Navigating the nexus: climate dynamics and microplastics pollution in coastal ecosystems.

Microplastics (MPs) pollution is an emerging environmental health concern, impacting soil, plants, animals, and humans through their entry into the food chain via bioaccumulation. Human activities such as improper solid waste dumping are significant sources that ultimately transport MPs into the water bodies of the coastal areas. Moreover, there is a complex interplay between the coastal climate dynamics, environmental factors, the burgeoning issue of MPs pollution and the complex web of coastal pollution. We embark on a comprehensive journey, synthesizing the latest research across multiple disciplines to provide a holistic understanding of how these inter-connected factors shape and reshape the coastal ecosystems. The comprehensive review also explores the impact of the current climatic patterns on coastal regions, the intricate pathways through which MPs can infiltrate marine environments, and the cascading effects of coastal pollution on ecosystems and human societies in terms of health and socio-economic impacts in coastal regions. The novelty of this review concludes the changes in climate patterns have crucial effects on coastal regions, proceeding MPs as more prevalent, deteriorating coastal ecosystems, and hastening the transfer of MPs. The continuous rising sea levels, ocean acidification, and strong storms result in habitat loss, decline in biodiversity, and economic repercussion. Feedback mechanisms intensify pollution effects, underlying the urgent demand for environmental conservation contribution. In addition, the complex interaction between human, industry, and biodiversity demanding cutting edge strategies, innovative approaches such as remote sensing with artificial intelligence for monitoring, biobased remediation techniques, global cooperation in governance, policies to lessen the negative socioeconomic and environmental effects of coastal pollution.

An experimental and modeling study on the penetration of spilled oil into thawing frozen soil.

Oil spills are significant environmental accidents that have significant impacts on environmental and ecological health. Spill pollution in the cold regions may pose a particular challenge. To achieve a fast response, the oil transport mode such as penetration should be well understood. In this study, the oil penetration behavior in thawing frozen soil at different temperatures and water contents were investigated. The results showed the penetration behavior of spilled oil in the thawing frozen soil and the influence of salinity level. The modified Green-Ampt model could simulate the penetration process well especially with high water content, relatively cold temperature, and slow thawing rate. This study reveals the new features of oil penetration behavior and distribution patterns in thawing frozen soil under different conditions. Hence, it is of significant importance to support the rapid response measures and reduce the contamination of oil spill accidents in cold regions.

Numerical simulation of multiphase oil behaviors in ice-covered nearshore water.

There has been an increase in marine transportation in cold regions, which in turn has led to an increasing risk of oil spills in these areas. To better support risk assessment and pollution control of oil spills, it is important to have a good understanding of oil transport in the environment. This information is essential to manage response priorities and help prepare contingency and mitigating measures. This study aims to simulate 3D wave propagation in shallow water with different broken-ice aerial coverage percentages to assess the fate and transport of oil spill in a nearshore area under different conditions. Based on the Reynolds-averaged Navier-Stokes momentum equations for an incompressible viscous fluid and the Volume of Fluid (VOF) method that is coupled with Six Degree of Freedom (6-DOF) model, a 3D numerical model of three-phase transient flow was developed. It was found that the presence of ice makes the spreading of spilled oil slower in the horizontal direction since the ice can build natural barriers to oil movement. The higher the ice concentration, the slower spilled oil migrates in all directions. The maximum oil volume fraction varies with increasing ice coverage on the water surface area. The wave frequency, the averaged flow velocity, and oil properties affect the oil spread extent and the oil volume fraction. The dumping effect of the wave due to the presence of ice makes the impact of this factor less critical than those in open water.

Exploring the effects of substrate mineral fines on oil translocation in the shoreline environment: Experimental analysis, numerical simulation, and implications for spill response.

Mineral fines act a pivotal part in determining the fate and behavior of oil. In this study, the infiltrations of oil emulsion in simulated sediments and natural shoreline sediments were investigated using a fixed bed experiment. Oil infiltration process was simulated based on fixed-bed dispersion model. The role of mineral fines in oil release was explored using simulated and natural sediments. Although mineral fines exhibited a higher affinity for oil, it was found that increasing fines fractions decreased the flow rate of oil emulsion, thereby decreasing the oil retention in the sediment column. In terms of oil release from the sediment, the highest level of oil mass was observed in the oil-mineral flocculation phase compared to the water column and the water surface compartments. Compared to light crude oil, the release of engine oil from sediment was less. The effects of mineral fines on oil infiltration and release were also confirmed by using natural shoreline sediments. Results of our detailed field studies also showed that current shoreline classification datasets do not characterize the presence and fraction of mineral fines at a level of detail required to accurately predict the significance of oil translocation following spill incidents.

Treatment of decentralized low-strength livestock wastewater using microcurrent-assisted multi-soil-layering systems: performance assessment and microbial analysis.

Discharge of decentralized livestock wastewater without effective treatment has become a common problem in rural areas, threatening the regional water environment. A new microcurrent-assisted multi-soil-layering (MSL) system was developed for treating rural decentralized livestock wastewater. The results showed the highest removal rates of chemical oxygen demand (COD) and total phosphorus (TP) in MSL systems reached 95.45% and 92.0%, respectively. The removal rate of total nitrogen (TN) in MSL systems ranged from 60 to 75%. The bacterial diversity changes among MSL systems showed that high-level height of bottom submergence had a positive effect on the abundance of denitrifying bacteria, while low-level height of bottom submergence had a positive impact on the abundance of nitrifying bacteria. The effect of low-level external voltage on bacterial abundance was better than that of high-level external voltage. Both high- and low-level influent C/N ratios had no significant effect on bacterial abundance. The metabolism and activity of microorganisms were promoted with microcurrent stimulation from the perspective of increased bacterial abundance in MSL systems with improved treatment performance.

A green initiative for oiled sand cleanup using chitosan/rhamnolipid complex dispersion with pH-stimulus response.

The released oil can affect the vulnerable shoreline environment if the oil spills happen in coastal waters. The stranded oil on shorelines is persistent, posing a long-term influence on the intertidal ecosystem after weathering. Therefore, shoreline cleanup techniques are required to remove the oil from the shoreline environment. In this study, a new shoreline cleanup initiative using chitosan/rhamnolipid (CS/RL) complex dispersion with pH-stimulus response was developed for oiled sand cleanup. The results of factorial and single-factor design revealed that the CS/RL complex dispersion maintained high removal efficiency for oiled sand with different levels of oil content in comparison to using rhamnolipid alone. However, the increase of salinity negatively affected the removal efficiency. The electrostatic screening effect of high ionic strength can hinder the formation of the CS/RL complex, and thus reduce removal efficiency. The pH-responsive characteristic of chitosan allows the easy separation of water and oil in washing effluent. The chitosan polyelectrolytes aggregated and precipitated due to the deprotonation of amino groups by adjusting the pH of the washing effluent to above 8. The microscope image demonstrated that the chitosan aggregates wrapped around the oil droplets and settled to the bottom together, thus achieving oil-water separation. Such pH-stimulus response may help achieve an easy oil-water separation after washing. These findings have important implications for developing the new strategies of oil spill response.

Hypersaline Pore Water in Gulf of Mexico Beaches Prevented Efficient Biodegradation of Deepwater Horizon Beached Oil.

The 2010 Deepwater Horizon (DWH) blowout released 3.19 million barrels (435 000 tons) of crude oil into the Gulf of Mexico. Driven by currents and wind, an estimated 22 000 tons of spilled oil were deposited onto the northeastern Gulf shorelines, adversely impacting the ecosystems and economies of the Gulf coast regions. In this work we present field work conducted at the Gulf beaches in three U.S. States during 2010-2011: Louisiana, Alabama, and Florida, to explore endogenous mechanisms that control persistence and biodegradation of the MC252-oil deposited within beach sediments as deep as 50 cm. The work involved over 1500 measurements incorporating oil chemistry, hydrocarbon-degrading microbial populations, nutrient and DO concentrations, and intrinsic beach properties. We found that intrinsic beach capillarity along with groundwater depth provides primary controls on aeration and infiltration of near-surface sediments, thereby modulating moisture and redox conditions within the oil-contaminated zone. In addition, atmosphere-ocean-groundwater interactions created hypersaline sediment environments near the beach surface at all the studied sites. The fact that the oil-contaminated sediments retained near or above 20% moisture content and were also eutrophic and aerobic suggests that the limiting factor for oil biodegradation is the hypersaline environment due to evaporation, a fact not reported in prior studies. These results highlight the importance of beach porewater hydrodynamics in generating unique hypersaline sediment environments that inhibited oil decomposition along the Gulf shorelines following DWH.

Formation of oil-particle aggregates: Impacts of mixing energy and duration.

Spilled oil slicks are likely to break into droplets offshore due to wave energy. The fate and transport of such droplets are affected by suspended particles in local marine environment, through forming oil particle aggregates (OPAs). OPA formation is affected by various factors, including the mixing energy and duration. To evaluate these two factors, lab experiments of OPA formation were conducted using kaolinite at two hydrophobicities in baffled flasks, as represented by the contact angle of 28.8° and 37.7° (original and modified kaolinite). Two mixing energies (energy dissipation rates of 0.05 and 0.5 W/kg) and four durations (10 min, 30 min, 3 h, and 24 h) were considered. Penetration to the oil droplets was observed at 3-5 µm and 5-7 µm for the original and modified kaolinite by confocal microscopy, respectively. At lower mixing energy, volume median diameter d50 of oil droplets increased from 45 µm to 60 µm after 24 h mixing by original kaolinite; for modified kaolinite, d50 decreased from 40 µm to 25 µm after 24 h mixing. The trapped oil amount in negatively buoyant OPAs decreased from 35% (3 h mixing) to 17% (24 h mixing) by original kaolinite; and from 18% to 12% after 24 h mixing by modified kaolinite. Results indicated that the negatively buoyant OPAs formed with original kaolinite at low mixing energy reaggregated after 24 h. At higher mixing energy, d50 decreased from 45 µm to 17 µm after 24 h mixing for both kaolinites. And the trapped oil amount in negatively buoyant OPAs increased to 72% and 49% after 24 h mixing for original and modified kaolinite, respectively. At higher mixing energy, the OPAs formed within 10 min and reached equilibrium at 3 h by original kaolinite. For modified kaolinite, the OPAs continued to form through 24 h.

Exploring the decentralized treatment of sulfamethoxazole-contained poultry wastewater through vertical-flow multi-soil-layering systems in rural communities.

Sulfamethoxazole (SMX) is the most widely distributed sulfonamide antibiotics detected in decentralized poultry wastewater in rural communities. As an economically-feasible and eco-friendly technology for decentralized wastewater treatment in rural areas, vertical-flow multi-soil-layering (MSL) system was promising to mitigate the ecological and human health risks from SMX in such areas. The treatment of SMX-contained poultry wastewater by using MSL systems was investigated for the first time, and the main and interactive effects of related multiple variables on system performance were explored through factorial analysis, including material of permeable layer, concentration of SMX, and pH of influent. Results indicated that SMX concentration and pH of influent showed significantly negative effects on SMX removal. Medical stone used in MSL systems with larger surface area could intensify the SMX removal compared to anthracite. MSL systems showed stable performances on SMX removal with the best SMX removal efficiency more than 91%. A novel stepwise-cluster inference (SCI) model was developed for the first time to map the multivariate numeric relationships between state variables and SMX removal under discrete and nonlinear complexities. It was demonstrated that the effect of SMX in wastewater with high concentration was significant on the differentiation of soil bacteria composition in MSL systems based on microbial diversity analysis. These results can help better understand the mechanism of SMX removal in MSL systems from perspectives of factorial analysis, numeric modeling, and microbiological change.

Investigation into the oil removal from sand using a surface washing agent under different environmental conditions.

Spilled oil frequently reaches the shorelines and affects coastal biota and communities. The application of surface washing agents is an important shoreline cleanup technique that can help remove stranded oil from substrate surfaces with the advantages of high removal efficiency, low toxicity, and strong economic viability. In this study, the investigation into the oil removal from contaminated sand using a surface washing agent under variable environmental conditions was conducted. A preliminary test was conducted to obtain the optimal combination of operating factors of surface washing agent-to-oil ratio (SOR) 2:1, mixing speed 150 rpm, and mixing time 30 min. The results of single-factor experiments showed that high temperature and humic acid concentration of flush water contributed to the performance of a surface washing agent, while salinity and kaolinite concentration could inhibit its performance. The factorial analysis revealed the main effects of temperature and salinity, and the interactive effects of temperature and salinity as well as salinity and humic acid concentration that were significant to the washing efficiency of the surface washing agent. In addition, the comprehensive assessment of a surface washing agent from the aspects of toxicity, detergency, dispersion properties, and field trials was conducted. The results have significant implications for future application of surface washing agents in the shoreline cleanup.

Performance analysis and life cycle greenhouse gas emission assessment of an integrated gravitational-flow wastewater treatment system for rural areas.

Due to the lack of appropriate wastewater treatment facility in rural areas, the discharging of wastewater without sufficient treatment results in many environmental issues and negative impact on the local economy. In this study, a novel integrated gravitational-flow wastewater treatment system (IGWTS) for treating domestic wastewater in rural areas was developed and evaluated. As the core module of IGWTS, the multi-soil-layering (MSL) system showed good performances for removing organic matters and nutrients in lab-scale experiments. Aeration was found to be the dominant positive factor for contaminant removal in factorial analysis, while bottom submersion had the most negative effect. Based on the critical operational factors obtained from lab-scale tests, the full-scale IGWTS consisting of multifunctional anaerobic tank (MFAT), MSL, and subsurface flow constructed wetland (SFCW) was designed, constructed, and operated successfully in the field application. The final effluent concentrations of COD, BOD5, TP, NH3-N, and TN reached 22.0, 8.0, 0.3, 4.0, and 11.0 mg/L, with removal rates of 92, 93, 92, 86, and 76%, respectively. The feasibility of IGWTS was also quantitatively evaluated from the perspectives of resource consumption, economic costs, water environment impact, and life cycle greenhouse gas (GHG) emissions. IGWTS has been proved to be a sound approach to mitigate GHG emissions compared with centralized wastewater treatment plant. It can also be featured as an eco-friendly technology to improve rural water environment, and an economic scenario with low construction and operation costs. Graphical abstract.

Enhanced nitrogen removal in the treatment of rural domestic sewage using vertical-flow multi-soil-layering systems: Experimental and modeling insights.

Domestic sewage in rural areas is often poorly treated and discharged into waters, resulting in negative impacts on regional environment, natural resources and human health. A cost-efficient decentralized sewage treatment technology is sustainably necessary for rural areas. In this study, a modified multi-soil-layering (MSL) system was developed to specifically treat low C/N ratio domestic sewage in rural areas. The results proved the good performance of MSLs in sewage treatment under complex conditions. The highest degradation rates of COD, TP, NH4+-N, NO3--N, TN among all the devices could reach 98.29%, 100%, 76.60%, 96.15% and 69.86%, respectively. During the operation, MSL5 and MSL6 showed the best overall performance of contaminant removal. The effects of single factors and their interactions on the performance of MSL systems were further revealed through factorial analyses. In order to simulate and predict nitrogen removal of MSL system, a statistical relationship between TN removal rate and operation parameters was also successfully developed based on stepwise cluster analysis. Such modeling of nitrogen removal model can help develop an optimal strategy for the operation of MSL in treating low C/N ratio sewage from rural areas.

Biophysiological and factorial analyses in the treatment of rural domestic wastewater using multi-soil-layering systems.

Multi-soil-layering (MSL) system was developed as an attractive alternative to traditional land-based treatment techniques. Within MSL system, the environmental cleanup capability of soil is maximized, while the soil microbial communities may also change during operation. This study aimed to reveal the nature of biophysiological changes in MSL systems during operation. The species diversity in soil mixture blocks was analyzed using Illumina HiSeq sequencing of the 16S rRNA gene. The interactive effects of operating factors on species richness, community diversity and bacteria abundance correlated with COD, N and P removal were revealed through factorial analysis. The results indicated the main factors, aeration, bottom submersion and microbial amendment, had different significant effects on microbial responses. The surface area and porosity of zeolites in permeable layers decreased due to the absorption of extracellular polymeric substances. The findings were applied for the design and building of a full-size MSL system in field and satisfied removal efficiency was achieved. The results of this study can help better understand the mechanisms of pollutant reduction within MSL systems from microbial insights. It will have important implications for developing appropriate strategies for operating MSL systems with high efficiency and less risks.

Insights into the Toxicity of Triclosan to Green Microalga Chlorococcum sp. Using Synchrotron-Based Fourier Transform Infrared Spectromicroscopy: Biophysiological Analyses and Roles of Environmental Factors.

This study investigated the toxicity of triclosan to the green microalga Chlorococcum sp. under multiple environmental stressors. The interactions between triclosan and environmental stressors were explored through full two-way factorial, synchrotron-based Fourier transform infrared spectromicroscopy and principal component analyses. Phosphorus concentration, pH * phosphorus concentration, and temperature * pH * NaCl concentration were the most statistically significant factors under triclosan exposure. The variation of those factors would have a huge impact on biophysiological performances. It is interesting to find Chlorococcum sp. may become more resistant against triclosan in phosphorus-enriched environment. Besides, particular significant factors from multiple environmental stressors showed the impacts of triclosan on the corresponding response of Chlorococcum sp. owing to the specific structure and performance of biomolecular components. Moreover, two high-order interactions of temperature * pH * NaCl concentration and temperature * pH * NaCl concentration * phosphorus concentration had more contributions than others at the subcellular level, which could be attributed to the interactive complexity of biomolecular components. Due to cellular self-regulation mechanism and short exposure time, the biophysiological changes of Chlorococcum sp. were undramatic. These findings can help reveal the interactive complexity among triclosan and multiple environmental stressors. It is suggested that multiple environmental stressors should be considered during ecological risk assessment and management of emerging pollutants.

Combined effects of DOM extracted from site soil/compost and biosurfactant on the sorption and desorption of PAHs in a soil-water system.

The combined effects of DOM and biosurfactant on the sorption/desorption behavior of phenanthrene (PHE) and pyrene (PYR) in soil water systems were systematically investigated. Two origins of DOMs (extracted from soil and extracted from food waste compost) and an anionic biosurfactant (rhamnolipid) were introduced. The presence of DOM in the aqueous phase could decrease the sorption of PAHs, thus influence their mobility. Desorption enhancement for both PHE and PYR in the system with compost DOM was greater than that in the soil DOM system. This is due to the differences in specific molecular structures and functional groups of two DOMs. With the co-existence of biosurfactant and DOM, partitioning is the predominant process and the desorption extent was much higher than the system with DOM or biosurfactant individually. For PHE, the desorption enhancement of combined DOM and biosurfactant was larger than the sum of DOM or biosurfactant; however desorption enhancement for PYR in the combined system was less than the additive enhancement in two individual system under low PAH concentration. This could be explained as the competition sorption among PAHs, DOM and biosurfactant. The results of this study will help to clarify the transport of petroleum pollutants in the remediation of HOCs-contaminated soils.