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This investigation aims to assess the levels of human exposure to airborne particulate matter (PM) in various locations of a natural stone quarry for the first time based on simultaneous measurements of both PM mass and number concentrations (PMC and PNC). A quarry located in Danang city, Vietnam, considered to be a "hotspot" of air pollution in the city, was selected for detailed investigations. Both PMC and PNC were found to be significantly higher (1.2-6.0 times) within the quarry compared to surrounding areas. Mechanical activities during mining, notably crushing, screening, hauling, and loading stones, contributed to increased emissions of PM in the coarser mode (1-10 μm) compared to the accumulation mode (0.1-1 μm) and thus increased deposition of PM 1-10 in the human upper respiratory tract. In contrast, combustion activities, especially the diesel engine exhaust from various machines and vehicles used in the quarry, resulted in increased emissions of small particles in the accumulation mode that dominated the PNC and in their deposition in the lower respiratory tract. Simultaneous measurements of PNC and PMC revealed that the PM counts were strongly associated with PM deposition in the alveolar region (accounting for ≈ 76% of total PNC of particles less than 10 μm, N 10 ), while the PM mass concentration was a better indicator of the deposition of PM in the head airway region (≈92% of total PMC of PM 10 ). Overall, this study demonstrates the significance of measuring both PNC and PMC to assess PM exposure levels, regional respiratory doses, and potential health effects associated with human exposure to PM generated from stone quarrying activities. The novelty of this work is the integration of real-time mass and number concentrations of PM over the size range from 20 nm to 10 μm to provide insights into respiratory deposited doses of size-fractionated PM among quarry workers., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)

The direct impacts of climate change involve a multitude of phenomena, including rising sea levels, intensified severe weather events such as droughts and flooding, increased temperatures leading to wildfires, and unpredictable fluctuations in rainfall. This comprehensive review intends to examine firstly the probable consequences of climate change on extreme weather events such as drought, flood and wildfire. This review subsequently examines the release and transformation of contaminants in terrestrial, aquatic, and atmospheric environments in response to extreme weather events driven by climate change. While drought and flood influence the dynamics of inorganic and organic contaminants in terrestrial and aquatic environments, thereby influencing their mobility and transport, wildfire results in the release and spread of organic contaminants in the atmosphere. There is a nascent awareness of climate change's influence of climate change-induced extreme weather events on the dynamics of environmental contaminants in the scientific community and decision-making processes. The remediation industry, in particular, lags behind in adopting adaptive measures for managing contaminated environments affected by climate change-induced extreme weather events. However, recognizing the need for assessment measures represents a pivotal first step towards fostering more adaptive practices in the management of contaminated environments. We highlight the urgency of collaboration between environmental chemists and climate change experts, emphasizing the importance of jointly assessing the fate of contaminants and rigorous action to augment risk assessment and remediation strategies to safeguard the health of our environment., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier B.V. All rights reserved.)

Silver (Ag), a naturally occurring, rare and precious metal, is found in major minerals such as cerargyrite (AgCl), pyrargyrite (Ag 3 SbS 3 ), proustite (Ag 3 AsS 3 ), and stephanite (Ag 5 SbS 4 ). From these minerals, Ag is released into soil and water through the weathering of rocks and mining activities. Silver also enters the environment by manufacturing and using Ag compounds in electroplating and photography, catalysts, medical devices, and batteries. With >400 t of Ag NPs produced yearly, Ag NPs have become a rapidly growing source of anthropogenic Ag input in the environment. In soils and natural waters, most Ag is sorbed to soil particles and sediments and precipitated as oxides, carbonates, sulphides, chlorides and hydroxides. Silver and its compounds are toxic, and humans and other animals are exposed to Ag through inhalation of air and the consumption of Ag-contaminated food and drinking water. Remediation of Ag-contaminated soil and water sources can be achieved through immobilization and mobilization processes. Immobilization of Ag in soil and groundwater reduces the bioavailability and mobility of Ag, while mobilization of Ag in the soil can facilitate its removal. This review provides an overview of the current understanding of the sources, geochemistry, health hazards, remediation practices and regulatory mandates of Ag contamination in complex environmental settings, including soil and aquatic ecosystems. Knowledge gaps and future research priorities in the sustainable management of Ag contamination in these settings are also discussed., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Adsorption is the most widely adopted, effective, and reliable treatment process for the removal of inorganic and organic contaminants from wastewater. One of the major issues with the adsorption-treatment process for the removal of contaminants from wastewater streams is the recovery and sustainable management of spent adsorbents. This review focuses on the effectiveness of emerging adsorbents and how the spent adsorbents could be recovered, regenerated, and further managed through reuse or safe disposal. The critical analysis of both conventional and emerging adsorbents on organic and inorganic contaminants in wastewater systems are evaluated. The various recovery and regeneration techniques of spent adsorbents including magnetic separation, filtration, thermal desorption and decomposition, chemical desorption, supercritical fluid desorption, advanced oxidation process and microbial assisted adsorbent regeneration are discussed in detail. The current challenges for the recovery and regeneration of adsorbents and the methodologies used for solving those problems are covered. The spent adsorbents are managed through regeneration for reuse (such as soil amendment, capacitor, catalyst/catalyst support) or safe disposal involving incineration and landfilling. Sustainable management of spent adsorbents, including processes involved in the recovery and regeneration of adsorbents for reuse, is examined in the context of resource recovery and circular economy. Finally, the review ends with the current drawbacks in the recovery and management of the spent adsorbents and the future directions for the economic and environmental feasibility of the system for industrial-scale application., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Biochar has been increasingly used as a filter medium in engineered low impact development systems (e.g., bioretention systems) for decontamination of urban stormwater and management of hydrology. This review paper critically analyzes the performance of biochar-based biofiltration systems for removal of chemical and microbial pollutants present in urban runoff. Biochar-amended biofiltration systems efficiently remove diverse pollutants such as total nitrogen (32 - 61%), total phosphorus: (45 - 94%), heavy metals (27 - 100%), organics (54 - 100%) and microbial pollutants (log 10 removal: 0.78 - 4.23) from urban runoff. The variation of biofiltration performance is due to changes in biochar characteristics, the abundance of dissolved organic matter and/or stormwater chemistry. The dominant mechanisms responsible for removal of chemical pollutants are sorption, ion exchange and/or biotransformation, whereas filtration/straining is the major mechanism for bacteria removal. The pseudo-second order and Langmuir isotherm are the best models that describe the kinetics and chemical equilibrium of pollutants, respectively. This critical review provides the fundamental scientific knowledge for designing highly efficient biochar-based bioretention systems for removal of diverse pollutants from urban stormwater. The key knowledge gaps that should be addressed in future research include long-term field-scale bioretention study, development of novel methods for filter media regeneration/reuse, and dynamics of filter media microbial communities., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Black carbon (BC), an important indicator of traffic-related air pollution (TRAP) in urban environments, is receiving increased attention because of its adverse health effects. Personal exposure (PE) of adults to BC has been widely studied, but little is known about the exposure of young children (toddlers) to BC in cities. We carried out a pilot study to investigate the integrated daily PE of toddlers to BC in a city-state with a high population density (Singapore). We studied the impact of urban traffic on the PE of toddlers to BC by comparing and contrasting on-road traffic flow (i.e., volume and composition) in Singapore in 2019 (before the COVID-19 pandemic) and in 2020 (during the COVID-19 pandemic). Our observations indicate that the daily BC exposure levels and inhaled doses increased by about 25% in 2020 (2.9 ± 0.3 μg m -3 and 35.5 μg day -1 ) compared to that in 2019 (2.3 ± 0.4 μg m -3 and 28.5 μg day -1 for exposure concentration and inhaled dose, respectively). The increased BC levels were associated with the increased traffic volume on both weekdays and weekends in 2020 compared to the same time period in 2019. Specifically, we observed an increase in the number of trucks as well as cars/taxis and motorcycles (private transport) and a decline in the number of buses (public transport) in 2020. The implementation of lockdown measures in 2020 resulted in significant changes in the time, place and duration of PE of toddlers to BC. The recorded daily time-activity patterns indicated that toddlers spent almost all the time in indoor environments during the measurement period in 2020. When we compared different ventilation options (natural ventilation (NV), air conditioning (AC), and portable air cleaner (PAC)) for mitigation of PE to BC in the home environment, we found a significant decrease (>30%) in daily BC exposure levels while using the PAC compared to the NV scenario. Our case study shows that the PE of toddlers to BC is of health concern in indoor environments in 2020 because of the migration of the increased TRAP into naturally ventilated residential homes and more time spent indoors than outdoors. Since toddlers' immune system is weak, technological intervention is necessary to protect their health against inhalation exposure to air pollutants., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Smoke haze episodes, resulting from uncontrolled biomass burning (BB) including forest and peat fires, continue to occur in Southeast Asia (SEA), affecting air quality, atmospheric visibility, climate, ecosystems, hydrologic cycle and human health. The pollutant of major concern in smoke haze is airborne particulate matter (PM). A number of fundamental laboratory, field and modeling studies have been conducted in SEA from 2010 to 2020 to investigate potential environmental and health impacts of BB-induced PM. The goal of this review is to bring together the most recent developments in our understanding of various aspects of BB-derived PM based on 127 research articles published from 2010 to 2020, which have not been conveyed in previous reviews. Specifically, this paper discusses the physical, chemical, toxicological and radiative properties of BB-derived PM. It also provides insights into the environmental and health impacts of BB-derived PM, summarizes the approaches taken to do the source apportionment of PM during BB events and discusses the mitigation of exposure to BB-derived PM. Suggestions for future research priorities are outlined. Policies needed to prevent future BB events in the SEA region are highlighted., (Copyright © 2020 Elsevier B.V. All rights reserved.)

During the 2019 smoke haze episode in Singapore, elevated levels of fine particulate matter (PM 2.5 ) were observed, deteriorating both ambient and indoor air quality (IAQ). We investigated the mitigation of indoor human exposure to PM 2.5 of outdoor origin under diverse exposure scenarios with and without filtration of PM 2.5 during both hazy and non-hazy days. The key objective of our study was to make a comparative evaluation of the effectiveness of portable air cleaners (PACs) and air conditioning (AC) systems equipped with particle filters in improving IAQ and to assess related long-term carcinogenic and non-carcinogenic health risks. We conducted real-time measurements of PM 2.5 , black carbon mass concentrations and particle number concentrations in both indoor and outdoor areas, quantified the relative concentrations of the water-soluble fraction of toxic trace elements in PM 2.5 for health risk assessment, and estimated the levels of thermal comfort. In addition, we calculated the total estimated cost of indoor air pollution control. Our findings suggest that indoor air cleaners are more effective at mitigating human exposure to airborne particles and reducing health risk with less consumption of electricity and better cost-effectiveness compared to AC. This information would be beneficial for public health interventions during major air pollution events., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Gas cooking is an important source of airborne particulate matter (PM) indoors. Exposure to cooking-derived PM can lead to adverse human health impacts on non-smokers, especially in poorly-ventilated residential homes. Most of the previous studies on gas cooking emissions mainly focused on fine particles (PM 2.5 ) with little information on their size-fractionation. Moreover, studies dealing with mitigation of indoor human exposure to cooking-derived PM are currently sparse. Therefore, a systematic study was conducted to investigate the characteristics of PM 2.5 and size-fractionated PM derived from five commonly used cooking methods, namely, steaming, boiling, stir-frying, pan-frying and deep-frying in a poorly-ventilated domestic kitchen under controlled experimental conditions. Additionally, an indoor portable air cleaner was employed as a mitigation device to capture cooking-derived PM and improve indoor air quality (IAQ). Results revealed that the oil-based deep-frying cooking released the highest airborne particles which were about 170 folds higher compared to the baseline levels for PM 2.5 mass concentrations. The use of the air cleaner showed a statistically significant (p < 0.05) reduction in the indoor PM 2.5 levels. Moreover, PM <0.25 (particles with diameter ≤ 250 nm) showed a very high mass concentration (378.2 μg/m 3 ) during deep-frying, raising human health concern. A substantial reduction (~60-85%) in PM <0.25 mass concentrations and their total respiratory deposition doses (RDD) in the human respiratory tract was observed while using the air cleaner during the five cooking methods. Furthermore, morphological characteristics and the relative abundance of trace elements in cooking-derived PM were also investigated. This study provides useful insights into the assessment and mitigation of indoor human exposure to cooking-derived PM., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Toxic particulate elements present in cigarette smoke pose health threats to the life of smokers due to direct inhalation and at the same time increase health risks to non-smokers present in the vicinity of smokers because of their exposure. This study conducted a series of experiments using a controlled experimental chamber, equipped with simulated smoking conditions for characterization of particulate trace elements in mainstream and sidestream cigarette smoke. Four popular commercial cigarette brands available in Singapore market were used in this study. The target elements for extraction and analysis were Al, As, B, Ba, Be, Bi, Ca, Cd, Co, Cr, Cs, Cu, Fe, Ga, Hg, K, Li, Mg, Mn, Na, Ni, Pb, Rb, Se, Sn, Sr, Te, Tl and Zn of both water-soluble and total constituents. The human health risk assessment results showed that the sidestream smoke had higher concentrations of toxic elements than those in the mainstream smoke. However, risk assessment analysis revealed that the sidestream smoke resulted in less human health risks compared to the mainstream smoke due to the influence of dilution of particulate emissions in sidestream smoke prior to inhalation exposure experienced by non-smokers. The cumulative non-cancer and cancer risks of toxic elements varied from 2.0 to 3.1 and from 398.4×10(-6) to 626.1×10(-6) due to inhalation of cigarette smoke by an active smoker. In the case of non-smokers, the risks were estimated under three possible cases of exposure. The cumulative cancer risks under three different cases were greater than the permissible limits. Therefore, it could be concluded that the toxic particulate elements present in cigarette smoke have significant carcinogenic and non-carcinogenic health effects due to inhalation exposure in the environment., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Adsorption technology is widely considered as the most promising and robust method of purifying water at low cost and with high-efficiency. Carbon-based materials have been extensively explored for adsorption applications because of their good chemical stability, structural diversity, low density, and suitability for large scale production. Graphene--a single atomic layer of graphite--is the newest member in the family of carbon allotropes and has emerged as the "celeb" material of the 21st century. Since its discovery in 2004 by Novoselov, Geim and co-workers, graphene has attracted increased attention in a wide range of applications due to its unprecedented electrical, mechanical, thermal, optical and transport properties. Graphene's infinitely high surface-to-volume ratio has resulted in a large number of investigations to study its application as a potential adsorbent for water purification. More recently, other graphene related materials such as graphene oxide, reduced graphene oxide, and few-layered graphene oxide sheets, as well as nanocomposites of graphene materials have also emerged as a promising group of adsorbent for the removal of various environmental pollutants from waste effluents. In this review article, we present a synthesis of the current knowledge available on this broad and versatile family of graphene nanomaterials for removal of dyes, potentially toxic elements, phenolic compounds and other organic chemicals from aquatic systems. The challenges involved in the development of these novel nanoadsorbents for decontamination of wastewaters have also been examined to help identify future directions for this emerging field to continue to grow., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Combustion experiments were conducted to evaluate the effects of using blends of ultralow sulfur diesel (ULSD) with biodiesel or n-butanol on physicochemical and toxicological characteristics of particulate emissions from a non-road diesel engine. The results indicated that compared to ULSD, both the blended fuels could effectively reduce the particulate mass and elemental carbon emissions, with butanol being more effective than biodiesel. The proportion of organic carbon and volatile organic compounds in particles increased for both blended fuels. However, biodiesel blended fuels showed lower total particle-phase polycyclic aromatic hydrocarbons (PAHs) emissions. The total number emissions of particles ≤560nm in diameter decreased gradually for the butanol blended fuels, but increased significantly for the biodiesel blended fuels. Both the blended fuels indicated lower soot ignition temperature and activation energy. All the particle extracts showed a decline in cell viability with the increased dose. However, the change in cell viability among test fuels is not statistically significant different with the exception of DB-4 (biodiesel-diesel blend containing 4% oxygen) used at 75% engine load., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Aerosol acidity is one of the most important parameters that can influence atmospheric visibility, climate change and human health. Based on continuous field measurements of inorganic aerosol species and their thermodynamic modeling on a time resolution of 1h, this study has investigated the acidic properties of PM2.5 and their relation with the formation of secondary inorganic aerosols (SIA). The study was conducted by taking into account the prevailing ambient temperature (T) and relative humidity (RH) in a tropical urban atmosphere. The in-situ aerosol pH (pH(IS)) on a 12h basis ranged from -0.20 to 1.46 during daytime with an average value of 0.48 and 0.23 to 1.53 during nighttime with an average value of 0.72. These diurnal variations suggest that the daytime aerosol was more acidic than that caused by the nighttime aerosol. The hourly values of pH(IS) showed a reverse trend as compared to that of in-situ aerosol acidity ([H(+)]Ins). The pH(IS) had its maximum values at 3:00 and at 20:00 and its minimum during 11:00 to 12:00. Correlation analyses revealed that the molar concentration ratio of ammonium to sulfate (R(N/S)), equivalent concentration ratio of cations to anions (RC/A), T and RH can be used as independent variables for prediction of pH(IS). A multi-linear regression model consisting of RN/S, RC/A, T and RH was developed to estimate aerosol pH(IS)., (Copyright © 2013 Elsevier B.V. All rights reserved.)

The presence of bacterial pathogens in airborne particulate matter (PM) has been of considerable concern from the public health standpoint. Conventional culture-based methods are tedious, time consuming and are unable to quantify stressed viable but non-culturable (VBNC) populations of these pathogens. This study reports the optimization, validation and application of a new and rapid quantitative method for enumeration of four live potential Gram-negative bacterial pathogens (Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Aeromonas hydrophila) in PM of biomass burning origin. This method makes use of an intercalating dye (propidium monoazide, PMA) in conjunction with real-time PCR (qPCR) analysis following DNA extraction from PM samples for distinguishing viable from non-viable potential bacterial pathogens. This method was not affected by the complex matrix of the environmental samples, nor by any PCR inhibition effects. The number of viable pathogens ranged from 0 to 8×10(4) gene copies/m(3) in PM. With the exception of A. hydrophilia, all the three pathogens were found to be present in PM. The correlation between the counts obtained using the PMA-qPCR (modified qPCR) and those from the culture-based method was very high with R(2)~1.0 and p value<0.0001., (Copyright © 2013 Elsevier B.V. All rights reserved.)

The occurrences of increased atmospheric nitrogen deposition (ADN) in Southeast Asia during smoke haze episodes have undesired consequences on receiving aquatic ecosystems. A successful prediction of episodic ADN will allow a quantitative understanding of its possible impacts. In this study, an artificial neural network (ANN) model is used to estimate atmospheric deposition of total nitrogen (TN) and organic nitrogen (ON) concentrations to coastal aquatic ecosystems. The selected model input variables were nitrogen species from atmospheric deposition, Total Suspended Particulates, Pollutant Standards Index and meteorological parameters. ANN models predictions were also compared with multiple linear regression model having the same inputs and output. ANN model performance was found relatively more accurate in its predictions and adequate even for high-concentration events with acceptable minimum error. The developed ANN model can be used as a forecasting tool to complement the current TN and ON analysis within the atmospheric deposition-monitoring program in the region., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

A cloud point extraction method has been developed using an ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate, BMiM PF(6)) for the determination of a widely studied cyanotoxin (microcystin leucine-arginine, MCLR) in natural waters. Extraction parameters such as sample pH, extraction temperature, extraction time, the amount of ionic liquid and the amount of extraction volume were investigated and optimized to achieve the maximum extraction efficiency. The results obtained indicated a good linearity with the correlation coefficient of 0.995 over the range of 0.5-50 μg L(-1). The relative standard deviation (RSD) of the method was 7.5% (n=6). The calculated method detection limit was 0.03 μg L(-1) (n=6). The practical applicability of the technique was demonstrated by analyzing water samples (n=9) collected from three different sites in local reservoirs., (Copyright © 2010 Elsevier B.V. All rights reserved.)

A simple and rapid extraction procedure was developed for determining aldehydes in rainwater samples. This extraction technique involved the use of micro-solid-phase extraction in which the sorbent was held within a polypropylene membrane envelope, followed by high-performance liquid chromatographic analysis. Aldehydes such as formaldehyde, acetaldehyde, propionaldehyde and valeraldehyde were used as model compounds. Extraction conditions were optimized. The method linearity ranged between 0.5 and 50 μgl(-1) with the correlation coefficient of 0.987-0.999. The relative standard deviations (RSDs) of the method ranged from 7 to 12%. Method detection limits were in the range of 0.07-0.15 μgl(-1), which is lower than those previously reported for solid-phase microextraction combined with gas chromatography-mass spectrometric techniques. The proposed extraction technique was used for determination of aldehydes in rainwater samples to demonstrate the applicability of the method., (Copyright © 2010 Elsevier B.V. All rights reserved.)

A microwave-assisted persulfate oxidation method followed by ion chromatographic determination of nitrate was developed for total nitrogen determination in atmospheric wet and dry deposition samples. Various operating parameters such as oxidation reagent concentrations, microwave power, and extraction time were optimized to maximize the conversion of total nitrogen to nitrate for subsequent chemical analysis. Under optimized conditions, 0.012 M K(2)S(2)O(8) and 0.024 M NaOH were found to be necessary for complete digestion of wet and dry deposition samples at 400 W for 7 min using microwave. The optimized extraction method was then validated by testing different forms of organic nitrogen loaded to pre-baked filter substrates and NIST SRM 1648 (urban particulate matter), and satisfactory results were obtained. In the case of wet deposition samples, standard addition experiments were performed. The suitability of the method for real-world application was assessed by analyzing a number of wet and dry deposition samples collected in Singapore during the period of March-April 2007. The organic nitrogen content was 15% (wet) and 30% (dry) of the total nitrogen. During the study period, the estimated wet fluxes for nitrate (NO(3)(-)), ammonium (NH(4)(+)), organic nitrogen (ON), and total nitrogen (TN) were 16.1+/-6.5 kg ha(-1)year(-1), 11.5+/-5.7 kg ha(-1)year(-1), 3.8+/-1.5 kg ha(-1)year(-1)and 31.5+/-13.2 kg ha(-1)year(-1), respectively, while the dry fluxes were 2.5+/-0.8 kg ha(-1)year(-1), 1.4+/-0.9 kg ha(-1)year(-1), 2.3+/-1.4 kg ha(-1)year(-1) and 7.5+/-2.6 kg ha(-1)year(-1), respectively.

For the first time hollow fiber-protected ionic liquid supported three-phase (liquid-liquid-liquid) microextraction (HFM-LLLME) was developed for the gas chromatography-mass spectrometric (GC-MS) analysis of aromatic and aliphatic hydrocarbons. The hydrocarbons were extracted from 10 ml of aqueous samples though small volumes of ionic liquid and organic solvent in the hollow fiber membrane HFM) wall and channel, respectively. The ionic liquid was immiscible with both the aqueous sample and the organic solvent (toluene). After extraction, the enriched solvent was directly injected into a GC-MS system for analysis without any further pretreatment. Ionic liquid supported HFM-LLLME shows better extraction performance than two-phase HFM-liquid-phase microextraction, in which only organic solvent is involved, and solid-phase microextraction. The ionic liquid and organic solvent combination found most suitable for HFM-LLLME was 1-butyl-3-methylimidazolium hexafluorophosphate, and toluene, respectively. This new technique provided up to 210-fold enrichment of aliphatic and aromatic hydrocarbons in 40 min with good reproducibility (<11%) and limits of detection (1-7 ng l(-1)).

The feasibility of using two different microwave-based sample preparation methods was investigated to determine the total and water-soluble trace metal fraction in airborne particulate matter. The extraction techniques were then applied to urban particulate matter of different sizes in order to evaluate their bioavailability of associated trace metals. While a combination of HNO3-HF-H2O2 was used for the total trace metal fraction of particulate matter, water was employed for the microwave-assisted extraction of water-soluble trace metal fractions. Inductively coupled plasma-mass spectrometry (ICP-MS) was used for the analysis of trace elements. The experimental protocol for the microwave assisted digestion was established using two different SRMs (1648, urban particulate matter and 1649a, urban dust). In the case of water-soluble trace metal fraction, the quantities extracted from the SRMs were compared between ultrasonic and microwave-assisted extractions, and there was a good agreement between the two extraction methods. Blanks values and limits of detection (LODs) for total and water-soluble trace metal concentrations were determined for three different filter substrates (Teflon, Zeflour, and Quartz). Subsequently, the proposed digestion method was evaluated for its extraction efficiency with these filter substrates. Finally, the real-world application of the proposed microwave-based sample preparation methods was demonstrated by analyzing trace elements in airborne particulate samples collected from different outdoor environments in Singapore. The solubility of 11 trace elements detected in the particulate samples is quantified.

This is the first publication which describes the development of a reference material (RM) for the determination of 11 trace elements (Cu, Pb, Mn, Ni, Zn, Fe, Cd, Co, V, As and Al) in rainwater at microgram per liter concentrations. An interlaboratory comparison study for the determination of trace elements in rainwater was carried out for material performance studies to establish analyte concentrations with a stated uncertainty. Fifteen reputed laboratories from Asia, Europe and North America participated in the study. These laboratories used their regular in-house methods to analyze the rainwater samples. The aim of this study is to establish concentration levels of trace elements in rainwater based on interlaboratory study results. Details of the production, homogeneity and stability of the reference sample are given in this article. The organization of the study and the quality assurance measures undertaken at the organizer's laboratory are described. The analytical results obtained from individual laboratories and the analytical methods used for the determination of trace elements in rainwater are discussed. Based on the results obtained from the intercomparison study, certified values as well as informative values are assigned to the 11 trace elements in rainwater.

A low temperature microwave-assisted extraction method (MAE) is reported for the analysis of polycyclic aromatic hydrocarbons (PAHs) in airborne particulate matter (PM). The main parameters affecting the extraction efficiency (choice of extractants, microwave power, and extraction time) were investigated and optimized. The optimized procedure requires a 20 ml mixture of acetone:n-hexane (1:1) for extraction of PAHs in PM at 150W of microwave energy (20 min extraction time). Clean-up of MAE extracts was not found to be necessary. The optimized method was validated using two different SRM (1648-urban particulate matter and 1649a, urban dust). The results obtained are in good agreement with certified values. PAHs recoveries for both reference materials were between 79 and 122% with relative standard deviation ranging from 3 to 21%. Detection limits were determined based on blank determination using two kinds of quartz filter substrates (n=10), which ranged from 0.001 (0.03) ng m(-3)(pg/microg) for B(k)Ft to 1.119 (37.3) for Naph in ng m(-3) (pg/microg), respectively. The repeatability and day-to-day reproducibility obtained in this study were in the range of 4-16 and 3-25% for spiked standards and SRM 1649, respectively. The optimized and validated MAE technique was applied to the extraction of PAHs from a set of real world PM samples collected in Singapore. The sum of particulate-bound PAHs in outdoor PM ranged from 1.05 to 3.45 ng m(-3) while that in indoor PM (cooking emissions) ranged from 27.6 to 75.7 ng m(-3), respectively.

A simple and rapid liquid-phase microextraction (LPME) method using a hollow fiber membrane (HFM) in conjunction with gas chromatography-mass spectrometry (GC-MS) is presented for the quantitative determination of 16 polycyclic aromatic hydrocarbons (PAHs) and 12 organochlorine pesticides (OCPs) in rainwater samples. The LPME conditions were optimized for achieving high enrichment of the analytes from aqueous samples, in terms of hollow fiber exposure time, stirring rate, sample pH, and composition. Enrichment factors of more than 100 could be achieved within 35 min of extraction with relative standard deviations (R.S.D.s) 1.3-13.6% for PAHs and 1.7-13.8% for OCPs, respectively, over a wide range of analyte concentrations. Detection limits ranged from 0.002 to 0.047 microg l(-1) for PAHs, and from 0.013 to 0.059 microg l(-1) for OCPs, respectively. The newly developed LPME-GC-MS method has been validated for the analysis of PAHs and OCPs in rainwater samples. Extraction recoveries from spiked synthetic rainwater samples varied from 73 to 115% for PAHs and from 75 to 113% for OCPs, respectively. Real rainwater samples were analyzed using the optimized method. The concentrations of PAHs and OCPs in real rainwater samples were between 0.005-0.162, and 0.063 microg l(-1), respectively.