Amy A. Ekechukwu

Gamma radiation interacts with melanin to alter its oxidation-reduction potential and results in electric current production.

The presence of melanin pigments in organisms is implicated in radioprotection and in some cases, enhanced growth in the presence of high levels of ionizing radiation. An understanding of this phenomenon will be useful in the design of radioprotective materials. However, the protective mechanism of microbial melanin in ionizing radiation fields has not yet been elucidated. Here we demonstrate through the electrochemical techniques of chronoamperometry, chronopotentiometry and cyclic voltammetry that microbial melanin is continuously oxidized in the presence of gamma radiation. Our findings establish that ionizing radiation interacts with melanin to alter its oxidation-reduction potential. Sustained oxidation resulted in electric current production and was most pronounced in the presence of a reductant, which extended the redox cycling capacity of melanin. This work is the first to establish that gamma radiation alters the oxidation-reduction behavior of melanin, resulting in electric current production. The significance of the work is that it provides the first step in understanding the initial interactions between melanin and ionizing radiation taking place and offers some insight for production of biomimetic radioprotective materials.

The role of 4‐hydroxyphenylpyruvate dioxygenase in enhancement of solid‐phase electron transfer by Shewanella oneidensis MR‐1

We hypothesized that Shewanella oneidensis MR-1, a model dissimilatory metal-reducing bacterium, could utilize environmentally relevant concentrations of tyrosine to produce pyomelanin for enhanced Fe(III) oxide reduction. Because homogentisate is an intermediate of the tyrosine degradation pathway, and a precursor of a redox-cycling metabolite, pyomelanin, we evaluated the process of homogentisate production by S. oneidensis MR-1, in order to identify the key steps involved in pyomelanin production. We determined that two enzymes involved in this pathway, 4-hydroxyphenylpyruvate dioxygenase and homogentisate 1,2-dioxygenase are responsible for homogentisate production and oxidation, respectively. We used genetic analysis and physiological characterization of MR-1 strains either deficient in or displaying substantially increased pyomelanin production. The relative significance imparted by pyomelanin on solid-phase electron transfer was also addressed using electrochemical techniques, which allowed us to extend the genetic and physiological findings to biogeochemical cycling of metals. Based on our findings, environmental production of pyomelanin from available organic precursors could contribute to the survival of S. oneidensis MR-1 when dissolved oxygen concentrations become low, by providing an increased capacity for solid-phase metal reduction. This study demonstrates the role of organic precursors and their concentrations in pyomelanin production, solid phase metal reduction and biogeochemical cycling of iron.

Beryllium environmental analysis and monitoring

Beryllium environmental analysis and monitoring , Beryllium environmental analysis and monitoring , کتابخانه دیجیتال جندی شاپور اهواز

Opportunities for Standardization of Beryllium Sampling and Analysis

Since the U. S. Department of Energy (DOE) published the DOE Beryllium Rule (10 CFR 850) in 1999, DOE sites have been required to measure beryllium in air filter and surface wipe samples for purposes of worker protection and for release of materials from beryllium-controlled areas. Measurements in the nanogram range on a filter or wipe are typically required. Industrial hygiene laboratories have applied methods from various analytical compendia, and a number of issues have emerged concerning sampling and analysis practices. As a result, a committee of analytical chemists, industrial hygienists, and laboratory managers was formed in November 2003 to address the issues. The committee developed a baseline questionnaire and distributed it to DOE sites and other agencies in the U.S., Canada, and the U.K. The results of the questionnaire are presented in this paper. These results confirmed that a wide variety of practices was in use in the areas of sampling, sample preparation, and analysis. Additionally, although these laboratories are generally accredited by the American Industrial Hygiene Association (AIHA), there are inconsistencies in execution among accredited laboratories. As a result, there are significant opportunities for development of standard methods that could improve consistency. The current availabilities and needs for standard methods are further discussed in a companion paper.

Properties and Function of Pyomelanin

Melanin pigments are the most common pigments produced in nature and these complex biopolymers are found in species of all biological kingdoms. There are several categories of melanins which include eumelanins, pheomelanins and allomelanins. Eumelanins and pheomelanins are produced from oxidation of tyrosine or phenylalanine to odihydroxyphenylalanine (DOPA) and dopaquinone. Pheomelanin results from cysteinylation of DOPA. Allomelanins include a heterogeneous group of polymers that include pyomelanin. Melanin biochemistry and synthesis has been reviewed previously (Plonka and Grabacka 2006). This chapter will focus on the properties and function of pyomelanin and their potential utility in biotechnology. Pyomelanin originates from the catabolism of tyrosine or phenylalanine (Lehninger, 1975) (Fig. 1). Complete breakdown of tyrosine to acetoacetate and fumarate requires the enzymes 4-hydroxyphenylpyruvic acid dioxygenase (4-HPPD) and homogentisic acid oxidase (HGA-oxidase). In the absence of HGA-oxidase, or if homogentisic acid (HGA) production exceeds that of HGA-oxidase activity, HGA is over-produced and excreted from the cell (Yabuuchi and Ohyama 1972; Ruzafa et al. 1994; Katob et al. 1995). Autooxidation and selfpolymerization of HGA then results in pyomelanin. In addition, deletion of the gene that encodes for HGA-oxidase results in hyper production of pyomelanin while deletion of the gene that encodes for 4HPPD results in the inability to produce pyomelanin (Coon et al. 1994; Ruzafa et al. 1995). In humans with loss-of-function mutations in HGA-oxidase, pyomelanin (also known as alkapton or ochronotic pigment) forms in the urine due to the spontaneous auto oxidation of excess HGA (Beltran-Valero de Bernabe, et al. 1999). This condition is known as alkaptonuria in humans and can result in arthritis in adults. Pyomelanin production in microorganisms often is associated with numerous survival advantages and was first characterized in bacteria among numerous species of the genus Pseudomonas (Yabuuchi & Ohyama 1972). Since then several fungi and a number of bacteria, especially in the ┛ Proteobacteria have been shown to produce pyomelanin.

Validation of Analytical Methods and Instrumentation for Beryllium Measurement: Review and Summary of Available Guides, Procedures, and Protocols

This document provides a listing of available sources that can be used to validate analytical methods and/or instrumentation for beryllium determination. A literature review was conducted of available standard methods and publications used for method validation and/or quality control. An annotated listing of the articles, papers, and books reviewed is given in the Appendix. Available validation documents and guides are listed therein; each has a brief description of application and use. In the referenced sources, there are varying approaches to validation and varying descriptions of the validation process at different stages in method development. This discussion focuses on validation and verification of fully developed methods and instrumentation that have been offered for use or approval by other laboratories or official consensus bodies such as ASTM International, the International Standards Organization, the International Electrotechnical Commission, and the Association of Official Analytical Chemists. This review was conducted as part of a collaborative effort to investigate and improve the state of validation for measuring beryllium in the workplace and the environment. Documents and publications from the United States and Europe are included.

Proceedings of the Third International Symposium on Beryllium Particulates and Their Detection November 17–19, 2008, Albuquerque, New Mexico

T he Third International Symposium on Beryllium Particulates and Their Detection was held November 17– 19, 2008, at the University of New Mexico in Albuquerque. This conference, which drew 80 registrants, was arranged by the Beryllium Health and Safety Committee (BHSC) under the chairmanship of Amy Ekechukwu of Savannah River National Laboratory (SRNL), and Melecita Archuleta of Sandia National Laboratory (SNL). The symposium, which is held triennially, followed two previous symposia that were held in Santa Fe, New Mexico, in 2002, and in Salt Lake City, Utah, in 2005. The organizing committee comprised symposium co-chairs and seven other members of the BHSC. The symposium was sponsored by numerous organizations having interest in beryllium health risks and related issues. A list of the sponsors and exhibitors, whose support was invaluable and is very much appreciated, follows. Health risk due to beryllium exposure is an important matter of concern in the United States and is an emergent issue globally. The symposium served as a technical forum for scientists, medical researchers, industrial hygienists, and other public health professionals to share current information about detecting beryllium particles and the health risks posed by exposure to beryllium. A call for papers was disseminated internationally, and ultimately, more than two dozen abstracts were received. The format of the symposium included oral technical presentations, vendor displays, and a tutorial on surface sampling. On the first day of the symposium, a beryllium surface sampling tutorial was presented by Geoff Braybrooke (U.S. Army Center for Health Promotion and Preventive Medicine [USACHPPM]), Steve Jahn (Savannah River Site), and Kevin Ashley (National Institute for Occupational Safety and Health). On the second day, a plenary session initiated the main portion of the symposium with an overview of beryllium research. An invited address by Paul Wambach (U.S. Department of Energy [DOE]) provided a history of beryllium exposure assessment. This was followed by a presentation on beryllium sampling issues and industrial hygiene aspects by Steve Jahn. Mike Brisson (Savannah River Nuclear Solutions) then gave an overview of beryllium analytical chemistry. Peggy Mroz (National Jewish Health) concluded the session with an overview of medical and epidemiologic issues. The first technical session dealt with medical and epidemiologic aspects; it included seven papers and was chaired by Peggy Mroz. Anthony James (Washington State University) presented a paper on beryllium in a repository of tissues from DOE weapons-site workers. Caroline Muller (University of Montréal) gave a talk on beryllium toxicity in relation to chemical form and particle size. Mike McCawley (West Virginia University) followed with a discourse on particle sizeselective sampling for beryllium. Akshay Sood (University of New Mexico) discussed his work on corticosteroid therapy in patients with chronic beryllium disease (CBD). Anu Chaudhary (Los Alamos National Laboratory [LANL]) spoke on the intracellular toxic effects of beryllium. Mike Van Dyke (National Jewish Health) presented on genetic effects in beryllium disease risk. The final paper in this session was given by Elizabeth Hong-Geller (LANL), whose talk covered response of airway epithelial cells to beryllium exposure. The third day of the symposium focused mainly on analytical issues. A session on sampling and sample preparation was chaired by Kevin Ashley and included nine presentations. In succession, Mike Brisson, Melecita Archuleta, and Warren Hendricks (Occupational Safety and Health Administration) discussed consideration of wall deposits inside workplace air samplers. Kevin Ashley followed with a presentation on interlaboratory data from inductively coupled plasma mass spectrometry (ICP-MS) measurement of beryllium. Cheryl Morton (AIHA ©R ) and Brian Connor (American Association for Laboratory Accreditation) then discussed