Bioavailability of atrazine, pyrene and benzo[a]pyrene in European river waters.

Thirteen river waters and one humic lake water were characterized. The effects of dissolved organic matter (DOM) on the bioavailability of atrazine, pyrene and benzo[a]pyrene (B[a]P) was evaluated. Binding of the chemicals by DOM was analyzed with the equilibrium dialysis technique. For each of the water samples, 24 h bioconcentration factors (BCFs) of the chemicals were measured in Daphnia magna. The relationship between DOM and other water characteristics (including conductivity, water hardness and pH), and bioavailability of the chemicals was studied by performing several statistical analyses, including multiple regression analyses, to determine how much of the variation of BCF values could be explained by the quantity and quality of DOM. The bioavailability of atrazine was not affected by DOM or any other water characteristics. Although equilibrium dialysis showed binding of pyrene to DOM, the bioavailability of pyrene was not significantly affected by DOM. The bioavailability of B[a]P was significantly affected by both the quality and quantity of DOM. Multiple regression analyses, using the quality (ABS270 and HbA%) and quantity of DOM as variables, explained up to 70% of the variation in BCF of B[a]P in the waters studied.     

Effects of photodegradation of dissolved organic matter on the binding of benzo(a)pyrene

Dissolved organic matter (DOM) in natural waters can bind various organic pollutants, and the affinity of this binding is strongly influenced by the chemical characteristics of the DOM and water pH. This study examined the effects of photochemically induced alteration of the DOM's chemical properties and water pH on the binding of benzo(a)pyrene (BaP). Time- and pH-series of solar-simulated irradiations were performed on a natural water sample and aqueous DOM solutions prepared from aquatic and soil humic substances. The binding affinity of BaP, expressed as a partition coefficient of a compound to DOM, decreased substantially after the DOM samples were irradiated over environmentally relevant radiation doses and pH ranges. The lowering of the pH due to the photoproduction of acidic products often partly offsets the reduction of the binding affinity caused by direct photoalteration of the DOM's chemical structure. The decrease of the binding affinity, after correction for the photoinduced pH change, was positively correlated with the decrease in the molecular weight and the aromaticity of the DOM in the course of irradiation. Increasing O(2) abundance accelerated the decrease of the binding affinity as a result of enhanced DOM photodegradation. Visible light played a more important role in reducing the molecular weight and aromaticity of the DOM than in reducing the content of dissolved organic carbon (DOC) via photoremineralization while the reverse was true for UV radiation, indicating that photochemical reduction of the binding affinity may occur in natural waters at depths greater than UV radiation can reach. A decrease of the affinity of DOM for binding BaP will increase the free dissolved fraction of BaP and thus its availability and toxicity to aquatic organisms. The results from this study may have similar implications for organic pollutants other than BaP.     

Negative effects of humic acid addition on phytoremediation of pyrene-contaminated sediments by mangrove seedlings

Vegetated (with Kandelia candel seedlings) and non-vegetated mangrove microcosms were employed to remove pyrene from contaminated sediments, and the effects of adding 6.7% humic acid (HA) on such removal were investigated. At the end of 6-month treatment, residual pyrene concentrations in surface sediments (0-2 cm) of the contaminated microcosms reduced from an initial 5.82 to 0.63 microg g(-1) dw, and the reduction was less in HA amended microcosms with the residual pyrene concentration remained at 3.12 microg g(-1) dw. The pyrene removal percentages in microcosms with HA amendment were 29% for surface aerobic sediments and 41% for bottom (anaerobic) sediments, while the respective removal percentages in microcosms without HA amendment were 89% (surface sediments) and 53% (bottom sediments). Microcosms planted with K. candel seedlings had a significantly higher pyrene removal when compared to the non-vegetated ones, and the average removal percentages were 70.9% and 61.4%, respectively. However, when humic acid was added, no significant difference was found between vegetated and non-vegetated microcosms in pyrene removal, both had less than 40% removal, probably because plant growth in humic acid amended contaminated microcosms, in terms of total biomass, was reduced by 50%. Roots of K. candel could accumulate pyrene from contaminated microcosms, and pyrene concentrations in roots harvested from microcosms with and without humic acid addition were 6.01 and 3.46 microg g(-1) dw, respectively. These results suggest that the addition of HA to contaminated sediments decreased the mangrove microcosm's ability to remove pyrene as pyrene was more tightly bound to the organic matter and plant growth was reduced.     

Combined effect of nonionic surfactant Tween 80 and DOM on the behaviors of PAHs in soil--water system

Batch experiments were performed to examine the desorption behavior of phenanthrene and pyrene in soil–water system in the presence of nonionic surfactant Tween 80 and dissolved organic matter (DOM) derived from pig manure or pig manure compost. Addition of 150 mg l⁻¹ Tween 80 desorbed 5.8% and 2.1% of phenanthrene and pyrene from soil into aqueous phase, respectively, while the addition of both Tween 80 and DOM derived from pig manure compost and pig manure could further enhance the desorption of phenanthrene to 15.8% and 16.2%, respectively, and 6.4% and 10.9%, respectively, for pyrene. In addition, our finding also suggested that subsequent addition of Tween 80 into the soil–water system could further enhance PAHs desorption. The enhancement effect of the co-existence of Tween 80 and DOM was more than the additive effect of the Tween 80 and DOM individually. It is likely that the formation of DOM–surfactant complex in the soil–water system may be a possible reason to explain such desorption enhancement phenomenon. Therefore, it is anticipated that the coexistence of both Tween 80 and DOM derived from pig manure or pig manure compost in soil environment will enhance the bioavailability of PAHs as well as other hydrophobic organic contaminants (HOCs) by enhancing the desorption during remediation process.     

Sulfamethoxazole sorption by sediment fractions in comparison to pyrene and bisphenol A

The environmental behavior of antibiotics has attracted great research attention. However, their sorption mechanisms in soils/sediments are still unknown. Comparison of the sorption properties between the widely-studied hydrophobic organic contaminants (HOCs) and antibiotics may provide valuable insight to antibiotic sorption mechanisms. Thus, in this study batch experiments for pyrene (PYR), bisphenol A (BPA), and sulfamethoxazole (SMX) sorption were conducted on a sediment sample and its separated fractions. Our results showed the high sorption of PYR on black carbon and organic matter. Although high sorption of SMX was observed for both separated organic fractions (humic acids) and inorganic mineral particles, the original sediment particles showed relatively low sorption. Competitive sorption between SMX and dissolved humic acid on mineral particles was observed in this study. This competitive interaction is a unique process for antibiotic sorption in soils/sediments compared with apolar HOCs and may be one of the important factors controlling the antibiotic sorption.     

Microbial degradation of dissolved organic matter (DOM) and its influence on phenanthrene-DOM interactions

Microbial degradation-induced changes in the characteristics of dissolved organic matter (DOM), and the subsequent effects on phenanthrene-DOM interactions were investigated based on the microbial incubation of DOM collected from four different sources for 28 d. Partially biodegraded DOM presented higher specific UV absorbance (SUVA), lower protein-like fluorescence, higher humic-like fluorescence, lower aliphatic carbon fraction, and higher hydrophobic neutral fractions compared to the original DOM. Microbial changes in DOM led to an increase in the isotherm nonlinearity as well as the extent of phenanthrene binding. A negative relationship between SUVA and the Freundlich n values was established for the original and the biodegraded DOM, suggesting that aromatic condensed structures may play important roles in providing nonlinear strong binding sites irrespective of microbial degradation. In contrast, there were two separate slopes of the correlations between the percentage of hydrophobic acid (HoA) fraction and the n values for the original and the biodegraded DOM with a higher slope exhibited for the latter, implying that the microbial utilization of oxygen-containing structures in the HoA fractions may contribute to enhancing the associated isotherm nonlinearity.     

Responses of kinetics and capacity of phenanthrene sorption on sediments to soil organic matter releasing

Soil organic matter (SOM) releasing with dissolved organic matter (DOM) formed in solution was confirmed in a sediment/water system, and the effects of SOM releasing on the sorption of phenanthrene on sediments were investigated. Inorganic salt (0–0.1 mol L^?1 NaCl) was used to adjust SOM releasing, and two sediments were prepared, the raw sediment (S1) from Weihe River, Shann’xi, China, and the eluted sediments with and without DOM supernatant remained, termed as S2a and S2b, respectively. The FTIR and ¹H NMR analysis indicate that the low molecular weight hydrophilic SOM fraction released prior to the high molecular weight hydrophobic fraction. As a response, phenanthrene sorption kinetics on S1 showed atypical and expressed as three stages: rapid sorption, pseudo sorption with partial desorption, and slow sorption, thus a defined “sorption valley” occurred in kinetic curve. In all cases, partition dominates the sorption, and sorption capacity (K_d) ranked as S2b > S1 > S2a. Compared with the alterations of sediment characters, DOM solubilization produced by SOM releasing exhibited a greater inhibitory effect on sorption with a relative contribution of 0.67. Distribution coefficients (K_doc) of PHE into DOM clusters were 2.10?×?10⁴–4.18?×?10⁴ L kg^?1, however a threshold concentration of 6.83 mg L^?1 existed in DOM solubilization. The study results will help to clarify PAHs transport and their biological fate in a sediment/water system.     

Evaluating spectroscopic and chromatographic techniques to resolve dissolved organic matter via end member mixing analysis

Real-time or near real-time in-situ monitoring of dissolved organic matter (DOM) composition in natural waters and engineered treatment systems provides critical information to water quality scientists and engineers, particularly when the monitoring techniques can provide some information about the chemical nature of DOM. The efficacy of various indices derived from rapid, low-cost spectroscopic and chromatographic techniques to discriminate DOM composition was tested for samples prepared from well-defined mixtures of purified Aldrich humic acid (PAHA) and Suwannee River fulvic acid (SRFA). Sensitivities of the discrimination indices were examined by comparing (1) the differences between measured values and those predicted based from mass balance and the end member characteristics, and (2) the linear correlations between index values and mass ratios of the DOM mixtures. Size exclusion chromatography (SEC) results revealed that the weight-average molecular weight (MW(w)) may be a useful approach for tracking DOM mixing processes, although the number-average molecular weight (MW(n)) may be better for distinguishing different DOM compositions. Specific ultraviolet absorbance measured at 254 nm (SUVA(254)) performed better as a discrimination index than did two previously recommended absorbance ratios, both in terms of making better predictions of intermediate compositions and in exhibiting a more linear correlation with PAHA mass ratio. Several well-defined peaks in the derivative absorption spectra (301 and 314 nm for the first derivative, 217 nm for the third derivative, and 211 and 224 nm for the fourth derivative) also were found to be promising potential DOM discrimination indices. Finally, a fluorescence ratio based on humic- versus fulvic-like fluorescence proved to be a superior DOM discrimination index for the two DOM end members studied here. In general, this study illustrates the evaluation process that should be followed to develop rapid, low-cost discrimination indices to monitor DOM compositions based on end member mixing analyses.     

Reverse quantitative structure-activity relationship for modelling the sorption of esfenvalerate to dissolved organic matter. A multivariate approach

The sorption of the pyrethroid, esfenvalerate, to the dissolved and/or dispersed fraction of eight different natural humic compounds has been investigated. The dissolved organic matters (DOMs) included in this study originate from ground water, soil pore water, and surface waters. Sorption was modelled at DOM concentration levels where equilibrium partitioning of esfenvalerate between DOM and the aqueous bulk phase prevails. The inherent characteristics of the eight different humic materials, quantified in the preceding paper by Thomsen et al. (2002, this issue (PII: S0045-6535(02)00335-1)), have been used as explanatory variables for modelling this equilibrium partitioning. Using a reverse QSAR approach based on by projection-into-latent-structure regression (PLS-R) inherent sorbent properties determining for the sorption affinity of esfenvalerate to DOM were analysed. For all humic substances a decrease in the DOM-normalised equilibrium-partitioning coefficient, K_DOM, with increasing concentration of DOM was observed. Significant variations in K_DOM values, as function of the inherent characteristics of the individual humic substances, were found at DOM concentrations of 75 and 100 ppm, respectively. The latter is a strong indication of variations in sorption mechanisms of esfenvalerate to DOM of varying inherent properties. Groupings in the principal property space quantifying DOMs may indicate that separate models are needed for quantifying the equilibrium partitioning to different classes of DOM.     

Association of benzo(a)pyrene with dissolved organic matter: Prediction of Kdom from structural and chemical properties of the organic matter

The affinity of dissolved organic matter (DOM) for binding a polycyclic aromatic hydrocarbon, benzo(a)pyrene (BaP), was measured for 11 surface and ground waters and a commercial humic acid. The hydrophobic-acid (HbA) and hydrophobic-neutral (HbN) compositions of the DOM, solution absorptivity at 270nm (ABS₂₇₀), and DOM molar volumes were determined. Waters enriched in HbA material had a larger molar volume and higher aromatic content (as indicated by the ABS₂₇₀). There was a good correlation between the size and HbA content of the DOM from the different sources and the K_dom for binding BaP. An excellent predictive relationship (r² = 0.9) was demonstrated between the ABS₂₇₀ of a water and the K_dom for binding BaP. Based on these results, it is suggested that binding of BaP to DOM depends not only on the hydrophobicity of DOM, but also on the existence of an open structure within the DOM to provide access of the aqueous solute to hydrophobic domains within the DOM.     

Evaluating the impacts of some environmentally relevant factors on the availability of bisphenol A with negligible-depletion SPME

The effect of some environmentally relevant factors including salinity, pH, and humic acids on the availability of bisphenol A (BPA) was evaluated by using the negligible-depletion solid-phase microextraction (nd-SPME) biomimetic method. With the variation of salinity (0–500 mM NaCl) and pH (5.0–8.5) of aqueous solutions, the partition coefficients of BPA between the nd-SPME fiber and the aqueous solution varied in the range of log D = 3.55–3.86, which indicates that the salinity and pH can influence the availability of BPA. By using Acros humic acid as model dissolved organic matter (DOM), it was also demonstrated that the environmental factors such as salinity and pH could affect the partitioning of BPA between DOM and aqueous solutions. The determined partition coefficients of BPA between dissolved organic carbon (DOC) and aqueous solutions were in the range of log D_DOC = 4.03–5.60 for Acros humic acid solutions with 1–50 mg l⁻¹ DOC. The influence of salinity and pH on log D_DOC was more significant at low concentration (0–5 mg l⁻¹) of DOC.     

乌梁素海沉积物孔隙水中溶解有机质的荧光及紫外光谱研究

运用紫外可见光吸收光谱与荧光光谱研究乌梁素海沉积物孔隙水中溶解有机质的来源、结构及腐殖化程度。r_(A,C)、HIX、SUVA₂₈₀和SUVA₂₅₄等被用于表征DOM的腐殖化程度和芳香构化程度及结构,f_450/500用于指示DOM的来源。研究结果表明：腐殖化程度最高的点为湖泊东部的W4样点,腐殖化程度最低的为总排干影响区域的W1样点。E_253/203表明湖泊入口处沉积物孔隙水中有机质主要为不可取代的芳香环结构。荧光指数f_450/500为1.57～1.82之间。总体而言,f_450/500的值更接近于1.6,处于2个端源中间,说明乌梁素海DOM中的腐殖质主要来源于陆源输入。相关分析的结果表明, DOM的不同来源对其腐殖化程度产生影响。随着腐殖化值的增大,DOM的来源由生物源向陆源过渡。     

An experimental design to probe the interactions of dissolved organic matter and xenobiotics: bioavailability of pyrene and 2,2',5,5'-tetrachlorobiphenyl to Daphnia magna

Experiments were conducted to probe the interactions between natural dissolved organic matter (DOM) and two xenobiotics, and to determine how DOM influences their bioavailability. The experimental set-up, using dialysis bags, was designed to expose test organisms to the same constant concentration of free dissolved chemical, while increasing the concentration of the bound-to-DOM fraction. Daphnia magna S. were exposed to pyrene or 2,2',5,5'-tetrachlorobiphenyl in the presence of 0, 1, 2, 5, 10 or 20 mg L(-1) of a reference riverine humic acid (Suwannee River Humic Acid). The physico-chemical parameters were well constrained in the microcosm, demonstrating its potential usefulness. However bioaccumulation by D. magna showed important variability between replicate treatments, sufficient to mask any trends as a function of DOM concentration. The organic-carbon-normalised partition coefficients (K(OC)) ranged from 52000 to 92000 L kg(-1) for pyrene and from 8200 to 89000 L kg(-1) for 2,2',5,5'-tetrachlorobiphenyl, with a marked "concentration effect" for the latter compound.     

Persistent organic pollutants in water and surface sediments of Taihu Lake,China and risk assessment

Organic pollutants, especially persistent organic pollutants were examined in the water and surface sediments of Taihu Lake, China. Both 12 water and 12 sediment samples were collected over the lake. C-18 solid-phase extraction technique was applied to extract organic pollutants in collected water samples. Soxhlet extraction procedure was used to extract organic pollutants in sediment samples. The analysis was performed by GC-MS controlled by a Hewlett Packard chemstation. Two hundred and seventy-three kinds of organic chemicals in water were examined, 200 more than that detected in 1985; 188 kinds of chemicals in sediments were detected as well. Among them 21 kinds of chemicals belong to priority pollutants as well as 17 kinds to be the endocrine disruptors. The concentrations of the pollutants were more than 2 times higher than that in 1985. The possible source and relation to anthropogenic activity were discussed.     

A comparative characterization of dissolved organic matter by means of original aqueous samples and isolated humic substances

The aim of our study is to test the use of less time-consuming spectroscopic methods applied on original water samples in order to obtain information about DOM composition without any sample preparation. These results were directly compared with results from a conventional isolation and characterization procedure of dissolved humic substances (fulvic acids – FA) isolated from the same water sample. FAs were characterized by UV-, fluorescence-, FTIR spectroscopy and elemental composition. UV absorbance and fluorescence behavior of FAs and original water samples follow the same pattern. A lower UV absorbance and a lower humification index (derived from the synchronous fluorescence spectra) of about 15% is typical for water samples compared to the FAs. We computed linear relationships between properties of the original water sample (UV-, synchronous fluorescence spectra) and the isolated FA (IR absorption, C/N ratio). The application of synchronous fluorescence and UV spectroscopy of aqueous samples has been proved to result in similar information about DOM composition as the characterization of isolated humic substances concerning the content of aromatic structures and the degree of humification.     

Influence of suspended clay minerals and humic matter on the solid phase extraction efficiency of selected pesticides from water

The purpose of this investigation was to determine the influence of humic acids (HA) and Ca-montmorillonite (CaM) on the solid-phase extraction (SPE) efficiency of atrazine, alachlor and alpha-cypermethrin from water samples at various pH-values. The nature and intensity of binding of the studied pesticides to CaM were determined by X-ray diffraction analysis and termogravimetric analysis (TGA) test. The studied pesticides eluted from discs were analysed by thin-layer chromatography (TLC). The effects of CaM and humic acid were generally pH-dependent and acted independently in extraction efficiency influence. Lower recovery of pesticides was observed at higher pH values when CaM was > or =0.1 g and was attributed to greater dispersion of clay, increased surface area and subsequent adsorption. Concentrations of dissolved organic carbon (DOC) in humic acid had less effect on the extraction efficiency when water was at pH 8 compared to water at pH 2, which was probably due to greater nonpolar interactions of the pesticides to the charge-neutralized humic acid molecule.     

Equilibrium partitioning of (14)C-benzo(a)pyrene and (14)C-benazolin between fractionated phases from an arable topsoil

Equilibrium partitioning of hydrophobic (14)C-benzo(a)pyrene and hydrophilic (14)C-benazolin between fractionated phases from an arable topsoil of Merzenhausen (Germany) was investigated. Topsoil samples were collected from lysimeters which were incubated with different residual crops. A physical soil fractionation based on sedimentation and centrifugation steps was performed after water extraction. Four soil phases were obtained designated sediment (SED) phase (>20 microm), microaggregate (MA) phase (2 microm-20 microm), colloid (COL) phase (<2 microm) and electrolyte (EL) phase. The distribution of (14)C-benzo(a)pyrene, (14)C-benazolin and organic carbon between the soil phases was established. Enrichment factors for the two chemicals and organic carbon are higher in the COL and MA phases than in the SED phase. The distribution constant K(d) of chemicals for Merzenhausen topsoil was calculated according to two-phase or three-phase partitioning models. The three-phase partitioning model presumes the contribution of the organic carbon for the binding of chemicals. A log K(oc) of 5.55 can be calculated in the case of (14)C-benzo(a)pyrene, which is typical of the hydrophobic association with the soil organic carbon. In the case of (14)C-benazolin, much higher K(d) and K(oc) values were calculated than found with parent molecules after short-time experiments. Long-term aging processes must be considered. Specific effects on the chemical distribution due to the different crop residues were not detected.     

Influence of Suspended Clay Minerals and Humic Matter on the Solid Phase Extraction Efficiency of Selected Pesticides from Water

The purpose of this investigation was to determine the influence of humic acids (HA) and Ca-montmorillonite (CaM) on the solid-phase extraction (SPE) efficiency of atrazine, alachlor and α-cypermethrin from water samples at various pH-values. The nature and intensity of binding of the studied pesticides to CaM were determined by X-ray diffraction analysis and termogravimetric analysis (TGA) test. The studied pesticides eluted from discs were analysed by thin-layer chromatography (TLC). The effects of CaM and humic acid were generally pH-dependent and acted independently in extraction efficiency influence. Lower recovery of pesticides was observed at higher pH values when CaM was ≥0.1 g and was attributed to greater dispersion of clay, increased surface area and subsequent adsorption. Concentrations of dissolved organic carbon (DOC) in humic acid had less effect on the extraction efficiency when water was at pH 8 compared to water at pH 2, which was probably due to greater nonpolar interactions of the pesticides to the charge-neutralized humic acid molecule.     

Distribution of DDT and benzo[a]pyrene between water and dissolved organic matter in natural humic water

DDT and benzo[a]pyrene (BaP) were added both separately and as a mixture to filtered (0.22 μm) humic surface water samples. Following a contact time of 1 d, the fraction bound to dissolved organic matter and the freely dissolved part were separated by using reversed-phase octadecyl silica cartridges. The enriched solutes were analysed by gas chromatography-mass spectrometry in the selective ion monitoring (GC-MS/SIM) mode. Partition coefficients to dissolved organic matter, calculated on the basis of the recovery data, varied between 2.0 × 10⁴ and 6.6 × 10⁴ mL/g for BaP depending on the experimental conditions, whereas the corresponding values for DDT (0.6 × 10⁴ mL/g) showed no significant variation.