Source apportionment of metal mine pollution in Wanlock Water using tracer injection and synoptic sampling

Scottish Environment Protection Agency Repo

Critical control of flooding and draining sequences on the environmental risk of Zn-contaminated riverbank sediments

Purpose: Diffuse pollution emanating from metal mining impacted sediment could serve as a barrier to achieving European Union Water Framework Directive and US Clean Water Act requirements. UK climate projections (UKCP09) predict increases in rainfall and aridity that will influence river stage alternately exposing and submersing contaminated riverbank sediment. Research focuses on the environmental contaminant dissolved Zn and investigates patterns of release, key geochemical mechanisms controlling Zn mobilisation and the environmental risk of sediment subjected to these perturbations. Materials and methods: Using two laboratory mesocosm experiments, metal mining-contaminated sediment was subjected to alternate wet and dry sequences of different duration and frequency. The first experiment was run to determine the influence of submersion and exposure of contaminated sediment on releases of Zn and to establish environmental risk. The second experiment utilised diffusional equilibration in thin film (DET) to observe the patterns of Zn release, with depth, in the sediment. Pore water chemical analysis at the sediment-water interface enabled elucidation of key geochemical mechanisms of control of Zn mobilisation. Results and discussion: Patterns of Zn release were found to be different, depending on the length of wet and dry period. High concentrations of dissolved Zn were released at the start of a flood for runs with longer dry periods. A buildup of soluble Zn sulphate minerals over long dry periods followed by dissolution on first flood wetting was a key geochemical mechanism controlling Zn release. For longer wet runs, increases in dissolved Mn and Zn were observed over the flood period. Key geochemical mechanisms controlling Zn mobilisation for these runs were: (i) reductive dissolution of Mn (hydr)oxides and release of partitioned Zn over prolonged flood periods followed by (ii) oxidation and precipitation of Mn (hydr)oxides and sorption of Zn on exposure to atmospheric conditions. Conclusions: Mesocosm experiments were a first step in understanding the effects of UK climate projections on the riverbank environment. Contaminated sediment was found to pose a significant environmental risk in response to hydrological perturbations. The ‘transient’ nature of dissolved Zn release could make identifying the exact sources of pollution a challenge; therefore, further field studies are advised to monitor contaminant releases under a range of hydrological conditions and account for complex hydrology at mining sites

Stormflow hydrochemistry in a river draining an abandoned metal mine: the Afon Twymyn, central Wales

Contaminated drainage from metal mines is a serious water-quality problem facing nations that exploit metal mineral resources. Measurements of river hydrochemistry during baseflow are common at mine sites, whilst detailed hydrochemical information regarding stormflow is limited and often confined to a single event. This study investigates the seasonal evolution of stormflow hydrochemistry at an abandoned metal mine in central Wales, UK, and the possible sources and mechanisms of metal release. Significant flushing of metals was observed during stormflow events, resulting in concentrations that severely exceeded water-quality guidelines. The relationship between metal concentrations and river discharge suggests dissolution of efflorescent metal sulphates on the surface of the mine spoil as the principal source of the contamination. High fluxes of Pb during stormflows are linked to extended periods of dry weather prior to storm events that produced water table drawdown and encouraged oxidation of Pb sulphide in the mine spoil. However, some Pb flushing also occurred following wet antecedent conditions. It is suggested that Fe oxide reduction in mine spoil and translatory flows involving metal-rich pore waters results in flushing during wetter periods. Detailed measurements of stormflow hydrochemistry at mine sites are essential for accurate forecasting of long-term trends in metals flux to understand metal sources and mechanisms of release, to assess potential risks to water quality and instream ecology, and to gauge the potential effectiveness of remediation. In order to protect riverine and riparian ecosystems, it is suggested that routine monitoring of stormflows becomes part of catchment management in mining-impacted regions

Environmental risk of severely Pb-contaminated riverbank sediment as a consequence of hydrometeorological perturbation

Metal mining activities have resulted in the widespread metal pollution of soils and sediments and are a worldwide health concern. Pb is often prolific in metal-mining impacted systems and has acute and chronic toxic effects. Environmental factors controlling diffuse pollution from contaminated riverbank sediment are currently seen as a “black box” from a process perspective. This limits our ability to accurately predict and model releases of dissolved Pb. Previous work by the authors uncovered key mechanisms responsible for the mobilisation of dissolved Zn. The current study identifies key mechanisms controlling the mobilisation of dissolved Pb, and the environmental risk these releases pose, in response to various sequences of “riverbank” inundation/drainage. Mesocosm experiments designed to mimic the riverbank environment were run using sediment severely contaminated with Pb, from a mining-impacted site. Results indicated that, although Pb is generally reported as less mobile than Zn, high concentrations of dissolved Pb are released in response to longer or more frequent flood events. Furthermore, the geochemical mechanisms of release for Zn and Pb were different. For Zn, mechanisms were related to reductive dissolution of Mn (hydr)oxides with higher concentrations released, at depth, over prolonged flood periods. For Pb, key mechanisms of release were related to the solubility of anglesite and the oxidation of primary mineral galena, where periodic drainage events serve to keep sediments oxic, particularly at the surface. The results are concerning because climate projections for the UK indicate a rise in the occurrence of localized heavy rainfall events that could increase flood frequency and/or duration. This study is unique in that it is the first to uncover key mechanisms responsible for dissolved Pb mobilisation from riverbank sediments. The mineralogy at the mining-impacted site is common to many sites worldwide and it is likely the mechanisms identified in this study are widespread

Short-term fluctuations in heavy metal concentrations during flood events through abandoned metal mines, with implications for aquatic ecology and mine water treatment

The variability in heavy metal concentrations and physico-chemical parameters during rain-fed river floods that pass through abandoned metal mines is poorly understood due to the difficulties of sampling these events. Such information is essential for the characterisation of contaminant dynamics and for investigations of contaminant/ecosystem relations and the effectiveness of remediation. This study investigates the role of flood flows in contaminant mobilisation and temporary increases in toxicity at an abandoned metal mine in central Wales, UK. Flood events substantially increase the potential toxicity of river water. The principal contaminants are dissolved Pb, mobilized by increased acidity resulting from the dissolution and flushing of efflourescent salts accumulated on the surface of mine spoil. The implications of flood runoff and contaminant mobilisation for aquatic ecology and mine water treatment are discussed

Comparison of electromagnetic wave sensors with optical and low-frequency spectroscopy methods for real-time monitoring of lead concentrations in mine water

The feasibility of using novel electromagnetic wave sensors for real-time monitoring of metal pollution in water was assessed. Five solutions with different concentrations of lead (0, 1, 10, 50, 100 mg/L) were measured using several sensing methods: UV-Vis spectroscopy, low frequency capacitance and resistance measurements, and two sensing systems based on microwave technology. With this last approach, two sensing devices were used: a resonant cavity and a planar sensor with gold interdigitated electrode design printed on a PTFE substrate with a protective PCB lacquer coating. Results confirmed the ability of these systems to quantify the lead concentration as changes in spectrum signal at specific frequencies of the electromagnetic spectrum. Spectra were unique, with clearly observed shifts in the resonant frequencies of the sensors when placed in direct contact with different lead solutions, demonstrating the possibility of continuous monitoring with great sensitivity, selectivity, and high spatial and temporal resolution. Consequently, determination of trace and toxic metals using microwave spectroscopy is a promising alternative to traditional grab-sampling and laboratory based analyses. On-line and continuous monitoring of real-time metal concentrations offers the potential for a more effective emergency response and the platform for better scientific understanding and remediation of contaminated mine drainage

Presentation for care and antenatal management of HIV in the United Kingdom:temporal trends and demographic variations, 2009-2014

OBJECTIVES: Despite very low rates of vertical transmission of HIV in the UK overall, rates are higher among women starting antenatal antiretroviral therapy (ART) late. We investigated the timing of key elements of the care of HIV‐positive pregnant women [antenatal care booking, HIV laboratory assessment (CD4 count and HIV viral load) and antenatal ART initiation], to assess whether clinical practice is changing in line with recommendations, and to investigate factors associated with delayed care. METHODS: We used the UK's National Study of HIV in Pregnancy and Childhood for 2009−2014. Data were analysed by fitting logistic regression and Cox proportional hazards models. RESULTS: A total of 5693 births were reported; 79.5% were in women diagnosed with HIV prior to that pregnancy. Median gestation at antenatal booking was 12.1 weeks [interquartile range (IQR) 10.0–15.6 weeks] and booking was significantly earlier during 2012–2014 vs. 2009–2011 (P < 0.001), although only in previously diagnosed women. Overall, 42.2% of pregnancies were booked late (≥ 13 gestational weeks). Among women not already on treatment, antenatal ART commenced at a median of 21.4 (IQR18.1–24.5) weeks and started significantly earlier in the most recent time period (P < 0.001). Compared with previously diagnosed women, those newly diagnosed during the current pregnancy booked later for antenatal care and started antenatal ART later (both P < 0.001). Multivariable analyses revealed demographic variations in access to or uptake of care, with groups including migrants and parous women initiating care later. CONCLUSIONS: Although women are accessing antenatal and HIV care earlier in pregnancy, some continue to face barriers to timely initiation of antenatal care and ART

Water quality impacts and river system recovery following the 2014 Mount Polley mine tailings dam spill, British Columbia, Canada

The Mount Polley mine tailings embankment breach on August 4th 2014, in British Columbia, Canada, is the second largest mine waste spill on record. The mine operator responded swiftly by removing significant quantities of tailings from the primary receiving watercourse, stabilizing the river corridor and beginning construction of a new river channel. This presented a unique opportunity to study spatial patterns of element cycling in a partially-restored and alkaline river system. Overall, water quality impacts are considered low with Cu, and to a lesser extent V, being the only elements of concern. However, the spatial pattern of stream Cu loading suggested chemical (dominant at low flow) and physical (dominant at high flow) mobilization processes operating in different parts of the watershed. Chemical mobilization was hypothesized to be due to Cu sulfide (chalcopyrite) oxidation in riparian tailings and reductive dissolution of Cu-bearing Fe oxides in tailings and streambed sediments whereas physical mobilization was due to erosion and suspension of Cu-rich stream sediments further downstream. Although elevated aqueous Cu was evident in Hazeltine Creek, this is considered a relatively minor perturbation to a watershed with naturally elevated stream Cu concentrations. The alkaline nature of the tailings and the receiving watercourse ensures most aqueous Cu is rapidly complexed with dissolved organic matter or precipitates as secondary mineral phases. Our data highlights how swift removal of spilled tailings and river corridor stabilization can limit chemical impacts in affected watersheds but also how chemical mobilization (of Cu) can still occur when the spilled tailings and the receiving environment are alkaline. We present a conceptual model of Cu cycling in the Hazeltine Creek watershed

Geochemical classification of global mine water drainage

This paper evaluates the geochemical distribution and classification of global Acid Mine Drainage (AMD) sources. The geochemical compositions of AMD from 72 mine water sites in 18 countries across 6 continents were referenced from literature. The secondary data were analysed for statistical distribution and mine water classification against the Hill (1968) framework. The research found that the global mine water displayed geochemical concentrations within 2%, 11%, 5%, 9% and 8% of the aluminium, sulphate, acidity, total iron and zinc distribution ranges, respectively, at the 75th percentile. The study also found that 46%, 11.1% and 2.7% of mine water sites met the criteria for Class I, Class II and Class III of the Hill (1968) framework, respectively, while the remaining 40% of sites were omitted by the framework’s geochemical specifications. The results were used to optimise the Hill (1968) framework. The revised framework was proposed for effective AMD geochemical classification, regulation and remediation

Co-remediation of acid mine drainage and industrial effluent using passive permeable reactive barrier pre-treatment and active co-bioremediation

This study evaluated the co-remediation performance of an active–passive process comprised of passive permeable reactive barrier acid mine drainage (AMD) pre-treatment and active anaerobic digestion treatment of AMD with effluent as a carbon source. The bioreactor was operated for 24 consecutive days with peak chemical oxygen demand (COD) and sulphate loading rates of 6.6 kg COD/m3/day and 0.89 kg SO42−/m3/day, respectively. The AMD pre-treatment was capable of removing 99%, 94% and 42% of iron (Fe), potassium (K), and aluminium (Al) concentrations, respectively. The biological treatment process was capable of removing 89.7% and 99% of COD and sulphate concentrations, respectively. The treated wastewater copper (Cu), sulphate (SO42−), and pH were within the effluent discharge limits and the potable water standards of South Africa. Fe, Al, manganese (Mn), nickel (Ni), and zinc (Zn) concentrations in the treated wastewater were marginally higher than the discharge and potable water limit with all concentrations exceeding the limit by less than 0.65 mg/L. The remediation performance of the process was found to be effective with limited operational inputs, which can enable low cost co-remediation