Characterising changes in fluorescence properties of dissolved organic matter and links to N cycling in agricultural floodplains

Sand and gravel aquifer systems are common features below and adjacent to river networks and are important in providing a hydrological link between terrestrial and aquatic ecosystems. They are often used for intensive agriculture and therefore provide a conduit for the transport of nutrients to aquatic systems. Understanding the biogeochemical cycles of C and N in such systems is essential in efforts to improve water quality, with a major link being the transfer and properties of DOM which drives microbial processing of nutrients. In this work undertaken in the Trent Valley, U.K., the differences in dissolved organic matter (DOM) properties in the soil, aquifer ground water and river water are examined using excitation–emission matrix fluorescence spectroscopy (EEM), in addition to chemical analysis. In the aquifer system studied the water table is ∼1.5 m below the land surface, suggesting that DOM and nutrient transfer would occur between the soil and groundwater. Nitrate levels in the ground water were ∼50 mg L−1 NO3-N. Soil DOM properties were measured in KCl extracts used to extract inorganic and organic N so that further information could be obtained regarding possible sources and properties of the DON and the biodegradability of the DOC pool. Within the soils tested, fulvic-like properties and the humification index (HI) were significantly (P < 0.05) higher in sandy soils suggesting that microbial accessibility to organic matter was greater. The applicability of assessing DOM characteristics in the different matrices were assessed and quantitative or qualitative comparisons made. Properties of DOM in both the soils and aquifer waters all showed a typical terrestrial source with principal component analysis (PCA) showing strong correlations between DOC, fulvic-like properties, the HI and tryptophan-like properties. A major finding was that the HI was generally higher in the groundwater, suggesting continued processing of DOM within the aquifer whilst qualitative comparisons showed the groundwater possessed a higher fluorescence index (FI). Whilst DON and the tyrosine-like proteins were correlated in the soil, the tryptophan-like proteins were strongly correlated to fulvic-like substances in both the soil and groundwater. This suggested that phenolic compounds were also being identified in this part of the EEM matrix, emphasising the need for additional compound analysis to fully understand the nature of DOM in these systems

Pesticides and metabolites in groundwater: examples from two major UK aquifers

Reducing the impact of anthropogenic pollution on groundwater bodies and ameliorating any deterioration of water quality is central to key legislative drivers such as the EU Water Framework Directive and the proposed daughter Directive relating to the protection of groundwater. Pesticide pollution has a direct impact on groundwater quality and an indirect impact on the associated aquatic ecosystems supported by groundwater. There is currently no legislative requirement to monitor pesticide metabolite concentrations in groundwater. Pesticide and metabolite results from two nationally important aquifers are presented, the Trassic Sandstone and the Chalk of Southern England. Aerobic microbial degradation of diuron in the soil can lead to the formation of three compounds; dichlorophenylmethyl urea (DCPMU), dichlorophenyl urea (DCPU) and dichloroanaline (DCA).Median diuron concentrations were significantly higher than each of the metabolites with outliers exceeding the PVC on at least one occasion. At nine sites in Kent, Southern England, (60%) metabolites were more prevalent than diuron. Both aquifers are an important source of water, locally supplying up to 80% of public drinking water. The sandstone site has a predominantly arable landuse with a potential diffuse source of pesticides although soakaways are possible point sources.The chalk site has a mixture of arable and industrial/urban landuse. A significant source has been from excessive applications of diuron (“over-spray”) on a number of public amenities. Data from both aquifers show that pesticide concentrations have a high degree of temporal variability. Elevated pesticide concentrations are associated with recharge events in both aquifer systems regardless of pesticide source terms. Pesticides from amenity use and diffuse agricultural sources both pose a threat to groundwater quality. Pesticide metabolites are present in significant concentrations in groundwaters. Systematic, long-term monitoring (5-10 years) is required to understand trends in groundwater quality

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 (0.06–39 μg/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

Molybdenum distributions and variability in drinking water from England and Wales

An investigation has been carried out of molybdenum in drinking water from a selection of public supply sources and domestic taps across England and Wales. This was to assess concentrations in relation to the World Health Organization (WHO) health-based value for Mo in drinking water of 70 μg/l and the decision to remove the element from the list of formal guideline values. Samples of treated drinking water from 12 water supply works were monitored up to four times over an 18-month period, and 24 domestic taps were sampled from three of their supply areas. Significant (p  0.05) were detected. Tap water samples collected from three towns (North Wales, the English Midlands, and South East England) supplied uniquely by upland reservoir water, river water, and Chalk groundwater, respectively, also showed a remarkable uniformity in Mo concentrations at each location. Within each, the variability was very small between houses (old and new), between pre-flush and post-flush samples, and between the tap water and respective source water samples. The results indicate that water distribution pipework has a negligible effect on supplied tap water Mo concentrations. The findings contrast with those for Cu, Zn, Ni, Pb, and Cd, which showed significant differences (p < 0.05) in concentrations between pre-flush and post-flush tap water samples. In two pre-flush samples, concentrations of Ni or Pb were above drinking water limits, although in all cases, post-flush waters were compliant. The high concentrations, most likely derived from metal pipework in the domestic distribution system, accumulated during overnight stagnation. The concentrations of Mo observed in British drinking water, in all cases less than 2 μg/l, were more than an order of magnitude below the WHO health-based value and suggest that Mo is unlikely to pose a significant health or water supply problem in England and Wales

Microplastics in groundwater : a literature review

Attention on microplastic (MP) pollution has increased greatly over the past decade, particularly in aquatic systems such as the marine and freshwater environments, where publications focus on both sources and fates of MPs, as well as the ecological/toxicological impacts of their presence on organisms within those environments. Literature exploring the extent to which MPs occur and interact with groundwater systems, however, remains limited. Within this limited body of research an even smaller subsect of publications focussing on specific studies with experimental designs exist. The potential significance of MP occurrence in groundwater from a perspective of risks to drinking water supply, groundwater dependant ecosystems and their toxicological potential to be enhanced by their ability to vector both organic and heavy metal pollutants, is slowly becoming clearer as new research emerges, but more research is needed on this topic. Using the following keyword search terms (groundwater + microplastics + FTIR) and search engines such as google scholar and Web of Science, this short literature review identified groundwater studies alongside wider literature on MPs. It explores the methodological designs, limitations of sampling, isolation and analytical techniques employed and identifies aspects for consideration in future groundwater research on this topic

Microplastics in UK groundwater and stygobites : protocols for sampling, analysis and pilot study results

A protocol for groundwater and stygobite microplastic (MP) sampling and analysis was developed and tested based on adapting established methods for drinking water sources. This study was undertaken to develop a protocol for groundwater that could be used for wider assessments of MP in groundwater sources in the UK and provide early evidence on the type and numbers of MP in groundwater sources and recommendations for future work on this topic. A total of 11 groundwater samples from 8 groundwater sources and a method blank were collected, processed and analysed for MP by Fourier Transform Infrared Spectroscopy (FTIR). Two stygobite samples and a method blank were also sampled and processed by FTIR. A total of nine MP compositions were analysed for by FTIR. Overall low numbers of MPs were detected in groundwaters, with the highest numbers being detected from pumped sources within the Thames gravels (up to 18 MPs) compared to the pumped Chalk (up to 5 MPs). After blank correction, a total of 40 MP particles were found across all samples using FTIR. A single polypropylene (PP) particle was found in the method blank. Overall, a very small proportion of the particles detected by FTIR were microplastics. Of those detected as MP the largest detected was 183 μm, 28% of particles were <50 μm, 78% <100 μm and 88% <150 μm. PP dominated the polymer composition of MPs found in samples collected from boreholes (80%), four other polymers were also detected including polyethylene (PE - 8%), polystyrene (PS - 5%) and acrylate, polycarbonates and artificial cellulose all ≤ 3%. No MP were detected above the method blank for stygobites samples. Two PP MPs were detected in the stygobite method blank and two PP MPs detected in one of the stygobite samples. The methodologies developed and tested are described in detail in this report and were adapted from existing methods previously used to sample treated drinking water sources and are highly suited to sampling pumped groundwater sources with low turbidity for MPs. The method was suitable for collecting large groundwaters samples and it was possible to filter up to 100 L in the field from the majority of sources within a relatively short time period (i.e. 1h). It would be possible to filter 2 or 3 times this volume in the field from many sites without the filter clogging, based on the small sub-sample used in this pilot study

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 1 km 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. 1.2 kt P/yr. 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

Phosphate dosing of mains water : novel approaches to water loss reduction through leakage detection and policy [abstract]

Detection and t racing of leakage in the environment are essential component s of water loss reduction strategies. Industry standard techniques for tracing leaks include analysis of chlorine and trihalomethane concentrations, but levels of these determinands can fall belo w detection limits due to their volatile nature 1 . Consequently additional tools to trace leakage in the environment are a useful step to move towards minimum losses

A field based method for pre-concentration of micro organics using solid phase extraction

British Geological Survey (BGS) have been researching micro-organic pollutants for many years in the UK (Gooddy et al 2004, Stuart et al 2012, White et al 2016) and overseas (Sorensen et al 2015). A hindrance to the research, especially overseas, has been the need to transport large volumes of water back to the laboratory and the worry of degradation during transportation prior to LCMS or GCMS analysis. The first step in the LCMS analytical procedure is the solid phase extraction of the micro-organic contaminants onto a small cartridge. This report details the field trial where by BGS, working in conjunction with NLS, carried out the pre-concentration step of sample processing in the field. NLS provided pre-conditioned sorbent Oasis® HLB cartridges supplied in sealed Corning centristar centrifuge tubes. Water samples were run through the cartridges by the field team using a small peristaltic pump prior to sending to NLS for semi-quantative broad screen LCMS analysis. To check the repeatability and the stability of this method the sorbed samples were analysed in duplicate and replicate analysis was carried out over set periods after storage for up to a month. The results from the duplicate replicates are compared to results from the original water sample analysed immediately after sampling. Laboratory and field equipment blanks were included in the trial to check for any contamination introduced by the sampling method and extraction process. Preliminary results demonstrate that for a large range of compounds, and different types of matrices, this method was able to preserve samples for up to a month. Once the procedure had been validated, it was used to investigate the occurrence of micro-pollutants in a rural groundwater, estuarine waters and a range of surface waters receiving treated sewerage outflows. The work was funded under the BGS Development Capabilities programme, and was also supported by the BGS Groundwater Science programme under the Groundwater Protection team. Analytical aspects of this work was undertaken in collaboration with Wayne Civil based at Star Cross National Science Laboratory (NLS)

Sampling and characterising groundwater nanoparticles in sub-oxic environments

Characterising nanoparticles is important for understanding physiochemical and biogeochemical processes occurring within groundwater bodies e.g. those impacted by the migration of leachates from waste storage sites as well as monitoring the use of engineered nanotechnology for pollution attenuation. While characterising nano-scale particles (both natural and engineered) within sub-oxic environments is a challenging task, it is critical for understanding pollution attenuation and migration within a number of different environments. The overall aim of this study was to develop a robust sampling and analytical methodology for characterising nanoparticles in sub-oxic environments using a range of complementary methods. This study has successfully sampled and characterised nano-scale particulate material in sub-oxic groundwaters within an alluvial floodplain aquifer impacted by a landfull plume. The integrity of the sample was maintained throughout the field and laboratory work to ensure that only nanoparticles representative of the sub-oxic environment were characterised. Nanoparticles from two pairs of nested boreholes were characterised by a number of state-of-the-art methods; atomic force microscopy (AFM), scanning electron microscopy (SEM), scanning transmisson electron microscopy (TEM) and field flow fractionation (FFF), to explore particle size distributions, morphology and surface chemistry. It is important to characterise nanoparticles in environmental contexts using multiple techniques as each method has its own benefits and limitations (Lead and Wilkinson 2006). As far as the authors are aware this is the first such study in the UK to isolate and characterise sub-oxic groundwater nanoparticles using these complimentary techniques. Groundwaters were found to have abundant iron and organic nanoparticles with diameters <30 nm. AFM results showed spherical nanoparticles with average diameters of ca 10 nm, while FFF with UV absorbance (254 nm) results indicated that smaller fulvic-like nanoparticles were present with average hydrodynamic diameters of ca. 1.5 nm. FFF with UV absorbance detection at 575 nm showed that another population of organic rich nanoparticles was present with larger hydrodynamic diameters (ca. 3 nm) in the groundwater at nest 26, but were not present in nest 28. These larger organic nanoparticles perhaps represent co-aggregated humic-like particles or another distinct type of organic matter. Scanning TEM analysis with energy-dispersive X-ray diffraction showed that Ca rich nanoparticles were present within the groundwater at a number of sites, and that P was associated with the surface of Fe rich particles in nest 28. Aeration of sub-oxic samples resulted in a dramatic shift in the nanoparticle size distribution. This was a result of the aggregation of smaller nanoparticles to form larger agglomerations with diameters typically >50-100 nm. This is analogous to processes that occur during groundwater aeration for water treatment, and mixing of anaerobic and aerobic environmental waters, e.g. during rapid recharge events, flooding, hyporheic zone mixing, waste water treatment and waste water inputs to surface waters. The techniques developed in this study have potential wider applications for understanding the occurrence and fate of natural and anthropogenic (engineered) nanoparticles in sub-oxic conditions, such as the fate of nanoparticles injected for pollution attenuation, those found below landfill sites, within waste water treatment works and the hyporheic zone which are all important redox hot-spots for pollution attenuation and biological activity