Higher Dissolved Organic Matter Research Articles

Novel insights into the predominant factors affecting the bioavailability of polycyclic aromatic hydrocarbons in industrial contaminated areas using PLS-developed model

Bioavailability is recognized as a useful technical standard for risk assessment and pollution rehabilitation. However, knowledge on the bioavailability of polycyclic aromatic hydrocarbons (PAHs) in contaminated site soils is still limited, especially concerning the influential mechanism. With an abundance of soil collections from nine industrial areas in China, the bioavailabilities, as conceptually defined as bioconcentration factors (BCFs) of PAHs were analyzed using biomimetic extraction of hydroxypropyl-β-cyclodextrin (HPCD). Apart from the total content of PAHs varying with the different pyrogenic sources, the BCFs were greatly dependent on the soil physicochemical properties from the spatial scale and inversely proportional to the number of rings. Pearson correlation analysis indicated a weak relationship between bioavailability and the soil dissolved organic matter (DOM), pH and particle size. To incorporate the soil physicochemical properties and structural characteristics of PAHs determined by density functional theory (DFT), the optimum model for bioavailability was developed for BCFs by partial least square (PLS) analysis. The PLS-derived model was shown to be predictive within the applicability domain (AD). The structural characteristics, e.g., molecular polarizability and frontier orbital energy level that favor the soil adsorption of PAH isomers via dispersion interactions, and electron exchanges were indicated to be more impactful on bioavailability than soil environmental factors. However, soil factors should not be neglected, because the pH, DOM, etc. were significantly influential. It makes sense that the higher DOM causes greater bioavailability via increasing the free-dissolved fractions of PAHs. Interestingly, the effect of pH on bioavailability was spectrally validated by excitation-emission matrix (EEM) fluorescence, showing that the interaction between DOM and pyrene strengthened the fluorescence quenching of chromophores with the decline in pH.

Changing Water Chemistry in One Thousand Norwegian Lakes During Three Decades of Cleaner Air and Climate Change

AbstractWe present long‐term changes in Norwegian lake water quality across regional gradients in atmospheric pollution, air temperature, hydrology, and vegetation using (a) a national representative lake survey carried out in 1995 and 2019 (ThousandLakes), and (b) an annual lake survey from acid‐sensitive catchments (78 lakes, TrendLakes) from 1990 to 2020. Our analysis encompasses all major chemical constituents, for example, anions and cations, dissolved organic matter (DOM), nutrients, iron (Fe), and silicate (SiO2). During these decades, environmental changes included declines in sulfur (S) and nitrogen (N) deposition, climate warming, and increase in forest biomass. Strong chemical recovery from acidification is found, attributed to large reductions in atmospheric deposition, moderated by catchment processing from land use and climate change. Browning counteracted chemical recovery in some regions, while Ca increased unexpectedly. We suggest that increased weathering, from enhanced terrestrial productivity, is an important driver of increased Ca—substantiated by widespread, substantial increases in SiO2. Light‐ and nutrient‐limitation has become more prevalent, indicated by higher DOM, lower nitrate (NO3), and lower NO3to total phosphorous ratios. Declines in lake NO3 occurred independently of N deposition, suggesting increased catchment N retention, possibly from increased terrestrial productivity. We conclude that decreased air pollution continues to be a dominant driver of long‐term trends in lake chemistry, but climate‐induced increase in terrestrial weathering processes, governed by increased biomass, is likely to have an increasing impact on future lake acidity, nutrient, and light status, that may cascade along the aquatic continuum from rivers to the coast.

Complex effects of dissolved organic matter, temperature, and initial bloom density on the efficacy of hydrogen peroxide to control cyanobacteria.

Harmful cyanobacterial blooms plague reservoirs and lakes used for a variety of purposes, such as recreation and drinking water. Chemical controls are frequently used to mitigate the occurrence of cyanobacterial blooms given that many are fast-acting and effective at reducing cyanobacterial abundance. Recent research has identified hydrogen peroxide (H2O2) as an environmentally friendly alternative to algaecides that have typically been used, such as copper sulfate. To build on past studies, these experiments sought to further understand how well H2O2 treatments reduce cyanobacteria in complex eutrophic conditions, as well as to assess treatment effects on a non-target phytoplankter, a green alga. We assessed the effectiveness of H2O2 (at treatments of 2-16mg L-1) under varying environmental conditions in a controlled laboratory setting, including (1) dissolved organic matter (DOM) concentrations (humic acid; 0-60mg L-1), (2) temperature (20, 25, and 32°C), and (3) initial algal biomass (chlorophyll-a; 82-371µg L-1). In contrast to our expectations, neither DOM concentration nor temperature meaningfully impacted the effectiveness of H2O2 at reducing cyanobacteria. However, initial algal biomass as well as H2O2 treatment dose greatly influenced the effectiveness of the algaecide on cyanobacteria. Treatments of ≥ 8mg H2O2 L-1 on algal biomass were significantly buffered with higher DOM and lower temperature, and the biological significance of these findings should be explored further. Across all experiments, H2O2 concentrations of 0.03-0.12mg H2O2 L-1µg chlorophyll L-1 were effective at significantly reducing cyanobacteria with varying effects on algal biomass. Thus, water resource managers are encouraged to consider how ambient levels of phytoplankton biomass may affect the ability of H2O2 to control cyanobacterial blooms prior to treatment.

Dissolved organic matter regulates nutrient limitation and growth of benthic algae in northern lakes through interacting effects on nutrient and light availability

AbstractWidespread increases in dissolved organic matter (DOM) concentration across northern lakes can alter rates of primary production by increasing nutrient availability and decreasing light availability. These dual effects of DOM generate a unimodal relationship in pelagic primary production and primary producer biomass among lakes over a gradient of DOM concentration. However, the responses of benthic algae to variation in DOM loading are less clear because of their potential to access sediment nutrients. We tested algal production and nutrient limitation along a DOM gradient in northern Sweden. Without added nutrients, benthic algal production showed a unimodal relationship with DOM, similar to reported pelagic responses. Nutrient addition revealed widespread nitrogen limitation, with decreasing severity in lakes with higher DOM. Because the majority of northern Swedish lakes currently fall below the inflection point in this unimodal relationship, moderate increases in DOM have the potential to increase benthic primary production, particularly for epilithic algae.

Linking optical and chemical signatures of dissolved organic matter in the southern Argentine shelf: Distribution and bioavailability

Fluorescence spectroscopy is commonly used to investigate the distribution and dynamics of dissolved organic matter (DOM) in marine systems. However, the direct comparison with chemical signatures is essential to substantiate the molecular composition of specific fluorescent components. Here we report the relation between optical and chemical signatures of DOM in waters of the Beagle Channel (BCW) (south-east of Tierra del Fuego, in the southern Argentine shelf) at the Pacific-Atlantic connection and neighboring coastal (CW) and oceanic (OW) waters (54.75–55.75°S, 64–68°W). The relationships among concentrations of total dissolved carbohydrates (TDCHO) and amino acids (TDAA), and fluorescent DOM (FDOM), including terrestrial “humic-like” (FDOM C ) and “protein-like” compounds (FDOM T ), and bioavailability of DOM components were assessed from field measurements acquired in the austral summer 2012. The maximal concentrations of TDCHO, dissolved organic carbon (DOC) and FDOMc intensities were found in BCW, while the minima in OW, displaying a negative correlation with salinity. This spatial distribution of biogeochemical signals suggests that humic compounds contributed by continental runoff contain refractory carbohydrates, and FDOM C resulted as a reliable tracer of carbon pathways in the Pacific-Atlantic connection. Conversely, TDAA and FDOM T showed the opposite distributional trend, with minimal concentrations in BCW and the maxima in CW and OW. The significant positive correlation of TDAA with salinity suggests open water sources of these components, however, phytoplankton biomass (Chla) in CW and OW was significantly lower than in BCW, ruling out the assumption of autochthonous source in open waters. TDAA were negatively correlated with the abundance of heterotrophic bacteria (HB), which displayed a consistent decrease from BCW towards OW, suggesting high bacterial uptake of TDAA in the BCW. This bacterial uptake is supported by the observed variation in carbon contribution of TDAA to DOC (amino acids carbon yield, in %), which is an indicator of DOM lability. The negative correlation found between amino acids carbon yield and HB abundance reflects intense bacterial activity in BCW, where phytoplankton biomass was maximum. Hence, higher DOM “freshness” occurs in the BCW, suggesting a tight coupling between microbial production and consumption. • The Pacific-Atlantic connection contains distinct chemical and fluorescence signals. • Continental input is a main source of carbohydrates, DOC and humics in the Beagle Channel. • The heterotrophic activity plays a key role in the modulation of amino acids distribution in the Atlantic-Pacific connection.

Stoichiometry, polarity, and organometallics in solid-phase extracted dissolved organic matter of the Elbe-Weser estuary.

Dissolved organic matter (DOM) is ubiquitous in natural waters and plays a central role in the biogeochemistry in riverine, estuarine and marine environments. This study quantifies and characterizes solid-phase extractable DOM and trace element complexation at different salinities in the Weser and Elbe River, northern Germany, and the North Sea. Dissolved organic carbon (DOC), total dissolved nitrogen (TDN), Co and Cu concentrations were analyzed in original water samples. Solid-phase extracted (SPE) water samples were analyzed for DOC (DOCSPE), dissolved organic nitrogen (DONSPE), sulfur (DOSSPE) and trace metal (51V, 52Cr, 59Co, 60Ni, 63Cu, 75As) concentrations. Additionally, different pre-treatment conditions (acidification vs. non-acidification prior to SPE) were tested. In agreement with previous studies, acidification led to generally higher recoveries for DOM and trace metals. Overall, higher DOM and trace metal concentrations and subsequently higher complexation of trace metals with carbon and sulfur-containing organic complexes were found in riverine compared to marine samples. With increasing salinity, the concentrations of DOM decreased due to estuarine mixing. However, the slightly lower relative decrease of both, DOCSPE and DONSPE (~77%) compared to DOSSPE (~86%) suggests slightly faster removal processes for DOSSPE. A similar distribution of trace metal and carbon and sulfur containing DOM concentrations with salinity indicates complexation of trace metals with organic ligands. This is further supported by an increase in Co and Cu concentration after oxidation of organic complexes by UV treatment. Additionally, the complexation of metals with organic ligands (analyzed by comparing metal/DOCSPE and metal/DOSSPE ratios) decreased in the order Cu > As > Ni > Cr > Co and thus followed the Irving-Williams order. Differences in riverine and marine trace metal containing DOMSPE are summarized by their average molar ratios of (C107N4P0.013S1)1000V0.05Cr0.33Co0.19Ni0.39Cu3.41As0.47 in the riverine endmember and (C163N7P0.055S1)1000V0.05Cr0.47Co0.16Ni0.07Cu4.05As0.58 in the marine endmember.

An Insight into Dissolved Organic Matter Removal Characteristics of Recycling Filter Backwash Water: A Comparative Study

It is necessary to put all aspects,,namely raw water characteristics, corresponding FBWW, and coagulation mechanisms, i.e., charge neutralization and sweep flocculation together to make clear the dissolved organic matter (DOM) removal characteristics and the fate of fractionations in recycle design. The DOM characteristics of molecular weight (MW) distribution, hydrophobicity, and fluorescence in source water W1 (synthesized water) and W2 (“Longtan” lake water), FBWW and treated water samples therefore are identified, and three recycling ratios of 2%, 5%, and 8% as compared to control (0%) are conducted. It is found that DOM within FBWW becomes more hydrophilic and lower MW as compared to corresponding source water. Recycling trials indicate that higher DOM concentrations and more low-MW fractions are not of any benefit to enhance UV254 and DOC removal. Hydrophobic acid can be further eliminated in case recycling particles mainly produced by sweep flocculation, while weakly hydrophobic acid and hydrophilic fraction can be enhanced and removed under recycling particles mainly formed by charge neutralization. Higher molecular weight fraction (>30 kDa) exhibits potentially enhanced removal at preferred recycling ratio of 5%. Fluorescent characteristics analysis demonstrate that recycling FBWW can effectively improve humic-like substances removal, but the protein-like matters are resistant to be eliminated with unvaried structure.

Factorial analysis of the trihalomethane formation in the reaction of colloidal, hydrophobic, and transphilic fractions of DOM with free chlorine

This study focuses on the factors that affect trihalomethane (THMs) formation when dissolved organic matter (DOM) fractions (colloidal, hydrophobic, and transphilic fractions) in aqueous solutions were disinfected with chlorine. DOM fractions were isolated and fractionated from filtered lake water and were characterized by elemental analysis. The investigation involved a screening Placket-Burman factorial analysis design of five factors (DOM concentration, chlorine dose, temperature, pH, and bromide concentration) and a Box-Behnken design for a detailed assessment of the three most important factor effects (DOM concentration, chlorine dose, and temperature). The results showed that colloidal fraction has a relatively low contribution to THM formation; transphilic fraction was responsible for about 50% of the chloroform generation, and the hydrophobic fraction was the most important to the brominated THM formation. When colloidal and hydrophobic fraction solutions were disinfected, the most significant factors were the following: higher DOM fraction concentration led to higher THM concentration, an increase of pH corresponded to higher concentration levels of chloroform and reduced bromoform, higher levels of chlorine dose and temperature produced a rise in the total THM formation, especially of the chlorinated THMs; higher bromide concentration generates higher concentrations of brominated THMs. Moreover, linear models were implemented and response surface plots were obtained for the four THM concentrations and their total sum in the disinfection solution as a function of the DOM concentration, chlorine dose, and temperature. Overall, results indicated that THM formation models were very complex due to individual factor effects and significant interactions among the factors. In order to reduce the concentration of THMs in drinking water, DOM concentrations must be reduced in the water prior to the disinfection. Fractionation of DOM, together with an elemental analysis of the fractions, is important issue in the revealing of the quality and quantity characteristics of DOM. Systematic study composed from DOM fraction investigation and factorial analysis of the responsible parameters in the THM formation reaction can, after an evaluation of the adjustment of the models with the reality, serves well for the evaluation of the spatial and temporal variability in the THM formation in dependence of DOM. However, taking into consideration the natural complexity of DOM, different operations and a strict control of them (like coagulation/flocculation and filtration) has to be used to quantitatively remove DOM from the raw water. Assuming that this study represents a local case study, similar experiments can be easily applied and will supply with relevant information every local water treatment plant meeting problems with THM formation. The coagulation/flocculation and the filtration stages are the main mechanisms to remove DOM, particularly the colloidal DOM fraction. With the objective to minimize THMs generation, different unit operation designed to quantitatively remove DOM from water must be optimized.

Rhizotoxicity of cadmium and copper in soil extracts

Dissolved organic matter (DOM) influences metal speciation in soil solutions and, hence, metal toxicity. Root-elongation experiments were conducted to examine the effect of soil solution components, such as Ca, H, and DOM, on metal rhizotoxicity. A biotic ligand model (BLM) was tested for its ability to predict the rhizotoxicity of Cd and Cu in soil extracts. It was hypothesized that the concentration of Cd and Cu bound to functional groups at the root surface estimated using a BLM would be a better predictor of rhizotoxicity than the free-metal ion activity in solution. Both metals became less toxic at higher DOM, Ca, and H concentrations. Solution speciation and the effect on root growth explained most of the variability observed in the DOM experiments, but not in the cation experiments. It was concluded that Ca and H inhibited the rhizotoxicity of both metals tested. Rhizotoxicity data correlated better with estimates of metal-root complexes that have been estimated with a BLM than with free-metal ion activity or with total metal concentrations. The BLM seems to be a promising approach for predicting metal availability in soils and for assessing the associated risk.