فهرست مطالب zohreh farzanegan

The present study was designed to investigate the effect of Nano hydroxyapatite (nHAP) on some soil bioindicators and availability of cadmium in a polluted calcareous soil. This research was carried out in a factorial arrangement based on completely randomized design with three replications. Treatments included two levels of Cd (0 and 40 mg kg-1 soil), two levels of nHAP (0 and 1%) and two incubation times (14 and 28 days). The cadmium chloride solution was uniformly sprayed on the soil surface and equilibrated for a month, then nHAP was added to the soil at 0 and 1 w/w %. The activity of urease, dehydrogenase, and alkaline phosphatase enzymes, basal respiration and bioavilable Cd were measured after 14 and 28 days. Bioavilable Cd was extracted by DTPA. The results showed that the addition of nHAP in the Cd contaminated soil decreased bioavailable Cd by 2.3%, increased the activity of urease enzyme by 98% while had no effect on the activity of phosphatase, dehydrogenase and basal respiration. Investigation of changes of bioindicators in 14 and 28 days incubation in Cd contaminated soil showed that the activity of urease and dehydrogenase enzyme had a declining trend but the activity of phosphatase enzyme and basal respiration did not significantly change. It was also found that bioavailable Cd decreased with incubation time by 10.7%. In general, it may be concluded that nHAP influenced biological index in the calcareous soil differently, but it caused reduction effect on bioavailable cadmium in soil, although this reduction was not considerable.

Cadmium (Cd) is one of the most common soil pollutants that can adversely affect all living organisms Therefore, proper remediation is necessary to reduce metal availability in soil. Owing to nano-material with higher reactivity and adsorption capacity than ordinary-sized materials, with the development of various nanotechnology applications in human life, the evaluation of the effectiveness of nanoparticles in remediation of polluted soils has been considered by researchers. However up to now it has been not reported information about heavy metal immobilization by nHAP in calcareous soils. This experiment was conducted to investigate efficiency of nHAP on stabilization of Cd in polluted soil. This experiment was conducted in a completely randomized design with factorial arrangement and three replications. First the soils were contaminated with Cd at three levels (0, 20 and 40 mg kg-1 using CdCl2) and then were incubated for one month in 70% field capacity. Then nHAP was applied to soils at three levels (0, 0.25 and 1%). After 30 days incubation, Cd was fractionated by sequential extraction and analyzed for DTPA extractable form. To quantify the effect of nHAP in binding intensity and mobility of loaded Cd, the reduced partition index (IR) and mobility factor were used. The results of sequential extraction showed that nHAP application significantly reduced concentration of Cd in the exchangeable and organic fraction and increased in the carbonate fraction. But there was no change for Cd in the residual fraction. The results of extraction with DTPA experiment indicated that at 40 mg kg-1 of Cd both of the levels of nHAP decreased DTPA-extractable Cd, but at 20 mg kg-1 of Cd, addition of nHAP at 0.25 % level did not significantly reduced concentration of DTPA extractable Cd. It was also found that efficiency of nHAP increased when Cd loading quantities to soils increased. However the role of nHAP in the reducing of bioavailability was not very large. The results also illustrated that the IR value increased when Cd and nHAP loading quantities to soils increased, demonstrating a decrease in the mobility of Cd in mobile fractions. Application of nHAP caused reduction of the mobility factor of Cd indicating decreasing availability and environmental risk of Cd. On the basis of results obtained in this study, it can be stated that although the nHAP addition has somewhat stabilized and reduced the mobility of Cd in the soil, it seems that the effect of nHAP on decreasing of Cd was not considerable. Therefore, further studies should be carried out more on the feasibility of application of nHAP at the widespread level and the economic status of its application.