Raman spectroscopy can be used for the rapid identification of a wide variety of minerals ranging from common iron oxy(hydroxides), such as ferrihydrite, to rare minerals, such as adelite. This study ...employed Raman spectroscopy (laser power 0.1%) to characterize both synthetic and common natural iron-bearing mineral phases, including oxides (hematite, magnetite), hydroxides (ferrihydrite, goethite, lepidocrocite, akaganéite), carbonate (siderite), sulfate (Na-jarosite), and ferric arsenates (scorodite, yukonite), found in acid mine drainage and mine tailings settings. X-ray diffraction (XRD) was conducted to verify the purity of phases and compared with associated Raman analyses. Samples with arsenate adsorbed onto ferrihydrite at varied As/Fe ratios (0.50, 0.10, and 0.05) at pH ~10 were also evaluated. Raman spectra were compared with the literature and recommendations made regarding Raman bands that are the most diagnostic for the individual iron minerals studied. Comparison of the Raman and XRD scans shows Raman can either augment or replace XRD for mineral identification. Lastly, some important applications of Raman spectrometry for evaluating significant environmental processes are discussed.
► Ferric (oxy)hydroxides and arsenate minerals characterized by Raman spectroscopy. ► As(V) adsorbed on ferrihydrite at varied As/Fe molar ratios was identified. ► Peak heights at ~836cm−1 linearly increase with increasing As/Fe molar ratios.
Under oxic aqueous conditions, two-line ferrihydrite gradually transforms to more thermodynamically stable and more crystalline phases, such as goethite and hematite. This temperature- and ...pH-dependent transformation can play an important role in the sequestration of metals and metalloids adsorbed onto ferrihydrite. A comprehensive assessment of the crystallization of two-line ferrihydrite with respect to temperature (25, 50, 75, and 100 °C) and pH (2, 7, and 10) as a function of reaction time (minutes to months) was conducted via batch experiments. Pure and transformed phases were characterized by X-ray diffraction (XRD), X-ray absorption near-edge spectroscopy (XANES), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The rate of transformation of two-line ferrihydrite to hematite increased with increasing temperature at all pHs studied and followed first-order reaction kinetics. XRD and XANES showed simultaneous formation of goethite and hematite at 50 and 75 °C at pH 10, with hematite being the dominant product at all pHs and temperatures. With extended reaction time, hematite increased while goethite decreased, and goethite reaches a minimum after 7 days. Observations suggest two-line ferrihydrite transforms to hematite via a two-stage crystallization process, with goethite being intermediary. The findings of this study can be used to estimate rates of crystallization of pure two-line ferrihydrite over the broad range of temperatures and pH found in nature.
Tenofovir (TDF) is an effective and widely used treatment for both human immunodeficiency virus (HIV) and hepatitis B virus infection. Although studies suggest that TDF has a low overall toxicity ...profile and only a modest effect on estimated glomerular filtration rate, numerous case reports have since appeared in the literature describing TDF-associated renal tubular dysfunction, and this is now a significant source of HIV-related referrals to nephrologists. The main target of toxicity appears to be the proximal tubule, and in severe cases, patients can develop renal Fanconi syndrome. We review findings from recent studies in this area performed by ourselves and others and discuss our direct experience as practicing nephrologists. In particular, we discuss: (1) the nature and extent of TDF-associated kidney toxicity in the HIV-infected population, (2) potential underlying mechanisms of toxicity in the proximal tubule, (3) risk factors for developing tubular dysfunction, and (4) suggested strategies to monitor patients on TDF therapy.
It is unclear whether more timely cancer diagnosis brings favourable outcomes, with much of the previous evidence, in some cancers, being equivocal. We set out to determine whether there is an ...association between time to diagnosis, treatment and clinical outcomes, across all cancers for symptomatic presentations.
Systematic review of the literature and narrative synthesis.
We included 177 articles reporting 209 studies. These studies varied in study design, the time intervals assessed and the outcomes reported. Study quality was variable, with a small number of higher-quality studies. Heterogeneity precluded definitive findings. The cancers with more reports of an association between shorter times to diagnosis and more favourable outcomes were breast, colorectal, head and neck, testicular and melanoma.
This is the first review encompassing many cancer types, and we have demonstrated those cancers in which more evidence of an association between shorter times to diagnosis and more favourable outcomes exists, and where it is lacking. We believe that it is reasonable to assume that efforts to expedite the diagnosis of symptomatic cancer are likely to have benefits for patients in terms of improved survival, earlier-stage diagnosis and improved quality of life, although these benefits vary between cancers.
Leaching of nitrate (NO3-) from animal waste or fertilisers at
agricultural operations can result in NO3- contamination of
groundwater, lakes, and streams. Understanding the sources and fate of
...nitrate in groundwater systems in glacial sediments, which underlie many
agricultural operations, is critical for managing impacts of human food
production on the environment. Elevated NO3- concentrations in
groundwater can be naturally attenuated through mixing or denitrification.
Here we use isotopic enrichment of the stable isotope values of
NO3- to quantify the amount of denitrification in groundwater at
two confined feeding operations overlying glacial sediments in Alberta,
Canada. Uncertainty in δ15NNO3 and
δ18ONO3 values of the NO3- source and
denitrification enrichment factors are accounted for using a Monte Carlo
approach. When denitrification could be quantified, we used these values to
constrain a mixing model based on NO3- and Cl−
concentrations. Using this novel approach we were able to reconstruct the
initial NO3−N concentration and NO3-N/Cl- ratio at the
point of entry to the groundwater system. Manure filtrate had
total nitrogen (TN) of up to 1820 mg L−1, which was predominantly
organic N and NH3. Groundwater had up to 85 mg L−1 TN, which
was predominantly NO3-. The addition of NO3- to the
local groundwater system from temporary manure piles and pens equalled or
exceeded NO3- additions from earthen manure storages at these
sites. On-farm management of manure waste should therefore increasingly focus
on limiting manure piles in direct contact with the soil and encourage
storage in lined lagoons. Nitrate attenuation at both sites is attributed to
a spatially variable combination of mixing and denitrification, but is
dominated by denitrification. Where identified, denitrification reduced
agriculturally derived NO3- concentrations by at least half and,
in some wells, completely. Infiltration to groundwater systems in glacial
sediments where NO3- can be naturally attenuated is likely
preferable to off-farm export via runoff or drainage networks, especially if
local groundwater is not used for potable water supply.
Coal has been a major global resource for at least the past 250 years. The major waste product of coal mining is waste rock, which is stored in dumps of various sizes. Although the adverse effects of ...coal waste rock dumps on ecosystems and human health are widely recognised, there is little information on their internal hydrological and geochemical processes in the peer-reviewed literature. Coal and conventional waste rock dumps share many similarities, but coal waste rock dumps differ in structure, organic matter content, and size, which can affect the timing and rate of aqueous chemical release. In this global systematic review, we identify limited links to climate setting and dump construction, and inconsistent reporting of sampling and monitoring approaches, as limitations to the generalisation of findings. Furthermore, sources of aqueous constituents of interest (COIs) are not routinely or adequately identified, which can lead to incorrect assumptions regarding COI availability and geochemical mobility. Water flow regimes within dumps are dominated by matrix and/or preferential flow, depending on dump texture; these flow mechanisms exert a primary control on patterns of aqueous COI release. The inability to successfully transfer COI release rates from laboratory or field scale trials to operational scale dumps is primarily due to limitations of testing methods and fundamental characteristics of scale. Prediction of future release rates is hampered by a lack of long-term studies that fully characterise geochemistry (e.g., source and COI production rates) as well as dump hydrology (e.g., water balance, water migration). Five critical elements to include in best practice investigations are climate setting, dump physical characteristics, geochemical processes, water regime, and environmental load over time, as aqueous release of COIs from coal waste rock dumps occurs over decades to centuries. Key considerations are identified for each of these elements to guide best practice.
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•Mechanistic understanding of hydrology and geochemistry limited by characterisation•Oxidation controls reactive contaminant transport; hydrology controls non-reactive•Internal geochemical sinks alter the general controls on contaminant transport•Combustion changes geochemical processes; effect on hydrology unknown•Need long-term data to assess temporal changes to aqueous contaminant export
► Ferrihydrite is the best adsorbent for Se(VI) at pH∼7 at any solid concentrations. ► For goethite and lepidocrocite, adsorption attained a maxima at ∼60–70%. ► Se(VI) tends to form strong ...inner-sphere complexes on all of these synthetic solids. ► Ferrihydrite can be used as a potential adsorbent for Se(VI).
This study evaluates the adsorption of dissolved Se(VI) onto three synthetic Fe oxy-hydroxides (i.e., 2-line ferrihydrite, goethite and lepidocrocite). Selenate adsorption was measured as a function of sorbent concentration (0.01–50gL−1) at near neutral pH (∼7) and room temperature (25°C) via batch experiments. Inductively coupled plasma-mass spectrometry (ICP-MS) analyses on the aqueous samples showed that 2-line ferrihydrite is by far the strongest adsorbent for Se(VI) when compared to goethite and lepidocrocite at all sorbate:sorbent ratios tested. Goethite has a slightly greater affinity for Se(VI) than lepidocrocite, irrespective of a lower specific surface area under similar experimental conditions (pH, solids concentration). Selenium(VI) surface complexes on the solids were not observed in Raman spectra or attenuated total reflectance-infrared (ATR-IR) spectra of selenate adsorbed phases, likely due to low surface coverage. However, X-ray absorption spectroscopy (XAS) showed that all three Fe oxy-hydroxides adsorbed Se(VI) via inner-sphere surface complexation irrespective of their dissimilar affinities for selenate at pH∼7. Similarly, sorption data for the three synthetic solids was modeled using the Langmuir isotherm. Overall, 2-line ferrihydrite appears to efficiently and effectively adsorb Se(VI) under near neutral conditions and, as such, should be considered a potential sink for Se(VI) in a transient system.
► Relationships between water resources of the Okanagan Valley remain poorly defined. ► Stable isotopes were used to characterize rainfall, rivers and lakes, and ground water resources. ► ...Precipitation isotopes resulted in a local meteoric water line of
δD
=
6.6 (
δ
18O)
−
22.7 for the Okanagan. ► Isotopic mass-balance modeling suggested ∼35% of precipitation falling upon the watershed is lost to evaporation. ► Ground water in the valley aquifers is anthropogenically recharged by irrigation water from the Okanagan River.
Rapid population growth in the intermontane, semi-arid, Okanagan Valley of Western Canada has led to water shortages with increasing debate over competing water interests. Nevertheless, the relationships between the various water resources of the Okanagan remain poorly defined. Stable isotopes of hydrogen (
δ
2H) and oxygen (
δ
18O) were used to assess rainfall importance and the sources and flux of water to and from rivers and lakes in watersheds, and to evaluate the origin of ground water resources. Precipitation isotopes resulted in a meteoric water line of
δ
2H
=
6.6 (
δ
18O)
−
22.7 for the Okanagan Valley. Isotopic seasonality in precipitation was evident, with summer precipitation clearly affected by local recycling of water vapor. The
2H and
18O of surface waters were more positive than mean annual precipitation, indicative of basin-scale evaporation of surface waters; however, Okanagan Lake and its downstream river and lake system were isotopically synchronous, indicating that they behaved as a single well-mixed hydrologic unit. Isotopic mass-balance modeling revealed ∼35% of inflow to the Lake Okanagan watershed was lost to evaporation, validating a meteorological water balance model for the region. Highland bedrock was recharged with snow-melt and early spring rains, with the isotopic composition dependent on elevation. Ground waters in the Valley bottom aquifers west of Osoyoos were recharged by irrigation water obtained from the Okanagan River system, with no evidence of recharge connections from the highland bedrock.
High-volume, hydraulic fracturing (HVHF) is widely applied for natural gas and oil production from shales, coals, or tight sandstone formations in the United States, Canada, and Australia, and is ...being widely considered by other countries with similar unconventional energy resources. Secure retention of fluids (natural gas, saline formation waters, oil, HVHF fluids) during and after well stimulation is important to prevent unintended environmental contamination, and release of greenhouse gases to the atmosphere. Here, we critically review state-of-the-art techniques and promising new approaches for identifying oil and gas production from unconventional reservoirs to resolve whether they are the source of fugitive methane and associated contaminants into shallow aquifers. We highlight future research needs and propose a phased program, from generic baseline to highly specific analyses, to inform HVHF and unconventional oil and gas production and impact assessment studies. These approaches may also be applied to broader subsurface exploration and development issues (e.g., groundwater resources), or new frontiers of low-carbon energy alternatives (e.g., subsurface H2 storage, nuclear waste isolation, geologic CO2 sequestration).
2-Line ferrihydrite, a form of iron in uranium mine tailings, is a dominant adsorbent for elements of concern (EOC), such as arsenic. As ferrihydrite is unstable under oxic conditions and can undergo ...dissolution and subsequent transformation to hematite and goethite over time, the impact of transformation on the long-term stability of EOC within tailings is of importance from an environmental standpoint. Here, studies were undertaken to assess the rate of 2-line ferrihydrite transformation at varying As/Fe ratios (0.500–0.010) to simulate tailings conditions at the Deilmann Tailings Management Facility of Cameco Corporation, Canada. Kinetics were evaluated under relevant physical (∼1 °C) and chemical conditions (pH ∼10). As the As/Fe ratio increased from 0.010 to 0.018, the rate of ferrihydrite transformation decreased by 2 orders of magnitude. No transformation of ferrihydrite was observed at higher As/Fe ratios (0.050, 0.100, and 0.500). Arsenic was found to retard ferrihydrite dissolution and transformation as well as goethite formation.
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