Transport of silver nanoparticles in intact columns of calcareous soils: The role of flow conditions and soil texture

Growing production of manufactured nanomaterials has increased the possibility of contamination of groundwater resources and soils by nanoparticles (NPs). It is crucial to study the fate of NPs in subsurface porous media in order to evaluate and control their risks to ecosystems and human health. Hence, this study was conducted to investigate the transport and retention of polyvinylpyrrolidone (PVP) stabilized silver nanoparticles (AgNPs, a diameter of 40 nm) under saturated and unsaturated conditions in intact columns of two calcareous sandy loam (TR) and loam (ZR) soils. Furthermore, similar experiments were conducted using sand quartz as a reference medium. A pulse of the AgNP suspension with an input concentration (C0) of 50 mg L−1 was injected into the columns for 3 pore volumes. The transport of bromide (Br), as a non-reactive inert tracer, was also examined. High mobility of AgNPs was observed through the sand columns due to unfavorable conditions for AgNP deposition on the quartz sand surfaces. Nearly all AgNPs introduced into the columns of both soils were retained in the soil. Percentages of AgNPs leached out of the columns were <1% of the total injected mass in both soils. Hyperexponential retention profiles (RPs) were observed in both soils and maximum concentrations of 100–130 mg kg−1 were determined near the columns’ inlet. However, slightly stronger retention of AgNPs and greater maximum retained concentrations on the solid phase (Smax) in the ZR soil compared with the TR soil may be attributed to smaller grain sizes of the ZR soil. Hydrodynamic forces adjacent to the solid surfaces near the column inlet can provide a viable explanation for the hyperexponential shape of RPs. The one-site kinetic attachment model in HYDRUS-1D, which accounted for time- and depth-dependent retention, was successfully used to analyze the retention of AgNPs. The results showed that the degree of saturation had little effect on the mobility of AgNPs through undisturbed soil columns. Our results suggested the limited transport of AgNPs in neutral/alkaline calcareous soils under both saturated and unsaturated conditions

Transport of silver nanoparticles in intact columns of calcareous soils: The role of flow conditions and soil texture

Growing production of manufactured nanomaterials has increased the possibility of contamination of groundwater resources and soils by nanoparticles (NPs). It is crucial to study the fate of NPs in subsurface porous media in order to evaluate and control their risks to ecosystems and human health. Hence, this study was conducted to investigate the transport and retention of polyvinylpyrrolidone (PVP) stabilized silver nanoparticles (AgNPs, a diameter of 40 nm) under saturated and unsaturated conditions in intact columns of two calcareous sandy loam (TR) and loam (ZR) soils. Furthermore, similar experiments were conducted using sand quartz as a reference medium. A pulse of the AgNP suspension with an input concentration (C0) of 50 mg L−1 was injected into the columns for 3 pore volumes. The transport of bromide (Br), as a non-reactive inert tracer, was also examined. High mobility of AgNPs was observed through the sand columns due to unfavorable conditions for AgNP deposition on the quartz sand surfaces. Nearly all AgNPs introduced into the columns of both soils were retained in the soil. Percentages of AgNPs leached out of the columns were <1% of the total injected mass in both soils. Hyperexponential retention profiles (RPs) were observed in both soils and maximum concentrations of 100–130 mg kg−1 were determined near the columns’ inlet. However, slightly stronger retention of AgNPs and greater maximum retained concentrations on the solid phase (Smax) in the ZR soil compared with the TR soil may be attributed to smaller grain sizes of the ZR soil. Hydrodynamic forces adjacent to the solid surfaces near the column inlet can provide a viable explanation for the hyperexponential shape of RPs. The one-site kinetic attachment model in HYDRUS-1D, which accounted for time- and depth-dependent retention, was successfully used to analyze the retention of AgNPs. The results showed that the degree of saturation had little effect on the mobility of AgNPs through undisturbed soil columns. Our results suggested the limited transport of AgNPs in neutral/alkaline calcareous soils under both saturated and unsaturated conditions

Comparing soil aggregate stability at different grazing intensities (case study: Bardasiab rangeland, Fereidounshahr)

Soil quality, aggregate stability and erosion sensibility are affected by different range management practices. This research aimed to evaluate the relationships between soil organic carbon, mean weight diameter (MWD) and aggregate size distribution in the surface soil layer (0- 20 cm) of various range sites with different grazing intensities (non, slightly and heavily grazed) in Bardasiab rangeland, Feridounshahr, Isfahan province. Stratified random sampling method was used to collect soil samples along the established transects. Some physical and chemical properties of soil samples such as texture, electrical conductivity (EC), organic carbon (OC), MWD and sodium absorption ratio (SAR) were measured in the soil laboratory. Simple linear regression and One-way ANOVA followed by the Fisher’s LSD test were used to analyze the data. Results of regression analysis showed that MWD and OC of the soil samples were significantly correlated ( α =1%, R 2 = 61.3 %). The soil MWD values of range sites with various grazing intensities were significantly different ( α =5%). Organic carbon was increased and SAR was decreased in the sites located inside exclosures, which lead to higher soil MWD. Aggregate size distribution among various sites were significantly different ( α =5%) only for the aggregate smaller than 0.25 mm. Soil aggregates sizes between non-grazed and heavily grazed sites were also significantly different only for the size ranges of 4- 8 mm ) α =5%, ( and less than 0.25 mm ) α=1% (. In addition, macro aggregates increased and micro aggregates decreased in range sites with no or slight grazing intensity, respectively as these sites experienced low trampling and increased litter and organic carbons. Soil aggregate stability can therefore be used as an appropriate indicator for monitoring the impact of different management practices on rangeland soil quality and health

Persistence and Leaching Potential of Microorganisms and Mineral N in Animal Manure Applied to Intact Soil Columns

Pathogens may reach agricultural soils through application of animal manure and thereby pose a risk of contaminating crops as well as surface and groundwater. Treatment and handling of manure for improved nutrient and odor management may also influence the amount and fate of manure-borne pathogens in the soil. A study was conducted to investigate the leaching potentials of a phage (Salmonella enterica serovar Typhimurium bacteriophage 28B) and two bacteria, Escherichia coli and Enterococcus species, in a liquid fraction of raw pig slurry obtained by solid-liquid separation of this slurry and in this liquid fraction after ozonation, when applied to intact soil columns by subsurface injection. We also compared leaching potentials of surface-applied and subsurface-injected raw slurry. The columns were exposed to irrigation events (3.5-h period at 10 mm h(−1)) after 1, 2, 3, and 4 weeks of incubation with collection of leachate. By the end of incubation, the distribution and survival of microorganisms in the soil of each treatment and in nonirrigated columns with injected raw slurry or liquid fraction were determined. E. coli in the leachates was quantified by both plate counts and quantitative PCR (qPCR) to assess the proportions of culturable and nonculturable (viable and nonviable) cells. Solid-liquid separation of slurry increased the redistribution in soil of contaminants in the liquid fraction compared to raw slurry, and the percent recovery of E. coli and Enterococcus species was higher for the liquid fraction than for raw slurry after the four leaching events. The liquid fraction also resulted in more leaching of all contaminants except Enterococcus species than did raw slurry. Ozonation reduced E. coli leaching only. Injection enhanced the leaching potential of the microorganisms investigated compared to surface application, probably because of a better survival with subsurface injection and a shorter leaching path