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Excess nitrogen in stormwater degrades surface water quality via eutrophication and related processes. Bioretention has been recognized as a highly effective low-impact development (LID) technology for the management of high runoff volumes and reduction of nitrogen (N) pollutants through various mechanisms. This paper provides a comprehensive and critical review of recent developments on the biological N removal processes occurring in bioretention systems. The key plant- and microbe-mediated N transformation processes include assimilation (N uptake by plants and microbes), nitrification, denitrification, and anammox (anaerobic ammonia oxidation), but denitrification is the major pathway of permanent N removal. Overall, both laboratory- and field-scale bioretention systems have demonstrated promising N removal performance (TN: >70%). The phyla Bacteroidetes and Proteobacteria are the most abundant microbial communities found to be enriched in biofilter media. Furthermore, the denitrifying communities contain several functional genes (e.g., nirK/nirS, and nosZ), and their concentrations increase near the surface of media depth. The N removal effectiveness of bioretention systems is largely impacted by the hydraulics and environmental factors. When a bioretention system operates at: low hydraulic/N loading rate, containing a saturation zone, vegetated with native plants, having deeper and multilayer biofilter media with warm climate temperature and wet storm events periods, the N removal efficiency can be high. This review highlights shortcomings and current knowledge gaps in the area of total nitrogen removal using bioretention systems, as well as identifies future research directions on this topic. [ABSTRACT FROM AUTHOR]

Bioleaching has emerged as a green technology with promising applications in mining industries in the context of recovery of precious metals from mineral ores. The authors synthesize the current knowledge available in the bioleaching of gold (Au) from ores by bringing together historical developments and recent endeavors. In addition, the role of the microbial community in the bio-oxidation of refractory ores for removal of base metal impurities and in the recovery of Au based on biocyanidation is reviewed. They also address the future research directions in the bioleaching of Au in order to make further advances toward practical industrial applications. [ABSTRACT FROM PUBLISHER]

Cyanobacterial toxins are considered as an emerging threat to natural water reservoirs and drinking water supplies. When they are ingested, these toxins are responsible for human and animal poisonings. The main goal of water quality monitoring programs is to predict harmful algal blooms and maintain the water quality of drinking water supplies. The current methods used for routine monitoring are not able to detect all the types and variants of cyanotoxins. The authors review the current state of the knowledge in detecting cyanotoxins in the environmental water samples and provides a comparative evaluation of methods ranging from conventional biological and analytical methods to recently advancing molecular and biosensor approaches in terms of their capabilities. In addition, the recent advances made in the area of cyanotoxins detection by molecular methods and biosensor-based technologies are discussed for their practical applications in terms of their use in a total analysis system. [ABSTRACT FROM PUBLISHER]

An accelerated solvent extraction (ASE) method has been developed for the determination of polycyclic aromatic hydrocarbons (PAHs) present in both atmospheric particulate and gaseous phases in this study. Extraction parameters such as the combination of solvents, extraction temperature, and static extraction time were investigated and optimized. Effective extraction was achieved using a 3:1 mixture of n-hexane and acetone as extraction solvents at 100°C in 30 min for all the compounds studied. The optimized extraction method was compared with conventional extraction methods and validated using National Institute of Standards and Technology (NIST)-certified standard reference material (SRM) 1649a. The recoveries obtained for certified 12 PAHs were in the range of 82-126% with relative standard deviation (RSD) between 6 and 28%. The validated ASE technique was used followed by gas chromatography-mass spectrometry (GC-MS) for the determination of PAHs distributed between gaseous and particulate phases in the atmosphere of Singapore. Total average concentrations of PAHs in air samples were 33.54 ± 19.32 ng m-3, with 4.72 ± 2.80 ng m-3 in particulate phase and 28.82 ± 16.92 ng m-3 in gaseous phase, respectively. The results obtained from this study are compared to those reported from other areas of the world. [ABSTRACT FROM AUTHOR]

Abstract: Incense is habitually burned in various religious settings ranging from the Eastern temples to the Western churches and in residential homes of their devotees, representing one of the most significant sources of combustion-derived particulate matter in indoor air. Incense smoke has been known to be associated with adverse health effects, which could be due to the release of the submicron-sized particles, including ultrafine and nanoparticles. However, there is currently a lack of information available in the literature on the emission rates of particles from incense smoke in terms of their particle number, a metric generally regarded as a better indicator of health risks rather than the particle mass. In this study, real-time characterization of the size distribution and number concentration of sub-micrometer-sized particles (5.6–560nm) emitted from incense smoke was made, for the first time, for four different brands of sandalwood and aloeswood incense sticks commonly used by different religious groups. In addition, the respective emission rates were determined on hourly and mass basis based on mass balance equations. The measurements showed that the particle emission rates ranged from 5.10×1012 to 1.42×1013 h−1 or 3.66×1012 to 1.23×1013 g−1 and that the peak diameters varied from 93.1 to 143.3nm. Airborne particles in the nanometer range (5.6–50nm), in the ultrafine range (50–100nm) and in the accumulation mode range (100–560nm) accounted for 1% to 6%, 16% to 55% and 40% to 60% of the total particle counts, respectively, depending on the brand of incense sticks. To assess the potential health threat due to inhalation of particles released from incense burning, the number of particles of different sizes that can be possibly deposited in the respiratory tract were evaluated for an exposed individual based on known deposition fractions in the literature. The findings indicate that incense smoke may pose adverse health effects depending on exposure duration and intensity. [Copyright &y& Elsevier]

The assessment of the vehicular contributions to urban pollution levels is of particular importance given the current interest in the possible adverse health effects. This study focused on human exposure to diesel-engine-derived particulate matter. Diesel vehicles are known to emit fine particulate matter (PM 2.5 ) containing carcinogens such as polycyclic aromatic hydrocarbons (PAHs), and have therefore received considerable attention. In this study, the physical (mass and number concentration, and size distribution) and chemical (PAHs) properties were investigated at a major bus interchange in Singapore, influenced only by diesel exhausts. Number concentration and size distribution of particles were determined in real time, while the mass concentrations of PM 2.5 , and PAHs were measured during operating and nonoperating hours. The average mass concentrations of PM 2.5 and PAHs increased by a factor of 2.34 and 5.18, respectively, during operating hours. The average number concentration was also elevated by a factor of 5.07 during operating hours. This increase in the concentration of PM 2.5 particles and their chemical constituents during operating hours was attributable to diesel emissions from in-use buses based on the particle size analysis, correlation among PAHs, and the commonly used PAHs diagnostic ratios. To evaluate the potential health threat due inhalation of air pollutants released from diesel engines, the incremental lifetime cancer risk was also calculated for a maximally exposed individual. The findings indicate that the air quality at the bus interchange poses adverse health effects. [ABSTRACT FROM AUTHOR]

Toxicological studies have implicated trace metals adsorbed onto airborne particles as possible contributors to respiratory and/or cardiovascular inflammation. In particular, the water-soluble metal content is considered to be a harmful component of airborne particulate matter. In this work, the trace metal characteristics of airborne particulate matter, PM 2.5 , collected in Singapore from February to March 2005 were investigated with specific reference to their bioavailability. PM 2.5 mass concentrations varied between 20.9 μg/m 3 and 46.3 μg/m 3 with an average mass of 32.8 μg/m 3 . During the sampling period, there were several bushfires in Singapore that contributed to sporadic increases in the particulate air pollution, accompanied by an acrid smell and asthma-related allergies. The aerosol samples were subjected to analysis of trace elements for determining their total concentrations as well as their water soluble fractions. Our results showed an increase in concentration of several water-soluble trace metals during bushfires compared to their urban background levels in Singapore. In order to measure the human exposure to particulate air pollution, the daily respiratory uptake (DRU) of several trace metals was calculated and compared between haze and nonhaze periods. The DRU values were significantly higher for several metals, including Zn, Cu, and Fe, during bushfires. Electron paramagnetic resonance (EPR) measurements showed that the particulate samples collected during bush fires generate more toxic hydroxyl radicals (OH · ) than those in the background air, due to the presence of more soluble iron ions. [ABSTRACT FROM AUTHOR]

The article presented various reports published within the issue, which includes the papers on toxicology and environmental issues in Singapore.