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Silver nanoparticles, enhanced with plant extracts, promotes plant growth: Study

Silver nanoparticles are nanoparticles of silver whose size varies from 1 nm to 100 nm. They are commonly used in the manufacture of about 200 consumer products, including clothing and cosmetics. While their antibacterial properties are hailed, reckless dumping of these nanoparticles is reported to pollute water and soil due to formation of toxins like silver sulfide. Now, a new study published in the Journal of Hazardous Materials has shown that silver nanoparticles, when enhanced with the extracts of the northern white-cedar (Thuja occidentalis), can help plant growth.

The northern white-cedar (Thuja occidentalis) is an evergreen coniferous tree native to Canada and the USA and is a widely cultivated ornamental plant. In this collaborative study, researchers from Tezpur University, India; Visva-Bharati University, India; Indian Statistical Institute, India; Govt. Emerson College, Pakistan and Hanyang University, South Korea, have used leaves from Thuja occidentalis to synthesise complex molecules of ‘green’ silver nanoparticles. The study also compared the effects of these nanoparticles on soil, with chemically manufactured silver nanoparticles that are otherwise dumped into the soil as waste.

The researchers treated alluvial soil samples with different concentrations of ‘green’ silver nanoparticles enhanced with extracts of northern white-cedar. They then sowed the seeds of Phaseolus vulgaris (French bean) in each of the samples and cultivated it for 60 days. After this period, they studied the soil particles using an electron microscope to understand the effect of green silver nanoparticles on different parameters of the soil.

The study found that green silver nanoparticles led to increased soil porosity—a property that determines the water-holding capacity of the soil—as compared to the natural soil condition. The study also found an increase in the soil's nitrogen content, another critical need for plant growth. According to the authors, the presence of green silver nanoparticles also stimulated the nitrogen uptake into plants and could improve the efficiency of nitrogen use by limiting the loss of nitrates by leaching.

Apart from the assessment of physical and chemical changes in the soil characteristics, the researchers also analysed the bacterial growth and plant health metabolism in the soil with green silver nanoparticles. The plants grown in this soil were found to have a higher chlorophyll content and enzyme activity as compared to plants cultivated in soil without silver nanoparticles.

The study shows how green silver nanoparticles improve the overall quality of soil and promote plant growth, thus opening up potential new applications for silver nanoparticles in the field of agriculture, and helping prevent pollution.