Abstract
This study investigated the impact of lime stabilization on the fate and transformation of AgNPs. It also evaluated the changes in the population and diversity of the five most relevant bacterial phyla in soil after applying lime-stabilized sludge containing AgNPs. The study was performed by spiking an environmentally relevant concentration of AgNPs (2 mg AgNPs/g TS) in sludge, applying lime stabilization to increase pH to above 12 for two hours, and applying lime-treated sludge to soil samples. Transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) were used to investigate the morphological and compositional changes of AgNPs during lime stabilization. After the application of lime stabilized sludge to the soil, soil samples were periodically analyzed for total genomic DNA and changes in bacterial phyla diversity using quantitative polymerase chain reaction (qPCR). The results showed that lime treatment effectively removed AgNPs from the aqueous phase, and AgNPs were deposited on the lime molecules. The results revealed that AgNPs did not significantly impact the presence and diversity of the assessed phyla in the soil. However, lime stabilized sludge with AgNPs affected the abundance of each phylum over time. No significant effects on the soil total organic carbon (TOC), heterotrophic plate count (HPC), and percentage of the live cells were observed.
Highlights
The nanoparticle industry is growing exponentially, and new nanomaterials and products are being introduced to consumers on an almost daily basis
Analysis after dilution of the stock solution with nanopure water; the Transmission electron microscopy (TEM) images revealed that the AgNPs suspension was extremely pure
TEM imaging, the AgNPs were well dispersed within the water, and agglomeration or aggregation of particles was not detected
Summary
The nanoparticle industry is growing exponentially, and new nanomaterials and products are being introduced to consumers on an almost daily basis. AgNPs are commonly used as antimicrobial agents and incorporated in a wide range of merchandise and applications. Many products such as textiles, antimicrobial coatings, keyboards, wound dressings, and biomedical devices contain AgNPs that continually release a low level of silver ions [1]. It was reported that just one wash cycle could increase the total amount of silver released from 1%. A large portion of the AgNPs ends up in wastewater treatment plants [5,6]. Studies have shown the toxicity of AgNPs on microorganisms that are necessary for wastewater treatment [7,8]
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