Use of an index to reflect the aggregate burden of long-term exposure to criteria air pollutants in the United States

Bronchiolitis recovery and the use of High Efficiency Particulate Air (HEPA) Filters (The BREATHE Study): study protocol for a multi-center, parallel, double-blind, randomized controlled clinical trial

BACKGROUND

Acute viral bronchiolitis is the most common reason for hospitalization of infants in the USA. Infants hospitalized for bronchiolitis are at high risk for recurrent respiratory symptoms and wheeze in the subsequent year, and longer-term adverse respiratory outcomes such as persistent childhood asthma. There are no effective secondary prevention strategies. Multiple factors, including air pollutant exposure, contribute to risk of adverse respiratory outcomes in these infants. Improvement in indoor air quality following hospitalization for bronchiolitis may be a prevention opportunity to reduce symptom burden. Use of stand-alone high efficiency particulate air (HEPA) filtration units is a simple method to reduce particulate matter ≤ 2.5 µm in diameter (PM2.5), a common component of household air pollution that is strongly linked to health effects.

METHODS

BREATHE is a multi-center, parallel, double-blind, randomized controlled clinical trial. Two hundred twenty-eight children < 12 months of age hospitalized for the first time with bronchiolitis will participate. Children will be randomized 1:1 to receive a 24-week home intervention with filtration units containing HEPA and carbon filters (in the child's sleep space and a common room) or to a control group with units that do not contain HEPA and carbon filters. The primary objective is to determine if use of HEPA filtration units reduces respiratory symptom burden for 24 weeks compared to use of control units. Secondary objectives are to assess the efficacy of the HEPA intervention relative to control on (1) number of unscheduled healthcare visits for respiratory complaints, (2) child quality of life, and (3) average PM2.5 levels in the home.

DISCUSSION

We propose to test the use of HEPA filtration to improve indoor air quality as a strategy to reduce post-bronchiolitis respiratory symptom burden in at-risk infants with severe bronchiolitis. If the intervention proves successful, this trial will support use of HEPA filtration for children with bronchiolitis to reduce respiratory symptom burden following hospitalization.

TRIAL REGISTRATION

NCT05615870. Registered on November 14, 2022.

Long-term exposure to air pollution and risk of insulin resistance: A systematic review and meta-analysis

OBJECTIVE

The effects of air pollution on metabolism have become a popular research topic, and a large number of studies had confirmed that air pollution exposure could induce insulin resistance (IR) to varying degrees, but the results were inconsistent, especially for the long-term exposures. The aim of the current study was to further investigate the potential effects of air pollution on IR.

METHODS

A systematic review and meta-analysis of four electronic databases, including PubMed, Embase, Web of Science and Cochrane were conducted, searching for relevant studies published before June 10, 2023, in order to explore the potential relationships between long-term exposure to air pollution and IR. A total of 10 studies were included for data analysis, including seven cohort studies and three cross-sectional studies. Four major components of air pollution, including PM2.5 (particulate matter with an aerodynamic diameter of 2.5 µm or less), PM10 (particulate matter with an aerodynamic diameter of 10 µm or less), NO2, and SO2 were selected, and each analyzed for the potential impacts on insulin resistance, in the form of adjusted percentage changes in the homeostasis assessment model of insulin resistance (HOMA-IR).

RESULTS

This systematic review and meta-analysis showed that for every 1 μg/m³ increase in the concentration of selected air pollutants, PM2.5 induced a 0.40% change in HOMA-IR (95%CI: -0.03, 0.84; I2 =67.4%, p = 0.009), while PM10 induced a 1.61% change (95%CI: 0.243, 2.968; I2 =49.1%, p = 0.001). Meanwhile, the change in HOMA-IR due to increased NO2 or SO2 exposure concentration was only 0.09% (95%CI: -0.01, 0.19; I2 =83.2%, p = 0.002) or 0.01% (95%CI: -0.04, 0.06; I2 =0.0%, p = 0.638), respectively.

CONCLUSIONS

Long-term exposures to PM2.5, PM10, NO2 or SO2 are indeed associated with the odds of IR. Among the analyzed pollutants, inhalable particulate matters appear to exert greater impacts on IR.

Long-Term Residential Environment Exposure and Subjective Wellbeing in Later Life in Guangzhou, China: Moderated by Residential Mobility History

With rapid global urbanization, the importance of understanding relationships between the changing environment and wellbeing is being increasingly recognized. However, there is still a lack of understanding of how long-term residential environment exposure affects subjective wellbeing under the dual changes of geographical environment and residential location. Based on a survey of the elderly (people over 60 years old) in Guangzhou, China, this study analyzes the effect of long-term residential environment exposure over 25 years on subjective wellbeing in later life in the context of residential mobility. The study found that subjective wellbeing in later life is not only related to the current residential environment but also the cumulative exposure to the long-term residential environment. The relationship between long-term residential environment exposure and subjective wellbeing in later life tends to be stable with the increase of cumulative time, especially the cumulative years over 15 years. Considering the importance of residential mobility history, the study further analyzes the moderating effects of relocation frequency and residential location. Relocation frequency can strengthen the positive effect of residential environment on subjective wellbeing and weaken the negative effect of residential environment on subjective wellbeing, which confirms the existence of residential self-selection. In addition, the direction of effect of residential environment on residents who move between living in the urban center and the periphery is consistent with that of residents who have always lived in the urban center, while the effects of the residential environment on residents who have always lived in the urban center and those who have always lived in the urban periphery are related in different directions. The conclusion of this study can provide guidance for individuals' residential choice and governance of the urban environment to improve wellbeing.

A critical evaluation of air quality index models (1960-2021)

The formulation of an adequate and practical Atmospheric Air Quality Management Plan at different spatial scales at local (micro), city (medium), national (macro)), and temporal (short and long term) is an indispensable solution to prevent the public from air pollution health risk. The air quality monitoring system provides regulatory agencies a comprehensive data of current air contaminants in a particular location. Then, air monitoring data of pollutants is processed into a dimensionless unit called the "Air Quality Index" (AQI); it serves as an information medium for the people to know the air quality health of their location and takes preventative steps accordingly (public participation). Thus, the AQI is a beneficial tool for the public, stakeholders, and regulators to understand the current state of air quality. AQI across the globe considers the number of pollutants (most of the developed countries and some developing countries considers PM_2.5 to measure the overall status of air quality being monitored), averaging time for which pollutants are measured, calculation method to compute air quality indices for each pollutant, calculation mode to aggregate the overall index, scale of an index, categories, colour coding scheme, and related descriptive terms of the pollutants. This article presents rationalized and extensive reviews of various Air Quality Index (AQI) models utilized worldwide from 1960 to 2021, comparing them based on several parameters such as types and number of pollutants (criteria or hazardous air pollutants), averaging time (long-term or short-term), calculation methods (linear or nonlinear), calculation modes [single-pollutant (maximum value) or multi-pollutants (combined effect)]. By analysing the strengths and flaws of all the AQI models developed so far, it is recommended to develop a more reliable, extensible, and comparable AQI model to be employed as an executive tool for designing strategic pollution abatement programs to preserve public health.

Time series analysis and spatial distribution map of aggregate risk index due to tropospheric NO2 and O3 based on satellite observation

A high increase in human activities has led to more emission of air pollutants in metropolises and industrial areas. Recently, remotely sensed data of tropospheric pollutants is used for environmental management and decision-making on large scale. The purpose of this study was a time series analysis of nitrogen dioxide Vertical Column Density (NO₂ VCD) and Ozone (O₃) using Ozone Monitoring Instrument (OMI) from 2005 to 2016 by Mann-Kendall test. Also, the aggregate risk index (ARI) was calculated to estimate the overall impact of exposure to tropospheric NO₂ and O₃ concentrations at the national scale in 2016. To estimate the surface NO₂ related drivers, The Radial Basis Function (RBF) neural network modeling was performed for different months of 2016. Results of Mann-Kendall test showed that tropospheric ozone concentration had an increasing trend in all parts of Iran and this increasing trend was significantly higher in the southern region of Iran and lower in the northern parts of Iran. NO₂ VCD in most parts of Iran had a significant increasing trend. The result of sensitivity analysis showed that NO₂ VCD (1.25), the distance to the industrial area, (1.20) and wind speed (1.07) were the most important variables for the estimation of surface NO₂ concentration. Spatial ARI with the highest risks is mainly located in the Northern half of Iran, especially in Tehran, Alborz, and Khorasan-e- Razavi provinces, where NO₂ and O₃ concentrations are very severe. In northern Iran and central cities, the ARI values are calculated from 1.5 to 2.08, indicating the highest human health risks in these regions. The human health risks based on OMI observation were obtained higher in comparison to AQM data because the satellite data coverage is larger than AQM station and monitors transmitted air pollution by the wind in addition to local pollution. Based on this research, using satellite observation for air quality monitoring is a suitable tool for environmental management on a national scale.

Investigating Health Context: Using Geospatial Big Data Ecosystem (Preprint)

Background

Objective

Methods

Results

Conclusions

Early Spread of COVID-19 in the Air-Polluted Regions of Eight Severely Affected Countries

COVID-19 escalated into a pandemic posing several humanitarian as well as scientific challenges. We here investigated the geographical character of the early spread of the infection and correlated it with several annual satellite and ground indexes of air quality in China, the United States, Italy, Iran, France, Spain, Germany, and the United Kingdom. The time of the analysis corresponded with the end of the first wave infection in China, namely June 2020. We found more viral infections in those areas afflicted by high PM 2.5 and nitrogen dioxide values. Higher mortality was also correlated with relatively poor air quality. In Italy, the correspondence between the Po Valley pollution and SARS-CoV-2 infections and induced mortality was the starkest, originating right in the most polluted European area. Spain and Germany did not present a noticeable gradient of pollution levels causing non-significant correlations. Densely populated areas were often hotspots of lower air quality levels but were not always correlated with a higher viral incidence. Air pollution has long been recognised as a high risk factor for several respiratory-related diseases and conditions, and it now appears to be a risk factor for COVID-19 as well. As such, air pollution should always be included as a factor for the study of airborne epidemics and further included in public health policies.

Relationship between Long-Term Residential Green Exposure and Individuals' Mental Health: Moderated by Income Differences and Residential Location in Urban China

Environmental health effects during urbanization have attracted much attention. However, knowledge is lacking on the relationship between long-term cumulative residential environment and health effects on individuals during rapid transformations in urban physical and social space. Taking Guangzhou, China, as a case example, this study analyzed the relationship between long-term exposure to green environments and residents’ mental health under urban spatial restructuring. Based on a household survey in 2016, 820 residents who have lived in Guangzhou for more than 15 years were used as the sample. High-resolution remote sensing images were used to assess the long-term green exposure of residents. The results indicate that long-term green exposure in residential areas had a negative correlation with residents’ mental health (p < 0.05), and the correlation was strongest for the cumulative green environment in the last five years. However, this significant effect was moderated by income and residential location. Green exposure had a positive relationship with mental health for low income groups, and a negative relationship for middle and high income groups. In addition, residents living farther away from the city center were likely to have fewer green environmental health benefits. Residential relocation in a rapidly urbanizing and transforming China has led to the continuous differentiation of residential green environments among different income groups, which has also caused different mental health effects from green exposure. It provides empirical evidence and theoretical support for policymakers to improve the urban environment and reduce environmental health disparities by considering social differences and residential location.

Effect of O3, PM10 and PM2.5 on cardiovascular and respiratory diseases in cities of France, Iran and Italy

At present, both tropospheric ozone (O₃) and particulate matters (PM) are among the most threatening air pollutants for human health in cities. The air pollution effects over public health include increased risk of hospital admissions and mortality for respiratory and cardiovascular diseases even when air pollutant concentrations are below European and international standards. The aim of this study was to (i) estimate the burden of mortality and morbidity for cardiovascular and respiratory diseases attributed to PM_2.5, PM₁₀ and O₃ in nine selected cities in France, Iran and Italy in 2015 and 2016 and to (ii) compare estimated burdens at current O₃ and PM levels with pre-industrial levels. The selected Mediterranean cities are among the most affected by the air pollution in Europe, in particular by rising O₃ while the selected Iranian cities rank as the most polluted by PM in the world. The software AirQ+ was used to estimate the short-term health effects, in terms of mortality and morbidity by using in situ air quality data, city-specific relative risk values and baseline incidence. Compared to pre-industrial levels, long-term exposures to ambient PM_2.5, PM₁₀ and O₃ have substantially contributed to mortality and hospital admissions in selected cities: about 8200 deaths for non-accidental causes, 2400 deaths for cardiovascular diseases, 540 deaths for respiratory diseases, 220 deaths for chronic obstructive pulmonary diseases as well as 18,800 hospital admissions for cardiovascular diseases and 3400 for respiratory diseases were reported in 2015. The study supports the need of city-specific epidemiological data and urgent strategies to mitigate the health burden of air pollution.

UVC LED Irradiation Effectively Inactivates Aerosolized Viruses, Bacteria, and Fungi in a Chamber-Type Air Disinfection System

In this study, the possibility of inactivating viral, bacterial, and fungal aerosols in a chamber-type air disinfection system by using a UVC light-emitting-diode (LED) array was investigated and inactivation rate constants of each microorganism were calculated in fitting curves of surviving populations. UVC LED array treatment effectively inactivated viral infectivity, achieving 5-log reductions within 45 mJ/cm² for MS2, Qβ, and ϕX174 viruses. UVC LED array effectiveness in inactivating Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium, Listeria monocytogenes, and Staphylococcus aureus aerosols achieved 2.5- to 4-log reductions within 1.5 to 4.6 mJ/cm² Also, 4-log reductions of Aspergillus flavus and Alternaria japonica were achieved at a dosage of 23 mJ/cm² using UVC LED array irradiation. The highest UV susceptibility, represented by the inactivation rate constant, was calculated for bacteria, followed by fungi and viruses. UVC LED, an innovative technology, can effectively inactivate microorganisms regardless of taxonomic classification and can sufficiently substitute for conventional mercury UV lamps.IMPORTANCE The United Nations Environment Programme (UNEP) convened the Minamata Convention on Mercury in 2013 to ban mercury-containing products in order to ensure human and environmental health. It will be effectuated in 2020 to discontinue use of low-pressure mercury lamps and new UV-emitting sources have to replace this conventional technology. However, the UV germicidal irradiation (UVGI) system still uses conventional UV lamps, and no research has been conducted for air disinfection using UVC LEDs. The research reported here investigated the inactivation effect of aerosolized microorganisms, including viruses, bacteria, and fungi, with an UVC LED module. The results can be utilized as a primary database to replace conventional UV lamps with UVC LEDs, a novel type of UV emitter. Implementation of UVC LED technology is truly expected to significantly reduce the extent of global mercury contamination, and this study provides important baseline data to help ensure a healthier environment and increased health for humanity.

Air quality and urban form in U.S. urban areas: evidence from regulatory monitors

The layout of an urban area can impact air pollution via changes in emissions and their spatial distribution. Here, we explore relationships between air quality and urban form based on cross-sectional observations for 111 U.S. urban areas. We employ stepwise linear regression to quantify how long-term population-weighted outdoor concentrations of ozone, fine particulate matter (PM(2.5)), and other criteria pollutants measured by the U.S. Environmental Protection Agency depend on urban form, climate, transportation, city size, income, and region. Aspects of urban form evaluated here include city shape, road density, jobs-housing imbalance, population density, and population centrality. We find that population density is associated with higher population-weighted PM(2.5) concentrations (p < 0.01); population centrality is associated with lower population-weighted ozone and PM(2.5) concentrations (p < 0.01); and transit supply is associated with lower population-weighted PM(2.5) concentrations (p < 0.1). Among pollutants, interquartile range changes in urban form variables are associated with 4%-12% changes in population-weighted concentrations-amounts comparable, for example, to changes in climatic factors. Our empirical findings are consistent with prior modeling research and suggest that urban form could potentially play a modest but important role in achieving (or not achieving) long-term air quality goals.

Environmental health indicators and a case study of air pollution in Latin American cities

Environmental health indicators (EHIs) are applied in a variety of research and decision-making settings to gauge the health consequences of environmental hazards, to summarize complex information, or to compare policy impacts across locations or time periods. While EHIs can provide a useful means of conveying information, they also can be misused. Additional research is needed to help researchers and policy-makers understand categories of indicators and their appropriate application. In this article, we review current frameworks for environmental health indicators and discuss the advantages and limitations of various forms. A case study EHI system was developed for air pollution and health for urban Latin American centers in order to explore how underlying assumptions affect indicator results. Sixteen cities were ranked according to five indicators that considered: population exposed, children exposed, comparison to health-based guidelines, and overall PM(10) levels. Results indicate that although some overall patterns in rankings were observed, cities' relative rankings were highly dependent on the indicator used. In fact, a city that was ranked best under one indicator was ranked worst with another. The sensitivity of rankings, even when considering a simple case of a single pollutant, highlights the need for clear understanding of EHIs and how they may be affected by underlying assumptions. Careful consideration should be given to the purpose, assumptions, and limitations of EHIs used individually or in combination in order to minimize misinterpretation of their implications and enhance their usefulness.

Detection and estimation trends linked to air quality and mortality on French Riviera over the 1990-2005 period

There is a profound relation between human health and well being from the one side and air pollution levels from the other. Air quality in South of France and more specifically in Nice, is known to be bad, especially in summer. The non-parametric Mann-Kendall test has been developed for detecting and estimating monotonic trends in the time series and applied in our study at annual values of pollutants air concentrations and mortality. An important objective of many environmental monitoring programs is to detect changes or trends in pollution levels over time. Over the period 1990-2005, concerning the emissions of main pollutants, we obtained significant decreasing trends. By considering the ozone mean values in urban areas over the 1997-2005 period, an increase of 3.0% year(-1) was obtained with annual averages and 3.9% year(-1) with median values. A clear increasing trend for PM(10) ambient concentrations is obtained. In addition, we observed an increase of the Olea (and Grass) pollination season. Over the same period, an annual change rate of +0.31% year(-1) for "airway diseases" and of +2.50% year(-1) for "unknown causes" were identified in the "Alpes Maritimes" county. To see the results, there seems to be a short-term link between the levels of these pollutants and mortality for respiratory causes. The other pollutants concentration showed a downward trend reflecting the reduction policy of the emissions. In addition, we obtained significant decreasing trends concerning the "ischemic heart diseases" (-1.20% year(-1)) and "asthma" (-4.03% year(-1)) categories. No significant gender-related difference was identified for these groups.

The sociobiologic integrative model (SBIM): enhancing the integration of sociobehavioral, environmental, and biomolecular knowledge in urban health and disparities research

Disentangling the myriad determinants of disease, within the context of urban health or health disparities, requires a transdisciplinary approach. Transdisciplinary approaches draw on concepts from multiple scientific disciplines to develop a novel, integrated perspective from which to conduct scientific investigation. Most historic and contemporary conceptual models of health were derived either from the sociobehavioral sciences or the biomolecular sciences. Those models deriving from the sociobehavioral sciences generally lack detail on involved biological mechanisms whereas those derived from the biomolecular sciences largely do not consider socioenvironmental determinants. As such, advances in transdisciplinary characterizations of health in complex systems like the urban environment or health disparities may be impeded. This paper suggests a sociobiologic organizing model that encourages a multilevel, integrative perspective in the study of urban health and health disparities.

Outdoor air pollution and female lung cancer in Taiwan

To investigate the relationship between air pollution and female lung cancer, the authors conducted a matched case-control study using female deaths that occurred in Taiwan from 1994 through 2003. Data on all eligible female lung cancer deaths were obtained from the Bureau of Vital Statistics of the Taiwan Provincial Department of Health. The control group consisted of women who died from causes other than cancer or diseases associated with respiratory problems. The controls were pair matched to the cases by sex, year of birth, and year of death. Each matched control was selected randomly from the set of possible controls for each case. A municipality-based aggregate index of long-term exposure to air pollution was created by dividing the annual average of the measured values for each pollutant by the National Ambient Air Quality Standard for that pollutant. The ratios for each pollutant were scaled to a 100-point scale and then averaged together to generate an index value representing the net burden of these pollutants, with each weighted equally. The subjects were divided into tertiles according to the levels of the index just described. Women who lived in the group of municipalities with highest levels of air pollution exposure index were at a statistically significant increased lung cancer risk compared to the group living in municipalities with the lowest air pollution exposure index after controlling for possible confounders (OR = 1.28, 95% CI = 1.02-1.61). The findings of this study warrant further investigation of the role of air pollutants in the etiology of lung cancer.

Estimation of the global evolution of atmospheric pollution in Salamanca (Spain) during the 1993-2001 period according to one global index (ORAQI)

The aim of this study has been to use a global index to measure the air quality in the city, apart from individual assessment of the values of the concentrations of the different pollutants. We calculated the ORAQI with the data obtained at four air-pollution monitoring stations located in the city of Salamanca over the period between 1993 and 2001. For the calculations, SO2, PM10, NO2, CO and O3 were used as the most significant pollutants for the surroundings of the monitoring stations. The evolution of this index over 9 years is reported, and the repercussion of the most characteristic pollutants of each season of the year on the ORAQI along the whole period analysed is studied. The importance of the summer pollution in the characterisation of the least polluted surroundings was observed. At the most polluted sites, a decrease in the values corresponding to winter occurs, leading the ORAQI to take similar values along the whole year. In general, taking into account the surroundings of all the monitoring stations, the quality of the air to which the inhabitants of the city of Salamanca are exposed to can be said to be good.

Aryl hydrocarbon receptor-mediated activity of particulate organic matter from the Paso del Norte airshed along the U.S.-Mexico border

In this study, we determined the biologic activity of dichloromethane-extracted particulate matter < 10 micro m in aerodynamic diameter (PM10) obtained from filters at three sites in the Paso del Norte airshed, which includes El Paso, Texas, USA; Juarez, Chihuahua, Mexico, and Sunland Park, New Mexico, USA. The extracts were rich in polycyclic aromatic hydrocarbons (PAHs) and had significant biologic activity, measured using two in vitro assay systems: ethoxyresorufin-(O-deethylase (EROD) induction and the aryl hydrocarbon-receptor luciferase reporter system. In most cases, both EROD (5.25 pmol/min/mg protein) and luciferase activities (994 relative light units/mg) were highest in extracts from the Advance site located in an industrial neighborhood in Juarez. These values represented 58% and 55%, respectively, of induction associated with 1 micro M ss-naphthoflavone exposures. In contrast, little activity was observed at the Northeast Clinic site in El Paso, the reference site. In most cases, luciferase and EROD activity from extracts collected from the Tillman Health Center site, situated in downtown El Paso, fell between those observed at the other two sites. Overall, a statistically significant correlation existed between PM10 and EROD and luciferase activities. Chemical analysis of extracts collected from the Advance site demonstrated that concentrations of most PAHs were higher than those reported in most other metropolitan areas in the United States. Calculations made with these data suggest a cancer risk of 5-12 cases per 100,000 people. This risk estimate, as well as comparisons with the work of other investigators, raises concern regarding the potential for adverse health effects to the residents of this airshed. Further work is needed to understand the sources, exposure, and effects of PM10 and particulate organic material in the Paso del Norte airshed.

Disparities in exposure to air pollution during pregnancy

Previous research shows poorer birth outcomes for racial and ethnic minorities and for persons with low socioeconomic status (SES). We evaluated whether mothers in groups at higher risk for poor birth outcomes live in areas of higher air pollution and whether higher exposure to air pollution contributes to poor birth outcomes. An index representing long-term exposure to criteria air pollutants was matched with birth certificate data at the county level for the United States in 1998-1999. We used linear regression to estimate associations between the air pollution index and maternal race and educational attainment, a marker for SES of the mother, controlling for age, parity, marital status, and region of the country. Then we used logistic regression models both to estimate likelihood of living in counties with the highest levels of air pollution for different racial groups and by educational attainment, adjusting for other maternal risk factors, and to estimate the effect of living in counties with higher levels of air pollution on preterm delivery and births small for gestational age (SGA). Hispanic, African-American, and Asian/Pacific Islander mothers experienced higher mean levels of air pollution and were more than twice as likely to live in the most polluted counties compared with white mothers after controlling for maternal risk factors, region, and educational status [Hispanic mothers: adjusted odds ratio (AOR) = 4.66; 95% confidence interval (95% CI), 1.92-11.32; African-American mothers: AOR = 2.58; 95% CI, 1.00-6.62; Asian/Pacific Islander mothers: AOR = 2.82; 95% CI, 1.07-7.39]. Educational attainment was not associated with living in counties with highest levels of the air pollution index (AOR = 0.95; 95% CI, 0.40-2.26) after adjusting for maternal risk factors, region of the country, and race/ethnicity. There was a small increase in the odds of preterm delivery (AOR = 1.05; 95% CI, 0.99-1.12) but not SGA (AOR = 0.96; 95% CI, 0.86-1.07) in a county with high air pollution. Additional risk of residing in areas with poor air quality may exacerbate health problems of infants and children already at increased risk for poor health.

Primary prevention protects public health

It is widely accepted that epidemiological data provide the only reliable evidence of a carcinogenic effect in humans, but epidemiology is unable to provide early warning of a cancer risk. The experimental approach to carcinogenicity can ascertain and predict potential cancer risks to humans in time for primary prevention to be successful. Unfortunately, only in rare instances were experimental data considered sufficiently convincing per se to stimulate the adoption of preventive measures. The experimental testing of environmental agents is the second line of defense against potential human carcinogens. The first line is the testing of synthesized agents, be these pesticides, medical drugs, or industrial chemical/physical agents, at the time of their development. We do not know, however, how many substances have been prevented from entering the environment because most tests are carried out by commercial or private laboratories and results are rarely released. A better understanding of the mechanisms underlying the sequence of events of the carcinogenesis process will eventually lead to a more accurate characterization and quantification of risks. However, the ways that mechanistic data have been used lately for evaluating evidence of carcinogenicity have not necessarily meant that the evaluations were more closely oriented toward public health. A tendency has surfaced to dismiss the relevance of long-term carcinogenicity studies. In the absence of absolute certainty, rarely if ever reached in biology, it is essential to adopt an attitude of responsible caution, in line with the principles of primary prevention, the only one that may prevent unlimited experimentation on the entire human species.