Silver sulfide nanoparticles (Ag₂S-NPs) are taken up by plants and are phytotoxic

Abstract

Silver nanoparticles (NPs) are used in more consumer products than any other nanomaterial and their release into the environment is unavoidable. Of primary concern is the wastewater stream in which most silver NPs are transformed to silver sulfide NPs (Ag2S-NPs) before being applied to agricultural soils within biosolids. While Ag2S-NPs are assumed to be biologically inert, nothing is known of their effects on terrestrial plants. The phytotoxicity of Ag and its accumulation was examined in short-term (24 h) and longer-term (2-week) solution culture experiments with cowpea (Vigna unguiculata L. Walp.) and wheat (Triticum aestivum L.) exposed to Ag2S-NPs (0-20 mg Ag L(-1)), metallic Ag-NPs (0-1.6 mg Ag L(-1)), or ionic Ag (AgNO3; 0-0.086 mg Ag L(-1)). Although not inducing any effects during 24-h exposure, Ag2S-NPs reduced growth by up to 52% over a 2-week period. This toxicity did not result from their dissolution and release of toxic Ag(+) in the rooting medium, with soluble Ag concentrations remaining below 0.001 mg Ag L(-1). Rather, Ag accumulated as Ag2S in the root and shoot tissues when plants were exposed to Ag2S-NPs, consistent with their direct uptake. Importantly, this differed from the form of Ag present in tissues of plants exposed to AgNO3. For the first time, our findings have shown that Ag2S-NPs exert toxic effects through their direct accumulation in terrestrial plant tissues. These findings need to be considered to ensure high yield of food crops, and to avoid increasing Ag in the food chain.

The toxicity of silver to soil organisms exposed to silver nanoparticles and silver nitrate in biosolids‐amended field soil

“…Although speciation techniques applied to the bulk soil suggested complete sulfidization, the researchers hypothesized that the amorphous, nano‐scale Ag 2 S and organically complexed Ag‐thiol transformation products likely presented more phyto‐available Ag than crystalline or micron‐scale Ag 2 S, particularly given further transformations likely to occur within the rhizosphere . Furthermore, there is increasing evidence that dispersed, Ag(0)‐enriched nanoparticles and nano‐sized Ag 2 S can accumulate within plant tissue and that Ag is more phyto‐available in soils amended with biosolids from WWTPs contaminated with engineered AgNPs than with more soluble (i.e., AgNO 3 ) inputs .…”

Fate of metallic engineered nanomaterials in constructed wetlands: prospection and future research perspectives

“…Zhu et al (2012), who studied the fate of Au-NPs with different surface functionalization, observed that the Au-NPs with a negatively charged coating were the least efficiently attached onto the root surface prior to uptake but more efficiently transported to leaves once inside the plant, compared to positively charged Au-NPs. (Wang et al 2015). In the same study of Wang et al (2015), they observed that Ag 2 S was taken up by the plant roots to a somewhat larger extent than Ag-NPs.…”

“…(Wang et al 2015). In the same study of Wang et al (2015), they observed that Ag 2 S was taken up by the plant roots to a somewhat larger extent than Ag-NPs. Also CuO-and ZnO-NPs are both mainly accumulated in the root zone of wetland plants Phragmites australis and Schoenoplectus tabernaemontani (Zhang et al 2014(Zhang et al , 2015.…”

Nanomaterial Transformations in the Environment: Effects of Changing Exposure Forms on Bioaccumulation and Toxicity

“…[ 50 ] This suggests that Ag 2 S NMs follow the same route for uptake and trafficking as the pristine materials. In studies with plants, Ag 2 S uptake into roots and from there translocation to shoots has been reported [ 52–54 ] with uptake often higher than that of invertebrates. [ 52–54 ] In the case of pristine NMs, uptake has often been related to the Ag + present in the system through dissolution.…”

“…In studies with plants, Ag 2 S uptake into roots and from there translocation to shoots has been reported [ 52–54 ] with uptake often higher than that of invertebrates. [ 52–54 ] In the case of pristine NMs, uptake has often been related to the Ag + present in the system through dissolution. However, the fact that Ag coordinated with S could be measured in the shoots in the absence of significant dissolution, suggests that the aged NMs themselves may be taken up and translocated.…”