Low Concentrations of Silver Nanoparticles in Biosolids Cause Adverse Ecosystem Responses under Realistic Field Scenario

Abstract

A large fraction of engineered nanomaterials in consumer and commercial products will reach natural ecosystems. To date, research on the biological impacts of environmental nanomaterial exposures has largely focused on high-concentration exposures in mechanistic lab studies with single strains of model organisms. These results are difficult to extrapolate to ecosystems, where exposures will likely be at low-concentrations and which are inhabited by a diversity of organisms. Here we show adverse responses of plants and microorganisms in a replicated long-term terrestrial mesocosm field experiment following a single low dose of silver nanoparticles (0.14 mg Ag kg−1 soil) applied via a likely route of exposure, sewage biosolid application. While total aboveground plant biomass did not differ between treatments receiving biosolids, one plant species, Microstegium vimeneum, had 32 % less biomass in the Slurry+AgNP treatment relative to the Slurry only treatment. Microorganisms were also affected by AgNP treatment, which gave a significantly different community composition of bacteria in the Slurry+AgNPs as opposed to the Slurry treatment one day after addition as analyzed by T-RFLP analysis of 16S-rRNA genes. After eight days, N2O flux was 4.5 fold higher in the Slurry+AgNPs treatment than the Slurry treatment. After fifty days, community composition and N2O flux of the Slurry+AgNPs treatment converged with the Slurry. However, the soil microbial extracellular enzymes leucine amino peptidase and phosphatase had 52 and 27% lower activities, respectively, while microbial biomass was 35% lower than the Slurry. We also show that the magnitude of these responses was in all cases as large as or larger than the positive control, AgNO3, added at 4-fold the Ag concentration of the silver nanoparticles.

Impact of engineered nanoparticles on the activity, abundance, and diversity of soil microbial communities: a review

“…Ag-NP has been found to reduce substrate-induced respiration and enzymatic activities after 50 days of exposure to a low concentration of Ag-NPs (0.14 mg kg −1 soil) applied in mesocosms via sewage sludge (Colman et al 2013). Another study using much lower concentrations of Ag-NPs (0.0032, 0.032, 0.32 mg kg −1 soil) did not show any changes in the different tested enzymatic activities (Hänsch and Emmerling 2010).…”

Emerging Contaminant or an Old Toxin in Disguise? Silver Nanoparticle Impacts on Ecosystems

“…15,20 Soils were blended and provided by Soils and Sand (Durham, U.S.A.), and were a blend of three soils ("Sandhills", from Lemon Springs, NC, U.S.A.; "Clay" and "Topsoil", from Durham, NC, U.S.A.). The final soil had a texture of 63.9% sand, 28.3% silt, and 13.0% clay, with 5.1% loss on ignition.…”

“…Direct comparisons within individual studies have led to mixed conclusions: some studies found higher toxicity and/or biouptake for AgNPs than AgNO 3 ; 7,8,15,16 other studies report the opposite conclusion. 17−19 Much of this discrepancy may be explained by differences in AgNP size or coatings; for that reason, we chose to compare the effects of two very different AgNPs with different published toxicity thresholds: the larger PVP-AgNPs are in general less toxic than the smaller GA-AgNPs, which in turn tend to be less toxic than AgNO 3 .…”

Effects of silver nanoparticles of different sizes on cytotoxicity and oxygen metabolism disorders in both reproductive and respiratory system cells

“…Biosolids recycled from sewage are incinerated or applied as an agricultural fertilizer, and represent an important route of exposure of ecosystems to AgNPs (Colman et al 2013, Schlich et al 2013. It has been shown that AgNPs can cause adverse effects to both aerobic and anaerobic bacteria in wastewater treatment plants (Choi and Hu 2008).…”