Phyto-Synthesized Silver Nanoparticle Toxicity Effect on Aquatic Plant Lemna minor L.

Abstract

Silver nanoparticles (AgNP) are made up about 55% of all nanomaterials produced and are widely used in consumer products. Its is inevitable that these particles are released to the aquatic environment during production, use and disposal. In this study, subacute toxicity of AgNPs obtained by phyto-synthesis was investigated on Lemna minor L. (duckweed) plants. Plant stock cultures were grown in the climate room according to OECD 221 guidelines. After 8 weeks of acclimation, the plants were treated with AgNP concentrations ranging from 0.005 to 50 mg L−1 for 7- and 14-days. The formation of silver nanoparticles obtained from laurel (Laurus nobilis L.) extract was determined by UV-VIS spectrophotometric measurements. The AgNPs synthesized by the phyto-synthesis method were characterized by Fourier transform infrared spectroscopy (FT-IR), Zeta size and potential, Inductively Coupled Plasma Mass Spectrometry and Scanning electron microscopy (SEM-EDS) analysis. The analysis results show that AgNPs are homogeneously distributed, spherical in shape with an average size of 34 nm and coated with phyto-content. The increase in AgNP concentration caused a decrease in frond numbers. Growth inhibition data showed that the EC50 value of phyto-synthesized AgNP was 4.78 mg L-1 and the lowest observed effect concentration (LOEC) was 0.5 mg L-1 for 7-days. AgNP concentrations below LOEC level (0.05, to 0.5 mg L-1) caused a significant decrease in growth rate by 20.07% after 7 days of exposure while it was found 4.03% for 14-days treatment at the highest AgNP concentration (0.5 mg L-1). Similar trend was observed in fresh-and dry weight of plants indicating prolonged exposure time triggering tolerance mechanism which was corroborated by chlorophyll a/b and carotenoids content results. Based on higher NOEC, LOEC and EC50 values, phyto-synthesized AgNP usage may lead less environmental toxicity.