Characterizing changes of dissolved organic matter composition with the use of distinct feeds in recirculating aquaculture systems via high-resolution mass spectrometry

Occurrence of traffic related trace elements and organic micropollutants in tunnel wash water

Substantially polluted tunnel wash water (TWW) is produced during road tunnel maintenance. Previous literature has reported the presence of trace elements and polycyclic aromatic hydrocarbons (PAHs). However, it was hypothesized that other organic pollutants are present, and more knowledge is needed to prevent environmental harm. This study reveals for the first time the presence of four short- and 17 long-chained per- and polyfluoroalkyl substances (PFASs), three benzothiazoles (BTHs), six benzotriazoles (BTRs), four bisphenols, and four benzophenones in TWW from a Norwegian road tunnel over a period of three years. Concentrations of PAHs, PFASs, BTHs, and BTRs were higher than previously reported in e.g., road runoff and municipal wastewater. Trace elements and PAHs were largely particulate matter associated, while PFASs, BTHs, BTRs, bisphenols, and benzophenones were predominantly dissolved. 26 of the determined contaminants were classified as persistent, mobile, and toxic (PMT) and are of special concern. It was recommended that regulations for TWW quality should be expanded to include PMT contaminants (such as PFPeA, PFBS, BTR, and 4-OH-BzP) and markers of pollution (like 2-M-BTH, 2-OH-BTH, and 2-S-BTH from tire wear particles). These findings highlight the need to treat TWW before discharge into the environment, addressing both, particulate matter associated and dissolved contaminants.

Molecular formula assignment of dissolved organic matter by ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry using two non-targeted data processing approaches: A case study from recirculating aquaculture systems

BACKGROUND

The accumulation of dissolved organic matter (DOM) poses an issue in the management of the water quality from recirculating aquaculture systems (RAS), but its characterization is often not detailed enough to understand the DOM transformations in RAS. In this study, we investigated the application of two distinct non-targeted data processing approaches using ultra-performance liquid chromatography (UPLC) with quadrupole time-of-flight mass spectrometry (QTOF-MS) and two software with different algorithmic designs: PetroOrg and Progenesis QI to accurately characterize the molecular composition of DOM in RAS by UPLC-QTOF-MS.

RESULTS

The UPLC-QTOF-MS resolution in combination with PetroOrg and Progenesis QI software successfully assigned 912 and 106 unique elemental compositions, respectively, including compounds containing carbon, hydrogen, and oxygen (CHO) and nitrogen-containing CHO compounds (CHON), in the DOM samples from RAS. The results of these two distinct data processing approaches were consistent with the list of DOM formulas from RAS identified by higher resolution mass spectrometry techniques confirming their reliability. PetroOrg approach revealed only compositional information in the DOM samples from RAS, while Progenesis QI in addition to identifying new elemental compositions, increased their chemical space by giving information about their polarity and their possible key structures. DOM samples from RAS were found to be rich in unsaturated CHO compounds, with tentatively key structures of terpenoids with medium polarity indicating natural origins in their composition. The analysis also revealed probable structures of sucrose fatty acid esters and polyethylene glycol, indicating anthropogenic sources.

SIGNIFICANCE AND NOVELTY

The combination of these two non-targeted data processing approaches significantly improves the characterization of the complex mixture of DOM from RAS by UPLC-QTOF-MS reporting for the first time accurate DOM results in terms of its composition, while proposing its key structures. The presented methods can also be used to analyze different DOM samples with other HRMS techniques and software.

Monitoring of water quality with HPLSEC and fluorescence method in the ozonated recirculating aquaculture system

In recirculating aquaculture systems (RAS), it is important to monitor the water quality to keep the fish healthy. Especially in water treatment with oxidizing agents, for example, ozone (O3) or hydrogen peroxide (H2O2), the monitoring of the quality of dissolved organic matter (DOM) in water is advisable to keep track of the treatment's effect. Previously in wastewater treatment plant (WWTP) studied, HPLSEC and fluorescence method for monitoring and characterization of organic matter was used here to track the effect of oxidative treatments; 5 duplicated treatments (2 × O3, 1 × O3 + H2O2, 1 × H2O2, 1 × control) were performed for four months with weekly samplings. Systems that contained O3 injection reduced fluorescence on average over 90%, except tyrosine-like fluorescence with removal of 80%. Combined O3 + H2O2 treatment did not bring any advantages over pure O3 treatment, and H2O2 had no significant effect on fluorescence. Humic and fulvic compounds were detected to largely be derived from inlet lake water, while large protein-like structures were mostly created in RAS. A peak of benzoic acid-like molecules was also detected in all RAS waters. Treatments did not change the molecular weight profile of DOM systems and inlet water, having most of their fluorescence coming from medium-sized (108-1322 Da) molecules. DOC was lower in O3 treatments, but the linear connection between DOC and fluorescence was not observed, although this was proposed in earlier studies. Most likely, the oxidizing treatments induce change to DOM in a way that such comparison becomes inaccurate, although this must be studied further in the future.

Positive and negative effects of recirculating aquaculture water advanced oxidation: O3 and O3/UV treatments improved water quality but increased antibiotic resistance genes

Recirculating aquaculture systems (RASs) can be efficiently used for aquaculture, and oxidation treatment is commonly used to improve water quality. However, the effects of oxidation treatments on aquaculture water safety and fish yield in RASs are poorly understood. In this study, we tested the effects of O₃ and O₃/UV treatments on aquaculture water quality and safety during culture of crucian carp. O₃ and O₃/UV treatments reduced the dissolved organic carbon (DOC) concentration by ∼40% and destroyed the refractory organic lignin-like features. There was enrichment of ammonia oxidizing (Nitrospira, Nitrosomonas, and Nitrosospira) and denitrifying (Pelomonas, Methyloversatilis, and Sphingomonas) bacteria, and N-cycling functional genes were enriched by 23% and 48%, respectively, after O₃ and O₃/UV treatments. Treatment with O₃ and O₃/UV reduced NH₄⁺-N and NO₂^--N in RASs. O₃/UV treatment increased fish length and weight as well as probiotics in fish intestine. However, high saturated intermediates and tannin-like features induced antibiotic resistance genes (ARGs) in O₃ and O₃/UV treatments, by 52% and ∼28%, respectively, and also enhanced horizontal transfer of ARGs. Overall, the application of O₃/UV achieved better effects. However, understanding the potential biological risks posed by ARGs in RASs and determining the most efficient water treatment strategies to mitigate these risks should be goals of future work.

Critical assessment of the Kendrick mass defect analysis as an innovative approach to process high resolution mass spectrometry data for environmental applications

The growing application of high resolution mass spectrometry (HRMS) over the last decades has dramatically improved our knowledge about the occurrence of environmental contaminants. However, most of the compounds detected remain unknown and the large volume of data generated requires specific processing approaches. Therefore, this study presents the concepts of mass defect (MD), Kendrick mass (KM) and Kendrick mass defect (KMD) to the expert and non-expert reader along with relevant examples of applications in environmental HRMS data processing. A preliminary bibliometric overview indicates that the potential benefits of KMD analysis are rather overlooked in environmental science. In practice, a simple calculation allows transforming a mass from the IUPAC system (normalized so that the mass of ¹²C is exactly 12) to its corresponding KM normalized on a specific moiety such as CH₂ (the mass of CH₂ is exactly 14). Then, plotting the KMD according to the nominal KM allows revealing groups of compounds that differ only by their number of CH₂ moieties. For instance, data processing using KM and KMD was proven particularly useful to characterize natural organic matter in a sample, to reveal the occurrence of polymers as well as poly/perfluorinated alkylated substances (PFASs), and to search for transformation products (TPs) of a given chemical.

Impact of ozone treatment on dissolved organic matter in land-based recirculating aquaculture systems studied by Fourier transform ion cyclotron resonance mass spectrometry

In land-based recirculating aquaculture systems (RAS), the accumulation of dissolved organic matter (DOM) can have detrimental effects on water quality impacting the system performance, microbial community, and consequently fish health and welfare. Ozone is used in the RAS water treatment process to improve water quality and remove DOM. However, little is known about the molecular composition of DOM in RAS and its transformation when exposed to ozone. In this study, we performed a detailed molecular characterization of DOM in RAS and explored its transformation induced by ozonation of RAS waters. Ultra-high resolution (UHR) Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) was used to characterize the DOM matrix of RAS waters (pump-sump and tanks) and to evaluate its transformation by ozonation. The analysis of DOM extracted from makeup water and feed samples allowed for the determination of DOM sources in RAS prior to ozonation. The CHO and unsaturated group of compounds were the most abundant class found in water samples. On the contrary, the DOM from feed samples was unique and consisted mainly of CHO, CHON and unsaturated group of compounds. After the ozonation of RAS waters, humic-like and unsaturated compounds [positive oxygen subtracted double bond equivalent per carbon (DBE-O)/C)] were decomposed, particularly the CHO-DOM that contained fewer -CH₂- features. Fulvic-like compounds and several hundred saturated compounds [negative (DBE-O)/C)] were formed post ozonation, particularly the CHON and CHONS group of compounds that were associated with fish diets, makeup waters and transformation products from the ozonation of the RAS waters. This study showed that the high accuracy of the ultra-high resolution FTICR MS can be applied to characterize and monitor the changes of DOM at a molecular level in RAS waters. To our knowledge, this is the first study where FTICR MS was incorporated for the characterization of DOM and its sources in RAS.

The Determination of Polycyclic Aromatic Hydrocarbons (PAHs) with HPLC-DAD-FLD and GC-MS Techniques in the Dissolved and Particulate Phase of Road-Tunnel Wash Water: A Case Study for Cross-Array Comparisons and Applications

Accelerated solvent extraction (ASE) and solid phase extraction (SPE) protocols tailored to either gas chromatography mass spectrometry (GC-MS) or high-performance liquid chromatography coupled to diode-array and fluorescence detection (HPLC-DAD-FLD) were developed for the determination of EPA 16 polycyclic aromatic hydrocarbons (PAHs) in the particulate and dissolved phase of road-tunnel wash water. An analytical approach was developed, assessed, and applied on environmental samples collected from five road tunnels in Norway. The absolute recoveries ranged from 57 to 104% for the particulates, and from 42 to 79% for the dissolved water phase. The target PAH compounds were separated in 34.75 min using the GC method and in 22.50 min by HPLC. In the particulate phases, higher molecular weight PAHs were detected in the range of 0.043 to 0.93 µg/g, and lower molecular weight PAHs were detected in the range of 0.020 to 1.0 µg/g, while the intermediate ones were present in the range of 0.075 to 2.0 µg/g. In contrast to the particulates, the dissolved phase mainly contained lower molecular weight PAHs in the range of 0.0098 to 0.50 µg/L. GC-MS demonstrated lower detection limits (LODs) than HPLC-DAD-FLD for 13 out of the 16 PAHs. A cross-array comparison of the two analytical techniques indicated that some target PAHs were detected solely or in higher concentrations with HPLC-DAD-FLD, indicating the occurrence of false positive peaks or/and co-eluting components. The resulting concentrations in the road tunnel wash water samples were used to calculate specific PAH forensic ratios to pinpoint the potential sources of PAH pollution. These ratios revealed that there are several potential sources for the origin of PAHs in tunnel wash water.

Progress in the interaction of dissolved organic matter and microbes (1991-2020): a bibliometric review

Dissolved organic matter (DOM) and microbes are key in the planetary carbon cycle, and research on them can lead to a better understanding of the global carbon cycle and an improved ability to cope with environmental challenges. Several papers have reviewed one or several aspects of the interaction of DOM and microbes, but no overall review has been performed. Here, we bibliometrically analyzed all publications from the Web of Science on DOM and microbes (1991-2020). The results showed that studies on DOM and microbes grew exponentially during this period; the USA contributed the most to the total publications, and China has had the fastest increasing rate since 2010. Moreover, we used the Latent Dirichlet Allocation model to identify topics and determine their (cold or hot) trends by analyzing the abstracts of 9851 publications related to DOM and microbes. A total of 96 topics were extracted, and these topics that are related to the source, composition, and removal path of DOM and the temporal-spatial patterns of DOM and microbes consistently rose from 1991 to 2020. Most studies have used accurate and rapid methods combined with microbiological genetic approaches to study the interaction of DOM and microbes in terrestrial and aquatic ecosystems. The results also showed that the impacts of climate change and land use on the interaction of DOM and microbes, and topics related to human health have received considerable attention. In the future, the interaction mechanism of DOM and microbes and its response to environmental change should be further elucidated.

Assessing inputs of aquaculture-derived nutrients to streams using dissolved organic matter fluorescence

Salmon aquaculture is an important economic activity globally where local freshwater supplies permit land-based salmon aquaculture facilities to cultivate early life stage salmon. Nitrogen, phosphorus and organic matter in aquaculture effluents contribute to the eutrophication of adjacent and downstream rivers and lakes. This study quantifies the enrichment of nutrients in land-based salmon aquaculture facility effluents compared to receiving waters. We measured nutrient concentrations and dissolved organic matter (DOM) quantity and quality via fluorescence spectroscopy in streams and effluent waters associated with 27 facilities in Chile. We found that facilities added on average 0.9 (s.d. = 2.0) mg-C L^-1, 542 (s.d. = 637) μg-total N L^-1, and 104 (s.d. = 104) μg-total P L^-1 to effluents compared to stream waters. DOM in stream water was enriched in humic-like fluorescence, while aquaculture effluents were enriched in protein-like DOM fluorophores. Principal component and correlation analysis revealed that tryptophan-like fluorescence was a good predictor of total N and P in effluents, but the strength of significant linear relationships varied among individual facilities (r²: 0.2 to 0.9). Agreement between laboratory fluorescence and a portable fluorometer indicates the utility of in-situ sensors for monitoring of both tryptophan-like fluorescence and covarying nutrients in effluents. Thus, continuous in-situ sensors are likely to improve industry management and allow more robust estimates of aquaculture-derived nutrients delivered to receiving waters.

Impact of aquaculture on distribution of dissolved organic matter in coastal Jeju Island, Korea, based on absorption and fluorescence spectroscopy

In Jeju Island, multiple land-based aquafarms were fully operational along most coastal region. However, the effect of effluent on distribution and behaviours of dissolved organic matter (DOM) in the coastal water are still unknown. To decipher characteristics of organic pollution, we compared physicochemical parameters with spectral optical properties near the coastal aquafarms in Jeju Island. Absorption spectra were measured to calculate the absorption coefficient, spectral slope coefficient, and specific UV absorbance. Fluorescent DOM was analysed using fluorescence spectroscopy coupled with parallel factor analysis. Dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) were measured using high-temperature catalytic oxidation. The DOC concentration near the discharge outlet was twice higher than that in natural groundwater, and the TDN concentration exponentially increased close to the outlet. These distribution patterns indicate that aquafarms are a significant source of DOM. Herein, principal component analysis was applied to categorise the DOM origins. There were two distinct groups, namely, aquaculture activity for TDN with humic-like and high molecular weights DOM (PC1: 48.1%) and natural biological activity in the coastal water for DOC enrichment and protein-like DOM (PC2: 18.8%). We conclude that the aquafarms significantly discharge organic nitrogen pollutants and provoke in situ production of organic carbon. Furthermore, these findings indicate the potential of optical techniques for the efficient monitoring of anthropogenic organic pollutants from aquafarms worldwide.

Current trends and advances in analytical techniques for the characterization and quantification of biologically recalcitrant organic species in sludge and wastewater: A review

The study of organic matter in wastewater is a major regulatory and environmental issue and requires new developments to identify non-biodegradable refractory compounds, produced mainly by thermal treatments. Recent advances linking physicochemical properties to spectroscopic analyzes (UV, Fluorescence, IR) have shown that the refractory property is favored by several physicochemical parameters: weight, hydrophobicity, aromaticity and chemical functions. Currently, the most effective developments for the quantification of refractory compounds are obtained with hyphenated methods, based on steric separation of the macromolecular species by steric exclusion chromatography (SEC)/PDA/Fluorescence systems. Hyphenated techniques using High Resolution Mass Spectrometry (HRMS), ultra-high-resolution mass spectrometry with Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and NMR have been developed to analyze macromolecules in wastewater with minor sample preparation procedures. A particular class has been identified, the melanoidins, generated by Maillard reactions between sugars, amino acids, peptides and proteins present in wastewater and sludge, but low molecular weight compounds formed as intermediates, such as ketones, aldehydes, pyrazines, pyridines or furans, are also recalcitrant and are complex to identify in the complex matrices. The lack of available standards for the study of these compounds requires the use of specific techniques and data processing. Advances in chemometrics are obtained in the development of molecular or physicochemical indices resulting from the data generated by the analytical detectors, such as aromaticity calculated by SUVA₂₅₄ and determined by UV, fluorescence, molar mass, H/C ratio or structural studies (measuring the amount of unsaturated carbon) given by hyphenated techniques with SEC. It is clear that nitrogen compounds are widely involved in refractoriness. New trends in nitrogen containing compounds characterization follow two axes: through SEC/PDA/Fluorescence and HRMS/NMR techniques with or without separation. Other techniques widely used in food or marine science are also being imported to this study, as it can be seen in the use of "omics" methods, high-performance thin layer chromatography (HPTLC) and chromatography at the critical condition, rounding out the important developments around SEC. While improving the performance of stationary phases is one of the challenges, it results in a fundamental understanding of the retention mechanisms that today provide us with more information on the structures identified. The main objective of this review is to present the spectroscopic and physicochemical techniques used to qualify and characterize refractoriness with a specific focus on chemometric approaches.