Aquatic organic matter: Classification and interaction with organic microcontaminants

Interactions of emerging contaminants with model colloidal microplastics, C60 fullerene, and natural organic matter - effect of surface functional group and adsorbate properties

Surface adsorption of two commonly detected emerging contaminants, amlodipine (AMP) and carbamazepine (CBZ), onto model colloidal microplastics, natural organic matter (NOM), and fullerene nanomaterials have been investigated. It is found that AMP accumulation at these colloidal-aqueous interfaces is markedly higher than that of CBZ. Measurements of surface excess and particle zeta potential, along with pH-dependent adsorption studies, reveal a distinct influence of colloidal functional group on the adsorption properties of these pharmaceuticals. AMP shows a clear preference for a surface containing carboxylic group compared to an amine modified surface. CBZ, in contrast, exhibit a pH-dependent surface proclivity for both of these microparticles. The type of interactions and molecular differences with respect to structural rigidity and charge properties explain these observed behaviors. In this work, we also demonstrate a facile approach in fabricating uniform microspheres coated with NOM and C₆₀ nanoclusters. Subsequent binding studies on these surfaces show considerable adsorption on the NOM surface but a minimal uptake of CBZ by C₆₀. Adsorption induced colloidal aggregation was not observed. These findings map out the extent of contaminant removal by colloids of different surface properties available in the aquatic environment. The methodology developed for the adsorption study also opens up the possibility for further investigations into colloidal-contaminant interactions.

Alterations in the sterol signature of detritivorous fish along pollution gradients in the Río de la Plata basin (Argentina): From plant to sewage-based diet

In order to assess the impact of sewage pollution on the diet of the strict detritivorous and migratory South American fish, Prochilodus lineatus, 16 sterol biomarkers were analyzed by gas chromatography-mass spectrometry from fish muscle (n: 144) collected along 1200 km in the Rio de la Plata basin. Sterol concentrations were fairly homogeneous (2.4 ± 1.3 mg g^-1 dry weight), but their proportion in lipids was highly variable and inversely related to both body mass and lipid contents, reflecting the more conservative character of sterols compared to the rapid accumulation of fat as fish grows. As expected, the muscle sterol signature was widely dominated by cholesterol (92 ± 4.5% of total sterols), but it exhibited a remarkable diversity with variable proportions of fecal coprostanol (4.0 ± 4.4%) and plant sterols (3.1 ± 1.9%, e.g. sitosterol and campesterol). Muscle sterols exhibited contrasting geographical differences associated with dietary shifts from plant-derived detritus in the northern reaches of the basin (N: Paraná and Uruguay Rivers), to sewage dominated inputs at Buenos Aires (BA). Fish from BA are fattier (lipids: 35 ± 18 vs. 15 ± 9.0% at N), with higher total sterol contents (2.6 ± 1.3 vs. 1.9 ± 1.0 mg g^-1), abundant coprostanol (5.3 ± 4.4 vs. 0.46 ± 1.1%) and lower plant sterols (2.6 ± 1.6 vs 4.6 ± 2.0%), reflecting a diet shifted to anthropogenic organic matter as opposed to vegetal detritus in the north. Accordingly, BA fish presented lower phyto/fecal sterol ratios (0.37 ± 0.21 vs. 0.91 ± 0.12 at N) and higher copro/epicoprostanol ratios (0.95 ± 0.082 vs 0.51 ± 0.25 at N), indicating fresh fecal inputs which provide a valuable supply of easily absorbed organic matter at this site. In addition, the sterol signature allowed to distinguish migratory fish from BA collected 900 km north (previously identified by their pollutant fingerprint and biochemical composition). In fact, coprostanol concentrations show a direct relationship with human populations along the basin, highlighting the usefulness of fecal sterol biomarkers as tracers of polluted fish stocks.

A model-based analysis of the reactive transport behaviour of 37 trace organic compounds during field-scale bank filtration

Though bank filtration diminishes the loads of many trace organic compounds (TOrCs) present in the source water, still there is a wide uncertainty on the influence of local environmental conditions on biodegradation processes. This research addresses the fate and transport behaviour of 37 trace organic compounds at a bank filtration site in Germany over a relatively long-time span of six years. Using two-dimensional heat and reactive transport modelling in FEFLOW, TOrCs are classified according to their occurrence in bank filtration wells with a residence time of up to 4 months. We identify 12 persistent compounds, 20 reactive compounds and 5 transformation products formed during aquifer passage. Estimates of first-order biodegradation rate constants are given for six reactive compounds. Minimum biodegradation rate constants (i.e. maximum half-lives) are approximated for eight compounds only present in the surface water. For some compounds, a simple first-order degradation model did not yield satisfactory results and the behaviour appears to be more complex. Processes like sorption, redox- and/or temperature-dependent biodegradation and temperature-dependent desorption are suspected but incorporating these into the model was beyond the scope of this paper that provides an overview for many compounds. Results highlight the ability of the sub-surface to improve the water quality during bank filtration, yet at the same time show the persistence of several compounds in the aquifer.

Characterizing DOC sources in China's Haihe River basin using spectroscopy and stable carbon isotopes

The Haihe River Basin is a polluted area affected by the developing industry and intensive agricultural activities in China. Dissolved organic matter (DOC) and light-absorbing characteristics of chromophoric dissolved organic matter (CDOM) were monitored in different tributaries of China within the Haihe River basin during spring and autumn. The concentration of DOC during spring was higher than during autumn (p < 0.01), and the evaporation was an important factor affecting the concentration of DOC in the basin. By contrast, the proportion of inputs due to terrigenous plants during autumn was higher than during spring. Carbon stable isotope analysis δ¹³C and C: N ratio of DOC, evidenced the inputs of DOC in the Haihe River basin from different sources including sewage, terrestrial plants, soil, and plankton. Isotopic analysis of δ¹³C and excitation-emission matrix (EEM) with fluorescence regional integration (FRI) analysis supported the hypothesis that allochthonous inputs contributed substantially to the inputs of DOC in the Haihe River basin, coming largely from sewage (9.8%-81.2%) and terrestrial plants (13.3%-65.8%). Depending on the source of DOC and contribution, four types with different EEM spectra were set. Type I, river water from sewage (81.2%); Type II, river water with input from terrestrial plants (65.8%); Type III, river water with plankton (36.4%), and Type IV, river water with soil-derived DOC (33.9%). The results demonstrated that the combined methodology using ¹³C stable isotope and EEM-FRI can be used to characterize the components of DOC in river waters. This approach was important for tracking the concentration and composition of DOC in river waters from different input sources and for better understanding concerning the local regulation of the terrestrial carbon cycle.

Municipal wastewater effluent influences dissolved organic matter quality and microbial community composition in an urbanized stream

Dissolved organic matter (DOM) from wastewater treatment plant (WWTP) effluent poses serious threats to the receiving aqueous ecosystems and their microbial communities. However, the correlation between effluent-derived DOM and microbial community diversity in urbanized rivers is still poorly understood. In this study, the response relationship between the microbial community dynamics and the DOM evolution process in the effluent-dominated Xiaohe River was revealed. The results showed that macromolecular humic acids were the main components of DOM in this river with more carboxylic acid groups and humic-like acid substances found upstream and protein-like substances dominated downstream. The bacterial abundance in the upstream section of Xiaohe River was low, while its community structure was unstable but exhibited good uniformity, and the bacterial diversity in the downstream was rich. The response of bacterial and eukaryotic communities to WWTP effluent was weak, while that of Actinobacteria to WWTP effluent was more prominent. Furthermore, different microbial communities were affected by different compositions and structure of DOM in the effluent of WWTP. The protein-like components in DOM had the most profound impact on the microbial community, followed by polysaccharides and components rich in hydroxyl and amino functional groups. The study grasped the migration and evolution of DOM in rivers with unconventional water recharge, and revealed their diverse effects on microbial community in urbanized rivers.

Aquatic Organic Matter in the Seine Basin: Sources, Spatio-Temporal Variability, Impact of Urban Discharges and Influence on Micro-pollutant Speciation

This research has been conducted over the last 10 years to characterise the spatio-temporal variability of aquatic organic matter (OM) composition in the Seine River watershed upstream and downstream of Paris Megacity and its effect on micro-pollutants. For this purpose, a large number of samples were collected under different hydrological conditions, and, over 1 year, three representative sites were monitored monthly. Furthermore, the evolution of the OM composition along an urbanisation gradient, from upstream to downstream of the Paris agglomeration, was characterised, highlighting the very strong impact of urban discharges, especially during low-water periods. Substantial differences in the chemical composition are emphasised relative to the urban or natural origin of the organic matter. Dissolved organic matter (DOM) interactions with metallic and organic micro-pollutants were studied, allowing us to (1) identify the key role of DOM on their speciation and bioavailability in aquatic systems and (2) demonstrate that these interactions depend on DOM composition and origin. The essential role of urban DOM on the speciation of trace metals in the Seine River downstream of the Paris agglomeration is also shown.

Occurrence and partitioning of antifouling booster biocides in sediments and porewaters from Brazilian Northeast

Fouling organisms attach and grow on submerged surfaces causing several economic losses. Thus, biocides have been introduced in antifouling paints in order to avoid this phenomenon, but their widespread use became a global problem, mainly in ports, leisure and fishing boat harbors, since these substances can be highly toxic to non-target organisms. The occurrence and environmental behavior of antifouling biocides are especially unknown in some peculiar regions, such as Amazon areas. Thus, the aim of this work was to evaluate, for the first time, levels and the partitioning behavior of the antifouling organic biocides irgarol, diuron and also stable degradation products of dichlofluanid and diuron (DMSA and DCPMU, respectively) in sediments and porewaters from a high boat traffic area located in the Northeast of Brazil, a pre-Amazon region. Our results showed high concentrations of irgarol (<1.0-89.7 μg kg^-1) and diuron (<5.0-55.2 μg kg^-1) in sediments. In porewater, DCPMU (<0.03-0.67 μg L^-1) and DMSA (<0.008-0.263 μg L^-1) were the mainly substances detected. High K_d and K_oc obtained for both irgarol and diuron showed a partitioning preference in the solid phase. This work represents one of the few registers of contamination by antifouling substances in Amazonian areas, despite their environmental relevance.

DOM as an indicator of occurrence and risks of antibiotics in a city-river-reservoir system with multiple pollution sources

Multiple sources contribute to the presence of antibiotic residues in water environments, and the environmental risks caused by antibiotics were paid more and more attention. This work aims to establish a relationship between optical properties of dissolved organic matter (DOM) and sources and risks of antibiotics. Occurrence of antibiotics and DOM in a city-river-reservoir freshwater system containing distinct antibiotic sources was investigated during three seasons using LC-MS and fluorescence excitation-emission matrix coupled with parallel factor analysis (EEM-PARAFAC), respectively. The results showed that antibiotics and DOM in the water had trends of increasing levels from the upstream to the midstream in the system. Five classes of antibiotics had statistically significant correlations with the humic-like component (C3) in the water (Pearson, p < 0.05). Especially, norfloxacin (NFX), which was dominant in the aquaculture source, significantly increased the fluorescence of C3 according to the fluorescence titration (R² = 0.86, p < 0.01). Furthermore, fluorescence signature in the aquaculture pond posed broad humic acid-like peaks with relatively higher abundances compared to other areas. These results suggested that C3 could be recognized as an indicator of NFX from aquaculture sources. Meanwhile, C3 can largely account for ecological risks of tetracyclines according to the results of redundancy analysis. This work highlights the roles of EEM-PARAFAC on tracing the source of antibiotics and the correlations between environmental risks of antibiotics and DOM in the aquatic environment.