United States Environmental Protection Agency

About: United States Environmental Protection Agency is a government organization based out in Washington D.C., District of Columbia, United States. It is known for research contribution in the topics: Population & Environmental exposure. The organization has 13873 authors who have published 26902 publications receiving 1191729 citations. The organization is also known as: EPA & Environmental Protection Agency.

Natural inorganic nanoparticles--formation, fate, and toxicity in the environment.

Abstract: The synthesis, stability, and toxicity of engineered metal nanoparticles (ENPs) have been extensively studied during the past two decades. In contrast, research on the formation, fate, and ecological effects of naturally-occurring nanoparticles (NNPs) has become a focus of attention only recently. The natural existence of metal nanoparticles and their oxides/sulfides in waters, wastewaters, ore deposits, mining regions, and hydrothermal vents, as exemplified by the formation of nanoparticles containing silver and gold (AgNPs and AuNPs), Fe, Mn, pyrite (FeS2), Ag2S, CuS, CdS, and ZnS, is dictated largely by environmental conditions (temperature, pH, oxic/anoxic, light, and concentration and characteristics of natural organic matter (NOM)). Examples include the formation of nanoparticles containing pyrite, Cu and Zn-containing pyrite, and iron in hydrothermal vent black smoker emissions. Metal sulfide nanoparticles can be formed directly from their precursor ions or indirectly by sulfide ion-assisted transformation of the corresponding metal oxides under anaerobic conditions. This tutorial focuses on the formation mechanisms, fate, and toxicity of natural metal nanoparticles. Natural waters containing Ag(I) and Au(III) ions in the presence of NOM generate AgNPs and AuNPs under thermal, non-thermal, and photochemical conditions. These processes are significantly accelerated by existing redox species of iron (Fe(II)/Fe(III)). NOM, metal–NOM complexes, and reactive oxygen species (ROS) such as O2˙−, ˙OH, and H2O2 are largely responsible for the natural occurrence of nanoparticles. AgNPs and AuNPs emanating from Ag(I)/Au(III)–NOM reactions are stable for several months, thus indicating their potential to be transported over long distances from their point of origin. However, endogenous cations present in natural waters can destabilize the nanoparticles, with divalent cations (e.g., Ca2+, Mg2+) being more influential than their monovalent equivalents (e.g., Na+, K+). The toxicity of NNPs may differ from that of ENPs because of differences in the coatings on the nanoparticle surfaces. An example of this phenomenon is presented and is briefly discussed.

Community structures of fecal bacteria in cattle from different animal feeding operations.

Abstract: The fecal microbiome of cattle plays a critical role not only in animal health and productivity but also in food safety, pathogen shedding, and the performance of fecal pollution detection methods. Unfortunately, most published molecular surveys fail to provide adequate detail about variability in the community structures of fecal bacteria within and across cattle populations. Using massively parallel pyrosequencing of a hypervariable region of the rRNA coding region, we profiled the fecal microbial communities of cattle from six different feeding operations where cattle were subjected to consistent management practices for a minimum of 90 days. We obtained a total of 633,877 high-quality sequences from the fecal samples of 30 adult beef cattle (5 individuals per operation). Sequence-based clustering and taxonomic analyses indicate less variability within a population than between populations. Overall, bacterial community composition correlated significantly with fecal starch concentrations, largely reflected in changes in the Bacteroidetes, Proteobacteria, and Firmicutes populations. In addition, network analysis demonstrated that annotated sequences clustered by management practice and fecal starch concentration, suggesting that the structures of bovine fecal bacterial communities can be dramatically different in different animal feeding operations, even at the phylum and family taxonomic levels, and that the feeding operation is a more important determinant of the cattle microbiome than is the geographic location of the feedlot.

Synthesis, characterization and biocompatibility of “green” synthesized silver nanoparticles using tea polyphenols

Abstract: Since ancient times, people have taken advantage of the antimicrobial effects of colloidal silver particles. Aside from the medical prospects, silver nanoparticles are found in a wide range of commercially available consumer products ranging from cosmetics to household cleansers. Current synthetic methods for creating silver nanoparticles typically call for potentially hazardous chemicals, extreme heat, and produce environmentally dangerous byproducts. Therefore, it is essential that novel “green” synthesis of nanoparticles becomes a reality, and it is imperative to fully analyze the potential toxic effects of these nanoparticles. In this study, we have shown that by reducing silver nitrate in solutions of tea extract or epicatechin of varying concentrations, spherical silver nanoparticles were formed that had controllable size distributions depending on the concentration of tea extract or epicatechin in the samples. Our ultra-resolution microscopy demonstrated that the nanoparticles were in fact interacting with the keratinocytes. Furthermore, evaluation of mitochondrial function (MTS) to assess cell viability and membrane integrity (LDH) in human keratinocytes showed that the silver nanoparticles were nontoxic. These results demonstrated that these nanoparicles are potentially biocompatible and warrant further evaluation in other biological systems.

Air Pollution and Mortality in Elderly People: A Time-Series Study in Sao Paulo, Brazil

Abstract: The relationship between daily mortality of elderly (65+ y) persons and air pollution in the metropolitan area of Sao Paulo, Brazil, for the period May 1990 to April 1991 was evaluated by time series regression, controlling for season, weather, and other factors. Mortality was associated with respirable particles (PM10), nitrogen oxides (NOx), sulfur dioxide (SO2), and carbon monoxide (CO). The association with PM10 was most statistically significant, robust, and independent of other air pollutants. An increase in PM10 equal to 100 micrograms/m3 was associated with an increase in overall mortality equal to approximately 13%. This association was consistent across various model specifications and estimation techniques. The dose-response relationship between mortality and respirable particulate pollution was almost linear, with no evidence of a "safe" threshold level. The results were similar to those observed in London and several U.S. cities. The results were also supportive of recent animal studies that have observed adverse health outcomes in experimental animals exposed to air pollution in Sao Paulo.