The objective of this study was to determine the concentrations, potential sources and evaluate the risks of heavy metals in selected plants from Awash River Basin, Ethiopia. A total of 57 samples were analyzed from four different plant species. Microwaveassisted digestion was applied to digest the .

Heavy metal accumulation in plants depends upon plant species, soil properties, and the efficiency of different plants in absorbing metals is evaluated by either plant uptake or soilto plant transfer factors of the metals (Rattan et al., 2005).

 · Concentration of metals in plant organs. Concentrations of Al, Cu, Fe, Mn, Ni, Zn, Ca and Mg in bulbs, leaves and seeds of T. luanica, T. kosovarica and are presented in Table 3. The concentrations of Al and Fe in bulbs and leaves of T. kosovarica and were higher compared with T. luanica.

 · Increasing concentration of heavy metals (HM) due to various anthropogenic activities is a serious problem. Plants are very much affected by HM pollution particularly in contaminated soils. Survival of plants becomes tough and its overall health under HM stress is impaired. Remediation of HM in contaminated soil is done by physical and chemical processes .

We examined the concentrations of metals (Cd, Zn, Cu, Fe and Mn) and potential metalbinding compounds [nicotianamine (NA), thiol compounds and citrate] in xylem and phloem saps from 4weekold castor bean plants (Ricinus communis) treated with 0 (control),,, and 10 μM Cd for 3 with and 1 μM Cd produced no visible damage, while 10 μM Cd retarded growth.

Plants can tolerate high heavy metals concentration from soil by two basic strategies (Baker, 1981). The first strategy is called accumulation strategy where metal can accumulate in plants at both high and low concentration from soil ( McGrath et al., 2001). These plants are capable of rendering the metals in various

Plant Responses to Heavy Metal Stress. Being sessile organisms, plants cannot escape unwanted changes in the environment. Exposure to heavy metals triggers a wide range of physiological and biochemical alterations, and plants have to develop and/or adopt a series of strategies that allow them to cope with the negative consequences of heavy metal toxicity.

Plants can tolerate high heavy metals concentration from soil by two basic strategies (Baker, 1981). The first strategy is called accumulation strategy where metal can accumulate in plants at both high and low concentration from soil ( McGrath et al., 2001). These plants are capable of rendering the metals .

Concentration of heavy metals (Al, Ba, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sr, V and Zn) as well as macronutrients (N, P, K, Ca, Mg, S) were measured in water, bottom sediments and plants from anthropogenic lakes in West Poland. The collected plants .

metal concentration. The accumulation strategy consists of high concentration of metals in plants tissues. Plant species vary in their capacity to remove and accumulate heavy metals (Zurayk et al., 2001). Differences also exist among plants as to whether the removed metal is accumulated in the root or transloed to the shoot.

 · The metal availability to plants depends on total concentration of metals in the soil and the forms in which they occur, pH, organic carbon, ionexchange capacity, stage of growth of plants, and microorganisms around the root zone [13, 14]. If these factors are constant, the uptake of a metal by different plant species may be compared.

 · The concentration of metals in plants, and in parts of plants, can be predicted by a simple kinetic model based on the concentration of metals in the soil. This fact can be linked to physiological absorption mechanisms in plants. Hamon et al. (1999) found

 · Increasing concentration of heavy metals (HM) due to various anthropogenic activities is a serious problem. Plants are very much affected by HM pollution particularly in contaminated soils. Survival of plants becomes tough and its overall health under HM stress is impaired. Remediation of HM in contaminated soil is done by physical and chemical processes which are costly, timeconsuming, .

The high concentration of heavy metals in soils is reflected by higher concentrations of metals in plants consequently in animal and human bodies. Small amounts of many heavy metals are required by plants to remain healthy. Assessment of the levels of Fe, Pb, Cd, Zn and Ni in dumpsite soils and vegetation around solid waste

Four heavy metals concentrations (Cu, Zn, Pb and Ni) were determined. Table 1 shows the concentration of heavy metal in soil samples in mg kg–1. The concentration of Cu had the highest value for each point of soil samples as expected. The heavy metal concentration ranges for the studied metals were observed as follows:

 · Heavy metal concentration in plants and different harvestable parts; A soilplant equilibrium model. Environmental Pollution 158:. [4] Chehregani, A., Malayeri, B. and Golmohammadi, R. (2005). Effect of heavy metals on the developmental stages of ovules and embryonic sac in Euphorbia cheirandenia.

 · In the defensive enhancement hypothesis, a plant able to take up and tolerate elevated levels of a metal derives a defensive benefit from that ability at a relatively low metal concentration.

 · Plants have the ability of tolerance to high concentrations of heavy metals through their mechanism by restricting transport from root to leaf, accumulation in trichomes, exudates that can complex the heavy metals, the type of link between the element and cell wall component, production of intracellular compounds with chelating properties, and active pumping to the .

This toxicity in plants varies with plant species, specific metal, concentration, chemical form, pH and soil composition, as many heavy metals are considered to be essential for plant growth.

 · The ability of plants to uptake trace metals from the soil was determined using the transfer factor model (Olowoyo 2013). The transfer factor is calculated as the concentration of heavy metals in plant parts to the concentration present in the soil. This is an index of soilplant .

Plants reflect frequent sensitivity to both low and high level concentration of heavy metals, at low level they serves as propitious constituent for plant growth and development but on increasing its concentration beyond threshold limit it will imposes several inimical impacts in plant constituely thereby adversely influencing the soil fertility and development.

 · Studies of heavy metal environmental pollution mainly focus on evaluating heavy metal concentration in soil or plants. Further research connecting heavy metal concentration and bioavailability or toxicology explores the damage caused by heavy metals to the environment (Fang and Cao, 2009; Angelovicova and Fazekasova, 2014; Jiméneza et al., 2011).

Heavy Metals Concentration in Some Medicinal Plants in Previously Published Results from Other Parts of the World Result as ppm S. Name Lead Cad Chro Manga Nickel Cobalt Zinc Copper Reference No. (Pb) mium mium nese (Ni) (Co) (Zn) (Cu) (Cd) (Cr) (Mn)