Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI–TOF–MS) coupled to XAD fractionation: Method to algal organic matter characterization

Differences in the composition, source, and stability of suspended particulate matter and sediment organic matter in Hulun Lake, China

The occurrence, migration, transformation, and stability of sediment (SOM) and suspended particulate (SPOM) organic matters have important effects on the environmental behaviors of carbon, nitrogen, phosphorus, and other pollutants in a water environment. The content, composition, fluorescence characteristics, source, and stability of SOM and SPOM in Hulun Lake, a typical lake in cold and arid region of China, were compared by sequential extraction, three-dimensional fluorescence spectroscopy, parallel factor technique, carbon-nitrogen ratio, and stable carbon isotope. Contents of SOM and SPOM in north and west were higher than those in east and south. The average content of SPOM (24.70 ± 4.63 g/kg) was slightly higher than that of SOM (23.04 ± 10.27 g/kg), but the difference was not significant. Humin was the dominant component in SOM and SPOM, accounting for 73.7% and 61.2%, respectively. Humus was the main fluorescence component of water-extractable organic matter in SOM and SPOM, accounting for 79.9% and 70.4%, respectively, of the total fluorescence intensity. SOM and SPOM were derived from terrestrial sources with a relative contribution rate of about 70%. SPOM was more influenced by autochthonous sources and had a significantly lower humification degree and stability than SOM. Effects of climate changes on migration, transformation, stability, and bioavailability of organic matters and endogenous pollutants closely related to organic matters in lakes of cold and arid regions should be paid attention in the future.

Development of antioxidant-rich edible active films and coatings incorporated with de-oiled ethanolic green algae extract: a candidate for prolonging the shelf life of fresh produce

The concept of sustainability and the substitution of non-biodegradable packaging using biodegradable packaging has attracted gigantic interest. The objective of the present study was to revalorize the biowaste "de-oiled green algae biomass (DAB)" of Dunaliella tertiolecta using a green approach and the development of biodegradable chitosan (CS)-based edible active biocomposite films and coatings for prolonging the shelf life of fresh produce. Ultrasound-assisted green extraction was conducted using food-grade solvent ethanol for obtaining the bio-actives, namely "crude algae ethanolic extract (CAEE)" from DAB. The edible films (CS/CAEE) and coating solutions were developed by incorporating CAEE with varying concentrations (0 to 28%). The CAEE was subjected to MALDI-TOF-MS, NMR, and other biochemical analyses, and was found to be rich in DPPH antioxidant activity (∼40%). The CS/CAEE films were fabricated using a solvent casting method and characterized by several biochemical and physicochemical (FESEM, TGA, FTIR, XRD, WVP, UTM, and rheological) characterization techniques. The addition of CAEE into the CS matrix reduced the maximum film transparency (∼20%), water vapor permeability (∼60%); improved the crystallinity (∼24%), tensile strength (∼25%), and antioxidant activity (∼27%); and exhibited UV-Vis blocking properties as compared to the control film. Besides, the developed coating solutions and CAEE showed biocompatibility with BHK-21 fibroblast cells and antimicrobial activity against common food pathogens. The developed coating solution was applied on green chilli using a dipping method and stored at ambient temperature (25 ± 2 °C, 50-70 % RH) for 10 days. The shelf life of chillies was extended without altering the quality as compared to uncoated green chillies. Therefore, the formulated coating could be applicable for prolonging the shelf life of fresh produce.

Analysis of environmental organic matters by Ultrahigh-Resolution mass spectrometry-A review on the development of analytical methods

Owing to the increasing environmental and climate changes globally, there is an increasing interest in the molecular-level understanding of environmental organic compound mixtures, that is, the pursuit of complete and detailed knowledge of the chemical compositions and related chemical reactions. Environmental organic molecule mixtures, including those in air, soil, rivers, and oceans, have extremely complex and heterogeneous chemical compositions. For their analyses, ultrahigh-resolution and sub-ppb level mass accuracy, achievable using Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS), are important. FT-ICR MS has been successfully used to analyze complex environmental organic molecule mixtures such as natural, soil, particulate, and dissolved organic matter. Despite its success, many limitations still need to be overcome. Sample preparation, ionization, structural identification, chromatographic separation, and data interpretation are some key areas that have been the focus of numerous studies. This review describes key developments in analytical techniques in these areas to aid researchers seeking to start or continue investigations for the molecular-level understanding of environmental organic compound mixtures.

Monitoring of the impact of the proliferations of cyanobacteria on the characteristics of Natural Organic Matter in a eutrophic water resource: Comparison between 2012-2013 and 2017-2018

The natural surface waters are widely impacted by the seasonal blooms of phytoplankton and in water rich in nutrients their developments are controlled by the climate. These proliferations modify the global quality of the water resources and the Algal Organic Matter (AOM) produced by the algae and the cyanobacteria impacts the content and the characteristics of the Natural Organic Matter (NOM). However, none study deals with the sustainable influence of the recurrent seasonal blooms of phytoplankton on the chemical quality of the water resources. The physico-chemical, chemical and biological quality of a water resource and more specifically the content and the characteristics of the NOM were thus in situ monitored in a eutrophic pond in 2017-2018 and compared to the characteristics observed in 2012-2013. The blooms of phytoplankton were more important in 2017-2018 and the increase of both the temperature of the air and the radiance promoted the domination of cyanobacteria. None significant evolution of the content in chlorophyll-a, the concentrations in nutrients and the pH was observed between 2012-2013 and 2017-2018. However, the concentrations in DOC increased, more in summer periods than winter, because of the production of AOM by the algae and the cyanobacteria and the NOM presented more hydrophilic and less aromatic characters. These evolutions of the characteristics of the NOM were more important in 2017-2018 than 2012-2013. The recurrent inputs of AOM every year in summer periods seemed thus to sustainably modify the intrinsic characteristics of the NOM.

Evaluating the contributions of different organic matter sources to urban river water during a storm event via optical indices and molecular composition

Dissolved organic matter (DOM) in river water dynamically changes with respect to its major sources during heavy rain events. However, there has been no established tool to estimate the relative contributions of different organic sources to river water DOM. In this study, the evolution in the contributions of ten different organic matter (OM) sources to storm water DOM was explored with a selected urban river, the Geumho River in South Korea, during storm events via an end-member mixing analysis (EMMA) based on fluorescence indices and Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). The OM source materials included treated effluent, road runoff, groundwater, topsoil, deep soil, leaves, reeds, riparian plants, attached algae, and suspended algae. The EMMA results provided quantitative estimates of the variations in the dominant OM sources with the progress of storms. Treated effluent was the prevailing source at the beginning period of the storm, while topsoil, leaves, riparian plants, and groundwater predominated during and after the peak period. The fluorescence indices-based evaluation was consistent with the statistical comparison of the molecular formulas derived from FT-ICR-MS conducted on the ten potential OM sources and the storm samples. The observed variations in the OM sources agreed with the typical characteristics of urban rivers in connection with anthropogenic inputs and the impact of surrounding impervious surfaces. This study demonstrates the application of intuitive and facile tools in estimating the relative impacts of OM sources in urban watersheds.

The Diversity of Cyanobacterial Toxins on Structural Characterization, Distribution and Identification: A Systematic Review

The widespread distribution of cyanobacteria in the aquatic environment is increasing the risk of water pollution caused by cyanotoxins, which poses a serious threat to human health. However, the structural characterization, distribution and identification techniques of cyanotoxins have not been comprehensively reviewed in previous studies. This paper aims to elaborate the existing information systematically on the diversity of cyanotoxins to identify valuable research avenues. According to the chemical structure, cyanotoxins are mainly classified into cyclic peptides, alkaloids, lipopeptides, nonprotein amino acids and lipoglycans. In terms of global distribution, the amount of cyanotoxins are unbalanced in different areas. The diversity of cyanotoxins is more obviously found in many developed countries than that in undeveloped countries. Moreover, the threat of cyanotoxins has promoted the development of identification and detection technology. Many emerging methods have been developed to detect cyanotoxins in the environment. This communication provides a comprehensive review of the diversity of cyanotoxins, and the detection and identification technology was discussed. This detailed information will be a valuable resource for identifying the various types of cyanotoxins which threaten the environment of different areas. The ability to accurately identify specific cyanotoxins is an obvious and essential aspect of cyanobacterial research.

Unique characteristics of algal dissolved organic matter and their association with membrane fouling behavior: a review

Over the last several decades, the frequent occurrence of algal bloom in drinking water supplies, driven by increasing anthropogenic input and climate change, has posed serious problems for membrane filtration processes, resulting in reduced membrane permeability and increased energy consumption. It is essential to comprehensively understand the characteristics of algal dissolved organic matter (DOM) and the subsequent effects on the filtration processes for better insight into membrane fouling mitigation. Many studies have revealed that algal DOM has displayed unique characteristics distinguished from other sources of DOM with respect to the chemical composition, the structures, and the molecular weight distributions. Algal DOM is considered to be a major obstacle in understanding membrane fouling due to its complicated interactions among dissimilar algal DOM constituents as well as between algal DOM and membrane material matrices. The present review article summarizes (1) recent characterizing methods for algal DOM, (2) environmental factors affecting the characteristics of algal DOM, (3) the discrepancies between algal DOM and other sources of aquatic DOM, particularly terrestrial sources, and (4) potential fouling effects of algal DOM on membrane filtration processes and their associations with algal DOM characteristics. A broad understanding of algal DOM-driven membrane fouling can lead to breakthroughs in efficient membrane filtration processes to treat algal bloom water sources.

Effect of ecosystem type and fire on chemistry of WEOM as measured by LDI-TOF-MS and NMR

Soil organic matter (SOM) and its water-soluble components play an important role in terrestrial carbon cycling and associated ecosystem functions. Chemically, they are complex mixtures of organic compounds derived from decomposing plant material, microbial residues, as well as root exudates, and soil biota. To test the effect of the ecosystem type (forest and grassland) and fires events on the chemistry of dissolved organic matter (DOM), we applied a combination of laser-desorption/ionization time-of-flight mass spectrometry (LDI-TOF-MS) and 2D (¹H and ¹³C) nuclear magnetic resonance (NMR) spectroscopy to water-extractable organic matter (WEOM) from a range of top soil samples. The aim was to assess the suitability of LDI-TOF-MS for the rapid characterization of WEOM. Therefore, we evaluated the effects of sample (pH and dilution) conditions and use of positive or negative reflector mode to identify the conditions under which LDI-TOF-MS best distinguished between WEOM from different sources. Thirty-six samples were measured with both analytical techniques and their chemical patterns were statistically evaluated to distinguish firstly the effect of the type of ecosystem (forest versus grassland) on WEOM characteristics, and secondly the impact of fire on the chemical composition of WEOM. The nonmetric multidimensional scaling (NMDS) analysis of the most suitable experimental LDI-TOF-MS conditions showed a clear separation between the type of vegetation and fire-induced changes, mostly reflecting the presence of poly(ethylene glycol) in grassland soils. Discrimination among WEOM from different vegetation types was preserved in the fire treated samples. The calculation of the relative abundance of certain functional structures in the WEOM samples revealed a common composition of forest and grassland WEOM, with polysaccharides and proteins making up to 60%. The compositional impact of forest fire on WEOM was more pronounced compared to the one of grassland, leading to a decline in the main components, and an increase in amino-sugars, fatty acids, and sterols. The recorded ¹H NMR and heteronuclear single quantum coherence (HSQC) spectra showed a decrease of the carbohydrate signal in WEOM from fire-treated samples, which was more pronounced in forest than in grassland soils.

Inhibition of alkaline flocculation by algal organic matter for Chlorella vulgaris

Alkaline flocculation is a promising strategy for the concentration of microalgae for bulk biomass production. However, previous studies have shown that biological changes during the cultivation negatively affect flocculation efficiency. The influence of changes in cell properties and in the quality and composition of algal organic matter (AOM) were studied using Chlorella vulgaris as a model species. In batch cultivation, flocculation was increasingly inhibited over time and mainly influenced by changes in medium composition, rather than biological changes at the cell surface. Total carbohydrate content of the organic matter fraction sized bigger than 3 kDa increased over time and this fraction was shown to be mainly responsible for the inhibition of alkaline flocculation. The monosaccharide identification of this fraction mainly showed the presence of neutral and anionic monosaccharides. The addition of 30-50 mg L(-1) alginic acid, as a model for anionic carbohydrate polymers containing uronic acids, resulted in a complete inhibition of flocculation. These results suggest that inhibition of alkaline flocculation was caused by interaction of anionic polysaccharides leading to an increased flocculant demand over time.

The impact of interactions between algal organic matter and humic substances on coagulation

This study focuses on the effects of molecular interactions between two natural organic matter (NOM) fractions, peptides/proteins derived from cyanobacterium Microcystis aeruginosa (MA proteins) and peat humic substances (HS), on their removal by coagulation. Coagulation behaviour was studied by the jar tests with MA protein/HS mixtures and with single compounds (MA proteins or HS). Aluminium sulphate was used as a coagulant. Besides MA proteins, bovine serum albumin (BSA) was used as a model protein. For the MA protein/HS mixture, the removal rates were higher (80% versus 65%) and the dose of coagulant substantially lower (2.8 versus 5.5 mg L(-1) Al) than for coagulation of single HS, indicating the positive effect of protein-HS interactions on the coagulation process. The optimum coagulation pH was 5.2-6.7 for MA proteins and 5.5-6 for HS by alum. The optimum pH for the removal of MA protein/HS mixture ranged between pH 5.5-6.2, where the charge neutralization of negatively charged acidic functional groups of organic molecules by positively charged coagulant hydroxopolymers lead to coagulation. MA proteins interacted with HS, probably through hydrophobic, dipole-dipole and electrostatic interactions, even in the absence the coagulant. These interactions are likely to occur within a wide pH range, but they result in coagulation only at low pH values (pH < 4). At this pH, the negative charge of both MA proteins and HS was suppressed due to the protonation of acidic functional groups and thus the molecules could approach and combine forming aggregates. Virtually the same trends were observed in the experiments with HS and BSA, indicating that BSA is a suitable model for MA proteins under experimental conditions used in this study. The study showed that increases in organic content in source water due to the release of algae products may not necessarily entail deterioration of the coagulation process and a rise in coagulant demand.

Assessing Transformations of Algal Organic Matter in the Long-Term: Impacts of Humification-Like Processes

Algae and cyanobacteria are important contributors to the natural organic matter (NOM) of eutrophic water resources. The objective of this work is to increase knowledge on the modifications of algal organic matter (AOM) properties in the long term to anticipate blooms footprint in such aquatic environments. The production of AOM from an alga (Euglena gracilis) and a cyanobacteria (Microcystis aeruginosa) was followed up and characterized during the stationary phase and after one year and four months of cultivation, in batch experiments. Specific UV absorbance (SUVA) index, organic matter fractionation according to hydrophobicity and apparent molecular weight were combined to assess the evolution of AOM. A comparison between humic substances (HS) mainly derived from allochthonous origins and AOM characteristics was performed to hypothesize impacts of AOM transformation processes on the water quality of eutrophic water resources. Each AOM fraction underwent a specific evolution pattern, depending on its composition. Impacts of humification-like processes were predominant over release of biopolymers due to cells decay and led to an increase in the hydrophobic compounds part and molecular weights over time. However, the hydrophilic fraction remained the major fraction whatever the growth stage. Organic compounds generated by maturation of these precursors corresponded to large and aliphatic structures.