Remediation of a chlorinated aromatic hydrocarbon in water by photoelectrocatalysis

Photoelectrocatalysis driven by visible light offers a new and potentially powerful technology for the remediation of water contaminated by organo-xenobiotics. In this study, the performance of a visible light-driven photoelectrocatalytic (PEC) batch reactor, applying a tungsten trioxide (WO₃) photoelectrode, to degrade the model pollutant 2,4-dichlorophenol (2,4-DCP) was monitored both by toxicological assessment (biosensing) and chemical analysis. The bacterial biosensor used to assess the presence of toxicity of the parent molecule and its breakdown products was a multicopy plasmid lux-marked E. coli HB101 pUCD607. The bacterial biosensor traced the removal of 2,4-DCP, and in some case, its toxicity response suggests the identification of transient toxic intermediates. The loss of the parent molecule, 2,4-DCP determined by HPLC, corresponded to the recorded photocurrents. Photoelectrocatalysis offers considerable potential for the remediation of chlorinated hydrocarbons, and that the biosensor based toxicity results identified likely compatibility of this technology with conventional, biological wastewater treatment.     

Bioaccumulation and bioavailability of polybrominated diphynel ethers (PBDEs) in soil

Earthworms were exposed to artificially contaminated soils of DE-71 and DE-79 to investigate the bioaccumulation and bioavailability of PBDEs in soil. All major congeners were bioavailable to earthworms. The uptake and elimination rate coefficients of PBDEs decreased with their logK_ows. The biota soil accumulation factors of PBDEs also declined with logK_ow. These may be due to the large molecular size and the high affinity of PBDEs to soil particles. The concentrations extracted by Tenax for 6 h correlated very well with those found in earthworms, suggesting that the bioavailability of PBDEs in soil is related to the fraction of rapid desorption from soil. This also indicates that 6 h Tenax extraction is a good proxy for the bioavailability of PBDEs to earthworms in soil. The BSAFs of PBDEs in aged soil decreased 22-84% compared to freshly spiked soil, indicating that aging may diminish the bioavailability of PBDEs in soil significantly.     

Predicting bioavailability of PAHs in field-contaminated soils by passive sampling with triolein embedded cellulose acetate membranes

Triolein embedded cellulose acetate membrane (TECAM) was used for passive sampling of the fraction of naphthalene, phenanthrene, pyrene and benzo[a]pyrene in 18 field-contaminated soils. The sampling process of PAHs by TECAM fitted well with a first-order kinetics model and PAHs reached 95% of equilibrium in TECAM within 20 h. Concentrations of PAHs in TECAM (C_TECAM) correlated well with the concentrations in soils (r² = 0.693-0.962, p < 0.001). Furthermore, concentrations of PAHs determined in the soil solution were very close to the values estimated by C_TECAM and the partition coefficient between TECAM and water (K_TECAM-w). After lipid normalization nearly 1:1 relationships were observed between PAH concentrations in TECAMs and earthworms exposed to the soils (r² = 0.591-0.824, n = 18, p < 0.01). These results suggest that TECAM can be a useful tool to predict bioavailability of PAHs in field-contaminated soils.     

Co-metabolic degradation of naphthalene and pyrene by acclimated strain and competitive inhibition kinetics

A dominant strain named Ochrobactrum sp. was isolated from soils contaminated with coal tar. The batch experiments were carried out to study the co-metabolic degradation of pyrene by Ochrobactrum MB-2 with naphthalene as the main substrate and the effects of several significant parameters such as naphthalene concentration, pH and temperature on removal efficiency were explored. The results showed that Ochrobactrum MB-2 effectively degraded naphthalene and that the addition of naphthalene favored the degradation of pyrene. The maximum elimination efficiency of naphthalene (10?mg?L^?1) and pyrene (1?mg?L^?1) was achieved at pH 7 and 25?°C, and the corresponding values were 99 and 41%, respectively. A competitive inhibition model based on the Michaelis–Menten equation was used to characterize the inhibitory effect of pyrene on naphthalene degradation. The values of the half-saturation coefficient for naphthalene (K_S) and dissociation constant of enzyme-inhibitor complex (K_C) were determined to be 4.93 and 1.38?mg?L^?1, respectively.     

Use of a packed-bed airlift reactor with net draft tube to study kinetics of naphthalene degradation by Ralstonia eutropha

Biodegradation of naphthalene by Ralstonia eutropha (also known as Cupriavidus necator) in a packed-bed airlift reactor with net draft tube (PBALR-nd) was studied; the Kissiris pieces were the packing material. The reactor hydrodynamics has been characterized under abiotic conditions and the dependencies of the superficial gas velocity (U _G) on the gas holdup (ε_G), liquid mixing time, and mass transfer coefficient were determined. The improving role of the net draft tube in this small column reactor (height 42 cm, ID 5 cm) was confirmed. The flow regime was described using the ε_G α U _G ⁿ expression, and bubbly flow was observed in PBALR-nd at U _G < 2.83 cm/s. In the second step of the present work, the kinetics of biodegradation was modeled using the Haldane and Aiba equations. The fitting of the experimental results to the models were done according to the nonlinear least square regression technique. The biokinetic constants (q _m, K _s, and K _i) were estimated and q _m as the specific biodegradation rate was equaled to 0.415 and 0.24 mg_naph./mg_cell?h for the Haldane and Aiba equations, respectively. The goodness of fit reported as R ² and root-mean-square error (RMSE) showed the adequate fitness of the Haldane and Aiba models in predicting naphthalene biodegradation kinetics. On the basis of the HPLC results, a hypothetical pathway for the biodegradation was presented.     

Sorption characteristics of cyromazine and its metabolite melamine in typical agricultural soils of China

A myriad of physical, chemical, and biological processes controls the fate of organic contaminants in soils. The knowledge of bioavailability of a contaminant in soil can be useful to conduct environmental risk assessment. We conducted batch equilibrium experiments to investigate the sorption of cyromazine (CA) and its metabolite melamine (MA) onto five typical soils of China belonging to suborders Ali-Perudic Ferrosols, Udic Argosols, Gleyic-Stagnic Anthrosols, Ustic Cambosols, and Udic Isohumosols. Results showed that sorption of CA and MA onto soils was linear, as indicated by the Freundlich and Langmuir models. Different sorption behaviors of CA and MA were observed on the five agricultural soils, with lgK _f values (Freundlich model) of 1.6505–2.6557 and 1.632–2.549, respectively. Moreover, the K _f values for CA and MA were positively correlated with soil organic matter (r?=?0.989, r?=?0.976) and significantly negatively correlated with pH (r?=??0.938, r?=??0.964). The free energy of sorption of CA and MA ranged from ?20.8 to ?23.0 kJ mol^?1 and ?20.8 to ?22.8 kJ mol^?1, respectively, suggesting that the sorption of CA and MA onto the soils is primarily a physical process.     

2,4-二氯苯酚在土壤中的吸附及其批实验与柱实验的分配系数比较

为了研究2,4-二氯苯酚在土壤中的吸附及比较其批实验与柱实验的分配系数Kd,开展了2,4-二氯苯酚的批实验（不同液固比条件下）和柱实验。通过分析结果可知,在批实验中,不同液固比条件下2,4-二氯苯酚达到平衡的时间类似,都在60～70 h,吸附动力学曲线符合伪二级动力学方程,吸附规律是：液固比越大,平衡吸附量增大,反应速率常数K2减小,初始吸附速率常数减小;Kd随液固比增大而降低,范围在2.91～2.12 L/kg。柱实验结果表明,2,4-二氯苯酚的贯穿曲线可以很好地用化学非平衡模型来拟合,通过模型拟合得到的Kd值要低于批实验的结果。该研究对表征2,4-二氯苯酚在环境中的行为、预测其对土壤和地下水的污染及其治理提供了依据。     

A study on As, Cu, Pb and Zn (bio)availability in an abandoned mine area (São Domingos, Portugal) using chemical and ecotoxicological tools

The aim of this study was to relate the results obtained by chemical methods, used to assess environmental (bio)availability, with the ecotoxic response and bioaccumulation of trace elements (TE) by the earthworm Eisenia fetida exposed to field-contaminated, metal-polluted soils from a sulphide mine. The extracting solution 0.5 M NH₄CH₃COO, 0.5 M CH₃COOH and 0.02 M EDTA (pH 4.7), was able to predict environmental bioavailability of TE to E. fetida. However, the toxicological bioavailability could not be predicted from the results of the chemical extractions or from the bioaccumulation results: E. fetida reproduction was higher in soils where environmental bioavailability of TE and bioaccumulation values were also higher. In this study, the toxic response of the organism seemed to be more influenced by the overall nutritional status of the soil (e.g. pH, organic matter, plant nutrient availability and cation exchange capacity) than by its TE contamination. In the case of anthropogenic multi-contaminated sites, the different soil characteristics exert an important and confounding influence in the toxic response and the relationship between different bioavailable fractions cannot be easily established, emphasising the need to combine results from chemical methods with those from bioassays when evaluating the bioavailability of TE in these soils.     

An integrated approach to understanding the sorption mechanism of phenanthrene by cork

Previous studies have shown the high sorption affinity of polycyclic aromatic hydrocarbons by cork. The aim of the present work is to go further by investigating the sorption mechanism of polycyclic aromatic hydrocarbons (exemplified by phenanthrene) on cork and the availability of the chemical components (i.e. lignin, suberin, holocellulose and extractives) to retain phenanthrene.Two approaches were integrated to reach this objective: (1) statistical multivariate analysis to obtain correlations between the sorption capacity, measured as K_oc, and the sorbent properties (i.e. polarity, acidic functional groups, %dichloromethane extractives, %ethanol and water extractives, %suberin, %lignin and %holocellulose) and (2) modeling calculations to obtain information on interaction at the molecular level.The statistical multivariate analysis demonstrated a strong and positive correlation between K_oc and the lignin content as well as negative correlations between K_oc and the phenolic groups and %dichloromethane extractives contents. The modeling study showed that the lignin–phenanthrene interaction is mostly hydrophobic in nature being largely determined by the π-stacking interaction between the aromatic groups of the interacting partners. This result justifies the observed correlations as dichloromethane extractives, being hydrophobic, compete with phenanthrene adsorption, whereas phenolic groups, as well as negatively charged groups, enhance the hydrophilic character of the sorbent surface, thus hindering the adsorption of phenanthrene.     

Quantifying interactions between propranolol and dissolved organic matter (DOM) from different sources using fluorescence spectroscopy

Beta blockers are widely used pharmaceuticals that have been detected in the environment. Interactions between beta blockers and dissolved organic matter (DOM) may mutually alter their environmental behaviors. To assess this potential, propranolol (PRO) was used as a model beta blocker to quantify the complexation with DOM from different sources using the fluorescence quenching titration method. The sources of studied DOM samples were identified by excitation–emission matrix spectroscopy (EEMs) combined with fluorescence regional integration analysis. The results show that PRO intrinsic fluorescence was statically quenched by DOM addition. The resulting binding constants (log K _oc) ranged from 3.90 to 5.20, with the surface-water-filtered DOM samples claiming the lower log K _oc and HA having the highest log K _oc. Log K _oc is negatively correlated with the fluorescence index, biological index, and the percent fluorescence response (P _i,n) of protein-like region (P _I,n) and the P _i,n of microbial byproduct-like region (P _II,n) of DOM EEMs, while it is correlated positively with humification index and the P _i,n of UVC humic-like region (P _III,n). These results indicate that DOM samples from allochthonous materials rich in aromatic and humic-like components would strongly bind PRO in aquatic systems, and autochthonous DOM containing high protein-like components would bind PRO more weakly.     

Feasibility of a simple laboratory approach for determining temperature influence on SPMD–air partition coefficients of selected compounds

Semipermeable membrane devices (SPMDs) are a widely used passive sampling methodology for both waterborne and airborne hydrophobic organic contaminants. The exchange kinetics and partition coefficients of an analyte in a SPMD are mediated by its physicochemical properties and certain environmental conditions. Controlled laboratory experiments are used for determining the SPMD–air (K_sa's) partition coefficients and the exchange kinetics of organic vapors. This study focused on determining a simple approach for measuring equilibrium K_sa's for naphthalene (Naph), o-chlorophenol (o-CPh) and p-dichlorobenzene (p-DCB) over a wide range of temperatures. SPMDs were exposed to test chemical vapors in small, gas-tight chambers at four different temperatures (−16, −4, 22 and 40 °C). The exposure times ranged from 6 h to 28 d depending on test temperature. K_sa's or non-equilibrium concentrations in SPMDs were determined for all compounds, temperatures and exposure periods with the exception of Naph, which could not be quantified in SPMDs until 4 weeks at the −16 °C temperature. To perform this study the assumption of constant and saturated atmospheric concentrations in test chambers was made. It could influence the results, which suggest that flow through experimental system and performance reference compounds should be used for SPMD calibration.     

Combined effects of soil moisture and carbaryl to earthworms and plants: simulation of flood and drought scenarios

Studying tolerance limits in organisms exposed to climatic variations is key to understanding effects on behaviour and physiology. The presence of pollutants may influence these tolerance limits, by altering the toxicity or bioavailability of the chemical. In this work, the plant species Brassica rapa and Triticum aestivum and the earthworm Eisenia andrei were exposed to different levels of soil moisture and carbaryl, as natural and chemical stressors, respectively. Both stress factors were tested individually, as well as in combination. Acute and chronic tests were performed and results were discussed in order to evaluate the responses of organisms to the combination of stressors. When possible, data was fitted to widely employed models for describing chemical mixture responses. Synergistic interactions were observed in earthworms exposed to carbaryl and drought conditions, while antagonistic interactions were more representative for plants, especially in relation to biomass loss under flood-simulation conditions.     

Sorption influenced transport of ionizable pharmaceuticals onto a natural sandy aquifer sediment at different pH

The pH-dependent transport of eight selected ionizable pharmaceuticals was investigated by using saturated column experiments. Seventy-eight different breakthrough curves on a natural sandy aquifer material were produced and compared for three different pH levels at otherwise constant conditions. The experimentally obtained K_OC data were compared with calculated K_OC values derived from two different log K_OW-log K_OC correlation approaches. A significant pH-dependence on sorption was observed for all compounds with pK_a in the considered pH range. Strong retardation was measured for several compounds despite their hydrophilic character. Besides an overall underestimation of K_OC, the comparison between calculated and measured values only yields meaningful results for the acidic and neutral compounds. Basic compounds retarded much stronger than expected, particularly at low pH when their cationic species dominated. This is caused by additional ionic interactions, such as cation exchange processes, which are insufficiently considered in the applied K_OC correlations.     

Correlations between in situ denitrification activity and nir-gene abundances in pristine and impacted prairie streams

Denitrification is a process that reduces nitrogen levels in headwaters and other streams. We compared nirS and nirK abundances with the absolute rate of denitrification, the longitudinal coefficient of denitrification (i.e., K_den, which represents optimal denitrification rates at given environmental conditions), and water quality in seven prairie streams to determine if nir-gene abundances explain denitrification activity. Previous work showed that absolute rates of denitrification correlate with nitrate levels; however, no correlation has been found for denitrification efficiency, which we hypothesise might be related to gene abundances. Water-column nitrate and soluble-reactive phosphorus levels significantly correlated with absolute rates of denitrification, but nir-gene abundances did not. However, nirS and nirK abundances significantly correlated with K_den, as well as phosphorus, although no correlation was found between K_den and nitrate. These data confirm that absolute denitrification rates are controlled by nitrate load, but intrinsic denitrification efficiency is linked to nirS and nirK gene abundances.     

Semi-specific Microbacterium phyllosphaerae-based microbial sensor for biochemical oxygen demand measurements in dairy wastewater

Although the long incubation time of biochemical oxygen demand (BOD₇) measurements has been addressed by the use of microbial biosensors, the resulting sensor-BOD values gained from the measurements with specific industrial wastewaters still underestimates the BOD value of such samples. This research aims to provide fast and more accurate BOD measurements in the dairy wastewater samples. Unlike municipal wastewater, wastewater from the dairy industry contains many substrates that are not easily accessible to a majority of microorganisms. Therefore, a bacterial culture, Microbacterium phyllosphaerae, isolated from dairy wastewater was used to construct a semi-specific microbial biosensor. A universal microbial biosensor based on Pseudomonas fluorescens, which has a wide substrate spectrum but is nonspecific to dairy wastewater, was used as a comparison. BOD biosensors were calibrated with OECD synthetic wastewater, and experiments with different synthetic and actual wastewater samples were carried out. Results show that the semi-specific M. phyllosphaerae-based microbial biosensor is more sensitive towards wastewaters that contain milk derivates and butter whey than the P. fluorescens-based biosensor. Although the M. phyllosphaerae biosensor underestimates the BOD₇ value of actual dairy wastewaters by 25–32 %, this bacterial culture is more suitable for BOD monitoring in dairy wastewater than P. fluorescens, which underestimated the same samples by 46–61 %.     

Competitive biosorption of lead, cadmium, copper, and arsenic ions using algae

The present study aims to evaluate the competitive biosorption of lead, cadmium, copper, and arsenic ions by using native algae. A series of experiments were carried out in a batch reactor to obtain equilibrium data for adsorption of single, binary, ternary, and quaternary metal solutions. The biosorption of these metals is based on ion exchange mechanism accompanied by the release of light metals such as calcium, magnesium, and sodium. Experimental parameters such as pH, initial metal concentrations, and temperature were studied. The optimum pH found for removal were 5 for Cd²⁺ and As³⁺ and 3 and 4 for Pb²⁺ and Cu²⁺, respectively. Fourier transformation infrared spectroscopy analysis was used to find the effects of functional groups of algae in biosorption process. The results showed that Pb²⁺ made a greater change in the functional groups of algal biomass due to high affinity to this metal. An ion exchange model was found suitable for describing the biosorption process. The affinity constants sequence calculated for single system was K _Pb > K _Cu > K _Cd > K _As; these values reduced in binary, ternary, and quaternary systems. In addition, the experimental data showed that the biosorption of the four metals fitted well the pseudo-second-order kinetics model.