to produce heat and electricity. Thus nickel levels are far below than the recommended daily dietary intake of nickel which is about 0.025 mg per day as shown in Table 4.

It is to be noted here that daily intake of these medicinal plants is such that the nickel assimilation per day is far below this limit of toxicity as shown in Table 2.

Chromium is one of the known toxic pollutants in the world. At an elevated concentration it is toxic for both plant and animals. The problems that are associated with chromium involve skin rashes, stomach ulcer, kidney, liver damages, lungs cancer and ultimate death. All of our plant samples bear the concentration level of chromium that fall into the range of 0.267-1.932 mg/g, except in leaves of Brassica rapa and Foeniculum vulgare which demonstrate approximately same concentration level i.e., 3.219 mg/g and 3.342 mg/g However, in Murraya koenigii chromium concentration was not detected. It has been reported that daily dietary intake of 0.05-0.2 mg of chromium contributes to well being of the human.

Major sources of Chromium in atmosphere involve Iron, steel and cement production and fuel combustion to produce heat and electricity.

Cobalt is beneficial for humans because it is a part of vitamin B 12, which is essential for human health. Cobalt is used to treat anemia in pregnant women, because it stimulates the production of red blood cells. However, too high concentrations of cobalt may damage human health. And it may cause asthma and pneumonia, vision problems, nausea, heart problems and thyroid damage.

When plants grow on contaminated soils they may accumulate very small particles of cobalt, especially in the parts of the plant that we eat, such as fruits and seeds. We find concentration of cobalt in the plant samples in the range of 0.195-1.837 mg/g where as recommended daily dietary intake of cobalt is about 0.04 mg by a person weighing 70 Kg, as shown in Table 4. These concentration levels of Cobalt are not considered to be injurious to human health which shows that these plant species are quite safe for human health. It is used to make alloys, colored pigments, and as a drier for paint and porcelain enamel used on steel bathroom fixtures, large appliances, and kitchen wares. lt is also released from burning coal and oil, and from car and truck exhaust.

Potassium usually enters in plants from soil as fertilizers contain a lot of Potassium. Potassium is a mineral that helps the kidneys function normally. It is crucial to heart function and plays a key role in skeletal and smooth muscle contraction, making it important for normal digestive and muscular function, too. Having too much Potassium in the blood is called hyperkalemia; having too little is known as hypokalemia. The concentration of Potassium was found to be very high in all the species.

Highest concentration of Potassium was recorded in Foeniculum vulgare i.e., 9038 mg /g while in other plant samples it ranges from 1494-2518. mg/g except in Brassica rapa (root) in which concentration of Potassium is found to be 4555 mg/g which may be due to the contact of roots of Brassica rapa with the potassium rich fertilizer. In general, most plants grow by absorbing nutrients from the soil. Their ability to do this depends on the nature of the soil. Depending on its location, a soil contains some combination of sand, silt, clay, and organic matter. The makeup of a soil texture and its acidity or pH determines the extent to which nutrients are available to plants. The path taken by mineral is: soil greater than roots greater than stems greater than leaves.

The minerals, dissolved in the water, get transported often accompanied by various organic molecules supplied by root cells. Once in the xylem, water with the minerals that have been deposited in it move up in the vessels and tracheids. Minerals enter the root by active transport into the symplast of epidermal cells and move toward and into the stele through the plasmodesmata connecting the cells. Usually metals preferentially concentrate in the roots, followed by the twigs and leaves.

Large number of factors control metal accumulation and bioavailability associated with soil and climatic conditions plant genotype and agronomic management, including: active/passive transfer processes, sequestration and speciation, redox states, the type of plant root system and the response of plants to elements in relation to seasonal cycles (Kabata-Pendias and Pendias, 1984).

In our study the same pattern seems to be followed. There was higher metal accumulation in roots than in leaves and other parts of plant including fruit and seed. Some of the metals contents found in Brassica rapa (root) were lower than that of its leaves which may be due to the fact that different parts even different leaves of the same plant may contain different proportion of same different metals, depending upon age of plant and because of other factors.

CORRELATIONS OF METALS

The correlation coefficients of various metals determined in different plants samples are shown in Table 5. This table indicates that there is no perfect correlation between metal loads, indicating that the metal content in different herbs has individual characteristics. The correlation coefficients for Cu, Fe, Zn, Co and Pb are however higher which may be due to the pH of soil. There seems to be some correlation of Iron with Zinc and Cobalt and that of Lead with Cobalt and that of Zinc with Cobalt. This is possibly through an increased biological demand for zinc and cobalt associated with dissolved organic compounds in soil. The reason for these correlations may include the use of fertilizers, manure, metal contaminated soil and water and because of the highly polluted air as large amount of lead evolves from motor vehicle and from the industrial waste.

Also Zinc, Cobalt and Lead are used in batteries which contaminate soil and water. One of the main reasons of presence of toxic metals in plants may be the use of contaminated sewage water for cultivation in many areas of Karachi. The distribution coefficient of cobalt in water varies due to pH, redox conditions, ionic strength, and dissolved organic matter concentrations (Mahara and Kudo, 1981). Higher values of correlation of Iron and lead content in plant samples which may be correlated with higher content of Zinc and Cobalt contents may show higher content of these metals in the soil and fertilizers of this area. It may also show that plants have higher uptake of these metals than any other metals present in this area.

Table 5. Correlation matrixes between metals in all selected plant samples:

Na###K###Fe###Pb###Ni###Co###Cu

K###-0.043

Fe###0.239###0.157

Pb###-0.199###-0.060###0.493

Ni###0.004###0.279###0.077###0.219

Co###0.297###0.027###0.504###0.505###-0.124

Cu###0.443###0.273###-0.174###0.298###0.200###0.301

Zn###-0.003###0.472###0.571###0.081###-0.188###0.461###-0.220

CONCLUSION

The present study revealed that the heavy and the trace metal content of the selected medicinal plants of Pakistan were within the safe limits.

Therefore it is concluded that these levels may not contribute to metal toxicity and the human health is unlikely to be directly affected by these medicinal plants when taken orally or in the form of tea or consumed a part of diet. It is imperative to regulate the metal load of elements in our cuisine. The present study provides a base line data for our efforts directed towards maintaining a healthy life style.

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Mahwash Zahra Kirmani, Sheikh Mohiuddin, Farah Naz, Iftikhar Imam Naqvi and Erum Zahir, Corresponding author: E-mail: mahwash_kirmani@yahoo.com, Department of Chemistry, University of Karachi, Karachi, Pakistan
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Author:Kirmani, Mahwash Zahra; Mohiuddin, Sheikh; Naz, Farah; Naqvi, Iftikhar Imam; Zahir, Erum
Publication:Journal of Basic & Applied Sciences
Article Type:Report
Geographic Code:9PAKI
Date:Dec 31, 2011
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