Environmental impact of silver nanoparticles
[3] Silver nanoparticles are not entirely cleared from the water during the wastewater treatment process, possibly leading to detrimental environmental effects.
[4] Along with its antimicrobial properties, its low mammalian cell toxicity makes these particles a common addition to consumer products.
[4] Silver nanoparticles were also found to attach to cellular membranes, eventually dissipating the proton motive force, leading to cell death.
[4] However, its toxicity to microorganisms is not overtly observed since the free silver ion is found in low concentrations in wastewater treatment systems and the natural environment due to its complexation with ligands such as chloride, sulfide, and thiosulfate.
[4] A majority of silver nanoparticles in consumer products go down the drain and are eventually released into sewer systems and reach wastewater treatment plants.
[2] The secondary wastewater treatment process involves suspended growth systems which allow bacteria to decompose organic matter within the water.
[8] A majority of the silver found in wastewater treatment plant effluent is associated with reduced sulfur as organic thiol groups and inorganic sulfides.
[10] This shell is often created with carboxylic acids functional groups, usually using citrate, leading to stabilization through adsorption or covalent attachment of organic compounds.
[11] Thioesters exhibit electrosteric repulsive forces due to amine functional groups and their size, which prevents aggregation.
Ca2+ ions are naturally found in seawater due to the weathering of calcareous rocks, and allow for dissolution of the oxide-coated particle at low electrolyte concentrations.
[6] When aggregation occurs, the silver nanoparticles lose microbial toxicity, but have greater exposure in the environment for larger organisms.
[13]Dissolution of Ag2O in Water:Ag2O + H2O → 2Ag− + 2OH− [11][13]The nano-size of the particles aids in oxidation since their smaller surface area increases their redox potential.
[18] Thus, the formation of Ag2S limits the amount of bioavailable sulfur and contributes to a reduction in toxicity of silver nanoparticles to nitrifying bacteria.
[13] Silver nanoparticles are experimentally shown to inhibit autotrophic nitrifying bacterial growth (86±3%) more than Ag+ ions (42±7%) or AgCl colloids (46±4%).
[4] The actual cause of these results is undetermined as growth conditions and cell properties differ between nitrifying bacteria and heterotrophic E.
[22] Filter feeding bivalves accumulate nanoparticles to concentrations 10,000 times greater than was added to seawater, and Ag+ ions are proven to be extremely toxic to them.
[23] As global temperatures rise and oceanic pH drops, some species, such as oysters, will be even more susceptible to the negative impacts of nanoparticles as they are stressed.
