Effects of anthropogenic surfactants on the conversion of marine dissolved organic carbon and microgels

An overview of electrokinetically enhanced chemistry technologies for organochlorine compounds (OCs) remediation from soil

In recent years, electrokinetic (EK) remediation technology has gained significant attention among researchers. This technology has proven effective in the remediation of low-permeability polluted soil. Organochlorines (OCs) are highly toxic, persistent, bioaccumulative, and capable of long-distance migration. They can also accumulate through the food chain, posing significant environmental risks. This paper provides a review of the reaction mechanism of combining chemical technology with EK remediation for the removal of several typical OCs. Furthermore, the factors influencing the efficiency of EK remediation, such as pH and ζ potential, voltage gradients, electrode materials, electrolytes, electrode arrangements, and soil types, are summarized. The paper also presents an overview of recent advancements in the methods of combining chemical technology with EK remediation for the treatment of OCs contaminated soil. Specifically, the research progress in surfactants-combined EK technology, chemical oxidation-combined EK technology, chemical reduction-combined EK technology, and chemical adsorption-combined EK technology is summarized. These findings serve as a foundation for ongoing and future research endeavors in the field. Further exploration and investigation in this area are essential for advancing the field and improving environmental remediation strategies.

Production and Characterisation of an Exopolysaccharide by Bacillus amyloliquefaciens: Biotechnological Applications

The Bacillus amyloliquefaciens RT7 strain was isolated from an extreme acidic environment and identified. The biodegradation capabilities of the strain using different carbon sources (glucose, oleic acid, Tween 80, PEG 200, and the combination of glucose-Tween 80) were evaluated via an indirect impedance technique. The glucose-Tween 80 combination was further studied using nuclear magnetic resonance (NMR). The exopolysaccharide (EPS_RT7) that had been produced with the strain when biodegrading glucose-Tween 80 was isolated and characterised using different techniques (GC-MS, HPLC/MSMS, ATR-FTIR, TGA, and DSC), and its molecular weight was estimated. The results show that the average molecular weight of EPS_RT7 was approximately 7.0794 × 10⁴ Da and a heteropolysaccharide composed of mannose, glucose, galactose, and xylose (molar ratio, 1:0.5:0.1:0.1) with good thermostability. EPS_RT7 showed good emulsifying activity against different natural oils and hydrocarbons at high concentrations (2 mg/mL) and at the studied pH range (3.1-7.2). It also presented good emulsifying activity compared to that of commercial emulsifiers. Lastly, EPS_RT7 showed antioxidant capacity for different free radicals, a lack of cytotoxicity, and antioxidant activity at the cellular level. EPS_RT7 has promising applications in bioremediation processes and other industrial applications.

Temperature Effects on Effluent Microgel Formation

Wastewater treatment plant effluent is considered an important hotspot of dissolved organic matter. The behavior and transformation of dissolved effluent organic matter (dEfOM) regulate particle sedimentation, pollutant fate, microbial attachment, and biofilm formation. However, studies have so far focused on the transformation of marine and riverine organic matter, and the current knowledge of dEfOM behavior is still limited. Fluctuations in water conditions, especially temperature, may directly alter the size, assembly speed, and structure of microgels, thereby potentially disturbing fate and the transportation of organic matter. In this study, we firstly investigated the effects of temperature on the behavior and capacity of dEfOM assembly into microgels and the possible mechanism. The microgel size and granularity of dEfOM were monitored by flow cytometry. Our results suggest that, with regard to microgels, a higher temperature leads to a higher assembly capacity but also a decrease in the size distribution. By contrast, assembly at 4 °C reduces the relative assembly capacity but increases the microgel size and granularity. The size distribution of the formed microgels at the various temperatures was ordered as follows: 4 °C > 20 °C > 35 °C. The size reduction in dEfOM assembly may be closely tied to the enhancement of hydrophobic interactions. The reduction in microgel granularity in warm conditions (35 °C) in terms of the effluent water may be caused by thermally induced condensation. Overall, the findings demonstrate the effects of temperature on dEfOM assembly and can facilitate further relevant studies on aquatic organic particle formation during current global warming scenarios.

Stickiness of extracellular polymeric substances on different surfaces via magnetic tweezers

Organic particle dynamics in the surface ocean plays a critical part in the marine carbon cycle. Aggregation of marine organic particles drives their downward transport to support various marine organisms on their transit to the sediments. Extracellular polymeric substances (EPS) from various microbes are a major contributor to the oceanic organic particle pool. The stickiness of EPS is expected to play a determining role in the aggregation process of particles; however, stickiness parameters are usually indirectly estimated through data fitting without direct assessment. Here a magnetic tweezer method was developed to quantitatively assess the stickiness of three model EPS produced by: Amphora sp., (diatom), Emiliania huxleyi (coccolithophore), and Sagittula stellata (bacteria), under different in vitro environmental conditions (salinity or EDTA complexed cations) and surface matrices (EPS-EPS and bare glass). Our results showed the stickiness of three microbial EPS decreasing for S. stellata > E. huxleyi > Amphora sp., in line with their decreasing protein-to-carbohydrate (P/C) ratios (related to their relative hydrophobicity). The data not only emphasize the importance of hydrophobicity on EPS stickiness, but also demonstrates that salinity and the nature of the substrate surface can influence the stickiness. Furthermore, we investigated stickiness between various types of EPS, and the observed selective stickiness of EPS between species may shed light on the interactions among heterogeneous marine microorganisms. Overall, this newly developed system provides a platform to assess the EPS stickiness to advance our understanding of the aggregation and sedimentation process of organic particles that are critical for the fate of organic carbon as well as for biofilm formation and microbial colonization of surfaces in the ocean.

Nano- and microplastics trigger secretion of protein-rich extracellular polymeric substances from phytoplankton

The substantial increase in plastic pollution in marine ecosystems raises concerns about its adverse impacts on the microbial community. Microorganisms (bacteria, phytoplankton) are important producers of exopolymeric substances (EPS), which govern the processes of marine organic aggregate formation, microbial colonization, and pollutant mobility. Until now, the effects of nano- and micro-plastics on characteristics of EPS composition have received little attention. This study investigated EPS secretion by four phytoplankton species following exposure to various concentrations of polystyrene nano- and microplastics (55 nm nanoparticles; 1 and 6 μm microparticles). The 55 nm nanoparticles induced less growth/survival (determined on a DNA basis) and produced EPS with higher protein-to-carbohydrate (P/C) ratios than the exposure to microplastic particles. The amount of DNA from the four marine phytoplankton showed a higher negative linear correlation with increasing P/C ratios, especially in response to nanoplastic exposure. These results provide evidence that marine phytoplankton are quite sensitive to smaller-sized plastics and actively modify their EPS chemical composition to cope with the stress from pollution. Furthermore, the release of protein-rich EPS was found to facilitate aggregate formation and surface modification of plastic particles, thereby affecting their fate and colonization. Overall, this work offers new insights into the potential harm of different-sized plastic particles and a better understanding of the responding mechanism of marine phytoplankton for plastic pollution. The data also provide needed information about the fate of marine plastics and biogenic aggregation and scavenging processes.

Enrichment behavior of contemporary PAHs and legacy PCBs at the sea-surface microlayer in harbor water

Polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) in the sea-surface microlayer (SML) and sub-surface water (SSW) were analyzed in and around Kaohsiung Harbor. The results confirm SML enrichments for PAHs, but PCBs less significantly, since PAHs are still produced while PCBs had banned years ago. However, PCBs still leak to the environment from contaminated sites. The results showed the sources and transport of PAHs and PCBs were different, but both are enriched in the SML. Total particulate PAHs at most sites are below the toxicity thresholds, with a few individual PAHs between the effects range-low and effect range-median even higher than the effect range-median. Total particulate PCBs might cause occasionally adverse effects in sensitive species and pose a risk to the organisms. The particulate phase in the SML poses a higher risk to the marine ecosystem than in the SSW although not all organisms will make direct use of the microlayer. Principal component analysis (PCA) of PAHs indicated the important contribution of traffic engine emission in the particulate samples of the SML and SSW and revealed that probably the petroleum pollutants are a predominant source for the dissolved phase. Cluster analysis revealed that PAH-PCB patterns in the river and anchorage channels were different to those in the wetlands and open harbor. However, PCA of PCBs showed differences in the congener profiles for the two phases, with highly chlorinated PCBs more abundant in particles, while less chlorinated PCBs were more abundant in dissolved.

Nano-plastics induce aquatic particulate organic matter (microgels) formation

The pervasive presence of plastic waste in the aquatic environment is widely viewed as one of the most serious environmental challenges for current and future generations. Microplastics ultimately degrade into nano and smaller-sizes. In turn, their biological and ecological impacts become more complicated and ambiguous. Nano-plastic particles travel from freshwater systems to estuarine and oceanic regions, during which they can interact with dissolved organic matter (DOM) to form microgels. Microgel formation is ubiquitous in aquatic systems, serving as a shunt between DOM and particulate organic matter (POM), as well as playing key roles in particle aggregation/sedimentation and pollutant transport. Currently the influences and mechanisms of the aggregation behavior and environmental fate of nano-plastics in different aquatic environments is poorly understood. Here, we report that 25 nm polystyrene nano-particles in lake and river water can promote POM (microgel) formation and accelerate the DOM-POM transition. We also adjusted various salinities of water samples to simulate scenarios based on plastic transport in waters flowing from rivers to seas. The results indicate polystyrene nanoparticles can interact with organic matter to form large organic particles, which may undergo further settling in response to specific salinity levels. Polystyrene-induced microgel formation appears to involve the hydrophobic interactions between plastics and DOM. Our data provides much needed information for modeling and understanding the retention and sedimentation of nano-plastics. We show that nano-plastics alter the DOM-POM shunt to cause unanticipated perturbations in the functionality of aquatic ecosystems.

Alkylphenol ethoxylate metabolites in coastal sediments off southwestern Taiwan: Spatiotemporal variations, possible sources, and ecological risk

Alkylphenol ethoxylates (APEOs) are one of the most widely used classes of surfactants, but they are also ubiquitous environmental pollutants and known endocrin-disrupting chemicals. This study is the first to investigate the spatiotemporal variations and possible sources of APEOs and their metabolites, including nonylphenol ethoxylates (NPEOs) and octylphenol ethoxylates (OPEOs), in coastal sediments off southwestern Taiwan. The highest APEO concentration in the dry season was observed for the Kaohsiung coastal area, whereas the highest alkylphenol (AP) concentration in the wet season was found offshore at the Tainan Canal exit. No continuous accumulation of alkylphenol metabolites was evident in the area. One possible reason is that seasonal current and wind waves disperse the coastal pollutants. Application of multivariate statistical tools (hierarchical cluster analysis and principal component analysis) confirmed the role of rivers and the Tainan Canal in transporting contaminants to coastal environments, suggesting influences of industrial and human activities on APEO distribution. A further comparison with the predicted no-effect concentrations (PNECs) proposed by the European Union indicates that nonylphenol (NP) and octylphenol (OP) might pose potential ecological risks to the aquatic environment in the studied area. These findings provide useful information for environmental policy implementation and ecological assessments of different types of endocrine-disrupting chemicals and raise warnings about surfactant applications.

Impact of exposure of crude oil and dispersant (Corexit) on aggregation of extracellular polymeric substances

Spilled oil treated with Corexit dispersant can cause unintended impacts on marine environment systems including altering marine organic matter dynamics; however, impacts on microgels and marine oil snow (MOS) formation are still debated and remain to be fully understood. Extracellular polymeric substances (EPS) are a major source of marine organic carbon for MOS and microgel formation. EPS initial aggregation plays key roles in the oil degrading process and various biogeochemical reactions. Here we used four types of EPS with water accommodated fraction (WAF), chemically-enhanced WAF (CEWAF) and Corexit, to represent potential situations during oil spills and post-application of Corexit. We found that Corexit alone can inhibit EPS aggregation and disperse pre-existing microgels. CEWAF can enhance EPS aggregation with efficiency by up to 80%-100% and more aggregates accumulated within the air-water interface. Additionally, more hydrophobic EPS aggregates showed high resistance to Corexit dispersion while hydrophilic EPS were more sensitive. Effects of oil spills on marine gel particle formation are primarily determined by chemical characteristics (hydrophobicity and protein content) of the constituent EPS. This study offers unique insights for organic particle dynamics and identifies controlling factors for MOS or gel particles associated with oil spills and Corexit dispersant used.

Superhydrophobic graphene-based sponge as a novel sorbent for crude oil removal under various environmental conditions

Mechanical recovery of oils using oil sorbents is one of the most important approaches to manage marine oil spills. However, the properties of the oils spilled into sea are influenced by external environmental conditions. In this study, we present a graphene-based (GB) sponge as a novel sorbent for crude oil removal and compare its performance with that of a commercial sorbent sheet under various environmental parameters. The GB sponge with excellent superhydrophobic and superoleophilic characteristics is demonstrated to be an efficient sorbent for crude oils, with high sorption capacity (up to 85-95 times its weight) and good reusability. The crude-oil-sorption capacity of our GB sponge is remarkably higher (about 4-5 times) than that of the commercial sheet and most other previously reported sponge sorbents. Moreover, several challenging environmental conditions were examined for their effects on the sorption performance, including the weathering time of oils, seawater temperature, and turbulence (wave effect). The results show that the viscosity of the oil increased with increasing weathering time or decreasing temperature; therefore, the sorption rate seemed to decrease with longer weathering times and lower temperatures. Turbulence can facilitate inner sorption and promote higher oil sorption. Our results indicate that the extent of the effects of weather and other environmental factors on crude oil should be considered in the assessment of the effective adsorption capacity and efficiency of sorbents. The present work also highlights the widespread potential applications of our GB sponge in marine spilled-oil cleanup and hydrophobic solvent removal.

Reduction in the exchange of coastal dissolved organic matter and microgels by inputs of extra riverine organic matter

Rivers drive large amounts of terrestrial and riverine organic matter into oceans. These organic materials may alter the self-assembly of marine dissolved organic matter (DOM) polymers into microgels and can even affect the behavior of existing natural microgels. We used Suwannee River humic acid, fulvic acid, and natural organic matter as a model of riverine organic matter (ROM) to investigate the impacts of ROM input on DOM polymer and microgel conversion. Our results indicated that the release of extra ROM, even at low concentrations (0.1-10 mg L^-1), into the marine organic matter pool decreased the size of self-assembled DOM polymers (from 4-5 μm to < 1 μm) and dispersed the existing natural microgels into smaller particles (from 4-5 μm to 2-3 μm). The particle size of the microgel phase was also less sensitive than that of the DOM polymers to external changes (addition of ROM). This size reduction in DOM aggregation and existing microgels may be closely tied to the surface chemistry of the organic matter, such as negative surface charge stabilization and Ca²⁺ cross-linking bridges. These findings reveal that ROM inputs may therefore impede the self-assembly of DOM polymers into particulate organic matter and reduce the sedimentation flux of organic carbon and other elements from surface water to the deep ocean, thereby disturbing the biological pump, the downward transportation of nutrients, and the marine organic carbon cycle.

Corexit, oil and marine microgels

Corexit, an EPA-approved chemical dispersant, was intensively used during the 2010 Deepwater Horizon Oil Spill in the Gulf of Mexico. Current studies surrounding Corexit have mainly focused on its toxicity and oil removal capacity. The potential impact of Corexit on the surface ocean carbon dynamics has remained largely unknown. The spontaneous assembly of DOM (dissolved organic matter) polymers into microgels (POM, particulate organic matter) was demonstrated previously that it can influence various critical processes, such as colloidal pump, microbial loops, and nutrition availability in the surface ocean. Here, we report that Corexit alone can significantly inhibit DOM microgel formation and reduce the stability of pre-existing microgels. However, Corexit and oil, Chemically Enhanced Water Accommodated Fraction (CEWAF), could effectively facilitate DOM microgel formation. The unanticipated disturbance of Corexit and oil spills on the critical DOM-POM continuum warrant particular caution and thus should be considered for future application of Corexit during oil spills.