Anna Grobelak, Małgorzata Kacprzak, Anna Grosser, Anna Napora
Assisted phytostabilisation involves the use of plants and soil additives for physical stabilization of the soil and chemical immobilization of contaminants. This technique aims to establish a vegetation cover with metal-tolerant plants and thus reduce leaching of metals. The main aim is to reduce the risk of incorporation of metal into the food chain. In the conducted experiment contaminated soil was collected from the area surrounding a zinc smelter in Miasteczko Slaskie, in the Silesia region of Poland. Soil in the study area has been contaminated with metals, especially Cd, Pb and Zn. Moreover, soils of the study area are also acidified. The role of sewage sludge and inorganic amendments as an immobilising agents in the attenuating phytostabilisation of metal-contaminated soil was evaluated using grass species Festucaarundinacea Schreb. The biosolid used was anaerobically digested sewage sludge, collected from the industrial waste water treatment plant and juices manufacturer (food industry). The soil was mixed with sewage sludge (sewage sludge accounted for 1and 3% of dry weight), lime and inorganic fertilizers (potassium phosphate, TSP at 0.8% each). A plant growth experiment was conducted in a growth chamber for 10 weeks. The plants were grown under artificial conditions, suitable for proper growth of plants. Plants growing on amended soil were devoid of any macroscopic symptoms of metal toxicity or nutrient deficiency, in contrast to plants grown on non-amended soil, where growth was inhibited and some phytotoxic effects were observed. For amended soil, plant growth was most likely influenced by improved soil conditions due to nutrient-rich amendments and metals immobilisation. Mobile fractions of metals decreased in amended soil, and the same pattern was observed for metal concentrations in plant tissues. However, the best results were obtained for the variants of combined application of sewage sludge and inorganic amendments. All investigated metals accumulated mainly in root tissues in combination with sewage sludge application. A significant reduction in metal uptake by plants was achieved after sewage sludge application, which is attributed to decreased bioavailability and the stabilisation of metals in soil. In the experiment the introduction of soil liming treatment allowed to maintain the pH at a constant level after 10 weeks of the experiment (5.5–7) (Fig. 1). The K5-K10 variants achieved a significant reduction in bioavailable forms (0.01 M CaCl2 extraction). In a study of biomass (Fig. 3) the highest yield (5.5 g DM) was obtained for the combined use of a combination of potassium and phosphate deposits and combinations of superphosphate and combined use of sewage sludge (2.5 g DM/pot). The highest immobilization effects were obtained for combined application of sewage sludge, lime fertilizer and superphosphate or potassium phosphate as compared to other options. The highest degree of immobilization of three tested heavy metals: cadmium, zinc and lead was obtained only with the application of sewage sludge and mineral amendments at a dose of TW +FP 0.8% + 1% d.m. sewage sludge. Effective process of chemophytostabilisation with the use of grass and organic additive and inorganic additives in situ sandy areas and heavily contaminated with heavy metals, can be obtained solely with the combined use of investigated additives and treatment.
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