A method for screening groundwater vulnerability from subsurface hydrocarbon extraction practices.

This paper describes a new screening method for assessing groundwater vulnerability to pollution from hydrocarbon exploitation in the subsurface. The method can be used for various hydrocarbon energy sources, including conventional oil and gas, shale gas and oil, coal bed methane and underground coal gasification. Intrinsic vulnerability of potential receptors is assessed at any particular location by identifying possible geological pathways for contaminant transport. This is followed by an assessment of specific vulnerability which takes into account the nature of the subsurface hydrocarbon activity and driving heads. A confidence rating is attached to each parameter in the assessment to provide an indication of the confidence in the screening. Risk categories and associated confidence ratings are designed to aid in environmental decision making, regulation and management, highlighting where additional information is required. The method is demonstrated for conventional gas and proposed shale gas operations in northern England but can be adapted for use in any geological or hydrogeological setting and for other subsurface activities.

Urban groundwater quality in sub-Saharan Africa: current status and implications for water security and public health.

Groundwater resources are important sources of drinking water in Africa, and they are hugely important in sustaining urban livelihoods and supporting a diverse range of commercial and agricultural activities. Groundwater has an important role in improving health in sub-Saharan Africa (SSA). An estimated 250 million people (40% of the total) live in urban centres across SSA. SSA has experienced a rapid expansion in urban populations since the 1950s, with increased population densities as well as expanding geographical coverage. Estimates suggest that the urban population in SSA will double between 2000 and 2030. The quality status of shallow urban groundwater resources is often very poor due to inadequate waste management and source protection, and poses a significant health risk to users, while deeper borehole sources often provide an important source of good quality drinking water. Given the growth in future demand from this finite resource, as well as potential changes in future climate in this region, a detailed understanding of both water quantity and quality is required to use this resource sustainably. This paper provides a comprehensive assessment of the water quality status, both microbial and chemical, of urban groundwater in SSA across a range of hydrogeological terrains and different groundwater point types. Lower storage basement terrains, which underlie a significant proportion of urban centres in SSA, are particularly vulnerable to contamination. The relationship between mean nitrate concentration and intrinsic aquifer pollution risk is assessed for urban centres across SSA. Current knowledge gaps are identified and future research needs highlighted.

Les ressources en eaux souterraines sont des sources importantes d'eau potable en Afrique, et elles sont d'une énorme importance pour les êtres vivants en milieu urbain et pour le soutien d'une gamme diversifiée d'activités commerciales et agricoles. Les eaux souterraines jouent un rôle important en améliorant la santé en Afrique sub-saharienne (ASS). 250 millions de personnes environ (40% du total) vivent dans des centres urbains à travers l'ASS. L'ASS a connu une expansion rapide de ses populations urbaines depuis les années 1950, avec une augmentation à la fois des densités de population et de leur extension géographique. Les estimations prévoient un doublement de la population urbaine de l'ASS entre 2000 et 2030. L'état qualitatif des ressources en eau souterraine urbaines peu profondes est souvent très pauvre du fait de l'insuffisance de la gestion des déchets et de la protection de la ressource, et pose un risque sanitaire significatif pour les utilisateurs, alors que des ressources plus profondes captées par forage fournissent souvent une source importante d'eau potable de bonne qualité. Etant donné la croissance de la demande future de cette ressource limitée, ainsi que le changement climatique potentiel dans cette région dans le futur, une compréhension détaillée de la quantité et la qualité de cette ressource est exigée pour son utilisation durable. Cet article fournit une évaluation complète de l'état qualitatif, à la fois microbien et chimique, des eaux souterraines urbaines en ASS à travers une gamme de contextes hydrogéologiques et de différents types de point d'eaux souterraines. Les terrains du sous-sol de faible emmagasinement, qui sont situés sous une proportion significative de centres urbains en ASS, sont particulièrement vulnérables à la contamination. Le rapport entre la concentration moyenne en nitrate et le risque intrinsèque de pollution des aquifères est évalué pour les centres urbains de l'ASS. Des lacunes actuelles en matière de connaissances sont identifiées et les besoins de recherches futurs sont mis en évidence.

Los recursos hídricos subterráneos son una fuente importante de agua potable en África y son sumamente importantes para mantener los medios de subsistencia urbanos y para apoyar una amplia gama de actividades comerciales y agrícolas. El agua subterránea tiene un papel importante en la mejora de la salud en el África Subsahariana (SSA). Se calcula que 250 millones de personas (40% del total) viven en centros urbanos en el África Subsahariana. El SSA ha experimentado una rápida expansión en las poblaciones urbanas desde la década de 1950, con el aumento de la densidad de población, así como la ampliación de la cobertura geográfica. Las estimaciones sugieren que la población urbana en África Subsahariana se duplicará entre 2000 y 2030. El estado de calidad del agua subterránea somera es a menudo muy pobre debido a la gestión inadecuada de los desechos y de la protección de las fuentes, representando un riesgo significativo para los usuarios, mientras que los pozos más profundos proporcionan una fuente importante de agua potable de buena calidad. Dado el crecimiento de la demanda futura de este recurso finito, así como los cambios potenciales en el clima futuro en esta región, una comprensión detallada de su cantidad y calidad es necesaria para utilizar este recurso de manera sostenible. Este artículo ofrece una evaluación integral del estado de la calidad del agua, tanto microbiana como química, del agua subterránea urbana en el SSA a lo largo de una serie de terrenos hidrogeológicos y diferentes tipos de puntos de agua subterránea. Los basamentos de bajo almacenamiento, que subyacen a una proporción significativa de los centros urbanos del África Subsahariana, son particularmente vulnerables a la contaminación. Se evalúa la relación entre la concentración media de nitratos y el riesgo intrínseco de contaminación acuífera para los centros urbanos a través de la SSA. Se identifican las deficiencias actuales de conocimientos y se destacan las necesidades de futuras investigaciones.

As águas subterrâneas são fontes importantes de água para consumo na África, e são amplamente importantes para sustentar o modo de vida urbano e dar suporte a uma amplitude diversa de atividades comerciais e agrícolas. As águas subterrâneas têm um papel importante no desenvolvimento da saúde na África subsaariana (ASS). São estimadas 250 milhões de pessoas (40% do total) vivendo nos centros urbanos na ASS. ASS tem vivenciado uma rápida expansão na população urbana desde os anos 50, com aumento das densidades populacionais assim como expansão da cobertura geográfica. As estimativas sugerem que a população urbana na ASS dobrará entre 2000 e 2030. As condições de qualidade dos aquíferos livres em áreas urbanas estão frequentemente muito pobres por causa do gerenciamento de perdas e proteção das fontes inadequados, e apresenta um risco significativo à saúde dos usuários, enquanto poços mais profundos frequentemente fornecem fontes importantes de água potável de boa qualidade. Dado o crescimento na demanda futura desse recurso finito, assim como mudanças potenciais no clima futuro da região, um entendimento detalhado da sua quantidade e qualidade é necessário para o uso sustentável deste recurso. Esse estudo fornece uma avaliação compreensiva das condições de qualidade da água, tanto microbiológica quanto química, das águas subterrâneas urbanas na ASS por uma gama de terrenos hidrogeológicos e diferentes tipos pontuais de águas subterrâneas. Terrenos de menor armazenamento de base, que fundamentam uma porção significante dos centros urbanos da ASS, são particularmente vulneráveis a contaminação. A relação entre a concentração média de nitrato e o risco intrínseco de poluição do aquífero é avaliado para os centros urbanos na ASS. Lacunas do conhecimento atual foram identificadas e destaca-se a necessidade de pesquisas futuras.

The nitrate time bomb: a numerical way to investigate nitrate storage and lag time in the unsaturated zone.

Nitrate pollution in groundwater, which is mainly from agricultural activities, remains an international problem. It threatens the environment, economics and human health. There is a rising trend in nitrate concentrations in many UK groundwater bodies. Research has shown it can take decades for leached nitrate from the soil to discharge into groundwater and surface water due to the 'store' of nitrate and its potentially long travel time in the unsaturated and saturated zones. However, this time lag is rarely considered in current water nitrate management and policy development. The aim of this study was to develop a catchment-scale integrated numerical method to investigate the nitrate lag time in the groundwater system, and the Eden Valley, UK, was selected as a case study area. The method involves three models, namely the nitrate time bomb-a process-based model to simulate the nitrate transport in the unsaturated zone (USZ), GISGroundwater--a GISGroundwater flow model, and N-FM--a model to simulate the nitrate transport in the saturated zone. This study answers the scientific questions of when the nitrate currently in the groundwater was loaded into the unsaturated zones and eventually reached the water table; is the rising groundwater nitrate concentration in the study area caused by historic nitrate load; what caused the uneven distribution of groundwater nitrate concentration in the study area; and whether the historic peak nitrate loading has reached the water table in the area. The groundwater nitrate in the area was mainly from the 1980s to 2000s, whilst the groundwater nitrate in most of the source protection zones leached into the system during 1940s-1970s; the large and spatially variable thickness of the USZ is one of the major reasons for unevenly distributed groundwater nitrate concentrations in the study area; the peak nitrate loading around 1983 has affected most of the study area. For areas around the Bowscar, Beacon Edge, Low Plains, Nord Vue, Dale Springs, Gamblesby, Bankwood Springs, and Cliburn, the peak nitrate loading will arrive at the water table in the next 34 years; statistical analysis shows that 8.7 % of the Penrith Sandstone and 7.3 % of the St Bees Sandstone have not been affected by peak nitrate. This research can improve the scientific understanding of nitrate processes in the groundwater system and support the effective management of groundwater nitrate pollution for the study area. With a limited number of parameters, the method and models developed in this study are readily transferable to other areas.

Global patterns of nitrate storage in the vadose zone.

Global-scale nitrogen budgets developed to quantify anthropogenic impacts on the nitrogen cycle do not explicitly consider nitrate stored in the vadose zone. Here we show that the vadose zone is an important store of nitrate that should be considered in future budgets for effective policymaking. Using estimates of groundwater depth and nitrate leaching for 1900-2000, we quantify the peak global storage of nitrate in the vadose zone as 605-1814 Teragrams (Tg). Estimates of nitrate storage are validated using basin-scale and national-scale estimates and observed groundwater nitrate data. Nitrate storage per unit area is greatest in North America, China and Europe where there are thick vadose zones and extensive historical agriculture. In these areas, long travel times in the vadose zone may delay the impact of changes in agricultural practices on groundwater quality. We argue that in these areas use of conventional nitrogen budget approaches is inappropriate.

Macronutrient status of UK groundwater: Nitrogen, phosphorus and organic carbon.

Groundwater is a large, slowly changing pool of the macronutrients nitrogen (N), phosphorus (P) and dissolved organic carbon (DOC), with impacts on receptors, surface waters, dependent wetlands and coastal marine ecosystems. Sources of N to groundwater include fertilisers, animal wastes and septic effluents. N species are well-quantified in groundwater and NO3-N has a wide range of median values (0-12mg/L). The highest concentrations are in the Chalk of East Anglia and Humberside and the Permo-Triassic Sandstone (PTS) of Staffordshire. The highest concentrations of NH4-N are found in confined aquifers. N concentrations have increased with time peaking during the 1980s. Changes in practice have led to the reduction observed in rapidly-responding aquifers. For the Chalk, where the unsaturated zone is thick, improvements may not be seen for decades. P is less well-characterised in UK groundwater reflecting the lack of historical interest in groundwater P, although it can be significant in some aquifer matrices. Groundwater P concentrations are elevated in sandstone formations compared to other lithology and highest in the PTS of the Midlands and northern England (median values>50µg/L). Overall half of the aquifers studied in the UK have median TDP>50µg/L, with values of up to 100µg/L under some urban areas, such as Manchester and Liverpool as well as the Lee Valley. P concentrations in arable areas are variable (20-100µg/L), whereas under semi-natural conditions they are lower (20-50µg/L). There is little information on P trends in groundwater. Most DOC is derived from soils, playing an important part in redox processes. The aquifer matrix can contain high OC and contribute significantly to groundwater DOC. Median values range between 0.4 and 9mg/L, but rarely exceed 5mg/L, except in the Chalk of Yorkshire and Humberside and PTS of Liverpool which have long legacies of anthropogenic pollution.

Temporal variability of micro-organic contaminants in lowland chalk catchments: New insights into contaminant sources and hydrological processes.

This paper explores the temporal variation of a broad suite of micro organic (MO) compounds within hydrologically linked compartments of a lowland Chalk catchment, the most important drinking water aquifer in the UK. It presents an assessment of results from relatively high frequency monitoring at a well-characterised site, including the type and concentrations of compounds detected and how they change under different hydrological conditions including exceptionally high groundwater levels and river flow conditions during 2014 and subsequent recovery. This study shows for the first time that within the Chalk groundwater there can be a greater diversity of the MOs compared to surface waters. Within the Chalk 26 different compounds were detected over the duration of the study compared to 17 in the surface water. Plasticisers (0.06-39µg/L) were found to dominate in the Chalk groundwater on 5 visits (38.4%) accounting for 14.5% of detections but contributing highest concentrations whilst other compounds dominated in the surface water. Trichloroethene and atrazine were among the most frequently detected compounds. The limit for the total pesticide concentration detected did not exceed EU/UK prescribed concentration values for drinking water. Emerging organic compounds such as caffeine, which currently do not have water quality limits, were also detected. The low numbers of compounds found within the hyporheic zone highlight the role of this transient interface in the attenuation and breakdown of the MOs, and provision of an important ecosystem service.

Estimating the leakage contribution of phosphate dosed drinking water to environmental phosphorus pollution at the national-scale.

Understanding sources of phosphorus (P) to the environment is critical for the management of freshwater and marine ecosystems. Phosphate is added at water treatment works for a variety of reasons: to reduce pipe corrosion, to lower dissolved lead and copper concentrations at customer's taps and to reduce the formation of iron and manganese precipitates which can lead to deterioration in the aesthetic quality of water. However, the spatial distribution of leakage into the environment of phosphate added to mains water for plumbosolvency control has not been quantified to date. Using water company leakage rates, leak susceptibility and road network mapping, we quantify the total flux of P from leaking water mains in England and Wales at a 1km grid scale. This is validated against reported leaks for the UKs largest water utility. For 2014, we estimate the total flux of P from leaking mains to the environment to be c. 1.2ktP/year. Spatially, P flux is concentrated in urban areas where pipe density is highest, with major cities acting as a significant source of P (e.g. London into the Thames, with potentially 30% of total flux). The model suggests the majority (69%) of the P flux is likely to be to surface water. This is due to leakage susceptibility being a function of soil corrosivity and shrink-swell behaviour which are both controlled by presence of low-permeability clays. The location of major cities such as London close to the coast results in a potentially significant flux of P from mains leakage to estuarine environments. The contribution of leakage of phosphate dosed mains water should be considered in future source apportionment and ecosystem management. The methodology presented is generic and can be applied in other countries where phosphate dosing is undertaken or used prior to dosing during investment planning.

Hydrochemical profiles in urban groundwater systems: New insights into contaminant sources and pathways in the subsurface from legacy and emerging contaminants.

It has long been known that groundwaters beneath urban areas carry a fingerprint from urban activities but finding a consistent tracer for anthropogenic influence has proved elusive. The varied sources of urban contaminants means that a single consistent and inexpensive means of tracing the fate of urban contaminants is not generally possible and multiple tracers are often required to understand the contaminant sources and pathways in these complex systems. This study has utilized a combination of micro-organic (MO) contaminants and inorganic hydrochemistry to trace recharge pathways and quantify the variability of groundwater quality in multi-level piezometers in the city of Doncaster, UK. A total of 23 MOs were detected during this study, with more compounds consistently detected during higher groundwater table conditions highlighting the importance of sampling under different hydrological conditions. Four of the compounds detected are EU Water Framework Directive priority substances: atrazine, simazine, naphthalene and DEHP, with a maximum concentration of 0.18, 0.03, 0.2, 16µg/l respectively. Our study shows that the burden of the banned pesticide atrazine persists in the Sherwood Sandstone and is detected at two of the three study sites. Emerging contaminants are seen throughout the borehole profiles and provide insights into transient pathways for contaminant migration in the sub-surface. Long term changes in inorganic hydrochemistry show possible changes in contaminant input or the dissolution of minerals. Nitrate was detected above 50mg/l but on the whole nitrate concentrations have declined in the intervening years either due to a reduction of nitrate application at the surface or a migration of peak nitrate concentrations laterally or to greater depth. This study shows that multiple tracers together with multi-level piezometers can give a better resolution of contaminant pathways and variable flow regimes within the relatively uncomplicated aquifer of the Sherwood Sandstone compared with single long screened wells.

The changing trend in nitrate concentrations in major aquifers due to historical nitrate loading from agricultural land across England and Wales from 1925 to 2150.

Nitrate is necessary for agricultural productivity, but can cause considerable problems if released into aquatic systems. Agricultural land is the major source of nitrates in UK groundwater. Due to the long time-lag in the groundwater system, it could take decades for leached nitrate from the soil to discharge into freshwaters. However, this nitrate time-lag has rarely been considered in environmental water management. Against this background, this paper presents an approach to modelling groundwater nitrate at the national scale, to simulate the impacts of historical nitrate loading from agricultural land on the evolution of groundwater nitrate concentrations. An additional process-based component was constructed for the saturated zone of significant aquifers in England and Wales. This uses a simple flow model which requires modelled recharge values, together with published aquifer properties and thickness data. A spatially distributed and temporally variable nitrate input function was also introduced. The sensitivity of parameters was analysed using Monte Carlo simulations. The model was calibrated using national nitrate monitoring data. Time series of annual average nitrate concentrations along with annual spatially distributed nitrate concentration maps from 1925 to 2150 were generated for 28 selected aquifer zones. The results show that 16 aquifer zones have an increasing trend in nitrate concentration, while average nitrate concentrations in the remaining 12 are declining. The results are also indicative of the trend in the flux of groundwater nitrate entering rivers through baseflow. The model thus enables the magnitude and timescale of groundwater nitrate response to be factored into source apportionment tools and to be taken into account alongside current planning of land-management options for reducing nitrate losses.

Persistent and emerging micro-organic contaminants in Chalk groundwater of England and France.

The Chalk aquifer of Northern Europe is an internationally important source of drinking water and sustains baseflow for surface water ecosystems. The areal distribution of microorganic (MO) contaminants, particularly non-regulated emerging MOs, in this aquifer is poorly understood. This study presents results from a reconnaissance survey of MOs in Chalk groundwater, including pharmaceuticals, personal care products and pesticides and their transformation products, conducted across the major Chalk aquifers of England and France. Data from a total of 345 sites collected during 2011 were included in this study to provide a representative baseline assessment of MO occurrence in groundwater. A suite of 42 MOs were analysed for at each site including industrial compounds (n=16), pesticides (n=14) and pharmaceuticals, personal care and lifestyle products (n=12). Occurrence data is evaluated in relation to land use, aquifer exposure, well depth and depth to groundwater to provide an understanding of vulnerable groundwater settings.

Emerging contaminants in urban groundwater sources in Africa.

The occurrence of emerging organic contaminants within the aquatic environment in Africa is currently unknown. This study provides early insights by characterising a broad range of emerging organic contaminants (n > 1000) in groundwater sources in Kabwe, Zambia. Groundwater samples were obtained during both the dry and wet seasons from a selection of deep boreholes and shallow wells completed within the bedrock and overlying superficial aquifers, respectively. Groundwater sources were distributed across the city to encompass peri-urban, lower cost housing, higher cost housing, and industrial land uses. The insect repellent DEET was ubiquitous within groundwater at concentrations up to 1.8 µg/L. Other compounds (n = 26) were detected in less than 15% of the sources and included the bactericide triclosan (up to 0.03 µg/L), chlorination by-products - trihalomethanes (up to 50 µg/L), and the surfactant 2,4,7,9-tetramethyl-5-decyne-4,7-diol (up to 0.6 µg/L). Emerging contaminants were most prevalent in shallow wells sited in low cost housing areas. This is attributed to localised vulnerability associated with inadequate well protection, sanitation, and household waste disposal. The five-fold increase in median DEET concentration following the onset of the seasonal rains highlights that more mobile compounds can rapidly migrate from the surface to the aquifer suggesting the aquifer is more vulnerable than previously considered. Furthermore it suggests DEET is potentially useful as a wastewater tracer in Africa. There was a general absence of personal care products, life-style compounds, and pharmaceuticals which are commonly detected in the aquatic environment in the developed world. This perhaps reflects some degree of attenuation within the subsurface, but could also be a result of the current limited use of products containing emerging contaminants by locals due to unaffordability and unavailability. As development and population increases in Africa, it is likely a wider-range of emerging contaminants will be released into the environment.

In-situ tryptophan-like fluorescence: A real-time indicator of faecal contamination in drinking water supplies.

Enteric pathogens are typically inferred from the presence of surrogate indicator organisms such as thermotolerant (faecal) coliforms (TTCs). The analysis of TTCs requires time-consuming incubation in suitable laboratories, which can limit sampling resolution, particularly during critical pollution events. Here, we demonstrate the use of in-situ fluorimeters targeting tryptophan-like compounds as a rapid, reagentless indicator of TTCs in groundwater-derived potable water supplies in Africa. A range of other common indicators of TTCs were also determined including nitrate, turbidity, and sanitary risk survey scores. Sampling was conducted during both the dry and wet seasons to investigate seasonality. Tryptophan-like fluorescence was the most effective predictor of both presence/absence and number of TTCs during both seasons. Seasonal changes in tryptophan-like fluorescence in deeper supplies suggest it is transported more efficiently through the aquifer than TTCs. Moreover, the perennial elevated concentrations in some wells suggest it is more resilient than TTCs in groundwater. Therefore tryptophan-like fluorescence could also be a better indicator of some smaller, more easily transported, and long-lived, pathogenic enteric viruses. These sensors have the potential to be included in real-time pollution alert systems for drinking water supplies throughout the world, as well as for mapping enteric pathogen risks in developing regions.

End-plate morphology in amyotrophic lateral sclerosis.

Intercostal muscle end-plates were measured in patients with amyotrophic lateral sclerosis (ALS) and more benign motor neuron disease (MND). The length of the intact end-plates in ALS and MND was not different from the controls. Segmented end-plates were increased in both ALS and benign MND, and the end-plate length was greatest in ALS. In individual ALS cases, no correlation was found between the end-plate abnormalities and relevant clinical variables.

Evidence for selective health maintenance organization enrollment among children and adolescents covered by Medicaid.

OBJECTIVE: To determine whether children and adolescents are selectively enrolled in health maintenance organizations (HMOs) based on age, gender, diagnosis, or prior utilization. DESIGN: Case-control study. New HMO enrollees were compared with a control population of non-HMO enrollees. SETTING: Medicaid claims data and HMO participation records for the Medicaid and Aid to Families of Dependent Children sector in Baltimore, Md. RESULTS: Controlling for age, significant differences in prior health care utilization as measured by Medicaid expenditures and hospital days were noted. Children enrolling in HMOs had significantly lower prior utilization than children from the control population as measured by dollar expenditures and hospital days. Young children enrolling in HMOs were only half as likely to have prior claims for asthma. Conversely, adolescents enrolling in HMOs had significantly higher prior utilization than adolescents from the control population. The difference among adolescents was due to a higher birth rate among new HMO enrollees in that age bracket. CONCLUSIONS: Voluntary HMO enrollment of children covered by Medicaid and Aid to Families of Dependent Children sector was subject to selection biases that may be economically favorable to the HMOs and may undermine the cost-containment goals of prepaid health care for Medicaid participants. Voluntary capitated systems where fee-for-service remains a significant alternative must monitor for these selection biases that are not allowed for in the adjustments to capitation rates.

Ambulatory care practice variation within a Medicaid program.

STUDY QUESTIONS: What is the extent of variation in patterns of ambulatory care practice across one state's Medicaid program once case mix is controlled for? How much of this variation in resource consumption is explained by factors linked to the provider, patient, and geographic subarea? DATA SOURCES/STUDY SETTING: Practices of all providers delivering care to persons who were continuously enrolled in the Maryland Medicaid program during FY 1988 were studied. A computerized summary of all services received during this year for 134,725 persons was developed using claims data. We also obtained data from the state's beneficiary and provider files and the American Medical Association's masterfile. Each patient was assigned a "usual source of care" (primary provider) based on the actual patterns of service. The Ambulatory Care Group (ACG) measure was used to help control for case mix. STUDY DESIGN: This was a cross-sectional study based on the universe of continuously enrolled Medicaid enrollees in one state. PRINCIPAL FINDINGS: After controlling for case mix, the variation in patient resource use by type of primary provider was 19 percent for ambulatory visits, 46 percent for ancillary testing, 61 percent for prescriptions, and 81 percent for hospitalizations. Across Maryland counties, comparing the low- to high-use jurisdiction, there was 41 percent variation in case mix-adjusted visit rates, 72 percent variation in pharmacy use, and 325 percent variation in hospital days. At the individual practice level, physician characteristics explain up to 17 percent of ambulatory resource use and geographic area explains only a few percent, while patient characteristics explain up to 60 percent of variation. CONCLUSIONS: Since a large proportion of variation was explained by patient case mix, it is evident that risk adjustment is essential for these types of analyses. However, even after adjustment, resource use varies considerably across types of ambulatory care provider and region, with consequent implications for efficiency of health services delivery.

Immediate pigment darkening: visual and reflectance spectrophotometric analysis of action spectrum.

Immediate pigment darkening (IPD) occurs in human skin upon exposure to ultraviolet-A and visible radiation. The spectral changes that occur during IPD were measured with a rapid scanning reflectance spectrophotometer (RS) which employs optical fiber bundles for delivery and detection of light between 400 and 750 nm. The radiation dose dependence and wavelength dependence (334-549 nm irradiation) of IPD were studied by both the classical visual grading method and by spectrophotometric scoring using the RS system. The spectral changes that occur at long wavelengths with IPD mimic the natural absorption spectrum of melanin. Therefore, the IPD was scored in terms of the apparent change in melanin optical density, using the method Kollias and Baqer [Photochem. Photobiol. 43, 49-54 (1986)], based on reflectance in the 620-720 nm range. The nonlinearity of the visual grading method is demonstrated. The degree of IPD is first-order with respect to delivered dose and saturates after high doses. The maximum amount of IPD attained at saturation is greater for shorter wavelengths. Extrapolation of the reflectance data suggests the longest wavelength capable of eliciting IPD is about 470 nm.

A comparison of ambulatory Medicaid claims to medical records: a reliability assessment.

This study compares the documentation of ambulatory care visits and diagnoses in Medicaid paid claims and in medical records. Data were obtained from Maryland Medicaid's 1988 paid claims files for 2407 individuals who were continuously enrolled for the fiscal year, had at least one billed visit for one of six indicator conditions, and had received the majority of their care from one provider. The patients sampled were also stratified on the basis of the case-mix adjusted cost of their usual source of care. The medical records for these individuals as maintained by their usual source of care were abstracted by trained nurse reviewers to compare claims and record information. Linked claim and medical record data for sampled patients were used to calculate: (i) the percent of billed visits documented in the record, (ii) the percent of medical record visits where both the date and the diagnosis agreed with the claims data, and (iii) the ratio of medical record visits to visits from billed claims. Included in the analysis were independent variables specifying place of residence, type and costliness of usual care source, level of patient utilization, and indicator condition on which patient was sampled. Ninety percent of the visits chronicled in the paid claims were documented in the medical record with 82% agreeing on both date and diagnosis. Compared to the medical records kept by private physicians and community health centers, a significantly lower percent of hospital medical records agreed with the claims data. Total volume of visits was 2.6% higher in the medical records than in the claims. Claims data substantially understated visits in the medical record by 25% for low cost providers and by 41% for patients with low use rates (based on claims information). Conversely, medical records substantially understated billed visits by 19% for rural patients and by 10% for persons with high visit rates. Although Medicaid claims are relatively accurate and useful for examining average ambulatory use patterns, they are subject to significant biases when comparing subgroups of providers classified by case-mix adjusted cost and patients classified by utilization rates. Medicaid programs are using claims data for profiling and performance assessment need to understand the limitations of administrative data.

Nursing: the endangered profession?

The history of nursing illustrates patterns that continue to threaten the recruitment and retention of nurses today. Three contemporary examples illustrate key dilemmas the nursing profession is facing. They also provide us with clues to patterns and themes that have recurred throughout our history.

Emerging organic contaminants in groundwater: A review of sources, fate and occurrence.

Emerging organic contaminants (EOCs) detected in groundwater may have adverse effects on human health and aquatic ecosystems. This paper reviews the existing occurrence data in groundwater for a range of EOCs including pharmaceutical, personal care, 'life-style' and selected industrial compounds. The main sources and pathways for organic EOCs in groundwater are reviewed, with occurrence data for EOCs in groundwater included from both targeted studies and broad reconnaissance surveys. Nanogram-microgram per litre concentrations are present in groundwater for a large range of EOCs as well as metabolites and transformation products and under certain conditions may pose a threat to freshwater bodies for decades due to relatively long groundwater residence times. In the coming decades, more of these EOCs are likely to have drinking water standards, environmental quality standards and/or groundwater threshold values defined, and therefore a better understanding of the spatial and temporal variation remains a priority.

A review of the impact of climate change on future nitrate concentrations in groundwater of the UK.

This paper reviews the potential impacts of climate change on nitrate concentrations in groundwater of the UK using a Source-Pathway-Receptor framework. Changes in temperature, precipitation quantity and distribution, and atmospheric carbon dioxide concentrations will affect the agricultural nitrate source term through changes in both soil processes and agricultural productivity. Non-agricultural source terms, such as urban areas and atmospheric deposition, are also expected to be affected. The implications for the rate of nitrate leaching to groundwater as a result of these changes are not yet fully understood but predictions suggest that leaching rate may increase under future climate scenarios. Climate change will affect the hydrological cycle with changes to recharge, groundwater levels and resources and flow processes. These changes will impact on concentrations of nitrate in abstracted water and other receptors, such as surface water and groundwater-fed wetlands. The implications for nitrate leaching to groundwater as a result of climate changes are not yet well enough understood to be able to make useful predictions without more site-specific data. The few studies which address the whole cycle show likely changes in nitrate leaching ranging from limited increases to a possible doubling of aquifer concentrations by 2100. These changes may be masked by nitrate reductions from improved agricultural practices, but a range of adaption measures need to be identified. Future impact may also be driven by economic responses to climate change.