Phytoremediation oil contaminated soils using plants carex hirta l.

Abstract

Abstract: Boryslav oil region is situated in Lviv area and is one of the oldest in the Europe. For its 150-years history of development there were extracted 40 million tons of oil and 15 billion m3 of gas. Today the deposit is being at a final stage of development because of it almost exhausted layers. An exploitation of the old wells is occurring at a low technological cultural level and creates a serious environmental problems: air, water and soil are chronically polluted.  At the same time there are resistant plant species in the areas of oil production, which can be used for environmental phytoremediation. Phytoremediation is a promising technology for purification of the soils: it is cheap, doesn’t require any special equipment and promotes a preservation and improvement of an environment. An aim of our researches was to investigate if  Carex hirta L. plants are usable  for this technology of contaminated soil purification. Crude Borislav oil was used in the experiments. The vegetative individuals of C. hirta were planted into contaminated soil three weeks after adding of oil (50 g/kg). Plants were analyzed after 30 days of growth on oil-contaminated soil. In order to establish (assess) the role of plants in the oil degradation, they were grown in sterile pots with sterile soil in the laboratory. Clean pots were treated with bleach, then were rinsed with running and distilled water. Dry sodpodzolic soil was sterilized in an autoclave at 1.5 atmospheres for 2 hours. Sterile contaminated soil was put into sterile pots. Half of the pots were planted by С.hirta plant with sterile roots. Pure plant roots were placed for 5-7 seconds in 70% ethanol, then were rinsed with chlorhexidine and with sterile distilled water. Oil content in the soil was determined by a modified method of oil extraction from the soil samples by carbon tetrachloride. Laid field experiments were aimed to study the plants as possible purifiers of contaminated soil from heavy metals. There were arranged four trenches with size of 4 m × 1 m, depth of 25 cm , bottom of which was covered by  plastic wrap. In order  to preserve water movement in the soil the holes were punched  in the film. Two trenches received 1,000 kg of pure ground (ground control) each, and two others - the same amount of oil-contaminated soil. All trenches were planted by plants C. hirta. The concentration of metals in soil and plant material was measured on X-ray fluorescent spectrometer Spectro Xepos. Callose accumulation in the cell walls was evaluated in living transverse cuts of sedge rhizome, stained with aniline blue. Fluorescence intensity was determined by cytometry, designed on fluorescent microscope ML-2 base. C. hirta plants with sterile rhizomes that grow on sterile oil-contaminated soil, caused soil purification by 8,6% compared with the control. Investigated plants accumulated heavy metals. The concentration of heavy metals in the plants elevated part exceeded the control level of: Ni and Mn -  9 times; Cu, Co - 5 times; Hg - 4.5 times; Zn, Cr, V, Pb, As, Cd - 4 times; Mo - 3 times. This can be explained by lack of natural barrier in the form of callose in the cell walls. Thus, the plant C. hirta is usable for phytoremediation of the areas contaminated by oil and associated heavy metals.