the potential of reed, typha and bermudagarss on the translocation factor and bioaccumulation of lead

introduction the lead is considered as one of the most toxic heavy metals in environment organizations of industrial and developing countries. therefore, refining of soil and water contaminated to this element is from most important environmental policies of this countries. lead metal is unnecessary for the body, so that trace amount in the body, indicating contamination with this element. lead substitute for calcium in the cells and disrupt the activities of the body. also cause liver and kidney dysfunction, genital organs and reproductive system, anemia, loss of intelligence interest and occurrence of the metabolic complications. remove and control pollution of heavy metals is very difficult due to their multiple and different sources of pollutions. because each pollutant requires its refining process. until now, different methods have been developed for the purification of sewage including the chemical precipitation, reverse osmosis and ion exchange of organic. each of which has its own advantages and disadvantages.moreover, phytoremediation is as the optimal method of biological for the removal of pollutants form water and soil. the phytoremediation is physiological potential of the green plants (variety of weeds, aquatic and marsh plants, crops and trees) for the control and absorption of organic and inorganic pollutants of wastewater along with other treatment methods. in other words, phytoremediation is a technique for the using of plants to control and clean up pollution species such as metals, pesticides, oils, etc. in this method, different species of plants can be considered as biological filters and play main role in the elimination of environmental pollutants. some heavy metals such as lead and cadmium can be accumulated in leaves or branches. in general plants are employed the five main processes to clean up the environment including phytoextraction, phytodegradation, phytostabilization, phytovolatilization and rhizofiltration that containing accumulation of the nutrients and heavy metals in the plant roots and rhizomes.       materials and methods project preparation and cultivation of plants in order to implement this study, plastic pots prepared with 60 cm in diameter and 40 cm in height. therefore from sand with grains diameter 1 to 5 mm and a depth 30 cm was used as the growth bed in pots that after preparing the pots and planting, were placed with a suitable interval each other. plants species seleceted including phragmites, thypha and bermudagrass based on their abundance in the region. young plant samples were collected from margin of dez river and immediately were transferred to the site of the research in experimental field of islamic azad university of dezful. after preparing of bed and adding nutrients to the cultivation medium, each pot was randomly assigned to a treatment in three replicates. the youngest seedlings were selected for the cultivation in each medium sample. three plants were cultivated at regular interval with the minimum distance 5 cm from the container wall and at a depth 10 cm (density of 25 plants per square meter) after washing of seedlings with water. after preparing the pots and planting, the desired species were irrigated with the common water in 40 days because irrigation with synthetic wastewater in the early stages of cultivation caused stress to the plant due to lack of root stability and compatibility with the new culture medium. so after elapsing of this period, irrigation is performed with simulated wastewater in different concentrations of 5, 10 and 15 mg lead/l.   results and discussion results showed that significant different was observed at 5% level between the mean square of lead accumulation in ground organs of studied species with low-level concentrations of wastewater. therefore  ground organs of studied species in the treatment of low levels of lead had a significant effect on the lead accumulation. additionally, comparasion of the means by duncan test was performed for the levels of lead concentration using spss18 software. the mean accumulation of lead in under-ground organs of bermudagrass, reed and typha was measured respectively 0.106, 0.179 and 0.096 mg/g in low-level concentrations of wastewater (table1).the results showed that the difference between the mean of accumulation in the three species was significant at the 5% level. the maximum accumulated amount was in the root of reed and the lowest amount also was in the root of bermudagrass. comparison of the squared means of the lead accumulation in above-ground organs showed that difference of the means was not significant at the 1% level in low-level concentration of wastewater.   table 1. the effect of plant species on the lead accumulation in different levels of concentration treatment under-ground organ above-ground organ c1=5 mg/l (low level) bermudagrass 0.025±a0.106 0.015±a0.066 phragmites 0.029±b0.179 0.013±a0.028 typha 0.026±a0.096 0.026±a0.044 result p˂0.05 p˃0.01 c2=10 mg/l (mean level) bermudagrass 0.036±a0.183 0.024±a0.103 phragmites 0.043±b0.397 0.021±a0.069 typha 0.038±a0.27 0.027±a0.109 result p˂0.01 p˃0.01 c3=15 mg/l (high level) bermudagrass 0.041±a0.27 0.033±a0.151 phragmites 0.055±b0.544 0.042±a0.127 typha 0.047±a0.316 0.035±a0.164 result p˂0.01 p˃0.05                                                                     interaction plants and concentration levels on the bioaccumulation and translocation factor the results showed that there was a significant difference at 5% level according to analysis of variance, between the mean square of lead accumulation in different treatments,. therefore air and ground organs of different species and different levels of concentration had significant interaction at 5% level on the lead accumulation. the highest accumulation of lead in the ground organs of reed in the treatment of high level of lead with concentration of 0.544 mg/g. lowest value found was in typha and in the treatment of low level of lead with concentration of 0.096 mg/g. the highest accumulation of lead in the above organs of typha in the treatment of high level of lead with concentration of 0.164 mg/gr. lowest value found in reed and in the treatment of low level of lead with concentration of 0.028 mg/g. the results also showed that the ground organs of reed by more biomass than the other two species had a higher potential for the lead accumulation. the results also showed the highest accumulation of above-ground organs was in typha due to more absorption of water and minerals in the aerial parts. in addition, the index of translocation factor is also calculated which expresses the ratio of accumulation of root to shoot. the results indicated translocation factor in the bermudagrass, reed and typha was 1.7, 5.5 and 2.2 ,respectively. therefore, the main mechanisms of phytoremediation in reed was mainly as rhizofiltration whereas in typha and bermudagrass were as rhizofiltration and phytoextraction. according to the study, reed tends to the lead accumulation in the root and rhizome at low concentration levels whereas it used from all its capacities especially in the above-ground organs with the increasing concentration levels of wastewater.