Influence of Particle Coating and Matrix Constituents on the Cloud Point Extraction Efficiency of Silver Nanoparticles (Ag-NPs) and Application for Monitoring the Formation of Ag-NPs from Ag⁺

For the quantification of silver nanoparticles (Ag-NPs) in environmental samples using cloud point extraction (CPE) for selective enrichment, surface modification of the Ag-NPs and matrix effects can play a key role. In this work we validate CPE with respect to the influence of different coatings and naturally occurring matrix components. The Ag-NPs tested were functionalized with inorganic and organic compounds as well as with biomolecules. Commercially available NPs and NPs synthesized according to methods published in the literature were used. We found that CPE can extract almost all Ag-NPs tested with very good efficiencies (82–105%). Only Ag-NPs functionalized with BSA (bovine serum albumin), which is a protein with the function to keep colloids in solution, cannot be extracted. No or little effect of environmentally relevant salts, organic matter, and inorganic colloids on the CPE of AgNPs was found. Additionally we used CPE to observe the <i>in situ</i> formation of Ag-NPs produced by the reduction of Ag⁺ with natural organic matter (NOM)

Quantification of Nanoscale Silver Particles Removal and Release from Municipal Wastewater Treatment Plants in Germany

The majority of pure silver nanoparticles in consumer products are likely released into sewer systems and usually end up in wastewater treatment plants (WWTPs). Research investigating the reduction in nanoscale silver particles (n-Ag-Ps) has focused on the biological treatment process, generally in controlled laboratory experiments. This study, analyzing the field-collected samples from nine municipal WWTPs in Germany, is the first to evaluate the reduction in n-Ag-Ps by mechanical and biological treatments in sequence in WWTPs. Additionally, the concentration of n-Ag-Ps in effluent was determined through two different methods that are presented here: novel ionic exchange resin (IER) and cloud point extraction (CPE) methods. The n-Ag-Ps concentrations in influent were all low (<1.5 μg/L) and decreased (average removal efficiency of ∼35%) significantly after mechanical treatment, indicating that the mechanical treatment contributes to the n-Ag-Ps removal. Afterward, more than 72% of the remaining n-Ag-Ps in the semi-treated wastewater (i.e., wastewater after mechanical treatment) were reduced by biological treatment. Together, these processes reduced 95% of the n-Ag-Ps that entered WWTPs, which resulted in low concentration of n-Ag-Ps in the effluents (<12 ng/L). For a WWTP with 520000 t/d treatment capacity, we estimated that the daily n-Ag-Ps load in effluent discharge equated to about 4.4 g/d. Obviously, WWTPs are not potential point sources for n-Ag-Ps in the aquatic environment

To What Extent Can Full-Scale Wastewater Treatment Plant Effluent Influence the Occurrence of Silver-Based Nanoparticles in Surface Waters?

Silver-based nanoparticles (Ag-<i>b</i>-NPs) emitted by wastewater treatment plants (WWTPs) are considered to be widely present in the natural environment. However, there is much that is unknown about the effect of WWTP effluent on the occurrence of Ag-<i>b</i>-NPs in surface waters. On the basis of field analysis of representative WWTPs in Germany, we demonstrate that more than 96.4% of Ag-<i>b</i>-NPs from wastewater influent are removed through WWTPs, even though influent contains Ag-<i>b</i>-NP concentrations of tens to hundreds ng L^–1, resulting in effluent Ag-<i>b</i>-NP concentrations of 0.7–11.1 ng L^–1 over the seasons. The estimated flux of Ag-<i>b</i>-NPs associated with WWTPs effluent discharge is ∼33 kg y^–1 in Germany. WWTPs effluent increases Ag-<i>b</i>-NP levels of the River Isar to 2.0–8.6 ng L^–1, while remarkable decreases are observed at sites ∼1.5 km downstream of each discharge point, and Ag-<i>b</i>-NP levels then keep stable (0.9–2.3 ng L^–1) until the next discharge point, showing subtle differences in Ag-<i>b</i>-NP levels between the river and reference lakes without industrial sources and WWTPs effluent discharge. Our results demonstrate that WWTPs effluent can exert a clear influence on the occurrence of Ag-<i>b</i>-NPs in surface waters

Gliotoxin Biosynthesis: Structure, Mechanism, and Metal Promiscuity of Carboxypeptidase GliJ

The formation of glutathione (GSH) conjugates, best known from the detoxification of xenobiotics, is a widespread strategy to incorporate sulfur into biomolecules. The biosynthesis of gliotoxin, a virulence factor of the human pathogenic fungus <i>Aspergillus fumigatus</i>, involves attachment of two GSH molecules and their sequential decomposition to yield two reactive thiol groups. The degradation of the GSH moieties requires the activity of the Cys–Gly carboxypeptidase GliJ, for which we describe the X-ray structure here. The enzyme forms a homodimer with each monomer comprising one active site. Two metal ions are present per proteolytic center, thus assigning GliJ to the diverse family of dinuclear metallohydrolases. Depending on availability, Zn²⁺, Fe²⁺, Fe³⁺, Mn²⁺, Cu²⁺, Co²⁺, or Ni²⁺ ions are accepted as cofactors. Despite this high metal promiscuity, a preference for zinc versus iron and manganese was noted. Mutagenesis experiments revealed details of metal coordination, and molecular modeling delivered insights into substrate recognition and processing by GliJ. The latter results suggest a reaction mechanism in which the two scissile peptide bonds of one gliotoxin precursor molecule are hydrolyzed sequentially and in a given order