The effects of metallic engineered nanoparticles upon plant systems: An analytic examination of scientific evidence

Abstract

Recent evidence for the effects of metallic engineered nanoparticles (ENPs) on plants and plant systems was examined together with its implications for other constituents of the Society-Environment-Economy (SEE) system. In this study, we were particularly interested to determine whether or not metallic ENPs have both stimulatory and inhibitory effects upon plant performance. An emphasis was made to analyze the scientific evidence on investigations examining both types of effects in the same studies. Analysis of evidence demonstrated that metallic ENPs have both stimulatory and inhibitory effects mostly in well-controlled environments and soilless media. Nano zero-valent iron (nZVI) and Cu ENPs have potential for use as micronutrients for plant systems, keeping in mind the proper formulation at the right dose for each type of ENP. The concentration levels for the stimulatory effects of Cu ENPs are lower than for those for nZVI. Newer findings showed that extremely smaller concentrations of Au ENPs (smaller than those for nZVI and Cu ENPs) induce positive effects for plant growth, which is attributed to effects on secondary metabolites. Ag ENPs have demonstrated their usage as antimicrobial/pesticidal agents for plant protection; however, precautions should be taken to avoid higher concentrations not only for plant systems, but also, other constituents in the SEE. Further research is warranted to investigate the stimulatory and inhibitory effects of metallic ENPs in soil media in order to broaden the horizon of sustainable agriculture production in terms of higher and safer yields so as to meet the food requirements of human population.

Keywords: Inhibitory effects; Metal ions; Metallic engineered nanoparticles; Plant system; Society-Environment-Economy; Stimulatory effects.

Figure 1.

Analysis of evidence by type of metallic ENPs: (a) Ag – n = 28; (b) Au – n = 3; (c) nZVI – n = 5; (d) Al – n = 1; (e) Cu – n = 4; (f) Pt – n = 1; and Zn – n = 1. Footnote: n = number of studies in the evidence compiled in this research.

Figure 2.

Stimulatory and inhibitory effects of nZVI on peanut root growth after 18 day exposure. (Results obtained from Li et al. (2015)).

Figure 3.

Stimulatory and inhibitory effects or nZVI upon projected surface area, root volume, and number of tips and forks (Li et al., 2015).

Figure 4.

Model demonstrating possible links between gene expression and changes in plant species upon exposure to low concentrations of Au ENPs. (Adapted from Kumar et al., 2013).