Proton beam characterization by proton-induced acoustic emission: simulation studies.

Due to their Bragg peak, proton beams are capable of delivering a targeted dose of radiation to a narrow volume, but range uncertainties currently limit their accuracy. One promising beam characterization technique, protoacoustic range verification, measures the acoustic emission generated by the proton beam. We simulated the pressure waves generated by proton radiation passing through water. We observed that the proton-induced acoustic signal consists of two peaks, labeled α and γ, with two originating sources. The α acoustic peak is generated by the pre-Bragg peak heated region whereas the source of the γ acoustic peak is the proton Bragg peak. The arrival time of the α and γ peaks at a transducer reveals the distance from the beam propagation axis and Bragg peak center, respectively. The maximum pressure is not observed directly above the Bragg peak due to interference of the acoustic signals. Range verification based on the arrival times is shown to be more effective than determining the Bragg peak position based on pressure amplitudes. The temporal width of the α and γ peaks are linearly proportional to the beam diameter and Bragg peak width, respectively. The temporal separation between compression and rarefaction peaks is proportional to the spill time width. The pressure wave expected from a spread out Bragg peak dose is characterized. The simulations also show that acoustic monitoring can verify the proton beam dose distribution and range by characterizing the Bragg peak position to within ~1 mm.

Creation and piloting of a new hospital capacity assessment tool in a major urban area.

OBJECTIVES: Crowded hospital emergency departments (EDs) can undermine the ability of a region's safety net to provide safe, timely care. However, data to measure hospital capacity community-wide is generally unavailable. This study aimed to assess hospital crowding, capacity and patient flow in an urban community using the newly developed hospital capacity assessment tool (HCAT). STUDY DESIGN: A survey of the eight acute care hospitals in the District of Columbia (DC) with active EDs. METHODS: Existing emergency care assessment tools were reviewed. Eighteen of the 57 questions on the HCAT were adapted from existing hospital surveys, while the remaining 39 questions were constructed de novo for use in this assessment. Hospitals were provided with paper and electronic versions of the HCAT. RESULTS: All eight DC hospitals completed the HCAT; however, three hospitals were unable to answer many of the questions due to a lack of regular data collection. The HCAT data shows throughput times in DC hospitals that are substantially longer than national averages. CONCLUSIONS: The HCAT is a promising tool for evaluating community-wide emergency care. Findings from the HCAT allowed for the introduction of new ED performance data into the local decision-making process.

Evidence for the "grasshopper" effect and fractionation during long-range atmospheric transport of organic contaminants.

Although there is indisputable evidence that long-range atmospheric transport (LRAT) of organic contaminants occurs on a global scale, uncertainties remain about the detailed mechanism and extent of this phenomenon as well as the physical-chemical properties which facilitate LRAT. In this study, we discuss how mass balance models and monitoring data can contribute to a fuller understanding of the mechanism and extent of LRAT. Specifically we address the issues of "grasshopping" or "hopping" (the extent to which molecules are subject to multiple hops as distinct from a single emission-deposition event) and "global fractionation" (the differing behavior of chemicals as they are transported). It is shown that simple mass balance models can be used to assist the interpretation of monitoring data while also providing an instrument that can be used to assess the LRAT potential and the extent of hopping that organic substances may experience. The available evidence supports the notion that many persistent organic pollutants experience varying degrees of "hopping" during their environmental journey and as a consequence become fractionated with distance from source.

Global distribution and budget of PCBs and HCB in background surface soils: implications for sources and environmental processes.

This paper presents data from a survey of polychlorinated biphenyls (PCBs) and hexachlorobenzene (HCB) concentrations in 191 global background surface (0-5 cm) soils. Differences of up to 4 orders of magnitude were found between sites for PCBs. The lowest and highest PCB concentrations (26 and 97,000 pg/g dw) were found in samples from Greenland and mainland Europe (France, Germany, Poland), respectively. Background soil PCB concentrations were strongly influenced by proximity to source region and soil organic matter (SOM) content Most (>80%) of the estimated soil PCB burden remains in the "global source region" of the Northern Hemisphere (NH) temperate latitudes (30-60 degrees N) or in the OM-rich soils just north of that %SOM correlated with PCB and HCB in the global data set, with the correlation coefficients being greater for HCB and the lighter PCBs than for heavier homologues. OM-rich soils in the NH consistently contained the highest burdens; such soils are a key global compartment for these compounds. Evidence for global fractionation of PCBs was found in the subset of soils from latitudes north of the global source region but was not discerned with the global data set The full data set was used to estimate the burden for individual congeners/homologues in surface background soils and a global soil total PCB burden of 21,000 t. The significance of the inventory is briefly discussed in relation to the latest estimates of global production and atmospheric emission.

Maintaining infusion therapy services in the long-term care setting.

The volume of infusion therapy services provided in the long-term care setting has declined. One major influence has been the changes in reimbursement experienced in this sector of the industry. This article is intended to stimulate the long-term care clinician to reexamine the service offered and to be creative in his or her approach to building infusion services. The article also explores parallels to the home infusion industry, which has evolved through similar changes, with the intent of learning from its experiences.

Bioavailability of persistent organic pollutants in soils and sediments--a perspective on mechanisms, consequences and assessment.

It has been observed that as soil-pollutant contact time increases, pollutant bioavailability and extractability decreases. This phenomenon has been termed 'ageing'. Decreased chemical extractability with increased soil-chemical contact time is evident where both 'harsh' techniques, e.g. dichloromethane Soxhlet extraction, and 'non-exhaustive' techniques, e.g. butanol shake extraction, have been used. It has also been observed that the amount of chemical extracted by these techniques varies considerably over time. Similarly, decreases in bioavailability with increased soil-pollutant contact time have been described in bacterial, earthworm and other organism studies. From these investigations, it has been shown that the fraction of pollutant determined to be bioavailable can vary between organisms. Thus, there is an immediate definition problem, what is bioavailability? Additionally, if bioavailability is to be assessed by a chemical means, which organisms should (or can) be mimicked by the extraction procedure? This review provides a background to the processes inherent to ageing, a discussion of its consequences on bioavailability and ends with some reflections on the appropriateness of chemical extraction techniques to mimic bioavailability

Assessment of organic contaminant fate in waste water treatment plants. I: Selected compounds and physicochemical properties.

An extensive and comprehensive literature review has been conducted for compounds which we hypothesise could be present in sludge and maintain their integrity following application to agricultural land. The following compounds have been selected for review; chlorinated paraffins, quintozene, brominated diphenyl ethers, polychlorinated naphthalenes, polydimethylsiloxanes, chloronitrobenzenes, and a range of biologically active and pharmaceutical compounds. All have received interest as a result of their persistence and/or toxicity in environmental media. Physicochemical property information has also been compiled and/or calculated. In this way, an accompanying paper will attempt to predict compound fate in waste water treatment plants (WWTPs) and assess likely transfers from soil/plants to grazing livestock. These papers describe a first attempt to predict the fate of these classes of compounds in the environment and prioritise those of greatest concern.

Consumer satisfaction: a key to financial success in the managed care environment.

To be successful a company must have the ability to change and be focused on meeting customer needs. The author proposes that health care providers must expand their attention beyond traditional purchasers of services, employers, and insurers and focus on redesigning consumer satisfaction programs and tools to fit the new market environment. Changing from a fee-for-service system to a managed care system means patients are paying an increasing portion of the costs for coverage and care.

Polynuclear aromatic hydrocarbons in the United Kingdom environment: a preliminary source inventory and budget.

This paper presents the first attempt to quantify the production, cycling, storage and loss of PAHs in the UK environment. Over 53 000 tonnes of sigmaPAHs (sum of 12 individual compounds) are estimated to reside in the contemporary UK environment, with soil being the major repository. If soils at contaminated sites are included, this estimate increases dramatically. Emission of PAHs to the UK atmosphere from primary combustion sources are estimated to be greater than 1000 tonnes sigmaPAHs per annum, with over 95% coming from domestic coal combustion, unregulated fires and vehicle emissions. It is estimated that approximately 210 tonnes of sigmaPAH are delivered to terrestrial surfaces each year via atmospheric deposition. Therefore, inputs of PAHs to the UK atmosphere outweigh the outputs by a factor of over 4. This may be explained by enhanced particulate deposition near point sources, PAH degradation in the atmosphere and transport away from the UK with prevailing winds. Disposal of waste residues is estimated to contribute a further 1000 tonnes of sigmaPAH per year to the terrestrial environment. It is illustrated that the use of creosote has the potential to release considerable quantities of PAHs to the UK environment. Temporal trends in PAH cycling are then considered. There is good evidence to suggest that air concentrations and fluxes to the UK surface are now lower than at any time throughout this century. Nonetheless, the UK sigmaPAH burden is still increasing at the present time, principally through retention by soils. However, there are marked differences in the behaviour of individual compounds: there is evidence, for example, that phenanthrene concentrations in soils have declined since the 1960s, although soil concentrations of benzo[a]pyrene and other heavier PAHs have continued to increase through this century. Volatilisation of low molecular weight PAHs accumulated in soils over previous decades may be making an important contribution to the current atmospheric burden. The major uncertainties identified by data on this budget are: (1) the lack of PAH concentrations in some environmental matrices; (2) the possible importance of contaminated soils as a major repository and source of PAHs; (3) the lack of emission data (especially vapour phase releases) for some PAH sources; (4) the importance of biodegradation and volatilisation as loss mechanisms for low molecular weight PAHs in soils; and (5) the importance of creosote use in the PAH cycle.

A source inventory and budget for chlorinated dioxins and furans in the United Kingdom environment.

Polychlorinated dibenzo-p-dioxins (PCDDs) and -furans (PCDFs) are ubiquitous in the environment. This paper estimates the present UK environmental loading of PCDD/Fs in soils, vegetation, air, water and sediments. Greater than 95% of the estimated total PCDD/F loading of 5.7 t in the UK environment is present in surface soils. Annual emissions from known primary sources of PCDDs and PCDFs are estimated. The most important of these include: municipal waste incinerator stack emissions (10.9 kg sigma PCDD/F per annum); industrial (7.7 kg/year) and domestic (5.1 kg/year) combustion of coal; clinical waste incinerators (1.7 kg/year); volatilisation from chlorophenol-treated substrates (1.7 kg/year) and combustion of leaded petrol by motor vehicles (0.7 kg/year). These sources are generally easy to define and reasonably reliable national estimates can be obtained. More difficult to quantify are secondary releases from the large UK stock of pentachlorophenol (PCP) and PCP-treated products, which may represent quantitatively one of the most important sources of total PCDD/Fs to the environment. Estimates of homologue-specific emissions indicate that combustion processes represent a far more significant source of tetra and penta CDD/Fs than do chlorophenols, which in turn constitute a greater source of hepta- and octachlorinated congeners. Direct emission of PCDD/Fs into the atmosphere from combustion processes facilitates their atmospheric transport to remote locations. This, coupled with the diffuse nature of combustion processes, means that the effects of PCDD/F contamination originating from anthropogenic combustion are more widespread than those from the use and disposal of chlorophenols. Contamination from chlorophenols will be more localised, owing to the insignificance of direct atmospheric release pathways for this source. Although there is reasonable agreement between the estimated current annual flux and the present UK environmental loading of PCDDs and PCDFs, a large discrepancy exists between the sum of the annual contributions from primary sources and this annual flux. Whilst the existence of an as yet unidentified source or sources or gross underestimates of known sources cannot be excluded, it is proposed that much of this discrepancy may be accounted for by secondary releases from the use and disposal of chlorophenols and the long-range transport, continued remobilisation and subsequent redeposition of PCDDs and PCDFs already present in the environment. Despite limited evidence for a modest decline in levels of PCDDs and PCDFs in some environmental compartments over the last 20 years, the environmental persistence of these chemicals means that they will remain in the UK environment for the foreseeable future despite recent action to curb primary emissions.

Human exposure to environmental polychlorinated dibenzo-p-dioxins and dibenzofurans: an exposure commitment assessment for 2,3,7,8-TCDD.

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs and PCDFs) are released into the environment from the use of chemicals contaminated with PCDDs/PCDFs, the improper disposal of contaminated production wastes and incineration/other high-temperature processes. Certain congeners are extremely stable compounds which are persistent in the environment once released. An assessment is made of the sources of human exposure to one particular dioxin congener, 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD). Representative values of 2,3,7,8-TCDD concentrations in the background environment and in man are selected from available data or, when not available, inferred from other relevant information. A pathway analysis is performed utilizing the exposure commitment method. Normal dietary intake of 2,3,7,8-TCDD is quite variable depending primarily on consumption of contaminated fish. Representative intake for the average adult of 0.1 ng day-1 may be associated with a human body burden of 100 ng (approximately 7 ng 2,3,7,8-TCDD kg-1 adipose tissue). The inferred biological half-time of this compound in the body is approximately 5 years. The exposure evaluation also accounts for secondary pathways to man of 2,3,7,8-TCDD in air and drinking water. Estimates of transfer factors obtained from the representative background levels should be generally relevant and may be applied to more specific cases of exposure.

Exposure of man to environmental aluminium--an exposure commitment assessment.

Aluminium is one of the most abundant elements in the environment and is released from both natural and anthropogenic sources. Representative values of aluminium concentrations in the background environment and in man are selected from available data and a pathway analysis is performed utilising the exposure commitment method. Using a derived estimate of the body burden (60 mg), a representative value for dietary intake (20 mg day-1) and fractional absorption of 0.01, a mean retention time of A1 in the body of 300 days is obtained. This corresponds to a biological half-time of 210 days. The assessment indicates that an average dietary intake rate of 20 mg day-1 contributes 660 micrograms kg-1 of aluminium to the body, while inhalation of aluminium in air makes, in comparison, a negligible contribution to the body content.