Biomonitoring of air pollution in urban regions by Platanus orientalis and Fraxinus excelsior (Case study: Shiraz city)

Environment is a very great and complexity collection which has been created by a process and evolution of live existences and composer elements of ground area, and so affect the human activities and is affected from that. Industrialization and modernization has let lots of heavy elements to entire into the atmosphere. Elements of the atmosphere will locate on the surface of soil and plants as dry or wet deposit, lastly. Heavy metals usage in industry and necessity of some of them, for influence in some physiologic activities for plants and animals, are different directions that more information from them seems important in environment With attention to the fact that plants are capable to absorb some pollutants by using their air organs especially leaves and reserve in themselves, so biomonitoring through plants is a useful way for approximating pollutants. Shiraz city is one of populated cities that involves air pollution. Due to the position of the city between two head Zagros Mountains, high population growth and also increasing pollutant quantity and quality it seems that the pollution problem has the creasing trend in time. The objective of the present study is to estimate the air pollution tensity for some heavy metals as cu, cd and pb in high traffic points of shiraz city by using fraxinus and platanus as nonactive biomonitors. Matherial and Methods Study area: In the study, four green spaces in different traffic points were selected as stations to determine heavy metal concentration of trees in Shiraz city. Then, the samples of leaf and bark of fraxinus and platanus which were common in the stations as studied tree samples were selected in two time June and September. Sampling, preparing and analyze of plant samples In each station, sampling from leaf and bark of tree was done in three repeat accidentally and two combination. Plant samples were first dried on clean paper plates and then all leaf and bark samples were dried in 60˚c, for 72 hours. The samples were became powder by mill and prepared for acid digestion tests. Lead and copper concentration in samples were measured by using atomic absorption device. Discussion of The density of cadmium in all samples was less then device diagnosis. Average concentration of heavy metals (pb, cu) in washed and unwashed leafs of fraxinus and platanus plants in different stations is brought in tables 1and 2. Although different stations show different amount of elements, but results show that is not a significant difference between for metal pb in washed and unwashed samples. Copper and lead concentration in leaf and bark of fraxinus tree in different stations and times brought in table 3. Maximum density of lead in leaf and bark of platanus tree in September was observed 2.80 and 4.16 µgg -1 respectively and for copper was 18.27 and 7.85 µgg -1. This amount for lead in leaf and bark of fraxinus tree was computed 1.79 and 3.50 µgg -1 in September respectively and for copper was 14.43 (September) and 7.95 (June) µgg -1 (Table 4). Maximum density of lead and copper in bark of fraxinus in Azadi station (with high traffic) was 10 and 11.14 respectively and for platanus was 4.33 and 15.58 µgg -1, although minimum amount for each metal and tree was observed in Golestan station as witness zone. The amount of absorbed lead and copper by leaf and bark in platanus sample is more than farxinus. This difference can be due to age of platanus samples respect to fraxinus that Haghighate khadem (1370) confirm it. Lead and copper concentration in leaf of the study trees is significantly lower in stations with low traffic (Golestan and Kholdebarin) than stations with high traffic as Azadi Park and Valiasr. The same results were also reported by Sawidis et al (1995). The most important lead pollution of tree leafs specially in cities is because of vehicles traffic. Copper concentration statistically is significantly higher in unwashed leafs than washed leafs in both trees. Heavy metals concentration in barks is more than leafs of the same tree. Generally lead and copper elements data in bark of platanus and fraxinus studied in Shiraz city show that they are very lower than the studies done by El-Hassan et al (2002) and standard given in this study. The present study showed that difference between lead and copper elements density in stations 1 and 2 with 3 and 4 in tree leaves and barks is because of heavy traffic in these zones. Urban development and industrial and commercial activities in city centers is the main source of many heavy metals pollution. However, both indicator species are suitable for comparative studies on bioindication of urban air pollution.