Regional-scale investigation of dissolved organic matter and lead binding in a large impacted lake with a focus on environmental risk assessment

Spatial distribution of sediment dissolved organic matter in oligotrophic lakes and its binding characteristics with Pb(II) and Cu(II)

Dissolved organic matter (DOM), the most active component in interstitial waters, determines the stability of heavy metals and secondary release in sediments. However, little is known about the composition and metal-binding patterns of DOM in interstitial water from oligotrophic lakes affected by different anthropogenic perturbations. Here, 18 interstitial water samples were prepared from sediments in agricultural, residential, tourist, and forest regions in an oligotrophic lake (Shengzhong Lake in Sichuan Province, China) watershed. Interstitial water quality and DOM composition, properties, and Cu(II)- and Pb(II)-binding characteristics were measured via physicochemical analysis, UV-vis spectroscopic, fluorescence excitation-emission matrix-parallel factor analysis (EEM-PARAFAC), and fluorescence titration methods. The DOM, which was produced mainly by microbial activities, had low molecular weights, humification degrees, and aromaticity. Based on EEM-PARAFAC results, the DOM was generally composed of tryptophan- (57.7%), terrestrial humic- (18.7%), microbial humic- (15.6%), and tyrosine-like (8.0%) substances. The DOM in the metal complexes was primarily composed of tryptophan-like substances, which accounted for ~42.6% of the DOM-Cu(II) complexes and ~72.0% of the DOM-Pb(II) complexes; however, microbial humic-like substances primarily contributed to the stability of DOM-Cu(II) (logKCu = 3.7-4.6) and DOM-Pb(II) (logKPb = 4.3-4.8). Water quality parameters did not significantly affect the stability of DOM-metal complexes. We demonstrated that the metal-binding patterns of DOM in interstitial water from oligotrophic lakes are highly dependent on microbial DOM composition and are affected by anthropogenic perturbations to a lesser extent.

Comprehensive assessment of exposure and environmental risk of potentially toxic elements in surface water and sediment across China: A synthesis study

China faces a serious challenge with water pollution posed by potentially toxic elements (PTEs). Comprehensive and reliable environmental risk assessment is paramount for precise pollution prevention and control. Previous studies generally focused on a single environmental compartment within small regions, and the uncertainty in risk calculation is not fully considered. This study revealed the current exposure status of 11 PTEs in surface water and sediment across China using previously reported concentration data in 301 well-screened articles. Ecological and human health risks were evaluated and the uncertainty related to calculation parameters and exposure dataset were quantified. PTEs of high concern were further identified. Results showed Mn and Zn had the highest concentration levels, while Hg and Cd had the lowest concentrations in both surface water and sediment. Risk assessment of individual PTE showed that high-risk PTEs varied by risk receptors and environmental compartments. Nationwide, the probability of aquatic organisms being affected by Mn, Zn, Cu, and As in surface water exceeded 10 %. In sediment, Cd and Hg exhibited high and considerable risk, respectively. As was identified as the major PTE threatening human health as its carcinogenic risk was 1.45 × 10-4 through direct ingestion. Combined risk assessment showed the PTE mixture in surface water and sediment posed medium and high ecological risk with the risk quotient and potential ecological risk index of 1.76 and 558.36, respectively. Adverse health effects through incidental ingestion and dermal contact during swimming were negligible. This study provides a nationwide risk assessment of PTEs in China's aquatic environment and the robustness is verified, which can serve as a practical basis for policymakers to guide the early warning and precise management of water pollution.

Unveiling changes in the complexation of dissolved organic matter with Pb(II) by photochemical and microbial degradation using fluorescence EEMs-PARAFAC

Dissolved organic matter (DOM) is very important in determining the speciation, behaviors, and risk of metal pollutants in aquatic ecosystems. Photochemical and microbial degradation are key processes in the cycling of DOM, yet their effects on the DOM-Pb(II) interaction remain largely unknown. This was studied by examining the complexation of river DOM with Pb(II) after degradation, using fluorescence quenching titration and excitation-emission matrices-parallel factor analysis (EEMs-PARAFAC). Three humic-like and two protein-like components were identified, with strong removals of humic-like components and decreasing average molecular weight and humification degree of DOM by photo- and photo-microbial degradation. The changes in humic-like abundance and structure resulted in notable weakening of their interaction with Pb(II). The tryptophan-like C2 was also mainly removed by photo-degradation, while the tyrosine-like C3 could be either removed or accumulated. The Pb(II)-binding of protein-like components was generally weaker but was enhanced in some degradation groups, which might be related to the lowering competition from humic-like components. The binding parameters correlated significantly with the DOM indices, which were dominated by photo-degradation for humic-like components but by seasonal variations for the tyrosine-like component. These results have implications for understanding the key mechanisms underlying the variability of the DOM-metal interaction in aquatic environments.

Whole-cell bioreporter application for rapid evaluation of hazardous metal bioavailability and toxicity in bioprocess

Assessing heavy metal bioavailability and toxicity during bioprocess is critical for advancing green biotechnology. The capability of whole-cell bioreporters to measure heavy metal bioavailability has been increasingly recognized. The advantages of this technology being applied to bioprocess monitoring are less studied. Here we investigate the potential of a cadmium- and lead-sensitive bioreporter to be used for heavy metals as a class, which holds great interest for bioprocess applications. We evaluated the bioavailability of eight individual heavy metals with bioreporter zntA, as well as the bioavailability and toxicity of mixed metals. The bioavailability and toxicity of heavy metals in bioprocess samples were also evaluated. We have demonstrated for the first time that the zntA bioreporter can effectively detect the bioavailability of zinc, nickel, and cobalt with limit of detection lower than 0.01, 0.08 and 0.5 mg·L-1, respectively. The detection limits meet the requirements of the WHO, the U.S. Environmental Protection Agency, and the China drinking water quality standards, which makes this approach reasonable for monitoring heavy metal bioavailability in bioprocess. LIVE/DEAD toxicity experiments have been conducted for the detection of mixed metal solution toxicity to zntA bioreporter which shows an EC50 (as EC50, concentration for 50% of maximal effect) value of mixed metal solution is 3.84 mg·L-1. Samples from wastewater treatment plants, sludge treatment plants and kitchen waste fermentation processes were analyzed to extend upon the laboratory results. The results of this study confirm the potential for practical applications of bioreporter technology in bioprocess monitoring. In turn, development for such practical applications is key to achieve the necessary level of commercialization to further make the routine use of bioreporters in bioprocess monitoring feasible.

Effects of acid mine drainage on photochemical and biological degradation of dissolved organic matter in karst river water

Dissolved organic matter (DOM) can be removed or transformed by photochemical and biological processes, producing the negative effect of transforming organic carbon into inorganic carbon, which plays a vital role in the karst carbon cycle. However, acid mine drainage (AMD) will affect this process, so the degradation of DOM in karst river water (KRW) needs to be studied in this context. In this study, to reveal the evolution processes of DOM under photochemical and biological conditions in AMD-impacted KRW, AMD and KRW were mixed in different ratios under conditions of visible light irradiation (VL), biodegradation (BD), ultraviolet irradiation (UV) and ultraviolet irradiation + biodegradation (UV+BD). The average DOC concentrations in samples after mixing AMD and KRW in different proportions decreased significantly (by 23%) in UV+BD, which was 1.2-1.4 times higher than under the other conditions and would lead to a significant release of inorganic carbon. Further analysis of the fluorescence parameters via parallel factor analysis (PARAFAC) revealed that the DOM fluorescence components in AMD comprised mainly protein-like substances derived from autochthonous components, while the DOM fluorescence components in KRW were mainly humic-like substances with both autochthonous and allochthonous sources. Therefore, AMD could promote both the photochemical and biological degradation of DOM in karst receiving streams, resulting in the conversion of DOC to inorganic carbon. The results showed that the synergistic effects of UV+BD and AMD accelerated the degradation of DOM and the release of inorganic carbon in KRW, thus affecting the stability of the karst carbon cycle.

Recognizing the variation of DNA-P during and after the algal bloom in lake Hulun

Eutrophication has spread from shallow lakes in temperature zones to lakes in cold regions as a result of a continuous warm climate and human activities. Little proof for the importance of dissolved organic phosphorus (DOP) in contributing to phosphorus cycling and algae growth has been generated for aquatic ecosystems, particularly in cold eutrophic lakes. In this study, a comprehensive in situ study was conducted in overlying water, suspended particulate matter, and sediment during and after algal bloom (in July and September, respectively) in Lake Hulun. Multiple methods of 31P NMR, enzymatic hydrolysis, and UV-visible technologies were combined to detect phosphorus occurrence, bioavailability, and molecular structure from a novel angle. The 31P NMR analysis results showed that DNA-P is mainly stored in the dissolved phase and has not been detected in suspended particulate matter or sediment. Enzymatic hydrolysis was used to determine the bioavailability of DOP, which revealed that in July and September, respectively, 85% and 79% of DOP were hydrolyzable. UV-visible analysis represented that the degree of humification and molecular weight of DOP were high during the algal bloom, but these values considerably dropped following the algal bloom. The large amount of DNA-P present in the overlying water is the main reason for the high degree of humification and high molecular weight of the water body. Besides, Lake Hulun's DNA-P remains highly bioavailable during algal blooms, despite its high degree of humification and molecular weight. These findings can serve as a theoretical basis for understanding the migration and transformation of DOP, as well as the persistence of algal blooms in eutrophic lakes located in cold regions.

Characteristics and mechanism of phosphate removal by lanthanum modified bentonite in the presence of dissolved organic matter

Lanthanum modified bentonite (LMB) is a widely used adsorbent for removing inorganic phosphorus from polluted water to prevent eutrophication. However, its efficiency can be affected by various environmental factors, including dissolved organic matter (DOM), which is still unclear. In this study, we systematically explored the influence of model DOMs, including HA, bovine serum albumin (BSA), and sodium alginate (SA), on phosphate adsorption by LMB, as well as to elucidate the underlying adsorption mechanisms. Our results showed that only HA had a significant effect on phosphate adsorption by LMB, causing inhibition. When three DOMs were mixed with phosphate in different proportions and DOM was mainly HA, the performance of phosphate adsorption on LMB became worse, while BSA can slightly offset this impact. The kinetics of HA and phosphate adsorption on LMB followed the pseudo-second-order kinetic model, and isotherms fitted the Langmuir model, with a maximum adsorption capacity of 5.7 mg g-1 for P and 12 mg g-1 for HA. However, when HA and phosphate were mixed based on their Qm, a C/P molar ratio of 5.35, LMB preferentially adsorbed phosphate. HA invasion was also disadvantageous for phosphate removal by LMB, in which P adsorption was less efficient at low-concentrations. However, during co-adsorption the adsorption capacity for HA was higher. With a secondary addition of higher levels of P, both pollutants were adsorbed more effectively. In the natural water experiment, phosphate concentration decreased with increasing shaking time, while the UV254 value showed a downward trend, indicating that LMB also adsorbed HA. Characterization results showed that La and phosphate formed LaPO4 precipitation, forming La-O-P inner-sphere complexes as the main mechanism of phosphate removal by LMB. La and HA formed La-HA complexes, with O-CO bonds from HA competing for lanthanum with phosphate. Despite HA obstructing pores from adsorbent, LMB still maintained a good binding ability with phosphate. It may form La-P-HA ternary complexes during adsorption to keep HA adsorption amount.

Dissolved organic matter composition and fluorescence characteristics of the river affected by coal mine drainage

Coal mine drainage (CMD) discharged into surface waters results in serious environmental pollution risk to rivers, lakes, and reservoirs. Coal mine drainage generally contains a variety of organic matter and heavy metals due to coal mining activities. Dissolved organic matter (DOM) plays an important role in the physicochemical and biological processes of many aquatic ecosystems. In this study, the investigations were carried out in the dry and wet seasons in 2021 to assess the characteristics of DOM compounds in coal mine drainage and the CMD-affected river. The results indicated that the pH of CMD-affected river pressed close to coal mine drainage. Besides, coal mine drainage lowered DO by 36% and increased total dissolved solids by 19% in the CMD-affected river. Coal mine drainage decreased absorption coefficient a(350) and absorption spectral slope S_275-295 of DOM in the CMD-affected river; hence, DOM molecular size increased with decreasing S_275-295. Three-dimensional fluorescence excitation-emission matrix spectroscopy and parallel factor analysis identified humic-like C1, tryptophan-like C2, and tyrosine-like C3 in the CMD-affected river and coal mine drainage. DOM in the CMD-affected river mainly originated from microbial and terrestrial sources, with strong endogenous characteristics. The ultra-high-resolution Fourier transform ion cyclotron resonance mass spectrometry analysis revealed that coal mine drainage had a higher relative abundance of CHO (44.79%), with a higher unsaturation degree of DOM. Coal mine drainage decreased the AI_mod,wa, DBE_wa (double bond equivalents), O_wa, N_wa, and S_wa values and increased the relative abundance of the O₃S₁ species with DBE of 3 and carbons number range of 15-17 at the CMD inlet to the river channel. Moreover, coal mine drainage with the higher protein content increased the protein content of water at the CMD inlet to the river channel and the downstream river. DOM compositions and proprieties in coal mine drainage were investigated to further understand the influence of organic matter on heavy metals in future study.

We need to plan streamlined environmental impact assessment for the future X-Press Pearl disasters

The X-Press Pearl disaster illustrates the urgent needs for streamlined environmental impact assessment to inform decision making. The environmental contamination caused by the disaster is complex, and the biological impact of different environmental stressors, and at different biological scales, needs to be determined. Traditional methods for analyzing complex environmental stressors are often inefficient and do not reflect the biological impact of pollution. The combination of chemical stressors and biological impacts is the key to environmental impact assessment based on integrated monitoring. Whole-cell bioreporters are tools for rapid, efficient and quantitative detection of the bioavailability, stressor effects, and toxicity of pollutants, i.e., spanning a wide range of applications. Here we propose the view that using whole-cell bioreporter technology to streamline short-term environmental impact assessment for maritime disasters such as the X-Press Pearl is more fit-for-purpose/practical than other approaches in use.

Nanoscale Iron trioxide catalyzes the synthesis of auxins analogs in artificial humic acids to enhance rice growth

Humic acids (HAs), kinds of valuable active carbon, are critical for improving soil fertility. However, the majority of soils are poor in HAs, arousing the development of artificial HAs. In this study, two iron-based catalysts (nanoscale iron trioxide (nFe₂O₃) and FeCl₃) were used to catalyze the hydrothermal humification of waste corn straw. With the help of ultra-performance liquid chromatography-mass spectrometry, we proposed the specific humification process with the action of catalysis for the first time, which is of great significance for the design, synthesis and application of artificial HAs in the future. Moreover, the growth-promoting effect and mechanisms of the artificial HAs were determined by rice planting in a greenhouse. Results showed that compared to no catalyst treatment, the FeCl₃ and nFe₂O₃ catalysts increased the decomposition rate of macromolecular biomass by 39 and 14 %, respectively, increasing the yield of artificial HAs. During the humification process, nFe₂O₃ catalysts benefit the formation of many aromatic structure monomers including furfural and hydroxycaproic acids. These monomers were condensed into growth hormone analogs such as vanillin and methionine sulfoxide and were further built in the artificial HAs. Therefore, the artificial HAs from nFe₂O₃ catalytic treatment promoted the rice growth the best, showing that the resultant germination rate, root activity, and photosynthetic rate of rice increased by 50, 167, and 72 %, respectively; moreover, the uptake and accumulation of water and nutrient by roots as well as the contents of soluble protein and sugar of rice are also significantly increased. This could be ascribed to the upregulated expression of functional genes including OsRHL1, OsZPT5-07, OsSHR2 and OsDCL. Considering both the economic and environmental benefits, we suggested that the artificial HAs, especially that produced with the action of nFe₂O₃ catalysis, are promising in alleviating environmental stress from waste biomass and sustainably improving agricultural production.

Critical evaluation of the interaction between fluorescent dissolved organic matter and Pb(II) under variable environmental conditions

Dissolved organic matter (DOM) can strongly influence the behavior and risk of metal pollutants in aquatic ecosystems. However, a comprehensive study on the effects of DOM level and environmental factors on the binding of DOM with Pb(II) is lacking. This study examined the DOM-Pb(II) interaction in the river water under variable DOM level, pH, and major ions, using fluorescence excitation-emission matrices-parallel factor analysis (EEMs-PARAFAC). Four humic-like and one protein-like component were identified, and the abundant humic-like components showed higher Pb(II)-binding fractions (f) than the protein-like component. The f of PARAFAC components decreased while the conditional stability constants (logK_M) increased for the diluted DOM, indicating the influence of DOM level on its metal binding. The DOM-Pb(II) interaction was sensitive to changes in pH, with generally higher f and lower logK_M at the alkaline condition due to changes in the DOM conformation. The addition of major ions significantly decreased the fluorescence quenching by Pb(II), due to competitive effects and potential DOM conformation changes at elevated ions. Overall, our results show that the DOM-Pb(II) complexation is highly dependent on both the DOM properties and environmental factors, which have implications for optimizing the experimental conditions and for comparing the results in different environments.

Regional-scale investigation of the molecular weight distribution and metal-binding behavior of dissolved organic matter from a shallow macrophytic lake using multispectral techniques

In this work, based on excitation-emission matrix spectroscopy combined with parallel factor analysis (EEM-FARAFAC) and two-dimensional correlation analysis of synchronous fluorescence spectroscopy, Fourier transform infrared spectroscopy, and combination of two spectra (2D-SF-COS, 2D-FTIR-COS, and Hetero-2D-COS), the characteristics and metal-binding behaviors of DOM in Dongping Lake were explored for molecular weight (MW), fluorescence components, and functional groups. The results showed that the entire lake was governed by protein-like materials with low MW(< 1 kDa). The complexation occurred preferentially in protein-like materials for bulk DOM after adding copper (Cu²⁺) and lead (Pb²⁺), which were changed by fractionation for MW. The active points were aliphatic C－OH for DOM-Cu and phenol －OH or polysaccharide for DOM-Pb from 2D-FTIR-COS. The protein-like components possessed higher LogK than humic-like component during binding to Cu²⁺ or Pb²⁺. Moreover, the complexing affinities of DOM-Cu (LogK_Cu: 3.26 ± 0.87-4.04 ± 0.49) were higher than those of DOM-Pb (LogK_Pb: 2.66 ± 0.52-3.78 ± 0.36). On a spatial scale, high LogK_Cu and LogK_Pb were found in the center and entrance of the lake, respectively. Humic-like component C2 in the LMW fraction possessed a stronger binding capacity with Cu²⁺. This study affords new insights into the migration and conversion of HMs in lakes.

Comparing the Pb(II) binding with different fluorescent components of dissolved organic matter from typical sources

Dissolved organic matter (DOM) is important for determining the speciation, environmental behavior, and effects of metal pollutants in aquatic environments. However, little is known about the difference between DOM from natural and anthropogenic sources for binding Pb(II). This study examined the Pb(II) binding with DOM from four typical sources including river, leaf litter leachate, and the influent and effluent of a wastewater treatment plant, using fluorescence quenching titration and excitation-emission matrices-parallel factor analysis (EEMs-PARAFAC). Four humic-like and one protein-like fluorescent components were identified, with much higher protein-like fraction and lower humification degree for the influent than for other sources. In the river water and leaf litter leachate, the abundant humic-like components were quenched by 6-17% while the protein-like component kept stable (2-4%) by the addition of Pb(II). In contrast, the influent DOM showed stronger fluorescence quenching of the protein-like component (46%) with higher conditional stability constant and binding fraction of fluorophore than the humic-like components (15-21%). The effluent DOM displayed weak quenching for all fluorescent components (4-6%) and thus weak complexation with Pb(II), indicating notable changes in the chemical composition and metal-binding affinity of DOM by wastewater treatments. These results demonstrated significant impacts of DOM source and chemical composition on its Pb(II) complexation properties, which have implications for understanding the interactions between DOM and heavy metals.

From speciation to toxicity: Using a "Two-in-One" whole-cell bioreporter approach to assess harmful effects of Cd and Pb

Due to the sheer number of contaminated sites, bioavailability-based measurement and modeling of toxicity is used to triage response; despite advances, both remain relatively cumbersome. Cadmium (Cd) and lead (Pb) are two of the most toxic and globally prevalent pollutants, disproportionately impacting disadvantaged communities. Here we demonstrate the use of high throughput lights-on bioreporter technology to measure both speciation and toxicity. The organism's response is fit-for-purpose to parameterize the Biotic Ligand Model used in risk assessment of aquatic ecotoxicity and setting environmental Water Quality Criteria. Toxicity endpoints for analogous Cd and Pb models reported in literature average 71st and 44th rank-percentile sensitivity of Genus Mean Acute Values for acute toxicity (i.e., insensitive) in comparison to the bioreporter, the unique dual-mode measurement ability of which can predict toxicity endpoints from below the 5th percentile up to the 50th rank-percentile. These results are extensible to other reporters, paving the way to cost-efficient environmental risk assessment of aquatic ecotoxicity for a wide range of priority toxic pollutants.

Multi-spectroscopic investigation of the molecular weight distribution and copper binding ability of dissolved organic matter in Dongping Lake, China

The properties and metal-binding abilities of dissolved organic matter (DOM) rely on its molecular weight (MW) structure. In this study, the spatial differences of DOM in compositions, MW structures, and binding mechanisms with copper (Cu²⁺) in Dongping Lake were investigated by applying excitation-emission matrix combining parallel factor analysis (EEM-PARAFAC), synchronous fluorescence (SF) spectra, two-dimensional correlation spectra (2D-COS), and Fourier transform infrared (FTIR) spectra. The EDOM for the entrance of the Dawen River and PDOM for the macrophyte-dominated region were divided from DOM of Dongping Lake based on hierarchical clustering analysis (HCA) and principal component analysis (PCA) and were size-fractioned into MW < 500 kDa and <100 kDa fractions. According to EEM-PARAFAC, Dongping Lake was dominated by tryptophan-like substances with MW < 500 kDa. The concentration of PDOM was higher than that of EDOM (p < 0.05). 2D-COS showed that protein-like components preceded humic-like components binding to Cu²⁺ regardless of sample type (215 nm > 285 nm > 310-360 nm). The Cu²⁺ binding capacity of DOM exhibited specific differences in space, components, and molecular weights. The humic-like component 1 (C1) and tryptophan-like component 4 (C4) of PDOM showed stronger binding abilities than those of EDOM. Endogenous tryptophan-like component 4 (C4) had a higher binding affinity for Cu²⁺ than humic-like components (logK_a: C4 > C1 > C2) in PDOM irrespective of MW. Humic-like components with MW < 500 kDa displayed higher binding potentials for Cu²⁺. FTIR spectra showed that the main participants of DOM-Cu complexation included aromatic hydrocarbons, aliphatic groups, amide Ⅰ bands, and carboxyl functional groups. This study provides spatial-scale insights into the molecular weight structure of DOM in influencing the behavior, fate, and bioavailability of heavy metals in lakes.

Enhanced removal of refractory humic- and fulvic-like organics from biotreated landfill leachate by ozonation in packed bubble columns

Biotreated landfill leachate contains much refractory organics such as humic and fulvic acids, which can be degraded by O₃. However, the low O₃ mass transfer and high energy cost limit its wide application in landfill leachate treatment. Previous studies proved that packed bubble columns could enhance the O₃ mass transfer and increase the synthetic humic acids wastewater degradation, but the performance of packed bubble columns in real wastewater treatment has not been investigated. Therefore, this study aims to evaluate the feasibility of application of packed bubble column in the real biotreated landfill leachates treatment and provide insights into the transformation of organic matters in leachates during ozonation. Packed bubble columns with lava rocks or metal pall rings (LBC or MBC) were applied and compared with a non-packed bubble column (BC). At an applied O₃ dose of 8.35 mg/(L_{water sample} min), the initial COD (400 mg/L) was only removed for 26% in BC and 32% in MBC while this was 46% in LBC, indicating LBC has the best performance. GC-MS analysis shows that raw biotreated leachate contains potential endocrine disruptors such as di(2-ethylhexyl) phthalate (DEHP). 61% of DEHP was removed in LBC and the least intermediate oxidation products from humic- and fulvic-like organics was detected in LBC. The highest O₃ utilization efficiency (89%) and hydroxyl radical (OH) exposure rate (3.0 × 10^-10 M s) were observed in LBC with lowest energy consumption (E_EO) for COD removal of 18 kWh/m³. The enhanced ozonation efficiency in LBC and MBC was attributed to the improved O₃ mass transfer. Besides, LBC had additional adsorptive and catalytic activity that promoted the decomposition of O₃ to generate OH. This study demonstrates that a packed bubble column increases removal and decreases energy use when treating landfill leachate, thus promoting the application of ozonation.

Restriction of dissolved organic matter on the stabilization of Cu(II) by phosphate

The precipitation of Cu(II) by phosphate and the influence of dissolved organic matter (DOM) on the precipitation are essential for the fate of Cu(II) in aquatic environments. In this study, the influence of DOM on the reaction of phosphate with Cu(II) was investigated. Here, 51.61%, 29.75%, and 24.32% of the added Cu(II) (50 μM) precipitated without DOM and with the addition of fulvic acid (FA) and humic acid (HA), respectively, owing to the reaction with phosphate (50 μM). Excitation-emission matrix spectroscopy-parallel factor (PARAFAC) and two-dimensional ultraviolet-visible correlation spectroscopy analyses were conducted to characterize the influence of DOM on the precipitation of Cu(II) with phosphate. One humic-like and two protein-like fluorescent components were identified by the PARAFAC model for FA, whereas two humic-like fluorescent components and one protein-like fluorescent component were validated for HA. The humic-like components had primary roles, whereas the protein-like components had secondary roles in limiting the precipitation of Cu(II) with phosphate. Cu(II) binding to DOM chromophores initially occurred at shorter wavelengths, and then at longer wavelengths. Phenolic and carboxylic constituents had important roles, and HA exhibited more binding sites than FA. Therefore, humic-like fluorescent components and chromophores containing phenolic and carboxylic groups and functional groups with peaks at short wavelengths (200-220 nm) were primarily responsible for restricting the precipitation of Cu(II) with phosphate.

Source identification and component characterization of dissolved organic matter in an acid mine drainage reservoir

Acid mine drainage (AMD) is one of the most serious environmental problems and extreme environments on the earth, with high concentrations of sulphate and dissolved metals. A comprehensive description of dissolved organic matter (DOM) in these reservoirs is lacking, and it can play an important role in AMD pollution treatment and ecosystem. Thus, the source, composition and property of DOM in an AMD reservoir in Ma'an shan, China were studied using Fourier transform ion cyclotron resonance mass spectrometry and three-dimension excitation emission matrix fluorescence spectroscopy. The results suggested that the autochthonous algal metabolites significantly contributed to the DOM pool in the AMD reservoir. Bioavailable substances with lower oxidation, unsaturation and aromaticity such as lipids and carbohydrates were lacking in the AMD reservoir especially in the deeper layers. In addition, the proportion of sulfur compounds was significantly higher than that in other waters, suggesting the potential formation of organic matter with sulfur atom in a sulfur-rich environment. These findings underscore that the investigation of DOM in AMD reservoirs may offer references for the AMD treatment with addition of organic matter and broaden the understanding of special carbon cycling in the extreme environment of AMD.

Source apportionment and source-oriented risk assessment of heavy metals in the sediments of an urban river-lake system

Heavy metal pollution in lakes has attracted concerns worldwide since long retention times in lakes allow metals to accumulate and may pose significant threat to ecosystem health. For designing targeted risk mitigation strategies, it is necessary to identify the source-specific risks of heavy metals in the environment. Although previous studies have addressed either risk assessment or source identification of heavy metals in the environment, few have attempted to establish a link between them. In the study, we perform a combination of source apportionment and risk assessment for characterizing the pollution sources and source-specific risks of heavy metals in the sediments of an urban river-lake system. To this end, positive matrix factorization (PMF) was employed to apportion the potential sources of heavy metals, combined with a support vector machine classifier and the referential source fingerprints of metals in the study area. Then, the apportionment results were incorporated into the environmental risk models to evaluate the ecological and human health risks posed by heavy metals from the identified pollution sources. Results showed the river-lake system was contaminated by Cd, Cu, Zn and other metals in varying degree. Particularly, the element of Cd presented moderate to heavy pollution level. In relative, the industrial activities were identified as the largest contributor (48.0%) of heavy metals in the river-lake sediments, mainly associating with electroplating and paper making, followed by the agricultural activities (27.3%) and mix source (24.7%). Overall, the non-carcinogenic and carcinogenic risks posed by the heavy metals were acceptable, however, the element of Cd showed moderate ecological effect. Further, source-oriented risk evaluation suggested industrial processes made higher contributions to the ecological risk of heavy metals in the river-lake system. The study will provide regulators help to update the information by adding apportionment analysis in the context of risk assessment to facilitate subsequent mitigation strategies.

Advances in freshwater risk assessment: improved accuracy of dissolved organic matter-metal speciation prediction and rapid biological validation

Speciation modeling of bioavailability has increasingly been used for environmental risk assessment (ERA). Heavy metal pollution is the most prevalent environmental pollution issue globally, and metal bioavailability is strongly affected by its chemical speciation. Dissolved organic matter (DOM) in freshwater will bind heavy metals thereby reducing bioavailability. While speciation modeling has been shown to be quite effective and is validated for use in ERA, there is an increasing body of literature reporting problems with the accuracy of metal-DOM binding in speciation models. In this study, we address this issue for a regional-scale field area (Lake Tai, with 2,400 km² surface area and a watershed of 36,000 km²) where speciation models in common use are not highly accurate, and we tested alternative approaches to predict metal-DOM speciation/bioavailability for lead (Pb) in this first trial work. We tested five site-specific approaches to quantify Pb-DOM binding that involve varying assumptions about conditional stability constants, binding capacities, and different components in DOM, and we compare these to what we call a one-size-fits-all approach that is commonly in use. We compare model results to results for bioavailable Pb measured using a whole-cell bioreporter, which has been validated against speciation models and is extremely rapid compared to many biological methods. The results show that all of the site-specific approaches we use provide more accurate estimates of bioavailability than the default model tested, however, the variation of the conditional stability constant on a site-specific basis is the most important consideration. By quantitative metrics, up to an order of magnitude improvement in model accuracy results from modeling active DOM as a single organic ligand type with site-specific variations in Pb-DOM conditional stability constants. Because the biological method is rapid and parameters for site-specific tailoring of the model may be obtained via high-throughput analysis, the approach that we report here in this first regional-scale freshwater demonstration shows excellent potential for practical use in streamlined ERA.

Quantitative high-throughput approach to chalkophore screening in freshwaters

There is an increasing need to study the effects of trace metal micronutrients on microorganisms in natural waters. For Fe, small Fe-binding ligands called siderophores, which are secreted from cells and bind Fe with high affinity, have been demonstrated to modulate bioavailability of this critical nutrient. Relatively little is known about secretion of strong Cu-binding ligands (chalkophores) that may help organisms navigate the divide between Cu nutrition and toxicity. A barrier to environmental chalkophore research is a lack of literature on chalkophore analysis. Here we report the development of a quantitative, high-throughput approach to chalkophore screening based on a popular competitive-ligand binding assay for siderophores wherein ligands compete for metal in a chromogenic ternary complex of chrome azurol sulfonate-metal-surfactant. We developed the assay for high-throughput analysis using a microplate reader. The method performance is slightly better than that of comparable screening approaches for siderophores. We find that levels of other metals in natural samples may be capable of causing matrix interferences (a neglected source of analytical uncertainty in siderophore screening) and that for our method this can be overcome by standard additions. In this respect the high-throughput nature of the technique is a distinct advantage. To demonstrate practical use, we tested samples from field mesocosm studies that were set up with and without Cu and Fe amendments; we find trends in results that are logical in the environmental context of our application. This approach will be useful in areas such as risk assessment for a rapid survey of metal speciation and bioavailability; investigators who perform structural studies might also benefit from this approach to rapidly screen and select samples with high Fe/Cu binding capacity for further study.