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

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

Characterization and Adaptation of Anaerobic Sludge Microbial Communities Exposed to Tetrabromobisphenol A

<div><p>The increasing occurrence of tetrabromobisphenol A (TBBPA) in the environment is raising questions about its potential ecological and human health impacts. TBBPA is microbially transformed under anaerobic conditions to bisphenol A (BPA). However, little is known about which taxa degrade TBBPA and the adaptation of microbial communities exposed to TBBPA. The objectives of this study were to characterize the effect of TBBPA on microbial community structure during the start-up phase of a bench-scale anaerobic sludge reactor, and identify taxa that may be associated with TBBPA degradation. TBBPA degradation was monitored using LC/MS-MS, and the microbial community was characterized using Ion Torrent sequencing and qPCR. TBBPA was nearly completely transformed to BPA <i>via</i> reductive debromination in 55 days. Anaerobic reactor performance was not negatively affected by the presence of TBBPA and the bulk of the microbial community did not experience significant shifts. Several taxa showed a positive response to TBBPA, suggesting they may be associated with TBBPA degradation. Some of these taxa had been previously identified as dehalogenating bacteria including <i>Dehalococcoides</i>, <i>Desulfovibrio</i>, <i>Propionibacterium</i>, and <i>Methylosinus</i> species, but most had not previously been identified as having dehalogenating capacities. This study is the first to provide in-depth information on the microbial dynamics of anaerobic microbial communities exposed to TBBPA.</p></div

Weighted UniFrac matrix-based Principal Coordinate Analysis (PCoA) and Analysis of Similarity (ANOSIM) results.

<p>The percentage of variation explained for the x and y-axis are indicated on the graph. The table indicates the results of the ANOSIM analyses performed on the weighted UniFrac matrix generated. The null hypothesis (H₀) states that there is no difference between groups in terms of community composition. H₀ is rejected if p>0.05. An R-value close to 1 indicates an important differences between the groups tested, while an R-value close to 0 indicates a small difference between the groups tested in terms of community composition.</p

TBBPA degradation and formation of BPA.

<p>Concentration of TBBPA, BPA, and degradation by-products (i.e., 3,3',5-tribromobisphenol, 3,3'-dibromobisphenol and 3-bromobisphenol A) in metabolic (a) and co-metabolic (b) reactors overtime. Error bars represent standard deviation from the mean. TBBPA reductive debromination pathway is shown above the graphs.</p

List of the 32 OTUs extracted from our Ion Torrent dataset that were more abundant in TBBPA-spiked than in the control reactors.

<p>List of the 32 OTUs extracted from our Ion Torrent dataset that were more abundant in TBBPA-spiked than in the control reactors.</p

Relative abundance of some of the OTUs having higher abundances in TBBPA-spiked reactors at Day 28 or 55.

<p>Error bars represent the standard deviation from the mean. If a bracket and an asterisk are present between two bars, it indicates that the two corresponding samples are significantly different according to a t-test (p ≤0.05) performed for each day separately.</p

Dynamics of methanogenic, archaeal, and bacterial populations.

<p>Quantification of the <i>mcrA</i> gene, archaeal 16S rDNA, and bacterial 16S rDNA as measured by qPCR. Efficiency and R² calculated from the standard curves were 89.7% and 0.911, 86.7% and 0.982, and 88.3% and 0.998, for the <i>mcrA</i>, archaeal, and bacterial 16S rDNA assays, respectively. Error bars represent the standard deviation from the mean. Different letters above bars indicate significant differences, according to a t-test (p ≤0.05), between days. If a bracket and an asterisk are present between two bars, it indicates that the two corresponding samples are significantly different, according to a t-test (p ≤0.05), performed within each day separately.</p