تاثیر سورفکتانت باکتریایی همراه با کاربرد کلات کننده‌ها بر کادمیم محلول در یک خاک آهکی

در این پژوهش تاثیر دو نوع سورفکتانت باکتریایی بر کادمیم محلول همراه با کاربرد سه نوع کلات کننده (اسید هیومیک، سیترات سدیم و na2edta) در یک خاک آهکی آلوده به کادمیم در چند آزمایش جداگانه در شرایط آزمایشگاه بررسی شد. زمان تعادل در کاربرد غلظت 1 میلی مولار کلات کننده ها در شش زمان (6، 12، 24، 36، 48، 72 ساعت) و غلظت موثر هر یک از کلات کننده ها در کاربرد غلظت های 0، 0.1، 0.25، 0.5، 1 و mm2 تعیین گردید. درنهایت تاثیر کاربرد هم زمان هر یک از کلات کننده ها و دو نوع سورفکتانت استخراج شده از باکتری های pseudomonas putida وbacillus subtilis در غلظت های صفر، 50،25 و mg l1100 بر کادمیم محلول بررسی شد. نتایج نشان داد با افزایش زمان تماس، کادمیم محلول خاک با کاربرد اسید هیومیک و na2edta به صورت معنی‌داری (p<0.05) افزایش یافت. کاربرد na2edta در همه غلظت های مورد مطالعه و کاربرد اسید هیومیک در غلظت های بالاتر از mm 25.0 موجب افزایش کادمیم محلول در مقایسه با شاهد شد. سیترات سدیم در هیچ یک از غلظت ها و زمان های مورد مطالعه تاثیر معنی‌داری بر کادمیم محلول نداشت. بیوسورفکتانت های مورد استفاده تاثیر معنی‌داری بر کارایی سیترات سدیم از نظر افزایش کادمیم محلول نداشتند. کاربرد سورفکتانت تولید شده بوسیله bacillus subtilis در غلظت mg l125 همراه با na2edta موجب افزایش کادمیم محلول گردید و افزایش غلظت این بیوسورفکتانت تاثیر معنی‌داری نسبت به غلظت mg l125 ایجاد نکرد. در حالی که کاربرد هم زمان na2edta و سورفکتانت pseudomonas putida تاثیری بر کادمیم محلول نداشت این بیوسورفکتانت در غلظت mg l1100 اسید هیومیک موجب تفاوت معنی‌داری در غلظت کادمیم محلول خاک شد.

Effect of Bacterial Surfactant along with Application of Chelators on Soluble Cadmium in a Calcareous Soil

Introduction Surfactants as surfaceactive substances with combined hydrophobic and hydrophilic properties are widely used in various fields. In soil remediation processes these substances can be used to increase the availability of organic and inorganic contaminants to improve microbial decomposition of organic pollutants or heavy metals adsorption. In recent years, researchers have been seeking to produce and use surfactants that are more environment friendly. In this regard, produced biosurfactants by microorganisms are of special importance due to their environmental benefits. Microorganisms produce a wide range of biosurfactants. Biosurfactants are extracellular compounds that can combine with metals such as zinc, copper, and cadmium and can increase the solubility of these metals and reduce their toxicity. Negatively charged anionic biosurfactants such as rhamnolipids and lipopeptides can increase heavy metals availability by combining to metals and changing the properties of soil solution. In this study, the effect of surfactant application from Pseudomonas putida and Bacillus subtilis and some chelators include sodium citrate, humic acid and Na2EDTA on soluble cadmium in a contaminated calcareous soil was investigated.Materials and MethodsThis study was conducted as factorial in a completely randomized design in laboratory conditions at several steps separately. A calcareous soil sample was contaminated with 15 mg kg1 cadmium from the source of Cd (NO3)2. Contaminated soil incubated for 4 weeks at field capacity. Acid deposition method was used for surfactant extraction from culture medium of Pseudomonas putida KT2440 and Bacillus subtilis 1795. The structure of extracted biosurfactants was investigated by FTIR. Equilibrium time was obtained by determining the amount of soluble cadmium at times 6, 12, 24, 36, 72 hours by adding 1mM sodium citrate, humic acid and Na2EDTA to the contaminated soil (ratio of 1 to 5 soil to solution).The concentrations of 0, 0.1, 0.25, 0.5, 1 and 2 mM of humic acid, sodium citrate and Na2EDTA were used to determine the appropriate concentration of each chelator. To investigate the interaction of chelators and biosurfactants on soluble cadmium, an experimental was conducted as a completely randomized design with factorial arrangement design. Experimental treatments consisted of three types of chelating agents (sodium citrate, humic acid, Na2EDTA and control), two types of surfactants from Pseudomonas putida and Bacillus subtilis, and five concentration levels of the biosurfactants (0, 25, 50, 100 mg L1).Results and DiscussionThe highest amount of soluble cadmium (11.59 mg L1) was observed in Na2EDTA treatment at 72 hours, which was significant compared to the other treatments. The lowest amount of soluble cadmium was obtained through application of sodium citrate (0.205 mg L1) at 36 hours. In all studied concentrations, Na2EDTA had the greatest effect and sodium citrate had the least effect on soluble cadmium. While the use of Na2EDTA at all concentrations caused a significant increase in soluble cadmium, sodium citrate had no significant effect on soluble cadmium at studied concentrations. Humic acid at concentrations higher than 0.5 mM significantly increased the soluble cadmium. Increasing the concentration of humic acid and citrate from 1 to 2 mM did not show any significant impact on soluble cadmium. At all levels of biosurfactant application, Na2EDTA and humic acid caused a significant increase in soluble cadmium concentration. In control and sodium citrate treatments, application of biosurfactants did not cause significant difference in the concentration of soluble cadmium. The highest amount of soluble cadmium was obtained as a result of the application of Bacillus subtilis surfactant and Na2EDTA. However, increasing the concentration of Bacillus subtilis surfactant from 25 to 100 mg L1 had no significant effect on increasing the efficiency of Na2EDTA.  Pseudomonas putida surfactant had no significant effect on soluble cadmium in Na2EDTA application. While in humic acid treatment, the application of the Pseudomonas putida surfactant at the highest concentration (100 mg L1) increased the concentration of soluble cadmium. Using Bacillus subtilis surfactant did not have effect on soluble cadmium in application of humic acid.ConclusionAmong the studied chelators (sodium citrate, humic acid and Na2EDTA), Na2EDTA had the greatest effect on soluble cadmium. While sodium citrate had no significant effect on soluble cadmium. Surfactants from Pseudomonas putida and Bacillus subtilis had different effects on increasing the efficiency of studied chelators and soluble cadmium in the studied soil. In Na2EDTA and humic acid application, surfactant from Bacillus subtilis at a concentration of 25 mg L1 and surfactant produced by Pseudomonas putida at a concentration of 100 mg L1 had a significant effect on soluble cadmium, respectively. It seems using biosurfactants and chelators on increasing soluble cadmium in soil can be useful for phytoremediation purposes to increase its uptake by plant. However, further research is needed.