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.

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.

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.

Trace-level beryllium analysis in the laboratory and in the field: state of the art, challenges and opportunities.

Control of workplace exposure to beryllium is a growing issue in the United States and other nations. As the health risks associated with low-level exposure to beryllium are better understood, the need increases for improved analytical techniques both in the laboratory and in the field. These techniques also require a greater degree of standardization to permit reliable comparison of data obtained from different locations and at different times. Analysis of low-level beryllium samples, in the form of air filters or surface wipes, is frequently required for workplace monitoring or to provide data to support decision-making on implementation of exposure controls. In the United States and the United Kingdom, the current permissible exposure level is 2 microg m(-3) (air) and the United States Department of Energy has implemented an action level of 0.2 microg m(-3) (air) and 0.2 microg/100 cm(2) (surface). These low-level samples present a number of analytical challenges, including (1) a lack of suitable standard reference materials, (2) unknown robustness of sample preparation techniques, (3) interferences during analysis, (4) sensitivity (sufficiently low detection limits), (5) specificity (beryllium speciation) and (6) data comparability among laboratories. Additionally, there is a need for portable, real-time (or near real-time) equipment for beryllium air monitoring and surface wipe analysis that is both laboratory-validated and field-validated in a manner that would be accepted by national and/or international standards organizations. This paper provides a review of the current analytical requirements for trace-level beryllium analysis for worker protection and also addresses issues that may change those requirements. The current analytical state of the art and relevant challenges facing the analytical community will be presented, followed by suggested criteria for real-time monitoring equipment. Recognizing and addressing these challenges will present opportunities for laboratories, research and development organizations, instrument manufacturers and others.