•The current findings of the heterogeneous composition of flocs are summarized.•The effect of the composition of flocs on their structure and dynamics is reviewed.•The interaction among heterogeneous ...components within flocs is explained.•Human activities affecting the heterogeneous composition of flocs are also summarized.
Flocculation is a key process for controlling the fate and transport of suspended particulate matter (SPM) in water environments and has received considerable attention in the field of water science (e.g., oceanography, limnology, and hydrology), remaining an active area of research. The research on flocculation has been conducted to elucidate the SPM dynamics and to diagnose various environmental issues. The flocculation, sedimentation, and transportation of SPM are closely linked to the compositional and structural properties of flocs. In fact, flocs are highly heterogeneous in terms of composition. However, the lack of comprehensive research on floc composition and structure has led to misconceptions regarding the temporal and spatial dynamics of SPM. This review summarizes the current understanding of the heterogeneous composition of flocs (e.g., minerals, organic matter, metals, microplastic, engineered nanoparticles) and its effect on their structure and on their fate and transport within aquatic environments. Furthermore, the effects of human activities (e.g., pollutant discharge, construction) on floc composition are discussed.
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Historically, solid wastes were commonly landfilled in the coastal zone in sites with limited engineering to isolate waste from adjacent coastal environments. Climate change is increasing the ...likelihood that these historic coastal landfills will be inundated or eroded resulting in the release of soluble contaminants to the coastal zone. Previously research has focussed on the environmental impacts of leaching from landfills in freshwater environments with little or no consideration being given to saline environments. This research investigated the magnitude, variability and potential environmental consequences of soluble metal release from solid wastes when historic coastal landfills are inundated, or wastes are eroded and released into fresh or saline waters. The proportions of the sites' total metal contents released to solution varied by up to an order of magnitude between different landfills due to the different physical and chemical characteristics of the solid wastes, but the proportions released were typically ≪1% in freshwater. Inundation by saline water significantly increases the proportions of the total metal contents released to solution, e.g. 5450% more Pb in one study site (median value), but again the proportions were typically ≪1%. The exception was Cd, where up to 9% of the total Cd load of one site was released in saline water. This puts into question the suitability of current landfill regulatory tests, e.g. the EU Waste Acceptance Criteria, and many risk assessment methods, which only consider freshwater inundation and leaching. However, the very low proportions of metals mobilised from the solid waste and the high dilution ratios in coastal waters, mean EQSs for the Protection of Surface Water are unlikely to be exceeded, and the release of solid wastes through coastal erosion poses a greater threat to coastal ecological health than leaching of soluble metals from contained solid wastes.
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•Climate change may increase soluble contaminant release from coastal landfills.•Soluble contaminant release is highly variable between historic landfills.•Seawater flooding of landfills significantly increases soluble contaminant release.•Environmental impact of leaching from inundated contained solid waste appears minimal.•Erosion of solid waste from historic landfills poses a greater threat than leaching.
Natural sediment flocs are fragile, highly irregular, loosely bound aggregates comprising minerogenic and organic material. They contribute a major component of suspended sediment load and are ...critical for the fate and flux of sediment, carbon and pollutants in aquatic environments. Understanding their behaviour is essential to the sustainable management of waterways, fisheries and marine industries. For several decades, modelling approaches have utilised fractal mathematics and observations of two dimensional (2D) floc size distributions to infer levels of aggregation and predict their behaviour. Whilst this is a computationally simple solution, it is highly unlikely to reflect the complexity of natural sediment flocs and current models predicting fine sediment hydrodynamics are not efficient. Here, we show how new observations of fragile floc structures in three dimensions (3D) demonstrate unequivocally that natural flocs are non-fractal. We propose that floc hierarchy is based on observations of 3D structure and function rather than 2D size distribution. In contrast to fractal theory, our data indicate that flocs possess characteristics of emergent systems including non-linearity and scale-dependent feedbacks. These concepts and new data to quantify floc structures offer the opportunity to explore new emergence-based floc frameworks which better represent natural floc behaviour and could advance our predictive capacity.
Light-emitting firefly luciferin analogues contain electron-donating groups in the 6′-position, but the scope of known 6′-substitution remains narrow. A two-step route to a broad range of ...6′-substituted luciferin analogues was developed to fill this void and enable more extensive study of the 6′-functionality. This chemistry allowed direct access to “caged” amide and bright azetidine analogues, but also revealed thioether inhibitors and unexpectedly luminogenic aryl amine derivatives.
Historically solid waste was commonly landfilled in the coastal zone in sites with limited engineering to isolate waste from adjacent coastal environments. Climate change is increasing the likelihood ...that these historic coastal landfills will erode releasing solid waste to the coastal zone. Historic coastal landfills are frequently located near designated ecological sites; yet, there is little understanding of the environmental risk posed by released waste. This research investigated inorganic and organic contaminant concentrations in a range of solid waste materials excavated from two historic coastal landfills, and the potential ecological impact should eroded waste be released to the coastal environment. Contaminant concentrations in the analysed waste materials exceeded sediment quality guidelines, indicating erosion of historic coastal landfills may pose a significant environmental threat. Paper and textile wastes were found to make a significant contribution to the total contaminant load, suggesting risk assessments should consider a wide range of solid waste materials.
•Climate change may increase the risk of historic waste eroding into the coastal zone.•Contaminant concentrations are highly variable between and within historic landfills.•Release of solid waste would have significant ecological impact.•Release of textiles, paper and wood may all present significant contamination risk.•A screening risk assessment method needs to be developed to prioritise management.
Prior to modern environmental regulation landfills in low-lying coastal environments were frequently constructed without leachate control, relying on natural attenuation within inter-tidal sediments ...to dilute and disperse contaminants reducing environmental impact. With sea level rise and coastal erosion these sites may now pose a pollution risk, yet have received little investigation. This work examines the extent of metal contamination in saltmarsh sediments surrounding a historic landfill in the UK.
Patterns of sediment metal data suggest typical anthropogenic pollution chronologies for saltmarsh sediments in industrialised nations. However, many metals were also enriched at depth in close proximity to the landfill boundary and are indicative of a historical leachate plume. Though this total metal load is low, e.g., c. 1200 and 1650kg Pb and Zn respectively, with >1000 historic landfills on flood risk or eroding coastlines in the UK this could represent a significant, yet under-investigated, source of diffuse pollution.
•Historic landfills were constructed prior to modern environmental regulation.•Historic metal-rich leachate plumes have contaminated adjacent fine-grained marine sediments.•This represents a small, but significant source of diffuse pollution in the coastal zone.
The vulnerability of saltmarshes to lateral erosion at their margin depends on the local biogeomorphological properties of the substrate. In particular, the 3D architecture of pore and root systems ...is expected to influence shear strength, with repercussions for the wider‐scale stability of saltmarshes. We apply X‐ray computed microtomography (μCT) to visualize and quantify subsurface structures in two UK saltmarshes at Tillingham Farm, Essex (silt/clay rich substrate) and Warton Sands (sand‐rich substrate), with four types of ground cover: bare ground, Spartina spp, Salicornia spp and Puccinellia spp. We extracted μCT structural parameters that characterize pore and root morphologies at each station, and compared them with field measurements of shear strength using a principal component analysis and correlation tests. The 3D volumes show that species‐dependent variations in root structures, plant colonization events and bioturbation activity control the morphology of macropores, while sediment cohesivity determines the structural stability and persistence of these pore structures over time, even after the vegetation has died. Areas of high porosity and high mean pore thickness were correlated to lower values of shear strength, especially at Tillingham Farm, where well‐connected vertical systems of macropores were associated with current or previous colonization by Spartina spp. However, while well‐connected systems of macropores may lower the local deformation threshold of the sediment, they also encourage drainage, promote vegetation growth and reduce the marsh vulnerability to hydrodynamic forces. The highest values of shear strength at both sites were found under Puccinellia spp, and were associated with a high density of mesh‐like root structures that bind the sediment and resist deformation. Future studies of marsh stability should ideally consider time series of vegetation cover, especially in silt/clay‐dominated saltmarshes, in order to consider the potential effect of preserved buried networks of macropores on water circulation, marsh functioning and cliff‐face erosion.
We use µCT to analyse 3D substrate structures in two UK saltmarshes (sand‐rich and clay‐rich) under different vegetation covers, and infer links between porosity, root architecture and shear strength. Spartina spp and Puccinellia spp have contrasting root architectures (tap root and fibrous respectively), with higher shear strength values found under Puccinellia spp. Well‐preserved and highly connected vertical systems of macropores at the muddy site lower the internal shear strength of the substrate but promote drainage, vegetation growth and marsh stability.
Many fluorophores, and all bright light-emitting substrates for firefly luciferase, contain hydroxyl or amine electron donors. Sulfonamides were found to be capable of serving as replacements for ...these canonical groups. Unlike “caged” carboxamides, sulfonamide donors enable bioluminescence, and sulfonamidyl luciferins, coumarins, rhodols, and rhodamines are fluorescent in water.
Despite growing interest in the environmental impact of microplastics, a standardized characterization method is not available. We carried out a systematic analysis of reliable global data detailing ...the relative abundance of polymers in freshwaters and estuaries. The polymers were identified according to seven main categories: polyethylene terephthalate, polyethylene, polyvinyl chloride, polypropylene, polystyrene, polyurethane and a final category of miscellaneous plastic. The results show that microplastics comprised of polyvinyl chloride and polyurethane are significantly less abundant than would be expected based on global production, possibly due to their use. This has implications for models of microplastic release into the environment based on production and fate. When analysed by matrix (water, sediment or biota) distinct profiles were obtained for each category. Polyethylene, polypropylene and polystyrene were more abundant in sediment than in biota, while miscellaneous plastics was more frequent in biota. The data suggest that environmental sorting of microplastic particles, influenced by physical, chemical and biological processes, may play a key role in environmental impact, although partitioning among matrices based on density was not realized. The distinct profile of microplastics in biota raises an important question regarding potential selectivity in uptake by organisms, highlighting the priority for more and better-informed laboratory exposure studies.
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