Determination of emitted airborne microorganisms from a BIO-PAK wastewater treatment plant

Results of a study conducted to assess the degree of airborne microbial contamination generated by a wastewater treatment plant (WWTP) with bioreactor “BIO-PAK” closed treatment system and evaluation of the dispersion of potential pathogens are described. Over the year aerosol samples were collected simultaneously with sedimentation and impact methods from several plant sites and the surroundings. External upwind sites were used as control. Total colony-forming counts of heterotrophic psychrophilic, psychrotrophic, mesophilic, haemolytic bacteria, as well as members of the Enterobacteriaceae family, Staphylococcus, Enterococcus and Pseudomonas genera, actinomycetes and fungi (moulds, yeasts and yeast-like fungi) were determined. Their highest concentrations ranged up to 10¹-10³ CFU/m³ (with the exception of moulds exceeding 2 × 10⁴) were determined in air sampled inside the bioreactor, its vicinity, and near the grate chamber. Higher species diversity of the family Enterobacteriaceae (including Shigella spp., Yersinia enterocolitica, Escherichia coli, Klebsiella pneumoniae ozaenae) in the air sampled inside or near the bioreactor may imply a health risk for staff exposed for longer periods of time. Notwithstanding, no increased emission of the analysed groups of microorganisms, including faecal bacteria, were found outside the WWTP.     

Diurnal distribution of airborne bacteria and fungi in the atmosphere of Helwan area, Egypt

Airborne bacterial and fungal composition in an industrial town of Helwan, Egypt, was studied using a slit impactor sampler during the period from March 2006 to February 2007. Airborne bacterial concentrations were usually higher than fungi. Bacteria and fungi had similar diurnal variation patterns. Airborne microorganisms reached their concentration peaks in the evening and gradually decreased during the night time. The hourly concentration peaks of the bacteria and fungi appeared at 20:00 h. A significant difference (P ≤ 0.05) was found between the hourly mean concentrations of airborne fungi in winter compared to other seasons. Fungi concentrations were significantly higher (P ≤ 0.05) on working weekdays than weekends. Aspergillus, Penicillium, Alternaria and Cladosporium were the most predominant airborne fungal genera. Aspergillus showed double peak patterns whereas Penicillium, Alternaria and Cladosporium showed one peak pattern. The diurnal variations of the bacteria and fungi could be divided into four periods: 1) the morning maximum concentration (6:00 h-10:00 h), 2) midday to afternoon pattern (10:00 h-16:00 h), 3) the evening concentration peak (18:00 h-20:00 h) and 4) the gradual decrease of night time concentration (22:00 h-24:00 h). Geographical location, human activity, growth cycle of organisms and meteorological factors were the main criteria controlling the temporal variations of the air microorganisms in the Wadi Hof area.     

Microorganisms and particles in AHU systems: Measurement and analysis

In this study, for better understanding the practical removal effect of air handling unit (AHU) system on airborne microorganisms (including bacteria and fungus) and particles and microbial growth, the samples of microorganisms and particles in 10 air handling unit (AHU) systems including fan coils and indoor air were collected and analyzed in air and component surfaces of such systems in two large public buildings. It is found that the removal efficiency is of the highest for bacteria 73.9% and the lowest for particles (0.5–2 μm) 24.4%. The surface concentration of equipment bacteria is 29 CFU/cm² and fungi 137 CFU/cm². Five of 10 systems have higher fungi concentrations on air intake than that on diffuser. The results also show that the central air supply system with common components (e.g., pre-filter and bag filter) has difficulty to achieve/maintain good performance once microorganisms and particles exist, especially for particle size D ≤ 3.3 μm. The size distribution has large influence on removal efficiency. The microbial growth on surfaces of duct and equipment was noticed and may be transferred into indoor air. This will decrease the indoor air quality and lead to adverse health effect.     

Exposure to culturable airborne bioaerosols during noodle manufacturing in central Taiwan

Biological hazards associated with the manufacturing of noodles have not been well characterized in Taiwan. This is an issue that flour workers can be exposed to bioaerosols (airborne fungi and bacteria) resulting flour-induced occupational asthma or allergic diseases. This study is to survey the species and concentrations of bioaerosols at different sites within a noodle factory for one year, and to investigate the effects of environmental factors on concentrations of bioaerosols. Air samples were taken twice a day, one day each month using a MAS-100 bioaerosol sampler.Nine species of culturable fungi were identified, with the main airborne fungi being Cladosporium, Penicillium, Aspergillus spp., non-sporing isolates and yeasts. Cladosporium, Penicillium and Aspergillus were the dominant fungal isolates in the indoor and outdoor air samples. Micrococcus spp. and Staphylococcus xylosus were the dominant bacterial isolates. Peak fungal and bacterial concentrations occurred at the crushing site, with mean values of 3082 and 12,616 CFU/m³. Meanwhile, the most prevalent fungi and bacteria at the crushing site were in ranges of 2.1-1.1 μm and 1.1-0.65 μm, respectively. Significant seasonal differences in total bacterial concentration were observed at all sampling sites (?P < 0.05). Moreover, significant seasonal differences were observed for most of the fungal genera except Fusarium. Levels of Aspergillus and Rhizopus differed significantly during the two sampling times, as did levels of Micrococcus spp. and Staphylococcus arlettae.Regarding the same operation procedures, relative humidity affected fungi levels more than temperature did. However, crushing generated the highest concentration of bioaerosols among all operation procedures. Furthermore, levels of bacteria at sites fitted with ventilation systems were lower than at sites without ventilation systems, especially at the crushing site. Therefore, we recommend these workers at the crushing site wear breathing protection and improve the local ventilation systems to minimize the biological hazards.     

An energy impact assessment of ventilation for indoor airborne bacteria exposure risk in air-conditioned offices

Treatment of fresh air in ventilation systems for air-conditioned offices consumes a significant amount of energy and affects the indoor air quality (IAQ). In this study, energy impact on the ventilation systems was examined against certain IAQ objectives for indoor airborne bacteria exposure risk in air-conditioned offices of Hong Kong. The relationship between thermal energy consumptions and indoor airborne bacteria exposure levels based on regional surveys was investigated. The thermal energy consumptions of ventilation systems operating for carbon dioxide (CO₂) exposure concentrations between 800 and 1200 ppmv for typical office buildings and the corresponding failure probability against some target bacteria exposure levels were evaluated. The results showed that, for a reference indoor environment at a CO₂ exposure concentration of 1000 ppmv, the predicted average thermal energy saving of ventilation system for a unit increment of the expected risk of unsatisfactory IAQ of 1% was 55 MJ m⁻² yr⁻¹ and for a unit decrement of 1%, the predicted additional thermal energy consumption was 58 MJ m⁻² yr⁻¹ respectively. This study would be a useful source of reference in evaluation of the energy performance of ventilation strategies in air-conditioned offices at a quantified exposure risk of airborne bacteria.     

Concentration and size distribution of bioaerosols in an outdoor environment in the Qingdao coastal region

Bioaerosol particles in the atmosphere were collected from the coastal region of Qingdao from Jul. 2009 to Jun. 2010. The concentrations of microorganisms (including culturable, nonculturable, terrestrial and marine microorganisms) were measured. Average concentrations of airborne terrestrial bacteria, marine bacteria, terrestrial fungi, marine fungi and total bioaerosol were in the ranges of 33-664 CFU/m³, 63-815 CFU/m³, 2-777 CFU/m³, 66-1128 CFU/m³ and 85,015-166,094 Cells/m³, respectively. The nonculturable microbes accounted for 99.13% of the total microbes. In addition, there were more culturable marine microbes than culturable terrestrial microbes, and more airborne fungi than bacteria. The concentration of airborne bacteria showed a skewed distribution pattern, while unimodal size distributions were observed for the concentrations of fungi and total microbes. The airborne microbes mainly existed in > 2.1 μm coarse particles. Pearson correlation analysis between the concentrations and meteorological parameters showed that the meteorological parameters had different effects on different kinds of microbes. Sandstorms increased the concentrations of both culturable microbes and total microbes in the bioaerosol.     

Occurrence of sulfonamide and tetracycline-resistant bacteria and resistance genes in aquaculture environment

The occurrence of sulfonamide and tetracycline resistance and their pollution profile in the aquaculture environment of Tianjin, northern China, were investigated. The presence of antibiotic-resistant bacteria was identified and the corresponding antibiotic resistance genes (ARGs) were quantified at 6 aquaculture farms in Tianjin. Sulfonamide-resistance genes were prevalent and their concentrations were the highest detected (3.0 × 10⁻⁵ to 3.3 × 10⁻⁴ for sul1/16S rDNA, 2.0 × 10⁻⁴ to 1.8 × 10⁻³ for sul2/16S rDNA) among the various ARGs, most likely because the use of sulfonamides is more prevalent than tetracyclines in this area. Bacillus was the most dominant bacterial genus in both sulfamethoxazole resistant bacteria (63.27% of the total resistant bacteria) and tetracycline-resistant bacteria (57.14% of the total resistant bacteria). At least two of those genes (tetM, tetO, tetT, tetW, sul1 and sul2) were detected in the isolates of Bacillus cereus, Bacillus subtilis, Bacillus megaterium and Acinetobacter lwofii, and all of the above genes were detected in B. cereus, suggesting the occurrence of multi-resistance in the studied area. The genetic transfer of sul1 between intestinal bacteria (e.g., Enterococcus spp.) and indigenous bacteria (e.g., Bacillus spp.) was implied by phylogenetic analysis. Several strains of resistant opportunistic pathogens (e.g., Acinetobacter spp.) were found in indigenous bacteria, which increase the risk of ARGs to public health. Overall, this is the first study to comprehensively investigate the antibiotic resistance profile by analyzing the species of antibiotic-resistant bacteria and adopting qualitative and quantitative methods to investigate ARGs at a typical aquaculture area in northern China.     

Occurrence of cocaine in the air of the World’s cities: An emerging problem? A new tool to investigate the social incidence of drugs?

The occurrence of illicit substances in the air was investigated in various world locations and ambient conditions. The analytical procedure optimized for cocaine, methadone and cocaethylene, based upon soxhlet extraction with organic solvent, clean-up through column chromatography, gas chromatographic separation and mass spectrometric detection, allowed the detection of the three compounds at levels as low as ~ 1 pg m^− 3 in air samples of ~ 500 m³. Apart from Algiers, Algeria, and Pan?evo, Serbia, cocaine was found in all cities investigated and its concentration ranged from picograms to nanograms/cubic meter (e.g., Rome, Italy, 22 ÷ 97 pg m^− 3; Santiago, Chile, 2.2 ÷ 3.3 ng m^− 3). By contrast, the concentrations of methadone and cocaethylene in the air were always lower than the limit-of-detection allowed by the method. The procedure adopted was unsuitable for measuring cannabinoids and allowed only the identification of cannabinol. It was also poor in limit-of-detection with regards to heroin (35 pg m^− 3), however this compound could be identified in airborne particulates in Oporto, Portugal. Atmospheric concentrations of cocaine appeared to correlate to drug prevalence in the Italian regions investigated.     

Identification of airborne bacterial and fungal community structures in an urban area by T-RFLP analysis and quantitative real-time PCR

This study explores the characteristics of bacterial and fungal communities of total suspended particles (TSP) in the atmosphere by using various molecular methods. TSP samples were collected on a glass fiber filter at an urban location in the middle of the Korean Peninsula (Seoul) between middle autumn and early winter in 2007. From the aerosol samples, DNA could be extracted and DNA sequences were determined for bacteria and fungi. Terminal restriction length polymorphism (T-RFLP) analysis was applied to analyze the community structure of them. To estimate the concentration of DNA originating from bacterial and fungal communities, we used the quantitative real-time polymerase chain reaction (Q-PCR). Sequence analyses were also used to determine the identity of biological organisms. The number of bacteria and fungi in the air were between 5.19 × 10¹ and 4.31 × 10³ cells m^− 3 and from 9.56 × 10¹ to 4.22 × 10⁴ cells m^− 3, respectively and bacterium/fungus ratios ranged from 0.09 to 0.76 across the seven sampling dates. Most of the bacterial sequences found in our TSP samples were from Proteobacteria, Actinobacteria, Firmicutes, and Bacteroidetes. The fungal sequences were characteristic for Ascomycota, Basidiomycota, and Glomeromycota which are known to actively discharge spores into the atmosphere. The plant sequences could be also detected. We found that large shifts in the community structure of bacteria and fungi were present in our TSP samples collected on different dates. The results demonstrated that in our TSP samples collected at the urban site; (1) there were very diverse bacterial and fungal groups including potential pathogens and allergens and (2) there were temporal shifts in both bacterial and fungal communities in terms of both diversity and abundances across an inter-seasonal period.     

Indoor exposure levels of bacteria and fungi in residences,schools, and offices in China: A systematic review

Microbes in buildings have attracted extensive attention from both the research community and the general public due to their close relationship with human health. However, there still lacks comprehensive information on the indoor exposure level of microbes in China. This study systematically reviews exposure levels, the community structures, and the impact factors of airborne bacteria and fungi in residences, schools, and offices in China. We reviewed the major literature databases between 1980 and 2019 and selected 55 original studies based on a set of criteria. Results show that the concentration of indoor bacteria varies from 72.5 to 7500 CFU/m³, with a median value of 1000 CFU/m³, and the concentration of fungi varies from 12 to 9730 CFU/m³, with a median value of 526 CFU/m³. The concentration level of microbes varies in different climate zones, with higher bacterial concentrations in the severe cold zone, and higher fungal concentrations in the hot summer and warm winter zone. Among different buildings, classrooms have the highest average bacteria and fungi levels. This review reveals that a unified assessment system based on health effects is needed for evaluating the exposure levels of bacteria and fungi.     

Distribution of the solvent-extractable organic compounds in fine (PM1) and coarse (PM1-10) particles in urban, industrial and forest atmospheres of Northern Algeria

The distribution of the solvent-extractable organic components in the fine (PM₁) and coarse (PM_1-10) fractions of airborne particulate was studied for the first time in Algeria. That was done during October 2006 concurrently in a big industrial district, a busy urban area, and a forest national park located in Algiers, Boumerdes, Blida, respectively, which are the three biggest provinces of Northern Algeria. Most of the organic matter identified in both particle size ranges consisted of n-alkanes and n-alkanoic acids, with minor contributions coming from polycyclic aromatic hydrocarbons (PAHs), nitrated polycyclic aromatic hydrocarbons (NPAHs), oxygenated PAHs, and other polar compounds (e.g., caffeine and nicotine). The potential emission sources of airborne contaminants were reconciled by combining the values of n-alkane carbon preference index (CPI) and selected diagnostic ratios of PAHs, calculated in both size ranges. The mean cumulative concentrations of PAHs reached 3.032 ng m^− 3 at the Boumerdes site, urban, 80% of which (i.e. 2.246 ng m^− 3) in the PM₁ fraction, 6.462 ng m^− 3 at Rouiba-Réghaia, industrial district, (5.135 ng m^− 3 or 80% in PM₁), and 0.512 ng m^− 3 at Chréa, forested mountains (0.370 ng m^− 3 or 72% in PM₁). Similar patterns were shown by all organic groups, which resulted overall enriched in the fine particles at the three sites. Carcinogenic and mutagenic potencies associated to PAHs were evaluated by multiplying the concentrations of “toxic” compounds times the corresponding potency factors normalized vs. benzo(a)pyrene (BaP), and were found to be both acceptable.     

Profiles and seasonal distribution of airborne fungi in indoor and outdoor environments at a French hospital

A one-year prospective survey of fungal air contamination was conducted in outdoor air and inside two haematological units of a French hospital. Air was sampled with a portable Air System Impactor. During this period of survey, the mean viable fungal load was 122.1 cfu/m³ in outdoor air samples, and 4.1 and 3.9 cfu/m³ in samples from adult and pediatric haematology units, respectively. In outdoor samples, Cladosporium was the dominant genus (55%) while in the clinical units, Penicillium sp. (23 to 25%), Aspergillus sp. (15 to 23%) and Bjerkandera adusta (11 to 13%) were the most frequently recovered airborne fungi. The outdoor fungal load was far higher in autumn (168 cfu/m³), spring (110 cfu/m³) and summer (138 cfu/m³) than in winter (49 cfu/m³). In indoor air, fungal concentrations were significantly lower in winter (2.7 to 3.1 cfu/m³) than in summer (4.2 to 5.0 cfu/m³) in both haematology units. In the outdoor environment, Penicillium sp. and Aspergillus sp. were more abundant in winter while the levels of Cladosporium were lowest during this season. In the haematological units, the presence of Aspergillus sp. was stable during the year (close to 20%), Bjerkandera sp. was particularly abundant in winter (close to 30%); levels of Penicillium sp. were highest in autumn while levels of Cladosporium sp. were highest in spring and summer.     

Heat balance and tracer gas technique for airflow rates measurement and gaseous emissions quantification in naturally ventilated livestock buildings

Experiments were performed to study the airflow rates (AFRs) in a naturally ventilated building through four summer seasons and three winter seasons. The AFRs were determined using heat balance (HB), tracer gas technique (TGT) and CO₂-balance as averages of the values of all experiments carried out through the different seasons. The statistical analyses were correlation analysis, regression model and t-test. Continuous measurements of gaseous concentrations (NH₃, CH₄, CO₂ and N₂O) and temperatures inside and outside the building were performed. The HB showed slightly acceptable results through summer seasons and unsatisfactory results through winter seasons. The CO₂-balance showed unexpected high differences to the other methods in some cases. The TGT showed reliable results compared to HB and CO₂-balance. The AFRs, subject to TGT, were 0.12 m³ s⁻¹ m⁻², 1.15 m³ s⁻¹ cow⁻¹, 0.88 m³ s⁻¹ LU⁻¹, 56 h⁻¹, 395 m³ s⁻¹ and 470 kg s⁻¹ through summer seasons, and 0.08 m³ s⁻¹ m⁻², 0.83 m³ s⁻¹ cow⁻¹, 0.64 m³ s⁻¹ LU⁻¹ 39 h⁻¹, 275 m³ s⁻¹ and 328 kg s⁻¹ through winter seasons. The AFRs are not independent values, rather they were estimated for specific reference values, which are: area, cow and LU as well as rates. The emission rates through summer seasons, subject to TGT, were 9.4, 40, 3538 and 2.3 g h⁻¹ cow⁻¹; and through winter seasons were 4.8, 19, 2332 and 2.6 g h⁻¹ cow⁻¹, for NH₃, CH₄, CO₂ and N₂O, respectively.     

Survey of 1012 moldy dwellings by culture fungal analysis: Threshold proposal for asthmatic patient management

Different countries have tried to define guidelines to quantify what levels of fungi are considered as inappropriate for housing. This retrospective study analyzes indoor fungi by cultures of airborne samples from 1012 dwellings. Altogether, 908 patients suffering from rhinitis, conjunctivitis, and asthma were compared to 104 controls free of allergies. Portuguese decree law no 118/2013 (PDL118), ANSES (a French environmental and health agency) recommendations, and health regulations of Besançon University Hospital were applied to determine the rates of non‐conforming dwellings, which were respectively 55.2%, 5.2%, and 19%. Environmental microbiological results and medical data were compared. The whole number of colonies per cubic meter of air was correlated with asthma (P < 0.001) and rhinitis (P = 0.002). Sixty‐seven genera and species were detected in bedrooms. Asthma was correlated to Aspergillus versicolor (P = 0.004) and Cladosporium spp. (P = 0.02). Thresholds of 300 cfu/m³ for A. versicolor or 495 cfu/m³ for Cladosporium spp. are able to discriminate 90% of the asthmatic dwellings. We propose a new protocol to obtain an optimal cost for indoor fungi surveys, excluding surface analyses, and a new guideline to interpret the results based on >1000 cfu/m³ of whole colonies and/or above threshold levels for A. versicolor or Cladosporium spp.     

An experimental study on ventilation efficiency of isolation room

This paper presents an experimental modeling of contaminant dispersion in a mock-up isolation room with different negative pressure differentials and ventilation rates. A hypothetical contaminant (sulfur hexafluoride, SF₆) is emitted from a patient lying on a bed in the mock-up isolation room. The impacts of ventilation rates 12 and 24 h⁻¹ and pressure differentials −2.5, −5.0, −8.0, and −15.0 Pa on the ventilation effectiveness in the room are evaluated quantitatively. A local air quality index and an exposure index for healthcare workers are introduced in the research to evaluate the ventilation efficiency of the isolation room. Based on the results of our experiment, the ventilation efficiency of the isolation room ranks the highest at −15.0 Pa/24 h⁻¹, followed, respectively, by −15.0 Pa/12 h⁻¹, −8.0 Pa/24 h⁻¹, −5.0 Pa/24 h⁻¹, −2.5 Pa/24 h⁻¹, −8.0 Pa/12 h⁻¹, −5.0 Pa/12 h⁻¹, and −2.5 Pa/12 h⁻¹.     

Particulate-bound polycyclic aromatic hydrocarbons in naturally ventilated multi-storey residential buildings of Singapore: Vertical distribution and potential health risks

The main objective of the study is to quantify the polycyclic aromatic hydrocarbons (PAHs) concentration levels (US EPA priority components) in fine traffic-generated particles (PM_2.5) at various heights of typical multi-storey public housing buildings located in close proximity, i.e. within 30 m and along a busy major expressway in Singapore. The secondary objective is to estimate the potential health risks associated with inhalation exposure, based on the toxic equivalency factors (TEFs) at the various floors of these buildings. Two typical public housing buildings, both naturally ventilated residential apartment blocks, of point block configuration (22-storey) and slab block configuration (16-storey) were selected for the study. Particulate samples were collected for chemical analysis at three representative floors: the lower, the mid, and the upper floors of the buildings. Key meteorological parameters such as wind speed, wind direction, ambient temperature, and relative humidity were also measured at the representative floors. All samples were analyzed for the 16 PAH priority pollutants listed by US EPA. The vertical PAH distribution profile varies with height of building depending on the type of block configuration. The total mean concentrations of particulate PAHs for point and slab blocks are 3.32±1.76 ng/m³ (0.56–7.2 ng/m³) and 6.0±1.88 ng/m³ (3.19–10.26 ng/m³), respectively. For the point block, the highest mean total PAH concentration occurred at the mid floor followed by the upper floor. The lower floor had the least mean total PAH concentration. For the slab block, the highest mean total PAH concentration occurred at the lower floor and remained almost constant up to the mid floor and thereafter gradually decreased from mid floor to upper floor of the building. These results suggest that the building configuration influences the vertical distribution of particulate PAHs. The dominant particulate PAHs measured at the point block are naphthalene, acenaphthylene, benzo(b)fluoranthene, and benzo(g,h,i)perylene while those for the slab block, the main particulate PAHs are naphthalene, phenanthrene, fluoranthene, and benzo(g,h,i)perylene. The Bpe/Ind ratio for both blocks ranged from 0.92±0.2 to 1.63±0.6 indicating particulate PAHs are contributed by a mixture of both diesel and petrol engine type of vehicles, with diesel engine vehicles contributing a higher percentage of particulate PAHs to the different floor levels of both buildings. The total BaP_eq concentrations for point and slab blocks are 1.06±0.64 ng/m³ (0.14–2.45 ng/m³) and 0.94±1.22 ng/m³ (0.10–4.59 ng/m³), respectively. The total BaP equivalency results showed the potential health risk to cancer due to inhalation exposure is of concern for residents living in both blocks since the total BaP_eq concentrations for both blocks were very close to, or slightly exceeded the maximum permissible risk level of 1 ng/m³ of benzo(a)pyrene.     

ERIC-PCR identification of the spread of airborne Escherichia coli in pig houses

To understand the spread of microbial aerosols in pig houses, with Escherichia coli (E. coli) as indicator, the airborne E. coli in 4 pig houses and their surroundings at different points 10, 50 m upwind and 10, 50, 100, 200 and 400 m downwind respectively from the pig houses were collected, and the concentrations were calculated at each sampling point. Furthermore, the feces of pigs were collected to separate E. coli. The ERIC-PCR (Enterobacterial Repetitive Intergenic Consensus-Polymerase Chain Reaction) technology was used to amplify the isolated E. coli DNA samples, then the amplified results were analyzed by NTSYS-pc (Version 2.10) to identify the similarity of isolated E. coli. The results showed that the airborne E. coli concentrations in indoor air of the 4 pig houses (21-35 CFU m⁻³ air) were much higher than those in upwind and downwind air (P < 0.05), but there were no significant differences (P > 0.05) at downwind distances. The ERIC-PCR results also showed that 52.4% of the fecal E. coli (four houses being respectively 2/4, 50%; 2/4, 50%; 3/6, 50%; 4/7, 57.1%) were identical to the indoor airborne E. coli isolates, and there was more than 90% similarity between the majority of E. coli (50%, 21/42) isolated from downwind air at 10, 50, 100 and 200 m and those from indoor air or feces. It could be concluded that the aerosols in pig houses can spread to the surroundings, and thus effective measures should be taken to control and minimize the spread of microbial aerosols.     

Measurement and source identification of polycyclic aromatic hydrocarbons (PAHs) in the aerosol in Xi'an, China, by using automated column chromatography and applying positive matrix factorization (PMF)

In this study, we measured polycyclic aromatic hydrocarbons (PAHs) in aerosols in Xi'an, China from 2005 to 2007, by using a modified Soxhlet extraction followed by a clean-up procedure using automated column chromatography followed by HPLC/fluorescence detection. The sources of PAHs were apportioned by using the positive matrix factorization (PMF) method. The PM₁₀ concentration in winter (161.1 ± 66.4 μg m^− 3, n = 242) was 1.5 times higher than that in summer (110.9 ± 34.7 μg m^− 3, n = 248). ΣPAH concentrations, which are the sum of the concentrations of all detected PAHs, in winter (344.2 ± 149.7 ng m^− 3, n = 45) was 2.5 times higher than that in summer (136.7 ± 56.7 ng m^− 3, n = 24) in this study. These strong seasonal variations in atmospheric PAH concentration are possibly due to coal combustion for residential heating. According to the source apportionment with PMF method in this study, the major sources of PAHs in Xi'an are categorized as (1) mobile sources such as vehicle exhaust that constantly contribute to PAH pollution, and (2) stationary sources such as coal combustion that have a large contribution to PAH pollution in winter.     

Effect of COD/SO4ratio and Fe(II) under the variable hydraulic retention time (HRT) on fermentative hydrogen production

The effect of chemical oxygen demand/sulfate (COD/SO₄²⁻) ratio on fermentative hydrogen production using enriched mixed microflora has been studied. The chemostat system maintained with a substrate (glucose) concentration of 15 g COD L⁻¹ exhibited stable H₂ production at inlet sulfate concentrations of 0-20 g L⁻¹ during 282 days. The tested COD/SO₄²⁻ ratios ranged from 150 to 0.75 (with control) at pH 5.5 with hydraulic retention time (HRT) of 24, 12 and 6 h. The hydrogen production at HRT 6 h and pH 5.5 was not influenced by decreasing the COD/SO₄²⁻ ratio from 150 to 15 (with control) followed by noticeable increase at COD/SO₄²⁻ ratios of 5 and 3, but it was slightly decreased when the COD/SO₄²⁻ ratio further decreased to 1.5 and 0.75. These results indicate that high sulfate concentrations (up to 20,000 mg L⁻¹) would not interfere with hydrogen production under the investigated experimental conditions. Maximum hydrogen production was 2.95, 4.60 and 9.40 L day⁻¹ with hydrogen yields of 2.0, 1.8 and 1.6 mol H₂ mol⁻¹ glucose at HRTs of 24, 12 and 6 h, respectively. The volatile fatty acid (VFA) fraction produced during the reaction was in the order of butyrate > acetate > ethanol > propionate in all experiments. Fluorescence In Situ Hybridization (FISH) analysis indicated the presence of Clostridium spp., Clostridium butyricum, Clostridium perfringens and Ruminococcus flavefaciens as hydrogen producing bacteria (HPB) and absence of sulfate reducing bacteria (SRB) in our study.     

Particle deposition fluxes of BDE-209, PAHs, DDTs and chlordane in the Pearl River Delta, South China

Year-round bulk air deposition samples were collected at 15 sites in the Pearl River Delta (PRD) on a bimonthly basis from Dec 2003 to Nov 2004, and the particle-phase deposition of BDE-209, PAHs, DDTs and chlordane was measured. The annual deposition fluxes of BDE-209, total PAHs (15 compounds), total DDT (sum of p,p′-DDE, p,p′-DDD, p,p′-DDT, and o,p′-DDT ), and chlordane (sum of trans-chlordane and cis-chlordane) varied from 32.6 to 1970 μg m^− 2 yr^− 1, 22 to 290 μg m^− 2 yr^− 1, 0.8 to 11 μg m^− 2 yr^− 1, and 0.25 to 1.9 μg m^− 2 yr^− 1, respectively. Spatial variations were higher in the centre of the PRD and lower at the coastal sites for all compounds. The seasonal variations of deposition were found to be compound-dependent, influenced by a number of factors, such as the timing of source input, temperature, and precipitation etc. In particular, source input time affected the deposition fluxes of BDE-209 and high-weight PAHs, while temperature-dependent gas-particle partitioning was a key factor for DDT and light-weight PAH deposition. During the whole sampling period, the atmospheric deposition of BDE-209, ΣPAHs, ΣDDTs, and chlordane onto Hong Kong reached about 93, 86, 2.1 and 2.1 kg yr^− 1, respectively, and onto the PRD reached about 13,400, 2950, 82, and 63 kg yr^− 1. By comparing the calculated total air deposition with the burden in the soils, the half residual time of BDE-209 in soils was estimated to be 3 years.