Partitioning of tetra- and pentabromo diphenyl ether and benzo[a]pyrene among water and dissolved and particulate organic carbon along a salinity gradient in coastal waters

This study assessed the partitioning of 2,2',4,4'-tetrabromo diphenyl ether (BDE-47), 2,2',4,4',5-pentabromo diphenyl ether (BDE-99) and benzo[a]pyrene (BaP) among water, dissolved organic carbon (DOC: 4.93-8.72?mg/L), and particulate organic carbon (POC: 191-462 μg/L) along the salinity gradient (0-5.5‰) of the Baltic Sea off the coast of Finland. Equilibrium dialysis and two solid-phase extraction techniques using polyoxymethylene polymer (POM) were used to determine partitioning coefficients. Experiments using artificial coastal water (ACW) with Nordic fulvic (FAs) and humic acids (HAs) were used to assess the effect of salinity (0 and 5.5‰) on the DOC-water partitioning of the model compounds. All three compounds bound more (2.2-3.8-fold) to the HAs than to the FAs. Increasing salinity from 0 to 5.5‰ decreased sorption to dissolved humic substances in the ACW and Baltic Sea water samples. Along the salinity gradient, the sorption of compounds to organic material decreased when the salinity increased. Particulate organic matter sorbed model compounds per unit of carbon more than dissolved organic matter. Along the studied salinity gradient, the freely dissolved portion increased from 10 to 29% to 52 to 80% in the coastal water samples, mainly because of the increasing salinity and changes in DOC and quality of POC.     

Effect of dissolved organic matter of various origins and biodegradabilities on the bioaccumulation of polycyclic aromatic hydrocarbons in Daphnia magna

As a preliminary study of the influence of urban organic matter on the bioavailability of polycyclic aromatic hydrocarbons (PAHs), the effect of different types of dissolved organic matter (DOM) on the bioaccumulation of fluoranthene, pyrene, or benzo[a]pyrene in Daphnia magna was studied. Commercial humic substances, DOM from the aeration basin of a wastewater treatment plant, and highly biodegradable DOM (algae or animal extracts) were tested. The bioaccumulation of benzo[a]pyrene was reduced by each DOM (up to 80% reduction with humic substances). Pyrene bioaccumulation was also decreased by each DOM to a lesser extent. Fluoranthene bioaccumulation was affected by the presence of humic acids only. In each experiment, the solution containing humic DOM led to the lowest bioaccumulation. Supposing that only dissolved PAHs were bioavailable, the reduction of bioaccumulation allowed a biological estimate of the partition coefficients of DOM and PAH, K(DOC). The estimated coefficients were positively related to the aromaticity of DOM and negatively related to its biodegradability.     

Statistical Implications of Pyrene and Phenanthrene Sorptive Phenomena: Effects of Sorbent and Solute Properties

A 3 × 2 factorial experiment in a generalized randomly complete block was conducted to assess the effects of soil type, soil preparation, and solute concentration on the sorptive behavior of pyrene (PYR) and phenanthrene (PHE). Three bulk soils were treated to remove the soil organic matter (SOM) or clay fractions, then spiked with an initial PYR/PHE concentration of either 3 or 15 mg/L. On average, 98.3% PYR and 91.3% PHE were sorbed to the bulk soils in 24 h, with 4.96 mg PYR kg⁻¹ soil and 22.48 mg PHE kg⁻¹ soil desorbed after three successive 24-h desorption steps. Both clay minerals and SOM greatly contributed to the sorptive behavior. For example, an average 95.1% and 96.1% of the initial PYR sorbed to the clay-removed and SOM-removed subsoils, respectively. Conversely, 16.5 mg/kg and 12.9 mg/kg of the sorbed PYR was desorbed from the clay-removed and SOM-removed subsoils, respectively. Received: 18 January 2002/Accepted: 13 May 2002     

Sorption of polar and nonpolar aromatic compounds to two humic acids with varied structural heterogeneity

The major objective of the present study was to evaluate the correlation between structural nature of humic acids (HAs) and sorption affinity of organic compounds with varied polarity. We compared the sorption behavior of three aromatic compounds-nonpolar phenanthrene (PHEN) and 1,2,4,5-tetrachlorobenzene (TeCB) and highly polar 2,4-dichlorophenol (DCP)-to a solid-phase coal humic acid (CHA) and a soil humic acid (SHA) suspended in aqueous solution. The structural nature of HAs was characterized using elemental analysis, ultraviolet absorbance, diffusive reflectance Fourier-transform infrared, and solid-state 13C nuclear magnetic resonance. The two tested HAs have very different structural properties: CHA consists primarily of poly(methylene)-rich aliphatics with high aromatic content and some COO/N-C=O but low polarity, while SHA consists of young materials of lignin, carbohydrates, and peptides with high polarity. In response to the structural heterogeneity of HAs, sorption of nonpolar and more hydrophobic solutes (PHEN, TeCB) to CHA is much greater than that to SHA because of the predominance of hydrophobic effects; however, disparities in sorption affinity between the two HAs become smaller for polar and less hydrophobic DCP because of the major role played by polar interactions. The influence of pH on the sorption of different solutes to the two HAs was also discussed. The results of the present work highlight the importance of structural heterogeneity of both solutes and HAs in the sorption process.     

Effect of molecular structures on the solubility enhancement of hydrophobic organic compounds by environmental amphiphiles

Amphiphilic molecules, such as humic substances and surfactants, are known to increase the apparent aqueous solubility of hydrophobic organic compounds (HOCs) in the aqueous phase because of their molecular structures, which consist of hydrophilic and hydrophobic moieties. In this study, we examined the effect of the structures of humic acid and HOCs on the sorption of four polycyclic aromatic hydrocarbons (PAHs) and an organochlorine pesticide, p,p'-DDT, to humic acid. As the number of aromatic rings was increased, the extent of solubility enhancement of PAHs by humic acid was increased. Although p,p'-DDT was more hydrophobic than pyrene in this study, the extent of solubility enhancement of p,p'-DDT by humic acid was lower than that of pyrene because of the molecular structures of the solutes. Anionic surfactants with and without aromatic rings also were studied for comparison, and the dianionic surfactant with two benzene rings exhibited similar results with humic acid, unlike the surfactants without and with one benzene ring. The results from this study indicate that bulky molecules, such as p,p'-DDT sorbed with more difficulty to the aggregates of amphiphiles with larger molecules, such as humic substances and the dianionic surfactants.     

Role of participate organic matter in decreasing accumulation of polynuclear aromatic hydrocarbons byDaphnia magna

Accumulation of benzo[a]pyrene (BaP) and anthracene (A) byDaphnia magna in the presence of suspended yeast cells was analyzed using multicompartment models. The rate coefficient for uptake of polynuclear aromatic hydrocarbon (PAH) due to ingestion of yeast cells laden with sorbed chemical was only 3 to 15% of the rate coefficient for uptake of dissolved PAH. Uptake and accumulation of BaP was reduced 97% due to sorption of PAH to naturally occurring organic matter (humic acids). Accumulation of hydrophobic chemicals in aqueous systems appears to depend on the amount of chemical in solution and on the amount of chemical sorbed to particles entering the food chain. Chemicals sorbed to suspended organic matter, including dissolved or colloidal organic matter, have greatly reduced availability.Research sponsored by the Office of Health and Environmental Research, U.S. Department of Energy, under contract W-7405eng-26 with Union Carbide Corp. Publication No. 2127, Environmental Sciences Division, ORNLBy acceptance of this article, the publisher or recipient acknowledges the U.S. Government's right to retain a nonexclusive, royalty-free license in and to any copyright covering the article     

Differential roles of humic acid and particulate organic matter in the equilibrium sorption of atrazine by soils

Recent studies have indicated that soil organic matter (SOM) may consist of physically and chemically different fractions, including particulate organic matter (POM), such as black carbon and unburned coal materials. The present study examined the differential roles of three different SOM fractions isolated from a peat and a topsoil in the equilibrium sorption of the herbicide atrazine (ATZ). The SOM fractions isolated from the two samples included humic acids (HAs), base-extracted humin (HM), and POM after demineralization of HM. A batch technique was employed to measure both the nonequilibrium ATZ sorption on the original and HA samples and the equilibrium ATZ sorption and desorption. The results showed that the phase-distribution relationships measured under nonequilibrium conditions were more linear and had lower sorption-capacity parameters compared with their respective isotherms measured under equilibrium conditions. The sorption isotherms were variously nonlinear, with POM exhibiting the greatest organic carbon-normalized sorption capacity. There existed apparent sorption-desorption hysteresis for each sorbent-sorbate system. It appeared that the extracted HAs could facilitate hydrolysis of ATZ when the reaction time extended to 4 d or longer. The equilibrium sorptive behavior of the HAs therefore was not examined. The present study indicated that both original samples showed lower organic carbon-normalized sorption distribution coefficients compared with their respective SOM fractions, suggesting that a fraction of sorption sites in soil aggregates were not accessed by ATZ.     

Sorption of humic acids and alpha-endosulfan by clay minerals

Sorption of alpha-endosulfan by kaolinite and montmorillonite alone and in the presence of sorbed and dissolved humic acid (HA) was investigated (pH 8 and 25 degrees C). Three types of HA, Elliot soil HA (EHA), Peat HA (PHA), and Summit Hill HA (SHHA), were used to represent typical humic substances found in soils. For sorption of HA by either mineral, Freundlich sorption coefficient (K(f)) values appeared to decrease in the order of EHA > PHA > SHHA, which followed increasing polarity (expressed as the O/C atomic ratio) and decreasing percent-carbon content. For both clays, sorption of alpha-endosulfan by the HA mineral complex was greater than for sorption by the clay alone. Sorption of alpha-endosulfan by the HA mineral complexes followed the same order as the K(f) of the HAs (EHA > PHA > SHHA). Based on the amount of HA adsorbed by each mineral, organic carbon partition coefficients (K(oc)) were determined for sorption of alpha-endosulfan by two of the HA mineral complexes. The value of K(oc) for alpha-endosulfan sorption was greater for kaolinite EHA than kaolinite SHHA. However, the opposite trend was found with the montmorillonite HA complexes. Montmorillonite appeared to sorb alpha-endosulfan and/or HA with higher affinity than kaolinite, which likely is due to its 2:1 layer structure and higher surface area. Sorption of endosulfan diol, a hydrolysis product, by the minerals was much less than the parent pesticide.     

Trace metal distribution in soluble organic matter from municipal solid waste compost determined by size-exclusion chromatography

Municipal solid waste (MSW) composts carry high amounts of trace metals and organic complexing agents that may influence metal bioavailability and mobility after application to soils. In order to assess the degree of organic complexation of trace metals in the solution phase of MSW compost and the relevance of organic ligand type, size exclusion chromatography (SEC) was applied to compost-extracted organic ligands. Adjustment of the elution conditions minimized the interaction with the gel matrix for compost humic substances and dissolved organic matter (DOM) fractions. The SEC was then used to separate the aqueous compost extract into samples with distinct differences in chemical constituents. The highest quantities of Cu, Zn, Ni, Mn, and Cd were found to coelute with the main peak of the SEC elution curve, which, as observed by Fourier-transformed infrared (FTIR) spectroscopy, also had the highest density of carboxyl groups. The ratio of aromatic to aliphatic structures was higher for eluates with low retention times, and cations such as Al, Cr, and Fe were preferably associated with these larger organic molecules. All trace metals in the compost solution phase were bound mostly to DOM rather than forming inorganic complexes.     

Enhancement of phenanthrene solubilization and biodegradation by trehalose lipid biosurfactants

Effects of trehalose lipid biosurfactants produced by Rhodococcus erythropolis on the solubilization and biodegradation of phenanthrene (PHE) were investigated. Based on surface tension measurements, the average critical micelle concentration (CMC) of trehalose lipids was determined to be approximately 16 mg total organic carbon (TOC)/L. In solubilization assays, the addition of biosurfactants at 20-fold the CMC increased the apparent solubility of PHE by more than 30-fold. Using a known PHE degrader (isolate P5-2), batch PHE biodegradation experiments were conducted, with and without trehalose lipids, in three systems: Water (devoid of soil solids), soil (Kenansville loamy sand having 0.72% organic matter), and soil-water slurry. Addition of trehalose lipids at 10-fold the CMC enhanced both the rate and the extent of PHE mineralization by isolate P5-2 in the liquid culture. The addition of biosurfactant (32.2 mg TOC/kg soil) to the soil system also increased both the initial rate (by more than twofold) and the extent of PHE mineralization. Biosurfactants increased the rate, but not the extent, of PHE mineralization in the soil-water slurry. The results obtained in the present study indicate that the trehalose lipid biosurfactants produced by R. erythropolis have good solubilization capacity for hydrophobic organic compounds and great potential for applications in bioremediation of sites contamination with polycyclic aromatic hydrocarbons.     

Methylmercury extraction from artificial sediments by the gut juice of the sipunculan, Sipunculus nudus

Artificially prepared sediments were used to investigate their binding with methylmercury (MeHg). The bioavailability of sediment-bound MeHg then was quantified by measuring the extraction by gut juice of the sipunculan Sipunculus nudus, as well as by different free amino acids and bovine serum albumin (BSA). Methylmercury distribution in different molecular weight- size fractions of gut juice also was determined using an ultrafiltration methodology. Organic and clay content were the two most important sediment components in MeHg partitioning, but most of the sediment-bound MeHg was complexed by organic matter (fulvic acid > humic acid) in sediments. Treatment with humic or fulvic acid generally increased the amount of bioavailable MeHg. Cysteine was more important than other amino acids in MeHg extraction. Proteins (especially >100 kDa fraction) in gut juice rather than free amino acids were the main agents in gut juice that extracted MeHg from sediments. Most extracted MeHg from artificial sediments was associated with the >100 kDa fraction (probably proteins) of gut juice but not with organic matter from sediments (humic acid and fulvic acid). Our results suggested that competition among different agents in gut juice (especially the large molecular-weight proteins) and the organic content of the sediments controlled the bioavailability of sediment-bound MeHg.     

Distribution of atrazine into three chemical fractions: impact of sediment depth and organic carbon content

The fate and transport of organic contaminants in aquatic sediments are impacted largely by microbial degradation and sorption to organic matter. Atrazine, a pre-emergent herbicide, has the potential to contaminate groundwater because of its slight water solubility, long half-life, and sorption to organic matter. Mineralization and distribution of 14C-atrazine into three chemical fractions were monitored over time in surface and subsurface coastal aquatic sediments of different land use. Sediments were extracted with an organic solvent followed by an alkali hydrolysis, and 14C activity was measured in the aqueous, solvent, and basic fractions (representing nonsorbed compounds, loosely sorbed compounds, and humic or fulvic acid bound compounds, respectively). Limited mineralization of atrazine occurred (< 4%). The 14C activity in the aqueous and basic fractions increased over time, was greater in surface versus subsurface sediments, and was positively correlated with sediment organic carbon (SOC) content, indicating greater biological and chemical activity. Total 14C recovered ranged from 50 to 90%, was less in surface versus subsurface sediments, and was not correlated with SOC after 80 d. These results suggest that in native aquatic surface sediments, atrazine sorption plays a major role, whereas in subsurface sediments atrazine may be available for degradation and transport to shallow groundwater.     

Sorption kinetics of toluene in humic acid: a computational approach

Molecular dynamics, a computational technique aiming to describe the time-dependent movement of molecules, has been applied to study the sorption kinetics of volatile organic contaminants in soil organic matter. The molecular dynamics simulation results obtain reasonably accurate estimates of diffusion rates and activation energy of the penetration of a volatile organic compound molecule into a model humic substance. The sorption rate of toluene to humic acid decreases with the density of the humic acid matrix and increases with temperature. All the present results indicate that the sorption of toluene into humic acid is mainly diffusion controlled. Finally, the present studies have shown that molecular dynamics of volatile organic compounds in humic substances yields meaningful results, which help in the understanding of diffusion at the molecular level and which facilitate the problem-solving capability for removing the contaminants from the soils.     

Influence of dissolved organic matter source on silver toxicity to Pimephales promelas

In the environment, the formation of organic and inorganic silver complexes can decrease Ag bioavailability (toxicity) to aquatic organisms. However, current water quality regulations do not consider the protective effects of water quality parameters such as dissolved organic carbon (DOC) concentration. To determine the effect of DOC concentration and source on silver toxicity, nine different natural organic matter isolates were used in 96-h static-renewal toxicity tests with fathead minnow (Pimephales promelas). The 96-h dissolved silver median lethal concentrations (LC50) among different sources of dissolved organic matter varied by up to fivefold (4.5-23.3 microg/L). Further, toxicity tests with organic matter from the site with the lowest 96-h LC50 value suggested only limited additional attenuation of silver toxicity when DOC concentration was increased from 5.1 to 14.0 mg/L. With this site excluded, we found little more than a twofold difference among 96-h dissolved Ag LC50s for the remaining sources (10.1-23.3 microg/L). However, significant toxicological differences among sites remained. It was apparent that organic matter from different sources varied both chemically and toxicologically, but no conclusions could be drawn that related compositional variation to observed Ag toxicity for these isolates.     

The relationship between disinfection by-product formation and structural characteristics of humic substances in chloramination

The influence of structural characteristics of humic substances on disinfection by-product (DBP) formation was investigated for seven humic substances isolated from aquatic and terrestrial sources. The structural characterizations included 13C nuclear magnetic resonance (13C NMR) spectroscopy and ultraviolet (UV) spectroscopy. The aqueous humic substances were chloraminated at pH 7.0 and 8.5, with and without the presence of the bromide ion, and analyzed for total organic halogen (TOX), trihalomethanes (THMs), and haloacetic acids (HAAs). Aromatic contents determined by 13C NMR and differential UV absorbance at 254 nm statistically correlated with TOX formation for the humic substances investigated at p < 0.08. In contrast, a lack of correlation was observed for THM and HAA formation and these parameters. This paper also compiles relevant literature and discusses the contrasting reaction response of DBP precursor material to chlorination and chloramination.     

Molecular simulation of a model of dissolved organic matter

A series of atomistic simulations was performed to assess the ability of the Schulten dissolved organic matter (DOM) molecule, a well-established model humic molecule, to reproduce the physical and chemical behavior of natural humic substances. The unhydrated DOM molecule had a bulk density value appropriate to humic matter, but its Hildebrand solubility parameter was lower than the range of current experimental estimates. Under hydrated conditions, the DOM molecule went through conformational adjustments that resulted in disruption of intramolecular hydrogen bonds (H-bonds), although few water molecules penetrated the organic interior. The radius of gyration of the hydrated DOM molecule was similar to those measured for aquatic humic substances. To simulate humic materials under aqueous conditions with varying pH levels, carboxyl groups were deprotonated, and hydrated Na+ or Ca2+ were added to balance the resulting negative charge. Because of intrusion of the cation hydrates, the model metal-humic structures were more porous, had greater solvent-accessible surface areas, and formed more H-bonds with water than the protonated, hydrated DOM molecule. Relative to Na+, Ca2+ was both more strongly bound to carboxylate groups and more fully hydrated. This difference was attributed to the higher charge of the divalent cation. The Ca-DOM hydrate, however, featured fewer H-bonds than the Na-DOM hydrate, perhaps because of the reduced orientational freedom of organic moieties and water molecules imposed by Ca2+. The present work is, to our knowledge, the first rigorous computational exploration regarding the behavior of a model humic molecule under a range of physical conditions typical of soil and water systems.     

Benzo[a]pyrene bioavailability from pristine soil and contaminated sediment assessed using two in vitro models

A major route of exposure to hydrophobic organic contaminants (HOCs), such as benzo[a]pyrene (BaP), is ingestion. Matrix-bound HOCs may become bioavailable after mobilization by the gastrointestinal fluids followed by sorption to the intestinal epithelium. The purpose of this research was to measure the bioavailability of [14C]-BaP bound to pristine soils or field-contaminated sediment using an in vitro model of gastrointestinal digestion followed by sorption to human enterocytes (Caco-2 cells) or to a surrogate membrane, ethylene vinyl acetate (EVA) thin film. Although Caco-2 cells had a twofold higher lipid-normalized fugacity capacity than EVA, [14C]-BaP uptake by Caco-2 lipids and EVA thin film demonstrated a linear relationship within the range of BaP concentrations tested. These results suggest that EVA thin film is a good membrane surrogate for passive uptake of BaP. The in vitro system provided enough sensitivity to detect matrix effects on bioavailability; after 5 h, significantly lower concentrations of [14C]-BaP were sorbed into Caco-2 cells from soil containing a higher percentage of organic matter compared to soil with a lower percentage of organic matter. The [14C]-BaP desorption rate from Caco-2 lipids consistently was twofold higher than from EVA thin film for all matrices tested. The more rapid kinetics observed with Caco-2 cells probably were due to the greater surface area available for absorption/desorption in the cells. After 5 h, the uptake of BaP into Caco-2 lipid was similar in live and metabolically inert Caco-2 cells, suggesting that the primary route of BaP uptake is by passive diffusion. Moreover, the driving force for uptake is the fugacity gradient that exists between the gastrointestinal fluid and the membrane.     

Heterogeneity in physicochemical properties explains differences in silver toxicity amelioration by natural organic matter to Daphnia magna

Recently collected data have shown that natural organic matter (NOM) source is an important parameter influencing the toxicity of silver to the freshwater crustacean Daphnia magna. The present study attempted to correlate the physicochemical properties of 11 naturally isolated and commercially available NOM sources with their ameliorative effects. The protection offered by these samples was standardized to the protective effect of Aldrich humic acid using geochemical modeling approaches that accounted for associated changes in water chemistry and, consequently, silver speciation. The protective ability of NOM was not correlated with reactive sulfide or nitrogen content, which are considered to be strong silver-binding ligands. Color (specific absorbance coefficient) was positively correlated with protection but narrowly eluded statistical significance. The peak wavelength of emission fluorescence following excitation at 370 nm and the fluorescence index values of NOM samples were significantly correlated with protective effects, suggesting that aromatic carbon content may govern the ameliorative actions of NOM. Simple optical properties may therefore act as a suitable indicator for the ability of a given NOM to protect against waterborne silver toxicity to D. magna as long as changes in water chemistry and, thus, silver speciation, are considered.     

A linear solvation energy relationship model of organic chemical partitioning to dissolved organic carbon

Predicting the association of contaminants with both particulate and dissolved organic matter is critical in determining the fate and bioavailability of chemicals in environmental risk assessment. To date, the association of a contaminant to particulate organic matter is considered in many multimedia transport models, but the effect of dissolved organic matter is typically ignored due to a lack of either reliable models or experimental data. The partition coefficient to dissolved organic carbon (K(DOC)) may be used to estimate the fraction of a contaminant that is associated with dissolved organic matter. Models relating K(DOC) to the octanol-water partition coefficient (K(OW)) have not been successful for many types of dissolved organic carbon in the environment. Instead, linear solvation energy relationships are proposed to model the association of chemicals with dissolved organic matter. However, more chemically diverse K(DOC) data are needed to produce a more robust model. For humic acid dissolved organic carbon, the linear solvation energy relationship predicts log K(DOC) with a root mean square error of 0.43.     

Polycyclic aromatic hydrocarbon behavior in bioactive soil slurry reactors amended with a nonionic surfactant

The effects of an ethoxylated sorbitan fatty ester nonionic surfactant (Tween 80) on the bioavailability of polycyclic aromatic hydrocarbons (PAHs) were examined by using soil-free and dense-slurry (67% solids content, by wt) systems containing a creosote-contaminated field soil. The dispersed-micelle-phase PAHs in soil-free systems were not readily bioavailable to the mixed consortium of microbes indigenous to the creosote-contaminated soil. Instead, the microbes partially and preferentially utilized readily available portions of the surfactant as carbon sources (16-18% of the initial surfactant dose). This selective microbial attack resulted in destabilization of dispersed-phase micelles and significant decreases in molar solubilization ratio and micelle-water partition coefficient values. Remarkably high dosages (>20 g/L) of Tween 80 were required to enhance mobilization of the sorbed PAHs via micelle association because of the sorption of Tween 80 to the soil employed. The PAHs released from the destabilized micelles in soil-slurry systems either associated with sorbed-phase surfactants or readsorbed to soil organic matter too rapidly to be biologically accessed, even by the acclimated PAH-degrading microbes present. The work provides important new information and practical insights to surfactant solubilization and mobilization technology applications for the bioremediation of PAH-contaminated soils and sediments.