Phytotoxicity Evaluation of Silver Nanoparticles Used in Agriculture: Stimulatory and Inhibitory Effects on Growth of Microalgae and Lettuce Seeds

Abstract

Silver nanoparticles (AgNP) have optical, electrical, thermal and antimicrobial properties that have been applied in several sectors, such as chemical / biological sensors and surgical materials. In the agricultural sector, formulations based on AgNP help to prevent plant pathogens through seed disinfection and control of plant diseases caused by bacteria. Therefore the consumption of products containing AgNP can lead to the release of these metallic nanoparticles in the environmental compartments. The purpose of the present work is to evaluate the effect of the nanomaterial in the bioindicator organisms Pseudokirchneriella subcapitata (unicellular microalgae) and Lactuca sativa (lettuce seed), the latter as a bioindicator of humid areas. At low concentrations of AgNP (0.1 to 1.0 mg L-1), biostimulation was associated with an increase in percentage of algae growth and with the elongation of root in L. sativa at 0,01 mg L-1. A dose-effect relationship was determined for both organisms by calculating the Mean Effective Concentration (EC50) associated with the inhibition of the growth rate. This was equivalent to 3.67 mg L-1 (EC50-168h) and 35.31 mg L-1 (EC50-96h), respectively for P. subcapitata and Lactuca sativa. The determination of the No Observed Effect Concentration (NOEC) values (0.58 and 1.45 mg L-1, respectively for P. subcapitata and L. sativa) is useful for the establishment of maximum permissible levels of the nanocomposite in the aquatic system and in adjacent areas to these compartments.