Natural Organic Matter Quality Research Articles

Evaluation of molecular properties of humic acids from vermicompost by 13 C-CPMAS-NMR spectroscopy and thermochemolysis–GC–MS

The molecular characteristics of different vermicomposts, produced with variable rates of cattle manure and cotton residues, and of related humic acids were determined by 13C-CPMAS NMR and Off-line pyrolysis THM-GC–MS. The analyses highlighted a composition of mature vermicomposts based on differential amounts of lignocellulosic fraction and alkyl compounds inherited from original biomasses, thus revealing a decrease of overall hydrophobic character at increasing amounts of cotton input. The evaluation of molecular parameters derived from both solid state NMR spectra and from the specific biomarkers released by thermochemolysis suggested that the humification process was mainly characterized by the selective preservation of specific lignin derivatives. The potential bioactive properties of humic acids were hence evaluated in a bioassays test on maize seedlings. The humic extracts showed a differential response in root growth-promoting effect, depending on the specific molecular features. The higher bioactivity found in humic components isolated from vermicompost with no or low addition of cotton residues, supported the role of the overall hydrophobic character and of the large content of bioavailable lignin units and nitrogen moieties. These results confirm that the combination of solid state NMR and thermochemolysis are valuable and efficient tools to assess the molecular quality of natural organic matter. The detailed molecular characterization of compost materials may hence represent a useful requirement to select the most suitable application of bulk biomasses and derived fractions for soil organic matter managements.

Natural organic matter fractions and their removal in full-scale drinking water treatment under cold climate conditions in Nordic capitals

Drinking water treatment plants (DWTPs) designed to remove natural organic matter (NOM) are challenged as concentrations of NOM in raw waters are increasing. Here, we assess seasonal differences in NOM quality and quantity, from raw waters to the distribution network, at three large DWTPs in Oslo, Stockholm and Helsinki. Samples, collected during stable stratification in both winter and summer and during the autumnal turnover, were analysed for NOM concentrations and composition. The NOM was characterized by common routine parameters, size and content (TFF, LC-OCD, fluorescence) and biodegradability. The NOM concentration decreased to 2.5 mg/L (55%), 4.0 mg/L (48%) and 5.7 mg/L (76%) at the respective DWTPs in Oslo, Stockholm and Helsinki. The NOM in raw waters were predominantly in the largest size fraction (>50 kDa), in particular from Oslo. High MW fractions >50 kDa and humics remained the largest fractions with minimum 30% and maximum 80% of the total NOM. The BDOC in treated water <0.3 mg/L and the conditions in the distribution network imply low probability for bacteria regrowth.The multi-step treatment consisting of coagulation/flocculation, sedimentation, rapid sand filtration, ozonation and biological activated carbon filtration (BAC) was most effective in removing NOM. Coagulation/flocculation followed by sedimentation and sand filtration were critical, especially for the removal of biopolymers and humics, and somewhat for building blocks. The sand filtration provided up to 25% additional removal of biopolymers and below 7% removal of other fractions. The ozonation and BAC was more effective and removed 11% of biopolymers, and about 35% of building blocks and LMW neutrals.

Tracking of Dissolved Effluent Organic Matter (dEfOM) in wastewater treatment plant by using fluorescence method

Discharge of wastewater into water body can change the quantity and quality of natural organic matter (NOM) in source water, because wastewater may contain dissolved effluent organic matter (dEfOM). dEfOM consists of a heterogenous mixture of organic compounds with various structures, such as dissolved organic matter, microbial by-products, endocrine disrupting compound, etc. The objectives of this study is to track the fate of dEfOM by using fluorescence excitation emission matrices (FEEMs) in order to apply of reclaimed water from industrial wastewater. Tracking of NOM was observed in industrial park of wastewater treatment, which is consist of equalization tank, coagulation, flocculation, sedimentation, activated sludge tank and clarifier tank. FEEMs with parallel factor analysis (PARAFAC) analysis decomposed the organic matter in wastewater into two components, namely component C1 at (Ex/Em): 330(235)/410 is humic acid like and fulvic, component C2 at (Ex/Em): 280(230)/350 is soluble microbial products and aromatic protein. Characteristic of dEfOM depends on the wastewater characteristic and its treatment processes.

New Insights into Trihalomethane and Haloacetic Acid Formation Potentials: Correlation with the Molecular Composition of Natural Organic Matter in Source Water.

Natural organic matter (NOM) represents the major source of precursors for disinfection byproducts (DBPs), such as trihalomethanes (THMs) and haloacetic acids (HAAs), formed during disinfection of drinking water, but the molecular composition and reactivity of NOM remain not well understood. In this study, electrospray ionization coupled to Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was used to characterize the molecular composition of NOM of 20 source waters taken across China for the purpose of determining the major precursors of THMs and HAAs at molecular level. It was found that there is a core of NOM compositions that are ubiquitous in different source waters, which is supposed to be more relevant for NOM quality. Formation potentials (FP) of THMs and HAAs were determined for NOM from different source waters during chlorination. Spearman's rank correlation was used to link THMFP and HAAFP with the individual molecular composition of NOM. Significant correlation (P < 0.001) was found between DBPFP and the NOM molecules with a high O/C ratio and low H/C ratio, indicating these molecules could contribute greatly to the formation of THMs and HAAs during chlorination. The link of THMFP and HAAFP with individual NOM molecules may allow us to develop more effective treatment strategies to achieve the drinking water safety objective: effective disinfection of waterborne pathogens while minimizing toxic DBPs.

Integrity breaches in a hollow fiber nanofilter – Effects on natural organic matter and virus-like particle removal

Ultrafiltration and nanofiltration have become common methods to treat surface water for drinking water purposes. Common aims of a membrane step are removal of natural organic matter (NOM), softening or adding an extra microbiological or chemical barrier. In most cases, the membrane is considered a good disinfection step; commonly the viral removal is at least 4–log. To ensure a working disinfection, reliable integrity tests are required. In the present pilot study with a hollow fiber nanofilter, the membrane achieved a high NOM reduction, and the difference in parameters related to NOM quality before and after treatment proved to be useful indicators of integrity breaches. Changes in total organic carbon (TOC) concentration, UV-absorbance at 254 nm (UVA254) and fluorescence derived parameters in the permeate flow were related to leaking fibers. On average, UVA254 in the permeate was 3 times higher for a membrane with compromised fibers (0.041 cm−1) compared to an intact membrane (0.013 cm−1), while TOC was less than 2 times as high on average. Thus, this membrane had a higher reduction of UVA254 than TOC and the sensitivity for changes from leakage was higher. Therefore, it is suggested that UVA254 could be used as an indicator for membrane integrity. Additionally, there is a significant (P < 0.01) difference in fluorescence derived parameters between a leaking and an intact fiber, showing that fluorescence also has potential to be applied for online monitoring of membrane processes. During fiber failure, around 2% of the permeate flow passes through one single leaking fiber. The transport depends on the distance between the inflow and the leak, which in most cases are similar and most likely close to the middle of the fiber.

Quantity and quality of natural organic matter influence the ecotoxicity of titanium dioxide nanoparticles

Nanoparticles’ fate is amongst other parameters determined by the quantity and quality of natural organic matter (NOM). Consequently, the ecotoxicity of nanoparticles is modified, while only little information is available on the NOM characteristics triggering this interplay. This study systematically examined how NOM quantity and quality influences the acute ecotoxicity of titanium dioxide nanoparticles (nTiO2) towards Daphnia magna. Therefore, two nTiO2 products (A-100 and P25; ∼100 nm) were investigated in combination with seven NOM types of variable quality at four levels each (up to 4.00 mg total organic carbon/L). The results showed that – independent of the applied nTiO2 product and NOM type – nTiO2 ecotoxicity decreased up to a factor of >18 with increasing NOM concentration. More importantly, increasing levels of aromaticity and hydrophobicity of the NOM decreased the magnitude of toxic effects caused by nTiO2, which was again independent of the nTiO2 product tested. In the light of the ubiquitary presence of NOM, the ecotoxicological risk of nTiO2 in surface waters with high NOM loads is likely moderate. However, interactions of nTiO2 and NOM in combination with other natural or chemical stressors are not well-understood but seem to be fundamental for a reliable risk assessment of nanoparticles.

Bioanalytical and chemical assessment of the disinfection by-product formation potential: Role of organic matter

Disinfection by-products (DBP) formed from natural organic matter and disinfectants like chlorine and chloramine may cause adverse health effects. Here, we evaluate how the quantity and quality of natural organic matter and other precursors influence the formation of DBPs during chlorination and chloramination using a comprehensive approach including chemical analysis of regulated and emerging DBPs, total organic halogen quantification, organic matter characterisation and bioanalytical tools. In vitro bioassays allow us to assess the hazard potential of DBPs early in the chain of cellular events, when the DBPs react with their molecular target(s) and activate stress response and defence mechanisms. Given the reactive properties of known DBPs, a suite of bioassays targeting reactive modes of toxic action including genotoxicity and sensitive early warning endpoints such as protein damage and oxidative stress were evaluated in addition to cytotoxicity. Coagulated surface water was collected from three different drinking water treatment plants, along with reverse osmosis permeate from a desalination plant, and DBP formation potential was assessed after chlorination and chloramination. While effects were low or below the limit of detection before disinfection, the observed effects and DBP levels increased after disinfection and were generally higher after chlorination than after chloramination, indicating that chlorination forms higher concentrations of DBPs or more potent DBPs in the studied waters. Bacterial cytotoxicity, assessed using the bioluminescence inhibition assay, and induction of the oxidative stress response were the most sensitive endpoints, followed by genotoxicity. Source waters with higher dissolved organic carbon levels induced increased DBP formation and caused greater effects in the endpoints related to DNA damage repair, glutathione conjugation/protein damage and the Nrf2 oxidative stress response pathway after disinfection. Fractionation studies indicated that all molecular weight fractions of organic carbon contributed to the DBP formation potential, with the humic rich fractions forming the greatest amount of DBPs, while the low molecular weight fractions formed more brominated DBPs due to the high bromide to organic carbon ratio. The presence of higher bromide concentrations also led to a higher fraction of brominated DBPs as well as proportionally higher effects. This study demonstrates how a suite of analytical and bioanalytical tools can be used to effectively characterise the precursors and formation potential of DBPs.

Effects of dissolved organic matter and reduced sulphur on copper bioavailability in coastal marine environments

Copper-induced toxicity in aqueous systems depends on its speciation and bioavailability. Natural organic matter (NOM) and reduced sulphur species can complex copper, influencing speciation and decreasing bioavailability. NOM composition in estuaries can vary, depending on inputs of terrigenous, autochthonous, or wastewater source material. At a molecular level, variability in NOM quality potentially results in different extents of copper binding. The aims of this study were to measure acute copper EC50 values in coastal marine and estuarine waters, and identify the relationships between total dissolved copper EC50 values and measured water chemistry parameters proportional to NOM and reduced sulphur composition. This has implications on the development of marine-specific toxicity prediction models. NOM was characterised using dissolved organic carbon (DOC) concentration and fluorescence measurements, combined with spectral resolution techniques, to quantify humic-, fulvic-, tryptophan-, and tyrosine-like fractions. Reduced sulphur was measured by the chromium-reducible sulphide (CRS) technique. Acute copper toxicity tests were performed on samples expressing extreme DOC, fluorescent terrigenous, autochthonous, and CRS concentrations. The results show significant differences in NOM quality, independent of DOC concentration. CRS is variable among the samples; concentrations ranging from 4 to 40nM. The toxicity results suggest DOC as a very good predictive measure of copper EC50 in estuaries (r2=0.87) independent of NOM quality. Furthermore, for filtered samples, CRS exists at concentrations that would be saturated with copper at measured EC50, suggesting that while CRS might bind Cu and decrease bioavailability, it does not control copper speciation at toxicologically relevant concentrations and therefore is not a good predictive measure of copper toxicity in filtered samples.

Fluorescence Analysis of Natural Organic Matter Fractionated by Ultrafiltration: Contrasting Between Urban-Impacted Water, and Radio-Contaminated Water from a Near-Pristine Site

Aqueous natural organic matter (NOM) impacted by two contrasting human impacts was analyzed using by multiresponse fluorescence, decoupled with the resolution routine PARAFAC. The first site is Chalk River, Ontario, Canada, near a pit formerly used to dispose low-level wastes. The second site is the Grand River in Cambridge, south-central Ontario, which is impacted by urban activities and agriculture. Our analysis included raw water, plus fractions from ultrafiltration and solid-phase extraction (SPE). The fluorescence spectra of the NOM, resolved with PARAFAC, showed three common features: humic-like components, at excitation/emission wavelengths 325–350/450–475 nm, fulvic-like components at 325/380–420 nm and protein-like components, at 275/300 nm. Ultrafiltration revealed that most of the NOM comprised fine material below 5,000 Da cut-off (<4% of the total) in the urban-impacted sites and the clean site at Chalk River, but the colloidal fraction (larger than 5,000 Da) was substantially higher in the contaminated water, with ∼18–26% of the total. The protein-like components in the contaminated Chalk River water were affected by ultrafiltration, but less so in the clean Chalk River sample and the urban-impacted waters. SPE preferentially removed the protein-like component in the contaminated Chalk River water (typically 89–95% signal decrease), but had a limited effect on humic- and fulvic-like components elsewhere. In conclusion, multiresponse fluorescence provided new information on the NOM quality from two contrasting sites, aided by ultrafiltration and SPE. These results are consistent with the in situ production of NOM in the Chalk River contaminated site, and natural production at the other sites.

Photodegradation of natural organic matter from diverse freshwater sources

Natural organic matter (NOM) is significant in determining fate, transport and toxicity of metals in aqueous systems but NOM is not a static component; NOM can undergo photochemical changes in chemical structure. These changes will modify NOM quality and in turn influence how metals are transported in the environment, as well as their toxicity to aquatic organisms. Natural organic matter was collected from five freshwater sources using a portable reverse osmosis unit, diluted to about 10 mg C L −1, then exposed for 13 days to summer temperatures either in the dark or exposed to sunlight. Light exposed NOM had decreases in total organic carbon (TOC) of 8–35% compared to samples kept in a refrigerator (dark, 4 °C), and the NOM became optically lighter, as shown by specific absorbance coefficients (SAC) taken at 340 nm (55–76% decreases in SAC 340). In contrast, dark exposed NOM showed much smaller decreases in TOC (≤3%) or SAC 340 (≤32%). For light exposed samples fluorescence excitation–emission matrix spectroscopy showed loss of fluorescence mainly in the 330 nm excitation, 420–450 nm emission range, consistent with loss of fulvic- and humic-like, aromatic groups in the NOM. Commercial (Aldrich) humic acid showed similar changes when exposed to light, with decreases in fulvic and humic fluorescence peaks. Finely ground fish food, used as a source of protein-rich organic matter, showed similar decreases in TOC and SAC 340 when exposed to light, but showed increased SAC 340 in the foil wrapped samples, presumably because bacteria were involved in decomposition of the food organic matter. Overall, these results indicate photodegradation of terrestrially derived, aromatic functional groups (e.g., from lignin) in natural organic matter from various freshwater sources.

NOM increase in drinking water reservoirs - relevance for drinking water production

In the last 10–15 years in some German drinking water reservoirs an increase in the NOM (natural organic matter) content has occurred. The impact of such a change on the drinking water quality was almost unknown. A research project was carried out at several drinking water reservoirs and water works concerning the change in the NOM quality and the nutrient situation. The results indicate that the NOM increase in the reservoir is predominately caused by an increasing input of high and intermediate molecular weight humic substances from the catchment area into the reservoir. The fractions of the polysaccharides and the high molecular weight humic substances are significantly reduced in the treatment process. In contrast, the elimination rate for the substances with an intermediate and low molecular weight was low. Due to the low elimination rate particularly of the intermediate humic fraction, the NOM content of the treated water increased with the change in the raw water. Furthermore, the BDOC of the treated water increased with the NOM content. For the AOC of the treated water no relationship was found with the NOM content. However, the change of this parameter was affected by the snowmelt and the circulation in the reservoir.

Photochemical degradation of PAHs in freshwaters and their impact on bacterial growth – influence of water chemistry

Solar ultraviolet radiation both degrades and alters the quality of natural organic matter as well as organic pollutants in surface waters. Still, it is only recently that this indirect influence of photochemical processes on aquatic organisms (e.g. bacteria) has received attention. We experimentally studied the photochemical degradation of three PAHs; anthracene, phenanthrene and naphthalene, in water. Anthracene and phenanthrene were rapidly photodegraded (half-lives of 1 and 20.4 hours, respectively), while the photochemical half-life of naphthalene exceeded 100 hours. Hence photodegradation is most likely a less important removal mechanism for the latter compound. The influence of humic substance additions (0–25 mg C l−1) on degradation rates was also assessed, and while photodegradation of anthracene was not affected by these additions, phenanthrene photodegradation slowed down considerably at the higher humic substance concentrations. These differential responses of anthracene and phenanthrene can at least partially be explained by differences in the spectral absorbance of the two compounds. In contrast, ionic strength did not have any appreciable effect on the estimated photodegradation rates of either compound. The influence of PAHs on growth of aquatic bacteria was assessed in dilution cultures with and without exposure to PAHs and simulated solar UV radiation. Separately, neither PAHs nor simulated solar UV radiation had any effect on bacterial growth. However, when combined, a marked inhibition of bacterial growth could be observed in water obtained from a clearwater lake. This could be due to the formation of toxic photodegradation products such as quinones (detected in our incubations) or other reactive species that affect bacteria negatively. Hence, in addition to influencing the fate and persistence of PAHs in aquatic systems, solar radiation and natural organic matter and regulate the toxicity of these compounds to indigenous micro-organisms.

Acid Rain and Natural Organic Matter (NOM)

Twentyfive years of research on the effects of acid rain on rivers and lakes has, to a very small extent, documented changes in the nature and properties of natural organic matter (NOM). In Western Norway, a "whole-watershed-artificial-acidification-experiment" took place in the period 1988–1996. The goals of this long-term experiment were to study the role of NOM in acidification of surface water and the effects of acid precipitation on the quality and properties of NOM. In the HUMEX project (Humic Lake Acidification Experiment) one half of a lake and the corresponding catchment was artificially acidified with H2SO4 and NH4NO3 over a period of 5 years. The other half of the lake and catchment served as a control. In addition to monitoring of the general chemical composition of the water from the two lake halves, a number of other chemical and biological characteristics were studied. Here, we report the results related to changes in the nature and chemical properties of NOM. During the first few years of acidification, a significantly lower concentration of NOM was recorded in the acidified half of the catchment, compared with the control. However, statistical analyses of all data (covering a 2-years pre-treatment period and 5 years of treatment) related to the concentration of NOM (TOC, colour, and UV absorbance) did not suggest any significant effect on the quantity of NOM. This apparent discrepancy between the initial decrease in the concentration of NOM and no effect when the whole 5-years period is considered, may be due to the results of two different simultaneous processes. The results suggest that there first was a reduction of TOC and colour, as a consequence of the acidification, followed by an increase, perhaps owing to increased fertilisation (nitrogen) and in addition to a general temperature increase during the period. In addition, short-term studies of the aquatic surface microlayers, lipophilicity of the NOM, content of organic sulfur, and molecular size indicate differences in the quality of the NOM between the two lake halves, which could affect light absorption. Saurer Regen und natürliche organische Wasserinhaltsstoffe In 25 Jahren Forschung zu den Auswirkungen des sauren Regens auf Flüsse und Seen wurden in geringem Ausmaß Veränderungen von Natur und Eigenschaften natürlicher organischer Wasserinhaltsstoffe (natural organic matter – NOM) dokumentiert. In Westnorwegen fand von 1988 bis 1996 ein Großversuch statt, in dem ein ganzes Wassereinzugsgebiet einer künstlichen Versauerung unterzogen wurde (whole watershed artificial acidification experiment). In diesem Langzeitexperiment sollten die Rolle der NOM bei der Versauerung von Oberflächenwasser und die Auswirkungen saurer Niederschläge auf Qualität und Eigenschaften der NOM untersucht werden. Im Rahmen des Projektes HUMEX (humic lake acidification experiment – künstliche Versauerung eines huminstoffreichen Sees) wurde ein See durch eine Absperrung in zwei Hälften unterteilt. In der einen Hälfte des Sees wurde über einen Zeitraum von 5 Jahren künstlich eine Versauerung herbeigeführt, indem die Wasserfläche und das umliegende Einzugsgebiet mit H2SO4 und NH4NO3-Lösung beregnet wurden. Die andere Hälfte des Sees mit ihrem Einzugsgebiet diente als unbeeinflußte Kontrolle. In dieser Zeit wurden die chemische Zusammensetzung des Wassers in den beiden Seehälften sowie eine Reihe weiterer chemischer und biologischer Meßgrößen verfolgt. In den ersten Jahren wurde in der versauerten Hälfte des Sees eine im Vergleich zur Kontrolle signifikant niedrigere Konzentration natürlicher organischer Wasserinhaltsstoffe gefunden. Über den gesamten Zeitraum jedoch – 2 Jahre Beobachtungszeit vor der künstlichen Versauerung und 5 Jahre Säureeintrag – ergab die statistische Analyse aller Daten zur Konzentration der NOM (gesamter organisch gebundener Kohlenstoff (TOC), Färbung und UV-Absorbanz) keinen Hinweis auf eine signifikante Beeinflussung der natürlichen organischen Wasserinhaltsstoffe bezüglich ihrer Quantität. Diese Diskrepanz zwischen der anfänglichen Abnahme der NOM-Konzentration und der bei Betrachtung des gesamten Versuchszeitraums beobachteten Konstanz konnte auf zwei unterschiedliche, gegenläufige Prozesse zurückzuführen sein: Zunächst nehmen TOC-Konzentration und Färbung als Folge der Versauerung ab, dann erfolgt eine NOM-Zunahme aufgrund des gestiegenen Nährstoffgehalts (Stickstoff). Zu berücksichtigen ist dabei auch, daß während des Versuchszeitraums ein Temperaturanstieg beobachtet wurde. Zusätzlich zur Langzeitbeobachtung grundlegender Parameter wurden einzelne Untersuchungen zu Lipophilie der NOM, Gehalt an organisch gebundenem Schwefel und Molekülgröße.