Thermal fluorescence quenching properties of dissolved organic matter

The fluorescence excitation-emission matrices of dissolved organic matter (DOM) are investigated between 10 and 45 degrees C for river and waste waters and organic matter standards. With increased temperature, fluorescence intensity is quenched. It is demonstrated that for a range of river and wastewater samples, that tryptophan-like fluorescence exhibits a greater range of quenching (between 20+/-4% and 35+/-5%) than fulvic-like fluorescence (19+/-4 to 26+/-3%) over this temperature range. Humic substance standards exhibit similar fulvic-like (23+/-4%) fluorescence thermal quenching properties to river water samples (23+/-3%); however none of the samples exhibit quenching of tryptophan-like fluorescence to the same extent as the tryptophan standards (approximately 50%). Thermal fluorescence quenching is related to the exposure of the fluorophores to the heat source; our findings suggest that the tryptophan-like groups within DOM is more exposed in untreated wastewaters than in treated wastewaters riverine DOM. Thermal fluorescence properties have the potential to be used to source DOM, to provide additional chemical structural information, to temperature correct laser-induced remotely sensed DOM fluorescence, and to characterise DOM through the wastewater treatment process.     

Development and application of functional assays for freshwater dissolved organic matter

A series of 11 standardised, reproducible, assays have been developed of physico-chemical functions of dissolved organic matter (DOM) in freshwaters. The assays provide quantitative information on light absorption, fluorescence, photochemical fading, pH buffering, copper binding, benzo(a)pyrene binding, hydrophilicity and adsorption to alumina. To obtain DOM for the assays, a 45 L sample of filtered freshwater was rotary-evaporated to reduce the volume to ca. 500 cm3. The concentrate was then passed through a strong cation exchanger, in the Na+ form, to remove alkaline-earth cations, and then through 0.7 and 0.2 microm filters. Eight samples, two each from a lake and three streamwaters, were processed. The yields of dissolved organic carbon (DOC) ranged from 70% to 107% (average 91%). The samples of DOM, stored in the dark at 4 degrees C, retained their functional assay characteristics for up to 7 months. When assaying the concentrates, parallel assays were performed with Suwannee River fulvic acid (SRFA), as a quality control standard. For most of the assays, the results for eight freshwater DOM samples are similar to those obtained with SRFA, the chief exception being the greater hydrophilicity of the DOM samples. For eight of the assays, variability among the DOM samples is significantly (p < 0.01) greater than can be explained by analytical error, i.e. by comparison with results for the SRFA quality standard; the three exceptional assays are photochemical fading, copper binding and benzo(a)pyrene binding. The two lakewater samples studied gave the most extreme assay results, probably because of the influence of phytoplankton-derived DOM. Significant correlations of hydrophilicity and adsorption with optical absorbance may mean that some DOM functional properties can be predicted from comparatively simple measurements.     

Modeling heavy metal uptake by sludge particulates in the presence of dissolved organic matter

The uptake of the seven heavy metal ions Cd(II), Co(II), Cr(III), Cu(II), Ni(II), Pb(II), and Zn(II) by sludge particulates in single-metal systems was investigated. Results showed that under acidic and neutral pH conditions, the uptake of all heavy metals by sludge particulates increases with the increase of pH. However, in the alkaline pH region, the uptake of Cu(II), Ni(II), and Co(II) decreases with the increase of pH, primarily due to the high dissolved organic matter (DOM) concentration in high pH conditions. Based on chemical reactions among heavy metal, sludge solids, and DOM, a mathematical model describing metal uptake as functions of DOM and pH was developed. The stability constants of metal–sludge and metal–DOM complexes can be determined using this model in conjunction with experimental metal uptake data. Results showed that, for the secondary sludge sample collected from Baltimore Back River Wastewater Treatment plant on March 1997, the stability constants of Cu(II)–sludge complex (log K_S) and Cu(II)–DOM complex (log K_L) are 5.3±0.2 and 4.7±0.3, respectively; for Ni(II), they are 4.0±0.2 and 3.9±0.2, respectively. Results also showed that under neutral and low pH conditions (pH<8), the DOM effects on metal uptake for all heavy metals are insignificant. Therefore, the DOM term in the model can be ignored. Results showed that, for the secondary sludge sample collected from Baltimore Back River Wastewater Treatment plant on December 1996, the estimated log K_S values of metal–sludge complexes for Cd(II), Co(II), Cr(III), Cu(II), Ni(II), Pb(II), and Zn(II) are, respectively, 3.6±0.2, 3.0±0.1, 5.5±0.1, 4.8±0.1, 3.1±0.1, 5.1±0.1, and 4.4±0.3.     

Photo-dissolution of flocculent, detrital material in aquatic environments: contributions to the dissolved organic matter pool

This study shows that light exposure of flocculent material (floc) from the Florida Coastal Everglades (FCE) results in significant dissolved organic matter (DOM) generation through photo-dissolution processes. Floc was collected at two sites along the Shark River Slough (SRS) and irradiated with artificial sunlight. The DOM generated was characterized using elemental analysis and excitation emission matrix fluorescence coupled with parallel factor analysis. To investigate the seasonal variations of DOM photo-generation from floc, this experiment was performed in typical dry (April) and wet (October) seasons for the FCE. Our results show that the dissolved organic carbon (DOC) for samples incubated under dark conditions displayed a relatively small increase, suggesting that microbial processes and/or leaching might be minor processes in comparison to photo-dissolution for the generation of DOM from floc. On the other hand, DOC increased substantially (as much as 259 mgC gC⁻¹) for samples exposed to artificial sunlight, indicating the release of DOM through photo-induced alterations of floc. The fluorescence intensity of both humic-like and protein-like components also increased with light exposure. Terrestrial humic-like components were found to be the main contributors (up to 70%) to the chromophoric DOM (CDOM) pool, while protein-like components comprised a relatively small percentage (up to 16%) of the total CDOM. Simultaneously to the generation of DOC, both total dissolved nitrogen and soluble reactive phosphorus also increased substantially during the photo-incubation period. Thus, the photo-dissolution of floc can be an important source of DOM to the FCE environment, with the potential to influence nutrient dynamics in this system.     

UV-induced photochemical heterogeneity of dissolved and attached organic matter associated with cyanobacterial blooms in a eutrophic freshwater lake

Cyanobacterial blooms represent a significant ecological and human health problem worldwide. In aquatic environments, cyanobacterial blooms are actually surrounded by dissolved organic matter (DOM) and attached organic matter (AOM) that bind with algal cells. In this study, DOM and AOM fractionated from blooming cyanobacteria in a eutrophic freshwater lake (Lake Taihu, China) were irradiated with a polychromatic UV lamp, and the photochemical heterogeneity was investigated using fluorescence excitation–emission matrix (EEM)-parallel factor (PARAFAC) analysis and synchronous fluorescence (SF)-two dimensional correlation spectroscopy (2DCOS). It was shown that a 6-day UV irradiation caused more pronounced mineralization for DOM than AOM (59.7% vs. 41.9%). The EEM-PARAFAC analysis identified one tyrosine-, one humic-, and two tryptophan-like components in both DOM and AOM, and high component photodegradation rates were observed for DOM versus AOM (k > 0.554 vs. <0.519). Moreover, SF-2DCOS found that the photodegradation of organic matters followed the sequence of tyrosine-like > humic-like > tryptophan-like substances. Humic-like substances promoted the indirect photochemical reactions, and were responsible for the higher photochemical rate for DOM. The lower photodegradation of AOM benefited the integrality of cells in cyanobacterial blooms against the negative impact of UV irradiation. Therefore, the photochemical behavior of organic matter was related to the adaptation of enhanced-duration cyanobacterial blooms in aquatic environments.     

Atrazine removal from water by polycation-clay composites: Effect of dissolved organic matter and comparison to activated carbon

Atrazine removal from water by two polycations pre-adsorbed on montmorillonite was studied. Batch experiments demonstrated that the most suitable composite poly (4-vinylpyridine-co-styrene)-montmorillonite (PVP-co-S90%-mont.) removed 90-99% of atrazine (0.5-28 ppm) within 20-40 min at 0.367% w/w. Calculations employing Langmuir's equation could simulate and predict the kinetics and final extents of atrazine adsorption. Column filter experiments (columns 20 × 1.6 cm) which included 2 g of the PVP-co-S90%-mont. composite mixed with excess sand removed 93-96% of atrazine (800 ppb) for the first 800 pore volumes, whereas the same amount of granular activated carbon (GAC) removed 83-75%. In the presence of dissolved organic matter (DOM; 3.7 ppm) the efficiency of the GAC filter to remove atrazine decreased significantly (68-52% removal), whereas the corresponding efficiency of the PVP-co-S90%-mont. filter was only slightly influenced by DOM. At lower atrazine concentration (7 ppb) the PVP-co-S90%-mont. filter reduced even after 3000 pore volumes the emerging atrazine concentration below 3 ppb (USEPA standard). In the case of the GAC filter the emerging atrazine concentration was between 2.4 and 5.3 μg/L even for the first 100 pore volumes. Thus, the PVP-co-S90%-mont. composite is a new efficient material for the removal of atrazine from water.     

Spectrofluorometric properties of dissolved organic matter from Central and Southern Ontario streams and the influence of iron and irradiation

Fluorescence measurements were used to compare characteristics of dissolved organic matter (DOM) from distinctly different origins: boreal, agricultural and urban streams as well as a storm runoff pond and the outlet of a tertiary wastewater treatment plant. The primary goal was to determine if differences among stream types could be detected using DOM fluorescence in lieu of isolated fulvic acids (FA). Differences in peak excitation and peak emission wavelengths, fluorescence integrated over the 3-D matrix volume integrated fluorescence (VIF), and in a fluorescence index (FI) were examined. In general, peak fluorescence excitation and emission wavelengths as well as FI best distinguished DOM from the various origins. Results suggested that DOM from the boreal streams was of a higher molecular weight and more complex than that of agricultural and urban streams. The effects of irradiation as well as Fe on fluorescence of natural stream waters were also investigated, both of which decreased the ability of optical properties to distinguish DOM source.     

Freeze/thaw and pH effects on freshwater dissolved organic matter fluorescence and absorbance properties from a number of UK locations

The UV-visible and fluorescence excitation-emission matrix spectrophotometric properties of dissolved organic matter (DOM) were compared for the effects of both pH and freeze/thaw on a wide range of freshwater DOM samples from the United Kingdom. It was observed that the spectrophotometric properties of our freshwater samples were sensitive to pH and that the recorded change varies with fluorescence and absorbance intensity, DOC concentration and the wavelength observed. Large and variable responses to pH were particularly severe at extremes of pH, but within the natural levels typically observed in freshwaters the response to pH was limited. For the same sample set large and variable responses were observed when subjected to freeze/thaw. From our data, knowledge of the original properties cannot be used to determine the amount of change that will occur with freezing and subsequent thawing. It is therefore recommended that in future research, to maintain the natural signal of the DOM, analysis is conducted at natural pH and without freezing to facilitate ease of comparison between studies. Our results also have implications for studies that utilise spectrophotometric techniques to investigate long-term trends in dissolved organic carbon in rivers. Spectrophotometric parameters from upland derived samples show varied responses of samples to pH and there is clear potential to complicate trends in the interpretation of long-term water colour data if pH is changing over time in a system or if samples are treated with different storage protocols with respect to acidification and freezing.     

Influence of dissolved organic matter on estrone removal by NF membranes and the role of their structures

The influence of different dissolved organic matter (DOM) on the removal of steroid hormone estrone during nanofiltration (NF) processes was investigated. Commercial dextran and humic acid (HA) as well as hydrophobic acid fraction (HpoA) derived from treated effluent were selected as DOM. To better understand the mechanism by which they affect estrone transport across NF membrane, the structural characteristics of DOM were also examined. The experimental results showed that DOM studied displayed obviously diverse impacts on estrone removal by NF membranes. These impacts were found to correlate with the structural characteristics of DOM. The presence of dextran without aromatic ring had little effects on the fate and transport of estrone during NF processes. The addition of HA without phenolic groups but great aromaticity improved estrone adsorption on membrane significantly while the “enhancement effect” on estrone rejection was limited. Moreover, estrone rejection by NF membranes was obviously increased by the presence of HpoA which possesses both phenolic groups and aromaticity. Some of the findings reported may be critically important for understanding the removal mechanism of estrone by NF membrane in real water matrix where various DOM co-present.     

Behavior and characteristics of dissolved organic matter during column studies of soil aquifer treatment

Soil column experiments were performed to investigate the behavior and characteristics of dissolved organic matter (DOM) during soil aquifer treatment (SAT), and to differentiate among the mechanisms responsible for the changes in the structural and functional properties of DOM during SAT. To determine the biological transformation of DOM, biodegradability tests using a biodegradation-column system were conducted. DOM was fractionated using XAD resins into 5 fractions: hydrophobic acid (HPO-A), hydrophobic neutral (HPO-N), transphilic acid (TPI-A), transphilic neutral (TPI-N) and hydrophilic fraction (HPI). Dissolved organic carbon (DOC) was removed by 70% during SAT, and the sorption and anaerobic biodegradation in SAT led to a DOC reduction of 27.4%. The significant changes in fluorescence properties of DOM were observed during SAT. However, the sorption and anaerobic biodegradation in SAT seemed to have no significant effect on the chemical structure of fluorescing constituents in DOM. The DOM fractions exhibited different changes in Fourier-transform infrared (FT-IR) spectra characteristics during SAT. Biodegradation resulted in the enrichment of aromatic structures and the decreased content of the oxygen-containing functional groups, such as CO and C-O, in DOM. On the other hand, the production of C-O and amide-2 functional groups occurred as a result of the sorption combined with anaerobic biodegradation in SAT.     

Effect of dissolved organic compounds on the photodegradation of the herbicide MCPA in aqueous solution

This work shows that the addition of phenol and 2-propanol as model organic compounds significantly decreases the direct photolysis quantum yield of 4-chloro-2-methylphenoxyacetic acid (MCPA) upon UVB irradiation in aqueous solution. Laser flash photolysis data suggest that 2-propanol is able to decrease the formation of the MCPA excited states under irradiation. A decrease from 0.54 to 0.34 of the photolysis quantum yield of the anionic form of MCPA (which prevails over the undissociated one in surface waters) could have a considerable impact on the MCPA lifetime in ecosystems where the direct photolysis is the main phototransformation pathway. In surface water bodies where the direct photolysis has comparable kinetics as the reaction with OH, a decrease of the quantum yield would enhance the relative importance of the OH pathway, which yields considerably less toxic intermediates than the direct photolysis.     

Transformation and characterisation of dissolved organic matter during the thermophilic aerobic biodegradation of faeces

We conducted a comparison of the characteristics of dissolved organic matter (DOM) taken from the bio-toilet and other sources. A characterisation of DOM was carried out to assess the stability of the compost generated during the thermophilic and aerobic biodegradation of faeces. In addition, levels of soluble microbial products generated in the bio-toilet composting reactor were compared with those taken from other sources. The results showed that (i) the main component of DOM from the bio-toilet are solutes with molecular weight (MW)>30,000 Da (40%), whereas micromolecules (MW< 1000 Da) constituted more than 60% of the DOM from other solid samples, while liquid samples reached even more than 90%; (ii) the DOM stabilisation level in the composting reactor of the bio-toilet system was greater than that shown by DOM from other sources; (iii) stabilisation of DOM in the bio-toilet system was characterised by an increasing amount of macromolecules (MW>30,000 Da) after a decreasing trend was observed in the early stages of the biodegradation process; and (iv) net production of lipopolysaccharide (LPS) in wastewater treatment plants is greater than in the bio-toilet.     

Combined ion exchange treatment for removal of dissolved organic matter and hardness

Dissolved organic matter (DOM) and hardness cations are two common constituents of natural waters that substantially impact water treatment processes. Anion exchange treatment, and in particular magnetic ion exchange (MIEX), has been shown to effectively remove DOM from natural waters. An important advantage of the MIEX process is that it is used as a slurry in a completely mixed flow reactor at the beginning of the treatment train. Hardness ions can be removed with cation exchange resins, although typically using a fixed bed reactor at the end of a treatment train. In this research, the feasibility of combining anion and cation exchange treatment in a single completely mixed reactor for treatment of raw water was investigated. The sequence of anion and cation exchange treatment, the number of regeneration cycles, and the chemistry of the regeneration solution were systematically explored. Simultaneous removal of DOM (70% as dissolved organic carbon) and hardness (>55% as total hardness) was achieved by combined ion exchange treatment. Combined ion exchange is expected to be useful as a pre-treatment for membrane systems because both DOM and divalent cations are major foulants of membranes.     

Characterization of dissolved organic matter in drinking water sources impacted by multiple tributaries

The characterization of dissolved organic matter (DOM) in drinking water sources is important as this material contributes to the formation of disinfection by-products (DBPs) and affects how water treatment unit operations are optimized. Drinking water utilities often draw water from sources impacted by multiple tributaries, with possible shifts in DOM concentrations and reactivity over time, depending on specific environmental conditions. In this study, results are presented on the characterization of DOM under varying ambient conditions from the four main tributaries of Lake Mead, a large reservoir in the southwest United States. The tributaries include the Las Vegas Wash (LVW), Muddy River (MR), Virgin River (VR) and the upper Colorado River (UCR). One additional sample was collected at the outflow of the reservoir (lower Colorado River (LCR)). The DOM was characterized by both bulk parameters (specific ultraviolet absorbance (SUVA)) and specific physicochemical properties, i.e. size, polarity and fluorescence. The analyses were performed emphasizing limited changes in its natural configuration by eliminating analytical preparation steps, excluding sample filtration (0.45 microm filter). Results indicate that each tributary had a different molecular weight distribution, as well as fluorescence properties, which helped in the identification of the relative source of DOM (allochthonous versus autochthonous). The largest apparent molecular weight distribution was observed for DOM samples collected at the MR site, which is fed mostly by groundwater seepage. The smallest apparent molecular weight was observed for DOM collected at the LCR site, suggesting that retention in the reservoir resulted in a decrease in molecular weight as a probable result of photo oxidation and microbial processes. Fluorescence analysis aided the differentiation of DOM by clearly identifying waters that were affected by microbial activity (LVW, UCR, and LCR), either by wastewater influence or by autochthonous processes, versus limited microbial influence (MR and VR). Polarity analysis revealed clear differences in the hydrophobic/hydrophilic nature between waters, including temporal differences within individual waters at a particular site. The DOM from the LVW and VR sites had higher hydrophobic character, as measured by retention onto non-polar sorbents. Additionally, the DOM collected at the LCR had the least hydrophobic character. This type of analysis would be beneficial to utilities who want to better understand and manage their source waters, especially in the evaluation of temporal variation within a watershed.     

Isolation of dissolved organic matter from the suwannee river using reverse osmosis

A portable reverse osmosis (RO) system was constructed and used to concentrate dissolved organic matter (DOM) from the Suwannee River in southeastern Georgia. Using this RO system, 150–180 1/h of river water could be processed with 90% recovery of DOM. After further cation exchange and lyophilization of the concentrated river water samples, large quantities of low-ash freeze-dried products were isolated. We highly recommend this RO method for concentration of DOM in fresh waters because (1) a very high percentage of DOM is recovered, which indicates minimal fractionation of the original sample; and (2) the process is quite rapid, which permits large quantities of DOM to be concentrated in a reasonable length of time.     

Photochemical generation of reactive species upon irradiation of rainwater: Negligible photoactivity of dissolved organic matter

This paper focuses on the study of the photochemical activity of dissolved organic matter present in rainwater. Formation rates of the reactive species hydroxyl radical (OH^•), singlet oxygen (¹O₂) and dissolved organic matter triplet states (³DOM^?) were determined by irradiation (UV-A) of wet-only rainwater samples collected in Turin (Italy) in the presence of specific scavengers (benzene, furfuryl alcohol and phenol, respectively). Photo-formation rates of OH^• (≈ 3 · 10⁻¹¹ M s⁻¹) and ¹O₂ (≈ 10⁻¹⁴ M s⁻¹) were lower (1 or 2 orders of magnitude) or largely lower (4 to 10 orders of magnitude) than those determined for fog and cloud samples in previous studies. ³DOM^? formation rate values were either negligible or quite low (≈ 10⁻¹² M s⁻¹) by comparison with those evaluated for surface water samples. Deduced steady-state [OH^•] were in the same range as those reported for fog samples in the literature (8.7 · 10⁻¹⁶ to 1.5 · 10⁻¹⁵ M), while [¹O₂] was often several orders of magnitude lower and, therefore, could be considered as negligible. Nitrite (NO₂⁻) constituted the main source of OH^• (69 ± 21 to 138 ± 36%), and the deduced contribution of DOM was low or nil. All the results obtained in this study tend to demonstrate that DOM (including HUmic LIke Substances, HULIS) present in rainwater is poorly or not photoactive. Therefore, there could be considerable difference between rainwater DOM (HULIS included) and the organic matter present in surface waters, particularly the humic substances, as far as the photochemical activity is concerned.     

Adsorption of Cu(II) to schwertmannite and goethite in presence of dissolved organic matter

Sorption processes involving secondary iron minerals may significantly contribute to immobilisation of metals in soils and surface waters. In the present work the effect of dissolved organic matter (DOM) from a concentrated bog-water on the adsorption of Cu(II) onto schwertmannite (Fe₈O₈(OH)₆SO₄) and goethite (α-FeOOH) has been studied. The acid/base behaviour of DOM up to pH 6 was explained by assuming a diprotic acid with a density of carboxylate groups of 6.90 μeq (mg C)⁻¹. The resulting acidity constants, recalculated to zero ionic strength were and .The uptake of DOM to schwertmannite and goethite was highest at low pH although adsorption was significant also under mildly alkaline conditions. Adsorption to the two minerals was similar although at high pH more DOM was adsorbed to schwertmannite than to goethite.DOM enhanced the adsorption of Cu(II) at moderately low pH in the goethite system but there was no effect of DOM in the case of schwertmannite. The presence of Cu(II) resulted in a decreased adsorption of DOM to goethite at weakly acidic pH and increased adsorption at high pH. In the case of schwertmannite, Cu(II) did not affect DOM uptake.     

Characterisation of dissolved organic matter in karst spring waters using intrinsic fluorescence: relationship with infiltration processes

From analysis of spectrophotometric properties of dissolved organic matter (OM) and the hydrochemical responses of some karst springs under different hydrologic conditions, an assessment of the origin and transfer pathway of OM present in karst spring waters, from soil and epikarst toward the spring, has been conducted for three karst aquifers in southern Spain: Alta Cadena, Sierra de Enmedio and Los Tajos. Intrinsic fluorescence (excitation-emission matrices or EEMs), together with major water chemistry (electrical conductivity, temperature, alkalinity, Cl⁻, Mg^+ 2) and P_CO2 along with natural hydrochemical tracers (TOC and NO₃⁻), have been monitored in 19 springs which drain the three karst aquifers examined in this study. The spring water EEM spectra indicate that fulvic acid-like substances, produced in the soil as a consequence of the decomposition of OM, are the dominant fluorophores, although some of the OM appears to originate from in situ microbiological activity but could be indicative of contamination present in recharge waters from livestock. During each recharge event, TOC and NO₃⁻ concentrations increased and variations in fluorescence intensities of peaks attributed to fulvic acid-like compounds were observed. In areas with minimal soil development, spatial and temporal variations in the fluorescence intensity of fulvic acid-like substances and other fluorophores derived from microbiological activity, together with other hydrochemical parameters, provide insights into the hydrogeological functioning of karst aquifers and the infiltration velocity of water from soil and facilitate assessment of contamination vulnerability in these aquifers.     

Estimation of the hydrophobic fraction of dissolved organic matter in water samples using UV photometry

In this study, we tested a simple and rapid method for the estimation of carbon in the hydrophobic fraction of dissolved organic matter (DOM) of different origin (spruce, pine, and beech litter) in soil water. The method is based on the fact that the hydrophobic fraction of DOM contains almost entirely the aromatic moieties of DOM. Thus, it showed a clearly distinct light absorption at 260 nm compared to the hydrophilic fraction. This light absorption was directly proportional to the concentration of the hydrophobic fraction. Moreover, it was independent of the concentration of the hydrophilic fraction. We compared the concentrations of hydrophobic DOM estimated by the UV method with those of the conventional fractionation using chromatographic columns of XAD-8 macroporous resin and found an excellent agreement between the two methods for both solutions from laboratory sorption experiments and field samples of forest floor leachates and subsoil porewaters. In addition, the absorption at 260 nm of hydrophobic DOM proved to be independent of pH values ranging from 2.0 to 6.5. Compared to the conventional chromatographic fractionation, the method using the UV absorption at 260 nm is less time consuming, needs a much smaller sample volume, and showed a better reproducibility. However, its use is restricted to water samples of low nitrate (<25 mg L⁻¹) and Fe (<5 mg L⁻¹) concentrations and, probably, with the hydrophobic fraction dominated by aromatic compounds deriving from degradation of lignin.     

Continuous fluorescence excitation-emission matrix monitoring of river organic matter

Real-time fluorescence monitoring has been mostly performed in marine systems, with little progress being made in the application of fluorescence excitation-emission matrix (EEM) spectroscopy, especially for freshwater monitoring. This paper presents a two weeks experiment where real-time fluorescence EEM data have been obtained for Bourn Brook, Birmingham, UK, using an in-situ fibre-optic probe. Fluorescence EEMs were measured every 3 min for two weeks, with control ‘grab’ samples every hour analyzed for fluorescence EEMs as well as pH, conductivity and dissolved organic carbon. Comparison of real-time and control samples showed an excellent agreement, with no evidence of fibre-optic probe fouling. EEMs of different character were identified using self-organizing maps, which demonstrated seven clusters of fluorescence EEMs which related to the intensity of fluorescence and relative intensities of peak T₁ and T₂ vs. peak C and peak A fluorescence. Fluorescence intensity of peaks A and C were observed to increase with rainfall, and a diesel pollution event was detected through an increase in T₂ fluorescence.