Healthy rivers are a powerful ally in mitigating the effects of climate change; they can protect communities from flood and drought events, and bolster ecosystem and biodiversity resilience (The Rivers Trust, 2024). However, our surface waters (rivers, lakes, estuaries and coastal waters) have historically been used as disposal routes for human, agricultural and industrial wastes, harming water quality. This article explores some of the pressures on UK water resources and, importantly, outlines ways in which we can maintain and enhance surface- and groundwater quality under a changing climate. Different point and non-point water pollution sources - including human, agricultural and wild animals - are explored and methods for monitoring, managing and mitigating water quality discussed. This includes nature-based solutions aimed at reducing surface water run-off during high-intensity rainfall events, such as leaky wooden dams and Sustainable Urban Drainage Schemes (SuDS). The article concludes with recommendations of what needs to happen in order to future-proof UK water resources from the worst effects of climate change.

This study investigated the spatio-temporal variability of microplastics (MPs) in the sediments of the River Thames (UK) catchment over 30 months (July 2019 - Dec 2021). The average MP concentration was 61 items kg-1 d.w., with fragments <1 mm being dominant and polyethylene (PE) the most common polymer. Adjacent land use influenced MP concentrations and types, with industrial sites showing particularly high levels and a prevalence of small beads and industrial polymers. MP concentrations generally decreased after higher winter flows, likely due to sediment rearrangement or winnowing. This study describes the seasonal concentrations and characteristics of MPs present in sediment from the River Thames catchment, and attempts to identify their likely origin. Further, the study provides new insights into the mobility and fate of MPs in riverine settings under varying flow conditions, which is vital given the predicted increases in flooding under various global heating scenarios.

Inappropriate or poorly constructed sanitation is becoming one of the major challenges confronting rapidly urbanizing cities in the global south such as Ethiopia. This study was carried out to understand the sanitation and solid waste management challenges present in the city of Mekelle, in order to identify opportunities for sustainable faecal and solid waste management. This involved conducting: (a) a review of previous studies, (b) field and laboratory investigations (water and faecal sludge quality), (c) assessments of the status of existing sanitation services, (d) analysis of hydrogeological connectivity between septic tanks and surface & ground waters, (e) participatory assessments of solid waste management issues, and (f) identification of good practice in terms of sustainable waste management. Our findings revealed that the water supply coverage in 2021 only reached 67.3% of the population with water mainly from treated groundwater wells and surface water (dam); with some communities using untreated water from other sources. Though 65.8% of the households were found to have access to toilet facilities, sanitation remains a major challenge due to multiple inter-related factors: (i) open defecation, (ii) dumping of liquid and solid waste into surface waters, and (iii) lack of maintenance of the municipal faecal sludge treatment facilities. Our study highlighted contamination pathways likely to be impacting shallow wells, streams/rivers and springs in the city. In order to reduce water consumption and promote sustainable circular waste management the following emerging practices should be supported and up-scaled: urban agriculture, green space development, waste separation at source, organic waste reuse, and support for small businesses involved in waste management. If the full benefits of sustainable waste management are to be recognized in Mekelle, then appropriate policies, strategies, and regulatory frameworks need to be developed and implemented, along with governmental support for capacity building and local innovation.

Sewage pollution leads to the contamination of bivalve shellfish by pathogenic microorganisms. Bacterial indicators support the management of risks associated with the consumption of shellfish; however, they often fail to indicate adequately the potential hazard to human health posed by certain human enteric viruses. Bacteriophages have been proposed as alternative indicators that may more effectively predict the presence of enteric viral pathogens. This study explored the relationships between bacterial indicators (Escherichia coli (E. coli), faecal coliforms (FC) and intestinal enterococci (IE)), phages (somatic (SOMPH), F-specific RNA (F + PH) and human-specific Bacteroides GB-124 phages (GB124PH)) and Norovirus (NoV) (GI/GII) in mussels (Mytilus edulis) and their overlying waters. The bioaccumulation of these indicators and Norovirus in shellfish matrices (e.g., flesh, digestive gland) was investigated bimonthly over a 12-month period in an English estuary. The findings revealed a marked seasonality in the distribution of all organisms, with the highest levels occurring during the autumn/winter months. The levels of all phages in shellfish and their overlying waters correlated better with the levels of Norovirus than with those of bacterial indicators. Somatic coliphages were the indicator that exhibited the strongest correlations with NoV (rho = 0.929). This study suggests that relatively low-cost culture-based phage enumeration appears to offer a more accurate indication of the likely presence of Norovirus in mussels than traditional bacterial indicators.

Rivers form major conduits for land-derived plastic waste, with the annual emission of plastics to the world’s oceans currently being quantified at as much as 2.7 million metric tons. In particular, riverbed sediments have been found to retain high levels of microplastics (plastics <5 mm in size) and multiple studies reported microplastic concentrations in the sediments to exceed those in the water column by as much as 600,000 times. Emerging evidence suggests that high flows may remobilise some of the sedimentary microplastic pool, resulting in high microplastic loads entering the adjacent seas following flood events. However, the transport mechanisms that microplastics undergo in river settings remain poorly understood. In this study, we investigated spatio-temporal variations in the microplastic contamination within river bed sediments in the R. Thames (UK) catchment. Sediment samples were taken on a seasonal basis over 3 years (2019-2021) from 12 sampling sites (classified as rural, urban and industrial) located on the main R. Thames and 8 of its tributaries. Microplastics were extracted from sediment using density flotation, then visually counted and investigated using a combination of ATR-FTIR and µATR-FTIR (Attenuated Total Reflectance - Fourier Transform Infrared Spectroscopy). Additional SEM analysis was carried out to describe the morphology (degradational patterns/occurrence of biofouling) of extracted microplastics. Microplastics were present in most sediment samples (85%), with fragments being the dominant shape (92% across all seasons), followed by beads/pellets (5%) and fibres (3%). Microplastic levels varied on a seasonal basis (0 - 4,200 MP·kg-1 range), increasing in the summer months and decreasing in the winter by up to 89%. This suggests the occurrence of microplastic accumulation in the summer low-flow conditions followed by subsequent flushing of microplastics as a result of higher winter flows. Inter-site variations in microplastic levels were evident in the summer months, with concentrations increasing in the order of industrial>urban>rural. Microplastics were also more abundant at inner river banks and near point sources (e.g. effluent outlets). In contrast, such inter- and intra-site variations were less clear in the winter. Urban and rural samples were dominated by fragments (96% on average) irrespective of season, with most items made out of polyethylene (PE), but also containing thermoplastic elastomers found in road marking paints (e.g. ethylene vinyl acetate (EVA), polyamide (PA)). Although samples taken from industrial locations were also dominated by fragments (84%), they contained higher numbers of microbeads and industrial pellets (12%) composed of polymers widely used for industrial applications (e.g. poly(methyl methacrylate) (PMMA) used as Perspex glass, poly(diallyl phthalate) used in the processing of thermosetting plastics and resins, or poly(1,4-butylene terephthalate) (PBT) used for insulation purposes in the electrical industry). Our study reveals a multitude of microplastic sources contributing to the pollution of the R. Thames catchment and confirms the existence of a strong seasonal pattern in microplastic deposition within riverbeds, suggesting a need to account for this process in the global models of microplastic export from land to sea.

The influence of landscapes – topography, soil, vegetation, geology – on water quality is an inherent part of the global water cycle. Land use has adverse impacts for example when soils are exposed, significant quantities of pollutants are released (including anthropogenic materials added to those naturally present), or pollutants are added directly to the water environment.Those impacts range from industrial development to farming and urbanisation. Whilst inefficient polluting industrial effluents are still tolerated in some countries, and poorly treated sewage globally remains a huge challenge for sanitation and public health, as well as the water environment, diffuse pollution is relatively poorly recognised or understood. The operator of a sewage or trade effluent treatment plant is consciously discharging effluent to the local river. But a farmer is simply growing crops or farming livestock, a city commuter driving to work is unlikely to be thinking how brake pad wear has released copper to the water (and air) environment and hydrocarbons and particulates too; no one is intending to cause pollution of the water environment. The same applies to industrial chemists creating fire-proofing chemicals, solvents, fertilisers, pesticides, cosmetics and many more substances which contaminate the environment. Understanding and ultimately minimising diffuse pollution is in that sense the science of unintended consequences. And the consequences can be severe, for water resources and ecosystems. It's a global problem.This book comprises 18 papers from experts around the globe, presenting evidence from tropical as well as temperate regions, and rural as well as urban land use challenges. The book explores the nature of diffuse pollution and exemplifies the issues at various scales, from high-level national overviews to particular catchment and pollutant issues.By contrast, natural or semi-natural forest cover has long been recognised as safeguarding water quality in reservoirs (examples from Australia to Thailand and UK). The final chapter looks at how landscapes generally, can be designed to minimise pollution risks from particular land-uses, arguing for a more widespread catchment approach to water-aware landscape design, allied with flood risk resilience, place-making for people, and biodiversity opportunities too.ISBN: 9781789061116 (Paperback)ISBN: 9781789061123 (eBook)ISBN: 9781789061130 (ePub)

Phages, such as those infecting Bacteroides spp., have been proven to be reliable indicators of human fecal contamination in microbial source tracking (MST) studies, and the efficacy of these MST markers found to vary geographically. This study reports the application and evaluation of candidate MST methods (phages infecting previously isolated B. fragilis strain GB-124, newly isolated Bacteroides strains (K10, K29, and K33) and recently isolated Kluyvera intermedia strain ASH-08), along with non-source specific somatic coliphages (SOMCPH infecting strain WG-5) and indicator bacteria (Escherichia coli) for identifying fecal contamination pathways in Kolkata, India. Source specificity of the phage-based methods was first tested using 60 known non-human fecal samples from common animals, before being evaluated with 56 known human samples (municipal sewage) collected during both the rainy and dry season. SOMCPH were present in 40-90% of samples from different animal species and in 100% of sewage samples. Phages infecting Bacteroides strain GB-124 were not detected from the majority (95%) of animal samples (except in three porcine samples) and were present in 93 and 71% of the sewage samples in the rainy and dry season (Mean = 1.42 and 1.83 log10PFU/100mL, respectively), though at lower levels than SOMCPH (Mean = 3.27 and 3.02 log10PFU/100mL, respectively). Phages infecting strain ASH-08 were detected in 89 and 96% of the sewage samples in the rainy and dry season, respectively, but were also present in all animal samples tested (except goats). Strains K10, K29, and K30 were not found to be useful MST markers due to low levels of phages and/or co-presence in non-human sources. GB-124 and SOMCPH were subsequently deployed within two low-income neighborhoods to determine the levels and origin of fecal contamination in 110 environmental samples. E. coli, SOMCPH, and phages of GB-124 were detected in 68, 42, and 28% of the samples, respectively. Analyses of 166 wastewater samples from shared community toilets and 21 samples from sewage pumping stations from the same districts showed that SOMCPH were present in 100% and GB-124 phages in 31% of shared toilet samples (Median = 5.59 and <1 log10 PFU/100 mL, respectively), and both SOMCPH and GB-124 phages were detected in 95% of pumping station samples (Median = 5.82 and 4.04 log10 PFU/100 mL, respectively). Our findings suggest that GB-124 and SOMCPH have utility as low-cost fecal indicator tools which can facilitate environmental surveillance of enteric organisms, elucidate human and non-human fecal exposure pathways, and inform interventions to mitigate exposure to fecal contamination in the residential environment of Kolkata, India.

Water deficit, exacerbated by global population increases and climate change, necessitates the investigation of alternative non-traditional water sources to augment existing supplies. Indirect potable reuse (IPR) represents a promising alternative water source in water-stressed regions. Of high concern is the presence of pathogenic microorganisms in wastewater, such as enteric viruses, protozoa and bacteria. Therefore, a greater understanding of the potential impact to human health is required. The aim of this research was to use a quantitative microbial risk assessment (QMRA) approach to calculate the probability of potential pathogen infection risk to the public in surface waters used for a range of recreational activities under scenarios: 1) existing de facto wastewater reuse conditions; 2) after augmentation with conventionally treated wastewater; and 3) after augmentation with reclaimed wastewater from proposed IPR schemes.

Determining the source of fecal contamination in a water body is important for the application of appropriate remediation measures. However, it has been suggested in the extant literature that this can best be achieved using a 'toolbox' of molecular- and culture-based methods. In response, this study deployed three indicators (Escherichia coli (EC), intestinal enterococci (IE) and somatic coliphages (SC)), one culture-dependent human marker (Bacteroides (GB-124) bacteriophage) and five culture-independent markers (human adenovirus (HAdV), human (HMMit), cattle (CWMit), pig (PGMit) and poultry (PLMit) mitochondrial DNA markers (mtDNA)) within the River Tagus catchment (n = 105). Water samples were collected monthly over a 13-month sampling campaign at four sites (impacted by significant specific human and non-human inputs and influenced by differing degrees of marine and freshwater mixing) to determine the dominant fecal inputs and assess geographical, temporal, and meteorological (precipitation, UV, temperature) fluctuations. Our results revealed that all sampling sites were not only highly impacted by fecal contamination but that this contamination originated from human and from a range of agricultural animal sources. HMMit was present in a higher percentage (83%) and concentration (4.20 log GC/100 mL) than HAdV (32%, 2.23 log GC/100 mL) and GB-124 bacteriophage with the latter being detected once. Animal mtDNA markers were detected, with CWMit found in 73% of samples with mean concentration of 3.74 log GC/100 mL. Correlation was found between concentrations of fecal indicators (EC, IE and SC), CWMit and season. Levels of CWMit were found to be related to physico-chemical parameters, such as temperature and UV radiation, possibly as a result of the increasing presence of livestock outside in warmer months. This study provides the first evaluation of such a source-associated 'toolbox' for monitoring surface water in Portugal, and the conclusions may inform future implementation of surveillance and remediation strategies for improving water quality.

It is currently predicted that rivers deliver as much as 80% of plastic waste into the marine environment, including microplastics (MP) <5 mm in size. Yet, the transfer mechanisms of MP in river systems remain poorly understood. While high flow events are thought to flush more microplastics into marine waters, their overall load may depend on factors such as river morphology, land-use, or local MP sources. Microplastic concentrations were monitored on a seasonal basis (summer 2019 - winter 2020/2021) across 13 sites located across the R. Thames catchment, UK. Sites were selected to include rural, urban and industrial locations with different hydrological characteristics and proximities to potential MP inputs (e.g. sewage or industrial effluents). At each site, bed sediment samples were manually extracted (n=55 samples), and surface water samples collected in 5 L clean polyethylene bottles (n=22 samples) and using a 500-µm plankton net (n=12 samples). Microplastics were extracted from sediment and plankton net samples using density flotation, whilst bulk water samples were filtered with no prior extraction steps. All samples were visually inspected under a stereomicroscope and their morphology recorded. The chemical composition is to be further investigated using µFTIR as part of future research. Sediment and water samples likely contained MP from different sources (e.g. in-situ breakdown of plastic litter, sewage effluent), which was reflected in the varying MP shapes and loads observed at the study sites. Microplastic levels ranged from -1 in sediments, -1 in bulk water samples and -3 in plankton net samples and were highest at sites downstream of known sewage inputs. There was also a clear variation in particle shapes and levels with respect to site, with fibres and fragments representing the dominant MP type present along urban river stretches, and microbeads most abundant near industrial locations. Microplastic levels varied on a temporal basis in both surface waters and sediments. Increasing river discharge generally had a diluting effect on MP levels observed in the water column (mean levels of 5 MP·L-1 and 2 MP·L-1 in summer 2019 and winter 2020, respectively). Mean microplastic levels in sediments also decreased from 15.1 MP·100 g-1 in the summer to 9.4 MP·100 g-1 in the winter, although some local increases in microplastic pollution were observed during high flow period, particularly at sites situated in close proximity to reported sewage discharges (e.g. from Combined Sewer Overflows). This study is one of the first few to report spatio-temporal variations in microplastic contamination of both river water and sediments. Our early findings suggest that variability in MP levels and composition in both media may correspond to local pollution sources, and plastic particles could be released from surface sediments during periods of increased precipitation, even in the absence of flooding. Understanding such patterns in MP flux will be crucial to accurately model plastic loads from terrestrial to marine environment and implement effective mitigation measures.

Microplastics (synthetic polymer particles <5 mm in size) are currently of major research interest due to their ubiquity and persistence in the environment, as well as their alleged adverse impact on aquatic biota. Although most research to date has targeted microplastic pollution within the marine environment, riverine pathways deliver up to 80 % of plastic debris into the seas and oceans. The transfer mechanisms of microplastics through river systems, however, remain largely understudied. A number of authors have attempted to assess the fate of plastic particles in river systems, often reporting contrasting findings. This is mainly due to the heterogeneity of river systems combined with a lack of standardisation between the sampling protocols adopted. Here, we summarise the current state of knowledge on the riverine transport pathways of plastic debris and examine the typical spatio-temporal patterns in microplastic occurrence in river waters and sediments. Furthermore, we critically evaluate the commonly used sampling techniques and provide guidelines for unified field study design. Lastly, we identify issues that warrant further research and propose recommendations for future studies to improve our understanding of microplastics in the riverine environment. Standardisation of sampling methods will be vital for the development of a more reliable microplastic monitoring strategy and, on a longer timescale, the implementation of appropriate mitigation measures.

BackgroundEmerging evidence suggests close domestic proximity of livestock and humans may lead to microbiological contamination of hands, objects, food and water supplies within domestic environments, adversely impacting public health. However, evidence quantifying the relationship between livestock, domestic animals, humans and microbiological contamination of household stored water remains limited.AimThis longitudinal study aimed to examine the relationship between domestic contact with livestock and domestic animals on microbiological contamination of household Point-of-Use (POU) stored drinking water in rural Kenya and assess the influence of choice of faecal indicator on such associations.MethodologyA survey was performed in 234 households in Siaya county, Kenya, to observe presence of livestock (cattle, goats, poultry) and domestic animals (cats, dogs) in household compounds, alongside other risk factors for contamination of POU stored drinking water such as sanitation, storage conditions and hygiene practices. Samples from water sources (e.g. piped, spring/wells, boreholes, surface and rainwater) and from POU storage containers were tested for E. coli and intestinal enterococci. Livestock-related risk factors for water contamination were examined through multinomial regression, controlling for confounders.ResultsRainwater was the main POU water source and was found to be highly susceptible to contamination. Multivariate analysis showed greater risk of gross (>100 CFU/100 mL) water contamination (with E. coli) for households where goats were observed, and/or where poultry roosted in proximity to stored household water (relative risk RR = 2.71; p = 0.001 and RR = 2.02; p = 0.012 respectively). Presence of a poultry coop was also associated with elevated intestinal enterococci densities (RR = 4.46; p = 0.001). Associations between contamination and livestock risk factors were thus similar for both bacteria groups, but E. coli counts declined more rapidly following collection from surface waters than enterococci counts (p = 0.024).ConclusionThe presence of livestock (particularly goats) and poultry within household compounds increases POU water contamination risk, suggesting the need for improved interventions to address cross-contamination within rural domestic settings. Within Siaya county, more effective community education is needed to raise awareness of POU water quality protection, particularly of rainwater.

Bacteroides spp. are part of the human intestinal microbiota but can under some circumstances become clinical pathogens. Phages are a potentially valuable therapeutic treatment option for many pathogens, but phage therapy for pathogenic Bacteroides spp. including Bacteroides fragilis is currently limited to three genome-sequenced phages. Here we describe the isolation from sewage wastewater and genome of a lytic phage, vB_BfrS_23, that infects and kills B. fragilis strain GB124. Transmission electron microscopy identified this phage as a member of the Siphoviridae family. The phage is stable when held at temperatures of 4 and 60°C for 1 h. It has a very narrow host range, only infecting one host from a panel of B. fragilis strains (n = 8). Whole-genome sequence analyses of vB_BfrS_23 determined it is double-stranded DNA phage and is circularly permuted, with a genome of 48,011 bp. The genome encodes 73 putative open reading frames. We also sequenced the host bacterium, B. fragilis GB124 (5.1 Mb), which has two plasmids of 43,923 and 4,138 bp. Although this phage is host specific, its isolation together with the detailed characterization of the host B. fragilis GB124 featured in this study represent a useful starting point from which to facilitate the future development of highly specific therapeutic agents. Furthermore, the phage could be a novel tool in determining water (and water reuse) treatment efficacy, and for identifying human fecal transmission pathways within contaminated environmental waters and foodstuffs.

Water deficit, exacerbated by global population increases and climate change, necessitates the investigation of alternative non-traditional water sources to augment existing supplies. Indirect potable reuse (IPR) represents a promising alternative water source in water-stressed regions. Of high concern is the presence of pathogenic microorganisms in wastewater, such as enteric viruses, protozoa and bacteria. Therefore, a greater understanding of the potential impact to human health is required. The aim of this research was to use a quantitative microbial risk assessment (QMRA) approach to calculate the probability of potential pathogen infection risk to the public in surface waters used for a range of recreational activities under scenarios: 1) existing de facto wastewater reuse conditions; 2) after augmentation with conventionally treated wastewater; and 3) after augmentation with reclaimed wastewater from proposed IPR schemes. Forty-four 31 l samples were collected from river sites and a coastal wastewater treatment works from July 2016-May 2017. Concentrations of faecal indicator organisms (enterococci, faecal coliforms, somatic coliphages and Bacteroides phages) determined using culture-based approaches and selected pathogens (adenovirus, Salmonella and Cryptosporidium) determined using molecular approaches (qPCR) were used to inform QMRA. The mean probability of infection from adenovirus under de facto conditions was high (>0.90) for all recreational activities, per single event. The risk of adenovirus and Cryptosporidium infection increased under augmentation scenario (2) (mean probability 0.95-1.00 and 0.01-0.06 per single event, respectively). Adenovirus and Cryptosporidium infection risk decreased under reclaimed water augmentation scenario (3) (mean probability <0.79, excluding swimming, which remained 1.00 and <0.01 per single event, respectively). Pathogen reduction after reclaimed water augmentation in surface waters impacted by de facto reuse, provides important evidence for alternative water supply option selection. As such, this evidence may inform water managers and the public of the potential benefits of IPR and improve acceptance of such practices in the future.

Microplastic burden in aquatic environments is now recognised as a potential threat to human and environmental health. Although microplastic transfers to the ocean from the terrestrial river network contributes up to 90% of the plastics in the oceans the factors controlling that transfer remain largely unconstrained. In rivers microplastics are stored within sediment beds and whilst they are there both the microplastic particles and the sediment grains can become colonised by biofilms. Biofilm growth on river sediments has been shown to increase a particles resistance to entrainment but the effects of such biostabilisation on microplastic flux has not yet been considered. This is despite the fact that biofilm growth can change the buoyancy, surface characteristics and aggregation properties of the plastic particles such as to cause them to be deposited rather than transported and hence increase their residence time. In order to quantify biostabilisation processes on microplastic flux a two stage experimental programme was run. During the first stage, bricks were submerged in a gravel-bed stream and biofilms allowed to colonise the bricks for 4 weeks. The biofilm covered bricks were then extracted and placed within a re-circulating ‘incubator’ flume which had been divided into 9 smaller channels. Within each of the 9 channels either a uniform sand, uniform gravel or a bimodal gravel mix were placed in Perspex boxes in the flume channels. Each sediment type was seeded with either high density PVC microplastic nurdles (D50 of 3mm, density of 1.33g/cm3) or polyester fibres (5 mm long, 0.5-1 mm wide, density of 1.38 g cm3), both at a concentration of 1%. Blanks were also run where the sediment mixtures did not contain any micropalstics. The flume was left to run with representative day/night cycles of lighting in order to let the biofilms colonise the test sediments for either 0 (control), 2, 4 or 6 weeks. At the end of the chosen colonisation periods the persepx boxes containing the sediment were removed from the incubator flume and placed within a glass-sided, flow-recirculating flume (8.2m x 0.6m x 0.5m); this constituted the second stage of the experiment. During this stage the samples were exposed to a series of flow steps of increasing discharge designed to establish the entrainment threshold of the D50 sediment grains. Entrainment thresholds were calculated for each of the growth stages such as to establish the effect of biostabilisation on sediment and microplastic flux. Bedload and microplastic transport rates were also measured at every flow step to establish biostabilisation effects on overall fluxes. Finally, photographs of the sediment surface were taken at each flow step in order to estimate the percentage loss of biofilm from the surface. Discussion concentrates on linking the changes in the degree of biofilm colonisation with the entrainment threshold of the sediment and the links between biofilm colonisation and the character of the bedload and microplastic flux. The outcome of this research is pertinent to developing understanding surrounding the role biostabilisation has to play in the residence times of microplastics within fluvial systems.

Up to 80% of the plastics in the oceans are believed to have been transferred from river networks. Microplastic contamination of river sediments has been found to be pervasive at the global scale and responsive to periods of flooding. However, the physical controls governing the storage, remobilization and pathways of transfer in fluvial sediments are unknown. This means it is not currently possible to determine the risks posed by microplastics retained within the world’s river systems. This problem will be further exacerbated in the future given projected changes to global flood risk and an increased likelihood of fluvial flooding. Using controlled flume experiments we show that the evolution of the sediment bed surface and the flood wave characteristics controls the transition from rivers being ‘sinks’ to ‘sources’ of microplastics under flood conditions. By linking bed surface evolution with microplastic transport characteristics we show that similarities exist between granular transport phenomena and the behavior, and hence predictability, of microplastic entrainment during floods. Our findings are significant as they suggest that microplastic release from sediment beds can be managed by altering the timing and magnitude of releases in flow managed systems. As such it may be possible to remediate or remove legacy microplastics in future.

Containment, safe handling and disinfection of human excreta in cholera treatment centers (CTC) are key to preventing the onward spread of the disease. This study compared the efficacy of three chlorine-based approaches at concentrations of 0.5%, 1%, and 2% and one hydrated lime-based (Ca(OH)2 at 30% w:v) approach. Experiments followed existing Médecins Sans Frontières (MSF) cholera guidelines. Three simulated human excreta matrices consisting of either raw municipal wastewater (4.5 liters), or raw municipal wastewater plus 1%, or 20% faecal sludge (w:v), were treated in 14 liter Oxfam® buckets containing 125 mL of chlorine solution or hydrated lime suspension. Bacterial indicators (faecal coliforms (FC) and intestinal enterococci (IE)) and viral indicator (somatic coliphages (SOMPH)) were used to determine treatment efficacy following contact times of 10, 30 and 60min. Results showed that efficacy improved as chlorine concentrations increased. No statistical differences were observed with respect to the various contact times. Overall median log removal for 0.5% chlorine were: FC (1.66), IE (1.41); SOMPH (1.28); for 1% chlorine: FC (1.98), IE (1.82); SOMPH (1.79); and for 2% chlorine: FC (2.88), IE (2.60), SOMPH (2.38). Hydrated lime (30%) provided the greatest overall log removal for bacterial indicators (FC (3.93) and IE (3.50), but not for the viral indicator, SOMPH (1.67)). These findings suggest that the use of 30% hydrated lime suspensions or 2% chlorine solutions may offer a simple public health protection measure for the containment, safe handling, and disinfection of human excreta during humanitarian emergencies.

Microplastic burden in aquatic environments is now recognised as one of the largest threats to human and environmental health of the 21st century. However, although microplastic transfers to the ocean from the terrestrial river network contributes up to 90% of the plastics in the oceans the pathways and mechanisms of transfers are largely unconstrained. Within river channels it is the sediment bed that plays a vital role in mediating transfers since microplastics are buried and stored within the sediments on the river bed. During flood events, erosion of the bed surface means microplastics buried within the bed are exchanged with the surface across the active layer and are potentially re-mobilised. However, we have very little grasp on the magnitudes of floods required to mobilise the sediment bed such as to re-mobilise the microplastics and hence very little understanding of microplastic recontamination risk.