The growing consumption of materials in our digital society represents an ever increasing waste stream containing novel and complex mixtures of chemicals, including many oxyanion forming contaminants (OFCs, e.g. As, B, Cr, Mo, Sb, V, Se, Sb, Te, etc.) that threaten freshwater security. Current industrial innovations (e.g. electric vehicles, domestic power storage, the internet of things) and policy drivers (e.g. acceleration of Energy from Waste (EfW) in UK/EU) will increase future usage of these elements, which gives rise to potential releases from cycles of production and consumption into the environment. Ecosystem health in lakes and rivers are underpinned by complex relationships between environmental drivers (e.g. nutrients, weather, contaminants etc.), and can be highly degraded by inputs of OFCs such as P and As. These effects can be persistent over decades as a result of interactions with sediments and biota under varying pH and redox. This project will produce a large scale assessment of key environmental pathways for key OFCs and combine field and experimental approaches to comprehensively study the effects of established OFCs across ecological scales (i.e. from molecular processes to impacted ecosystems). Data from these approaches can be used to inform ecotoxicological risk assessments and predictive models, with which future management and policy approaches, developed to mitigate the effects of future waste stream scenarios, can be evaluated.
Figure 1 Landfill leachate from poorly controlled waste management, Gurgaon, India, enters local rivers.
OFCs can be released from a wide range of industrial sources, including EfW incinerator ashes, petroleum combustion residues, and many different mining and metal processing wastes (e.g. iron and aluminium ore processing). A common factor across all sources is the occurrence of multiple different oxyanion contaminants present in elevated concentrations, which are often then readily mobilised in associated leachates and leaching tests [1-2]. This has helped define a short list of oxyanion contaminants, including toxic OFCs such as As, V, and Se for inclusion in this project.
- Utilising available data and literature, develop a conceptual model of OFE risk including waste streams, critical exposure pathways, transformation processes, ecosystem effects and risk assessment from catchment to global scales, with a focus on the UK scale.
- Investigation of actively polluted rivers and lakes, to establish relationships between OFE composition and behaviour in the field, catchment scale flux models, and net ecosystem effects in control versus impacted sites.
- Produce experimental and molecular level data to quantify the drivers of interactions between OFEs (as individual components and mixtures) and other chemical components of receiving waters to define the potential for significant ecotoxicological effects in affected environments.
Background and rationale:
Lakes and reservoirs provide essential ecosystem services (ES) with which to support sustainable growth in the UK and globally. Their role in retaining and processing pollutants is essential, especially in well-developed and urban catchments, but also in agricultural catchments. However, this key ES can result in catastrophic collapse of ecosystem function (EF) and of the delivery of other vital ESs. These predictions are based on previous work demonstrating the devastating ecological and human health impacts of other established OFCs including P, As and Cr leading to large scale loss of ES in freshwater catchments (e.g. ). OFCs are, therefore, of increasing significance as potential environmental pollutants, yet, critical knowledge gaps in their chemical and toxicological behaviour currently preclude robust development of policies for managing their environmental risks. Confounding the issue is the complete lack of knowledge on their potential interactions between established problems in freshwater ecosystems, including eutrophication and climate change. These interactions will lead to novel ecosystem net effects-thresholds for OFCs that have not yet been quantified. Despite these knowledge gaps, the UK and EU have developed policies towards the expansion of waste incineration and the rapid increase in use of e-tech elements for green technologies. Associated waste management processes are likely to cause OFCs to become more prevalent in UK and EU waste waters leading to wide spread contamination of receiving high value fresh water ecosystems. This has already occurred in some cases, in the form of actively or legacy contaminated sites (e.g. e-Waste pollution in Bangalore Lakes, India; bauxite residue pollution in Kinghorn Loch, UK; Marcal-Danube catchments; Hungary). Therefore, understanding interactions and cycling of mixed groups of oxyanion contaminants is imperative for effective assessment of the risks posed by their release into natural environments.
Figure 2 Kinghorn Loch, Fife, received OFCs (e.g. As, V) from aluminium industry for many years effecting its ecosystem function and health.
OFCs are typically associated with high temperature industrial processing (e.g. metal processing residues, incinerator ashes), many of which are dramatically increasing in production in recent years to meet global demand for raw materials and increased energy recovery. They are also increasingly found in a range of new disruptive industries crucial to current and future green technologies. Since the start of the new millennium there has been a marked increase (> 100%) in production of several elements (e.g. Mo, Se, Te, V, ) critical to new disruptive industries related to advanced manufacturing and electronics such as V / Se (batteries for mobile and domestic power storage) and Te (photovoltaics) . Waste streams from the life cycle of these practices (i.e. from; mining and production sites, dispersed and pervasive use, e-waste recycling facilities, and the final treatment and disposal of wastes) represent a series of complex environmental exposure routes. There is a growing need to quantify these exposure routes, especially the net loads of OFCs to terrestrial and freshwater ecosystems. In the UK and EU, environmental data are available with which atmospheric and surface water OFC concentrations and fluxes can be assessed to identify areas of ecological sensitivity in relation to sources and existing land uses.
OFCs are understudied with respect to their environmental behaviour and ecotoxicity , which is reflected in regulatory guidance being absent or uncertain . The geochemical behaviour and ecological risks of some OFEs have been reasonably well characterised, for example P, As and Cr, for which established environmental quality standards are prescribed. For others, however, these are absent and only the P standards are based on net ecosystem effects associated with ecological quality. We know that the risks posed by these OFCs can be long lasting given the potential for geochemical mimicry of toxic oxyanions (e.g. arsenate) with essential macronutrients (phosphate). Examples of lakes receiving complex mixtures of OFCs are characterised by eutrophication, direct ecotoxicological effects, and bio-accumulation through the food web. At some contaminated sites, this has led to catastrophic ecological collapse with recovery taking decades  although the underlying environmental processes occurring remain largely unclear.
Methodology and approach:
This project will focus on 3 specific objectives determining the likely environmental sources, fate, behaviour and impact of OFC mixtures in freshwater environments The project will build understanding of pollutant fluxes and exposure routes using existing datasets from CEH intensive focus catchments in Scotland, scaling up to UK and EU scale using available data sets. Established and cutting edge laboratory approaches (for single elements and simple mixtures) in molecular environmental science (e.g. XAS) to determine the exact mechanisms of contaminant mobility in controlled mineral and sediment experiments. These approaches will be complemented by field studies which will investigate the net effects of mixed metal contamination (at selected field sites) in the presence of other environmental stressors (e.g. changes in pH, increased nutrient loadings).
Objective 1: Sources, Trends and Drivers: A review of published and grey literature (e.g. industry reports) on production (e.g. USGS) releases (Pollutant Release & Transfer Registers) and single species toxicity data of OFCs will be conducted. Analysis of catchment, UK, EU and global scale data on atmospheric, surface water, sediment and groundwater OFE concentrations and fluxes will be used to produce risk maps and trends in exposure. We will review evidence on interactions between occurrence and exposure levels of OFC pollution and other established freshwater stressors (e.g. climate change and eutrophication). A conceptual model will be produced of key pathways, forms, effects, and locations of releases across scales, in line with current and future policy and to inform future scenarios and experimental design for laboratory experiments.
Objective 2: Ecosystem Effects: A combination of intensive and extensive field campaigns will be conducted to generate data for comparison against model and experimental WPs. An Intensive year-long survey (4-6 visits to investigate seasonal effects) will be conducted at a previously studied UK catchment (Kinghorn Loch, Fife Scotland ) in which OFCs and nutrient stressors have previously been confirmed to quantify at the catchment scale sources and loads, transformation, and effects levels and forms (using well established ecosystem function and services indicators) of OFCs in relation to other environmental stressors. This will be augmented by an extensive field campaign consisting of single visits to a larger number of contaminated sites across the UK to produce data on ecosystem effects levels and forms across a wide range of contaminant concentrations. Site selection will be instructed by initial literature studies and an existing CEH water quality database including 41 target polluted freshwater ecosystems.
Objective 3: Fundamental Chemical Behaviour: In order to assess the fundamental interactions of single and mixed oxyanionic contaminants (in environmental settings defined from fieldwork) with selected clay and iron oxide minerals, including the effect of reducing conditions (e.g. for V, Se), pH and contact with sources of organic carbon (e.g. humic acids). High resolution electron microscopy (at the Leeds centre of electron microscopy and spectroscopy) and XAS analysis (e.g. at the Diamond Light source synchrotron, UK or the European Synchrotron Radiation Facility, France) will be used to determine metal speciation at the molecular scale across a wide range of relevant environmental conditions. We will also use sediment samples recovered from field sites and experimental mesocosms for determination of metal fate and behaviour in more realistic situations.
Figure 3 The UKs synchrotron facility at the Diamond light source will be used to investigate oxyanion behaviour in environmental samples.
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