Review and analysis of inhalation dosimetry methods for application to children's risk assessment

Intra-Continental Transport of Western Wildfire Smoke Heightens Health Risks Across North America

Wildfires in North America, particularly in western states, have caused widespread environmental, economic, social, and health impacts. Smoke from these fires travels long distances, spreading pollutants and worsening the air quality across continents. Vulnerable groups, such as children, the elderly, and those with preexisting conditions, face heightened health risks, as do firefighters working in extreme conditions. Wildfire firefighters are of particular concern as they are fighting fires in extreme conditions with minimal protective equipment. This study examined wildfire smoke during July-August 2021, when intense fires in Canada and the western U.S. led to cross-continental smoke transport and caused significant impacts on the air quality across North America. Using the GEOS-Chem model, we simulated the transport and distribution of PM2.5 (particulate matter with a diameter of 2.5 μm or smaller), identifying significant carcinogenic risks for adults, children, and firefighters using dosimetry risk methodologies established by the U.S. EPA. Significant carcinogenic risks for adult, child, and firefighter populations due to exposure to PM2.5 were identified over the two-month period of evaluation. The findings emphasize the need for future studies to assess the toxic chemical mixtures in wildfire smoke and consider the risks to underrepresented communities.

Air quality and wheeze symptoms in a rural children's cohort near a drying saline lake

BACKGROUND

In California, climate change and competing water demands are intensifying the desiccation of the Salton Sea, a large land-locked "sea" situated near the southeastern rural US-Mexico border region known as the Imperial Valley.

METHODS

To examine the possible effects of living near a saline lake on children's respiratory health, we analyzed the relationship between respiratory health symptoms and ambient PM concentrations among a predominantly Latino/Hispanic cohort of 722 school age children. Guardians completed a survey of their child's wheeze and respiratory health symptoms over the past 12 months, adapted from the International Study of Asthma and Allergies in Childhood (ISAAC). Exposure to dust storm hours (hourly concentrations >150 μg/m3 for PM10) was estimated using a network of regulatory monitors.

RESULTS

Between 2017 and 2019, children were exposed to 98 to 395 dust event hours annually. We observed disparate effects for dust events and wheeze among children living near the Salton Sea. Every additional 100 dust storm hours per year among children living near the Sea (<11 km) was associated with a 9.5 percentage point increase in wheeze (95% CI: 3.5, 15.4), a 4.6 percentage point increase in bronchitic symptoms (95% CI: 0.18, 10.2) and a 6.7 percentage point increase in sleep disturbance due to wheeze (95% CI: 0.96, 12.4). Similarly, increases in PM10 were also associated with greater reported wheeze and bronchitic symptoms among those living near the Sea, compared to children living ≥11 km from the Sea. There was no association of dust storms or PM10 with wheeze or bronchitic symptoms among the children residing farther from the Sea.

CONCLUSION

We observed stronger adverse impacts of PM10 and dust events on respiratory health among those living closer to the drying Salton Sea, compared to children living farther away. In this community of predominantly low-income residents of color, these impacts raise environmental justice concerns about the effects of the drying Salton Sea on public health.

Climate change and children's respiratory health

Climate change has significant consequences for children's respiratory health. Rising temperatures and extreme weather events increase children's exposure to allergens, mould, and air pollutants. Children are particularly vulnerable to these airborne particles due to their higher ventilation per unit of body weight, more frequent mouth breathing, and outdoor activities. Children with asthma and cystic fibrosis are at particularly high risk, with increased risks of exacerbation, but the effects of climate change could also be observed in the general population, with a risk of impaired lung development and growth. Mitigation measures, including reducing greenhouse gas emissions by healthcare professionals and healthcare systems, and adaptation measures, such as limiting outdoor activities during pollution peaks, are essential to preserve children's respiratory health. The mobilisation of society as a whole, including paediatricians, is crucial to limit the impact of climate change on children's respiratory health.

Exposure limits for indoor volatile substances concerning the general population: The role of population-based differences in sensory irritation of the eyes and airways for assessment factors

Assessment factors (AFs) are essential in the derivation of occupational exposure limits (OELs) and indoor air quality guidelines. The factors shall accommodate differences in sensitivity between subgroups, i.e., workers, healthy and sick people, and occupational exposure versus life-long exposure for the general population. Derivation of AFs itself is based on empirical knowledge from human and animal exposure studies with immanent uncertainty in the empirical evidence due to knowledge gaps and experimental reliability. Sensory irritation in the eyes and airways constitute about 30-40% of OELs and is an abundant symptom in non-industrial buildings characterizing the indoor air quality and general health. Intraspecies differences between subgroups of the general population should be quantified for the proposal of more 'empirical' based AFs. In this review, we focus on sensitivity differences in sensory irritation about gender, age, health status, and vulnerability in people, based solely on human exposure studies. Females are more sensitive to sensory irritation than males for few volatile substances. Older people appear less sensitive than younger ones. However, impaired defense mechanisms may increase vulnerability in the long term. Empirical evidence of sensory irritation in children is rare and limited to children down to the age of six years. Studies of the nervous system in children compared to adults suggest a higher sensitivity in children; however, some defense mechanisms are more efficient in children than in adults. Usually, exposure studies are performed with healthy subjects. Exposure studies with sick people are not representative due to the deselection of subjects with moderate or severe eye or airway diseases, which likely underestimates the sensitivity of the group of people with diseases. Psychological characterization like personality factors shows that concentrations of volatile substances far below their sensory irritation thresholds may influence the sensitivity, in part biased by odor perception. Thus, the protection of people with extreme personality traits is not feasible by an AF and other mitigation strategies are required. The available empirical evidence comprising age, lifestyle, and health supports an AF of not greater than up to 2 for sensory irritation. Further, general AFs are discouraged for derivation, rather substance-specific derivation of AFs is recommended based on the risk assessment of empirical data, deposition in the airways depending on the substance's water solubility and compensating for knowledge and experimental gaps. Modeling of sensory irritation would be a better 'empirical' starting point for derivation of AFs for children, older, and sick people, as human exposure studies are not possible (due to ethical reasons) or not generalizable (due to self-selection). Dedicated AFs may be derived for environments where dry air, high room temperature, and visually demanding tasks aggravate the eyes or airways than for places in which the workload is balanced, while indoor playgrounds might need other AFs due to physical workload and affected groups of the general population.

Health risks for children exercising in an air-polluted environment can be reduced by monitoring air quality with low-cost particle sensors

A child's body is highly sensitive to air quality, especially regarding the concentration of particulate matter (PM). Nevertheless, due to the high cost of precision instruments, measurements of PM concentrations are rarely carried out in school areas where children spend most of their daily time. This paper presents the results of PM measurements made by a validated, low-cost university air pollution measurement system operating in a rural area near schools. An assessment of children's exposure to PM during school hours (8 a.m.-6 p.m.) at different times of the year was carried out. We show that PM10 concentrations in the air, particularly in winter, often exceeded the alert values of 50 µg m-3, posing a health risk to children, especially when children exercise outside the school building. We also calculated the rate and total PM10 deposition in the respiratory tract during various physical activities performed in clean and polluted air. Monitoring actual PM10 concentrations as presented in this paper, using a low cost sensors, offer school authorities and teachers an opportunity to reduce health risks for children. This can be achieved by adjusting the duration and exercise intensity of children's outdoor physical activities according to the measured air quality.

Comparative susceptibility of children and adults to neurological effects of inhaled manganese: A review of the published literature

BACKGROUND

Manganese (Mn) is neurotoxic in adults and children. Current assessments are based on the more extensive adult epidemiological data, but the potential for greater childhood susceptibility remains a concern. To better understand potential lifestage-based variations, we compared susceptibilities to neurotoxicity in children and adults using Mn biomarker data.

METHODS

We developed a literature search strategy based on a Population, Exposures, Comparators, and Outcomes statement focusing on inhalation exposures and neurological outcomes in humans. Screening was performed using DistillerSR. Hair biomarker studies were selected for evaluation because studies with air measurements were unavailable or considered inadequate for children. Studies were paired based on concordant Mn source, biomarker, and outcome. Comparisons were made based on reported dose-response slopes (children vs. adults). Study evaluation was conducted to understand the confidence in our comparisons.

RESULTS

We identified five studies evaluating seven pairings of hair Mn and neurological outcomes (cognition and motor effects) in children and adults matched on sources of environmental Mn inhalation exposure. Two Brazilian studies of children and one of adults reported intelligent quotient (IQ) effects; effects in both comparisons were stronger in children (1.21 to 2.03-fold difference). In paired analyses of children and adults from the United States, children exhibited both stronger and weaker effects compared to adults (0.37 to 1.75-fold differences) on postural sway metrics.

CONCLUSION

There is limited information on the comparative susceptibility of children and adults to inhaled Mn. We report that children may be 0.37 to 2.03 times as susceptible as adults to neurotoxic effects of Mn, thereby providing a quantitative estimate for some aspects of lifestage variation. Due to the limited number of paired studies available in the literature, this quantitative estimate should be interpreted with caution. Our analyses do not account for other sources of inter-individual variation. Additional studies of Mn-exposed children with direct air concentration measurements would improve the evidence base.

Evaluation and updates to the Leggett model for pharmacokinetic modeling of exposure to lead in the workplace - Part II adjustments to the adult exposure model, confirmation of Leggett+, and modeling of workplace exposure

California's Office of Environmental Health Hazard Assessment has updated the comprehensive age-specific model of lead metabolism in humans published by Richard W. Leggett in 1993. The updated model, called Leggett+, was introduced in a peer-reviewed report in 2013. The Leggett + model simulates the relationship between blood lead and exposure in the workplace. Leggett + includes a workplace exposure model comprising respiratory tract intake (workplace lead inhaled by a worker) and uptake (lead absorbed into the blood from the respiratory tract plus uptake from ambient air and diet). The latter is calculated as intake times an inhalation transfer coefficient plus background uptake. An adjusted adult systemic model describes the metabolism of the absorbed lead. This paper provides details about the workplace exposure and uptake elements of Leggett+, an updated approach to calibrating an inhalation transfer coefficient, confirmation of the model's performance in predicting blood lead levels from workplace studies, and predictions of blood lead levels from simulated exposures to workplace airborne lead over a working lifetime. Blood lead relative to airborne lead concentrations in a standard workplace scenario predicted by Leggett + was similar to corresponding relationships from four published workplace studies. Leggett + predictions displayed a good fit to regression equations when other key factors were considered such as pre-employment blood lead and ongoing background intake of lead, workplace air concentration, lead aerosol characteristics, and worker activity levels. The comprehensive Leggett + model can simulate plausible workplace air-blood lead relationships from a broad range of worker exposures. The inhalation transfer coefficient of 0.30, derived from empirical data described in the 2013 report has been reexamined. The original estimate continues to represent a plausible mid-point for a coefficient derived from an expanded range of theoretical particle size distributions deposited in the upper and lower regions of the respiratory tract considering intake during sedentary and outdoor activity breathing scenarios. This coefficient is slightly lower than the value of 0.35 estimated for unknown forms of lead by Leggett in 1993.

Association between PM1 Exposure and Lung Function in Children and Adolescents: A Systematic Review and Meta-Analysis

The detrimental effects of PM_2.5 and PM₁₀ (particulate matter less than 2.5 or 10 μm) on human respiratory system, including lung function, have been widely assessed. However, the associations between PM₁ (particulate matter of less than 1 μm) and lung function in children and adolescents are less explored, and current evidence is inconsistent. We conducted a meta-analysis of the literature on the association between PM₁ and lung function in children and adolescents to fill this gap. With no date or language constraints, we used a combination of MeSH (Medical Subject Headings) terms and free text to search PubMed, EMBASE and Web of Science databases through, 1 October 2022 for "PM₁ exposure" and "lung function". A total of 6420 relevant studies were identified through our initial search, and seven studies were included in our study. In this meta-analysis, the fixed effect and random effects statistical models were used to estimate the synthesized effects of the seven included studies. For every 10 μg/m³ increase in short-term PM₁ exposure, forced vital capacity (FVC), forced expiratory volume in the first second (FEV₁), peak expiratory flow (PEF) and maximal mid-expiratory flow (MMEF) decreased by 31.82 mL (95% CI: 20.18, 43.45), 32.28 mL (95% CI: 16.73, 48.91), 36.85 mL/s (95% CI: 15.33, 58.38) and 34.51 mL/s (95% CI: 19.61, 49.41), respectively. For each 10 μg/m³ increase in long-term PM₁ exposure, FVC, FEV₁, PEF and MMEF decreased by 102.34 mL (95% CI: 49.30, 155.38), 75.17 mL (95% CI: 39.61, 110.73), 119.01 mL/s (95% CI: 72.14, 165.88) and 44.94 mL/s (95% CI: 4.70, 85.18), respectively. Our study provides further scientific evidence for the harmful effects of PM₁ exposure on lung function in children and adolescents, indicating that exposure to PM₁ is detrimental to pulmonary health. To reduce the adverse health effects of air pollution on children and adolescents, effective preventive measures should be taken.

Source apportionment of children daily exposure to particulate matter

The present study aims to investigate the sources of particulate pollution in indoor and outdoor environments, with focus on determining their contribution to the exposure of children to airborne particulate matter (PM). To this end, parallel indoor and outdoor measurements were carried out for a selection of 40 homes and 5 schools between September 2017 and October 2018. PM2.5 and PM2.5-10 samples were collected during five days in each microenvironment (ME) and analysed by X-Ray Fluorescence (XRF), for the determination of elements, and by a thermal-optical technique, for the measurement of organic and elemental carbon. The source apportionment analysis of the PM composition data, by means of the receptor model SoFi (Source Finder) 8 Pro, resulted in the identification of nine sources: exhaust and non-exhaust emissions from traffic, secondary particles, heavy oil combustion, industry, sea salt, soil, city dust, and an indoor source characterized by high levels of organic carbon. Integrated daily exposure to PM2.5 was on average 21 μg/m³. The organic matter, resulting from cleaning, cooking, smoking and biological material, was the major source contributing by 31% to the PM2.5 exposure. The source city dust, which was highly influenced by the resuspension of dust in classrooms, was the second main source (26%), followed by traffic (24%). The major sources affecting the integrated exposure to PM10, which was on average 33 μg/m³, were the city dust (39%), indoor organics (24%) and traffic (16%). This study provides important information for the design of measures to reduce the exposure of children to PM.

The impact of Traffic-Related air pollution on child and adolescent academic Performance: A systematic review

BACKGROUND

The negative health impacts of traffic-related air pollution (TRAP) have been investigated for many decades, however, less attention has been paid to the effect of TRAP on children's academic performance. Understanding the TRAP-academic performance relationship will assist in identifying mechanisms for improving students' learning and aid policy makers in developing guidance for protecting children in school environments.

METHODS

This systematic review assessed the relationship between TRAP and academic performance. Web of Science, PubMed, CINAHL, Medline, PsycINFO, SPORTDiscus, Scopus and ERIC databases were searched for relevant, peer reviewed, articles published in English. Articles assessing exposure to TRAP pollutants (through direct measurement, local air quality monitoring, modelling, or road proximity/density proxy measures) and academic performance (using standardised tests) in children and adolescents were included. Risk of bias was assessed within and between studies.

RESULTS

Of 3519 search results, 10 relevant articles were included. Nine studies reported that increased exposure to some TRAP was associated with poorer student academic performance. Study methodologies were highly heterogeneous and no consistent patterns of association between specific pollutants, age groups, learning domains, exposure windows, and exposure locations were established. There was a serious risk of bias within individual studies and confidence in the body of evidence was low.

CONCLUSIONS

This review found evidence suggestive of a negative association between TRAP and academic performance. However, the quality of this evidence was low. The existing body of literature is small, lacks the inclusion of high-quality exposure measures, and presents limitations in reporting. Future research should focus on using valid and reliable exposure measures, individual-level data, consistent controlling for confounders and longitudinal study designs.

Quantification of air pollution exposure to in-pram babies and mitigation strategies

Young children are particularly vulnerable to air pollution exposure during their early childhood development, yet research on exposure to in-pram babies in different types of single/double prams is limited. This work aims to mimick their exposure to multiple air pollutants - particulate matter ≤10 µm in aerodynamic diameter (PM₁₀), ≤2.5 µm (PM_2.5; fine particles), ≤1 µm (PM₁), ≤0.10 µm (measured as particle number concentration, PNC) - in three different types of prams (single pram facing the road; single pram facing parents; double pram facing the road). We also assessed the differences in exposure concentrations between typical adult and in-pram baby breathing height via simultaneous measurements besides assessing their physico-chemical properties (morphology and elemental composition). In addition, we analysed the impact of pram covers in mitigating in-pram exposure concentrations of selected pollutants. We carried out a total of 89 single runs, repeating on a 2.1 km long pre-defined route between an origin-destination pair (the University of Surrey to a local school) during the morning (08:00-10:00 h; local time) and afternoon (15:00-17:00 h) hours. These run simulated morning drop-off and afternoon pick-off times of school children. Overall, the experimental runs took about 66 h and covered the total length of 145 km. Substantial variability is observed in measured concentrations of different pollutants within each run (e.g., up to 290-times for PNC) and between different runs performed during different times of the day (e.g., ~62% variability in average PNC; ~7% for PM₁ and 8% for PM_2.5 during morning versus afternoon). The average in-pram concentration of fine particles was always higher by up to 44% compared with adult breathing height during both morning and afternoon runs. The comparison of exposure concentrations at two different sitting heights of double pram showed that PNC concentrations were higher by about 72% at the bottom seat compared to the top seat. Scanning electron microscope (SEM) analysis of PM_2.5-10 revealed traces of brake wear, tyre wear and re-suspended dust minerals with the predominance of brake and tyre wear emissions at baby height compared with a relatively larger share of earth crust elements at adult height. For mitigation measures, pram covers reduced concentrations of small-sized particles by as much as 39% (fine particles) and 43% (coarse particles). Our results reinforce the need for mitigating exposures to in-pram babies, especially at urban pollution hotspots such as busy congested roads, bus stops, and traffic intersections.

Exposure to Submicron Particles and Estimation of the Dose Received by Children in School and Non-School Environments

In the present study, the daily dose in terms of submicron particle surface area received by children attending schools located in three different areas (rural, suburban, and urban), characterized by different outdoor concentrations, was evaluated. For this purpose, the exposure to submicron particle concentration levels of the children were measured through a direct exposure assessment approach. In particular, measurements of particle number and lung-deposited surface area concentrations at “personal scale” of 60 children were performed through a handheld particle counter to obtain exposure data in the different microenvironments they resided. Such data were combined with the time–activity pattern data, characteristics of each child, and inhalation rates (related to the activity performed) to obtain the total daily dose in terms of particle surface area. The highest daily dose was estimated for children attending the schools located in the urban and suburban areas (>1000 mm2), whereas the lowest value was estimated for children attending the school located in a rural area (646 mm2). Non-school indoor environments were recognized as the most influential in terms of children’s exposure and, thus, of received dose (>70%), whereas school environments contribute not significantly to the children daily dose, with dose fractions of 15–19% for schools located in urban and suburban areas and just 6% for the rural one. Therefore, the study clearly demonstrates that, whatever the school location, the children daily dose cannot be determined on the basis of the exposures in outdoor or school environments, but a direct assessment able to investigate the exposure of children during indoor environment is essential.

Surfactant delivery in rat lungs: Comparing 3D geometrical simulation model with experimental instillation

Surfactant Replacement Therapy (SRT), which involves instillation of a liquid-surfactant mixture directly into the lung airway tree, is a major therapeutic treatment in neonatal patients with respiratory distress syndrome (RDS). This procedure has proved to be remarkably effective in premature newborns, inducing a five-fold decrease of mortality in the past 35 years. Disappointingly, its use in adults for treating acute respiratory distress syndrome (ARDS) experienced initial success followed by failures. Our recently developed numerical model has demonstrated that transition from success to failure of SRT in adults could, in fact, have a fluid mechanical origin that is potentially reversible. Here, we present the first numerical simulations of surfactant delivery into a realistic asymmetric conducting airway tree of the rat lung and compare them with experimental results. The roles of dose volume (VD), flow rate, and multiple aliquot delivery are investigated. We find that our simulations of surfactant delivery in rat lungs are in good agreement with our experimental data. In particular, we show that the monopodial architecture of the rat airway tree plays a major role in surfactant delivery, contributing to the poor homogeneity of the end distribution of surfactant. In addition, we observe that increasing VD increases the amount of surfactant delivered to the acini after losing a portion to coating the involved airways, the coating cost volume, VCC. Finally, we quantitatively assess the improvement resulting from a multiple aliquot delivery, a method sometimes employed clinically, and find that a much larger fraction of surfactant reaches the alveolar regions in this case. This is the first direct qualitative and quantitative comparison of our numerical model with experimental studies, which enhances our previous predictions in adults and neonates while providing a tool for predicting, engineering, and optimizing patient-specific surfactant delivery in complex situations.

Soy Biodiesel Exhaust is More Toxic than Mineral Diesel Exhaust in Primary Human Airway Epithelial Cells

As global biodiesel production increases, there are concerns over the potential health impact of exposure to the exhaust, particularly in regard to young children who are at high risk because of their continuing lung development. Using human airway epithelial cells obtained from young children, we compared the effects of exposure to exhaust generated by a diesel engine with Euro V/VI emission controls running on conventional diesel (ultra-low-sulfur mineral diesel, ULSD), soy biodiesel (B100), or a 20% blend of soy biodiesel with diesel (B20). The exhaust output of biodiesel was found to contain significantly more respiratory irritants, including NO_x, CO, and CO₂, and a larger overall particle mass. Exposure to biodiesel exhaust resulted in significantly greater cell death and a greater release of immune mediators compared to both air controls and ULSD exhaust. These results have concerning implications for potential global health impacts, particularly for the pediatric population.

Airborne, Vehicle-Derived Fe-Bearing Nanoparticles in the Urban Environment: A Review

Airborne particulate matter poses a serious threat to human health. Exposure to nanosized (<0.1 μm), vehicle-derived particulates may be hazardous due to their bioreactivity, their ability to penetrate every organ, including the brain, and their abundance in the urban atmosphere. Fe-bearing nanoparticles (<0.1 μm) in urban environments may be especially important because of their pathogenicity and possible association with neurodegenerative diseases, such as Alzheimer's and Parkinson's diseases. This review examines current knowledge regarding the sources of vehicle-derived Fe-bearing nanoparticles, their chemical and mineralogical compositions, grain size distribution and potential hazard to human health. We focus on data reported for the following sources of Fe-bearing nanoparticles: exhaust emissions (both diesel and gasoline), brake wear, tire and road surface wear, resuspension of roadside dust, underground, train and tram emissions, and aircraft and shipping emissions. We identify limitations and gaps in existing knowledge as well as future challenges and perspectives for studies of airborne Fe-bearing nanoparticles.

Association between ambient PM2.5 and children's hospital admissions for respiratory diseases in Jinan, China

To determine the association between daily air pollution and the hospital admissions for respiratory diseases in children aged from 0 to 17 years in Jinan, China. Generalized linear models were used to explore the acute effects of ambient fine particulate matter (PM_2.5) on the children's hospital admissions for respiratory diseases. We evaluated the lag associations (including lag 0 to lag 3, lag 01, and lag 03) between daily PM_2.5 and the number of children's hospital admissions for respiratory diseases, and stratified by gender, age group (baby group: age 0-1 years; child group: age 1-5 years; student group: age 6-17 years), and cause-specific disease (including upper infection, pneumonia, and acute bronchitis) during 2011-2015. PM_2.5 had significant positive impacts on the number of children's hospital admissions for respiratory disease. The results showed that per 10 μg/m³ increase of PM_2.5 at lag 1 was associated with an increase in total and male hospital admissions of 0.23% (95% CI, 0.02%-0.45%) and 0.32% (95% CI, 0.04%-0.06%). The corresponding risk of the student group (age 6-17 years) hospital admissions was increased 0.90% (95% CI, 0.39%-1.42%) at lag 1 day. The corresponding risk of the upper infection was increased 0.96% (95% CI, 0.37-1.55%) at lag 1 day. Males and student groups (age 6-17 years) were more vulnerable to PM_2.5 exposure. Upper infection admission was identified as the sensitive disease for children. It is a better way to reduce children's outdoor activities to avoid health effects when the air pollution increases.

Evernia Goes to School: Bioaccumulation of Heavy Metals and Photosynthetic Performance in Lichen Transplants Exposed Indoors and Outdoors in Public and Private Environments

Recently indoor air quality (IAQ) has become a key issue, especially in schools, where children spend most of the day. Only in a few cases IAQ was investigated using lichens as biomonitors. During autumn 2017, lichens (Evernia prunastri) were exposed for two months indoors and outdoors in public (schools) and private (dwellings) environments, in both rural and urban areas of Slovakia. The bioaccumulation of selected elements and the physiological status of the samples were considered. The content of heavy metals increased in samples exposed outdoors for 11 out of 12 elements (Al, As, Cd, Cr, Cu, Fe, Pb, S, Sb, V and Zn, but not Ca) in the urban area and for 5 (As, Cd, Cu, Pb and Sb) in the rural area. Indoor concentrations were overall similar, both in rural and urban buildings, independently of the outdoor conditions. An indoor accumulation occurred only for Cd, Cu and Pb. An indoor origin was suggested for Cd, while for Cu and Pb, outdoor penetration (car traffic) is the likely cause of indoor values. Indoor exposed lichens maintained their vitality (as reflected by chlorophyll a fluorescence emission). This latter result further supports the use of lichen biomonitoring as a suitable method for assessing IAQ.

The disappearing Salton Sea: A critical reflection on the emerging environmental threat of disappearing saline lakes and potential impacts on children's health

Changing weather patterns, droughts and competing water demands are dramatically altering the landscape and creating conditions conducive to the production of wind-blown dust and dust storms. In California, such factors are leading to the rapid shrinking of the Salton Sea, a 345 mile² land-locked "sea" situated near the southeastern rural border region known as the Imperial Valley. The region is anticipated to experience a dramatic increase in wind-blown dust and existing studies suggest a significant impact on the health and quality of life for nearby residents of this predominantly low-income, Mexican-American community. The discussion calls attention to the public health dimensions of the Salton Sea crisis. We know little about the possible long-term health effects of exposure to mobilized lakebed sediments or the numerous toxic contaminants that may become respirable on entrained particles. We draw on existing epidemiological literature of other known sources of wind-blown dust, such as desert dust storms, and related health effects to begin to understand the potential public health impact of wind-blown dust exposure. The increased production of wind-blown dust and environmental exposures to such non-combustion related sources of particulate matter are a growing health threat, due in part to drought coupled with increasing pressures on limited water resources. Recent population-based studies have linked dust storms with cardiovascular mortality, asthma hospitalization and decrease in pulmonary function in both adults and children. A growing number of studies provide evidence of the acute health effects of wind-blown dust exposures among children, which with repeated insults have the potential to influence respiratory health over time. The shrinking of the Salton Sea illustrates a public health and environmental justice crisis that requires action and attention to protect the health and well-being of local communities.

A review of factors surrounding the air pollution exposure to in-pram babies and mitigation strategies

Air pollution exposure to in-pram babies poses a serious threat to their early childhood development, necessitating a need for effective mitigation measures. We reviewed the scientific and grey literature on in-pram babies and their personal exposure to traffic generated air pollutants such as particulate matter ≤10 μm (PM₁₀), ≤2.5 μm (PM_2.5), ≤0.10 μm (ultrafine particles) in size, black carbon and nitrogen oxides and potential mitigation pathways. In-pram babies can be exposed up to ~60% higher average concentrations depending on the pollutant types compared with adults. The air within the first few meters above the road level is usually most polluted. Therefore, we classified various pram types based on criteria such as height, width and the seating capacity (single versus twin) and assessed the breathing heights of sitting babies in various pram types available in the market. This classification revealed the pram widths between 0.56 and 0.82 m and top handle heights up to ~1.25 m as opposed to breathing height between 0.55 and 0.85 m, suggesting that the concentration within the first meter above the road level is critical for exposure to in-pram babies. The assessment of flow features around the prams suggests that meteorological conditions (e.g., wind speed and direction) and traffic-produced turbulence affect the pollution dispersion around them. A survey of the physicochemical properties of particles from roadside environment demonstrated the dominance of toxic metals that have been shown to damage their frontal lobe as well as cognition and brain development when inhaled by in-pram babies. We then assessed a wide range of active and passive exposure mitigation strategies, including a passive control at the receptor such as the enhanced filtration around the breathing zone and protection of prams via covers. Technological solutions such as creating a clean air zone around the breathing area can provide instant solutions. However, a holistic approach involving a mix of innovative technological solutions, community empowerment and exposure-centric policies are needed to help limit personal exposure of in-pram babies.

Acute effects of PM2.5 on lung function parameters in schoolchildren in Nanjing, China: a panel study

The association between exposure to ambient particulate matter (PM) and reduced lung function parameters has been reported in many works. However, few studies have been conducted in developing countries with high levels of air pollution like China, and little attention has been paid to the acute effects of short-term exposure to air pollution on lung function. The study design consisted of a panel comprising 86 children from the same school in Nanjing, China. Four measurements of lung function were performed. A mixed-effects regression model with study participant as a random effect was used to investigate the relationship between PM_2.5 and lung function. An increase in the current day, 1-day and 2-day moving average PM_2.5 concentration was associated with decreases in lung function indicators. The greatest effect of PM_2.5 on lung function was detected at 1-day moving average PM_2.5 exposure. An increase of 10 μg/m³ in the 1-day moving average PM_2.5 concentration was associated with a 23.22 mL decrease (95% CI: 13.19, 33.25) in Forced Vital Capacity (FVC), a 18.93 mL decrease (95% CI: 9.34, 28.52) in 1-s Forced Expiratory Volume (FEV₁), a 29.38 mL/s decrease (95% CI: -0.40, 59.15) in Peak Expiratory Flow (PEF), and a 27.21 mL/s decrease (95% CI: 8.38, 46.04) in forced expiratory flow 25-75% (FEF_25-75%). The effects of PM_2.5 on lung function had significant lag effects. After an air pollution event, the health effects last for several days and we still need to pay attention to health protection.

Particle-related exposure, dose and lung cancer risk of primary school children in two European countries

Schools represent a critical microenvironment in terms of air quality due to the proximity to outdoor particle sources and the frequent lack of proper ventilation and filtering systems. Moreover, the population exposed in schools (i.e. children) represents a susceptible population due to their age. Air quality-based studies involving students' exposure at schools are still scarce and often limited to mass-based particle metrics and may thus underestimate the possible effect of sub-micron particles and particle toxicity. To this purpose, the present paper aims to evaluate the exposure to different airborne particle metrics (including both sub- and super-micron particles) and attached carcinogenic compounds. Measurements in terms of particle number, lung-deposited surface area, and PM fraction concentrations were measured inside and outside schools in Barcelona (Spain) and Cassino (Italy). Simultaneously, PM samples were collected and chemically analysed to obtain mass fractions of carcinogenic compounds. School time airborne particle doses received by students in classrooms were evaluated as well as their excess lung cancer risk due to a five-year primary school period. Median surface area dose received by students during school time in Barcelona and Cassino resulted equal to 110mm² and 303mm², respectively. The risk related to the five-year primary school period was estimated as about 2.9×10^-5 and 1.4×10^-4 for students of Barcelona and Cassino, respectively. The risk in Barcelona is slightly higher with respect to the maximum tolerable value (10^-5, according to the U.S. Environmental Protection Agency), mainly due to toxic compounds on particles generated from anthropogenic emissions (mainly industry). On the other hand, the excess lung cancer risk in Cassino is cause of concern, being one order of magnitude higher than the above-mentioned threshold value due to the presence of biomass burning heating systems and winter thermal inversion that cause larger doses and great amount of toxic compounds on particles.

Acute effects of ambient air pollution on lower respiratory infections in Hanoi children: An eight-year time series study

BACKGROUND

Lower respiratory diseases are the most frequent causes of hospital admission in children worldwide, particularly in developing countries. Daily levels of air pollution are associated with lower respiratory diseases, as documented in many time-series studies. However, investigations in low-and-middle-income countries, such as Vietnam, remain sparse.

OBJECTIVE

This study investigated the short-term association of ambient air pollution with daily counts of hospital admissions due to pneumonia, bronchitis and asthma among children aged 0-17 in Hanoi, Vietnam. We explored the impact of age, gender and season on these associations.

METHODS

Daily ambient air pollution concentrations and hospital admission counts were extracted from electronic databases received from authorities in Hanoi for the years 2007-2014. The associations between outdoor air pollution levels and hospital admissions were estimated for time lags of zero up to seven days using Quasi-Poisson regression models, adjusted for seasonal variations, meteorological variables, holidays, influenza epidemics and day of week.

RESULTS

All ambient air pollutants were positively associated with pneumonia hospitalizations. Significant associations were found for most pollutants except for ozone and sulfur dioxide in children aged 0-17. Increments of an interquartile range (21.9μg/m³) in the 7-day-average level of NO₂ were associated with a 6.1% (95%CI 2.5% to 9.8%) increase in pneumonia hospitalizations. These associations remained stable in two-pollutant models. All pollutants other than CO were positively associated with hospitalizations for bronchitis and asthma. Associations were weaker in infants than in children aged 1-5.

CONCLUSION

Strong associations between hospital admissions for lower respiratory infections and daily levels of air pollution confirm the need to adopt sustainable clean air policies in Vietnam to protect children's health.

Influence of PM1 and PM2.5 on lung function parameters in healthy schoolchildren-a panel study

To evaluate lung function responses to short-term indoor PM₁ and PM_2.5 concentrations, we conducted a panel study of healthy schoolchildren aged 13-14 years. The following lung function parameters FVC, FEV₁, PEF, and mid expiratory flows MEF₂₅, MEF₅₀, and MEF₇₅ were measured in 141 schoolchildren of the secondary school in Wroclaw, Poland in years 2009-2010. On days when spirometry tests were conducted, simultaneously, PM₁ and PM_2.5 samples were collected inside the school premises. Information about differentiating factors for children including smoking parents, sex, living close to busy streets, dust, mold, and pollen allergies were collected by means of questionnaires. To account for repeated measurements, the method of generalized estimating equations (GEE) was used. The GEE models for the entire group of children revealed the adverse effects (p < 0.05) of PM₁ and PM_2.5. Small differences in effects estimates per interquartile range (IQR) of PM₁ and PM_2.5 on MEF₂₅ (5.1 and 4.8 %), MEF₅₀ (3.7 and 3.9 %), MEF₇₅ (3.5 and 3.6 %) and FEV₁ (1.3 and 1.0 %) imply that PM₁ was likely the component of PM_2.5 that might have a principal health effect on these lung function parameters. However, the reduction of FVC and PEF per IQR for PM_2.5 (2.1 and 5.2 %, respectively) was higher than for PM₁ (1.0 and 4.4 %, respectively). Adjustment for potential confounders did not change the unadjusted analysis.

Assessing human variability in kinetics for exposures to multiple environmental chemicals: a physiologically based pharmacokinetic modeling case study with dichloromethane, benzene, toluene, ethylbenzene, and m-xylene

The objective of this study was to compare the magnitude of interindividual variability in internal dose for inhalation exposure to single versus multiple chemicals. Physiologically based pharmacokinetic models for adults (AD), neonates (NEO), toddlers (TODD), and pregnant women (PW) were used to simulate inhalation exposure to "low" (RfC-like) or "high" (AEGL-like) air concentrations of benzene (Bz) or dichloromethane (DCM), along with various levels of toluene alone or toluene with ethylbenzene and xylene. Monte Carlo simulations were performed and distributions of relevant internal dose metrics of either Bz or DCM were computed. Area under the blood concentration of parent compound versus time curve (AUC)-based variability in AD, TODD, and PW rose for Bz when concomitant "low" exposure to mixtures of increasing complexities occurred (coefficient of variation (CV) = 16-24%, vs. 12-15% for Bz alone), but remained unchanged considering DCM. Conversely, AUC-based CV in NEO fell (15 to 5% for Bz; 12 to 6% for DCM). Comparable trends were observed considering production of metabolites (AMET), except for NEO's CYP2E1-mediated metabolites of Bz, where an increased CV was observed (20 to 71%). For "high" exposure scenarios, Cmax-based variability of Bz and DCM remained unchanged in AD and PW, but decreased in NEO (CV= 11-16% to 2-6%) and TODD (CV= 12-13% to 7-9%). Conversely, AMET-based variability for both substrates rose in every subpopulation. This study analyzed for the first time the impact of multiple exposures on interindividual variability in toxicokinetics. Evidence indicates that this impact depends upon chemical concentrations and biochemical properties, as well as the subpopulation and internal dose metrics considered.

[Health effects of nanoparticles and nanomaterials (III). Toxicity and health effects of nanoparticles]

As described before in the first Frontier Report of this series, there are two types of nanoparticles to be considered in hygiene science; One is the environmental nanoparticle emitted from automobiles and the other is the manufactured nanoparticle. In general nanoparticles (less than 100 nm) are reported to be permeable through cell membrane and tissues and their large surface area is responsible for the greater toxicity compared to larger particles. However, there are contradictory reports on the health effects of nanoparticles. Recent reports suggest that carbon nanotubes, fiber-shaped biopersistent nanoparticles, resemble asbestos in the pathogenesis of granuloma and mesothelioma. As such we summarize health effects of environmental and manufactured nanoparticles in the literature so far including our studies, in this report.

Characterization of the human kinetic adjustment factor for the health risk assessment of environmental contaminants

A default uncertainty factor of 3.16 (√10) is applied to account for interindividual variability in toxicokinetics when performing non-cancer risk assessments. Using relevant human data for specific chemicals, as WHO/IPCS suggests, it is possible to evaluate, and replace when appropriate, this default factor by quantifying chemical-specific adjustment factors for interindividual variability in toxicokinetics (also referred to as the human kinetic adjustment factor, HKAF). The HKAF has been determined based on the distributions of pharmacokinetic parameters (e.g., half-life, area under the curve, maximum blood concentration) in relevant populations. This article focuses on the current state of knowledge of the use of physiologically based algorithms and models in characterizing the HKAF for environmental contaminants. The recent modeling efforts on the computation of HKAF as a function of the characteristics of the population, chemical and its mode of action (dose metrics), as well as exposure scenario of relevance to the assessment are reviewed here. The results of these studies, taken together, suggest the HKAF varies as a function of the sensitive subpopulation and dose metrics of interest, exposure conditions considered (route, duration, and intensity), metabolic pathways involved and theoretical model underlying its computation. The HKAF seldom exceeded the default value of 3.16, except in very young children (i.e., <≈ 3 months) and when the parent compound is the toxic moiety. Overall, from a public health perspective, the current state of knowledge generally suggest that the default uncertainty factor is sufficient to account for human variability in non-cancer risk assessments of environmental contaminants.

Assessing the impact of child/adult differences in hepatic first-pass effect on the human kinetic adjustment factor for ingested toxicants

The objective of this study was to evaluate the impact of interindividual differences in hepatic first-pass effect (FPE) on the magnitude of the human kinetic adjustment factor (HKAF) for ingested toxicants. This factor aims at replacing a default value of 3.2 used in non-cancer risk assessment. Coupled with Monte Carlo simulations, steady-state equations that account for FPE were used to obtain distributions of arterial blood concentrations (CAss) and rates of metabolism in adults, neonates, infants and toddlers continuously exposed to an oral dose of 1 μg/kg/d of theoretical CYP2E1 and CYP1A2 substrates. For such substrates exhibiting a range of blood:air partition coefficients (Pb: 1-10,000) and hepatic extraction ratios in an average adult (E(ad): 0.01-0.99), HKAFs were computed as the ratio of the 95th percentile of dose metrics for each subpopulation over the 50th percentile value in adults. The reduced hepatic enzyme content in neonates as compared to adults resulted in correspondingly diminished FPE. Consequently, HKAFs greater than 3.2 could be observed, based on CAss only, in the following cases: for some CYP2E1 substrates with E(ad) ≤ 0.3, in neonates (max.: 6.3); and for some CYP1A2 substrates with E(ad) ≤ 0.1 and 0.7, in, respectively, neonates and infants (max.: 28.3). Overall, this study pointed out the importance of accounting for child/adult differences in FPE when determining the HKAF for oral exposure.

Daily inhalation rate and time-activity/location pattern in Japanese preschool children

Lack of data on daily inhalation rate and activity of children has been an issue in health risk assessment of air pollutants. This study aimed to obtain the daily inhalation rate and intensity and frequency of physical activity in relation to the environment in Japanese preschool children. Children aged four-six years (n= 138) in the suburbs of Tokyo participated in this study, which involved three days' continuous monitoring of physical activity using a tri-axial accelerometer and parent's completion of a time/location diary during daily life. The estimated three-day mean daily inhalation rate (body temperature, pressure, saturated with water vapor) was 9.9 ± 1.6 m(3) /day (0.52 ± 0.09 m(3) /kg/day). The current daily inhalation rate value of 0.580 m(3) /kg/day proposed for use in health risk assessment in Japan is confirmed to be valid to calculate central value of inhaled dose of air pollutants in five- to six-year-old children. However, the 95th percentile daily inhalation rate of 0.83 m(3) /kg/day based on measurement for five-year-old children is recommended to be used to provide an upper bound estimate of exposure that ensure the protection of all five- to six-year-old children from the health risk of air pollutants. Children spent the majority of their time in sedentary and light level of physical activity (LPA) when indoors, while 85% of their time when outdoors was spent in LPA and moderate-to-vigorous physical activity. The results suggest the need to consider variability of minute respiratory ventilation rate according to the environment for more refined short-term health risk assessment.

Ambient particulate matter and lung function growth in Chinese children

BACKGROUND

Exposure to particulate matter (PM) has been associated with deficits in lung function growth among children in Western countries. However, few studies have explored this association in developing countries, where PM levels are often substantially higher.

METHODS

Children (n = 3273) 6-12 years of age were recruited from 8 schools in 4 Chinese cities. The lung function parameters of forced vital capacity (FVC) and forced expiratory volume in 1 second (FEV1) were measured using computerized spirometers twice a year for up to 3 years (1993-1996). Dichotomous samplers placed in each schoolyard were used to measure PM2.5 and PM10 (PM with diameter ≤ 2.5 μm and ≤ 10 μm, respectively). Multivariable generalized estimating equations were used to examine the association between the quarterly average PM levels and lung function growth during the period of follow-up.

RESULTS

Annual average PM2.5 and PM10 levels in the 4 cities ranged from 57 to 158 μg/m and 95 to 268 μg/m, respectively. In multivariable models, an increase of 10 μg/m of PM2.5 was associated with decreases of 2.7 mL FEV1 (95% confidence interval = -3.5 to -2.0), 3.5 mL FVC (-4.3 to -2.7), 1.4 mL/year FEV1 growth (-1.8 to -0.9), and 1.5 mL/year FVC growth (-2.0 to -1.0). Similar results were seen with PM10 exposure.

CONCLUSIONS

Exposure to ambient particulate matter was associated with decreased growth in lung function among Chinese children.

The occurrence of ultrafine particles in the specific environment of children

Interest in ultrafine particles (UFP) has been increasing due to their specific physico-chemical characteristics. Ultrafine particles are those with an aerodynamic diameter of <0.1 μm and are also commonly know as nanoparticles (0.1 μm = 100 nm). Due to their small size UFP contribute mostly to particle number concentrations and are therefore underestimated in actual pollution measurements, which commonly measure mass concentration. Children represent the most vulnerable group in regard to particulate exposure due to their developing status and different exposures compared to adults. This review discusses the sources of ultrafine particles as well as the specific exposures of children highlighting the importance and uniqueness of this age group.

Options for incorporating children's inhaled dose into human health risk assessment

Increasing attention has been placed on inhalation dosimetry in children because of children's greater air intake rate and unique windows of vulnerability for various toxicants and health outcomes. However, risk assessments have not incorporated this information because dosimetric adjustments have focused upon extrapolation across species rather than across age groups within the human population. The objectives of this study were to synthesize information regarding child/adult intake and dosimetry differences for particles and gases for potential application to risk assessment. Data and models gathered at a 2006 workshop and more recent studies were reviewed to better understand lung development and inhaled dose in children. The results show that child/adult differences exist both on a chemical intake basis and on a deposited or systemic dose basis. These differences can persist for several years and are not captured by standard intraspecies uncertainty factors or by USEPA's reference concentration (RfC) methodology. Options for incorporating children's inhalation exposures into human risk assessments include (1) 3-fold default air intake adjustment for the first 3 years of life with a reduced factor for older children; (2) superseding this default via simplified dosimetry models akin to USEPA's RfC methodology modified for children; (3) utilizing more sophisticated models with better anatomical and air flow descriptions; (4) running these models with input distributions to reflect interchild variability; (5) developing more advanced approaches involving imaging techniques and computational fluid dynamic (CFD) models. These options will enable children's inhaled dose to have a quantitative role in risk assessment that has been lacking and will establish a basis for ongoing research.

New developments in aerosol dosimetry

Dosimetry provides information linking environmental exposures to sites of deposition, removal from these sites, and translocation of deposited materials. Dosimetry also aids in extrapolating laboratory animal and in vitro data to humans. Recent progress has shed light on: properties of particles in relation to their fates in the body; influence of age, gender, body size, and lung diseases on inhaled particle doses; particle movement to the brain via the olfactory nerves; and particle deposition hot spots in the respiratory tract. Ultrafine size has emerged as an important dosimetric characteristic. Particle count, composition, and surface properties are recognized as potentially important toxicology-related considerations. Differences in body size influence airway sizes, inhaled particle deposition, specific ventilation, and specific doses (e.g. per unit body mass). Related to body size, age, gender, species, and strain are also dosimetric considerations. Diseases, such as chronic obstructive pulmonary disease (COPD) and bronchitis, produce uneven doses within the respiratory tract. Traditional concepts of the translocation and clearance of deposited particles have been challenged. Ultrafine particles can translocate to the brain via olfactory nerves, and from the lung to other organs. The clearance rates of particles from tracheobronchial airways are slowed by respiratory tract infections, but newer evidence implies that slow particle clearance from this region also exists in healthy lungs. Finally, hot spots of particle deposition are seen in hollow models, lung tissue, and dosimetric simulations. Local doses to groups of epithelial cells can be much greater than those to surrounding cells. The new insights challenge dosimetry scientists.

Dosimetry of nasal uptake of water-soluble and reactive gases: a first study of interhuman variability

Certain inhaled chemicals, such as reactive, water-soluble gases, are readily absorbed by the nasal mucosa upon inhalation and may cause damage to the nasal epithelium. Comparisons of the spatial distribution of nasal lesions in laboratory animals exposed to formaldehyde with gas uptake rates predicted by computational models reveal that lesions usually occur in regions of the susceptible epithelium where gas absorption is highest. Since the uptake patterns are influenced by air currents in the nose, interindividual variability in nasal anatomy and ventilation rates due to age, body size, and gender will affect the patterns of gas absorption in humans, potentially putting some age groups at higher risk when exposed to toxic gases. In this study, interhuman variability in the nasal dosimetry of reactive, water-soluble gases was investigated by means of computational fluid dynamics (CFD) models in 5 adults and 2 children, aged 7 and 8 years old. Airflow patterns were investigated for allometrically scaled inhalation rates corresponding to resting breathing. The spatial distribution of uptake at the airway walls was predicted to be nonuniform, with most of the gas being absorbed in the anterior portion of the nasal passages. Under the conditions of these simulations, interhuman variability in dose to the whole nose (mass per time per nasal surface area) due to differences in anatomy and ventilation was predicted to be 1.6-fold among the 7 individuals studied. Children and adults displayed very similar patterns of nasal gas uptake; no significant differences were noted between the two age groups.

Acrolein health effects

Acrolein is a chemical used as an intermediate reactive aldehyde in chemical industry. It is used for synthesis of many organic substances, methionine production, and methyl chloride refrigerant. The general population is exposed to acrolein via smoking, second-hand smoke, exposure to wood and plastic smoke. Firefighters and population living or working in areas with heavy automotive traffic may expose to higher level of acrolein via inhalation of smoke or automotive exhaust. Degradation of acrolein in all environmental media occurs rapidly, therefore, environmental accumulation is not expected. Acrolein degrade in 6A days when applied to surface water, and it has not been found as a contaminant in municipal drinking water. Acrolein vapor may cause eye, nasal and respiratory tract irritations in low level exposure. A decrease in breathing rate was reported by volunteers acutely exposed to 0.3A ppm of acrolein. At similar level, mild nasal epithelial dysplasia, necrosis, and focal basal cell metaplasia have been observed in rats. The acrolein effects on gastrointestinal mucosa in the animals include epithelial hyperplasia, ulceration, and hemorrhage. The severity of the effects is dose dependent. Acrolein induces the respiratory, ocular, and gastrointestinal irritations by inducing the release of peptides in nerve terminals innervating these systems. Levels of acrolein between 22 and 249 ppm for 10 min induced a dose-related decrease in substance P (a short-chain polypeptide that functions as a neurotransmitter or neuromodulator).

The effects of fine particle components on respiratory hospital admissions in children

BACKGROUND

Epidemiologic studies have demonstrated an association between acute exposure to ambient fine particles and both mortality and morbidity. Less is known about the relative impacts of the specific chemical constituents of particulate matter<2.5 microm in aerodynamic diameter (PM2.5) on hospital admissions.

OBJECTIVE

This study was designed to estimate the risks of exposure to PM2.5 and several species on hospital admissions for respiratory diseases among children.

DATA AND METHODS

We obtained data on daily counts of hospitalizations for children<19 and <5 years of age for total respiratory diseases and several subcategories including pneumonia, acute bronchitis, and asthma for six California counties from 2000 through 2003, as well as ambient concentrations of PM2.5 and its constituents, including elemental carbon (EC), organic carbon (OC), and nitrates (NO3). We used Poisson regression to estimate risks while controlling for important covariates.

RESULTS

We observed associations between several components of PM2.5 and hospitalization for all of the respiratory outcomes examined. For example, for total respiratory admissions for children<19 years of age, the interquartile range for a 3-day lag of PM2.5, EC, OC, NO3, and sulfates was associated with an excess risk of 4.1% [95% confidence interval (CI), 1.8-6.4], 5.4% (95% CI, 0.8-10.3), 3.4% (95% CI, 1.1-5.7), 3.3% (95% CI, 1.1-5.5), and 3.0% (95% CI, 0.4-5.7), respectively. We also observed associations for several metals. Additional associations with several of the species, including potassium, were observed in the cool season.

CONCLUSION

Components of PM2.5 were associated with hospitalization for several childhood respiratory diseases including pneumonia, bronchitis, and asthma. Because exposure to components (e.g., EC, OC, NO3, and K) and their related sources, including diesel and gasoline exhaust, wood smoke, and other combustion sources, are ubiquitous in the urban environment, it likely represents an identifiable and preventable risk factor for hospitalization for children.

Mechanistic and dose considerations for supporting adverse pulmonary physiology in response to formaldehyde

Induction of airway hyperresponsiveness and asthma from formaldehyde inhalation exposure remains a debated and controversial issue. Yet, recent evidences on pulmonary biology and the pharmacokinetics and toxicity of formaldehyde lend support for such adverse effects. Specifically, altered thiol biology from accelerated enzymatic reduction of the endogenous bronchodilator S-nitrosoglutathione and pulmonary inflammation from involvement of Th2-mediated immune responses might serve as key events and cooperate in airway pathophysiology. Understanding what role these mechanisms play in various species and lifestages (e.g., child vs. adult) could be crucial for making more meaningful inter- and intra-species dosimetric extrapolations in human health risk assessment.

Modeling approaches for estimating the dosimetry of inhaled toxicants in children

Risk assessment of inhaled toxicants has typically focused upon adults, with modeling used to extrapolate dosimetry and risks from lab animals to humans. However, behavioral factors such as time spent playing outdoors may lead to more exposure to inhaled toxicants in children. Depending on the inhaled agent and the age and size of the child, children may receive a greater internal dose than adults because of greater ventilation rate per body weight or lung surface area, or metabolic differences may result in different tissue burdens. Thus, modeling techniques need to be adapted to children in order to estimate inhaled dose and risk in this potentially susceptible life stage. This paper summarizes a series of inhalation dosimetry presentations from the U.S. EPA's Workshop on Inhalation Risk Assessment in Children held on June 8-9, 2006 in Washington, DC. These presentations demonstrate how existing default models for particles and gases may be adapted for children, and how more advanced modeling of toxicant deposition and interaction in respiratory airways takes into account children's anatomy and physiology. These modeling efforts identify child-adult dosimetry differences in respiratory tract regions that may have implications for children's vulnerability to inhaled toxicants. A decision framework is discussed that considers these different approaches and modeling structures including assessment of parameter values, supporting data, reliability, and selection of dose metrics.

Children's response to air pollutants

It is important to focus on children with respect to air pollution because (1) their lungs are not completely developed, (2) they can have greater exposures than adults, and (3) those exposures can deliver higher doses of different composition that may remain in the lung for greater duration. The undeveloped lung is more vulnerable to assault and less able to fully repair itself when injury disrupts morphogenesis. Children spend more time outside, where concentrations of combustion-generated air pollution are generally higher. Children have higher baseline ventilation rates and are more physically active than adults, thus exposing their lungs to more air pollution. Nasal breathing in adults reduces some pollution concentrations, but children are more typically mouth-breathers--suggesting that the composition of the exposure mixture at the alveolar level may be different. Finally, higher ventilation rates and mouth-breathing may pull air pollutants deeper into children's lungs, thereby making clearance slower and more difficult. Children also have immature immune systems, which plays a significant role in asthma. The observed consequences of early life exposure to adverse levels of air pollutants include diminished lung function and increased susceptibility to acute respiratory illness and asthma. Exposure to diesel exhaust, in particular, is an area of concern for multiple endpoints, and deserves further research.

Potential new approaches for children's inhalation risk assessment

The U.S. Environmental Protection Agency (EPA) practice of risk assessment is moving toward more thoroughly considering children's unique susceptibilities and exposure potential. Childhood is assessed as a sequence of life stages that reflects the fact that as humans develop, windows of susceptibility may appear that lead to enhanced sensitivity to exposure of environmental agents, while changes in behavior and physiology may increase exposure and dose. The U.S. EPA developed guidance in the past few years that addresses some aspects of increased susceptibility and exposure and dose. However, when it comes to considering inhalation exposure, dose, and risk, current U.S. EPA practice does not explicitly address children. The purpose here is to begin studying the adequacy of practice for children's health and to explore possible next steps in developing new methods to more accurately assess life-stage-specific differences. The existing guidelines and policies used to address potentially unique susceptibilities of children for inhaled environmental chemicals were considered, as well as what may be learned from examples of approaches that have been applied by state agencies (such as the California Environmental Protection Agency) or in the literature, to incorporate potentially unique susceptibilities and exposures to children. Finally, there is a discussion of possible approaches for considering inhalation exposure and susceptibility in U.S. EPA risk assessments.

Age-dependent partition coefficients for a mixture of volatile organic solvents in Sprague-Dawley rats and humans

The absorption, distribution, metabolism, and excretion of volatile organic compounds (VOCs) are critically determined by a few chemical-specific factors, notably their blood and tissue partition coefficients (PC) and metabolism. Age-specific values for PCs in rats have rarely been reported or utilized in pharmacokinetic modeling for predicting dosimetry in toxicity studies with rats progressing through their lifestages. A mixture of six VOCs (benzene, chloroform, methyl ethyl ketone, methylene chloride, trichloroethylene, and perchloroethylene) was used to determine blood:air and tissue:air PCs in rats at three different ages (postnatal d 10, 60 d, and 2 yr) and blood:air PCs in pediatric and adult human blood. No differences with age in human blood:air PCs for the six compounds were observed. Rat blood:air PCs increased with age varying with compound. Tissue:air PCs showed tissue-specific changes with age. Water-soluble methyl ethyl ketone showed no age-dependent differences. Partition coefficients, particularly the blood:air PC, are key determinants of the rodent and human blood concentrations; age-appropriate values improve the accuracy of pharmacokinetic model predictions of population variability and age-specific exposures.

Think globally, breathe locally

Why the worldwide health impact of air pollution on young children begins in our neighbourhoods