The number of products containing engineered nanomaterials (ENMs) has increased due to their high industrial relevance as well as their use in diverse consumer products. At the end of their life cycle ENMs might be released to the environment and therefore concerns arise regarding their environmental impact. In order to track their fate upon disposal, it is crucial to establish methods to trace ENMs in complex environmental samples and to differentiate them from naturally-occurring nanoparticles. The goal of this study was to distinctively trace ENMs by (non-invasive) detection methods. For this, fluorescent ENMs, namely quantum dots (QDs), were distinctively traced in complex aqueous matrices, and were still detectable after a period of two months using fluorescence spectroscopy. In particular, two water-dispersible QD-species, namely CdTe/CdS QDs with N-acetyl-l-cysteine as capping agent (NAC-QDs) and surfactant-stabilized CdSe/ZnS QDs (Brij®58-QDs), were synthesized to examine their environmental fate during disposal as well as their potential interaction with naturally-occurring substances present in landfill leachates. When QDs were spiked into a leachate from an old landfill site, alteration processes, such as sorption, aggregation, agglomeration, and interactions with dissolved organic carbon (DOC), led to modifications of the optical properties of QDs. The spectral signatures of NAC-QDs deteriorated depending on residence time and storage temperature, while Brij®58-QDs retained their photoluminescence fingerprints, indicating their high colloidal stability. The observed change in photoluminescence intensity was mainly caused by DOC-interaction and association with complexing agents, such as fulvic or humic acids, typically present in mature landfill leachates. For both QD-species, the results also indicated that pH of the leachate had no significant impact on their optical properties. As a result, the unique spectroscopic fingerprints of QDs, specifically surfactant-stabilized QDs, allowed distinctive tracing in complex aqueous waste matrices in order to study their long-term behavior and ultimate fate.

The distribution of polycyclic aromatic hydrocarbons (PAHs) in the micro-zones of mangrove sediment is a predominant factors determining PAH bioavailability. In this study, a novel method for the in situ visualization (via microscope) and quantitative investigation of the PAH distribution in the micro-zones of mangrove sediment was established using microscopic fluorescence spectral analysis combined with derivative synchronous fluorescence spectroscopy (MFSA-DSFS). The MFSA-DSFS method significantly suppressed the background fluorescence signal of the sediment (the S/N values increased by over two orders of magnitude). The proportion of the nonpolar organic carbon content in the particulate organic matter (POM) rather than its content in the total organic matter (TOM) showed a significantly positive correlation with the uneven PAH distribution (Relative DC-M values) evaluated using the established method (p < 0.05). The extent of the uneven PAH distribution in the micro-zones of aged sediment was higher than that in the spiked sediment. Moreover, the distribution pattern of the PAHs within the mangrove sediment changed to become more homogeneous in the presence of low-molecular-weight organic acids (LMWOAs), which primarily contribute to increasing the POM content.

Dissolved organic carbon (DOC) plays diverse roles in carbon biogeochemical cycles. Here, we explored the link between DOC and pCO2 using high-performance size-exclusion chromatography (HPSEC) with UV254 detection and excitation emission matrix (EEM) fluorescence spectroscopy to determine the molecular weight distribution (MW) and the spectral characteristics of DOC, respectively. The relationship between DOC and pCO2 was investigated in the Poyang Lake wetlands and their adjacent aquatic systems. The results indicated significant spatial variation in the DOC concentrations, MW distributions, and pCO2. The DOC concentration was higher in the wetlands than in the rivers and lakes. pCO2 was high in wetlands in which the dominant vegetation was Phragmites australis, whereas it was low in wetlands in which Carex tristachya was the dominant species. DOC was divided into five fractions according to MW, as follows: super-low MW (SLMW, <1 kDa); low MW (LMW, 1–2.5 kDa); intermediate MW (IMW, 2.5–3.5 kDa); high MW (HMW, 3.5–6 kDa); and super-high MW (SMW, > 40 kDa). Rivers contained high proportions of HMW and extremely low amounts of SLMW, whereas wetlands had relatively high proportions of SLMW. The proportion of SMW (SMWp) was particularly high in wetlands. We found that pCO2 significantly positively correlated with the proportion of IMW, and significantly negatively correlated with SMWp. These data improve our understanding of the MW of bioavailable DOC and its conversion to CO2. The present results demonstrate that both the content and characteristics of DOC significantly affect pCO2. pCO2 and DOC must be studied further to help understanding the role of the wetland on the regional CO2 budget.

The behavior of photoactive TiO2 nanoparticles in an aquatic environment under UV irradiation was investigated. When there was no UV light irradiation, the attachment of humic acid (HA) onto the TiO2 nanoparticles improved their stability due to an increase in the electrostatic and steric repulsions between the particles. However, our study demonstrated that UV light clearly influenced the aggregation of TiO2 nanoparticles. Half an hour of UV irradiation caused the particles to aggregate from 331.0 nm to 1505.0 nm at a pH of 3.0. Similarly, the particles aggregated from 533.2 nm to 1037.0 nm at a pH of 6.5 and from 319.0 nm to 930.0 nm at a pH of 9.0. The aggregation continued with increased irradiation time, except for the condition at pH 3.0, which demonstrated disaggregation. Furthermore, we determined that the photocatalytic degradation of the HA dominated the behavior of TiO2 in our study. From the results of HA removal and 3DEEM fluorescence spectra data for the solution, a change in the HA was in accordance with the size change of the TiO2. The results illustrated that the UV irradiation affected the behavior of light-active nanomaterial (such as TiO2) in an aquatic system, thus influencing their bioavailability and reactivity.

Microcystis aeruginosa is a common cause of algal bloom outbreaks in Chinese lakes. This study investigated the effects of phosphate loading on the algal growth and extracellular organic matter (EOM) production of M. aeruginosa. The cell density was monitored by cell counting, and EOMs were characterized by dissolved organic carbon (DOC), carbohydrate, protein, and excitation/emission matrix fluorescence spectroscopy (EEM). DOC concentration peaked during the stationary phase and was contributed primarily by amino acid- and fulvic-like substances. Carbohydrate was a substantially larger fraction than protein. Phosphate showed positive influence on the cell growth and EOMs. As its concentration increased, the EOMs concentration increased. So did EOM and β-ionone as typical taste and odor compounds. Whatever the phosphate concentration was, the peak of β-ionone concentration exceeded its odor threshold (7.0 ng/L), resulting in a severe fruit-like odor. Additionally, the disinfection by-products involved with EOM were evaluated in both chlorination and chloramination, indicating that trihalomethanes were the dominated toxic by-products and the chloramination showed more significant effect on its formation as an interesting result.

Excitation-emission matrix (EEM) fluorescence spectroscopy combined with parallel factor analysis (PARAFAC) and multivariable analysis were employed to compare components of dissolved (DOM) and particulate (POM) organic matter and to reveal their correlations with water quality in Baitapuhe River and Xihe River in Shenyang City of northeast China. Eighteen water samples in Baitapuhe River and 16 water samples in Xihe River were collected along a human impact gradient. The DOM concentrations in Baitapuhe River were lower than those in Xihe River, so were the POM concentrations. The DOM in Baitapuhe River mainly derived from livestock wastewater and domestic sewage, which had strong biodegradability. However, the DOM in Xihe River mainly originated from industrial wastewater, which exhibited weak biodegradability. Four PARAFAC components (C1 to C4) were extracted from the DOM and POM. C1 was defined as fulvic-like component, and C2 was assigned as microbial humic component. C3 and C4 were ubiquitous protein-like component, which were referred as tryptophan-like and tyrosine-like components, respectively. The C3 was representative for the DOM in Baitapuhe River. The C3 and C4 were the main fractions of the DOM in Xihe River across the centralized wastewater-discharge region, whereas the C2 was the major component across the dispersed wastewater-discharge region. POM was dominated by the C4 in both rivers. Latent factors of water quality included the DOM, DO, Chl a, NO₃-N, and NH₄-N in Baitapuhe River, but the latent factors contained DOM, DO, BOD₅, and COD in Xihe River. Baitapuhe River was under the aerobic condition, but Xihe River was under the anaerobic condition.

For the purpose of investigating the effect of landfill leachate on the characteristics of organic matter in groundwater, groundwater samples were collected near and in a landfill site, and dissolved organic matter (DOM) was extracted from the groundwater samples and characterized by excitation–emission matrix (EEM) fluorescence spectra combined with fluorescence regional integration (FRI) and self-organizing map (SOM). The results showed that the groundwater DOM comprised humic-, fulvic-, and protein-like substances. The concentration of humic-like matter showed no obvious variation for all groundwater except the sample collected in the landfill site. Fulvic-like substance content decreased when the groundwater was polluted by landfill leachates. There were two kinds of protein-like matter in the groundwater. One kind was bound to humic-like substances, and its content did not change along with groundwater pollution. However, the other kind was present as “free” molecules or else bound in proteins, and its concentration increased significantly when the groundwater was polluted by landfill leachates. The FRI and SOM methods both can characterize the composition and evolution of DOM in the groundwater. However, the SOM analysis can identify whether protein-like moieties was bound to humic-like matter.

Biological aerated filters (BAFs) are widely used for the treatment of micropolluted surface water. However, the biological process produces dissolved organic nitrogen (DON), which, as precursors of nitrogenous disinfection by-products, pose potential threats to drinking water safety. Therefore, to control DON in BAF effluent, it is necessary to study the influence of BAF operation parameters on DON production. In this study, the influence of filtration velocity in a BAF on DON production was investigated. Under different filtration velocity (0.5, 2, and 4 m/h) conditions, profiles of DON concentrations along the media layer were measured. The profile at a filtration velocity of 0.5 m/h showed a decreasing trend, and the ones under filtration velocities of 2 and 4 m/h fluctuated in a small range (from 0.1 to 0.4 mg/L). Moreover, the relatively high filtration velocities of 2 and 4 m/h resulted in a lower level of DON concentration. Additionally, 3D excitation-emission matrix fluorescence spectroscopy was used to characterize DON. It is found that the patterns of DON at a relatively high filtration velocity condition (4 m/h) were obviously different from the ones under low filtration velocity conditions (0.5 and 2 m/h).

To explore the role of exopolymeric substances (EPS) in the process of polycyclic aromatic hydrocarbons (PAH) biodegradation, the characteristics of EPS isolated from a PAH-degrading fungus were investigated firstly by spectrometric determination, microscopic observation, Fourier transform-infrared spectroscopy (FT-IR), and three-dimensional excitation-emission matrix fluorescence spectroscopy (3D-EEM), and then the PAH-degrading ability of isolated EPS was evaluated. The EPS compositions and morphology varied significantly with the extraction methods. EPS were mainly composed of proteins, carbohydrate, and humic-like substances, and the cation exchange resin (CER)-extracted EPS were granular while other EPS samples were all powders. Heating was the most effective treatment method, followed by the CER, centrifugation, and ultrasonication methods. However, 3D-EEM data demonstrated that heating treatment makes the mycelia lyse the most. Overall, therefore, the CER was the best EPS extraction method for Mucor mucedo (M. mucedo). The PAH degradation results indicated that 87 % of pyrene and 81 % of benzo[a]pyrene (B[a]P) were removed by M. mucedo over 12 days and 9 % more pyrene and 7 % more B[a]P were reduced after CER-extracted EPS addition of 465 mg l⁻¹. The investigation of EPS characterization and EPS enhancing PAH biodegradation is the premise for further in-depth exploration of the role of EPS contribution to PAH biodegradation.

The water quality improvement of landfill leachate after sequencing batch reactor (SBR) activated sludge process were evaluated by chemical oxygen demand (COD), dissolved organic matter (DOM) fractions, and three-dimensional excitation-emission matrix (EEM), from which the new understanding was obtained. The results indicated that less than 14 % COD was removed by SBR. The EEM of leachate and SBR effluent showed that HPO-A and TPI-A were appeared in the peak C, while the HPI, HPO-N, and TPI-N could not be found due to dilution. Although humic acid appeared in peak C, not all the organic materials in peak C are humic acid. And because landfill leachate is a kind of complicated wastewater, therefore, only EEM cannot efficiently reflect the water quality.