استفاده از روش گياه‌پالايي در پالايش سزيم پايدار از محلول‌ها

PHYTOREMEDIATION OF STABLE CESIUM FROM SOLUTIONS

در اين نوشتار، كارايي براي گياه‌پالايي محلول‌هاي آلوده به سزيم مطالعه شده است. گياهان در شرايط كنترل‌شده به‌صورت هايدروپونيك رشد و سپس در معرض جذب سزيم از محلول‌هاي سزيم كلرايد قرار گرفتند كه حاوي 47/0، 58/1، و 95/3 گرم يون سزيم بود. در پايان 14 روز، غلظت سزيم باقيمانده در محلول به‌ترتيب 01/0 ± 15/0، 05 /0 ± 95/0، و 29/0 ± 85/1 ميلي‌گرم بر ليتر بود كه نشان داد 12/2± 08/68%، 48/3 ± 66/39%، و 57/7 ± 99/52% سزيم محلول‌ها مورد پالايش قرار گرفته است. تجزيه ‌و تحليل‌هاي گياهي نشان داد كه به‌ترتيب: 33/6 ± 16/396، 65/45 ± 4/521، و 07/93 ± 66/1256 ميلي‌گرم بر كيلوگرم سزيم در گياهان تجمع يافته است. همچنين مشاهدات ميكروسكوپي اندام‌هاي هوايي نشان داد كه ساختمان بافتي اين اندام‌ها هيچ تغييري نكرده است و با افزايش غلظت سزيم، تراكم آوندهاي چوبي و بلورها بيشتر مي‌شود كه نشان‌دهنده‌ي افزايش جذب سزيم و پاسخ گياه به اثرات سمي آن است.

Cesium is vastly observed in nuclear wastewaters and is potentially considered a hazardous material, therefore, its removal from nuclear site wastewaters is an important task. Removal of radionuclides and heavy metals by phytoremediation is fast becoming attractive, due to its high efficiency and low cost. Furthermore, native plants, in terms of survival, growth and also reproduction under environmental stresses, have more stability than plants introduced from other environments. For phytoremedition purposes, it is essential to choose metal tolerant and accumulator plant species that are capable of contaminant transport and accumulation in a relatively short treatment time. In this research, the potential of Chenopodium album for phytoremediation of solutions contaminated with cesium was studied. Chenopodium album seeds were germinated in sand, and then one-month-old plantlets were transplanted in plastic trays containing nutrient solutions. Hydroponically grown plants were incubated in different concentrations of cesium chloride, representing 0.47, 1.58, 3.95 mg l-1 of cesium ions in the solutions, for a set period. At the end of 14 days, cesium concentrations in the solutions were 0.15 ± 0.01, 0.95 ± 0.05 and 1.85 ± 0.29 mg l-1, respectively, meaning that 68.08 ± 2.12%, 39.66 ± 3.48% and 52.99 ± 7.57% of cesium has been remediated from the contaminated solutions. Chenopodium album plants were found to be efficient in remediating cesium in all concentrations tested. Plant analysis indicated that 396.16 ± 6.33, 521.4 ± 45.65 and 1256.66 ± 93.07 mg kg-1 of cesium were accumulated in plants after 14 days. Furthermore, the uptake and accumulation increased with increasing metal concentrations in the solutions. At lowest cesium concentration, plant uptake of cesium was found to be higher. For anatomical studies aerial organs of plants, including the stem and leaf, were fixed, handy sections were prepared and colored and, consequently, photographed. Anatomical studies were performed in many parts, including the primary and secondary structure of the control plants, the structure of control leaves and the anatomical structure of aerial organs after treatment with cesium. Microscopic observation of aerial organs indicated that the tissue structures of these organs had not changed. Moreover, increasing cesium concentration in solutions caused a high level of cesium accumulation in shoots, followed by development in xylem organs and crystalline. Cooperating cesium in the crystal structure and its accumulation in vacuoles permit the plant to uptake more radioactive cesium from the environment without any seriously incurred damage to the plant. These changes could be accounted as plant responses to cesium toxicity. It is concluded that hydroponically grown Chenopodium album could be used as a potential candidate plant for phytoremediation of solutions contaminated with cesium. Moreover, the present study offers an effective and highly economical means of controlling radioactive wastewater.