A novel approach to evaluation of adsorbents for sampling indoor volatile organic compounds associated with symptom reports

This article addresses problems that complicate attempts to compare methods when several factors may be associated with an effect, but it is not known which factors are relevant. Chemicals that may contribute to 'sick building syndrome' (SBS), and thus should be sampled in investigations of SBS, are not currently known. A study was undertaken to compare the utility of three adsorbents (Carbopack B, Chromosorb 106 and Tenax TA) for detecting differences in personal chemical exposure to volatile organic compounds in indoor air, between persons with and without SBS symptoms (cases and controls). On the basis of office workers' responses to a questionnaire, 15 cases and 15 controls were chosen. They simultaneously carried diffusive samplers with adsorbents during a week at work, and the acquired samples were analysed by gas chromatography/mass spectrometry (GC/MS). The adsorbents were then compared in terms of their ability to separate cases and controls in partial least square discriminant analysis (PLS-DA) models. This method of comparison takes into account detected differences in chemical exposure between cases and controls measured with the different adsorbents. Tenax TA gave the best PLS-DA models for separating cases and controls, but a combination of measurements with Tenax TA and Carbopack B gave better PLS-DA models than models based on measurements from either adsorbent alone. Adding measurements from Chromosorb 106 did not improve the results.     

Diffusive Sampling of VOCs as an Aid to Monitoring Urban Air Quality

Diffusive sampling of Volatile Organic Compounds (VOCs) onto thermal desorption tubes, followed by gas chromatography, is an established technique for area or personal monitoring of typical workplace concentrations and there has been increasing interest in extending the application to environmental levels, particularly for benzene, toluene and xylene (BTX). Diffusive sampling rates for BTX on Chromosorb 106 and Carbograph-1 (a graphitised carbon) were measured over periods of 1-4 weeks in field validation experiments using ambient air and parallel pumped sampling (the reference method) at the HSL site in central Sheffield. The reference method was also used to investigate the possible bias of an open-path spectrophotometer (OPSIS) used by Sheffield City Council. A bias for BTX was suspected from results of a two-week initial exercise in which several diffusive samplers were placed close to the light path. In the full field validation of the diffusive samplers carried out subsequently, the significant bias of BTX concentrations reported by OPSIS were confirmed when compared with concurrent results from the reference method. OPSIS gave benzene and toluene values up to eight times higher than expected from the GC measurements. Xylene discrepancies were smaller, but in one 3-day peak episode, OPSIS demonstrated a negative correlation with GC.     

Evaluation of VOC measurments in the EXPOLIS study. Air Pollution Exposure Distributions within Adult Urban Urban Populations in Europe

Personal exposures and microenvironment concentrations of 30 target VOCs were measured for 401 participants living in five European cities as a part of the EXPOLIS (Air Pollution Exposure Distributions within Adult Urban Populations in Europe) study. Measurements in Basel used an active charcoal (Carbotech) adsorbent as opposed to the Tenax TA used in the other study centres. In addition, within each centre, personal and microenvironment VOC sampling required different sampling pumps and, because of different sampling durations, different sampling flow rates. Thus, careful testing of the sampling and analysis procedures was required to ensure accuracy and comparability of collected data. Monitor comparison tests using Tenax TA showed a mean VOC concentration ratio of 0.95 between the personal and microenvironment monitors. The LODs for the target VOCs using Tenax TA ranged from 0.7 to 5.2 microg m(-3). The LODs for the 14 target compounds quantifiable using Carbotech ranged from 0.9 to 3.2 microg m(-3). Tenax TA field blanks showed no remarkable contamination with the target VOCs, except benzaldehyde, a known artefact with this adsorbent. Thus, the diffusion barrier system used prevented contamination of Tenax TA samples by passive diffusion during non-sampling periods. Duplicate and parallel evaluations of the Tenax TA and Carbotech showed an average difference of < 17% in VOC concentrations within the sampling methods, but a systematic difference between the methods (Tenax TA: Carbotech concentration ratio = 1.18-2.36). These field evaluations and quality assurance tests showed that interpretation and comparison of the results in any VOC monitoring exercise should be done on a compound by compound basis. It is also apparent that carefully planned and realised QA and QC (QA/QC) procedures are needed in multi-centre studies, where a common sampling method and laboratory analysis technique are not used, to strengthen and simplify the interpretation of observed VOC levels between participating centres.     

Diffusive uptake in passive and active adsorbent sampling using thermal desorption tubes

Low flow active sampling techniques collecting vapors and gases using thermally desorbable adsorbents are now feasible and desirable in many applications as they permit long integration times, the potential for miniaturized sampling configurations, and other advantages. At very low air flow rates (< 1 ml min(-1)), diffusive uptake on adsorbents in conventional sorbent tubes may equal or exceed the active (pumped) uptake rate, and even at low flow rates (1-4 ml min(-1)), diffusive uptake may significantly bias measurements. Thus, corrections to account for the diffusive flux or means to limit the diffusive uptake are needed in low flow applications. This paper presents (1) a theoretical analysis of the role of diffusive and advective uptake for several sampling geometries of tube-type samplers; (2) experimental confirmation using both laboratory and field studies; (3) estimates of the tortuosity and porosity of the glass wool packing used to retain the adsorbent, parameters needed to estimate diffusive fluxes in passive and active sampling; (4) a demonstration that orifice-equipped low flow active samplers can reduce diffusive uptake and improve precision, and (5) a model predicting the saturated adsorbent layer that helps to account for the gradual decline in uptake rates seen in passive sampling. Diffusive uptake will depend on the tube configuration and diffusion coefficient of the substance of interest, but for conventional sampling tubes (0.4-0.5 cm id, 1.5 cm air gap), sample flow rates should be maintained above 1 to 4 ml min(-1) to keep errors below 5%. Laboratory experiments showed close agreement with theoretical calculations, and the field study using 1 to 4 d sampling periods and 0.3 ml min(-1) flows demonstrated that the orifice-equipped samplers essentially eliminated diffusive uptake. No significant practical difficulties are encountered using orifices, e.g., pressure drop is minimal. Experimental estimates of tortuosity (0.79 +/- 0.02) and porosity (0.92 +/- 0.10) of the glass wool packing (0.3 cm length) represent relatively little resistance to diffusion; however, variation in the packing and adsorbent placement can degrade the precision achievable by passive samplers. Diffusion barriers, consisting most simply of an orifice, may be used to lower the diffusive uptake. A needle-type orifice permits flows below 0.1 ml min(-1) and is suitable for sampling periods as long as several weeks, and it provided greater precision than conventional open-ended sampling tubes (8% compared to 13%). Finally, the gradual decrease in diffusive fluxes often seen in passive sampling is attributed to additional resistance posed by a saturated adsorbent layer, in agreement with a simple model based on total VOCs and specific adsorptivity of the adsorbent.     

Diffusive Sampling of Volatile Organic Compounds in Ambient Air

The Building Research Establishment (BRE) has been using diffusive samplers for the study of VOCs in indoor and outdoor air since 1989. The Perkin Elmer type sampler packed with Tenax TA adsorbent is used for the diffusive sampling of C6-C16 organic compounds. This method was applied in a major study of relationships between the environment and child health carried out during 1990-1993 in the Avon area of the UK. The present paper reports results of an investigation into the repeatability of the sampler in outdoor air and measurements of 6 aromatic hydrocarbons inside and outside a home over a 5 year period and inside and outside an office building over a 12 month period. Both the home and the office were located in Hertfordshire, England. Concentrations of VOCs recorded are similar to those found in the Avon area. Higher concentrations of each of the six compounds were recorded inside the home than outside, whilst greater amounts of benzene and toluene were found inside the office than outside. Seasonal variations in concentrations are observed and measurements recorded outdoors are similar to those recorded by other workers.     

Background concentrations of individual and total volatile organic compounds in residential indoor air of Schleswig-Holstein, Germany

During a monitoring campaign concentrations of volatile organic compounds (VOCs) were measured in indoor air of 79 dwellings where occupants had not complained about health problems or unpleasant odour. Parameters monitored were the individual concentration of 68 VOCs and the total concentration of all VOCs inside the room. VOCs adsorbed by Tenax TA were then analysed by means of thermal desorption, gas chromatography and mass spectrometry. The analytical procedure and quantification was done according to the recommendation of the ECA-IAQ Working Group 13 which gave a definition of the total volatile organic compound (TVOC) concentration. Using this recommendation TVOC-concentrations ranged between 33 and 1600 microg m(-3) with a median of 289 microg m(-3). Compounds found in every sample and with the highest concentrations were 2-propanol, alpha-pinene and toluene. Save for a few samples, all concentrations measured have been a factor 2 to 10 lower, compared to data from similar studies. Only a few terpenes and aldehydes were found exceeding published reference data or odour threshold concentrations. However, it has been found that sampling and analysing methods do have a considerable impact on the results, making direct comparisons of studies somewhat questionable. 47% of all samples revealed concentrations exceeding the threshold value of 300 microg TVOC m(-3) set by the German Federal Environmental Agency as a target for indoor air quality. Using the TVOC concentration as defined in the ECA-IAQ methodology is instrumental in assessing exposure to VOCs and identifying sources of VOCs. The background concentrations determined in this study can be used to discuss and interpret target values for individual and total volatile organic compounds in indoor air.     

Low-flow active and passive sampling of VOCs using thermal desorption tubes: theory and application at an offset printing facility

While air sampling techniques using adsorbent-based collection, thermal desorption and chromatographic analysis have found a niche in ambient air sampling, occupational applications have been more limited. This paper evaluates the use of thermal desorption techniques for low flow active and passive sampling configurations which allow conveniently long duration sampling in occupational settings and other high concentration environments. The use of an orifice enables flows as low as 0.5 ml min(-1) and sampling periods up to several days without significant biases. A model is used to predict sampling rates of a passive sampler encompassing an orifice, a void space, glass wool, and the adsorbent. Laboratory and field tests conducted at a commercial offset printing facility, which contained a variety of volatile organic compounds (primarily aromatic but also a few chlorinated and terpene compounds at levels from 1 to 67,000 microg m(-3)), are used to evaluate the approach. Tenax GR and Carbosieve SIII, both singly and together, were employed as adsorbents. Side-by-side tests comparing high flow, low flow and passive samplers show excellent agreement and high linearity (r = 0.95) for concentrations spanning nearly five orders of magnitude. Active samplers were tested at flows as low as 0.5 ml min(-1), compared to typical flows up to 40 ml min(-1). Passive samplers demonstrated a linear range and agreement with predictions for adsorbate loadings from approximately 1 ng to nearly 10 microg. Using a chemical mass balance receptor model, concentrations in the facility were apportioned to solvents, inks and other indoor and outdoor sources. Overall, the use of low flow active and passive sampling approaches employing thermal desorption techniques provides good performance and tremendous flexibility that facilitates use in many applications, including workplace settings.     

Development of active and diffusive sampling methods for determination of 3-methoxybutyl acetate in workplace air

Monitoring of the workplace concentration of 3-methoxybutyl acetate (MBA), which is used in printer's ink and thinner for screen-printing and as an organic solvent to dissolve various resins, is important for health reasons. An active and a diffusive sampling method, using a gas chromatograph equipped with a flame ionization detector, were developed for the determination of MBA in workplace air. For the active sampling method using an activated charcoal tube, the overall desorption efficiency was 101%, the overall recovery was 104%, and the recovery after 8 days of storage in a refrigerator was more than 90%. For the diffusive sampling method using the 3M 3500 organic vapor monitor, the MBA sampling rate was 19.89 cm(3) min(-1). The linear range was from 0.01 to 96.00 microg ml(-1), with a correlation coefficient of 0.999, and the detection limits of the active and diffusive samplers were 0.04 and 0.07 microg sample(-1), respectively. The geometric mean of stationary sampling and personal sampling in a screen-printing factory were 12.61 and 16.52 ppm, respectively, indicating that both methods can be used to measure MBA in workplace air.     

Laboratory and field comparison of measurements obtained using the available diffusive samplers for ozone and nitrogen dioxide in ambient air

This study presents an evaluation of the extent of differences between measurements performed by O(3) and NO(2) diffusive samplers and by the reference methods for diffusive samplers commercially available. The tests were performed in an exposure chamber under extreme conditions of controlling factors and under field conditions. For NO(2), the results of the laboratory experiments showed that most of the diffusive samplers were affected by extreme exposure conditions. The agreement between the samplers and the reference method was better for the field tests than for the laboratory ones. The estimate of the uptake rate for the exposure conditions using a model equation improved the agreement between the diffusive samplers and the reference methods. The agreement between O(3) measured by the diffusive samplers and by the reference method was satisfactory for 1-week exposure. For 8-hour exposures, the diffusive samplers with high uptake rates quantified better the O(3) concentration than the samplers with low uptake rates. As for NO(2), the results of the O(3) field tests were in better agreement with the reference method than the ones of the laboratory tests. The field tests showed that the majority of diffusive samplers fulfils the 25% uncertainty requirement of the NO(2) European Directive and the 30% uncertainty requirement of the O(3) European Directive for 1-week exposure.     

Airborne chemical compounds on dairy farms

The chemical environment that dairy farmers are exposed to during milking was investigated. Volatile organic compounds (VOCs) were analysed and identified, and the levels of formaldehyde, ammonia and carbon dioxide were measured in eight farms in northern Sweden. Both stationary and personal samples were taken. A total of 70 VOCs were identified from the adsorbent samples, with p-cresol, 2-butanone, ethyl acetate, alpha-pinene and delta 3-carene occurring at the highest levels. All monitored levels were significantly lower for compounds having a stated highest occupational exposure level (OEL). Using multivariate techniques some differences in the composition of the workplace air between and within the farms were found. No difference was found between personal exposure and the surrounding environment in the cowshed.     

Continuous, intermittent and passive sampling of airborne VOCs

Long sampling periods are often advantageous or required for measuring air quality and characterizing exposures. However, sampling periods exceeding 8 to 24 h using thermally desorbable adsorbent tube (TDT) samplers for the measurement of airborne volatile organic compounds (VOCs) face several challenges, including maintaining stable and low flow rates, and avoiding breakthrough of the adsorbent. These problems may be avoided using intermittent sampling; however, the literature contains few if any reports that have evaluated this technique in environmental, occupational or other applications. The purpose of this study is to evaluate continuous, intermittent and passive sampling methods using both laboratory and real-world tests. Laboratory tests compared continuous and intermittent (active) samplers in a controlled dynamic test gas generation system. Field tests used side-by-side active and passive samplers in an office, home workshop and four smokers' homes. All samples were analyzed for a wide range of VOCs by GC-MS. In most instances, intermittent sampling yielded better reproducibility (duplicate precision of 10 +/- 6%) than continuous low-flow sampling (18 +/- 5%), in part due to difficulty maintaining low flows. Concentrations obtained using intermittent sampling agreed with those for continuous sampling, with downward biases resulting primarily from errors in flow rate measurements. In the field, more VOC species were detected using active rather than passive sampling. Passive measurements were 12% lower than continuous measurements, a difference attributed to declining uptake rates at higher concentrations over the 3 to 4 d sampling period. Overall, most measurements obtained using the three sampling methods agreed within 20% for a wide range of concentrations (0.1 to 230 microg m(-3)). Both passive and intermittent sampling approaches are suitable for long sampling periods, but intermittent sampling provides greater flexibility with respect to sampling period, and permits the use of multi-bed adsorbents that can capture a wider range of VOCs.     

Portable XRF analysis of occupational air filter samples from different workplaces using different samplers: final results, summary and conclusions

This paper concludes a five-year program on research into the use of a portable X-ray fluorescence (XRF) analyzer for analyzing lead in air sampling filters from different industrial environments, including mining, manufacturing and recycling. The results from four of these environments have already been reported. The results from two additional metal processes are presented here. At both of these sites, lead was a minor component of the total airborne metals and interferences from other elements were minimal. Nevertheless, only results from the three sites where lead was the most abundant metal were used in the overall calculation of method accuracy. The XRF analyzer was used to interrogate the filters, which were then subjected to acid digestion and analysis by inductively-coupled plasma optical-emission spectroscopy (ICP-OES). The filter samples were collected using different filter-holders or "samplers" where the size (diameter), depth and homogeneity of aerosol deposit varied from sampler to sampler. The aerosol collection efficiencies of the samplers were expected to differ, especially for larger particles. The distribution of particles once having entered the sampler was also expected to differ between samplers. Samplers were paired to allow the between-sampler variability to be addressed, and, in some cases, internal sampler wall deposits were evaluated and compared to the filter catch. It was found, rather surprisingly, that analysis of the filter deposits (by ICP-OES) of all the samplers gave equivalent results. It was also found that deposits on some of the sampler walls, which in some protocols are considered part of the sample, could be significant in comparison to the filter deposit. If it is concluded that wall-deposits should be analyzed, then XRF analysis of the filter can only give a minimum estimate of the concentration. Techniques for the statistical analysis of field data were also developed as part of this program and have been reported elsewhere. The results, based on data from the three workplaces where lead was the major element present in the samples, are summarized here. A limit of detection and a limit of quantitation are provided. Analysis of some samples using a second analyzer with a different X-ray source technology indicated reasonable agreement for some metals (but this was not evaluated for lead). Provided it is only necessary to analyze the filters, most personal samplers will provide acceptable results when used with portable XRF analysis for lead around applicable limit values.     

Validation of diffusive mini-samplers for aldehyde and VOC and its feasibility for measuring the exposure levels of elementary school children

Exposure to various chemicals can cause adverse effects to health, such as asthma and allergies, especially in children. Data on personal exposure levels in children are scarce, thus small lightweight diffusive mini-samplers for aldehydes and volatile organic compounds (VOCs) were designed to measure the exposure level of children to these chemicals. The aim of the study was to validate and examine the applicability of these mini-samplers for measuring daily chemical exposure. The diffusive mini-samplers are 20 mm in length, 11 mm in diameter, and 1.67 g in weight. The devices are cylindrically shaped with polytetrafluoroethylene membrane filters placed at each end. To measure aldehydes and acetone, 20 mg of 2,4-dinitrophenylhydrazine was used as an absorbent. To measure VOCs, a carbon molecular sieve was used. The sampling rate for each chemical was determined by parallel sampling with active samplers in a closed exposure bag. The blank levels of the chemicals and the storage stability of the device were tested. The mini-samplers were compared to commercially available diffusive samplers. To examine the applicability of the samplers, 65 elementary school children carried them for 24 h. The sampling rates for formaldehyde, acetaldehyde, and acetone were 20.9, 22.9, and 19.7 mL min(-1), respectively. The limits of quantification (LOQ) for the 24-hour sampling by high-performance liquid chromatography/ultraviolet (HPLC/UV) analysis were 8.3, 7.6, and 8.8 μg m(-3) for formaldehyde, acetaldehyde, and acetone, respectively. The sampling rates for the 11 VOCs were determined and ranged from 3.3 mL min(-1) for styrene and 2-ethyl-1-hexanol to 11.7 mL min(-1) for benzene. The LOQ for the 24-hour sampling by gas chromatography-mass spectrometry (GC-MS) analysis ranged from 5.9-105.2 μg m(-3), 1.1-24.7 parts per billion. The storage stability after 5 days ranged from 94.8 to 118.2%. Formaldehyde, acetone, benzene, and toluene were detected above the LOQ in more than 90% of the children, and the median concentrations were 21.7, 20.9, 10.1, and 21.5 μg m(-3), respectively. This study shows that the diffusive samplers developed were suitable for children to carry and were capable of measuring the children's daily chemical exposure.     

BTX measurements with diffusive samplers in the vicinity of a cokery: comparison between ORSA-type samplers and pumped sampling

In the framework of new European directives in the field of ambient air quality assessment specific requirements for measurement methods for benzene will be defined and have to be met in the future. In a residential area in the vicinity of a cokery a comprehensive monitoring programme for BTX compounds (benzene, toluene, xylenes) was carried out with diffusive samplers. Measurement results from 20 sites show a distinct spatial distribution of benzene concentrations which is caused by the emissions of the plant. Comparisons with two pumped measurement methods reveal excellent agreement in the case of benzene. An assessment of measurement uncertainty for the diffusive method is presented in terms of standard deviations from parallel measurements (precision) and by comparison with a reference method according to national and international standards. Data quality objectives required by an upcoming European directive for benzene can be met by diffusive sampling.     

Comparison of 24 h averaged VOC monitoring results for residential indoor and outdoor air using Carbopack X-filled diffusive samplers and active sampling--a pilot study

Analytical results obtained by thermal desorption GC/MS for 24 h diffusive sampling of 11 volatile organic compounds (VOCs) are compared with results of time-averaged active sampling at a known constant flow rate. Air samples were collected with co-located duplicate diffusive sampling tubes and one passivated canister. A total of eight multiple-component sampling events took place at fixed positions inside and outside three private homes. Subsequently, a known amount of sample air was transferred from the canister to an adsorbent tube for analysis by thermal desorption GC/MS. Results for the 11 most prevalent compounds--Freon 11, 1,3-butadiene, benzene, toluene, tetrachloroethene, ethylbenzene, m,p-xylene, o-xylene, 4-ethyltoluene, 1,3,5-trimethylbenzene, and p-dichlorobenzene--show that the ratio of average study values (diffusive sampling to active sampling) is 0.92 with 0.70 and 1.14 extreme ratios. Absolute percent difference for duplicate samples using diffusive sampling was <10% for the four most prevalent compounds. Agreement between the two sampling approaches indicates that the prediction of approximately constant diffusive sampling rates based on previous laboratory studies is valid under the field conditions.     

Personal exposures and microenvironmental concentrations of particles and bioaerosols

The aim of this study was to compare the personal exposure to particles and bioaerosols with that measured by stationary samplers in the main microenvironments, i.e., the home and the workplace. A random sample of 81 elementary school teachers was selected from the 823 teachers working for two councils in eastern Finland for the winter time measurement period. Bioaerosol and other particles were collected on filters by button samplers using personal sampling and microenvironmental measurements in homes and workplaces. The 24-hour sampling period was repeated twice for each teacher. Particle mass, absorption coefficient of the filter and the concentration of viable and total microorganisms were analyzed from each filter. In this paper, the study design, quality assurance principles and results of particle and bioaerosol exposure are described. The results show that particle mass concentrations, absorption coefficient and fungi were higher in personal exposure samples than in home and workplace samples. Furthermore, these concentrations were usually lower in the home than in the workplace. Bacterial concentrations were highest in heavily populated workplaces, while the viable fungi concentrations were lowest in workplaces. The fungi and bacteria results showed high variation, which emphasises the importance of quality assurance (duplicates and field blanks) in the microbial field measurements. Our results indicate that personal exposure measurements of bioaerosols in indoor environments are feasible and supplement the information obtained by stationary samplers.     

Performance of semipermeable membrane devices for sampling of organic contaminants in groundwater

Lipid-filled semipermeable membrane devices (SPMDs) are receiving increasing attention as passive, in situ samplers for the assessment of environmental pollutant exposure. Although SPMDs have been successfully used in a variety of field studies in surface waters, only a few studies have addressed their characteristics as groundwater samplers. In this study, the performance of the SPMDs for monitoring organic contaminants in groundwater was evaluated in a pilot field application in an area severely contaminated by chemical waste, especially by chlorinated hydrocarbons. The spatial distribution of hydrophobic groundwater contaminants was assessed using a combination of passive sampling with SPMDs and non-target semiquantitative GC-MS analysis. More than 100 contaminants were identified and semiquantitatively determined in SPMD samples. Along the 6 field sites under investigation, a large concentration gradient was observed, which confirms a very limited mobility of hydrophobic substances in dissolved form in the aquifer. The in situ extraction potential of the SPMD is limited by groundwater flow, when the exchange volume of well water during an exposure is lower than the SPMD clearance volume for the analytes. This study demonstrates that SPMDs present a useful tool for sampling and analyzing of groundwater polluted with complex mixtures of hydrophobic chemicals and provides guidance for further development of passive sampling technology for groundwater.     

A comparison of portable XRF and ICP-OES analysis for lead on air filter samples from a lead ore concentrator mill and a lead-acid battery recycler

Personal and area samples for airborne lead were taken at a lead mine concentrator mill, and at a lead-acid battery recycler. Lead is mined as its sulfidic ore, galena, which is often associated with zinc and silver. The ore typically is concentrated, and partially separated, on site by crushing and differential froth flotation of the ore minerals before being sent to a primary smelter. Besides lead, zinc and iron are also present in the airborne dusts, together with insignificant levels of copper and silver, and, in one area, manganese. The disposal of used lead-acid batteries presents environmental issues, and is also a waste of recoverable materials. Recycling operations allow for the recovery of lead, which can then be sold back to battery manufacturers to form a closed loop. At the recycling facility lead is the chief airborne metal, together with minor antimony and tin, but several other metals are generally present in much smaller quantities, including copper, chromium, manganese and cadmium. Samplers used in these studies included the closed-face 37 mm filter cassette (the current US standard method for lead sampling), the 37 mm GSP or "cone" sampler, the 25 mm Institute of Occupational Medicine (IOM) inhalable sampler, the 25 mm Button sampler, and the open-face 25 mm cassette. Mixed cellulose-ester filters were used in all samplers. The filters were analyzed after sampling for their content of the various metals, particularly lead, that could be analyzed by the specific portable X-ray fluorescence (XRF) analyzer under study, and then were extracted with acid and analyzed by inductively coupled plasma optical emission spectroscopy (ICP-OES). The 25 mm filters were analyzed using a single XRF reading, while three readings on different parts of the filter were taken from the 37 mm filters. For lead at the mine concentrate mill, all five samplers gave good correlations (r2 > 0.96) between the two analytical methods over the entire range of found lead mass, which encompassed the permissible exposure limit of 150 mg m(-3) enforced in the USA by the Mine Safety and Health Administration (MSHA). Linear regression on the results from most samplers gave almost 1 ratio 1 correlations without additional correction, indicating an absence of matrix effects from the presence of iron and zinc in the samples. An approximately 10% negative bias was found for the slope of the Button sampler regression, in line with other studies, but it did not significantly affect the accuracy as all XRF results from this sampler were within 20% of the corresponding ICP values. As in previous studies, the best results were obtained with the GSP sampler using the average of three readings, with all XRF results within 20% of the corresponding ICP values and a slope close to 1 (0.99). Greater than 95% of XRF results were within 20% of the corresponding ICP values for the closed-face 37 mm cassette using the OSHA algorithm, and the IOM sampler using a sample area of 3.46 cm2. As in previous studies, considerable material was found on the interior walls of all samplers that possess an internal surface for deposition, at approximately the same proportion for all samplers. At the lead-acid battery recycler all five samplers in their optimal configurations gave good correlations (r2 > 0.92) between the two analytical methods over the entire range of found lead mass, which included the permissible exposure limit enforced in the USA by the Occupational Safety and Health Administration (OSHA). Linear regression on the results from most samplers gave almost 1 ratio 1 correlations (except for the Button sampler), indicating an absence of matrix effects from the presence of the smaller quantities of the other metals in the samples. A negative bias was found for the slope of the button sampler regression, in line with other studies. Even though very high concentrations of lead were encountered (up to almost 6 mg m(-3)) no saturation of the detector was observed. Most samplers performed well, with >90% of XRF results within +/- 25% of the corresponding ICP results for the optimum configurations. The OSHA algorithm for the CFC worked best without including the back-up pad with the filter.     

Evaluation of the Chemcatcher and DGT passive samplers for monitoring metals with highly fluctuating water concentrations

Passive sampling devices accumulate chemicals continuously from water and can provide time weighted average (TWA) concentrations of pollutants over the exposure period. Hence, they offer a number of advantages over other conventional monitoring techniques such as spot or grab sampling. The diffusive gradient in thin film (DGT) and the Chemcatcher passive samplers can be used to provide TWA concentrations of labile metals, but the approaches to their calibration differ. DGT uses diffusion coefficients of metals in the hydrogel layer, whereas Chemcatcher uses metal specific uptake rates, with both sets of values obtained under controlled laboratory conditions with constant aqueous metal concentrations. However, little is known of how such samplers respond to fluctuating concentrations. We evaluated the responsiveness of these two passive sampling devices to rapidly changing concentrations of Cd, Cu, Ni, Pb and Zn in natural freshwater, over a relatively short deployment time. Maximum metal concentrations in water were varied between 70 and 140 microg L(-1). Experiments were carried out in a tank with a rotating carousel system and filled with Meuse river water, allowing a degree of control over experimental conditions while using natural river water. Fluctuating concentrations were obtained by stepwise addition of standard solutions of the metals. The reliability and accuracy of the TWA concentrations measured by the samplers were assessed by comparison with concentrations of the metals in spot samples of water taken regularly over the deployment period. The spot samples of water were either unfiltered (total), filtered (0.45 microm) or ultrafiltered (5 kDa). Predictive speciation modelling using the visual MINTEQ programme was also undertaken. There was reasonable agreement between the TWA concentrations of Cd and Ni obtained with Chemcatcher and DGT and the total Cd and Ni concentrations measured in repeated unfiltered spot samples. For elements (i.e. Cu, Pb, Zn) that associate to a significant degree with suspended solids, colloids or dissolved organic carbon, or form complexes with large organic ligands, optimum agreement was with the filtered or ultrafiltered fractions and with the predicted inorganic and inorganic-fulvic acid associated fractions. While Chemcatcher-based TWA concentration ranges for Cu and Zn were in best agreement with the total filtered fraction, there was lack of agreement for Pb. The combined use of DGT devices with open pore (OP) and restricted pore (RP) gels allowed the labile fraction of metal associated with large organic ligands or DOC to be differentiated and quantified, since this is available to DGT OP but unable to diffuse into the DGT RP. This evaluation of the two sampling devices clearly demonstrated their ability to react reliably to transient peaks in concentration of metal pollutants in water and indicated where future efforts are needed to improve calibration data. Such samplers may prove valuable in responding to the monitoring requirements of the European Union's Water Framework Directive.     

A passive sampling method to determine ammonia in ambient air

Ambient ammonia concentrations, mainly originating from agricultural activities, have increased in the last few decades in Europe. As a consequence, critical loads on oligotrophic ecosystems such as forests and mires are greatly exceeded. Monitoring of ambient ammonia concentrations is necessary in order to investigate source-receptor relationships. Measuring ambient ammonia concentrations continuously with high time resolution is very expensive and cost-efficient systems are required. Where time resolution is of minor importance, several cost-effective systems, mainly dry denuder and passive samplers, can be applied. In this paper the Zürcher passive sampler, a diffusive sampling system, is presented. It is a Palmes type sampler with an acidic solution as absorbent and is easy to handle. It was tested at 46 sites in Switzerland over one year. The average concentration in ambient air was 2.5 microg m(-3) +/- 0.4 microg m(-3). The average of the blank values were 0.21 microg m(-3). The detection limit (double the standard deviation of the blank values) was 0.36 microg m(-3). Three passive samplers were exposed at each site and each period. The mean standard deviation of these triplicate measurements was 9.5%. Compared with a discontinuous tubular denuder system and a continuous annular denuder system, the deviation was less than 10%. The Zürcher passive sampler is a useful and cost-efficient tool to determine long-term average ammonia concentrations (one- to four-week periods) in ambient air for mean concentrations above 1 microg m(-3).