The dissolution and microbial degradation of mobile aromatic hydrocarbons from a Pintsch gas tar DNAPL source zone.

Source zones containing tar, a dense non-aqueous phase liquid (DNAPL), can contaminate groundwater for centuries. A common occurrence of tar is at former Pintsch gas factories. Little is known about the composition and fate of contaminants dissolving from Pintsch gas tar DNAPL. In this study, we determined the composition and water-soluble characteristics of mobile aromatic hydrocarbons and their biodegradation metabolites in the DNAPL contaminated groundwater at a former Pintsch gas tar plant. We assessed the factors that determine the fate of observed groundwater contaminants. Measured values of density (1.03-1.06 kg/m3) and viscosity (18.6-39.4 cP) were found to be relatively low compared to common coal tars. Analysis showed that unlike common coal tars phenanthrene is the primary component rather than naphthalene. Moreover, it was found that Pintsch gas tar contains a relatively high amount of light molecular aromatic hydrocarbon compounds, such as benzene, toluene, ethylbenzene and xylenes (BTEX). Less commonly reported components, such as styrene, ethyltoluenes, di-ethylbenzene, 1,2,4,5-tetramethylbenzene, were also detected in water extracts from Pintsch gas tar. Moreover, 46 relatively hydrophilic metabolites were found within the tar samples. Metabolites present within the tar suggest biodegradation of mobile aromatic Pintsch gas tar compounds occurred near the DNAPL. Based on eleven detected suspect metabolites, a novel anaerobic biodegradation pathway is proposed for indene. Overall, our findings indicate that Pintsch gas tar has higher invasive and higher flux properties than most coal tars due to its relatively low density, low viscosity and, high content of water-soluble compounds. The partitioning of contaminants from multi-component DNAPL into the aqueous phase and re-dissolution of their slightly less hydrophobic metabolites back from the aqueous phase into the DNAPL is feasible and demonstrates the complexity of assessing degradation processes within a source zone.

Determination of metal-based nanoparticles in the river Dommel in the Netherlands via ultrafiltration, HR-ICP-MS and SEM.

We investigated the occurrence of metal-based nanoparticles in a natural system, the river Dommel in the Netherlands. The river itself is well-studied as far as hydrology and water quality is concerned, easily accessible and contains one major wastewater treatment plant discharging onto this river. We sampled water from various locations along the river and collected samples of influent, effluent and sewage sludge from the wastewater treatment plant. The sampling campaign was carried out in June 2015 and these samples were analysed for seven elements using high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS), ultrafiltration with a sequence of mesh sizes and scanning electron microscopy (SEM). From the results we conclude that there are indeed nanoparticles present in the treatment plant we studied, as we found titanium and gold particles in the influent and effluent. In the river water only 10 to 20% of the mass concentration of titanium, cerium and other elements we examined is made up of free, i.e. unattached, particles with a size smaller than 20 nm or of dissolved material. The rest is attached to natural colloids or is present as individual particles or clusters of smaller particles, as it could be filtered out with 450 nm ultrafilters. We found evidence that there is no appreciable anthropogenic emission of cerium into the river, based on the geochemical relationship between cerium and lanthanum. Besides, the effluent of the treatment plant has lower concentrations of some examined elements than the surface water upstream. The treatment plant discharges much less of these elements than estimated using previous publications. However, a potential diffuse source of titanium dioxide in the form of nanoparticles or of larger particles is their use in paints and coatings, as the concentration of titanium increased considerably in the urbanised area of the river Dommel.

Modelling the transport of engineered metallic nanoparticles in the river Rhine.

As engineered nanoparticles of zinc oxide, titanium dioxide and silver, are increasingly used in consumer products, they will most probably enter the natural environment via wastewater, atmospheric deposition and other routes. The aim of this study is to predict the concentrations of these nanoparticles via wastewater emissions in a typical river system by means of a numerical model. The calculations rely on estimates of the use of nanomaterials in consumer products and the removal efficiency in wastewater treatment plants as well as model calculations of the fate and transport of nanoparticles in a riverine system. The river Rhine was chosen for this work as it is one of the major and best studied rivers in Europe. The study gives insight in the concentrations that can be expected and, by comparing the model results with measurements of the total metal concentrations, of the relative contribution of these emerging contaminants. Six scenarios were examined. Two scenarios concerned the total emission: in the first it was assumed that nanoparticles are only released via wastewater (treated or untreated) and in the second it was assumed that in addition nanoparticles can enter the river system via runoff from the application of sludge as a fertilizer. In both cases the assumption was that the nanoparticles enter the river system as free, unattached particles. Four additional scenarios, based on the total emissions from the second scenario, were examined to highlight the consequences of the assumption of free nanoparticles and the uncertainties about the aggregation processes. If all nanoparticles enter as free particles, roughly a third would end up attached to suspended particulate matter due to the aggregation processes nanoparticles are subject to. For the other scenarios the contribution varies from 20 to 45%. Since the Rhine is a fast flowing river, sedimentation is unlikely to occur, except at the floodplains and the lakes in the downstream regions, as in fact shown by the sediment mass balance. Nanoparticles will therefore be transported along the whole river until they enter the North Sea. For the first scenario, the concentrations predicted for zinc oxide and titanium dioxide nanoparticles are in the order of 0.5 µg/l, for silver nanoparticles in the order of 5 ng/l. For zinc and titanium compounds this amounts to 5-10% of the measured total metal concentrations, for silver to 2%. For the other scenarios, the predicted nanoparticle concentrations are two to three times higher. While there are still considerable uncertainties in the inputs and consequently the model results, this study predicts that nanoparticles are capable of being transported over long distances, in much the same way as suspended particulate matter.

Modeling aggregation and sedimentation of nanoparticles in the aquatic environment.

With nanoparticles being used more and more in consumer and industrial products it is almost inevitable that they will be released into the aquatic environment. In order to understand the possible environmental risks it is important to understand their behavior in the aquatic environment. From laboratory studies it is known that nanoparticles in the aquatic environment are subjected to a variety of processes: homoaggregation, heteroaggregation to suspended particulate matter and subsequent sedimentation, dissolution and chemical transformation. This article presents a mathematical model that describes these processes and their relative contribution to the behavior of nanoparticles in the aquatic environment. After calibrating the model with existing data, it is able to adequately describe the published experimental data with a single set of parameters, covering a wide range of initial concentrations. The model shows that at the concentrations used in the laboratory, homoaggregation and sedimentation of the aggregates are the most important processes. As for the natural environment much lower concentrations are expected, heteroaggregation will play the most important role instead. More experimental datasets are required to determine if the process parameters that were found here are generally applicable. Nonetheless it is a promising tool for modeling the transport and fate of nanoparticles in watersheds and other natural water bodies.

Predicting the contribution of nanoparticles (Zn, Ti, Ag) to the annual metal load in the Dutch reaches of the Rhine and Meuse.

Although nanoparticles are being increasingly used in consumer products, the risks they may pose to the environment and to human health remain largely unknown. One important reason for this is the lack of quantitative techniques for identifying and measuring the amount of nanomaterials in environmentally relevant circumstances. Such techniques should also discriminate between manufactured and naturally occurring nanoparticles, so that the influence of human activities can be identified. This article describes a technique for estimating nanoparticles by calculating the potential releases of nano-forms of zinc, titanium and silver, the three metals that are widely used for nano-enhanced products, and comparing them to the total loads, based on measurements of the total concentration. We use The Netherlands for our case study. Combining the scarce available data (indicative figures on the content of nanomaterials in various products and usage profiles found in an unrelated category of research) we were able to estimate the total use of such materials in The Netherlands and therefore the potential release into the environment. The calculations indicate that nanomaterials contribute a small but discernible fraction (5 to 20%) to the total loads of zinc and titanium in the Dutch reaches of the Rhine and Meuse. For silver the contribution is at most 3%. The contribution is, however, close to the minimum that can be detected, given the variability in the measured concentrations.

Ecotoxicological assessment of grey water treatment systems with Daphnia magna and Chironomus riparius.

In order to meet environmental quality criteria, grey water was treated in four different ways: 1) aerobic 2) anaerobic+aerobic 3) aerobic+activated carbon 4) aerobic+ozone. Since each treatment has its own specific advantages and disadvantages, the aim of this study was to compare the ecotoxicity of differently treated grey water using Chironomus riparius (96 h test) and Daphnia magna (48 h and 21d test) as test organisms. Grey water exhibited acute toxicity to both test organisms. The aerobic and combined anaerobic+aerobic treatment eliminated mortality in the acute tests, but growth of C. riparius was still affected by these two effluents. Post-treatment by ozone and activated carbon completely removed the acute toxicity from grey water. In the chronic toxicity test the combined anaerobic+aerobic treatment strongly affected D. magna population growth rate (47%), while the aerobic treatment had a small (9%) but significant effect. Hence, aerobic treatment is the best option for biological treatment of grey water, removing most of the toxic effects of grey water. If advanced treatment is required, the treatment with either ozone or GAC were shown to be very effective in complete removal of toxicity from grey water.

Molecular simulation of polycyclic aromatic hydrocarbon sorption to black carbon.

Strong sorption of hydrophobic organic contaminants to soot or black carbon (BC) is an important environmental process limiting the bioremediation potential of contaminated soils and sediments. Reliable methods to predict BC sorption coefficients for organic contaminants are therefore required. A computer simulation based on molecular mechanics using force field methods has been applied in this study to calculate BC sorption coefficients of polycyclic aromatic hydrocarbons (PAHs). The free energy difference between PAHs dissolved in water and in water containing a model structure of BC was calculated by thermodynamic integration of Monte Carlo simulated energies of transfer. The free energies were calculated with a hypothetical reference state that has equal free energies in both phases and is therefore cancelled in the calculated free energy difference. The calculated sorption coefficient of phenanthrene (log K(BC) = 5.17 +/- 0.54 L/kg C), fluoranthene (6.33 +/- 0.64 L/kg C) and benzo[a]pyrene (7.38 +/- 0.36 L/kg C) corresponded very well to experimental values available in the literature. Furthermore, an average spacing distance of 3.73 A between PAHs and BC was determined that is only slightly lower than an experimentally determined value of 4.1 A. The method applied in this study enables the calculation of the extent of PAH sorption to a soot surface for which no experimental values are available nor data for related compounds as required in quantitative structure-activity relationships.

Resilience of microbial systems towards disturbances.

In this paper we aim at summarizing the current definitions of resilience in systems ecology with particular attention towards microbial systems. The recent advances of biomolecular techniques have provided scientists with new tools to investigate these systems in greater detail and with higher resolution. Therefore existing concepts and hypotheses have been revisited and discussed with respect to their applicability for ecosystems ruled by microbial processes. This review has also led to some reflections on the suitability of the term "resilience" as a general goal in environmental policies.

Cytochrome P450cam-monoterpene interactions.

The use of the molecular mechanics AMBER force field (FF) to predict product profiles for the hydroxylation of the monoterpenes 1R-camphor, 1S-camphor, 1R-norcamphor, 1S-norcamphor and camphane by the enzyme cytochrome P450cam from the soil bacterium Pseudomonas putida was investigated. Predictions were carried out by applying multiple substrate (starting) orientations in the enzyme pocket in two procedures: a procedure based on molecular dynamics (MD) and a procedure based on short MD simulations followed by geometry optimisations. The latter (GO) procedure is faster and enabled the use of more monoterpene starting orientations. Monoterpene orientations were transformed into product profiles by applying both energetic and geometrical criteria appropriate for the (monoterpene) hydrogen abstraction reaction. Good predictions compared to experimental data were obtained for most compounds in both the MD and GO procedures. Prior to the product profile calculations, the FF was calibrated by reproducing the experimental data for the binding energy of 1R-camphor and 1S-camphor to P450cam and the energy of vaporisation of water. Focus of the calibration was on the value for the scaling factor for the electrostatic interactions.

Dissolved organic carbon--contaminant interaction descriptors found by 3D force field calculations.

Enthalpies of transfer at 300 K of various partitioning processes were calculated in order to study the suitability of 3D force fields for the calculation of partitioning constants. A 3D fulvic acid (FA) model of dissolved organic carbon (DOC) was built in a MM+ force field using AMI atomic charges and geometrical optimization (GO). 3,5-Dichlorobiphenyl (PCB14), 4,4'-dichlorobiphenyl (PCB15), 1,1,1-trichloro-2,2-bis-(4-chlorophenyl)-ethane (PPDDT) and 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (Atrazine) were inserted into different sites and their interaction energies with FA were calculated. Energies of hydration were calculated and subtracted from FA-contaminant interactions of selected sites. The resulting values for the enthalpies of transfer from water to DOC were 2.8, -1.4, -6.4 and 0.0 kcal/mol for PCB 14, PCB15, PPDDT and Atrazine, respectively. The value of PPDDT compared favorably with the experimental value of -5.0 kcal/mol. Prior to this, the method was studied by the calculation of the enthalpies of vaporization and aqueous solution using various force fields. In the MM + force field GO predicted enthalpies of vaporization deviated by +0.7 (PCB14), +3.6 (PCB15) and -0.7 (PPDDT)kcal/mol from experimental data, whereas enthalpies of aqueous solution deviated by -3.6 (PCB14), +5.8 (PCB15) and +3.7 (PPDDT) kcal/mol. Only for PCB14 the wrong sign of this enthalpy value was predicted. Potential advantages and limitations of the approach were discussed.

In vitro longitudinal assessment of coronal discoloration from endodontic sealers.

A major cause of tooth discoloration may be sealer remnants in the chamber. The objective of this study was to evaluate, longitudinally, coronal discoloration from four sealers. Extracted premolars were sectioned in the coronal third of the root. The chamber contents were removed and instrumentation was via the canal. The following sealers were bulk introduced into the chamber: AH26, Kerr Pulp Canal Sealer, Roths 801 (nonstaining), and Sealapex. The apical access was sealed with white sticky wax. Teeth were maintained in a moist environment at 37 degrees C. Initial (immediate pretreatment) digital images of the teeth were made for base line comparison. Subsequent images were at 1-, 3-, 9-, and 12-month intervals. Then images were mixed and descriptively evaluated blindly by trained evaluators. Discoloration was induced by the four sealers, with slight to moderate visible changes that increased through 12 months. There was slightly more discoloration with AH26 and Kerr Pulp Canal Sealer. In conclusion discoloration induced by the endodontic sealers produced slight to moderate and generally progressive discoloration over 12 months.

Three-dimensional printing and porous metallic surfaces: a new orthopedic application.

As-cast, porous surfaced CoCr implants were tested for bone interfacial shear strength in a canine transcortical model. Three-dimensional printing (3DP) was used to create complex molds with a dimensional resolution of 175 microm. 3DP is a solid freeform fabrication technique that can generate ceramic pieces by printing binder onto a bed of ceramic powder. A printhead is rastered across the powder, building a monolithic mold, layer by layer. Using these 3DP molds, surfaces can be textured "as-cast," eliminating the need for additional processing as with commercially available sintered beads or wire mesh surfaces. Three experimental textures were fabricated, each consisting of a surface layer and deep layer with distinct individual porosities. The surface layer ranged from a porosity of 38% (Surface Y) to 67% (Surface Z), whereas the deep layer ranged from 39% (Surface Z) to 63% (Surface Y). An intermediate texture was fabricated that consisted of 43% porosity in both surface and deep layers (Surface X). Control surfaces were commercial sintered beaded coatings with a nominal porosity of 37%. A well-documented canine transcortical implant model was utilized to evaluate these experimental surfaces. In this model, five cylindrical implants were placed in transverse bicortical defects in each femur of purpose bred coonhounds. A Latin Square technique was used to randomize the experimental implants left to right and proximal to distal within a given animal and among animals. Each experimental site was paired with a porous coated control site located at the same level in the contralateral limb. Thus, for each of the three time periods (6, 12, and 26 weeks) five dogs were utilized, yielding a total of 24 experimental sites and 24 matched pair control sites. At each time period, mechanical push-out tests were used to evaluate interfacial shear strength. Other specimens were subjected to histomorphometric analysis. Macrotexture Z, with the highest surface porosity, failed at a significantly higher shear stress (p = 0.05) than the porous coated controls at 26 weeks. It is postulated that an increased volume of ingrown bone, resulting from a combination of high surface porosity and a high percentage of ingrowth, was responsible for the observed improvement in strength. Macrotextures X and Y also had significantly greater bone ingrowth than the controls (p = 0.05 at 26 weeks), and displayed, on average, greater interfacial shear strengths than controls, although they were not statistically significant.

Fluorene degradation by Sphingomonas sp. LB126 proceeds through protocatechuic acid: a genetic analysis.

Sphingomonas sp. LB126 is able to utilize fluorene as sole source of carbon and energy. In the present study, a mutagenic vector was constructed and a "plasmid rescue" strategy was set up to isolate a 16.5-kb DNA fragment containing genes required for fluorene degradation. A 14.5-kb portion of the cloned DNA was sequenced revealing thirteen open reading frames. Two encoded hypothetical proteins (FldE and FldY) similar to transcriptional regulators and one (ORF360) located on an IS-like element (ISSsp126) encoded a putative transposase. Three other putative proteins (FldB, FldU and FldV) displayed strong similarity with enzymes of the protocatechuate 4,5-degradation pathway utilized by Sphingomonaspaucimobilis SYK-6 for the degradation of lignin breakdown products. The remaining hypothetical proteins displayed only limited similarity with enzyme sequences available from databases. Suicide plasmid-directed mutagenesis and genetic complementations showed that integrity of the protocatechuate catabolic pathway was an absolute requirement for fluorene degradation to proceed. These findings were further supported by the analysis of metabolites in bacterial culture supernatants obtained from appropriate mutants. The results presented here demonstrated the suitability of the genetic tool constructed and supplied the first genetic evidence for the participation of a protocatechuate 4,5-degradation pathway in a bacterial fluorene degradation pathway.

A chemostat system for investigating pesticide biodegradation in continuous mixed bacteria cultures originating from surface water.

To be able to predict the degradation (rate) of organic chemicals (e.g. pesticides) in the field, knowledge of the environmental conditions that are of influence on the degradation process are of importance. In the present study an experimental system is described which is used to study the degradation of organic pollutants in mixed bacteria cultures originating from surface water With this system the degradation of compounds can be followed for relatively long experimental periods (months). In addition, it is possible to vary different environmental parameters in order to investigate their influences on the degradation of the chemical. These preliminary experiments show that growth and 'composition' of the bacteria culture have comparable patterns in parallel experiments. The first order degradation rate constant for the test compound dichloran, as calculated from these experiments under these circumstances, is about 0.002 h(-1).

Mechanical environment affects allograft incorporation.

In a bilateral canine tibial model, the mechanical, radiologic, and histologic characteristics of intercalary allografts stabilized with locked intramedullary nails were compared with those of allografts fixed with compression plates. Both methods of fixation achieved healing to host bone. Tibiae that were plated had more callus with statistically greater mean torsional rigidity and strength than those treated with nails (paired t-test, p

Small changes in polymer chemistry have a large effect on the bone-implant interface: evaluation of a series of degradable tyrosine-derived polycarbonates in bone defects.

In a series of homologous, tyrosine-based polycarbonates, small changes in the chemical structure of the polymer pendent chain were found to affect the bone response in a long-term (1280 d) implantation study. Identically sized pins, prepared from poly(DTE carbonate), poly(DTB carbonate), poly(DTH carbonate), and poly(DTO carbonate) were implanted transcortically in the proximal tibia and the distal femur of skeletally mature New Zealand White Rabbits. The tissue response at the bone-implant interface was characterized in terms of the absence of a fibrous capsule (direct bone apposition, indicative of a bone bonding response) or the presence of a fibrous capsule (referred to as the encapsulation response). The relative frequency of direct bone apposition versus encapsulation was recorded for each polymer throughout the entire period of the study. While all four polymers were tissue compatible, there was a correlation between the chemical structure of the pendent chain and the type of bone response observed, with poly(DTE carbonate) having the highest tendency to elicit direct bone apposition. Based on in vivo degradation data and the ability of model polymers with carboxylate groups at their surface to chelate calcium ions, it is proposed that the ability of poly(DTE carbonate) to bond to bone is caused by the facile hydrolysis of the pendent ethyl ester groups which creates calcium ion chelation sites on the polymer surface. The incorporation of calcium chelation sites into the chemical structure of an implant material appears to be a key requirement if direct bone apposition/bone bonding is desired. This study demonstrates that very subtle changes in the chemical composition of an implant material can have significant effects on the long-term tissue response in a clinically relevant model.

Pathologic supracondylar fracture due to osteolytic pseudotumor of knee following cementless total knee replacement.

Wear debris of polyethylene, polymethylmethacrylate, and metal have been recognized to be associated with foreign body reactions, osteolysis, and aseptic prosthetic loosening after joint replacement arthroplasty. Further, foreign body reaction due to the presence of extensive wear debris can cause aggressive granulomatous lesions and pathologic fracture. To our knowledge, there has been no previous report of pathologic fracture of the femur due to an agressive pseudotumor. This report describes a case of pathologic supracondylar fracture of the femur 6 years and 5 months after cementless total knee replacement arthroplasty. The fracture occurred through an aggressive expanding soft tissue mass that was a tumorlike lesion secondary to polyethylene wear debris. The lesion was associated with massive osteolysis around the femoral component of the total knee prosthesis.

Biodegradation pathway of 2-chlorodibenzo-p-dioxin and 2-chlorodibenzofuran in the biphenyl-utilising strain JB1.

The biphenyl-utilising Burkholderia (previously Alcaligenes) strain JB1 is also able to degrade a number of chlorinated dibenzo-p-dioxins and dibenzofurans. In this study, 4-chlorocatechol and a chlorotrihydroxydiphenyl ether were identified as metabolites of 2-chlorodibenzo-p-dioxin. 5-Chlorosalicylic acid and a chlorotrihydroxybiphenyl were metabolites of 2-chlorodibenzofuran. These results show that degradation of these compounds follows pathways in which the initial reaction is angular dioxygenation, followed by cleavage of an ether bridge. This pathway is similar to that used by dibenzofuran-degrading strains such as Sphingomonas sp. strain RW1.

Micromechanical properties of epiphyseal trabecular bone and primary spongiosa around the physis: an in situ nanoindentation study.

The elastic modulus and hardness of the mineralized bone around the growth plate was measured to determine its regional micromechanical properties. Multiple nanoindentation tests, >10 sessions, with depths ranging from 100 to 1,000 nm at loading rates of 12.5 and 750 microN/s, were performed on the trabecular bone in the epiphysis, trabecular bone at the junction of the physis and epiphysis, primary spongiosa in the metaphysis, and surrounding cortical bone of the distal femur of 300-gm Sprague-Dawley rats. The indentation load-displacement data obtained in these tests were analyzed to determine the elastic modulus and hardness of the tissues. The nanoindentation results highlighted the regional variations in the material properties of the mineralized tissues around the growth plate. The primary spongiosa had a lower elastic modulus and hardness than both epiphyseal trabecular and cortical bone (p < 0.01). A relatively well-defined thick trabecular band at the physeal-epiphyseal junction had modulus and hardness values comparable to those of cortical bone (p > 0.05). These findings support the hypothesis that the primary spongiosa has micromechanical properties that are significantly lower than the epiphyseal trabecular bone. On this basis, it is speculated that the fracture patterns commonly seen in patients with physeal injuries are influenced by the micromechanical properties of these tissues, as well as by the nature and direction of the applied force.

Mechanical properties of bone in a paraplegic rat model.

Pathologic fractures may occur with minimal trauma after spinal cord injury (SCI) because of osteoporosis. Rats were evaluated to determine whether they could be used as an SCI animal model. Male Sprague-Dawley rats underwent spinal cord transection at the ninth thoracic vertebrae. Control rats underwent a sham procedure. Mechanical testing of the humeral shaft, femoral shaft, tibial shaft, femoral neck, distal femur, and proximal tibia was performed separately at 0, 8, and 24 weeks after surgery. At 24 weeks, significant differences between SCI and control rats were found in maximum torque needed to produce failure in the femoral shaft (63 percent of control, p < 0.05) and tibial shaft (63 percent, p < 0.01), and in compressive load to produce failure in cross-sectional specimens of the distal femur (51 percent, p < 0.05) and proximal tibia (50 percent, p < 0.01). No differences were found in the maximum torque needed to produce failure of the humeral shaft (106 percent, p = 0.77) between SCI and control rats. Reductions in relative bone strength in SCI rats at 24 weeks were similar in magnitude to bone mineral density changes reported in humans with chronic paraplegia. Thus, Sprague-Dawley rats appear to be good animal models in which to evaluate changes in bone strength following SCI.