Tolerance of Vallisneria sp. for Different Concentrations of Cadmium and

This study was done to recognize the tolerance of Vallisneria sp. for different concentrations of cadmium and lead in aqueous ecosystem. The concentrations of 30, 40, 50 mg/L were used for Cd and Pb in three replications for each concentration for 30 days. The results found that the plant was tolerated 50 mg/L of Pb, and 40 mg/L of Cd. Significant differences were found in removing capacity by plant for Cd and Pb, in all concentrations 30, 40, 50 mg/L during experiment period. There were no morphological changes in the first day of the experiment period, but it was appeared after the threeth days of the experiment, and it continued till the end of the experiment. The highest removal ratio for Pb was 97.66% in the concentration 30 mg/L, and the lowest removal ratio was 57.4% in the concentration 50 mg/L. For Cd the highest removal ratio 80.06% in concentrations 30 mg/L and the lowest removal ratio was 76.2% mg/L in concentrations 50 mg/L.


Introduction
The contamination of soils and aquatic systems by toxic metals and organic pollutants has recently increased and this due to anthropogenic activity (Mejare etal., 2001).
Phytoremediation is defined as a process of decontaminating soil and aquatic systems by using plants, fungi or algae to absorb heavy metals. Recently, the use of aquatic plants has received much attention because of their ability to absorption of metals and taking up toxic elements from the environment or rendering them less harmful (Mitra etal., 2012).
The plant used in the phytoremediation technique must have a considerable capacity of metal absorption, its accumulation, and reducing the time of decontamination of an ecosystem (Mudgal etal., 2010).
Metals are introduced into the aquatic ecosystems as a result of weathering of soil and rocks, from volcanic eruptions and from a variety of 382 human activities involving mining, processing and use of metals and/or substances containing metal contaminants (Jian, 2004).
Cd is a relatively rare element and it is not found in a pure state in nature. It easily reacts with carbon dioxide, water vapor, sulphur dioxide, sulphur trioxide, or hydrogen chloride and produces cadmium carbonate, hydroxide, sulphide, or chloride. Cd can undergo weak bonding to carbon and other more electronegative atoms (Jain , 2004).
Small amounts of lead may enter rivers, lakes, and streams when soil particles are moved by rainwater. Small amounts of lead from lead pipe or solder may be released into water when the water is acidic lead (Pourrut et al., 2011).
Vallsneria sp. occurs in both fresh and brackish water habitats and can sustain a relatively high biomass even in turbid, brackish systems. Thus, Vallsneria sp. is often found in waters with relatively high light attenuation and salinities >12 ppt (Doering et al., 2001).

ethods M Materials and Collection and Growing of Vallisneria Plant
Vallisneria Plant samples were collected from Diyala River in Diyala, Iraq. Plants were well washed and placed in two glass containers (40cm *50cm *80cm) filled with water from the same river. After a month period plants put to experimental containers (15cm *10cm *20cm) and capacity 2L of water . Care was taken to prevent the decrease in water level by adding the same oxygenated water.

Physical and Chemical Measurements
Some Physical and chemical measurements were done for river water directly as following: 1-Temperature was measured by thermometer. 2-Electrical conductivity and salinity were measured by Conductivity meter type (MILWAUKEE, ROMANIA). 3-pH was measured by pH meter type (MILWAUKEE, ROMANIA) 4-Total dissolved solids (TDS) were measured by TDS meter type (MILWAUKEE, ROMANIA).

Plant Acclimatization
Plants were transferred to laboratory and put in glass container contain 30L of distilled water, the laboratory temperature was adjusted to 20 ± 2 C°. 100 plant samples were put in each container.

Heavy Metals Measurement
Leaves and roots were put at 40 C° in oven (MEMMERT, GERMANY) until the sample dry weights were fixed. 1 gram of plants dry sample was digested by 16ml of mixture from HNO 3 (64%) (BDH, England) and H 2 O 2 (30%) (BDH, England) in ratio 6:2 and the mixture was put in the oven at 120 C° for two hours. After cooling, 10 ml of distilled water were added, and the mixture was filtered through filter papers (0.45µM,Whatman) and diluted to 50 ml (Senila etal., 2011). Flame Atomic Absorption Spectrophotometer type (VGP 2010 Buck, England) was used to measured the heavy metal concentrations in plants sample.

Result and
The results showed that the range of water temperature was 18-22 C° in glass container, average 20 C° as shown in the table 1. This results was agree with Raehetti etal., 2010 as he found the temperature in which the plant can grow was 18.1-39 C°. This result also agrees with Turpin and Brotone 2000 as he declares that this plant can tolerate the cold weather in winter, but it is flowering and flourishing in the last summer.
The pH values were between 7.3-7.7, as average 7.5 for both elements (Cd, Pb) as showm in the The concentrations of Pb and Cd in Vallisneria sp. were measured for plants taken directly from Diyala River. The results showed that the concentration of Pb higher than Cd, the average of the concentration of Pb was 0.55 mg/kg and the concentration of Cd was 0.52 mg/kg as shown in the table 2 and figure 1. These concentration are lower than other plant in the same area for example Typha domingensis has 0.97mg/kg pb (Alkam, 2002), Ceratophylum demersum has 0.77mg/kg Pb (Salman, 2006), Phragmitis australis has 1.03mg/kg Pb (Salman, 2006).
Found that there is increase in the concentration of Pb in libratory plants (  The vallisneria sp. Tolerated the concentration of 50 ppm of Pb it also tolerated a 40 ppm of Cd. The plant did not die at the concentration of 50 ppm of Pb , but it died at the concentration of 50 ppm of Cd , so the lethal concentration was 50 ppm for Cd and sub lethal was 40 ppm , but the sub lethal concentration was 50 ppm of Pb as shown in the figures (3,4,5,6,7,8,9) and table 3 .
There were no morphological changes on plant in the first day of experimental period , but it appeared after three days of experiment , and it continued till the end of the experiment, this result agree with other study were shown the Vallisneria sp. can decrease the concentration of the lead of water from 48 mg/L to 4.6 mg/L in the second day of the experiment period and from concentration 89 mg/L to 44.5 mg/L for cadmium in the same period (Dumitrescu, 2013) as shown in figure (3,4,5,6,7,8,9) and tables 3 and 4.