Abstract
Industrialization advances have led to an increase soil contamination by heavy metals. Among different technologies, in situ stabilization of metals combined with revegetation attracted attention. Therefore, this study aimed at comparing effects of biochars [rice husk biochar (RHB), maple leaves biochar (MLB)] and common inorganic amendments [red mud (RM), and steel slag (SS)] at different rates (0.5, 1, and 2% w/w) on leaching, and phytoavailability of metals (assessed using mustard green “Brassica juncea”). Soil pH in treated soils significantly (p < 0.01) increased, with the optimal pH ranges for plant growth observed in biochar-treated soils. The leaching of Cd, Cu, Pb, and Zn through soil significantly (p < 0.05) decreased in treated soils. Plant uptake and accumulation of Cd, Cu, Pb, and Zn decreased by 79–66, 13–19, 87–86, and 37–36% in RHB- and MLB-treated soils, respectively. Sequential extraction analysis pointed out that the major stabilization mechanism for metals using biochars involved the formation of organic and carbonate bonds, while for RM and SS was believed to involve the formation of inner sphere complexes with Fe/Al (hydr)oxides. The plant available fractions for Cd were generally higher than those for others. Overall, high dosage addition (2%) of each amendment offered the best compromise as it successfully reduced both leaching and phytoavailability of metals. Using MLB for the first time, showed promising results to immobilize metals with an increase in plant biomass.
Highlights
Among the hazardous contaminants which are found in the environment, heavy metals gained the majority of concerns
This study aimed at comparing effects of biochars [rice husk biochar (RHB), maple leaves biochar (MLB)] and common inorganic amendments [red mud (RM), and steel slag (SS)] at different rates (0.5, 1, and 2% w/w) on leaching, and phytoavailability of metals
According to the results reported by Park et al [42], much of the silica was observed in the outer epidermis cells and concentrated in hair- and dome-shaped protrusions and as dispersed silica inside the husk (Fig. 2a)
Summary
Among the hazardous contaminants which are found in the environment, heavy metals gained the majority of concerns. Several human activities have the potential of producing heavy metals as side effects. Movement of such contaminants into surrounding areas in form of dust, leachates through the soil, and spreading of sewage sludge is a common example of contamination of the ecosystems [1]. Mining and corresponding activities are recognized as point sources of toxic element pollution that can damage the surface environment [2]. If the soil immobilization technique is employed, simplicity and rapidity (besides high public acceptability) will be achieved. This method is relatively inexpensive, while covering a broad spectrum of inorganic pollutants [5]
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