The dance of contaminants: How silver nanoparticles and cadmium alter the quality of deionized water

Abstract

The rapid increase in the presence of both nanoparticles and heavy metals in aquatic ecosystems brought up concerns regarding their combined effect on the quality of water as they enter aquatic ecosystems at an alarming rate. This study underscores the combinatorial effect of silver nanoparticles (AgNPs) (0.05 ppm) and cadmium (0.03 ppm) upon the fundamental physicochemical properties of deionized (DI) water at their environmentally relevant concentrations. Purity and consistency of DI water provide a controlled environment, ideal for isolating and studying the specific interactions between AgNPs and Cd. Chitosan-stabilized silver nanoparticles (cs–AgNPs) were synthesized using chitosan as a stabilizing and reducing agent. The synthesis involved addition of 0.5 g chitosan into 0.5 L of 2 mM AgNO3 solution. Afterwards, NaOH was added in two portions: 1.0 mL of 1% solution after 5 minutes and 1.5 mL after 10 minutes. The formation of AgNPs was confirmed by the solution’s color change to reddish-brown and the appearance of a Surface Plasmon Resonance (SPR) band at 420 nm in the UV– visible spectrum. Transmission Electron Microscopy (TEM) revealed an average particle size of 5.94 ± 2.95 nm, with a 2-12 nm range. To test physicochemical parameters, samples containing AgNPs and Cd individually and in combination, were sonicated for one hour along with a control group. AgNPs exposure resulted significant increase in conductivity suggesting potential alterations in ionic mobility in water. pH was slightly lower in both individual treatments than the control, whereas the combined treatment exhibited a higher pH value indicating a shift towards alkalinity. Turbidity increased in the combined exposure whereas the dissolved oxygen (DO) level was slightly lower, implying a potential interference with oxygen availability in the water, which could adversely impact aquatic organisms. Notably, only the combined treatment significantly increased the Total Dissolved Solid (TDS) value. The findings highlight the fact that AgNPs and Cd act synergistically to alter water quality posing risks to aquatic ecosystems providing crucial insights for water treatment strategies and aiding in safeguarding ecosystems and public health.