Absence Of Dissolved Organic Carbon Research Articles

Effects of dissolved organic carbon on potentially toxic element desorption in stormwater bioretention systems

Stormwater runoff contains dissolved organic carbon (DOC) and potentially toxic elements (PTEs). Interactions between DOC and PTEs can impact PTE speciation and mobility, but are not fully understood. Soil samples were collected from a vegetated bioretention bed to investigate the effects of DOC (0, 15, and 50 mg-C/L) on the desorption of 10 PTEs captured by the soil media: Mn, Fe, Co, Cu, Zn, As, Cd, Sn, Sb, and Pb. In the absence of DOC, the desorbed PTE concentration from bioretention media into the aqueous phase ranking was as follows: Fe > Mn ∼ Zn > Cu > Pb > Sb > As > Co > Sn ∼ Cd. Increased DOC concentrations resulted in a reduction of the soil-water distribution coefficient (Kd) values. The greatest shift in Kd was observed for Cu and lowest for Sb. The PTE sorption capacities were lower for surficial soil samples (lower Kd) compared to the deep soil samples. Overall, the desorbed PTE (average midchannel 55.7 μg/g) fraction accounted for <1.1 % of the total extracted PTEs (5364 μg/g), and while this is a small percentage of the total, this is the fraction that is mobile. The extracted PTE fractions revealed that DOC reduced the organic matter-bound and carbonate-bound fractions. The PTE desorption trends suggest that reducing DOC in stormwater runoff could be an effective measure to mitigate the release of PTEs into the environment.

The in situ Production of Aquatic Fluorescent Organic Matter in a Simulated Freshwater Laboratory Model.

Dissolved organic matter (DOM) is ubiquitous throughout aquatic systems. Fluorescence techniques can be used to characterize the fluorescing proportion of DOM, aquatic fluorescent organic matter (AFOM). AFOM is conventionally named in association with specific fluorescence “peaks,” which fluoresce in similar optical regions as microbially-derived proteinaceous material (Peak T), and terrestrially-derived humic-like compounds (Peaks C/C+), with Peak T previously being investigated as a tool for bacterial enumeration within freshwaters. The impact of anthropogenic nutrient loading on the processing of DOM by microbial communities is largely unknown. Previous laboratory studies utilizing environmental freshwater have employed growth media with complex background fluorescence, or very high nutrient concentrations, preventing the investigation of AFOM production under a range of more representative nutrient concentrations within a matrix exhibiting very low background fluorescence. We describe a laboratory-based model with Pseudomonas aeruginosa that incorporates a low fluorescence growth matrix consisting of a simulated freshwater (SFW), representative of low-hardness freshwater systems allowing controlled nutrient conditions to be studied. The effects of microbial processing of DOM as a function of available nitrogen, phosphorous, and dissolved organic carbon (DOC) in the form of glucose were investigated over 48 h at highly resolved time increments. The model system demonstrates the production of a range of complex AFOM peaks in the presence and absence of DOC, revealing no linear relationship between cell numbers and any of the peaks for the bacterial species studied, with AFOM peaks increasing with microbial cell number, ranging from 55.2 quinine sulfate units (QSU) per 106 cells to 155 QSU per 106 cells (p < 0.05) for Peak T during the exponential growth phase of P. aeruginosa under high nutrient conditions with 5 mg L−1 DOC. Nutrient and DOC concentration was found to cause differential production of autochthonous- or allochthonous-like AFOM, with lower DOC concentrations resulting in higher Peak T production relative to Peaks C/C+ upon the addition of nutrients, and high DOC concentrations resulting in higher Peak C/C+ production relative to Peak T. Our results show the production of allochthonous-like AFOM from a simple and non-fluorescent carbon source, and provide uncertainty in the use of Peak T as a reliable surrogate for specific bacterial enumeration, particularly in dynamic or nutrient-impacted environments, pointing toward the use of fluorescence as an indicator for microbial metabolism.

The physiology of fish in acidic waters rich in dissolved organic carbon, with specific reference to the Amazon basin: Ionoregulation, acid-base regulation, ammonia excretion, and metal toxicity.

Although blackwaters, named for their rich content of dissolved organic carbon (DOC), are often very poor in ions and very acidic, they support great fish biodiversity. Indeed, about 8% of all freshwater fish species live in the blackwaters of the Rio Negro watershed in the Amazon basin. We review how native fish survive these harsh conditions that would kill most freshwater fish, with a particular focus on the role of DOC, a water quality parameter that has been relatively understudied. DOC, which is functionally defined by its ability to pass through a 0.45-µm filter, comprises a diverse range of compounds formed by the breakdown of organic matter and is quantified by its carbon component that is approximately 50% by mass. Adaptations of fish to acidic blackwaters include minimal acid-base disturbances associated with a unique, largely unknown, high-affinity Na+ uptake system that is resistant to inhibition by low pH in members of the Characiformes, and very tight regulation of Na+ efflux at low pH in the Cichliformes. Allochthonous (terrigenous) DOC, which predominates in blackwaters, consists of larger, more highly colored, reactive molecules than autochthonous DOC. The dissociation of protons from allochthonous components such as humic and fulvic acids is largely responsible for the acidity of these blackwaters, yet at the same time, these components may help protect organisms against the damaging effects of low water pH. DOC lowers the transepithelial potential (TEP), mitigates the inhibition of Na+ uptake and ammonia excretion, and protects against the elevation of diffusive Na+ loss in fish exposed to acidic waters. It also reduces the gill binding and toxicity of metals. At least in part, these actions reflect direct biological effects of DOC on the gills that are beneficial to ionoregulation. After chronic exposure to DOC, some of these protective effects persist even in the absence of DOC. Two characteristics of allochthonous DOC, the specific absorbance coefficient at 340 nm (determined optically) and the PBI (determined by titration), are indicative of both the biological effectiveness of DOC and the ability to protect against metal toxicity. Future research needs are highlighted, including a greater mechanistic understanding of the actions of DOCs on gill ionoregulatory function, morphology, TEP, and metal toxicity. These should be investigated in a wider range of native fish Orders that inhabit one of the world's greatest biodiversity hotspots for freshwater fishes.

Does dissolved organic carbon from Amazon black water (Brazil) help a native species, the tambaqui Colossoma macropomum to maintain ionic homeostasis in acidic water?

To assess how the quality and properties of the natural dissolved organic carbon (DOC) could drive different effects on gill physiology, we analysed the ionoregulatory responses of a native Amazonian fish species, the tambaqui Colossoma macropomum, to the presence of dissolved organic carbon (DOC; 10 mg l-1 ) at both pH 7.0 and pH 4.0 in ion-poor water. The DOC was isolated from black water from São Gabriel da Cachoeira (SGC) in the upper Rio Negro of the Amazon (Brazil) that earlier been shown to protect a non-native species, zebrafish Danio rerio against low pH under similar conditions. Transepithelial potential (TEP), net flux rates of Na+ , Cl- and ammonia and their concentrations in plasma and Na+ , K+ ATPase; v-type H+ ATPase and carbonic anhydrase activities in gills were measured. The presence of DOC had negligible effects at pH 7.0 apart from lowering the TEP, but it prevented the depolarization of TEP that occurred at pH 4.0 in the absence of DOC. However, contrary to our initial hypothesis, SGC DOC was not protective against the effects of low pH. Colossoma macropomum exposed to SGC DOC at pH 4.0 experienced greater net Na+ and Cl- losses, decreases of Na+ and Cl- concentrations in plasma and elevated plasma ammonia levels and excretion rates, relative to those exposed in the absence of DOC. Species-specific differences and changes in DOC properties during storage are discussed as possible factors influencing the effectiveness of SGC DOC in ameliorating the effects of the acid exposure.

Dissolution and aggregation kinetics of zero valent copper nanoparticles in (simulated) natural surface waters: Simultaneous effects of pH, NOM and ionic strength

The combined effects of pH, dissolved organic carbon (DOC) and Ca2+/Mg2+ on the dissolution and aggregation kinetics of zero valent copper engineered nanoparticles (Cu0 ENPs) were investigated. The dissolution and aggregation of the particles were studied in (a) synthetic aqueous media, similar in chemistry to natural surface waters, and (b) natural surface waters samples, for up to 32 or 24 h. The DOC stabilized the particles and prevented aggregation, and thus increased the available surface area. The higher available surface area in turn accelerated the dissolution of the particles. The presence of Ca2+/Mg2+, however, changed the aggregation and the dissolution of the DOC-stabilized particles. The influence of Ca2+/Mg2+ on DOC-stabilized particles was different at different pH's. In the absence of DOC, 10 mM of Ca2+/Mg2+ induced charge reversal on the particles and caused particle stability against aggregation. This subsequently increased particles dissolution. The results obtained with regard to dissolution and aggregation of the particles in natural surface waters were compared with those determined for the synthetic waters. This comparison showed that the behavior of the particles in the natural surface waters was mostly similar to the behavior determined for media at pH 9. Overall, the current study provides some novel insights into the simultaneous effects of physicochemical parameters of water on particle stability against aggregation and dissolution, and provides data about how the processes of aggregation and dissolution of Cu0 ENPs interact and jointly determine the overall particle fate.

On the mechanism of nanoparticulate CeO2 toxicity to freshwater algae

The factors affecting the chronic (72-h) toxicity of three nanoparticulate (10–34nm) and one micron-sized form of CeO2 to the green alga, Pseudokirchneriella subcapitata were investigated. To characterise transformations in solution, hydrodynamic diameters (HDD) were measured by dynamic light scatter, zeta potential values by electrophoretic mobility, and dissolution by equilibrium dialysis. The protective effects of humic and fulvic dissolved organic carbon (DOC) on toxicity were also assessed. To investigate the mechanisms of algal toxicity, the CytoViva hyperspectral imaging system was used to visualise algal–CeO2 interactions in the presence and absence of DOC, and the role of reactive oxygen species (ROS) was investigated by ‘switching off’ ROS production using UV-filtered lighting conditions.The nanoparticulate CeO2 immediately aggregated in solution to HDDs measured in the range 113–193nm, whereas the HDD and zeta potential values were significantly lower in the presence of DOC. Negligible CeO2 dissolution over the time course of the bioassay ruled out potential toxicity from dissolved cerium. The nanoparticulate CeO2 concentration that caused 50% inhibition of algal growth rate (IC50) was in the range 7.6–28mg/L compared with 59mg/L for micron-sized ceria, indicating that smaller particles were more toxic. The presence of DOC mitigated toxicity, with IC50s increasing to greater than 100mg/L. Significant ROS were generated in the nanoparticulate CeO2 bioassays under normal light conditions. However, ‘switching off’ ROS under UV-filtered light conditions resulted in a similar IC50, indicating that ROS generation was not the toxic mechanism. The CytoViva imaging showed negligible sorption of nanoparticulate CeO2 to algal cells in the presence of DOC, and strong sorption in its absence, suggesting that this was the toxic mechanism. The results suggest that DOC in natural waters will coat CeO2 particles and mitigate toxicity to algal cells.

Photodegradation of estrone enhanced by dissolved organic matter under simulated sunlight

In the present work the degradation of estrone (E1) a natural estrogenic hormone has been studied under simulated solar irradiation. The photodegradation of E1 has been investigated in the absence and in the presence of 7.7–8.9 mg L −1 of dissolved organic carbon (DOC), under solar light simulation with irradiance approximating that of the sun. DOC extracts from different origins have been used. Half-lives ranging between 3.9 h and 7.9 h were observed. Results indicated that E1 was photodegraded even in the absence of DOC. The presence of DOC was found to enhance the degradation of E1. Experiments performed with the addition of reactive species scavengers (azide ions and 2-propanol) have shown that these two species play a significant role in the photodegradation. Some experiments have been performed with a DOC previously submitted to solar irradiation. Changes in optical and physico-chemical properties of DOC strongly affect its photoinductive properties, and hence its efficiency on E1 degradation. A part of the study consisted in the investigation of photoproducts structures. Five photoproducts were shown by chromatographic analysis: one arising from direct photolysis and the four others from DOC photoinduced degradation.

The influence of dissolved organic carbon on sorption of heavy metals on urea-treated pine bark

A previous study showed considerably higher metal adsorption by urea-treated pine bark (UTB) compared to non-treated bark (NTB) at metal adsorption from their individual relatively concentrated solutions. Comparison of the sorption characteristics of the two pine barks at low but environmentally relevant metal concentrations, and investigation of the influence of pH and dissolved organic carbon (DOC) on the sorption process are the aims of the present study. Sorption of Cu(2+), Ni(2+), Zn(2+) and Pb(2+) on pine bark of the species Pinus sylvestris was measured in multi-metal solutions in the presence and absence of DOC. In the absence of DOC, UTB gave lower residual metal concentrations (2-7 microg/l for copper, 1-5 microg/l for nickel, <0.05 microg/l for zinc and lead) in the range of initial concentrations up to 0.7 mg/l, compared to NTB (6-15 microg/l for copper, 2-24 microg/l for nickel, 2-9 microg/l for zinc, 2-3 microg/l for lead). In the presence of DOC, sorption of Zn, Ni and Pb decreased by up to 75% depending on the DOC concentration. Metal sorption on UTB is less sensitive to pH and more adsorbed metal ions are retained compared to NTB. The potential use of urea-treated bark for treatment of waste water containing DOC and low concentrations of metals is discussed.

Formation of brominated products in irradiated titanium dioxide suspensions containing bromide and dissolved organic carbon

We report the irradiation of TiO 2 suspensions containing Br - and dissolved organic carbon (DOC). In the absence of DOC, we found no evidence for the formation of BrO 3 - upon irradiation of 1 g L - 1 P25 suspensions with UV light for initial Br - concentrations up to 10 mg L - 1 . In the presence of DOC (Lake Hohloh, Germany and salicylic acid), we found no evidence for the formation of either BrO 3 - or trihalomethanes (THMs). However, small amounts of adsorbable organic halogen (AOX) were formed at high bromide concentrations ( 3 mg L - 1 ). When irradiating P25 suspensions containing bromide and 2,4-dihydroxybenzoic acid (DHBA, high bromoform formation potential), we observed the formation of significant amounts of bromoform (up to 10 μ g L - 1 ). Bromoform appeared only after the DHBA had been degraded.

Root-zone modeling of heavy metal uptake and leaching in the presence of organic ligands

We present a mechanistic model which describes root uptake and leaching of heavy metals in the plant root zone, accounting for solution- and surface-complexation, (kinetic) mineral dissolution, heavy metal diffusion towards the root, root uptake, root exudation, ligand degradation and convective-dispersive transport of the soluble species. The model was used to simulate the influence of EDTA addition on Cu transport and plant uptake and the effect of oxalate exudation by roots on Cu transport and bioavailability using parameter values from the literature. In the simulations we assumed that free Cu2+ is the bioavailable form. Under slightly acidic conditions (pH 6) the model predicted that EDTA stabilizes Cu while at a slightly alkaline pH (pH 7.5), EDTA mobilizes Cu. The addition of EDTA approximately halved the cumulative Cu uptake after 360 days at pH 4.5, and reduced the uptake by a factor of 100 and 1000 at pH 6 and 7.5, respectively. Although the total dissolved concentration was increased, plant uptake was reduced by the formation of bio-inavailable complexes. The exudation of oxalate resulted in a decrease of the Cu concentration breaking through below the root zone, due to sorption of Cu-oxalate. In the presence of dissolved organic carbon (DOC), the exudation of oxalate increased Cu leaching considerably at pH 6 and 7.5. In the absence of DOC, the exudation of oxalate reduced Cu uptake due to the formation and adsorption of Cu-oxalate on goethite surface sites. Exudation of oxalate in the presence of DOC resulted in a further decrease of Cu uptake. Oxalate gradually takes over from DOC in binding Cu due to simultaneous production of oxalate and leaching of DOC. The simulations show that addition or exudation of ligands does not necessarily increase the solubility, transport and bioavailability of metals. Depending on the conditions (mainly the pH), also reduced transport and uptake can be observed, either by formation of ternary surface complexes or reduction of free metal concentration. The model can be easily extended to include further processes.

Methylmercury artifact formation during solid-phase extraction of water samples using sulfhydryl cotton fiber adsorbent

Preconcentration of methylmercury from dilute water samples by solid-phase extraction on a column packed with sulfhydryl cotton causes methylation of inorganic mercury. The effect is most severe for low concentrations of mercury in deionized water and environmental water samples, such as melted snow or rainwater, with low dissolved organic carbon (DOC) contents, resulting in up to 40% conversion of inorganic mercury to methylmercury. Although, in previous studies artifact methylmercury was attributed to the presence of naturally occurring DOC in the water, we find evidence for methylation especially in the absence of DOC. Indeed, high DOC content appears to suppress artifact formation. In such cases, binding of inorganic mercury by organic matter protects the mercury from methylation under the analysis conditions.

Effect of Water Extract of Compost on the Adsorption of Arsenate by Two Calcareous Soils

The increasing mobility of arsenate will increase its leachingpotential to groundwater and uptake by plants. The mobility ofarsenate in soils is related to the competitive adsorption with other substances. The effect of organic substances on the adsorption of arsenate by soils was evaluated using the water extract of compost (WEC) as a complex anion source in a batch experiment. Two calcareous slate alluvial soils, Chiwulan andShuipientou, with higher arsenic contents of 23.7 and 12.9 mg kg-1, respectively, were used. The Langmuir equation has been used to describe successfully the As adsorption isotherm for the two soils. The maximum adsorption of As was 6.098 and 4.785 μmol g-1 for Chiwulan and Shuipientou soils, respectively. There was competitive adsorption for binding siteson the soils between arsenate oxyanions and organic anions derived from the dissolved organic carbon (DOC) of WEC. Differentcritical pH values were for arsenate addition related to arsenateadsorption on both soils in the absence of DOC of WEC but not inthe presence of DOC of WEC. The soil properties related to arsenate adsorption by the two soils may govern the critical pH values.

Influence of Dissolved Organic Carbon and Initial Moisture on Zinc Sorption by Two Arid Soils

Sorption of added zinc to irrigated soils in arid regions is an important process that may control the availability of zinc to growing plants . Two soil surface samples varying in clay , organic matter , and calcium carbonate content were selected from central and southwestern regions of Saudi Arabia and prepared in order to give different initial moisture contents ranging from air dried to 100 % of field capacity . The sorption experiment was conducted using Zn concentrations ranging from 5 to 25 mg L 1, prepared from ZnSO4 either in distilled water or in solutions containing 75 mg L 1 dissolved organic carbon (DOC). Results indicate that the amount of Zn sorbed in the presence of DOC was relatively high compared with the absence of DOC and Zn retention was strongly affected by the initial soil moisture content . Also , equilibrium Zn concentrations were quite low , while Zn retentions were high in all treatments . Data of Zn sorption were described by the Freundlich isotherm , and two linear portions were found in most cases . In the absence of DOC , retentions of added Zn were controlled by the available exchange sites and / or the precipitation of Zn as sparingly soluble forms. Zn ions in the presence of DOC were able to form soluble - Zn organic complexes that adsorb on the soil surfaces . The extent of such behavior was related to the variations in clay , organic matter , and calcium carbonate contents as well as the initial moisture of the soil . Results indicate that addition of DOC reduces the amount of extractable Zn from either soil Zn or the sorbed Zn by ammonium bicarbonate diethylenetriamine pentaacetic acid ( AB DTPA ). More than 80 % of the sorbed Zn was extracted by AB-DTPA , and the percentage of extracted / sorbed Zn decreased with the increase in sorbed Zn . The obtained results give evidence that initial moisture content and addition of DOC reduce the extractability of applied inorganic Zn by AB-DTPA extract in arid soils.

Distribution of pesticides in the sediment of the small Teufelsweiher pond (southern Germany)

Within the scope of the joint research project “Research Network on Agroecosystems Munich (FAM)” in Scheyern, Upper Bavaria, Germany, the concentration and distribution of pesticides were studied in sediment samples in order to elucidate their fate in the aquatic environment. Of seven recently applied pesticides, only atrazine, bifenox and their metabolites were measured both in the solid sediment and the proewater isolated from the Teufelsweiher pond (area 3155 m 2, depth 0.3–1.3 m) near Scheyern from 1992 to 1994. The mean total concentrations ranged from 33–76 ng litre −1 in the porewater and 1.3–4.9 μg kg −1 in the solid sediment for atrazine and 9.5–23 ng litre −1 and 4.1–18.3 μg kg −1 for bifenox, respectively. They exhibited a small spatial but obviously no temporal variation. This variation depends on the sediment particle-size distribution, because the highest pesticide concentrations were found in both the smallest ( < 6.3 μm) and the largest fraction (63–200 μm). The organic matter content of the sediment contributes mainly to this concentration distribution. In addition, comparing the in situ measured K oc with the K oc determined in the laboratory, the generally lower K oc values indicate that dissolved organic carbon (DOC) adsorbs pesticides, resulting in a higher total concentration in the porewater than in the absence of DOC. This “solubilization effect” may increase pesticide remobilization and availability in the aquatic environment. Atrazine and bifenox were mainly transported by runoff from the inclined areas nearby into the Teufelsweiher, but their transport pattern and metabolism schemes show some differences according to the different physiochemical properties.