Assessment of contamination by anthropogenic dissolved organic matter in the aquifer that underlies the agricultural area

Spectral and molecular insights into the characteristics of dissolved organic matter in nitrate-contaminated groundwater

The characteristics of dissolved organic matter (DOM) serve as indicators of nitrate pollution in groundwater. However, the specific DOM components associated with nitrate in groundwater systems remain unclear. In this study, dual isotopes of nitrate, three-dimensional Excitation emission matrices (EEMs) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) were utilized to uncover the sources of nitrate and their associations with DOM characteristics. The predominant nitrate in the targeted aquifer was derived from soil organic nitrogen (mean 46.0%) and manure &sewage (mean 34.3%). The DOM in nitrate-contaminated groundwater (nitrate-nitrogen >20 mg/L) exhibited evident exogenous characteristics, with a bioavailable content 2.58 times greater than that of uncontaminated groundwater. Regarding the molecular characteristics, DOM molecules characterized by CHO + 3N, featuring lower molecular weights and H/C ratios, indicated potential for mineralization, while CHONS formulas indicated the exogenous features, providing the potential for accurate traceability. These findings provided insights at the molecular level into the characterization of DOM in nitrate-contaminated groundwater and offer scientific guidance for decision-making regarding the remediation of groundwater nitrate pollution.

A review on fluorescence spectroscopic analysis of water and wastewater

In recent years, the application of fluorescence spectroscopy has been widely recognized in water environment studies. The sensitiveness, simplicity, and efficiency of fluorescence spectroscopy are proved to be a promising tool for effective monitoring of water and wastewater. The fluorescence excitation-emission matrix (EEMs) and synchronous fluorescence spectra have been widely used analysis techniques of fluorescence measurement. The presence of organic matter in water and wastewater defines the degree and type of pollution in water. The application of fluorescence spectroscopy to characterize dissolved organic matter (DOM) has made the water quality assessment simple and easy. With the recent advances in this technology, components of DOM are identified by employing parallel factor analysis (PARAFAC), a mathematical trilinear data modeling with EEMs. The majority of wastewater studies indicated that the fluorescence peak of EX/EM at 275 nm/340 nm is referred to tryptophan region (Peak T1). However, some researchers identified another fluorescence peak in the region of EX/EM at 225-237 nm/340-381 nm, which described the tryptophan region and labeled it as Peak T2. Generally, peak T is a protein-like component in the water sample, where T1 and T2 signals were derived from the <0.20μm fraction of pollution. Therefore, a more advanced approach, such as an online fluorescence spectrofluorometer, can be used for the online monitoring of water. The results of various waters studied by fluorescence spectroscopy indicate that changes in peak T intensity could be used for real-time wastewater quality assessment and process control of wastewater treatment works. Finally, due to its effective use in water quality assessment, the fluorescence technique is proved to be a surrogate online monitoring tool and early warning equipment.

Assessment of Physicochemical Groundwater Quality and Hydrogeochemical Processes in an Area near a Municipal Landfill Site: A Case Study of the Toluca Valley

Sanitary landfills are considered one of the main sources of contamination of water resources due to the generation of leachate with a high content of dissolved organic matter (DOM), inorganic material, and toxic elements. This study aimed to determine the influence of leachate on the physicochemical quality and hydrogeochemical processes which determine the chemical composition of groundwater in an area near a municipal sanitary landfill site. In situ parameters (pH, temperature, electrical conductivity, dissolved oxygen, ORP), physicochemical parameters (HCO₃⁻, PO₄³⁻, Cl⁻, NO₃⁻, SO₄²⁻, NH₄⁺, Ca²⁺, Mg²⁺, Na⁺, K⁺), and dissolved organic matter were analyzed. The content of dissolved organic matter (DOM) was determined by 3D fluorescence microscopy. The presence of Cl⁻, NO₃⁻, NH₄⁺, PO₄³⁻, BOD, and COD indicated the presence of contamination. The significant correlation between NO₃⁻ and PO₄³⁻ ions (r = 0.940) and DOM of anthropogenic origin in the 3D fluorescence spectra confirm that its presence in the water is associated with the municipal landfill site in question. The type of water in the area is Mg-HCO₃, with a tendency to Na-HCO₃ and Na-SO₊-Cl. The water-rock interaction process predominates in the chemical composition of water; however, significant correlations between Na⁺ and Ca²⁺ (r = 0.876), and between K⁺ and Mg²⁺ (r = 0.980) showed that an ion exchange process had taken place. Likewise, there is enrichment by HCO₃⁻ and SO₄²⁻ ions due to the mineralization of the organic matter from the leachate. The groundwater quality that supplies the study area is being affected by leachate infiltration from the sanitary landfill.