Novel mold‐resistant building materials impregnated with thermally reduced nano‐silver

In this study, we evaluated the long‐term antifungal effectiveness of 3 types of interior building materials (gypsum board [GB], cement board [CB], and softwood plywood [S‐PW]) impregnated with thermally reduced silver nanoparticles supported by titanium dioxide (AgNPs/TiO₂) under 95% relative humidity for 4 weeks. AgNPs/TiO₂ was synthesized at 2 thermal reduction temperatures (TRTs, 120 and 200°C) with 2 different AgNP weight percentages (2 and 5 wt%). Four different silver‐loading levels (SLLs, 0.025, 0.05, and 0.5 μg/cm² and the critical concentration required to inhibit fungal growth on agar plates) and 3 fungal species (Aspergillus niger, Penicillium spinulosum, and Stachybotrys chartarum) were used in the experiments. Higher temperature reduced more ionic Ag⁺ to metallic Ag⁰ and increased the dispersion of Ag on TiO₂ surface. The 200°C thermally reduced AgNPs/TiO₂ demonstrated excellent antifungal efficiency: Mold growth was almost completely inhibited for 28 days at the low SLL of 0.5 μg/cm². Additionally, AgNPs/TiO₂ exhibited higher antifungal activity on GB and CB than on S‐PW. The stepwise regression results indicated that the TRT of AgNPs/TiO₂ (β = ?0.739 to ?0.51), the SLL (β = ?0.477 to ?0.269), and the Ag⁰ level in the AgNPs (β = ?0.379 to ?0.136) were the major factors influencing antifungal activity and TRT might be the most significant one.     

Indoor mold levels and current asthma among school‐aged children in Saskatchewan,Canada

Current knowledge regarding the association between indoor mold exposures and asthma is still limited. The objective of this case–control study was to investigate the relationship between objectively measured indoor mold levels and current asthma among school‐aged children. Parents completed a questionnaire survey of health history and home environmental conditions. Asthma cases had a history of doctor‐diagnosed asthma or current wheeze without a cold in the past 12 months. Controls were age‐ and sex‐matched to cases. Vacuumed dust samples were collected from the child's indoor play area and mattress. Samples were assessed for mold levels and quantified in colony‐forming units (CFU). Sensitization to mold allergens was also determined by skin testing. Being a case was associated with family history of asthma, pet ownership, and mold allergy. Mold levels (CFU/m²) in the dust samples of children's mattress and play area floors were moderately correlated (r = 0.56; P < 0.05). High mold levels (≥30 000 CFU/m²) in dust samples from play [adjusted odds ratio (aOR) = 2.6; 95% CI: 1.03–6.43] and mattress (aOR) = 3.0; 95% CI: 1.11–8.00) areas were significantly associated with current asthma. In this study high levels of mold are a risk factor for asthma in children.     

Ultrafine,fine, and black carbon particle concentrations in California child‐care facilities

Although many U.S. children spend time in child care, little information exists on exposures to airborne particulate matter (PM) in this environment, even though PM may be associated with asthma and other respiratory illness, which is a key concern for young children. To address this data gap, we measured ultrafine particles (UFP), PM_2.5, PM₁₀, and black carbon in 40 California child‐care facilities and examined associations with potential determinants. We also tested a low‐cost optical particle measuring device (Dylos monitor). Median (interquartile range) concentrations for indoor UFP, gravimetric PM_2.5, real‐time PM_2.5, gravimetric PM₁₀, and black carbon over the course of a child‐care day were 14 000 (11 000‐29 000) particles/cm³, 15 (9.6‐21) μg/m³, 15 (11‐23) μg/m³, 48 (33‐73) μg/m³, and 0.43 (0.25‐0.65) ng/m³, respectively. Indoor black carbon concentrations were inversely associated with air exchange rate (Spearman's rho = ?.36) and positively associated with the sum of all Gaussian‐adjusted traffic volume within a one‐kilometer radius (Spearman's rho = .45) (P‐values <.05). Finally, the Dylos may be a valid low‐cost alternative to monitor PM levels indoors in future studies. Overall, results indicate the need for additional studies examining particle levels, potential health risks, and mitigation strategies in child‐care facilities.     

Adolescent lung function associated with incense burning and other environmental exposures at home

Incense burning is a popular cultural and religious practice, but whether exposure to incense smoke has effects on lung function is unclear. We investigated association between lung function and incense burning exposure and other household exposures in adolescents who participated in a mass asthma‐screening program. Information on asthmatic status and associated factors was obtained from parent‐completed questionnaires and student‐completed video questionnaires. Approximately 10% of students received lung function examinations. Valid lung function data of 5010 students aged 14‐16 years in northern Taiwan were analyzed. Forced vital capacity (FVC) and forced expiratory flow in 1 second (FEV₁) were compared by incense burning status and other types of exposures for adolescents. Overall, 70.6% of students were exposed to incense smoke at home. The mean FVC and FEV₁ measures were lower among adolescents with daily exposure to incense burning than those without such exposure (P<.05). Sharing bedroom was also associated with decreased FVC and FEV₁. After controlling for confounding factors, multivariable linear regression analysis with generalized estimation equation showed that FVC was negatively associated with daily exposure to incense burning, sharing a bedroom, and living in a house adjacent to a traffic road. Such associations were also observed in FEV₁. Daily exposure to incense burning is associated with impaired adolescent lung function.     

A comparative study of walking‐induced dust resuspension using a consistent test mechanism

Human walking influences indoor air quality mainly by resuspending dust particles settled on the floor. This study characterized walking‐induced particle resuspension as a function of flooring type, relative humidity (RH), surface dust loading, and particle size using a consistent resuspension mechanism. Five types of flooring, including hardwood, vinyl, high‐density cut pile carpet, low‐density cut pile carpet, and high‐density loop carpet, were tested with two levels of RH (40% and 70%) and surface dust loading (2 and 8 g/m²), respectively. Resuspension fraction r_a (fraction of surface dust resuspended per step) for house dust was found to be varied from 10^?7 to 10^?4 (particle size: 0.4–10 µm). Results showed that for particles at 0.4–3.0 µm, the difference in resuspension fraction between carpets and hard floorings was not significant. For particles at 3.0–10.0 µm, carpets exhibited higher resuspension fractions compared with hard floorings. Increased RH level enhanced resuspension on high‐density cut pile carpet, whereas the opposite effect was observed on hard floorings. Higher surface dust loading was associated with lower resuspension fractions on carpets, while on hard floorings the effect of surface dust loading varied with different RH levels.     

Impact of a cleaner‐burning cookstove intervention on blood pressure in Nicaraguan women

Few studies have evaluated the cardiovascular‐related effects of indoor biomass burning or the role of characteristics such as age and obesity status, in this relationship. We examined the impact of a cleaner‐burning cookstove intervention on blood pressure among Nicaraguan women using an open fire at baseline; we also evaluated heterogeneity of the impact by subgroups of the population. We evaluated changes in systolic and diastolic blood pressure from baseline to post‐intervention (range: 273–383 days) among 74 female cooks. We measured indoor fine particulate matter (PM_2.5; N = 25), indoor carbon monoxide (CO; N = 32), and personal CO (N = 30) concentrations. Large mean reductions in pollutant concentrations were observed for all pollutants; for example, indoor PM_2.5 was reduced 77% following the intervention. However, pollution distributions (baseline and post‐intervention) were wide and overlapping. Although substantial reductions in blood pressure were not observed among the entire population, a 5.9 mmHg reduction [95% confidence interval (CI): ?11.3, ?0.4] in systolic blood pressure was observed among women aged 40 or more years and a 4.6 mmHg reduction (95% CI: ?10.0, 0.8) was observed among obese women. Results from this study provide an indication that certain subgroups may be more likely to experience improvements in blood pressure following a cookstove intervention.     

Allergy and respiratory health effects of dampness and dampness‐related agents in schools and homes: a cross‐sectional study in Danish pupils

Little is known about the health effects of school‐related indoor dampness and microbial exposures. In this study, we investigated dampness and dampness‐related agents in both homes and schools and their association with allergy and respiratory health effects in 330 Danish pupils. Classroom dampness was identified based on technical inspection and bedroom dampness on parents' self‐report. Classroom and bedroom dust was analyzed for seven microbial components. Skin prick testing determined atopic sensitization. Lung function was expressed as z‐scores for forced expiratory volume in one‐second (zFEV₁), forced vital capacity (zFVC) and the ratio zFEV₁/zFVC using GLI‐2012 prediction equations. The parents reported children's allergies, airway symptoms, and doctor‐diagnosed asthma. High classroom dampness, but not bedroom dampness, was negatively associated with zFEV₁ (β‐coef. ?0.71; 95% CI ?1.17 to ?0.23) and zFVC (β‐coef. ?0.52; 95% CI ?0.98 to ?0.06) and positively with wheezing (OR 8.09; 95% CI 1.49 to 43.97). No consistent findings were found between any individual microbial components or combination of microbial components and health outcomes. Among other indoor risk factors, environmental tobacco smoke (ETS) decreased zFEV₁ (β‐coef. ?0.22; 95% CI ?0.42 to ?0.02) and zFEV₁/zFVCratio (β‐coef. ?0.26; 95% CI ?0.44 to ?0.07) and increased upper airway symptoms (OR 1.66; 95% CI 1.03–2.66). In conclusion, dampness in classrooms may have adverse respiratory health effects in pupils, but microbial agents responsible for this effect remain unknown.     

Determinants of house dust,endotoxin, and β‐(1→3)‐D‐glucan in homes of Danish children

Little is known about the geographic variation and determinants of bacterial endotoxin and β ‐(1,3)‐d ‐glucan in Danish house dust. In a population of 317 children, we: (i) described loads and concentrations of floor dust, endotoxin, and β‐(1→3)‐d ‐glucan and (ii) their correlations and (iii) assessed their determinants; (iv) Finally, we compared our findings with previous European studies. Bedroom floor dust was analyzed for endotoxin content by the kinetic limulus amoebocyte lysate assay and for β‐(1→3)‐d ‐glucan by the inhibition enzyme immunoassay. The parents answered questions regarding potential determinants. We found: geometric means (geometric standard deviations) 186 mg/m² (4.3) for dust; 5.46 × 10³EU/m² (8.0) and 31.1 × 10³EU/g (2.6) for endotoxin; and 142 μg/m² (14.3) and 0.71 × 10³ μg/g (7.3) for β‐(1→3)‐d ‐glucan. High correlations (r > 0.75) were found between floor dust and endotoxin and β‐(1→3)‐d ‐glucan loads, while endotoxin and β‐(1→3)‐d ‐glucan concentrations were moderately correlated (r = 0.36–0.41) with the dust load. Having a carpet was positively associated with dust load and with endotoxin and β‐(1→3)‐d ‐glucan concentrations. Pet keeping, dwelling type, and dwelling location were determinants of endotoxin concentrations. No other determinants were associated with β‐(1→3)‐d ‐glucan concentrations. Compared with other European studies, we found lower β‐(1→3)‐d ‐glucan loads and concentrations but higher endotoxin loads and concentrations suggesting a geographically determined different composition of Danish floor dust compared with other European regions.     

Heterogeneous oxidation of indoor surfaces by gas‐phase hydroxyl radicals

We investigate heterogeneous oxidation kinetics of monolayer‐thick, surface‐sorbed organics, namely di‐n‐octyl phthalate (DnOP) and palmitic acid (PA), with gas‐phase OH. The pseudo‐first order rate constants for organic loss at OH concentrations of 1.6 × 10⁸ molecules/cm³ are: (2.3 ± 0.1) × 10^?4 to (4.8 ± 0.8) × 10^?4 s^?1, and (1.3 ± 0.5) × 10^?4 s^?1 for DnOP and PA, respectively. Films developed in indoor office environments over a few weeks are also oxidized using the same OH concentration. Heterogeneous decay rate constants of mass signals from these films, attributed to phthalates (MW = 390.6) and to PA, are similar to those for the single‐component films, ie, (1.9 ± 0.4) × 10^?4 to (3.4 ± 0.5) × 10^?4 s^?1, and (1.1 ± 0.4) × 10^?4 s^?1, respectively. These results suggest that the lifetimes for OH heterogeneous oxidation of monolayer‐thick indoor organic films will be on the timescale of weeks to months. To support this argument, we present the first analysis of the mass transfer processes that occur when short‐lived gas‐phase molecules, such as OH, are taken up by reactive indoor surfaces. Due to rapid chemical production, the diffusion limitation to mass transfer is less important for short‐lived molecules than for molecules with little chemical production, such as ozone.     

The preparation,characterization of FeC micro‐electrolysis materials using low‐cost biochar and the removal of ultra‐high COD pesticide wastewater

Two kinds of Fe? C micro‐electrolysis materials (Fe? C MEMs) named Fe⁰/Fe? C MEMs and Fe₃O₄/Fe? C MEMs were prepared using low‐cost biochar, chemical grade Fe⁰ powder and industrial iron powder. The Fe? C MEMs were characterized by XRD, SEM and FT‐IR. Meanwhile, the effects of sintering temperatures and mass ratios of Fe to C on the treatment high chemical oxygen demand (COD) pesticide wastewater were studied. The results display that the relative removal rate of COD reached 64% for Fe⁰/Fe? C MEMs when the sintering temperature was 400°C and the mass ratio of Fe to C was 1 : 1. For Fe₃O₄/Fe? C MEMs, and the mass ratio of Fe₃O₄ to C was 1 : 3, the relative removal rate of COD reached 63.71%. Hence, the chemical grade Fe⁰ powder could be replaced with industrial iron powder to achieve the goal of low‐cost treatment of the high COD pesticide wastewater.     

Pre‐natal and post‐natal exposure to pet ownership and lung function in children: The Seven Northeastern Cities Study

To evaluate the association between pre‐natal and post‐natal exposure to pet ownership and lung function in children, a cross‐sectional study named Seven Northeastern Cities (SNEC) study was conducted. In this study, children's lung function including the forced expiratory volume in 1 second (FEV₁), forced vital capacity (FVC), maximal mid‐expiratory flow (MMEF), and peak expiratory flow (PEF) were measured by spirometers, and pet ownership situations were collected by questionnaire. Analyzed by multiple logistic regression and generalized linear modeling, we found that for all subjects, pet exposure in the first 2 years of life was significantly associated with lung function impairment of FVC<85% predicted (adjusted odds ratio [aOR]=1.28; 95% confidence interval [CI]: 1.01, 1.63). For current pet exposure, the increased odds of lung function impairment ranged from 35% (aOR=1.35; 95%CI: 1.12, 1.62) for FVC<85% predicted to 57% (aOR=1.57; 95%CI: 1.29, 1.93) for FEV₁<85% predicted. The in utero exposure was not related to lung function impairment. Compared with other pets, higher odds were observed among children with dogs. When stratified by gender, girls with current pet exposure were more likely to have lung function impairment than boys. It implies self‐reported exposures to pets were negatively associated with lung function among the children under study.     

A comparative study of human exposures to household air pollution from commonly used cookstoves in Sri Lanka

Solid fuel burning cookstoves are a major source of household air pollution (HAP) and a significant environmental health risk in Sri Lanka. We report results of the first field study in Sri Lanka to include direct measurements of both real‐time indoor concentrations and personal exposures of fine particulate matter (PM_2.5) in households using the two most common stove types in Sri Lanka. A purposive sample of 53 households was selected in the rural community of Kopiwatta in central Sri Lanka, roughly balanced for stove type (traditional or improved ‘Anagi’) and ventilation (chimney present or absent). At each household, 48‐h continuous real‐time measurements of indoor kitchen PM_2.5 and personal (primary cook) PM_2.5 concentrations were measured using the RTI MicroPEM^? personal exposure monitor. Questionnaires were used to collect data related to household demographics, characteristics, and self‐reported health symptoms. All primary cooks were female and of an average age of 47 years, with 66% having completed primary education. Median income was slightly over half the national median monthly income. Use of Anagi stoves was positively associated with a higher education level of the primary cook (P = 0.026), although not associated with household income (P = 0.18). The MicroPEM monitors were well‐received by participants, and this study's valid data capture rate exceeded 97%. Participant wearing compliance during waking hours was on average 87.2% on Day 1 and 83.3% on Day 2. Periods of non‐compliance occurred solely during non‐cooking times. The measured median 48‐h average indoor PM_2.5 concentration for households with Anagi stoves was 64 μg/m³ if a chimney was present and 181 μg/m³ if not. For households using traditional stoves, these values were 70 μg/m³ if a chimney was present and 371 μg/m³ if not. Overall, measured indoor PM_2.5 concentrations ranged from a minimum of 33 μg/m³ to a maximum of 940 μg/m³, while personal exposure concentrations ranged from 34 to 522 μg/m³. Linear mixed effects modeling of the dependence of indoor concentrations on stove type and presence or absence of chimney showed a significant chimney effect (65% reduction; P < 0.001) and an almost significant stove effect (24% reduction; P = 0.054). Primary cooks in households without chimneys were exposed to substantially higher levels of HAP than those in households with chimneys, while exposures in households with traditional stoves were moderately higher than those with improved Anagi stoves. As expected, simultaneously measuring both indoor concentrations and personal exposure levels indicate significant exposure misclassification bias will likely result from the use of a stationary monitor as a proxy for personal exposure. While personal exposure monitoring is more complex and expensive than deploying simple stationary devices, the value an active personal PM monitor like the MicroPEM adds to an exposure study should be considered in future study designs.     

Combined use of an electrostatic precipitator and a high‐efficiency particulate air filter in building ventilation systems: Effects on cardiorespiratory health indicators in healthy adults

High‐efficiency particulate air (HEPA) filtration in combination with an electrostatic precipitator (ESP) can be a cost‐effective approach to reducing indoor particulate exposure, but ESPs produce ozone. The health effect of combined ESP‐HEPA filtration has not been examined. We conducted an intervention study in 89 volunteers. At baseline, the air‐handling units of offices and residences for all subjects were comprised of coarse, ESP, and HEPA filtration. During the 5‐week long intervention, the subjects were split into 2 groups, 1 with just the ESP removed and the other with both the ESP and HEPA removed. Each subject was measured for cardiopulmonary risk indicators once at baseline, twice during the intervention, and once 2 weeks after baseline conditions were restored. Measured indoor and outdoor PM_2.5 and ozone concentrations, coupled with time‐activity data, were used to calculate exposures. Removal of HEPA filters increased 24‐hour mean PM_2.5 exposure by 38 (95% CI: 31, 45) μg/m³. Removal of ESPs decreased 24‐hour mean ozone exposure by 2.2 (2.0, 2.5) ppb. No biomarkers were significantly associated with HEPA filter removal. In contrast, ESP removal was associated with a ?16.1% (?21.5%, ?10.4%) change in plasma‐soluble P‐selectin and a ?3.0% (?5.1%, ?0.8%) change in systolic blood pressure, suggesting reduced cardiovascular risks.     

Microbial characteristics in homes of asthmatic and non‐asthmatic adults in the ECRHS cohort

Microbial exposures in homes of asthmatic adults have been rarely investigated; specificities and implications for respiratory health are not well understood. The objectives of this study were to investigate associations of microbial levels with asthma status, asthma symptoms, bronchial hyperresponsiveness (BHR), and atopy. Mattress dust samples of 199 asthmatics and 198 control subjects from 7 European countries participating in the European Community Respiratory Health Survey II study were analyzed for fungal and bacterial cell wall components and individual taxa. We observed trends for protective associations of higher levels of mostly bacterial markers. Increased levels of muramic acid, a cell wall component predominant in Gram‐positive bacteria, tended to be inversely associated with asthma (OR's for different quartiles: II 0.71 [0.39‐1.30], III 0.44 [0.23‐0.82], and IV 0.60 [0.31‐1.18] P for trend .07) and with asthma score (P for trend .06) and with atopy (P for trend .02). These associations were more pronounced in northern Europe. This study among adults across Europe supports a potential protective effect of Gram‐positive bacteria in mattress dust and points out that this may be more pronounced in areas where microbial exposure levels are generally lower.     

Effective disinfection of airborne microbial contamination in hospital wards using a zero‐valent nano‐silver/TiO2‐chitosan composite

A novel antimicrobial composite of zero‐valent silver nanoparticles (AgNPs), titania (TiO₂), and chitosan (CS) was prepared via photochemical deposition of AgNPs on a CS‐TiO₂ matrix (AgNPs@CS‐TiO₂). Electron microscopy showed that the AgNPs were well dispersed on the CS‐TiO₂, with diameters of 6.69‐8.84 nm. X‐ray photoelectron spectra indicated that most of the AgNPs were reduced to metallic Ag. Fourier‐transform infrared spectroscopy indicated that some AgNPs formed a chelate with CS through coordination of Ag⁺ with the CS amide II groups. The zones of inhibition of AgNPs@CS‐TiO₂ for bacteria (Escherichia coli and Staphylococcus epidermidis) and fungi (Aspergillus niger and Penicillium spinulosum) were 6.72‐11.08 and 5.45‐5.77 mm, respectively, and the minimum (critical) concentrations of AgNPs required to inhibit the growth of bacteria and fungi were 7.57 and 16.51 µg‐Ag/mm², respectively. The removal efficiency of a AgNPs@TiO₂‐CS bed filter for bioaerosols (η) increased with the packing depth, and the optimal filter quality (qF) occurred for packing depths of 2‐4 cm (qF = 0.0285‐0.103 Pa^?1; η = 57.6%‐98.2%). When AgNPs@TiO₂‐CS bed filters were installed in the ventilation systems of hospital wards, up to 88% of bacteria and 97% of fungi were removed within 30 minutes. Consequently, AgNPs@TiO₂‐CS has promising potentials in bioaerosol purification.     

Outdoor,indoor, and personal black carbon exposure from cookstoves burning solid fuels

Black carbon (BC) emissions from solid fuel combustion are associated with increased morbidity and mortality and are important drivers of climate change. We studied BC measurements, approximated by particulate matter (PM_2.5) absorbance, in rural Yunnan province, China, whose residents use a variety of solid fuels for cooking and heating including bituminous and anthracite coal, and wood. Measurements were taken over two consecutive 24‐h periods from 163 households in 30 villages. PM_2.5 absorbance (PM_abs) was measured using an EEL 043 Smoke Stain Reflectometer. PM_abs measurements were higher in wood burning households (16.3 × 10^?5/m) than bituminous and anthracite coal households (12 and 5.1 × 10^?5/m, respectively). Among bituminous coal users, measurements varied by a factor of two depending on the coal source. Portable stoves (which are lit outdoors and brought indoors for use) were associated with reduced PM_abs levels, but no other impact of stove design was observed. Outdoor measurements were positively correlated with and approximately half the level of indoor measurements (r = 0.49, P < 0.01). Measurements of BC (as approximated by PM_abs) in this population are modulated by fuel type and source. This provides valuable insight into potential morbidity, mortality, and climate change contributions of domestic usage of solid fuels.     

Exposure to organophosphate and polybrominated diphenyl ether flame retardants via indoor dust and childhood asthma

Although the ubiquitous detection of polybrominated diphenyl ether (PBDE) and organophosphate flame retardants (PFRs) in indoor dust has raised health concerns, only very few epidemiological studies have assessed their impact on human health. Inhalation of dust is one of the exposure routes of FRs, especially in children and can be hazardous for the respiratory health. Moreover, PFRs are structurally similar to organophosphate pesticides, which have been associated with allergic asthma. Thus, we investigated whether the concentrations of PFRs and PBDEs in indoor dust are associated with the development of childhood asthma. We selected 110 children who developed asthma at 4 or at 8 years old and 110 matched controls from a large prospective birth cohort (BAMSE – Barn, Allergy, Milieu Stockholm Epidemiology). We analyzed the concentrations of 7 PFRs and 21 PBDEs in dust collected around 2 months after birth from the mother's mattress. The abundance rank in dust was as follows: TBOEP?TPHP>mmp‐TMPP>EHDPHP~TDCIPP>TCEP~TCIPP~BDE‐209?BDE‐99>BDE‐47>BDE‐153>BDE‐183>BDE‐100. There was no positive association between the FRs in mattress dust and the development of childhood asthma. In contrast, dust collected from mattresses of the mothers of children who would develop asthma contained significant lower levels of TPHP and mmp‐TMPP. This study provides data on a wide range of PFRs and PBDEs in dust samples and development of asthma in children.     

House dust‐mite allergen exposure is associated with serum specific IgE but not with respiratory outcomes

Exposure to house dust has been associated with asthma in adults, and this is commonly interpreted as a direct immunologic response to dust‐mite allergens in those who are IgE sensitized to house dust‐mite. Mattress house dust‐mite concentrations were measured in a population‐based sample of 2890 adults aged between 27 and 56 years living in 22 centers in 10 countries. Generalized linear mixed models were employed to explore the association of respiratory symptoms with house dust‐mite concentrations, adjusting for individual and household confounders. There was no overall association of respiratory outcomes with measured house dust‐mite concentrations, even in those who reported they had symptoms on exposure to dust and those who had physician‐diagnosed asthma. However, there was a positive association of high serum specific IgE levels to HDM (>3.5 kU_A/l) with mattress house dust‐mite concentrations and a negative association of sensitization to cat with increasing house dust‐mite concentrations. In conclusion, there was no evidence that respiratory symptoms in adults were associated with exposure to house dust‐mite allergen in the mattress, but an association of house mite with strong sensitization was observed.     

Size‐resolved fluorescent biological aerosol particle concentrations and occupant emissions in a university classroom

This study is among the first to apply laser‐induced fluorescence to characterize bioaerosols at high time and size resolution in an occupied, common‐use indoor environment. Using an ultraviolet aerodynamic particle sizer, we characterized total and fluorescent biological aerosol particle (FBAP) levels (1–15 μm diameter) in a classroom, sampling with 5‐min resolution continuously during eighteen occupied and eight unoccupied days distributed throughout a one‐year period. A material‐balance model was applied to quantify per‐person FBAP emission rates as a function of particle size. Day‐to‐day and seasonal changes in FBAP number concentration (N_F) values in the classroom were small compared to the variability within a day that was attributable to variable levels of occupancy, occupant activities, and the operational state of the ventilation system. Occupancy conditions characteristic of lecture classes were associated with mean N_F source strengths of 2 × 10⁶ particles/h/person, and 9 × 10⁴ particles per metabolic g CO₂. During transitions between lectures, occupant activity was more vigorous, and estimated mean, per‐person N_F emissions were 0.8 × 10⁶ particles per transition. The observed classroom peak in FBAP size at 3–4 μm is similar to the peak in fluorescent and biological aerosols reported from several studies outdoors.     

Microbial secondary metabolites in homes in association with moisture damage and asthma

We aimed to characterize the presence of microbial secondary metabolites in homes and their association with moisture damage, mold, and asthma development. Living room floor dust was analyzed by LC‐MS/MS for 333 secondary metabolites from 93 homes of 1‐year‐old children. Moisture damage was present in 15 living rooms. At 6 years, 8 children had active and 15 lifetime doctor‐diagnosed asthma. The median number of different metabolites per house was 17 (range 8–29) and median sum load 65 (4–865) ng/m². Overall 42 different metabolites were detected. The number of metabolites present tended to be higher in homes with mold odor or moisture damage. The higher sum loads and number of metabolites with loads over 10 ng/m² were associated with lower prevalence of active asthma at 6 years (aOR 0.06 (95% CI <0.001–0.96) and 0.05 (<0.001–0.56), respectively). None of the individual metabolites, which presence tended (P < 0.2) to be increased by moisture damage or mold, were associated with increased risk of asthma. Microbial secondary metabolites are ubiquitously present in home floor dust. Moisture damage and mold tend to increase their numbers and amount. There was no evidence indicating that the secondary metabolites determined would explain the association between moisture damage, mold, and the development of asthma.