Comparative cytotoxicity of fourteen trivalent and pentavalent arsenic species determined using real-time cell sensing

The occurrence of a large number of diverse arsenic species in the environment and in biological systems makes it important to compare their relative toxicity. The toxicity of arsenic species has been examined in various cell lines using different assays, making comparison difficult. We report real-time cell sensing of two human cell lines to examine the cytotoxicity of fourteen arsenic species: arsenite(As~Ⅲ), monomethylarsonous acid(MMA~Ⅲ) originating from the oxide and iodide forms, dimethylarsinous acid(DMA~Ⅲ), dimethylarsinic glutathione(DMAG~Ⅲ), phenylarsine oxide(PAO~Ⅲ), arsenate(AsV), monomethylarsonic acid(MMA~Ⅴ), dimethylarsinic acid(DMA~Ⅴ),monomethyltrithioarsonate(MMTTA~Ⅴ), dimethylmonothioarsinate(DMMTA~Ⅴ),dimethyldithioarsinate(DMDTA~Ⅴ), 3-nitro-4-hydroxyphenylarsonic acid(Roxarsone, Rox),and 4-aminobenzenearsenic acid(p-arsanilic acid, p-ASA). Cellular responses were measured in real time for 72 hr in human lung(A549) and bladder(T24) cells. IC50 values for the arsenicals were determined continuously over the exposure time, giving rise to IC50 histograms and unique cell response profiles. Arsenic accumulation and speciation were analyzed using inductively coupled plasma-mass spectrometry(ICP-MS). On the basis of the 24-hr IC50 values, the relative cytotoxicity of the tested arsenicals was in the following decreasing order: PAO~Ⅲ? MMA~Ⅲ≥ DMA~Ⅲ≥ DMAG~Ⅲ≈ DMMTA~Ⅴ≥ As~Ⅲ? MMTTA~Ⅴ AsV DMDTA~ⅤDMA~Ⅴ MMA~Ⅴ≥ Rox ≥ p-ASA. Stepwise shapes of cell response profiles for DMA~Ⅲ, DMAG~Ⅲ,and DMMTA~Ⅴcoincided with the conversion of these arsenicals to the less toxic pentavalent DMA~Ⅴ. Dynamic monitoring of real-time cellular responses to fourteen arsenicals provided useful information for comparison of their relative cytotoxicity.     

The derivation of job designs

This paper presents a theoretical account of the derivation of job designs incorporating consideration of technology, structure and managerial control, viewed from an information processing perspective. A conceptual distinction is made between tasks and roles which has practical relevance in that organizations have independent choices regarding their design. These choices are underpinned by economic and psychological values as well as by managerial needs for control. The paper argues that whilst options exist, organizations typically choose to simplify jobs, a strategy which may well be ineffective, especially under conditions of uncertainty. New, more complex job designs may be very difficult to implement for economic, psychological, managerial and political reasons. Research and development should now be directed towards a more detailed cognitive and social psychological understanding of the derivation and impact of job designs as well as towards study of the introduction and impact of new technology. These represent qualitative shifts in research emphasis.     

THE OPTIMALITY OF CAPACITY SHARING IN STOCHASTIC DYNAMIC PROGRAMMING PROBLEMS OF SHARED RESERVOIR OPERATION1

ABSTRACT: This paper is concerned with finding an optimal allocation of water entitlements for each of two users of water who share a reservoir. Two instruments of allocation are considered. The first, release sharing, involves sharing the releases from the reservoir; the second, capacity sharing, is concerned with allocating to each user of water a share of inflows, reservoir capacity and leakage and evaporation losses. Stochastic dynamic programming problems of reservoir operation under each type of sharing arrangement are formulated. It is shown that the maximum discounted expected profit from reservoir operation over the life of the storage using capacity sharing is at least as large as that obtained using release sharing and that release sharing is not Pareto efficient.     

Remediation of the Radioactive Waste Landfill and Chemical Disposal Pits Sites at Sandia National Laboratories

Sandia National Laboratories' Environmental Restoration (ER) Project remediated the Radioactive Waste Landfill and Chemical Disposal Pits (RWL/CDPs) sites located in Albuquerque, New Mexico. The remediation was conducted in 1996 using conventional excavation, as well as hybrid remote robotic manipulation technology at a cost of approximately $3 million. Wastes generated included approximately 73 cubic meters (m³) of debris (including thermal batteries, spark gap tubes, radioactive sources, weapons components, and some classified material), 535 m³ of plutonium-contaminated soil, and 2,294 m³ of soil contaminated with thorium, cesium, uranium, and tritium. The remediation was successful since the project goal of risk reduction was accomplished and no injuries or negative occurrences resulted. This cleanup is one example of the Department of Energy's (DOE's) accelerated approach to environmental restoration. The remediation was performed as a voluntary corrective measure to reduce schedule and budget, compared with the traditional approach following Resource Conservation and Recovery Act (RCRA) regulations.     

Spatial and temporal trends in surface water and sediment contamination in the Laurentian Great Lakes

Data from recent sediment and surface water surveys have been collated and mapped to illustrate the spatial distribution of contaminants across the entire Great Lakes basin. Information from historical surveys, together with data from surface water monitoring programs in three major connecting channels, has also been collated in order to evaluate temporal trends. In general, Lakes Superior and Michigan exhibited the lowest levels of sediment contamination while Lake Ontario had the highest. Contaminants such as gamma-HCH (lindane) and dieldrin were ubiquitous in surface waters across the entire basin, which was indicative of atmospheric sources. The distribution of other compounds including hexachlorobenzene, octachlorostyrene and mirex indicated the presence of local sources within the watersheds of the connecting channels. Surficial sediment contamination was found to have decreased markedly since the late 1960s and 1970s. Similarly, surface water contamination decreased over the period 1986-1997 with concentrations of dieldrin, hexachlorobenzene, octachlorostyrene and mirex reduced by over 50%. However, the spatial distributions of both sediment and surface water contamination indicate that further effort is warranted in reducing local sources of contaminants, particularly in Lake Ontario.