Association of hydrophobic organic contaminants with soluble organic matter: evaluation of the database of K doc values

Assessment of tolerance limits of petroleum residues in soil organic matter: sorption of dichlorobenzene by soil

Soil organic matter can protect plants and microorganisms from toxic substances. Beyond the tolerance limit, the toxicity of petroleum pollution to soil organisms may increase rapidly with the increase of petroleum content. However, the method for evaluating the petroleum tolerance limit of soil organic matter (SOM) is still lacking. In this study, the petroleum saturation limit in SOM was first evaluated by the sorption coefficient (Kd) of 1,2-dichlorobenzene (DCB) from water to soils containing different petroleum levels. The sorption isotherm of dichlorobenzene in several petroleum-contaminated soils with different organic matter content and the microbial toxicity test of several petroleum-contaminated soils were determined. It is found that when the petroleum content is about 5% of the soil organic matter content, the sorption of petroleum to organic matter reached saturation limit. When organic matter reaches petroleum saturation limit, the sorption coefficient of DCB by soil particles increased linearly with the increase of petroleum content (R2 > 0.991). The results provided important insights into the understanding the fate of petroleum pollutants in soil and the analysis of soil toxicity.

Environmental factors strongly influence the leaching of di(2-ethylhexyl) phthalate from polyvinyl chloride microplastics

Phthalic acid esters (phthalates) are an important group of additives (plasticizers) to ensure the flexibility and stability especially of polyvinyl chloride (PVC) and to enable its processing. However, phthalates like di(2-ethylhexyl) phthalate (DEHP) are harmful for aquatic organisms due to their endocrine disrupting effects and toxicity. For the assessment of exposure concentrations, thorough understanding of leaching kinetics of phthalates from PVC (micro-) plastics into aqueous environments is necessary. This study investigates how environmental factors influence the leaching of phthalates from PVC microplastics into aquatic systems. The leaching of phthalates from PVC microplastics into aqueous media is limited by aqueous boundary layer diffusion (ABLD) and thus, process-specific parameters can be affected by environmental factors such as salinity and the flow conditions. We conducted batch leaching experiments to assess the influence of salinity and flow conditions (turbulence) on the leaching of DEHP from PVC microplastics into aqueous media. DEHP is salted out with increasing salinity of the solution and a salting-out coefficient for DEHP of 0.46 was determined. The partitioning coefficient of DEHP between PVC and water KPVC/W increased with increasing salinity from 108.52 L kg-1 in a 1 mM KCl solution to 108.75 L kg-1 in artificial seawater thereby slowing down leaching. Increasing flow velocities led to higher leaching rates because the ABL thickness decreased from 1315 µm at 0 rpm shaking speed (no-flow conditions) to 38.4 µm at 125 rpm (turbulent conditions). Compared to salinity, turbulence had a more pronounced effect on leaching. Increasing the flow velocity led to a 35-fold decrease in the leaching rate, while increasing salinity led to a 2-fold increase. By calculating specific leaching times, that is, leaching half-lives (t1/2), time frames for leaching in different aquatic systems such as rivers and the ocean were determined. Given ABLD-limited leaching, DEHP is leached faster from PVC microplastics in rivers (t1/2 > 49 years) than in the ocean (t1/2 > 398 years). In both systems, PVC microplastics are a long-term source of phthalates.

Polyvinyl Chloride Microplastics Leach Phthalates into the Aquatic Environment over Decades

Phthalic acid esters (phthalates) have been detected everywhere in the environment, but data on leaching kinetics and the governing mass transfer process into aqueous systems remain largely unknown. In this study, we experimentally determined time-dependent leaching curves for three phthalates di(2-ethylhexyl) phthalate, di(2-ethylhexyl) terephthalate, and diisononyl phthalate from polyvinyl chloride (PVC) microplastics and thereby enabled a better understanding of their leaching kinetics. This is essential for exposure assessment and to predict microplastic-bound environmental concentrations of phthalates. Leaching curves were analyzed using models for intraparticle diffusion (IPD) and aqueous boundary layer diffusion (ABLD). We show that ABLD is the governing diffusion process for the continuous leaching of phthalates because phthalates are very hydrophobic (partitioning coefficients between PVC and water log K_PVC/W were higher than 8.6), slowing down the diffusion through the ABL. Also, the diffusion coefficient in the polymer D_PVC is relatively high (∼8 × 10^-14 m² s^-1) and thus enhances IPD. Desorption half-lives of the studied PVC microplastics are greater than 500 years but can be strongly influenced by environmental factors. By combining leaching experiments and modeling, our results reveal that PVC microplastics are a long-term source of phthalates in the environment.

A comparison of adsorption of organic micropollutants onto activated carbon following chemically enhanced primary treatment with microsieving, direct membrane filtration and tertiary treatment of municipal wastewater

The adsorption of organic micropollutants onto powdered activated carbon (PAC) was investigated in laboratory scale based on samples from four wastewater process streams (matrices); three from a pilot-scale plant with different degrees of physicochemical treatment of municipal wastewater and one from a full-scale activated sludge plant with post-precipitation. The pilot-scale treatment consisted of chemically enhanced primary treatment with microsieving followed by direct membrane filtration as microfiltration or ultrafiltration. The results showed highest adsorption of micropollutants in the tertiary (biologically and chemically) treated wastewater and lowest adsorption in the microsieve filtrate. Adsorption of micropollutants in the direct membrane microfiltration (200 nm) permeate was generally similar to that in the direct membrane ultrafiltration (3 nm) permeate. The higher adsorption of micropollutants in the tertiary treated wastewater could be related to a lower concentration of dissolved organic carbon (DOC) and lower affinity of DOC for PAC at low dosage (<15 mg PAC/L) in this matrix. At a PAC dose of 10 mg/L, sulfamethoxazole was removed by 33% in the tertiary treated wastewater and 7% in the direct membrane microfiltration permeate. In addition to the PAC experiments, a pilot scale sand filter and a proceeding GAC filter was operated on tertiary treated wastewater from the full-scale treatment plant. Similar removal trends in the PAC and GAC experiments were observed when studying a weighted average micropollutant removal in the GAC filter and a similar dose of activated carbon for both PAC and GAC. Positively charged micropollutants were removed to a higher extent than negatively charged ones by both PAC and GAC.

Fluorescence excitation/emission matrices as a tool to monitor the removal of organic micropollutants from wastewater effluents by adsorption onto activated carbon

Monitoring the removal of organic micropollutants (OMPs) in advanced wastewater treatment facilities requires expensive and time-consuming analytical methods that cannot be installed online. Spectroscopic techniques such as fluorescence excitation/emission spectroscopy were demonstrated to offer the potential for monitoring OMPs removal in conventional wastewater treatment plants or ozonation pilots but their application to activated carbon (AC) adsorption processes was only investigated at lab scale and not in real treatment facilities. In this study, indexes from fluorescence emission/excitation matrices (EEMs) were used to find correlations with the removal of 28 OMPs from a large-scale AC pilot in fluidized bed employed for wastewater advanced treatment, as well as from batch experiments. Differences in OMPs removal could be observed depending on the operational conditions (i.e. pilot or batch experiments, contact time, type of AC) and the physico-chemical properties of the molecules. 7 PARAFAC components were derived from the fluorescence EEMs of 60 samples obtained before and after adsorption. Positive correlations were obtained between the removal of fluorescence indexes and most OMPs, and correlation coefficients were much higher than the ones obtained with UV₂₅₄, confirming the interesting potential of fluorescence spectroscopy to accurately monitor adsorption performances at the industrial scale. The highest correlation coefficients were obtained for OMPs having the best removals while the ones that were refractory to adsorption, as well as to interactions with DOM, exhibited weak correlations. These results suggest that interactions between OMPs and fluorescing DOM and their subsequent co-adsorption onto AC were at the origin of the correlations found. Lower correlations were also found for the most biodegradable OMPs, which indicated that the occurrence of biological effects could make the monitoring of these compounds more challenging.

Sorption Constant of Bisphenol A and Octylphenol Onto Size-Fractioned Dissolved Organic Matter Using a Fluorescence Method

Dissolved organic matter (DOM) is a complex and heterogeneous mixture ubiquitously present in aquatic systems. DOM affects octylphenol (OP) and bisphenol A (BPA) distribution, transport, bioavailability, and toxicity. This study investigated OP and BPA sorption constants, log K_COC, with three size-fractioned DOM. The molecular weights of the sized fractions were low molecular weight DOM (LDOM, <1 kDa), middle molecular weight DOM (MDOM, 1–10 kDa), and high molecular weight DOM (HDOM, 10 kDa–0.45 μm). The log K_COC ranged from 5.34 to 6.14 L/kg-C for OP and from 5.59 to 6.04 L/kg-C for BPA. The OP and BPA log K_COC values were insignificantly different (p = 0.37) and had a strong positive correlation (r = 0.85, p < 0.001). The OP and BPA LDOM log K_COC was significantly higher than the HDOM and MDOM log K_COC (p = 0.012 for BPA, p = 0.023 for OP). The average specific ultraviolet absorption (SUVA₂₅₄) values were 32.0 ± 5.4, 13.8 ± 1.0, and 17.9 ± 2.8 L/mg-C/m for LDOM, MDOM, and HDOM, respectively. The log K_COC values for both OP and BPA had a moderately positive correlation with the SUVA₂₅₄ values (r = 0.79–0.84, p < 0.002), which suggested the aromatic group content in the DOM had a positive impact on sorption behavior.

Glomalin-related soil protein reduces the sorption of polycyclic aromatic hydrocarbons by soils

Large amounts of glomalin-related soil protein (GRSP) are present in the soil; however, the impacts of GRSP on the chemical process of soil polycyclic aromatic hydrocarbons (PAHs) are far under investigation. This research sought to elucidate the sorption of phenanthrene as a representative PAH by soils, including Kandiudult, TypicPaleudalf, and Mollisols with co-existing GRSP (0-50 mg/L). The results indicated that soil sorption capacities for phenanthrene reduced significantly. Notably, GRSP changed the sorption process of phenanthrene by Kandiudult, well described as the Freundlich model. In contrast, the phenanthrene sorption isotherms were well described with the Linear model for TypicPaleudalf and Mollisols. The reduced percentage of phenanthrene sorption due to GRSP addition was 7.01%-49.21%, 23.92%-68.71%, and17.26%-66.80% for Kandiudult, TypicPaleudalf and Mollisols, respectively. It was noted that GRSP has a strong capacity for phenanthrene sorption in aqueous solutions and elevates the availability of phenanthrene for microorganisms or plants. During the sorption process, the introduction of GRSP resulted in the reduction of organic matter in soils and elevated the concentrations of dissolved organic matter in solutions, which was the primary mechanism of GRSP-reduced phenanthrene sorption by soils. The findings revealed that GRSP enrichment can increase the mobility of PAHs in contaminated soils.

Elevated temperature enhances the bioavailability of pyrene to Daphnia magna in the presence of dissolved organic matter: Implications for the effect of climate warming

Dissolved organic matter (DOM) is an essential factor in natural waters to affect the bioavailability of hydrophobic organic compounds (HOCs). Climate warming may influence the partition of HOCs between DOM and water as well as the physiology of organisms. Thus, we hypothesized that elevated temperature might affect the bioavailability of HOCs in the presence of DOM. To test this hypothesis, the effect of temperature on the bioavailability of pyrene to Daphnia magna (D. magna) in water-DOM (fulvic acid) system was investigated. The results showed that, although the concentration of freely dissolved pyrene increased slightly with temperature in the presence of DOM when the level of total dissolved pyrene was kept constant, D. magna immobilization (increased by 50.0-167%) and internal body burden of pyrene (increased by 18.4-41.5%) increased significantly with every 4 °C increase in temperature (16, 20, 24 °C). The main reasonable explanation for this result is that elevated temperature promoted pyrene uptake by D. magna. It was found that the increase percentage of 1-hydroxypyrene (main metabolite of pyrene) concentrations with temperature was higher than that of pyrene concentrations in the body except gut of D. magna. This result indicated that increased temperature might enhance the metabolic rates of D. magna, thus leading to increased uptake rate of freely dissolved and DOM-associated pyrene. This study suggests that elevated temperature might enhance the bioavailability of HOCs in natural waters through influencing both the bioavailable fraction of HOCs and their uptake rates in aquatic organisms, and this should be considered for evaluating their eco-environmental risks under the context of climate warming.

Vertical distribution of polycyclic aromatic hydrocarbons in the brackish sea water column: ex situ experiment

Background

Oil spills can cause severe damage within a marine ecosystem. Following a spill, the soluble fraction of polycyclic aromatic hydrocarbons is rapidly released into the water column. These remain dissolved in seawater over an extended period of time, even should the insoluble fraction be removed. The vertical distribution of the aromatic hydrocarbon component and how these become transferred is poorly understood in brackish waters. This study examines the vertical distribution of polycyclic aromatic hydrocarbons having been released from a controlled film of spilled oil onto the surface of brackish water.

Methods

The study was undertaken under controlled conditions so as to minimize the variability of environmental factors such as temperature and hydrodynamics. The distribution of polycyclic aromatic hydrocarbons was measured in the dissolved and suspended phases throughout the 1 m water column with different intensity of water sampling: 1, 2, 4, 7, 72, 120, 336, 504 and 984 h.

Results

The total concentration of polycyclic aromatic hydrocarbons ranged from 19.01 to 214.85 ng L^–1 in the dissolved phase and from 5.14 to 63.92 ng L^–1 in the suspended phase. These hydrocarbons were released immediately following a controlled spill attaining 214.9 ng L^–1 in the dissolved phase and 54.4 ng L^–1 in the suspended phase near the cylinder bottom after 1–2 h. The 2–3 ring polycyclic aromatic hydrocarbons dominated in the dissolved phase (60–80%), whereas the greater amount of 4–6 ring polycyclic aromatic hydrocarbons (55–90%) occurred in the suspended phase. A relatively low negative correlation (r_S = –0.41) was determined between the concentration of phenanthrene and suspended matter, whereas a high negative correlation (r =  − 0.79) was found between the concentration of pyrene and suspended matter. Despite the differences in the relationships between the concentration ratio and amount of suspended matter the obtained regressions allow roughly to predict the concentration of polycyclic aromatic hydrocarbons.

Influence of dissolved organic matter on the removal of 12 organic micropollutants from wastewater effluent by powdered activated carbon adsorption

The presence of dissolved organic matter (DOM) in wastewater effluents is recognized as the main factor limiting the adsorption of organic micropollutants (OMPs) onto activated carbon. The degree of the negative effect that DOM, depending on its quality, exerts on OMPs adsorption is still unclear. The influence of the interactions between DOM and OMPs on their removal is also not fully understood. Adsorption isotherms and conventional batch tests were performed in ultra-pure water and in wastewater effluent to study the influence of DOM on the adsorption of 12 OMPs onto powdered activated carbon. Best fit of adsorption pseudo-isotherms was obtained with the Freundlich equation and showed, as expected, that OMPs adsorption was higher in ultra-pure water than in wastewater effluent due to the presence of DOM leading to pore blockage and competition for adsorption sites. LC-OCD analysis revealed that biopolymers and hydrophobic molecules were the most adsorbed fractions while humic acids were not removed after a contact time of either 30 min or 72 h. The presence of DOM had a negative impact on the removal of all OMPs after 30 min of adsorption, but similar removals to ultra-pure water were obtained for 6 OMPs after 72 h of adsorption. This demonstrated that competition between DOM and OMPs for adsorption sites was not a major mechanism as compared to pore blockage, which only slowed down the adsorption and did not prevent it. The charge of OMPs had a clear impact: the adsorption of negatively charged compounds was reduced in the presence of wastewater effluent due to repulsive electrostatic interactions with the adsorbed DOM and the PAC surface. On the other hand, the removal of positively charged compounds was improved. A 24 h pre-equilibrium between OMPs and DOM improved their removal onto PAC, which suggest that OMPs and DOM interacted in solution which decreased the negative effects caused by the presence of DOM, e.g. through co-adsorption of an OMP-DOM complex.

Simultaneous quantification of humic acid-water and silanized glass-water partition constants for PCBs, PCDDs and OCDF

Super-hydrophobic organic contaminants (SHOCs) such as polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs) and octachlorodibenzofuran (OCDF) can sorb to dissolved hydrophobic materials including humic acids (HAs), enhancing their apparent aqueous solubility and potentially resulting in increased groundwater contamination and offsite transport. To manage risks associated with transport of and contamination by SHOCs, modelling approaches incorporating partitioning data, i.e. dissolved organic carbon-water partition constants (K_DOC), are necessary. Measurement of K_DOC can however be compromised by SHOC sorption to glassware surfaces leading to an overestimation of experimental values resulting in larger K_DOC. A method for simultaneous derivation of K_DOC and glass-water partition constants (K_GW) is described. It involves a mass balance approach combined with HA as a co-solvent at various concentrations and accounts for SHOC losses to silanized glassware. Measured log K_DOC values ranged from 5.28 to 7.64 for tetra- to decachlorinated PCBs, 6.67 to 7.93 for tetra- to octachlorinated PCDDs and 8.20 for OCDF. These data were linear functions of log K_OW and consistent with relationships reported for more polar compounds. Log K_GW (mm³ mm^-2) values (1.62 to 4.06 for PCBs, 2.96 to 3.90 for PCDDs, 3.77 for OCDF) were one order of magnitude greater compared to literature PCB borosilicate glass-water partition constants. Techniques such as those presented in this work present simple, versatile means to provide prediction of the SHOC proportion remaining in aqueous solutions after loss to glassware that was inversely related to container surface area/volume ratio and log K_OW in our study.

Fluorescence of Size-Fractioned Humic Substance Extracted from Sediment and Its Effect on the Sorption of Phenanthrene

Phenanthrene (Phe) is a toxin and is ubiquitous in the environment. The sediment humic substances (HS) that bind Phe affect the fate, transport, degradation, and ecotoxicology of Phe. This study investigated Phe sorption constants on size-fractioned HS extracted from river sediment. Fractions were identified as HHS (10 kDa to 0.45 μm), MHS (1-10 kDa), and LHS (<1 kDa). A fluorescence quenching (FQ) method was used to determine the Phe log K_HS on size-fractioned HS; the values ranged from 3.97 to 4.68 L/kg-C. The sorption constant (log K_HS) is a surrogate of the binding capacity between HS and Phe, where a high log K_HS reduces the toxicity and degradation of Phe. The log K_HS values on HHS and MHS were significantly higher than the values on LHS (p = 0.015). The SUVA₂₅₄ values of HHS and MHS were also significantly higher than the LHS value (p = 0.047), while fluorescence index (FI) and S_275-295 values were significantly lower than the LHS values (p < 0.005). The HHS and MHS had a higher aromaticity and more terrestrial sources than LHS. The log K_HS had a significant correlation with the selected optical indicators (p < 0.002), which suggested that the HS-bound Phe was positively affected by high aromaticity, terrestrial sources, and HS molecular weight. The results demonstrated that optical methods successfully obtained log K_HS and the chemical properties of fractioned HS as well as the influenced factors of log K_HS. Moreover, even the LHS had a capacity to bind with Phe.

Colonization of polycyclic aromatic hydrocarbon-degrading bacteria on roots reduces the risk of PAH contamination in vegetables

This is a primary investigation on the mitigation of polycyclic aromatic hydrocarbon (phenanthrene as a model PAH) contamination in vegetables including water spinach (Ipomoea aquatica Forsk), pakchoi (Brassica campestris) and Chinese cabbage (Brassica chinensis) using a gfp-labeled PAH-degrading bacterium (RS1-gfp). Effective root colonization led to dense RS1-gfp populations inhabiting the rhizosphere and endosphere of the vegetables, which subsequently led to a reduction in phenanthrene accumulation and risk in vegetables. When compared with the controls without RS1-gfp, the amount of phenanthrene accumulation due to strain RS1-gfp colonization reduced by up to ~93.7% in roots and ~75.2% in shoots of vegetables, respectively. The estimated incremental lifetime cancer risk (ILCR) for adults due to phenanthrene in vegetables was reduced by 24.6%-48% through RS1-gfp inoculation. The proposed method was developed to circumvent the risk of phenanthrene contamination in vegetables by inoculating PAH-degrading bacteria. The findings provide an in-depth understanding of PAH detoxification in agricultural plants grown on contaminated sites by exploiting bacteria like RS1-gfp, which portray both rhizo- and endophytic lifestyles.

Glomalin-related soil protein enhances the sorption of polycyclic aromatic hydrocarbons on cation-modified montmorillonite

This study investigated the sorption of phenanthrene (as a representative PAH) by cation-modified montmorillonites (Ca-MMT and Fe-MMT) under the influence of Glomalin-related soil protein (GRSP) fractions (EE-GRSP and T-GRSP). Batch sorption studies were carried out as a function of GRSP concentrations (0-500 mg/L), results suggested that the sorption capacities of Ca-MMT and Fe-MMT for phenanthrene were greatly enhanced. The phenanthrene sorption isotherms were in good agreement with the Linear and Freundlich models (R² = 0.886-0.999). The K_d values increased from 4.14 to 60.76 L/kg for Ca-MMT and from 15.57 to 153.80 L/kg for Fe-MMT with the GRSP concentrations adding from 0 to 500 mg/L, respectively. Furthermore, the sorption of phenanthrene was higher on Fe-MMT than that on Ca-MMT. It is believed that GRSP developed a higher sorption level on Fe-MMT, resulting in higher phenanthrene sorption. Microscopic and Spectroscopic analyses confirmed that the effects of GRSP on phenanthrene sorption were attributed to the changes in the surface structure and the hydrophobic property of montmorillonites. In the sorption process, GRSP may sorb onto montmorillonites through cation-π interaction when a bridge linkage was formed, and phenanthrene bound with GRSP mainly via π-π electron donor-accepter interaction. The findings could provide an in-depth understanding of the ecological functions of GRSP and provide new insights into the pathways of PAH transport and fate in the contaminated fields.

Partitioning of chemical contaminants to microplastics: Sorption mechanisms, environmental distribution and effects on toxicity and bioaccumulation

There is an increasing awareness of the threats posed by the worldwide presence of microplastics (MPs) in the environment. Due to their high persistence, MPs will accumulate in the environment and their quantities tend to increase with time. MPs end up in environments where often also chemical contaminants are present. Since the early 2000s, the number of studies on the sorption of chemicals to plastic particles has exponentially increased. The objective of this study was to critically review the literature to identify the most important factors affecting the sorption of chemical contaminants to MPs. These factors include the physicochemical properties of both the MPs and the chemical contaminants as well as environmental characteristics. A limited number of studies on soil together with an increased notion of the importance of this compartment as a final sink for MPs was observed. Therefore, we assessed the distribution of model chemicals (two PCBs and phenanthrene) in the soil compartment in the presence of MPs using a mass balance model. The results showed a high variation among chemicals and microplastic types. Overall, a higher partitioning to MPs of chemical contaminants in soil is expected in comparison to aquatic environments. As sorption to a large extent determines bioavailability, the effects of combined exposure to chemicals and MPs on the toxicity and bioaccumulation in biota are discussed. Finally, some considerations regarding sorption and toxicity studies using MPs are given.

A review of the predictive models estimating association of neutral and ionizable organic chemicals with dissolved organic carbon

Dissolved organic carbon (DOC) plays a key role in environmental transport, fate and bioavailability of organic chemicals in terrestrial and aquatic ecosystems. Predicting the association of contaminants to DOC is therefore crucial in modelling chemical exposure and risk assessment. The models proposed so far to describe interaction mechanisms between chemicals and DOC and the most influential variables have been reviewed. The single-parameter linear free energy relationships (sp-LFERs) and the poly-parameter linear free energy relationships (pp-LFERs) in the form of linear solvation energy relationships (LSERs) currently available in literature for estimating dissolved organic carbon/water partition (K_DOC) and distribution (D_DOC) coefficients for organic chemicals were discussed, and limits of the existing approaches explored. For neutral chemicals many predictive equations are currently available in literature, but the quality of the input data on which they are based is often questionable, due to the lack of an unequivocal definition of DOC among different references and to the different and often unreliable K_DOC measurement method. For ionizable chemicals instead there is a substantial lack of predictive approaches that need to be fulfilled since just few models are nowadays available to predict D_DOC of ionized species. This paper reviews the current approaches for neutral and ionizable chemicals proposing guidelines to select conditions for obtaining reliable data and predictive equations for an improved estimation of K_DOC and D_DOC.

Predicting dissolved organic carbon partition and distribution coefficients of neutral and ionizable organic chemicals

Estimating K_DOC (dissolved organic carbon/water partition coefficient) and D_DOC (dissolved organic carbon/water distribution coefficient) of neutral and ionizable organic chemicals is a crucial task for assessing mobility, modelling transport, environmental fate of a variety of chemicals and for evaluating their bioavailability in terrestrial and aquatic environments. A critical literature search of reliability-selected K_DOC and D_DOC values was performed to setup novel predictive relationships for K_DOC and D_DOC of neutral and ionizable organic chemicals. This goal was pursued by using: 1) LSER (linear solvation energy relationship) models to predict K_DOC for neutral chemicals using Abraham solute parameters calculated for different DOC sources (all DOC sources together, soil porewater, surface water, wastewater and Aldrich humic acid (HA)); 2) linear regressions for predicting D_DOC of organic acids from the octanol/water partition coefficient (Log K_OW or Log P) and the dissociation constant (pKa), accounting separately for the contribution of the neutral and ionic fraction. The proposed models predicted Log K_DOC and D_DOC values within a root mean square deviation (RMSD) generally smaller than 0.3 log units.

A critical review of the application of chelating agents to enable Fenton and Fenton-like reactions at high pH values

To overcome the drawback of low pH requirement of the classical Fenton reaction, researchers have applied chelating agents to form complexes with Fe and enable Fenton reaction at high pHs, which is reviewed in this article. The chelating agents reviewed include humic substances, polycarboxylates, aminopolycarboxylic acids, and polyoxometalates. Ligands affect the reactivity of Fe-complexes by changing their redox potentials, promoting their reaction with H₂O₂, and competing with target contaminants for the oxidative species. Fe(III)-complexes are reduced to Fe(II)-complexes by O₂^- not H₂O₂, as indicated by their redox potentials. The stability constants of Fe-complexes increase with increasing pK_a values of the corresponding ligands and also with increasing charge density of the metal ions. A higher stability constant of Fe(III)-complex indicates higher reaction rate of corresponding Fe(II)-complex with H₂O₂ and lower reduction rate of Fe(III)-complex to Fe(II)-complex. OH, O₂^-, and ferryl species were reported to be the reactive species on the contaminant removal in the chelate-modified Fenton process. The generation of these species depends on the chelating agents and reaction conditions. The process is very efficient in degrading contaminants, indicating a potential treatment approach for the pollution remediation at natural pH.

Influence of dissolved organic matter on sorption and desorption of MCPA in ferralsol

MCPA (4-chloro-2-methylphenoxyacetic acid) is an acidic herbicide, widely used in paddy fields. The presence of dissolved organic matter (DOM) modifies the sorption-desorption of herbicides in soils. In this study, effects of DOM on sorption- desorption of MCPA were tested using three typical ferralsol soil types from China: rhodic ferralsol, haplic ferralsol and paddy soil. DOM preparations were extracted from the paddy soil (DOM_P), from a compost mixture of cassava stems with chicken manure (DOM_C), and from rice straw (DOM_R). Sorption-desorption of MCPA in the tested soil types was shown to follow pseudo first-order kinetics, and the calculated isotherm data fitted well with a Freundlich equilibrium model in the range of the studied concentrations. MCPA was weakly sorbed by the soils, producing low Freundlich coefficient values (K_f) (0.854 to 4.237). The presence of DOM reduced the K_f whereby DOM_C had the strongest and DOM_R the weakest effect. Presence of DOM also promoted MCPA desorption from the soils, again with DOM_C having the strongest effect and DOM_R the weakest. DOM coating changed the soil particle surface, as demonstrated by electron microscopy, and DOM also directly interacted with MCPA, as shown by Fourier-transform infrared spectroscopy. The experimental data were interpreted to suggest a competing sorption of DOM to ferralsol and an increased solubility of MCPA in the presence of DOM. The results indicate that the environmental risk of MCPA leaching to groundwater and surface flow is increased by presence of DOM, for instance as a result of organic fertilizer use.

Effect of root exudates on sorption, desorption, and transport of phenanthrene in mangrove sediments

The effect of root exudates on the environmental behaviors of phenanthrene in mangrove sediments is poorly understood. In order to evaluate their influence, comprehensive laboratory experiments were performed using batch equilibrium and thin-layer chromatography (TLC) analyses. In the presence of root exudates, sorption of phenanthrene was inhibited, whereas desorption and mobility were promoted, and were elevated as root exudate concentrations increased. Among the three representative low molecular weight organic acids (LMWOAs) (citric, oxalic, and acetic acids), citric acid promoted desorption and mobility of phenanthrene more effectively than the other two. In addition, application of artificial root exudates (AREs) enhanced phenanthrene desorption, and mobility was always lower than that with the same concentration of LMWOAs, suggesting that LMWOAs predominantly affected the fate of phenanthrene in sediments. The results of this study could enhance our understanding of the mobility of persistent organic pollutants in sediment-water system.

Photochemical Transformation of Aminoglycoside Antibiotics in Simulated Natural Waters

Aminoglycoside antibiotics are widely used in human therapy and veterinary medicine. We report herein a detailed study on the natural-organic-matter- (NOM-) photosensitized degradation of aminoglycosides in aqueous media under simulated solar irradiation. It appears that the direct reaction of the excited states of NOM ((3)NOM*) with aminoglycosides is minor. The contributions of reactive oxygen species (ROSs) in the bulk solutions are also unimportant, as determined by an assessment based on steady-state concentrations and bimolecular reaction rate constants in a homogeneous reaction model. The inhibition of the photodegradation by isopropamide is rationalized through competitive sorption with aminoglycosides on the NOM surface, whereas the addition of isopropanol negligibly affects degradation because it quenches HO(•) in the bulk solution but not HO(•) localized on the NOM surface where aminoglycosides reside. Therefore, a sorption-enhanced phototransformation mechanism is proposed. The sorption of aminoglycosides on NOM follows a dual-mode model involving Langmuir and linear isotherms. The steady-state concentration of HO(•) on the surface of NOM was calculated as 10(-14) M, 2 orders of magnitude higher than that in the bulk solution. This fundamental information is important in the assessment of the fate and transport of aminoglycosides in aqueous environments.

Kinetics and thermodynamics of interaction between sulfonamide antibiotics and humic acids: Surface plasmon resonance and isothermal titration microcalorimetry analysis

The presence of sulfonamide antibiotics in the environments has been recognized as a crucial issue. Their migration and transformation in the environment is determined by natural organic matters that widely exist in natural water and soil. In this study, the kinetics and thermodynamics of interactions between humic acids (HA) and sulfamethazine (SMZ) were investigated by employing surface plasmon resonance (SPR) combined with isothermal titration microcalorimetry (ITC) technologies. Results show that SMZ could be effectively bound with HA. The binding strength could be enhanced by increasing ionic strength and decreasing temperature. High pH was not favorable for the interaction. Hydrogen bond and electrostatic interaction may play important roles in driving the binding process, with auxiliary contribution from hydrophobic interaction. The results implied that HA existed in the environment may have a significant influence on the migration and transformation of organic pollutants through the binding process.

Influences of binding to dissolved organic matter on hydrophobic organic compounds in a multi-contaminant system: Coefficients, mechanisms and ecological risks

The complexation flocculation (CF) method was successfully employed to identify binding coefficients (Kdoc) of specific organic contaminants to dissolved organic matter (DOM, often indicated by dissolved organic carbon, DOC) in a multi-contaminant hydrophobic organic contaminant (HOC) system. Kdoc values were obtained for most of the evaluated 33 HOCs, indicating the feasibility and applicability of the CF method in a multi-contaminant system. Significant positive correlations were observed between binding coefficients and octanol-water partition coefficients (Kow) for organic halogen compounds, such as polybrominated diphenyl ethers (PBDEs) (R(2) = 0.95, p < 0.05) and organic chlorine pesticides (OCPs) (methoxychlor excluded, R(2) = 0.82, p < 0.05). The positive correlations identified between the lgKdoc and lgBCF (bioconcentration factor) for PBDEs and OCPs, as well as the negative correlation observed for polycyclic aromatic hydrocarbons (PAHs), indicated that different binding or partition mechanisms between PAHs and organic halogen compounds exist. These differences further result in discriminative competition partitions of HOCs between DOM and organisms. Assuming that only freely dissolved HOCs are bioconcentrative, the results of DOM-influenced bioconcentration factor (BCFDOM) and DOM-influenced lowest observed effect level (LOELDOM) indicate that the ecological risk of HOCs is decreased by DOM.

Partitioning of the pesticide trifluralin between dissolved organic matter and water using automated SPME-GC/MS

Solid-phase microextraction (SPME) was used to determine the equilibrium association constant for a pesticide, trifluralin (TFR), with dissolved organic matter (DOM). After optimization of the SPME method for the analysis of TFR, partition coefficients (K DOM) with three different sources of DOM were determined in buffered solutions at pH 7. Commercial humic acids and DOM fractions isolated from two surface waters were used. The values of log K DOM varied from 4.3 to 5.8, depending on the nature of the organic material. A good correlation was established between log K DOM and DOM properties (as measured with the H/O atomic ratio and UV absorbance), in agreement with literature data. This is consistent with the effect of polarity and aromaticity for governing DOM-pollutant associations, regardless of the origin of DOM. This association phenomenon is relevant to better understand the behavior of pesticides in the environment since it controls part of pesticide leaching and fate in aquatic systems.

Low-molecular-weight organic acids influence the sorption of phenanthrene by different soil particle size fractions

The impact of low-molecular-weight organic acids (LMWOAs) on the sorption of phenanthrene (a representative polycyclic aromatic hydrocarbon) by different particle size fractions of a soil was investigated using a batch technique. Citric and malic acids were used in experiments. Four soil fractions were fractionated: fine sand, silt, coarse clay, and fine clay. Laser granulometry confirmed the suitability of the fractionation method used for the particle size distributions in this investigation. The sorption of phenanthrene by the different soil fractions was described well using a linear distribution-type model, and the distribution coefficients () followed a descending order of fine sand > fine clay > coarse clay > silt, irrespective of the addition of organic acids. This order was significantly positively correlated with the organic carbon content of test soil solids. The values for phenanthrene sorption by soil fractions initially increased but then decreased as the concentrations of citric and malic acids increased (0-1000 mmol L). The presence of citric and malic acid at lower concentrations (<100 mmol L) generally promoted the sorption of phenanthrene, while higher concentrations (>100 mmol L) inhibited sorption irrespective of the soil fraction. The mechanism of the LMWOA-influenced sorption of phenanthrene by test solids is discussed based on the observed sorption of organic acid, the dissolution of metal cations and minerals in soil, and the competition from dissolved organic matter in solution that were released from soil solids.

Quantifying the dynamic fluorescence quenching of phenanthrene and ofloxacin by dissolved humic acids

Fluorescence quenching includes dynamic and static quenching, and both processes can alter the behavior and reactivity of the fluorescer. However, dynamic quenching is seldom quantified. This study combined dialysis equilibrium and fluorescence quenching methods to compare the contribution of dynamic and static quenching. The results indicate that phenanthrene (PHE)-DHA binding increased with DHA hydrophobicity, while ofloxacin (OFL)-DHA interaction showed the opposite effect. For PHE,the contribution of dynamic quenching to the overall fluorescence quenching was in the range of 50%~82% and decreased to 11%~58% with increased DHA hydrophobicity. However, OFL dynamic quenching increased from 2%~27% to 31%~61% with DHA hydrophobicity. Combining the results using model chemicals, we concluded that the carboxyl groups in DHA might be the primary components for PHE dynamic quenching and might be responsible for both dynamic and static quenching of OFL. Extensive study is needed to explore the quantitative relationship of dynamic quenching and chemical/DHA properties.

Use of fluorescence quenching method to measure sorption constants of phenolic xenoestrogens onto humic fractions from sediment

Humic substance (HS) in sediment can affect hydrophobic organic compound distribution, transportation, bioavailability, and toxicity. This study investigated the HS (BKHS) extracted from sediment and separated it into low molecular humic (LMHS, <1kDa) and high molecular humic substances (HMHS, 1kDa-0.45μm). Nonylphenol (NP), octylphenol (OP), and bisphenol A (BPA) have a significant sorption capacity for HMHS and BKHS solutions. They are xenoestrogenic endocrine-disrupting compounds that are widely produced and discharged to the environment. The log KHS values of the BKHS and HMHS solutions were between 4.74-5.09Lkg-C(-1) and 4.57-5.09Lkg-C(-1), respectively. However, the three compounds were not sorbed by the LMHS solution. The average values of SUVA254 for HMHS and LMHS were 4.29 and 1.31Lm(-1)mg-C(-1) and the average values of A250-400 for HMHS and LMHS were 18.1 and 4.51nmcm(-1), respectively. The HMHS peak position in the fluorescence excitation/emission matrix at longer wavelengths corresponded to the peak position of LMHS, which indicates that the HMHS had a higher degree of humification than the LMHS. The results suggested that the KHS value's dominant factor was the degree of HS humification.

Evaluating the sorption of organophosphate esters to different sourced humic acids and its effects on the toxicity to Daphnia magna

Because of large usage as flame retardants and additives, organophosphate esters (OPEs) are widely detected in the environment and regarded as emerging contaminants. However, the sorption of OPEs to organic matter and its effects have scarcely been studied. In the present study, the sorption of 9 commonly used OPEs to 4 representative humic acids--Elliott Soil humic acid, Suwannee River humic acid, Aldrich humic acid, and Acros humic acid--in the range of 0 mg/L to 50 mg/L dissolved organic carbon (DOC), was evaluated with negligible-depletion solid-phase microextraction and verified by its impacts on the toxicity to the aquatic invertebrate Daphnia magna. Whereas OPEs with a high octanol/water partition coefficient (log K(OW)=4.51-6.64) were associated with humic acids mainly by hydrophobic interaction with DOC partition coefficient (K(DOC)) in the range of 10²·²² to 10⁵·³¹, the sorption of low-K(OW) OPEs (log K(OW)=-0.65 to 2.59) to humic acids was not hydrophobic interaction-dominant, with K(DOC) in the range of 10³·⁴⁷ to 10⁴·²⁹. These results were corroborated by the effects of humic acids on the acute toxicity of 3 high-K(OW) OPEs to D. magna. The sorption of OPEs to Suwannee River humic acid was weak and had negligible effects on the toxicity of high-K(OW) OPEs; the presence of terrestrial Acros humic acid (50 mg/L DOC), however, significantly decreased the toxicity by 53% to 60%. The results indicated that the strong sorption between high-K(OW) OPEs and terrestrial humic acid might affect their transportation and bioavailability.

Development of solid-phase microextraction to study dissolved organic matter--polycyclic aromatic hydrocarbon interactions in aquatic environment

Solid-phase microextraction coupled with gas chromatography and mass spectrometry (SPME-GC-MS) was developed for the study of interactions between polycyclic aromatic hydrocarbons (PAHs) and dissolved organic matter (DOM). After the determination of the best conditions of extraction, the tool was applied to spiked water to calculate the dissolved organic carbon water distribution coefficient (K(DOC)) in presence of different mixtures of PAHs and Aldrich humic acid. The use of deuterated naphthalene as internal standard for freely dissolved PAH quantification was shown to provide more accuracy than regular external calibration. For the first time, K(DOC) values of 18 PAHs were calculated using data from SPME-GC-MS and fluorescence quenching; they were in agreement with the results of previous studies. Competition between PAHs, deuterated PAHs and DOM was demonstrated, pointing out the non-linearity of PAH-DOM interactions and the stronger interactions of light molecular weight PAHs (higher K(DOC) values) in absence of high molecular weight PAHs.

Distribution coefficients of potentially toxic elements in soils from the eastern Amazon

The solid-solution distribution or partition coefficient (Kd) is a measure of affinity of potentially toxic elements (PTE) for soil colloids. Kd plays a key role in several models for defining PTE guideline values in soils and for assessing environmental risks, and its value depends on edaphic and climatic conditions of the sites where the soils occur. This study quantified Kd values for Cd, Co, Cr, Cu, Hg, Ni, Pb, and Zn from representative soil samples from Brazil's eastern Amazon region, which measures 1.2 million km(2). The Kd values obtained were lower than those set by both international and Brazilian environmental agencies and were correlated with the pH, Fe and Mn oxide content, and cationic exchange capacity of the soils. The following order of decreasing affinity was observed: Pb>Cu>Hg>Cr>Cd≈Co>Ni>Zn.

Solubility and leaching risks of organic carbon in paddy soils as affected by irrigation managements

Influence of nonflooding controlled irrigation (NFI) on solubility and leaching risk of soil organic carbon (SOC) were investigated. Compared with flooding irrigation (FI) paddies, soil water extractable organic carbon (WEOC) and dissolved organic carbon (DOC) in NFI paddies increased in surface soil but decreased in deep soil. The DOC leaching loss in NFI field was 63.3 kg C ha⁻¹, reduced by 46.4% than in the FI fields. It indicated that multi-wet-dry cycles in NFI paddies enhanced the decomposition of SOC in surface soils, and less carbon moved downward to deep soils due to less percolation. That also led to lower SOC in surface soils in NFI paddies than in FI paddies, which implied that more carbon was released into the atmosphere from the surface soil in NFI paddies. Change of solubility of SOC in NFI paddies might lead to potential change in soil fertility and sustainability, greenhouse gas emission, and bioavailability of trace metals or organic pollutants.

Ca2+ promoted the low transformation efficiency of plasmid DNA exposed to PAH contaminants

The effects of interactions between genetic materials and polycyclic aromatic hydrocarbons (PAHs) on gene expression in the extracellular environment remain to be elucidated and little information is currently available on the effect of ionic strength on the transformation of plasmid DNA exposed to PAHs. Phenanthrene and pyrene were used as representative PAHs to evaluate the transformation of plasmid DNA after PAH exposure and to determine the role of Ca²⁺ during the transformation. Plasmid DNA exposed to the test PAHs demonstrated low transformation efficiency. In the absence of PAHs, the transformation efficiency was 4.7 log units; however, the efficiency decreased to 3.72–3.14 log units with phenanthrene/pyrene exposures of 50 µg·L^–1. The addition of Ca²⁺ enhanced the low transformation efficiency of DNA exposed to PAHs. Based on the co-sorption of Ca²⁺ and phenanthrene/pyrene by DNA, we employed Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and mass spectrometry (MS) to determine the mechanisms involved in PAH-induced DNA transformation. The observed low transformation efficiency of DNA exposed to either phenanthrene or pyrene can be attributed to a broken hydrogen bond in the double helix caused by planar PAHs. Added Ca²⁺ formed strong electrovalent bonds with “–POO^––” groups in the DNA, weakening the interaction between PAHs and DNA based on weak molecular forces. This decreased the damage of PAHs to hydrogen bonds in double-stranded DNA by isolating DNA molecules from PAHs and consequently enhanced the transformation efficiency of DNA exposed to PAH contaminants. The findings provide insight into the effects of anthropogenic trace PAHs on DNA transfer in natural environments.

Binding interactions of 1-naphthol with dissolved organic matter of Lake Biwa and treated sewage wastewater: The role of microbial fulvic acid

The binding interactions of 1-naphthol with effluent and whole natural dissolved organic matter (DOM) samples were analyzed by using a fluorescence quenching technique. Nonfractionated DOM samples from Lake Biwa (Japan), creek water, treated sewage effluents, and an extracted Lake Biwa fulvic acid (LBFA) standard were used as quenchers and compared at the same 1-naphthol with DOM organic carbon ratios found for low natural dissolved organic carbon (DOC) levels (∼4.5 mg/L). Natural and effluent DOM (eDOM) samples were characterized by the DOC level, relative hydrophobicity (RH%), ultraviolet (UV)-visible absorbance and fluorescence excitation emission spectroscopy. These parameters were compared with those of the reference LBFA standard. Concave-up Stern-Volmer plots accounted for both the partitioning and the adsorptive binding in the eDOM-polycyclic aromatic hydrocarbons (PAH) system as compared with the nonspecific partitioning in the natural DOM-PAH system. Strong linear regressions (r(2)  > 0.80) between the log K(DOC) values, the RH%, the UV absorbances, and the Fl(340-435) -UV(340) indices for the structural composition and molecular weights of the DOM samples were obtained. These results suggest that low molecular weight microbial fulvic acid (<800 Da) is dominant in the eDOM-PAH binding interactions, as well as in the distinct molecular structure of the eDOM samples, which resulted in fivefold to sixfold higher binding magnitude for 1-naphthol than for the other samples.

Release of pentachlorophenol from black carbon-inclusive sediments under different environmental conditions

To investigate the feasibility of using black carbon (BC) in the control of hydrophobic organic contaminants (HOCs) in sediment, we added BCs from various sources (rice straw charcoal (RC), fly ash (FC) and soot (SC)) to sediment to create different BC-inclusive sediments and studied the release of pentachlorophenol (PCP) in the sediments under different condition. Different pH values had no obvious effect on the release of PCP in BC-inclusive sediment, but solid/liquid ratio, temperature, salinity and dissolved organic matter (DOM) content had significant influences on the release of PCP in all sediments except the RC-inclusive sediment. Adding 2% RC to sediment resulted in a 90% decrease in PCP release, which was a greater decrease than observed with FC- and SC-inclusive sediments. Therefore, from the standpoint of HOC release, the application of RC is feasible for organic pollution control in the water environment.

Kinetics of polychlorinated biphenyl partitioning to marine Chrysophyte Isochrysis galbana

This study focused on the uptake kinetics of polychlorinated biphenyl (PCB) congeners by the Chrysophyte, Isochrysis galbana. A gas-purging experimental system was used to maintain constant dissolved PCB concentrations. Three phases of absorption were observed: first, a rapid absorption phase within the first 15min, second, a first order process reaching the maximum concentration within 48h of exposure, and third, a plateau phase as yet to be determined with very slight increases in concentration. In this study, the percentage of the maximum concentration reached within the first phase varied from 10% to 67%, depending on the size of the PCB (as determined by molecular weight and total surface area), whereas the uptake rate (k(u)) during the second phase was more comparable across different PCBs. In addition, for the first phase, the bioconcentration factor (BCF) of PCBs deviated from its expected relationship with hydrophobicity, as determined by K(ow), and was instead related to the molecular structure of the compound.

Sorption to dissolved humic acid and its impacts on the toxicity of imidazolium based ionic liquids

Two typical ionic liquids (ILs), 1-butyl-3-methylimidazolium chloride ([C4MIM]Cl) and 1-octyl-3-methylimidazolium chloride ([C8MIM]Cl), are demonstrated to associate strongly with dissolved organic matter (DOM) with distribution coefficients (KDOC) in the range of 10(4.2) to 10(4.6) for Aldrich humic acid (used as model DOM). With the increase of humic acid concentration to 11 μg/mL DOC (dissolved organic carbon), the free fraction (ratio of freely dissolved to total concentration) of [C4MIM]Cl and [C8MIM]Cl reduced to about 0.85 and 0.79, respectively. This reduction of freely dissolved concentration gave rise to remarkable reduction of bioavailability and toxicity of the two ILs. MTT assay with HepG2 cell lines showed that the EC50 values were 459 μmol/L for [C4MIM]Cl and 12 μmol/L for [C8MIM]Cl, respectively, and the cell viability increased about 50% in the presence of trace amount of humic acid (1 μg/mL DOC). The SOS/umu test indicated mutagenicity for [C4MIM]Cl at levels above 664 μmol/L, and the genotoxicity was diminished with the addition of trace humic acid (0.00000374-0.374 μg/mL DOC). The studied ILs showed acute toxicity toward model fish medaka with a 96 h median lethal concentration (LC50) of 2254 μmol/L for [C4MIM]Cl and 366 μmol/L for [C8MIM]Cl. The addition of humic acid (5.49 μg/mL DOC for [C8MIM]Cl, 1.37 μg/mL DOC for [C4MIM]Cl) to IL solutions reduced the death rate of medaka to a minimum value of ∼25% of that at zero DOC. Our results suggest that DOM may play an important role in determining the environmental fate and toxicity of imidazolium-based ILs, and its effects should be taken into account in assessing the environmental risk of ILs.

Binding characteristics of perylene, phenanthrene and anthracene to different DOM fractions from lake water

Six hydrophobic and hydrophilic fractions were isolated using XAD-8 and XAD-4 resins, and were extensively characterized. Partition coefficients of perylene, phenanthrene and anthracene binding to the six fractions were determined by fluorescence quenching titration. The Kdoc values obtained for the polycyclic aromatic hydrocarbons (PAHs) binding to the hydrophobic fractions were larger than those to the hydrophilic fractions. Nonlinear Stern-Volmer plots were observed when binding phenanthrene and anthracene to some hydrophilic fraction samples, suggesting saturation of polar interaction binding sites. A significant correlation of logKdoc values with molecular weights and molar absorptivities at 280 nm was observed, while atomic ratio of C/H was found to be a poor indicator for aromaticity. Other structural descriptors such as paraffinic carbon and polarity influenced the DOM-fraction ability to bind PAHs. Different interaction mechanisms underlying binding of the different fractions to the PAHs were also discussed.

Interaction of the macrolide antimicrobial clarithromycin with dissolved humic acid

The association of the cationic macrolide antimicrobial clarithromycin (CLA) with dissolved Elliot soil humic acid (ESHA) was investigated as a function of solution chemistry. CLA-ESHA association was strongly pH-dependent, reaching a maximum near pH 6.5, and was modeled successfully using FITEQL as a 1:1 complexation reaction between CLA+ and discreet deprotonated acidic functional groups with pKa values of 4 and 6. Approximate order of magnitude increases in ionic strength produced approximately 10-fold decreases in CLA+ -ESHA association. Coefficients for CLA+ -ESHA association were significantly smaller in the presence of K+ vs Na+. Sorption data were well-fit by the Freundlich model; the Freundlich exponent was <1, suggesting CLA+ interacted with sites having a range of binding energies. Sorption appeared largely reversible; little sorption-desorption hysteresis was observed. The affinities of erythromycin and CLA+ for ESHA association sites were indistinguishable, suggesting interaction with specific sorption sites. Comparison of experimentally determined CLA-ESHA association coefficients with those predicted from single-parameter linear free energy relationships based on log Kow suggested limited contribution of hydrophobic interactions to CLA-ESHA association at environmentally relevant pH values. CLA-ESHA association constants were similar in magnitude (10(3.9)-10(4.6) to those of many nonpolar organic contaminants, and macroscopic binding data were consistent with cation exchange dominating CLA+ -ESHA association.

Accurate quantification of freely dissolved organochlorine pesticides in water in the presence of dissolved organic matter using triolein-embedded cellulose acetate membrane

A novel method is described using triolein-embedded cellulose acetate membrane (TECAM) for accurate determination of the freely dissolved fraction of organochlorine pesticides (OCPs) in waters rich in dissolved organic matter (DOM). The performance of the method was tested with an air-bridge system for extracting OCPs from aqueous solutions with and without humic acid. In addition, the partition coefficients between humic acid and water (K (doc)s) for 20 OCPs were determined by TECAM with negligible depletion extraction. Results show that TECAM predominantly extracts the freely dissolved compounds and its extraction efficiency decreases significantly with an increase in concentration of humic acid in water. The proposed methodology is suitable for facile laboratory K (doc) measurement for moderate to high hydrophobic compounds (log K (ow) > 4). The linear relationship between log K (ow) and log K (doc) obtained in this study agrees well with the results reported earlier. The kinetic uptake rate constants (k (u)s) and TECAM-water partition coefficients (K (TECAM)s) for the 20 OCPs were obtained using the controlled laboratory continuous-flow and static exposure system, respectively. These calibration parameters were used in the field experiment to estimate the freely dissolved concentrations of OCPs in the water of Taihu Lake in China. Our results show that TECAM can be used successfully to determine the freely dissolved OCPs in aquatic environments containing DOM, and the method is particularly suited for long-term water sampling. Figure Schematic diagram of water sampling with a triolein-embedded cellulose acetate membrane (TECAM).

Impact of exotic and inherent dissolved organic matter on sorption of phenanthrene by soils

The impacts of exotic and inherent dissolved organic matter (DOM) on phenanthrene sorption by six zonal soils of China, chosen so as to have different soil organic carbon (SOC) contents, were investigated using a batch technique. The exotic DOM was extracted from straw waste. In all cases, the sorption of phenanthrene by soils could be well described by the linear equation. The presence of inherent DOM in soils was found to impede phenanthrene sorption, since the apparent distribution coefficients (K(d)(*)) for phenanthrene sorption by deionized water-eluted soils were 3.13-21.5% larger than the distribution coefficients (K(d)) by control soils. Moreover, the enhanced sorption of phenanthrene by eluted versus control soils was in positive correlation with SOC contents. On the other hand, it was observed that the influence of exotic DOM on phenanthrene sorption was related to DOM concentrations. The K(d)(*) values for sorption of phenanthrene in the presence of exotic DOM increased first and decreased thereafter with increasing the added DOM concentrations (0-106mgDOC/L). The K(d)(*) values at a low exotic DOM concentration (< or =28mgDOC/L) were 14.7-48.4% larger than their control K(d) values. In contrast, higher concentrations (> or =52mgDOC/L) of added exotic DOM clearly impeded the distribution of phenanthrene between soil and water. The effects of exotic and inherent DOM on phenanthrene sorption by soils may primarily be described as 'cumulative sorption', association of phenanthene with DOM in solution, and modified surface nature of soil solids due to DOM binding.

Partitioning of selected environmental pollutants into organic matter as determined by solid-phase microextraction

Partitioning/sorption of selected environmental pollutants (PCBs, organochlorine insecticides, triazine and amide herbicides) into dissolved humic acids (HA), soil and mineral substances was evaluated by measuring their free concentrations by solid-phase microextraction (SPME). Compounds were chosen to cover a wide range of logK(ow) (2.2-7.6). Two different types of partitioning behaviour for dissolved HA were observed. Compounds with logK(ow)>5 partitioned almost instantly into HA fraction and the remaining free fraction remained rather constant. LogK(HA) and logK(DOC) were calculated and found to be similar for commercial HA, HA standard and isolated HA. The behaviour of these compounds in soil suspension was similar, but strong sorption on CaCO3 and Florisil was also noticed. For compounds with logK(ow)<5, we have not noticed significant changes in free concentrations in HA solutions over time. In soil suspension, however, some sorption/partitioning was observed over time for some compounds, but it was matching the sorption on CaCO3 and Florisil.

Sorption of phenanthrene by soils contaminated with heavy metals

The fate of polycyclic aromatic hydrocarbons (PAHs) in soils with co-contaminants of heavy metals has yet to be elucidated. This study examined sorption of phenanthrene as a representative of PAHs by three soils contaminated with Pb, Zn or Cu. Phenanthrene sorption was clearly higher after the addition of heavy metals. The distribution coefficient (K(d)) and the organic carbon-normalized distribution coefficient (K(oc)) for phenanthrene sorption by soils spiked with Pb, Zn or Cu (0-1000 mg kg(-1)) were approximately 24% larger than those by unspiked ones, and the higher contents of heavy metals added into soils resulted in the larger K(d) and K(oc) values. The enhanced sorption of phenanthrene in the case of heavy metal-contaminated soils could be ascribed to the decreased dissolved organic matter (DOM) in solution and increased soil organic matter (SOM) as a consequence of DOM sorption onto soil solids. Concentrations of DOM in equilibrium solution for phenanthrene sorption were lower in the case of the heavy metal-spiked than unspiked soils. However, the decreased DOM in solution contributed little to the enhanced sorption of phenanthrene in the presence of metals. On the other hand, the sorbed DOM on soil solids after the addition of heavy metals in soils was found to be much more reactive and have far stronger capacity of phenanthrene uptake than the inherent SOM. The distribution coefficients of phenanthrene between water and the sorbed DOM on soil solids (K(ph/soc)) were about 2-3 magnitude larger than K(d) between water and inherent SOM, which may be the dominant mechanism of the enhanced sorption of phenanthrene by soils with the addition of heavy metals.

Effects of dissolved organic matter from sewage sludge on the atrazine sorption by soils

The effects of dissolved organic matter (DOM), water soluble organic matter derived from sewage sludge, on the sorption of atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-trazine) by soils were studied using a batch equilibrium technique. Six paddy soils, chosen so as to have different organic carbon contents, were experimented in this investigation. Atrazine sorption isotherms on soils were described by the linear equation, and the distribution coefficients without DOM (Kd) or with DOM (Kd*) were obtained. Generally, the values of Kd*/Kd initially increased and decreased thereafter with increasing DOM concentrations of 0-60 mg DOC x L(-1) in soil-solution system form. Critical concentrations of DOM (DOM(np)) were obtained where the value of Kd* was equal to Kd. The presence of DOM with concentrations lower than DOM(np) promoted atrazine sorption on soils (Kd* > Kd), whereas the presence of DOM with concentrations higher than DOM(np) tended to inhibit atrazine sorption (Kd* < Kd). Interestingly, DOM(np) for tested soils was negatively correlated to the soil organic carbon content, and the maximum of Kd*/Kd (i.e. Kmax) correlated positively with the maximum of DOM sorption on soil (Xmax). Further investigations showed that the presence of hydrophobic fraction of DOM evidently promoted the atrazine sorption on soils, whereas the presence of hydrophilic DOM fraction obviously tended to inhibit the atrazine sorption. Interactions of soil surfaces with DOM and its fractions were suggested to be the major processes determining atrazine sorption on soils. The results of this work provide a reference to the agricultural use of organic amendment such as sewage sludge for improving the availability of atrazine in soils.