Display omitted
•Mismatch between field and laboratory studies in plastic types and end-points assessed.•Fibres are most prevalent in field studies while particles dominate laboratory studies.•There ...is a requirement to shift towards a harmonised approach to effects testing.•Sampling standards and parameter selection are suggested for field and laboratory studies.•Principal toxicity endpoints recommended for main trophic levels to aid data integration.
Current understanding of nano- and microplastic movement, propagation and potential effects on biota in freshwater environments is developing rapidly. Still, there are significant disconnects in the integration of knowledge derived from laboratory and field studies. This review synthesises the current understanding of nano- and microplastic impacts on freshwater biota from field studies and combines it with the more mechanistic insights derived from laboratory studies. Several discrepancies between the field and laboratory studies, impacting progress in process understanding, were identified including that the most prevalent plastic morphologies found in the field (fibres) are not those used in most of the laboratory studies (particles). Solutions to overcome these disparities are proposed to aid comparability of future studies. For example, environmental sampling and separation of biota into its constituents is encouraged when conducting field studies to map microplastic uptake preferences. In laboratory studies, recommendations include performing toxicity studies to systematically test possible factors affecting toxicity of nano- and microplastics, including morphology, chemical makeup (e.g., additives) and effects of plastic size. Consideration should be given to environmentally relevant exposure factors in laboratory studies, such as realistic exposure medium and effects of plastic ageing. Furthermore, based on this comprehensive review recommendations of principal toxicity endpoints for each of the main trophic levels (microbes, primary producers, primary consumers and secondary consumers) that should be reported to make toxicity studies more comparable in the future are given.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Given the persistence of microplastics in the environment and their potential toxicity to ecosystems, understanding of likely microplastic accumulation ‘hotspots’ in rivers is urgently needed. To ...contribute to this challenge, this paper reports results of a microplastic survey from a heavily urbanised catchment, the River Tame and four of its tributaries, which flows through the city of Birmingham, UK. All sediment sampled was found to contain microplastics with an average abundance of 165 particles kg−1. While urban areas generally have a greater abundance of microplastics as compared with rural, there is no simple relationship between microplastic numbers and population density or proximity to wastewater treatment sites. The greatest change in microplastic abundance was due to the presence of a lake along the course of the River Tame—i.e., flow velocities are reduced on entering the lake, which promotes the deposition of fine sediment and potentially microplastics. This suggests that the greatest concentrations of microplastics will not be found in-channel but rather on the floodplain and other low velocity environments such as meander cutoffs. We also identified a new mechanism of microplastic fixation in freshwater environments through ecological engineers, specifically caddisflies, that incorporated microplastics into their casing. These results highlight the need to explore further hydrodynamic and ecological impacts on microplastics fate and transport in rivers.
The identification of microplastic hotspots is vital to our long-term understanding of their environmental fate and distribution. Although case studies have increased globally, sampling campaigns are ...often restricted geographically, with poor spatial resolution. Here, we use citizen science to increase our geographical reach, which improved our understanding of microplastic distribution in estuarine and beach sediment along the south-west coast of England. Hotspots (>700 particles per kg dry sediment) were identified on the Scilly Islands and in close proximity to major metropolitan hubs (i.e. Falmouth and Plymouth). Particles extracted from the Scilly Island sites were composed of polyethylene and polypropylene. With low population density on the Isle of Scilly, hotspots may suggest that microplastics originate from distant sources, while Falmouth and Plymouth, on mainland UK, are locally supplied. This information supports the design of future campaigns and targeted mitigation strategies in areas of highest concentrations.
Display omitted
•Hotspots (>700 particles per kg dry sediment) were detected on the Scilly Islands.•Microplastic hotspots were also associated with major metropolitan hubs.•Distant and local sources were discussed.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Microplastics are ubiquitous in the environment, with high concentrations being detected now also in river corridors and sediments globally. Whilst there has been increasing field evidence of ...microplastics accumulation in the guts and tissues of freshwater and marine aquatic species, the uptake mechanisms of microplastics into freshwater food webs, and the physical and geological controls on pathway-specific exposures to microplastics, are not well understood. This knowledge gap is hampering the assessment of exposure risks, and potential ecotoxicological and public health impacts from microplastics.
This review provides a comprehensive synthesis of key research challenges in analysing the environmental fate and transport of microplastics in freshwater ecosystems, including the identification of hydrological, sedimentological and particle property controls on microplastic accumulation in aquatic ecosystems. This mechanistic analysis outlines the dominant pathways for exposure to microplastics in freshwater ecosystems and identifies potentially critical uptake mechanisms and entry pathways for microplastics and associated contaminants into aquatic food webs as well as their risk to accumulate and biomagnify.
We identify seven key research challenges that, if overcome, will permit the advancement beyond current conceptual limitations and provide the mechanistic process understanding required to assess microplastic exposure, uptake, hazard, and overall risk to aquatic systems and humans, and provide key insights into the priority impact pathways in freshwater ecosystems to support environmental management decision making.
Display omitted
•Environmental risks are affected by pathway-specific exposures to microplastics.•Particle properties and flow dynamics control exposure to microplastics.•We identify uptake mechanisms and microplastic entry points into aquatic food webs.•Ecotoxicological impacts are controlled by fate and transport of microplastics.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Paired catchment approach for microplastic loading under contrasting land cover.•Microplastic concentration increases with higher degree of urbanization.•Water diversions causes dispersal of ...microplastics back into wider catchment area.•Models on microplastic fluxes need to account for water management.
While microplastic inputs into rivers are assumed to be correlated with anthropogenic activities and to accumulate towards the sea, the impacts of water management on downstream microplastic transport are largely unexplored. A comparative study of microplastic abundance in Boulder Creek (BC), and its less urbanized tributary South Boulder Creek (SBC), (Colorado USA), characterized the downstream evolution of microplastics in surface water and sediments, evaluating the effects of urbanization and flow diversions on the up-to-downstream profiles of microplastic concentrations and loads. Water and sediment samples were collected from 21 locations along both rivers and microplastic properties determined by fluorescence microscopy and Raman spectroscopy. The degree of catchment urbanization affected microplastic patterns, as evidenced by greater water and sediment concentrations and loads in BC than the less densely populated SBC, which is consistent with the differences in the degree of urbanization between both catchments. Microplastic removal through flow diversions was quantified, showing that water diversions removed over 500 microplastic particles per second from the river, and caused stepwise reductions of downstream loads at diversion points. This redistribution of microplastics back into the catchment should be considered in large scale models quantifying plastic fate and transport to the oceans.
Display omitted
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Beyond simple identification of either the presence or absence of microplastic particles in the environment, quantitative accuracy has been criticised as being neither comparable nor reproducible. ...This is, in part, due to difficulties in the identification of synthetic particles amidst naturally occurring organic and inorganic components. The fluorescent stain Nile red has been proposed as a tool to overcome this issue, but to date, has been used without consideration of polymer specific fluorescent variability. The aim of this study was to evaluate the efficacy of Nile red for microplastic detection by systematically investigating what drives variations in particle pixel brightness (PPB). The results showed that PPB varied between polymer type, shape, size, colour and by staining procedure. Sand, an inorganic component of the sample matrix does not fluoresce when stained with Nile red. In contrast the organic components, wood and chitin, fluoresce between 1.40 and 12 arbitrary units (a.u.) and 32 and 74 a.u. after Nile red staining, respectively. These data informed the use of a PPB threshold limit of 100 a.u., which improved the detection of EPS, HDPE, PP and PA-6 from the 6 polymers tested and reduced analysis time by 30–58% compared to unstained samples. Conversely, as with traditional illumination, PET and PVC were not accurately estimated using this approach. This study shows that picking a threshold limit is not arbitrary but rather must be informed by polymer specific fluorescent variability and matrix considerations. This is an essential step needed to facilitate comparability and reproducibility between individual studies.
Display omitted
•Nile red improved the detection of EPS, HDPE, PP and PA-6.•PET and rigid-PVC were not accurately estimated using this approach.•Plasticised-PVC did fluoresce above a detectable limit.•Additives may alter detectability of microplastics stained with Nile red.•Potential false positives were not detected above the chosen threshold.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Rivers can adjust to natural and anthropogenic stresses through changes in flow regime and sediment dynamics. Flow regulation due to dam construction can modify sediment transport processes, causing ...morphological adjustments and changes in conveyance capacity. In this study, we explored morphological adjustments along a 46 km segment of the Yamuna River in the Himalayan foothills from Dakpathar Barrage to Hathni Kund Barrage using a combination of remote sensing approaches. The cloud computing platform Google Earth Engine (GEE) was used to analyse multi‐temporal collections of Landsat satellite imagery acquired between 1989 and 2021. Active river channels (including water and exposed sediment) were classified using an MNDWI and NDVI thresholding approach from annually resolved temporal composite images. Declassified CORONA satellite imagery (acquired in 1965, 1973 and 1976) was manually digitized to provide longer‐term insights into channel change. Morphological adjustments were assessed using the RivMAP toolbox, providing quantitative information on the rates of bank erosion and accretion, bank line shifts and changes in active channel width. Results showed a substantial narrowing of the active channel after 2013, which coincided with the construction of the Lakhwar‐Vyasi Dam. We calculated a 67% reduction in mean active channel width, narrowing from ~800 m in 1989 to ~250 m in 2021. During the same period, evidence of sand mining in the active channel indicates a substantial increase in mining activities after 2015. The concept of stasis was explored under different flow regulation scenarios to suggest that the river has undergone a state of inactivity, where the river is doing nothing for much longer durations. We suggest that the combined effects of flow regulation and increased mining activities during the same period have altered river morphology, and further stresses due to a combination of human activities can be damaging for the river regime. This study sheds light on the potential implications of multiple stresses acting on the Yamuna River at the same time, which can inform future sustainable river management activities.
The Yamuna River segment in the Himalayan foothills underwent substantial narrowing after 2013–2014, coinciding with the construction of Lakhwar‐Vyasi dam and increased mining activities. The flow regulation due to dam has rendered the river system to mainly accretional in the last decade, disrupting the balance between accretional and erosional areas. The accretional regime and flow regulation activities indicate an increase in the proportion of stasis, when the river is doing nothing for much longer durations.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
This paper uses particle imaging velocimetry to provide the first measurements detailing the flow field over a porous bed in the presence of bed forms. The results demonstrate that flow downstream of ...coarse‐grained bed forms on permeable beds is fundamentally different to that over impermeable beds. Most significantly, the leeside flow separation cell is greatly modified by jets of fluid emerging from the subsurface, such that reattachment of the separated flow does not occur and the Reynolds stresses bounding the separation zone are substantially lessened. These results shed new light on the underlying flow physics and advance our understanding of both ecological and geomorphological processes associated with permeable bed forms. Water fluxes at the bed interface are critically important for biogeochemical cycling in all rivers, yet mass and momentum exchanges across the bed interface are not routinely incorporated into flow models. Our observations suggest that ignoring such exchange processes in coarse‐grained rivers may overlook important implications. These new results also provide insight to explain the distinctive morphology of coarse‐grained bed forms, the production of openwork textures in gravels, and the absence of ripples in coarse sands, all of which have implications for modeling and prediction of sediment entrainment and flow resistance.
Key Points
Wall permeability allows mass and momentum exchanges at the interfaceSubsurface‐surface flow exchange modifies flow structure in the bed form leesideEffects of permeability on morphology of coarse‐grained bed forms
Full text
Available for:
FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Climate change is expected to intensify the effect of environmental stressors on riverine ecosystems. Extreme events, such as low flow and heatwaves, could have profound consequences for stream ...ecosystem functioning, but research on the impact of these stressors and their interaction across multiple processes, remains scarce. Here, we report the results of a two-month stream mesocosm experiment testing the effect of low flow (66% water level reduction, without gravel exposure) and heatwaves (three 8-d episodes of +5 °C above ambient with 10–15 days recovery between each episode) on a suite of ecosystem processes (i.e. detrital decomposition, biofilm accrual, ecosystem metabolism and DOC quantity and quality). Low flow reduced whole system metabolism, suppressing the rates of gross primary production (GPP) and ecosystem respiration (ER), but elevated DOC concentration. Overall, habitat contraction was the main driver of reduced ecosystem functioning in the low flow treatment. By contrast, heatwaves increased decomposition, algal accrual, and humic-like DOC, but reduced leaf decomposition efficiency. Net ecosystem production (NEP) generally decreased across the experiment but was most pronounced for low flow and heatwaves when occurring independently. Assessment of NEP responses to the three successive heatwave events revealed that responses later in the sequence were more reduced (i.e. more similar to controls), suggesting biofilm communities may acclimate to autumn heatwaves. However, when heatwaves co-occurred with low flow, a strong reduction in both ER and GPP was observed, suggesting increased microbial mortality and reduced acclimation. Our study reveals autumn heatwaves potentially elongate the growth season for primary producers and stimulate decomposers. With climate change, river ecosystems may become more heterotrophic, with faster processing of recalcitrant carbon. Further research is required to identify the impacts on higher trophic levels, meta-community dynamics and the potential for legacy effects generated by successive low flows and heatwaves.
Display omitted
•Heatwaves and low flow effects on stream microbial processes•A mesocosm experiment using groundwater fed semi-recirculating flumes•Short and long-term stream metabolism responses to discrete heatwave events.•Heatwaves stimulated process rates, and low flow reduced whole-system metabolism.•Low flow and heatwaves combination enhanced metabolism reduction during heatwaves.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
► Sterically stabilised gold nanoparticles do not aggregate or interact with natural organic macromolecules. ► This was under a range of environmentally relevant conditions. ► Meaning they are likely ...to have a high mobility and bioavailability.
Nanoparticles are a major product from the nanotechnology industry and have been shown to have a potentially large environmental exposure and hazard. In this study, sterically stabilised polyvinyl pyrrolidone (PVP) 7nm gold nanoparticles (NPs) were produced and characterised as prepared by surface plasmon resonance (SPR), size and aggregation, morphology and surface charge. Changes in these properties with changes in environmentally relevant conditions (pH, ionic strength, Ca concentration and fulvic acid presence) were quantified. These sterically stabilised NPs showed no aggregation with changes in pH or inorganic ions, even under high (0.1M) Ca concentrations. In addition, the presence of fulvic acid resulted in no observable changes in SPR, size, aggregation or surface chemistry, suggesting limited interaction between the PVP stabilised nanoparticles and fulvic acid. Due to the lack of aggregation and interaction, these NPs are expected to be highly mobile and potentially bioavailable in the environment.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
PDF
