Fig 1.
Schematic overview of the study.
The techniques that were used to investigate each parameter are shown on the arrows.
Fig 2.
Dose-response curves for NO3- production in soil over 28 d.
Ionic Ag (Ag+–dashed line); Ag nanoparticles (AgNP–short dashed line); and Ag sulfide nanoparticles (Ag2S-NP–long dashed line). Mean values (n = 3) ± 1 standard deviation are shown. Silver concentrations are on a log10 scale.
Table 1.
Silver concentrations (mg Ag kg soil-1) that correspond to a 10%, 20% and 50% reduction in soil nitrate production compared to the control (EC10, EC20 and EC50, respectively).
Mean values are shown with 95% confidence intervals in parentheses. For a given ECx, significant differences (p<0.05) between Ag treatments are indicated by different superscript letters.
Fig 3.
Dose-response curves showing the decrease in total abundance of bacterial amoA gene over 28 d.
Results are shown for each Ag treatment: (A) ionic Ag (Ag+), (B) Ag nanoaparticles (AgNP) and (C) Ag sulfide nanoparticles (Ag2S-NP). Mean values (n = 4) ± 1 standard deviation are shown. Silver concentrations are on a log scale. All Ag treatments were fitted to the five parameter Brain-Cousens hormesis model as hormesis was significant (p<0.05).
Fig 4.
The abundance of bacteria and archaea, as indicated by the number of 16S ribosomal DNA (rDNA) copies measured using quantitative PCR (qPCR).
Results are shown for each Ag treatment: (A) ionic Ag (Ag+), (B) Ag nanoaparticles (AgNP) and (C) Ag sulfide nanoparticles (Ag2S-NP). A likely outlier is circled in the AgNP treatment.
Fig 5.
Taxonomy of the OTUs that were successfully fitted to the dose-response models.
For clarity, only the bacterial families that contributed ≥2% to the overall distribution are shown. Unassigned OTUs are unclassified at the family level but are classified at higher taxonomic levels.
Fig 6.
Operational taxonomic unit (OTU) sensitivity distributions (OSD) comparing the sensitivity of OTUs to each Ag treatment.
Results are shown for each Ag treatment: (A) ionic Ag (Ag+), (B) Ag nanoaparticles (AgNP) and (C) Ag sulfide nanoparticles (Ag2S-NP). Each data point corresponds to the Ag concentration that decreased the absolute abundance of a specific OTU by 20% (EC20). Data were fitted to a Burr Type III function, where the fitted function is shown in green and 95% confidence intervals are indicated by the blue dashed line.
Table 2.
Hazardous concentrations (HC) for ionic Ag (Ag+), Ag nanoparticles (AgNP) and Ag sulfide nanoparticles (Ag2S-NP) at which 95%, 90% and 80% of soil OTUs are protected (HC5, HC10 and HC20, respectively).
Upper and lower 95% confidence intervals are shown in parentheses. Hazardous concentrations at which only 20% of soil OTUs are protected (HC80) were calculated to define the less sensitive OTUs. For a given HC, significant differences (p<0.05) between Ag treatments are indicated by different superscript letters.