Flue gas desulfurization (FGD) steel slag ameliorates salinity, sodicity, and adverse physical properties of saline-sodic soil of middle Yellow River, China

Desulfurization steel slag improves the saline-sodic soil quality by replacing sodium ions and affecting soil pore structure

Flue gas desulfurization steel slag (DS), a solid waste produced by coal power plants and steelworks, was proposed as an amendment for the remediation of saline-sodic soil. A pot experiment including three dosages of DS alone (1%, 5%, 10% w/w) and their combination with fulvic acid (FA, 1%, w/w) was conducted to evaluate the potentials of DS as an amendment and to explore remediation mechanism of DS combined with FA on saline-sodic soil. The soil salinity, nutrition, pore structure, water retention, consistency, and desiccation cracking of DS and FA-amended soils were determined. Application of DS resulted in a significant reduction of pH, sodium adsorption ratio (SAR), and exchangeable sodium percentage (ESP) of saline-sodic soil. The DS amendment significantly increased the 6-15 μm pore volume of soil. The combination application of DS and FA showed better effect than the DS alone. The DS amendments at 5% and 10% significantly increased the field water capacity, permanent wilting point, and available water content of the soil, whereas significantly decreased the plastic limit, liquid limit, and plastic index. The DS alone and combined with FA could effectively control the development of desiccation cracking, reduced significantly the crack area density and average width of cracks of the soil. Consequently, the improvement of alkalinity and soil physical properties by DS amendment significantly increased the yield of alfalfa grown on saline-sodic soil. The remarkable improvement of physical properties of saline-sodic soil contributed to the decrease of SAR and ESP by the Ca2+ in DS replacing the Na + at soil colloid sites. Our results suggested that DS amendments alone or combined with fulvic acid have great potential as saline-alkali soil amendment.

Effects of cadmium and copper mixtures on antibiotic resistance genes in rhizosphere soil

The evolvement and development of antibiotic resistance in microorganisms may be influenced by metals; however, it is still unclear how cadmium (Cd) and copper (Cu) combined affect the distribution and presence of antibiotic-resistance genes (ARGs) in rhizosphere soil. The aims of this research were to (1) compare the distribution patterns of bacterial communities and ARGs in response to the effects of Cd and Cu both separately and combined; (2) explore the possible mechanisms underlying the variation in soil bacterial communities and ARGs in addition to the combined effects of Cd, Cu, and various environmental variables (nutrients, pH, etc.); and (3) provide a reference for assessing the risks of metals (Cd and Cu) and ARGs. The findings showed that the multidrug resistance genes acrA and acrB and the transposon gene intI-1 were present in high relative abundance in bacterial communities. Cadmium and Cu had a substantial interaction effect on the abundance of acrA, whereas Cu had a notable main effect on the abundance of intI-1. According to the network analysis, the strong links between bacterial taxa and specific ARGs revealed that most ARGs were hosted by Proteobacteria, Actinobacteria, and Bacteroidetes. According to structural equation modeling, Cd had a larger effect on ARGs than Cu. Compared to previous analyses of ARGs, bacterial community diversity had little effect on ARGs in this study. Overall, the results may have important consequences for determining the possible hazard of soil metals and extend the understanding of how Cd and Cu co-select ARGs in rhizosphere soils.

Heavy metal pollution risk of desulfurized steel slag as a soil amendment in cycling use of solid wastes

The by-product of wet flue gas desulfurization, desulfurized steel slag (DS), had chemical characteristics like natural gypsum that can be used to improve saline-sodic soil. However, contamination risk of heavy metals for cycling utilization of DS in agriculture was concerned mostly. Both pot and field experiments were conducted for evaluating the potential pollution risk of DS as the amendment of saline-sodic soil. Results showed that application of DS decreased the contents of Cd, Cu, Zn, and Pb, while significantly increasing chromium (Cr) content in DS-amended soils. The field experiment demonstrated that the migration of heavy metals (Cd, Zn, Cu, and Pb) in the soil profile was negligible. The application of DS at the dosage of 22.5-225 tons/ha significantly increased the Cr content in alfalfa (Medicago sativa L.) but lower than the national standard for feed in China (GB 13078-2017). DS altered the chemical fraction of heavy metals (Zn, Cu, and Pb), transferred exchangeable, reducible into oxidizable and residual forms in DS-amended soil. Application of DS combined with fulvic acid (FA) could effectively reduce the movement of heavy metals in soil and the accumulation of Cr in alfalfa. Based on our results, DS was a safe and feasible material for agricultural use and presented relatively little pollution risk of heavy metals. However, the results also showed that DS to a certain extent had a potential environmental risk of Cr if larger dosages of DS were used.