Analytical approach and occurrence for the determination of mass concentration of PCDD/PCDF and dl-PCB in flue gas emissions using long-term sampling devices

In this work, a reliable methodology for the simultaneous analysis of PCDD/PCDF and dioxin-like PCB (dl-PCB) in flue gas emissions collected using continuous sampling devices is proposed. The analytical scheme followed the minimum requirements described in the EU standard EN-1948:1,2,3,4 according to samples containing large amounts of dioxins and dl-PCBs or samples collected over a long period of time of about 4 weeks. Parameters, such as reproducibility, precision, limits of detection (LOD), limits of quantification (LOQ), extract aliquot size, analytical blanks, extraction efficiency, as well as the amount of internal standards required for an accurate determination, were assessed. The findings demonstrate the suitability of the proposed analytical scheme for the analysis of PCDD/PCDF and PCB in samples collected using long-term sampling devices. The analysis of five different 5% v/v sample aliquots reported %RSD values lower than 10% for all of the 29 congeners at both low and high levels. Similarly, %RSD values were 3.2 and 2.0 for the low level samples and 0.9 and 1.1%RSD for the high level extracts for PCDD/PCDF and dl-PCB, respectively expressed in total TEQ units. Re-extraction provided values less than 3%, expressed in TEQ. Based on blank analyses, LOD values of 100 pg I-TEQ for PCDD/PCDF and 10 pg WHO-TEQ for dl-PCB were achieved when 5% v/v aliquots were analyzed. Finally, the proposed analytical approach was tested with samples from a wide range of combustion processes such as hazardous and municipal waste incinerators, as well as cement kilns (with and without waste co-incineration).

Improvement of scanning tunneling microscopy resolution with H-sensitized tips

Recent scanning tunneling hydrogen microscopy (STHM) experiments on PTCDA (perylene-3,4,9,10-tetracarboxylic-3,4,9,10-dianhydride)/Au(111) have shown unprecedented intramolecular and intermolecular spatial resolution. The origin of this resolution is studied using an accurate STHM theoretical simulation technique that includes a detailed description of the electronic structure of both the tip and sample. Our results show that H2 molecules are dissociated on the Au tip; the adsorbed H atoms change the density of states at the Fermi level (E(F)) of the tip, increasing its p-orbital character and reducing the s-orbital contribution. Also, due to the interaction with the H-decorated tip, E(F) is shifted to the middle of the PTCDA lowest unoccupied molecular orbital peak, increasing dramatically the density of states of the sample at E(F). These effects give rise to the enhanced STHM resolution.

Current use of high-resolution mass spectrometry in the environmental sciences

During the last two decades, mass spectrometry (MS) has been increasingly used in the environmental sciences with the objective of investigating the presence of organic pollutants. MS has been widely coupled with chromatographic techniques, both gas chromatography (GC) and liquid chromatography (LC), because of their complementary nature when facing a broad range of organic pollutants of different polarity and volatility. A clear trend has been observed, from the very popular GC-MS with a single quadrupole mass analyser, to tandem mass spectrometry (MS-MS) and, more recently, high-resolution mass spectrometry (HRMS). For years GC has been coupled to HR magnetic sector instruments, mostly for dioxin analysis, although in the last ten years there has been growing interest in HRMS with time-of-flight (TOF) and Orbitrap mass analyzers, especially in LC-MS analysis. The increasing interest in the use of HRMS in the environmental sciences is because of its suitability for both targeted and untargeted analysis, owing to its sensitivity in full-scan acquisition mode and high mass accuracy. With the same instrument one can perform a variety of tasks: pre- and post-target analysis, retrospective analysis, discovery of metabolite and transformation products, and non-target analysis. All these functions are relevant to the environmental sciences, in which the analyst encounters thousands of different organic contaminants. Thus, wide-scope screening of environmental samples is one of the main applications of HRMS. This paper is a critical review of current use of HRMS in the environmental sciences. Needless to say, it is not the intention of the authors to summarise all contributions of HRMS in this field, as in classic descriptive reviews, but to give an overview of the main characteristics of HRMS, its strong potential in environmental mass spectrometry and the trends observed over the last few years. Most of the literature has been acquired since 2005, coinciding with the growth and popularity of HRMS in this field, with a few exceptions that deserve to be mentioned because of their relevance.

Evolution of PCDD/Fs and dioxin-like PCBs in the general adult population living close to a MSW incinerator

It is well known that municipal solid waste incinerators (MSWI) produce dioxins and furans. The aim of this study was to assess the serum levels of compounds with dioxin-like activity such as polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and dioxin-like PCBs after the commissioning of a MSWI plant. In 2006 and 2008 serum samples were obtained from 322 and 326 volunteers, respectively, from the general population, some living in the vicinity of the plant and others, as a control group, living further away from the MSWI plant and out of the path of prevailing winds. Samples for sets of 20 individuals, grouped by age and sex, were pooled, obtaining 16 pooled samples per year. No significant differences were observed in PCDD/Fs as a function of area of residence or proximity to the plant over the time of the study, with levels of WHO-TEQ/g lipid nearby and far from the MSWI being 26.9 and 20.0pg, respectively, in 2006 and 20.8 and 26.4pg, respectively, in 2008. There was a significant decrease in the concentration of non-ortho PCBs in the nearby areas, whilst there was a significant increase in the concentration of mono-ortho PCBs, both in the nearby areas and in those further away from the MSWI. Age was significantly associated with PCDD/Fs and dioxin-like PCBs, but sex showed no significant association. Overall, this study found that there was no increase in the levels of compounds with dioxin-like activity in a population living close to an MSWI, in agreement with the literature reviewed, for plants of recent construction using state-of-the-art technology.

Polychlorinated dibenzo-p-dioxin and dibenzofuran in urban air of an Andean city

Particle-bound polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) in ambient air were monitored together with particulate matter less than 10 μm (PM(10)) at three sampling sites of the Andean city of Manizales, Colombia; during September 2009 and July 2010. PCDD/Fs ambient air emissions ranged from 1 fg WHO-TEQ m(-3) to 52 fg WHO-TEQ m(-3) in particulate fraction. The PM(10) concentrations ranged from 23 μg m(-3) to 54 μg m(-3). Concentrations of PM(10) and PCDD/Fs in ambient air observed for Manizales - a medium sized city with a population of 380,000 - were comparable to concentrations in larger cities. The highest concentrations of PCDD/Fs and PM(10) found in this study were determined at the central zone of the city, characterized by public transportation density, where diesel as principal fuel is used. In addition, hypothetical gas fractions of PCDD/Fs were calculated from theoretical K(p) data. Congener profiles of PCDD/Fs exhibited ratios associated with different combustion sources at the different sampling locations, ranging from steel recycling to gasoline and diesel engines. Taking into account particle and gas hypothetical fraction of PCDD/Fs, Manizales exhibited values of PCDD/Fs equivalent to rural and urban-industrial sites in the southeast and center of the city respectively. Poor correlation of PCDDs with PM(10) (r=-0.55 and r=0.52) suggests ambient air PCDDs were derived from various combustion sources. Stronger correlation was observed of PCDFs with PM(10). Poor correlation between precipitation and reduced PM(10) concentration in ambient air (r=-0.45) suggested low PM(10) removal by rainfall.

C6H6/Au(111): interface dipoles, band alignment, charging energy, and van der Waals interaction

We analyze the benzene/Au(111) interface taking into account charging energy effects to properly describe the electronic structure of the interface and van der Waals interactions to obtain the adsorption energy and geometry. We also analyze the interface dipoles and discuss the barrier formation as a function of the metal work-function. We interpret our DFT calculations within the induced density of interface states (IDIS) model. Our results compare well with experimental and other theoretical results, showing that the dipole formation of these interfaces is due to the charge transfer between the metal and benzene, as described in the IDIS model.

Assessment of polychlorinated dibenzo-p-dioxin and dibenzofuran emissions from a hazardous waste incineration plant using long-term sampling equipment

The aim of this work is to evaluate the performance of a continuous monitoring system for the analysis of the mass concentration of PCDD/Fs from stationary sources. Data was acquired from a modern, state of the art, hazardous waste thermal treatment plant for a period of more than 2 years using a commercial available continuous monitoring system. The study consisted of a total of 16 samples, collected in periods from 1 week to 2 months resulting in an average of 360 m³ sampled flue gas per sample. The study showed the system was able to confirm that for a period of more than 2 years the plant was complying with the limit of 0.1 ng I-TEQ/Nm(3). In addition, the data showed the typical fingerprint of such installations which is useful for example in impact studies. Long-term samples were compared to five short-term samples (6 h) collected every 6 months during the study period. Principal component analysis was applied to PCDD/Fs obtained data as useful statistical tool to find out trends and similarities between different samples. Improvement in terms of representativeness of data was achieved through continuous assessment since the starts of the project. The obtained data was further used to determine the emission factor for this activity and the total annual PCDD/Fs release to the atmosphere.

Reaction-subdiffusion model of morphogen gradient formation

We study gradient formation of subdiffusive morphogens. The morphogens are produced at a source point at a constant rate. From there they move subdiffusively and are also subject to degradation at a rate that may depend on location and on time. Our analysis is based on a reaction-subdiffusion equation obtained from a continuous time random-walk model with a long-tailed waiting time distribution that also incorporates an evanescence process. Spatially uniform degradation at a constant rate leads to an exponentially decreasing stationary concentration profile hardly distinguishable from that obtained with normal diffusion. On the other hand, with location-dependent degradation we find a rich gamut of profiles, some qualitatively quite different from those occurring with normal diffusion. We conclude that long-time morphogen concentration profiles are very sensitive to the spatial dependence of the reactivity and may also serve as a sensitive measure of the occurrence of anomalous diffusion.

Barrier formation and charging energy for a variable nanogap organic molecular junction: a tip/C60/Au(111) configuration

We analyze the nanogap organic molecular junction formed by a C(60) molecule in between an Au-tip and an Au(111)-surface. In our approach, we first calculate the atomic geometry of the tip/C(60)/Au(111) nanocontact as a function of the tip-surface distance and molecule adsorption site using a density functional theory-local density approximation (DFT-LDA) technique. The electronic structure and metal/organic barrier height formation (for a single molecule) are analyzed using the induced density of interface states model for metal/organic interfaces. From this analysis we calculate the charging energy U(eff) of the C(60) molecule at the nanocontact and determine self-consistently the transport energy gap and the organic molecule density of states. Our results are shown to be in good agreement with the experimental evidence.

Reaction-subdiffusion and reaction-superdiffusion equations for evanescent particles performing continuous-time random walks

Starting from a continuous-time random-walk (CTRW) model of particles that may evanesce as they walk, our goal is to arrive at macroscopic integrodifferential equations for the probability density for a particle to be found at point r at time t given that it started its walk from r_{0} at time t=0 . The passage from the CTRW to an integrodifferential equation is well understood when the particles are not evanescent. Depending on the distribution of stepping times and distances, one arrives at standard macroscopic equations that may be "normal" (diffusion) or "anomalous" (subdiffusion and/or superdiffusion). The macroscopic description becomes considerably more complicated and not particularly intuitive if the particles can die during their walk. While such equations have been derived for specific cases, e.g., for location-independent exponential evanescence, we present a more general derivation valid under less stringent constraints than those found in the current literature.

Divergent series and memory of the initial condition in the long-time solution of some anomalous diffusion problems

We consider various anomalous d -dimensional diffusion problems in the presence of an absorbing boundary with radial symmetry. The motion of particles is described by a fractional diffusion equation. Their mean-square displacement is given by r(2) proportional, variant t(gamma)(0<gamma< or =1) , resulting in normal diffusive motion if gamma=1 and subdiffusive motion otherwise. For the subdiffusive case in sufficiently high dimensions, divergent series appear when the concentration or survival probabilities are evaluated via the method of separation of variables. While the solution for normal diffusion problems is, at most, divergent as t-->0 , the emergence of such series in the long-time domain is a specific feature of subdiffusion problems. We present a method to regularize such series, and, in some cases, validate the procedure by using alternative techniques (Laplace transform method and numerical simulations). In the normal diffusion case, we find that the signature of the initial condition on the approach to the steady state rapidly fades away and the solution approaches a single (the main) decay mode in the long-time regime. In remarkable contrast, long-time memory of the initial condition is present in the subdiffusive case as the spatial part Psi1(r) describing the long-time decay of the solution to the steady state is determined by a weighted superposition of all spatial modes characteristic of the normal diffusion problem, the weight being dependent on the initial condition. Interestingly, Psi1(r) turns out to be independent of the anomalous diffusion exponent gamma .

Survival probability of a subdiffusive particle in a d-dimensional sea of mobile traps

We investigate the long-time behavior of the survival probability P(t) of a mobile particle in d-dimensional continuous Euclidean media doped with noninteracting mobile traps. The particle is strictly subdiffusive, implying that its mean-square displacement grows as tgamma' with 0<gamma'<1. Initially, the traps are scattered randomly and their subsequent mean-square displacement grows as tgamma with 0<gamma<or=1. Instantaneous annihilation of the particle takes place upon contact with any of the traps. The solution to this problem is obtained by deriving lower and upper asymptotic bounds of the survival probability and showing that they converge to one another for long times, thereby unambiguously determining the long-time decay of P(t). For d>or=2 we find that at late times the survival probability is that of the pure target problem (the problem where the particle remains immobile) in agreement with previous studies for the d=1 case. These decay laws remain invariant over the whole gamma range as opposed to the dynamical crossover observed for the case of a purely diffusive particle (gamma'=1) where, for gamma<2/(2+d) , the survival probability becomes that of the so-called trapping problem (the problem where the particle moves in a sea of static traps). This behavior implies that for sufficiently low values of gamma(gamma<2/(2+d)) the survival probability becomes singular in the limit gamma'-->1: trappinglike for gamma'=1 and targetlike for any gamma'<1.

Serum levels of polychlorinated dibenzodioxins and dibenzofurans and PCBs in the general population living near an urban waste treatment plant in Biscay, Basque Country

Levels of PCDD/Fs and dioxin-like PCBs were measured in 16 pooled samples of serum from a total of 322 adults in the general population, to coincide with the start-up of a new municipal solid urban waste treatment plant in Biscay, Basque Country (Spain). Two hundred and eighty-three individual serum samples were also obtained, in which the most common PCBs (28, 52, 101, 118, 138, 153 and 180) were quantified. The samples were taken from four geographical zones: two from the metropolitan area of Bilbao, located less than 2 km from the plant and with high traffic density (Zones E1 and E2), a third located 5 km from the plant in an urban area of Bilbao, also with high traffic density (Zone C1) and the fourth located 20 km from the plant, in a municipality with minimal industrial activity and low traffic density (Zone C2), the latter two being out of the path of the prevailing winds. The median levels of dioxins+furans were similar by zone: E1=24.3, E2=27.3, C1=21.3, C2=18.8 pg g(-1) lipid (p=0.362); by sex: 20.2 vs. 22.6 pg g(-1) lipid in men and women (p=0.328); and by age: 20.8 vs. 21.3 pg g(-1) lipid in subjects aged 20-44 and 45-69 (p=0.505). No detectable levels of PCBs 52 and 101 were found. Significant differences by zone were found only for PCB 180 (p=0.041), with higher values in Zone C2, the zone with the lowest presumed contamination levels. Dioxin-like PCBs (p<0.001) and the most common PCBs (138, 153, 180) (p<0.001) were both statistically associated with age, higher values being found in the 45-69 age group.

Baseline levels of dioxin and furan emissions from waste thermal treatment in Colombia

Background data of polychlorinated dibenzodioxin and dibenzofuran (PCDD/Fs) emissions from the incineration sector in Colombia are presented. Monitoring was carried out during a two-year period, 2003-2005. Twelve plants were sampled for stack gas emissions of dioxins and total solid particulate (TSP). Additionally, PCDD/Fs in several fly ash samples were analyzed. Most incinerators burned industrial refuse materials and medical residues. A wide range of PCDD/Fs emission levels were found. In particular, levels ranging from 6.9 to 343.8 ng I-TEQ/N m(3) were determined in plants without any air pollution control system (APCS). In contrast, 0.5-39.2 ng I-TEQ/N m(3) levels were found in plants with APCS while 8.5-67.5 ng I-TEQ/g were measured in fly ash samples. TSP values ranged from 14 to 448 mg/N m(3). This study also evaluated the impact of implementing different control systems in an incinerator. Finally, for comparison purposes several samples were analyzed by both high resolution gas chromatography coupled to high resolution mass spectrometry (HRGC-HRMS) and high resolution gas chromatography coupled to ion-trap low resolution mass spectrometry-mass spectrometry (HRGC-IT LRMS/MS). Overall, I-TEQ values deviated about 20-30% between both techniques.

Occurrence and bioaccumulation study of PCDD and PCDF from mineral feed additives

Extraction of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) was evaluated in sepiolite matrices. Soxhlet extraction using different extracting strategies and acid treatment were tested. Acid treatment or Soxhlet extraction using a mixture of toluene:ethanol as solvent allowed to reach the minimum requirements for recovery rates. However, Soxhlet extraction using a mixture cyclohexane:toluene as extracting solvent did not allow to comply with these minimum requirements. Significant differences were obtained in TEQ units when acid treatment was applied in comparison to Soxhlet extraction. This fact can be explained because the use of drastic acid conditions allows removing strongly adsorbed analytes which can be uniquely extracted after a total destruction of the crystalline. On the contrary, Soxhlet extraction was not able to destroy the structure of sepiolite and as a consequence the PCDDs/Fs remain adsorbed in the internal structure of the mineral. A bioaccumulation study was also conducted to evaluate the transference of PCDDs/Fs from the sepiolite into the animal when fed with feed containing sepiolite. Four groups of chickens were exposed through diet to a control feed, feed with 3% w/w sepiolite, spiked feed contaminated with PCDDs/Fs and feed containing contaminated kaolinitic clay. Livers of animals were analyzed throughout the exposure period. Results of this trial showed that the performance of broilers was not affected by the presence of dioxins at levels tested, and chickens did not show any abnormal behaviour. Dioxins intentionally added to the diet were significantly absorbed and accumulated in liver, whereas the PCDDs/Fs from sepiolite were not available for chickens since livers from broilers fed 3% sepiolite presented similar WHO-TEQ values than those from broilers fed control diet.

PCDD/Fs and DL-PCBs in feeding fats obtained as co-products or by-products derived from the food chain

Among the tasks included in the "Quality and safety of feeding fats obtained from co-products or by-products of the food chain" Project, supported by the European Union and included in the 6th Framework Program, a number of fats and oils collected as co- or by-products from the food chain were selected for the determination of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and 'dioxin-like' polychlorinated biphenyls (DL-PCBs). In the majority of the cases these samples are currently employed as feed ingredients. Nevertheless, additional fats, which are forbidden for feedstuff purposes were also considered in this study. In general terms, fats and oils were classified taking into account their nature and the processes applied to obtain these co- or by-products. PCDD/F and DL-PCB levels were evaluated in a first group of samples composed of fish oils, animal fats and lecithins. As expected, fats and oils with an animal origin presented higher concentrations, expressed in pg WHO-TEQ/g, compared to the levels found in vegetable samples like lecithins. The category of fish oils had the highest values for both PCDD/Fs and the sum of PCDD/Fs and DL-PCBs, with some samples showing levels above the maximum established at the present legislation related to the presence of PCDD/Fs and DL-PCBs in animal feed [Commission Directive 2006/13/EC of 3 February 2006 amending Annexes I and II to Directive 2002/32/EC of the European Parliament and of the Council on undesirable substances in animal feed as regards dioxins and dioxin-like PCBs. Official Journal of the European Communities L32, 44-53]. In a second group, fats and oils with a more complex composition obtained from different transformation processes or even mixtures of fats were considered; thus, acid oils from chemical refining, acid oils from physical refining, recycled cooking oils, oils extracted from exhausted bleaching earths, hydrogenated by-products, fatty acids calcium soaps and miscellaneous fats were analyzed. The data revealed a significant variability in PCDD/F and DL-PCB levels, expressed in pg WHO-TEQ/g, in these products. It has to be pointed out that the analyses of fats and oils belonging to these categories of products were sometimes difficult due to the complexity of the samples. In terms of legislation most of these samples cannot be easily included into one of the specific categories of substances intended for feedstuff purposes that are regulated in Commission Directive 2006/13/EC.

Efficiency of trapping processes in regular and disordered networks

We use a Markov method to study the efficiency of trapping processes involving both a random walker and a deep trap in regular and disordered networks. The efficiency is gauged by the mean absorption time (average of the mean number of steps performed by the random walker before being absorbed by the trap). We compute this quantity in terms of different control parameters, namely, the length of the walker jumps, the mobility of the trap, and the degree of spatial disorder of the network. For a proper choice of the system size, we find in all cases a nonmonotonic behavior of the efficiency in terms of the corresponding control parameter. We thus arrive at the conclusion that, despite the decrease of the effective system size underlying the increase of the control parameter, the efficiency is reduced as a result of an increase of the escape probability of the walker once it finds itself in the interaction zone of the trap. This somewhat anti-intuitive effect is very robust in the sense that it is observed regardless of the specific choice of the control parameter. For the case of a ring lattice, results for the mean absorption time in systems of arbitrary size are given in terms of a two-parameter scaling function. For the case of a mobile trap, we deal with both trapping via a single channel (walker-trap overlap) and via two channels (walker-trap overlap and walker-trap crossing), thereby generalizing previous work. As for the disordered case, our analysis concerns small world networks, for which we see several crossovers of the absorption time as a function of the control parameter and the system size. The methodology used may be well suited to exploring characteristic time scales of encounter-controlled phenomena in networks with a few interacting elements and the effect of geometric constraints in nanoscale systems with a very small number of particles.

Assessment of polychlorinated dibenzo-p-dioxins and dibenzofurans in sludges according to the European environmental policy

The amount of sewage sludge generated in Europe is expected to surpass the 10 million tons/year in 2006 as a result of the waste water treatment process according to the Water Policy in European Union. Sewage sludge is what is left behind after water is cleaned in waste treatment plants and is characterized for this high content in nitrogen and phosphorous that could be of great importance in agriculture as fertilizer or soil conditioner. On the other hand, pollutants like metals and organic contaminants are usually removed from water and are accumulated in the sewage sludge, reaching the food chain if their concentrations are not below the safe limits established by the European legislation. The latter issue is of great concern nowadays and in this sense, different works alert against the use of the sewage sludge in agriculture arguing that serious illnesses, even resulting in death as well as adverse environmental impacts are associated to the application of sewage sludge. This work is a continuation of a former comprehensive survey on of priority organic pollutant in sludges for agricultural purposes carried out by our group in Catalonia and this time is focused on the polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F), one of the most toxic group of organic compounds listed in the Work Document on Sludge which is the reference tool in this field in Europe and is also included in the Stockholm Convention. Eighty eight samples were collected from the end of 2003 to April 2006 and the concentrations detected were lower than the 100 ng/kg I-TEQ limit recommended by the European legislation (EC, 2000). Thus, sewage sludges generated in Catalonia do not represent a threat to human health if they are used as fertilizers in agriculture.