Air pollution and childhood cancer: A review of the epidemiological literature

Mobile Source Benzene Regulations and Risk of Childhood and Young Adult Hematologic Cancers in Alaska: A Quasi-experimental Study

BACKGROUND

We aimed to evaluate the impact of the EPA's Mobile Source Air Toxics rules (MSAT), which targeted benzene emissions, on childhood and young adult leukemia and lymphoma incidence in Alaska.

METHODS

MSAT was implemented in 2011 and produced a dramatic decline in ambient benzene in Alaska. Due to previous benzene-related regulations enacted in the continental United States, MSAT had relatively modest impacts in other states. This created quasi-experimental conditions leveraged in this study. Using 2-year state-level incidence rates of childhood and young adult leukemia and lymphoma for each US state 2001-2018, we examined MSAT-attributable changes in incidence by applying a difference-in-differences approach.

RESULTS

We found evidence of a substantial reduction associated with MSAT in incidence of childhood and young adult lymphoma (-1.23 [-1.84, -0.62] cases per 100,000), but not in leukemia (-0.13 [-0.77, 0.51] cases per 100,000).

CONCLUSIONS

Our findings are consistent with the hypothesis that MSAT, which reduced benzene levels in Alaska, led to a decline in lymphoma incidence in children and young adults.

Persistently high incidence rates of childhood acute leukemias from 2010 to 2017 in Mexico City: A population study from the MIGICCL

Introduction

Over the years, the Hispanic population living in the United States has consistently shown high incidence rates of childhood acute leukemias (AL). Similarly, high AL incidence was previously observed in Mexico City (MC). Here, we estimated the AL incidence rates among children under 15 years of age in MC during the period 2010-2017.

Methods

The Mexican Interinstitutional Group for the Identification of the Causes of Childhood Leukemia conducted a study gathering clinical and epidemiological information regarding children newly diagnosed with AL at public health institutions of MC. Crude age incidence rates (cAIR) were obtained. Age-standardized incidence rates worldwide (ASIRw) and by municipalities (ASIRm) were calculated by the direct and indirect methods, respectively. These were reported per million population <15 years of age; stratified by age group, sex, AL subtypes, immunophenotype and gene rearrangements.

Results

A total of 903 AL cases were registered. The ASIRw was 63.3 (cases per million) for AL, 53.1 for acute lymphoblastic leukemia (ALL), and 9.4 for acute myeloblastic leukemia. The highest cAIR for AL was observed in the age group between 1 and 4 years (male: 102.34 and female: 82.73). By immunophenotype, the ASIRw was 47.3 for B-cell and 3.7 for T-cell. The incidence did not show any significant trends during the study period. The ASIRm for ALL were 68.6, 66.6 and 62.8 at Iztacalco, Venustiano Carranza and Benito Juárez, respectively, whereas, other municipalities exhibited null values mainly for AML.

Conclusion

The ASIRw for childhood AL in MC is among the highest reported worldwide. We observed spatial heterogeneity of rates by municipalities. The elevated AL incidence observed in Mexican children may be explained by a combination of genetic background and exposure to environmental risk factors.

Germline De Novo Mutations as a Cause of Childhood Cancer

Germline de novo mutations (DNMs) represent one of the important topics that need extensive attention from epidemiologists, geneticists, and other relevant stakeholders. Advances in next-generation sequencing technologies allowed examination of parent-offspring trios to ascertain the frequency of germline DNMs. Many epidemiological risk factors for childhood cancer are indicative of DNMs as a mechanism. The aim of this review was to give an overview of germline DNMs, their causes in general, and to discuss their relation to childhood cancer risk. In addition, we highlighted existing gaps in knowledge in many topics of germline DNMs in childhood cancer that need exploration and collaborative efforts.

Resilience and Equity in a Time of Crises: Investing in Public Urban Greenspace Is Now More Essential Than Ever in the US and Beyond

The intersecting negative effects of structural racism, COVID-19, climate change, and chronic diseases disproportionately affect racial and ethnic minorities in the US and around the world. Urban populations of color are concentrated in historically redlined, segregated, disinvested, and marginalized neighborhoods with inadequate quality housing and limited access to resources, including quality greenspaces designed to support natural ecosystems and healthy outdoor activities while mitigating urban environmental challenges such as air pollution, heat island effects, combined sewer overflows and poor water quality. Disinvested urban environments thus contribute to health inequity via physical and social environmental exposures, resulting in disparities across numerous health outcomes, including COVID-19 and chronic diseases such as cancer and cardiovascular diseases (CVD). In this paper, we build off an existing conceptual framework and propose another conceptual framework for the role of greenspace in contributing to resilience and health equity in the US and beyond. We argue that strategic investments in public greenspaces in urban neighborhoods impacted by long term economic disinvestment are critically needed to adapt and build resilience in communities of color, with urgency due to immediate health threats of climate change, COVID-19, and endemic disparities in chronic diseases. We suggest that equity-focused investments in public urban greenspaces are needed to reduce social inequalities, expand economic opportunities with diversity in workforce initiatives, build resilient urban ecosystems, and improve health equity. We recommend key strategies and considerations to guide this investment, drawing upon a robust compilation of scientific literature along with decades of community-based work, using strategic partnerships from multiple efforts in Milwaukee Wisconsin as examples of success.

Indoor volatile organic compounds exposures and risk of childhood acute leukemia: a case-control study in shanghai

A case-control study was conducted to investigate the relationship between indoor air pollution and childhood acute leukemia (AL) in Shanghai. 97 cases and 148 gender-, age-, and residence-matched controls were included. Indoor air pollution was evaluated by questionnaires and quantitative measurement including 14 volatile organic compounds (VOCs) and nitrogen dioxide (NO₂) in the homes of the two groups. The levels of individual VOCs, VOC families, TVOC (sum of the concentrations of the individual VOCs) and NO₂ were compared between the two groups. Exposure to styrene and butyl alcohol were associated with an increased risk of childhood AL (styrene: odds ratio (OR)=2.33, 95% confidence interval (CI): 1.07-5.07; butyl alcohol: OR = 2.51, 95%CI: 1.19-5.28); 4th quartile of chlorinated hydrocarbons (OR = 2.52, 95%CI: 1.02-6.26) and 3rd quartile of TVOC (OR = 4.03, 95%CI: 1.06-6.81) had significant higher ORs for childhood AL compared with that in the lowest quartiles. Elevated levels of individual VOCs, VOC families and TVOC were also associated with self-reported risk factors. Our findings suggest that VOCs exposure was associated with an elevated risk of childhood AL, underscore that more attention should be paid to indoor air pollution as a risk factor of childhood AL.

Residential Exposure to PM2.5 Components and Risk of Childhood Non-Hodgkin Lymphoma in Denmark: A Nationwide Register-Based Case-Control Study

In a recent study, we observed an increased risk of childhood non-Hodgkin lymphoma (NHL) associated with exposure to fine atmospheric particulate matter (PM_2.5) and black carbon (BC). In this nationwide register-based case-control study, we focus on specific components of PM_2.5 in relation to childhood NHL in Denmark (1981–2013) by identifying all incidents of childhood NHL cases in the Danish Cancer Registry (n = 170) and four (cancer-free) randomly selected controls matched by date of birth and sex. We applied PM_2.5 concentrations and the following sub-components: secondary organic aerosols (SOA), secondary inorganic aerosols (SIA; i.e., NO₃⁻, NH₄⁺ and SO₄²⁻), BC, organic carbon (OC) and sea salt. We calculated a time-weighted exposure average from birth to index-date at all addresses. Odds ratios (ORs) were adjusted for register-based socio-demographic variables. We observed adjusted ORs and 95% confidence intervals (95% CI) of 2.05 (1.10, 3.83) per interquartile range (IQR, 4.83 µg/m³) PM_2.5 and 1.73 (0.68, 4.41) per IQR (3.71 µg/m³) SIA, 0.95 (0.71, 1.29) per IQR (0.05 µg/m³) SOA, 1.22 (1.02, 1.46) per IQR (0.39 µg/m³) BC, 1.02 (0.83, 1.26) per IQR (0.56 µg/m³) OC and 1.01 (0.79, 1.30) per IQR (0.87 µg/m3) sea salt, respectively. The estimates were attenuated after adjustment for PM_2.5, whereas the OR for PM_2.5 remained increased regardless of adjustment for specific components. The findings indicate that the previously observed relation between PM_2.5 and childhood NHL may be related to BC (as reported in our previous study) but also partly to SIA, but the role of specific chemical components of PM_2.5 remains ambiguous.

Ambient ultrafine particle concentrations and incidence of childhood cancers

BACKGROUND

Ambient air pollution has been associated with childhood cancer. However, little is known about the possible impact of ambient ultrafine particles (<0.1 μm) (UFPs) on childhood cancer incidence.

OBJECTIVE

This study aimed to evaluate the association between prenatal and childhood exposure to UFPs and development of childhood cancer.

METHODS

We conducted a population-based cohort study of within-city spatiotemporal variations in ambient UFPs across the City of Toronto, Canada using 653,702 singleton live births occurring between April 1, 1998 and March 31, 2017. Incident cases of 13 subtypes of paediatric cancers among children up to age 14 were ascertained using a cancer registry. Associations between ambient air pollutant concentrations and childhood cancer incidence were estimated using random-effects Cox proportional hazards models. We investigated both single- and multi-pollutant models accounting for co-exposures to PM_2.5 and NO₂.

RESULTS

A total of 1,066 childhood cancers were identified. We found that first trimester exposure to UFPs (Hazard Ratio (HR) per 10,000/cm³ increase = 1.13, 95% CI: 1.03-1.22) was associated with overall cancer incidence diagnosed before 6 years of age after adjusting for PM_2.5, NO₂, and for personal and neighborhood-level covariates. Association between UFPs and overall cancer incidence exhibited a linear shape. No statistically significant associations were found for specific cancer subtypes.

CONCLUSION

Ambient UFPs may represent a previously unrecognized risk factor in the aetiology of cancers in children. Our findings reinforce the importance of conducting further research on the effects of UFPs given their high prevalence of exposure in urban areas.

Air pollution exposure at the residence and risk of childhood cancers in Denmark: A nationwide register-based case-control study

BACKGROUND

The etiology of childhood cancer is poorly understood. The role of environmental factors, including air pollution (AP) exposure, has been addressed previously, but results so far have been inconclusive. In this study, we investigate the association between long-term AP exposures in relation to childhood cancer subtypes in Denmark (1981-2013).

METHODS

We conducted a nationwide register-based case-control study. We identified 7745 incident cases of childhood cancers (<20 years) in the Danish Cancer Registry. Four randomly selected (cancer-free) controls were matched to each case according to sex and date of birth. We modelled concentrations of nitrogen dioxide (NO₂), fine particles (PM_2·5), and black carbon (BC) at all addresses and calculated a time-weighted average from birth to index-date with a state-of-the-art multiscale AP modelling system. We analyzed the risk of childhood cancer in conditional logistic regression models adjusted for socio-demographic variables obtained from registers at the individual and neighborhood level.

FINDINGS

The main analyses included 5045 cases and 18,179 controls. For all cancers combined, we observed odds ratios (ORs) and 95% confidence intervals (95% CI) of 0·97 (0·94, 1·01) per 10 µg/m³ NO₂, 0·89 (0·82, 0·98) per 5 µg/m³ PM_2·5, and 0·94 (0·88, 1·01) per 1 µg/m³ BC, respectively. Most notably, we observed a higher risk of Non-Hodgkin Lymphoma (NHL) with higher childhood AP exposure with ORs and 95% CIs of 1·21 (0·94, 1·55) per 10 µg/m³ NO₂, 2·11 (1·10, 4·01) per 5 µg/m³ PM_2·5, and 1·68 (1·06, 2·66) per 1 µg/m³ BC, respectively. We observed indications of increased risks for other types of childhood cancer, however, with very wide CIs including 1.

INTERPRETATIONS

The findings of this nation-wide study propose a role of AP in the development of childhood NHL, but more large-scale studies are needed.

FUNDING

NordForsk Project #75007.

Childhood Leukemia in Small Geographical Areas and Proximity to Industrial Sources of Air Pollutants in Three Colombian Cities

Acute leukemia is the most common childhood cancer and has been associated with exposure to environmental carcinogens. This study aimed to identify clusters of acute childhood leukemia (ACL) cases and analyze their relationship with proximity to industrial sources of air pollution in three capital cities in Colombia during 2000-2015. Incident ACL cases were obtained from the population cancer registries for the cities of Bucaramanga, Cali, and Medellín. The inventory of industrial sources of emissions to the air was obtained from the regional environmental authorities and industrial conglomerates were identified. The Kulldorf's circular scan test was used to detect city clusters and to identify clusters around industrial conglomerates. Multivariable spatial modeling assessed the effect of distance and direction from the industrial conglomerates controlling for socioeconomic status. We identified industrials sectors within a buffer of 1 km around industrial conglomerates related to the ACL clusters. Incidence rates showed geographical heterogeneity with low spatial autocorrelation within cities. The spatio-temporal tests identified one cluster in each city. The industries located within 1 km around the ACL clusters identified in the three cities represent different sectors. Exposure to air pollution from industrial sources might be contributing to the incidence of ACL cases in urban settings in Colombia.

Fine Particulate Matter Air Pollution and Mortality among Pediatric, Adolescent, and Young Adult Cancer Patients

BACKGROUND

Air pollution is a carcinogen and causes pulmonary and cardiac complications. We examined the association of fine particulate matter pollution (PM_2.5) and mortality from cancer and all causes among pediatric, adolescent, and young adult (AYA) patients with cancer in Utah, a state with considerable variation in PM_2.5.

METHODS

We followed 2,444 pediatric (diagnosed ages 0-14) and 13,459 AYA (diagnosed ages 15-39) patients diagnosed in 1986-2015 from diagnosis to 5 and 10 years postdiagnosis, death, or emigration. We measured average monthly PM_2.5 by ZIP code during follow-up. Separate pediatric and AYA multivariable Cox models estimated the association of PM_2.5 and mortality. Among AYAs, we examined effect modification of PM_2.5 and mortality by stage while controlling for cancer type.

RESULTS

Increases in PM_2.5 per 5 μg/m³ were associated with cancer mortality in pediatric lymphomas and central nervous system (CNS) tumors at both time points, and all cause mortality in lymphoid leukemias [HR_5-year = 1.32 (1.02-1.71)]. Among AYAs, PM_2.5 per 5 μg/m³ was associated with cancer mortality in CNS tumors and carcinomas at both time points, and all cause mortality for all AYA cancer types [HR_5-year = 1.06 (1.01-1.13)]. PM_2.5 ≥12 μg/m³ was associated with cancer mortality among breast [HR_5-year = 1.50 (1.29-1.74); HR_10-year = 1.30 (1.13-1.50)] and colorectal cancers [HR_5-year = 1.74 (1.29-2.35); HR_10-year = 1.67 (1.20-2.31)] at both time points. Effect modification by stage was significant, with local tumors at highest risk.

CONCLUSIONS

PM_2.5 was associated with mortality in pediatric and AYA patients with specific cancers.

IMPACT

Limiting PM_2.5 exposure may be important for young cancer patients with certain cancers.See all articles in this CEBP Focus section, "Environmental Carcinogenesis: Pathways to Prevention."

Air quality, health impacts and burden of disease due to air pollution (PM10, PM2.5, NO2 and O3): Application of AirQ+ model to the Camp de Tarragona County (Catalonia, Spain)

The purpose of this study was to assess the impact to human health of air pollutants, through the integration of different technics: data statistics (spatial and temporal trends), population attributable fraction using AIRQ+ model developed by the WHO, and burden of disease using Disability-Adjusted Life Years (DALYs). The levels of SO₂, NO, NO₂, O₃, H₂S, benzene, PM₁₀, PM_2.5, CO, benzo(a)pyrene and metals, obtained between 2005 and 2017 from the air quality monitoring network across Camp de Tarragona County, were temporally and spatially determined. Health impacts were evaluated using the AIRQ+ model. Finally, the burden of disease was assessed through the calculation of Years of Lost life (YLL) and Years Lost due to Disability (YLD). In general terms, air quality was good according to European quality standards, but it did not fulfil the WHO guidelines, especially for O₃, PM₁₀ and PM_2.5. Several decreasing (NO, NO₂, SO₂, PM₁₀ and benzene) and an increasing (O₃) temporal trend were found. Correlation between unemployment rate and air pollutant levels was found, pointing that the economic crisis (2008-2014) was a factor influencing the air pollutant levels. Reduction of air pollutant levels (PM_2.5) to WHO guidelines in the Camp de Tarragona County would decrease the adult mortality between 23 and 297 cases per year, which means between 0.5 and 7% of all mortality in the area. In this County, for lung cancer, ischemic heart disease, stroke, and chronic obstructive pulmonary disease due to levels of PM_2.5 above the WHO threshold limits, DAYLs were 240 years. This means around 80 DALYs for 100,000 persons every year -between 2005 and 2017. Population attributable fraction (PAF) and burden of disease (DALYs) methodologies are suitable tools for regional and national policymakers, who must take decisions to prevent and to control air pollution and to analyse the cost-effectiveness of interventions.

Responses of serum chemokines to dramatic changes of air pollution levels, a panel study

Background: Despite the in vitro and in vivo evidence, studies are limited in evaluating whether chemokines are potential inflammatory mediators in response to air pollution exposure in humans. Methods: We conducted a panel study coinciding with the Beijing Olympics, when temporary air pollution controls were implemented. We measured a suite of serum chemokines among healthy adults before, during and after the Olympics, respectively. Linear mixed-effect models were used to evaluate changes in chemokine levels over the three time periods. Results: In response to the 50% drop in air pollution levels during the games, levels of RANTES, MCP-2, and TARC decreased by 25.8%, 20.9% and 35.3%, respectively (p < 0.001) from pre-Olympics, and then increased by 45.8%, 34.9% and 61.5%, respectively (p < 0.001) after the games when air pollution levels went up again. Similar patterns were observed in subgroup analyses by sex, age, smoking and body mass index. GRO-α and IL-8 decreased significantly during the games (22.5% and 30.4%), and increased non-significantly after the games. Eotaxin-1 only increased significantly from during- to post-games. Conclusions: The strongest associations with air pollution levels were observed among RANTES, TARC and MCP-2. Those chemokines may play important roles in the air pollution-induced inflammatory pathway.

Exposure to ambient air pollution and risk of childhood cancers: A population-based study in Tehran, Iran

The relationship between air pollution and childhood cancer is inconclusive. We investigated the associations between exposure to ambient air pollution and childhood cancers in Tehran, Iran. This project included children between 1 and 15 years-of-age with a cancer diagnosis by the Center for the Control of Non Communicable Disease (n = 161) during 2007 to 2009. Controls were selected randomly within the city using a Geographic Information System (GIS) (n = 761). The cases were geocoded based on exact home addresses. Air pollution exposure of cases and random controls were estimated by a previously developed Land Use Regression (LUR) model for the 2010 calendar year. The annual mean concentrations of Particulate Matter ≤ 10 μm (PM₁₀), nitrogen dioxide (NO₂) and sulfur dioxide (SO₂) in the locations of cancer cases were 101.97 μg/m³, 49.42 ppb and 38.92 ppb respectively, while in the random control group, respective mean exposures were 98.63 μg/m³, 45.98 ppb and 38.95 ppb. A logistic regression model was used to find the probability of childhood cancer per unit increase in PM₁₀, NO₂ and SO₂. We observed a positive association between exposures to PM₁₀ with childhood cancers. We did, however, observe a positive, but not statistically significant association between NO₂ exposure and childhood cancer. Our study is the first to highlight an association between air pollution exposure and childhood cancer risk in Iran, however these findings require replication through future studies.

Childhood leukaemia risk and residential proximity to busy roads

BACKGROUND

Current evidence suggests that childhood leukaemia can be associated with residential traffic exposure; nevertheless, more results are needed to support this conclusion.

OBJECTIVES

To ascertain the possible effects of residential proximity to road traffic on childhood leukaemia, taking into account traffic density, road proximity and the type of leukaemia (acute lymphoid leukaemia or acute myeloid leukaemia).

METHODS

We conducted a population-based case-control study of childhood leukaemia in Spain, covering the period 1990-2011. It included 1061 incidence cases gathered from the Spanish National Childhood Cancer Registry and those Autonomous Regions with 100% coverage, and 6447 controls, individually matched by year of birth, sex and autonomous region of residence. Distances were computed from the respective participant's residential locations to the different types of roads and four different buffers. Using logistic regression, odds ratios (ORs) and 95% confidence intervals (95%CIs), were calculated for four different categories of distance to roads.

RESULTS

Cases of childhood leukaemia had more than three-fold increased odds of living at <50 m of the busiest motorways compared to controls (OR = 2.90; 95%CI = 1.30-6.49). The estimates for acute lymphoid leukaemia (ALL) were slightly higher (OR = 2.95; 95%CI = 1.22-7.14), while estimates for cases with the same address at birth and at diagnosis were lower (OR = 2.40; 95%CI = 0.70-8.30).

CONCLUSIONS

Our study agrees with the literature and furnishes some evidence that living near a busy motorway could be a risk factor for childhood leukaemia.

Road Traffic Pollution and Childhood Leukemia: A Nationwide Case-control Study in Italy

BACKGROUND

The association of childhood leukemia with traffic pollution was considered in a number of studies from 1989 onwards, with results not entirely consistent and little information regarding subtypes.

AIM OF THE STUDY

We used the data of the Italian SETIL case-control on childhood leukemia to explore the risk by leukemia subtypes associated to exposure to vehicular traffic.

METHODS

We included in the analyses 648 cases of childhood leukemia (565 Acute lymphoblastic-ALL and 80 Acute non lymphoblastic-AnLL) and 980 controls. Information on traffic exposure was collected from questionnaire interviews and from the geocoding of house addresses, for all periods of life of the children.

RESULTS

We observed an increase in risk for AnLL, and at a lower extent for ALL, with indicators of exposure to traffic pollutants. In particular, the risk was associated to the report of closeness of the house to traffic lights and to the passage of trucks (OR: 1.76; 95% CI 1.03-3.01 for ALL and 6.35; 95% CI 2.59-15.6 for AnLL). The association was shown also in the analyses limited to AML and in the stratified analyses and in respect to the house in different period of life.

CONCLUSIONS

Results from the SETIL study provide some support to the association of traffic related exposure and risk for AnLL, but at a lesser extent for ALL. Our conclusion highlights the need for leukemia type specific analyses in future studies. Results support the need of controlling exposure from traffic pollution, even if knowledge is not complete.

Maternal exposure to ambient air pollution and risk of early childhood cancers: A population-based study in Ontario, Canada

BACKGROUND

There are increasing concerns regarding the role of exposure to ambient air pollution during pregnancy in the development of early childhood cancers.

OBJECTIVE

This population based study examined whether prenatal and early life (<1year of age) exposures to ambient air pollutants, including nitrogen dioxide (NO₂) and particulate matter with aerodynamic diameters ≤2.5μm (PM_2.5), were associated with selected common early childhood cancers in Canada.

METHODS

2,350,898 singleton live births occurring between 1988 and 2012 were identified in the province of Ontario, Canada. We assigned temporally varying satellite-derived estimates of PM_2.5 and land-use regression model estimates of NO₂ to maternal residences during pregnancy. Incident cases of 13 subtypes of pediatric cancers among children up to age 6 until 2013 were ascertained through administrative health data linkages. Associations of trimester-specific, overall pregnancy and first year of life exposures were evaluated using Cox proportional hazards models, adjusting for potential confounders.

RESULTS

A total of 2044 childhood cancers were identified. Exposure to PM_2.5, per interquartile range increase, over the entire pregnancy, and during the first trimester was associated with an increased risk of astrocytoma (hazard ratio (HR) per 3.9μg/m3=1.38 (95% CI: 1.01, 1.88) and, HR per 4.0μg/m³=1.40 (95% CI: 1.05-1.86), respectively). We also found a positive association between first trimester NO₂ and acute lymphoblastic leukemia (ALL) (HR=1.20 (95% CI: 1.02-1.41) per IQR (13.3ppb)).

CONCLUSIONS

In this population-based study in the largest province of Canada, results suggest an association between exposure to ambient air pollution during pregnancy, especially in the first trimester and an increased risk of astrocytoma and ALL. Further studies are required to replicate the findings of this study with adjustment for important individual-level confounders.

Risk of bone tumors in children and residential proximity to industrial and urban areas: New findings from a case-control study

Few epidemiologic studies have explored risk factors for bone tumors in children, and the role of environmental factors needs to be analyzed. Our objective was to ascertain the association between residential proximity to industrial plants and urban areas and risk of bone tumors in children, taking into account industrial groups and toxic pollutants released. A population-based case-control study of childhood bone cancer in Spain was carried out, covering 114 incident cases obtained from the Spanish Registry of Childhood Tumors (between 1996 and 2011), and 684 controls individually matched by sex, year of birth, and autonomous region of residence. Distances from the subject's residences to the 1271 industries and the 30 urban areas (towns) with ≥75,000 inhabitants located in the study area were computed. Unconditional logistic regression models were fitted to estimate odds ratios (ORs) and 95% confidence intervals (95%CIs) for categories of distance (from 1km to 3km) to industrial and urban areas, with adjustment for matching variables and sociodemographic indicators. Excess risk (OR; 95%CI) of bone tumors in children was detected for children close to industrial facilities as a whole (2.33; 1.17-4.63 at 3km) - particularly surface treatment of metals (OR=2.50; 95%CI=1.13-5.56 at 2km), production and processing of metals (OR=3.30; 95%CI=1.41-7.77 at 2.5km), urban waste-water treatment plants (OR=4.41; 95%CI=1.62-11.98 at 2km), hazardous waste (OR=4.63; 95%CI=1.37-15.61 at 2km), disposal or recycling of animal waste (OR=4.73; 95%CI=1.40-15.97 at 2km), cement and lime (OR=3.89; 95%CI=1.19-12.77 at 2.5km), and combustion installations (OR=3.85; 95%CI=1.39-10.66 at 3km)-, and urban areas (4.43; 1.80-10.92). These findings support the need for more detailed exposure assessment of certain toxics released by these facilities.

Differences in environmental exposure assignment due to residential mobility among children with a central nervous system tumor: Texas, 1995-2009

In epidemiologic studies of childhood cancer, environmental exposures are often assigned based on either residence at birth or diagnosis without considering the impact of residential mobility. Therefore, we evaluated residential mobility and exposure assignment differences to hazardous air pollutants between birth and diagnosis in children with a central nervous system (CNS) tumor. Children diagnosed with CNS tumors during 1995-2009 (N=1,196) were identified from the Texas Cancer Registry. Census tract-level estimates of 1,3-butadiene and benzene were used to assign quartiles of exposure based on the maternal residence at birth and the child's residence at diagnosis. Overall, 64% of younger (0-4 years) children and 79% of older (5-14 years) children moved between birth and diagnosis. Using mixed-effects ordinal logistic regression, residence at diagnosis compared to birth did not result in a significant change in exposure assignment for younger children; however, older children were more likely to be placed in a lower 1,3-butadiene or benzene exposure quartile based on residence at diagnosis compared to birth (odds ratio (OR)=0.58, 95% confidence interval (CI)=0.45-0.76; OR=0.57, 95% CI=0.44-0.75, respectively). In conclusion, while the majority of children moved between birth and CNS tumor diagnosis, mobility did not significantly impact 1,3-butadiene and benzene exposure assessment in younger children.

Maternal residential proximity to major roadways at delivery and childhood central nervous system tumors

BACKGROUND

Due to concerns over the impact of traffic-related air pollution on childhood cancers, we evaluated the association between residential proximity to major roadways and childhood central nervous system (CNS) tumors.

METHODS

The Texas Cancer Registry provided information on children diagnosed with a CNS tumor at <5 years of age and born in Texas for the period 2003-2009 (n=315). Birth certificate controls were frequency matched to cases (5:1) on birth year (n=1575). We assigned exposures to traffic-related air pollution using residential proximity to major roadways based on the maternal residence at the time of delivery. Logistic regression was used to generate unadjusted and adjusted odds ratios and 95% confidence intervals (CI). We evaluated CNS tumors as a group and by histologic type.

RESULTS

Maternal residential proximity to major roadways at delivery was positively associated with the odds of offspring having a CNS tumor. Specifically, for every kilometer closer to a major roadway, the odds of offspring having a CNS tumor increased by 30% (95% CI: 1.0, 1.7). Mothers living ≤500 meters (m) from a major roadway were 31% (95% CI: 1.0, 1.8) more likely to have offspring with any CNS tumor and 3.1-times (95% CI: 0.9, 10.4) more likely to have offspring with an ependymoma compared to mothers living >500m from the nearest major roadway. Moreover, compared to mothers living in areas with low roadway density, those living in areas with high roadway density were 51% (95% CI: 1.1, 2.1) more likely to have offspring with any CNS tumor and 4.2-times (95% CI: 1.2, 14.9) more likely to have offspring with an ependymoma. There were no statistically significant associations observed between continuous distance to major roadways and ependymoma as well as between the proximity measures and the other evaluated CNS tumor phenotypic groups.

CONCLUSIONS

The results of this large population-based study indicate that mothers who live near major roadways or in areas with high roadway density may be more likely to have offspring with a CNS tumor, particularly an ependymoma.

Parental, In Utero, and Early-Life Exposure to Benzene and the Risk of Childhood Leukemia: A Meta-Analysis

Benzene is an established cause of adult leukemia, but whether it is associated with childhood leukemia remains unclear. We conducted a meta-analysis in which we reviewed the epidemiologic literature on this topic and explored causal inference, bias, and heterogeneity. The exposure metrics that we evaluated included occupational and household use of benzenes and solvents, traffic density, and traffic-related air pollution. For studies of occupational and household product exposure published from 1987 to 2014, the summary relative risk for childhood leukemia was 1.96 (95% confidence interval (CI): 1.53, 2.52; n = 20). In these studies, the summary relative risk was higher for acute myeloid leukemia (summary relative risk (sRR) = 2.34, 95% CI: 1.72, 3.18; n = 6) than for acute lymphoblastic leukemia (sRR = 1.57; 95% CI: 1.21, 2.05; n = 14). The summary relative risk was higher for maternal versus paternal exposure, in studies that assessed benzene versus all solvents, and in studies of gestational exposure. In studies of traffic density or traffic-related air pollution published from 1999 to 2014, the summary relative risk was 1.48 (95% CI: 1.10, 1.99; n = 12); it was higher for acute myeloid leukemia (sRR = 2.07; 95% CI: 1.34, 3.20) than for acute lymphoblastic leukemia (sRR = 1.49; 95% CI: 1.07, 2.08) and in studies that involved detailed models of traffic pollution (sRR = 1.70; 95% CI: 1.16, 2.49). Overall, we identified evidence of associations between childhood leukemia and several different potential metrics of benzene exposure.

Childhood cancer and residential exposure to highways: a nationwide cohort study

Children living near highways are exposed to higher concentrations of traffic-related carcinogenic pollutants. Several studies reported an increased risk of childhood cancer associated with traffic exposure, but the published evidence is inconclusive. We investigated whether cancer risk is associated with proximity of residence to highways in a nation-wide cohort study including all children aged <16 years from Swiss national censuses in 1990 and 2000. Cancer incidence was investigated in time to event analyses (1990-2008) using Cox proportional hazards models and incidence density analyses (1985-2008) using Poisson regression. Adjustments were made for socio-economic factors, ionising background radiation and electromagnetic fields. In time to event analysis based on 532 cases the adjusted hazard ratio for leukaemia comparing children living <100 m from a highway with unexposed children (≥500 m) was 1.43 (95 % CI 0.79, 2.61). Results were similar in incidence density analysis including 1367 leukaemia cases (incidence rate ratio (IRR) 1.57; 95 % CI 1.09, 2.25). Associations were similar for acute lymphoblastic leukaemia (IRR 1.64; 95 % CI 1.10, 2.43) and stronger for leukaemia in children aged <5 years (IRR 1.92; 95 % CI 1.22, 3.04). Little evidence of association was found for other tumours. Our study suggests that young children living close to highways are at increased risk of developing leukaemia.

Exposure to ambient air pollution in Canada and the risk of adult leukemia

There is a paucity of studies investigating adult leukemia and air pollution. To address this gap, we analyzed data from a Canadian population-based case-control study conducted in 1994-1997. Cases were 1064 adults with incident leukemia and controls were 5039 healthy adults. We used data from satellites and fixed-site monitoring stations to estimate residential concentrations of NO2 and fine particulate matter (PM2.5) for the period prior to diagnosis, starting in 1975 and ending in 1994. We modeled the average annual exposure of each subject. Odds ratios (OR) and their 95% confidence intervals (CI) were estimated using logistic regression, adjusted for age, gender, province, smoking, education, body mass index, income, and self-reported exposures to ionizing radiation and benzene. We found an 'n-shaped' response function between exposure to NO2 and all forms of leukemia: from the tenth percentile to the median (4.51 to 14.66 ppb), the OR was 1.20; 95% CI: 0.97-1.48 and from the 75th percentile to the 90th (22.75 to 29.7 ppb), the OR was 0.79; 95% CI 0.68-0.93. For PM2.5 we found a response function consistent with a linear model, with an OR per 10 μg/m(3) of 0.97 (95% CI 0.75-1.26). For chronic lymphocytic leukemia we found response functions that were consistent with a simple linear model, with an OR per 5 ppb of NO2 of 0.93 (95% CI 0.86-1.00) and an OR per 10 μg/m(3) of PM2.5 of 0.62 (95% CI 0.42-0.93). In summary, for chronic lymphocytic leukemia we found no evidence of an association with air pollution and with all forms of leukemia we found weak evidence of an association only at low concentrations of NO2. It is possible that these inconsistent results may have arisen because of unaccounted urban/rural differences or possibly from a selection effect, especially among controls.

Childhood cancer and exposure to corona ions from power lines: an epidemiological test

We previously reported an association between childhood leukaemia in Britain and proximity of the child's address at birth to high-voltage power lines that declines from the 1960s to the 2000s. We test here whether a 'corona-ion hypothesis' could explain these results. This hypothesis proposes that corona ions, atmospheric ions produced by power lines and blown away from them by the wind, increase the retention of airborne pollutants in the airways when breathed in and hence cause disease. We develop an improved model for calculating exposure to corona ions, using data on winds from meteorological stations and considering the whole length of power line within 600 m of each subject's address. Corona-ion exposure is highly correlated with proximity to power lines, and hence the results parallel the elevations in leukaemia risk seen with distance analyses. But our model explains the observed pattern of leukaemia rates around power lines less well than straightforward distance measurements, and ecological considerations also argue against the hypothesis. This does not disprove the corona-ion hypothesis as the explanation for our previous results, but nor does it provide support for it, or, by extension, any other hypothesis dependent on wind direction.

Polycyclic aromatic hydrocarbons in residential dust and risk of childhood acute lymphoblastic leukemia

Several polycyclic aromatic hydrocarbons (PAHs) are known or probable human carcinogens. We evaluated the relationship between PAH exposure and risk of childhood acute lymphoblastic leukemia (ALL) using concentrations in residential dust as an exposure indicator. We conducted a population-based case-control study (251 ALL cases, 306 birth-certificate controls) in Northern and Central California from 2001 to 2007. We collected residential dust using a high volume small surface sampler (HVS3) (n=185 cases, 212 controls) or by sampling from participants' household vacuum cleaners (n=66 cases, 94 controls). We evaluated log-transformed concentrations of 9 individual PAHs, the summed PAHs, and the summed PAHs weighted by their carcinogenic potency (the toxic equivalence). We calculated odds ratios (ORs) and 95% confidence intervals (CI) using logistic regression adjusting for demographic characteristics and duration between diagnosis/reference date and dust collection. Among participants with HVS3 dust, risk of ALL was not associated with increasing concentration of any PAHs based on OR perln(ng/g). Among participants with vacuum dust, we observed positive associations between ALL risk and increasing concentrations of benzo[a]pyrene (OR perln[ng/g]=1.42, 95% CI=0.95, 2.12), dibenzo[a,h]anthracene (OR=1.98, 95% CI=1.11, 3.55), benzo[k]fluoranthene (OR=1.71, 95% CI=0.91, 3.22), indeno[1,2,3-cd]pyrene (OR=1.81, 95% CI=1.04, 3.16), and the toxic equivalence (OR=2.35, 95% CI=1.18, 4.69). The increased ALL risk among participants with vacuum dust suggests that PAH exposure may increase the risk of childhood ALL; however, reasons for the different results based on HVS3 dust samples deserve further study.

Prenatal exposure to traffic-related air pollution and risk of early childhood cancers

Exposure to air pollution during pregnancy has been linked to the risk of childhood cancer, but the evidence remains inconclusive. In the present study, we used land use regression modeling to estimate prenatal exposures to traffic exhaust and evaluate the associations with cancer risk in very young children. Participants in the Air Pollution and Childhood Cancers Study who were 5 years of age or younger and diagnosed with cancer between 1988 and 2008 were had their records linked to California birth certificates, and controls were selected from birth certificates. Land use regression-based estimates of exposures to nitric oxide, nitrogen dioxide, and nitrogen oxides were assigned based on birthplace residence and temporally adjusted using routine monitoring station data to evaluate air pollution exposures during specific pregnancy periods. Logistic regression models were adjusted for maternal age, race/ethnicity, educational level, parity, insurance type, and Census-based socioeconomic status, as well as child's sex and birth year. The odds of acute lymphoblastic leukemia increased by 9%, 23%, and 8% for each 25-ppb increase in average nitric oxide, nitrogen dioxide, and nitrogen oxide levels, respectively, over the entire pregnancy. Second- and third-trimester exposures increased the odds of bilateral retinoblastoma. No associations were found for annual average exposures without temporal components or for any other cancer type. These results lend support to a link between prenatal exposure to traffic exhaust and the risk of acute lymphoblastic leukemia and bilateral retinoblastoma.

Environmental Toxicology: Children at Risk

Children today live in a world that is vastly different from a few generations ago. While industrialization has maximized (for many) children’s opportunities to survive, develop and enjoy high levels of health, education, recreation, and fulfillment, it has also added significant challenges to their development.

Genetic polymorphisms of NQO1, CYP1A1 and TPMT and susceptibility to acute lymphoblastic leukemia in a Tunisian population

Acute lymphoblastic leukemia (ALL) is the major pediatric cancer in developed countries. The etiology of ALL remains poorly understood, with few established environmental risk factors. These risks were influenced by co-inheritance of multiple low-risk genetic polymorphisms such as variants within cytochrome P450A1 (CYP1A1), NADPH: quinone oxidoreductase (NQO1) and Thiopurine methyltransferase (TPMT) genes. In this work, we conduct a case-control study to assess the impact of CYP1A1*2A (CYP1A1 T6235C); NQO1*2 (NQO1 C609T); TPMT*2 (TPMT G238C) and TPMT A719G polymorphisms on the risk of developing ALL. The frequencies of TPMT*2, TPMT A719G, NQO1*2 and CYP1A1*2 variants were examined in 100 patients with ALL and 106 healthy controls by allele specific PCR and/or PCR-RFLP methods using blood samples. We have found that NQO1 609CT genotype was overrepresented in patients and was associated with an aggravating effect compared to the reference group with NQO1 609CC genotype (p = 0.028, OR = 1.41; CI 95 %: 1.04-1.93). However, TPMT*2, TPMT 719*G and CYP1A1*2 variants did not appear to influence ALL susceptibility (p > 0.05). Moreover we have not found a significant correlation between the studied variants and Bcr-Abl transcript. In conclusion we retain that leukemogenesis of ALL is associated with carcinogens metabolism and consequently related to environmental exposures.

GIS-modeled indicators of traffic-related air pollutants and adverse pulmonary health among children in El Paso, Texas

Investigators examined 5,654 children enrolled in the El Paso, Texas, public school district by questionnaire in 2001. Exposure measurements were first collected in the late fall of 1999. School-level and residence-level exposures to traffic-related air pollutants were estimated using a land use regression model. For 1,529 children with spirometry, overall geographic information system (GIS)-modeled residential levels of traffic-related ambient air pollution (calibrated to a 10-ppb increment in nitrogen dioxide levels) were associated with a 2.4% decrement in forced vital capacity (95% confidence interval (CI): -4.0, -0.7) after adjustment for demographic, anthropomorphic, and socioeconomic factors and spirometer/technician effects. After adjustment for these potential covariates, overall GIS-modeled residential levels of traffic-related ambient air pollution (calibrated to a 10-ppb increment in nitrogen dioxide levels) were associated with pulmonary function levels below 85% of those predicted for both forced vital capacity (odds ratio (OR) = 3.10, 95% CI: 1.65, 5.78) and forced expiratory volume in 1 second (OR = 2.35, 95% CI: 1.38, 4.01). For children attending schools at elevations above 1,170 m, a 10-ppb increment in modeled nitrogen dioxide levels was associated with current asthma (OR = 1.56, 95% CI: 1.08, 2.50) after adjustment for demographic, socioeconomic, and parental factors and random school effects. These results are consistent with previous studies in Europe and California that found adverse health outcomes in children associated with modeled traffic-related air pollutants.

DNA double-strand breaks and DNA recombination in benzene metabolite-induced genotoxicity

In utero exposure to environmental carcinogens, including the ubiquitous pollutant benzene, may cause DNA damage in the fetus, leading to an increased risk for the development of childhood cancer. Benzene metabolite-induced DNA double-strand breaks (DSBs) may undergo erroneous repair, leading to chromosomal aberrations including chromosomal inversions and translocations. In this study, fetal murine hematopoietic cells from pZK1 transgenic mice were exposed to p-benzoquinone (BQ), a toxic metabolite of benzene, and assessed for DNA recombination, DNA damage including DNA DSBs as measured by γ-H2A.X foci and oxidative DNA damage, and reactive oxygen species (ROS) production. The pZK1 transgenic mouse model contains a DNA construct allowing for the detection of intrachromosomal recombination events. Using this model, a significant increase in recombination was observed following exposure to BQ (25 and 50μM) at various time points. Additionally, increased γ-H2A.X foci were observed following exposure to 25μM BQ for 30 min, 45 min, and 1 h, whereas this exposure did not significantly increase oxidative DNA damage. Pretreatment with 400 U/ml polyethylene glycol-conjugated-catalase attenuated increases in DNA recombination as compared with treatment with BQ alone. An increase in ROS production (30 min and 1 h), as measured by dichlorodihydrofluorescein diacetate fluorescence, was also observed following exposure to 25μM BQ. These studies indicate that BQ is able to induce DNA damage and recombination in fetal liver cells and that ROS may be important in the mechanism of toxicity.

Traffic air pollution and risk of death from ovarian cancer in Taiwan: fine particulate matter (PM2.5) as a proxy marker

The relationship between mortality attributed to ovarian cancer and exposure to ambient air pollutants was examined using an ecological design. The study areas consisted of 61 municipalities in Taiwan. Air quality data for recorded concentrations of fine particulate matter (PM2.5) from study municipalities for 2006-2009 were obtained as a marker of traffic emissions. These were used as a proxy for polycyclic aromatic hydrocarbons (PAH) exposure. Age-standardized mortality rates for ovarian cancer were calculated for the study municipalities for the years 1999-2008. A weighted multiple regression model was employed to calculate the adjusted risk ratio (RR) in relation to PM2.5 levels. After adjusting for urbanization level and fertility rate, the adjusted RR values (95% confidence interval [CI]) for ovarian cancer were 1.2 (1.02-1.41) for the municipalities with PM2.5 levels between 30.48 μg/m3 and 39.41 μg/m3 and 1.2 (1.03-1.39) for the municipalities with PM2.5 levels between 39.48 μg/m3 and 51.1 μg/m3, compared to the municipalities with PM2.5 levels less than 30.39 μg/m3. Results showed that individuals who resided in municipalities with higher levels of PM2.5, a proxy measure of PAH, were at an increased risk of death from ovarian cancer compared to those subjects living in municipalities with the lowest PM2.5. The findings of this study warrant further investigation into the role of exposure to air pollutants in the etiology of ovarian cancer development.

Childhood cancer and nuclear power plants in Switzerland: a census-based cohort study

BACKGROUND

Previous studies on childhood cancer and nuclear power plants (NPPs) produced conflicting results. We used a cohort approach to examine whether residence near NPPs was associated with leukaemia or any childhood cancer in Switzerland.

METHODS

We computed person-years at risk for children aged 0-15 years born in Switzerland from 1985 to 2009, based on the Swiss censuses 1990 and 2000 and identified cancer cases from the Swiss Childhood Cancer Registry. We geo-coded place of residence at birth and calculated incidence rate ratios (IRRs) with 95% confidence intervals (CIs) comparing the risk of cancer in children born <5 km, 5-10 km and 10-15 km from the nearest NPP with children born >15 km away, using Poisson regression models.

RESULTS

We included 2925 children diagnosed with cancer during 21 117 524 person-years of follow-up; 953 (32.6%) had leukaemia. Eight and 12 children diagnosed with leukaemia at ages 0-4 and 0-15 years, and 18 and 31 children diagnosed with any cancer were born <5 km from a NPP. Compared with children born >15 km away, the IRRs (95% CI) for leukaemia in 0-4 and 0-15 year olds were 1.20 (0.60-2.41) and 1.05 (0.60-1.86), respectively. For any cancer, corresponding IRRs were 0.97 (0.61-1.54) and 0.89 (0.63-1.27). There was no evidence of a dose-response relationship with distance (P > 0.30). Results were similar for residence at diagnosis and at birth, and when adjusted for potential confounders. Results from sensitivity analyses were consistent with main results.

CONCLUSIONS

This nationwide cohort study found little evidence of an association between residence near NPPs and the risk of leukaemia or any childhood cancer.

Traffic air pollution and risk of death from gastric cancer in Taiwan: petrol station density as an indicator of air pollutant exposure

To investigate the relationship between air pollution and risk of death attributed to gastric cancer, a matched cancer case-control study was conducted using deaths that occurred in Taiwan from 2004 through 2008. Data for all eligible gastric cancer deaths were obtained and compared to a control group consisting of individuals who died from causes other than neoplasms and diseases that were associated with gastrointestinal (GIT) disorders. The controls were pair-matched to the cancer cases by gender, year of birth, and year of death. Each matched control was randomly selected from the set of possible controls for each cancer case. Data for the number of petrol stations in study municipalities were collected from two major petroleum supply companies. The petrol station density (per square kilometer) (PSD) for study municipalities was used as an indicator of a subject's exposure to benzene and other hydrocarbons present in ambient evaporative losses of petrol or to air emissions from motor vehicles. The exposed individuals were subdivided into three categories (≤25th percentile; 25th-75th percentile; >75th percentile) according to PSD in the residential municipality. Results showed that individuals who resided in municipalities with the highest PSD were at an increased risk of death attributed to gastric cancer compared to those subjects living in municipalities with the lowest PSD. The findings of this study warrant further investigation of the role of traffic air pollution exposure in the etiology of gastric cancer.

Traffic air pollution and risk of death from bladder cancer in Taiwan using petrol station density as a pollutant indicator

To investigate the relationship between air pollution and risk of death from bladder cancer, a matched cancer case-control study was conducted using deaths that occurred in Taiwan from 1997 through 2006. Data for all eligible bladder cancer deaths were obtained from the Bureau of Vital Statistics of the Taiwan Provincial Department of Health. The control group consisted of individuals who died from causes other than cancer or diseases associated with genitourinary problems. The controls were pair matched to the cases by gender, year of birth, and year of death. Each matched control was selected randomly from the set of possible controls for each case. Data for the number of petrol stations in study municipalities were collected from the two major petroleum supply companies, Chinese Petroleum Corporation (CPC) and Formosa Petrochemical Corporation (FPCC). The petrol station density (per square kilometer) (PSD) for study municipalities was used as an indicator of a subject's exposure to benzene and other hydrocarbons present in ambient evaporative losses of petrol or to air emissions from motor vehicles. The subjects were divided into tertiles according to PSD in their residential municipality. The present study showed that individuals who resided in municipalities with high PSD levels were at an increased risk of death from bladder cancer compared to subjects living in municipalities with a low PSD level; however, the differences are not statistically significant. The findings of this study warrant further investigation of the role of vehicular air pollutant emissions in the etiology of bladder cancer development.

Increased micronuclei and bulky DNA adducts in cord blood after maternal exposures to traffic-related air pollution

Exposure to traffic-related air pollution in urban environment is common and has been associated with adverse human health effects. In utero exposures that result in DNA damage may affect health later in life. Early effects of maternal and in utero exposures to traffic-related air pollution were assessed through the use of validated biomarkers in blood cells from mother-newborn pairs. A cross-sectional biomonitoring study with healthy pregnant women living in the Greater Copenhagen area, Denmark, was conducted. Bulky DNA adducts and micronuclei (MN) were measured in blood from 75 women and 69 umbilical cords, concurrently collected at the time of planned Caesarean section. Modeled residential traffic density, a proxy measure of traffic-related air pollution exposures, was validated by indoor levels of nitrogen dioxide and polycyclic aromatic hydrocarbons in 42 non-smoking homes. DNA adduct levels were similar and positively correlated in maternal and cord blood (1.40 vs. 1.37 n/10(8) nucleotides; r=0.99; p<0.01). Maternal MN frequencies were significantly associated with age (p<0.01), and higher than those of the newborns (7.0 vs. 3.2 MN per 1000 binucleated cells). Adduct levels were highest among mother-newborn pairs who lived near medium-traffic-density (>400-2500 vehicle km/24h; p<0.01) places. MN frequencies among newborns from women who lived at high-traffic-density homes (>2500 vehicle km/24h) were significantly increased (p=0.02). This trend remained after adjusting for potential confounders and effect modifiers. For the first time increased bulky DNA adducts and MN in cord blood after maternal exposures to traffic-related air pollution are found, demonstrating that these transplacental environmental exposures induce DNA damage in newborns. Given that increased DNA damage early in life indicate an increased risk for adverse health effects later in life, these findings justify intervention of pregnant women.

Ambient air pollution and brain cancer mortality

OBJECTIVE

Growing evidence that ultrafine particles in ambient air can cause brain lesions in animals led us to investigate whether particulate components of air pollution may be associated with brain cancer risk in humans. Air pollution has been associated with respiratory disorders and cardiovascular morbidity and mortality, but associations between air pollutants and brain cancer have not been investigated in adults.

METHODS

The analyses included 1,284 deaths due to brain cancer from the Cancer Prevention Study-II, an ongoing prospective mortality study of adults in the United States and Puerto Rico conducted by the American Cancer Society. Air pollution data from national databases for metropolitan areas were combined with residential history and vital status data to estimate exposure to particulate and gaseous air pollution.

RESULTS

We found no elevated risk for estimated measures of air pollutants, an unanticipated reduction in risk was found between gaseous air pollutants and brain cancer mortality.

CONCLUSION

The findings do not provide evidence of increased risk of brain cancer mortality due to air pollutants.

Factors associated with residential mobility in children with leukemia: implications for assigning exposures

PURPOSE

In epidemiologic studies, neighborhood characteristics are often assigned to individuals based on a single residence despite the fact that people frequently move and, for most cancer outcomes, the relevant time-window of exposure is not known. The authors evaluated residential mobility patterns for a population-based series of childhood leukemia cases enrolled in the Northern California Childhood Leukemia Study.

METHODS

Complete residential history from 1 year before birth to date of diagnosis was obtained for 380 cases diagnosed between 1995 and 2002. All residences were assigned U.S. Census block group designations using a geographic information system.

RESULTS

Overall, two-thirds (65.8%) of children had moved between birth and diagnosis, and one-third (34.5%) moved during the first year of life. Approximately 25% of the mothers had moved during the year before the child's birth. Multivariable analysis indicated greater residential mobility to be associated with older age of the child at diagnosis, younger age of the mother at child's birth, and lower household income. Among those who had moved, residential urban/rural status for birth and diagnosis residences changed for about 20% of subjects, and neighborhood socioeconomic status for 35%.

CONCLUSIONS

These results suggest that neighborhood attribute estimates in health studies should account for patterns of residential mobility. Estimates based on a single residential location at a single point in time may lead to different inferences.

Traffic air pollution and lung cancer in females in Taiwan: petrol station density as an indicator of disease development

To investigate the relationship between traffic air pollution exposure and development of lung cancer in females, studies were conducted using a matched cancer case-control model into deaths that occurred in Taiwan from 1997 through 2006. Data on all eligible lung cancer deaths in females 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 neoplasms or diseases that were associated with respiratory problems. The controls were pair matched to the cancer cases by year of birth and year of death. Each matched control was selected randomly from the set of possible controls for each case. Data on the number of petrol stations in study municipalities were collected from the two major petroleum supply companies, Chinese Petroleum Corporation (CPC) and Formosa Petrochemical Corporation (FPCC). The petrol station density (per square kilometer; PSD) for study municipalities was used as an indicator of a subject's exposure to benzene and other hydrocarbons present in ambient evaporative losses of petrol or to air emissions from motor vehicles. The subjects were divided into tertiles according to PSD in their residential municipality. The results showed that there was a significant exposure-response relationship between PSD and risk of lung cancer in females after controlling for possible confounders. The findings of this study warrant further investigation of the role of traffic air pollution exposure in the etiology of lung cancer.

Childhood leukemia and traffic air pollution in Taiwan: petrol station density as an indicator

To investigate the relationship between traffic air pollution exposure and development of childhood leukemia (14 yr of age or younger), a matched case-control study was conducted using childhood deaths that occurred in Taiwan from 1996 through 2006. Data on all eligible childhood leukemia deaths were obtained from the Bureau of Vital Statistics of the Taiwan Provincial Department of Health. The control group consisted of children who died from causes other than neoplasms or diseases that were not associated with respiratory complications. The controls were pair matched to the cancer cases by gender, year of birth, and year of death. Each matched control was selected randomly from the set of possible controls for each case. Data on the number of petrol stations in study municipalities were collected from the two major petroleum supply companies, Chinese Petroleum Corporation (CPC) and Formosa Petrochemical Corporation (FPCC). The petrol station density (per square kilometer) (PSD) for study municipalities was used as an indicator of a subject's exposure to benzene and other hydrocarbons present in evaporative losses of petrol or to air emissions from motor vehicles. The subjects were divided into tertiles according to PSD in their residential municipality. The results showed that there was a significant exposure-response relationship between PSD and the risk of leukemia development in young children after controlling for possible confounders. The findings of this study warrant further investigation of the role of traffic air pollution exposure in the etiology of childhood leukemia.

Childhood lymphohematopoietic cancer incidence and hazardous air pollutants in southeast Texas, 1995-2004

BACKGROUND

Cancer is the second leading cause of death among U.S. children with few known risk factors. There is increasing interest in the role of air pollutants, including benzene and 1,3-butadiene, in the etiology of childhood cancers.

OBJECTIVE

Our goal was to assess whether census tracts with the highest benzene or 1,3-butadiene ambient air levels have increased childhood lymphohematopoietic cancer incidence.

METHODS

Our ecologic analysis included 977 cases of childhood lymphohematopoietic cancer diagnosed from 1995-2004. We obtained the U.S. Environmental Protection Agency's 1999 modeled estimates of benzene and 1,3-butadiene for 886 census tracts surrounding Houston, Texas. We ran Poisson regression models by pollutant to explore the associations between pollutant levels and census-tract cancer rates. We adjusted models for age, sex, race/ethnicity, and community-level socioeconomic status (cSES).

RESULTS

Census tracts with the highest benzene levels had elevated rates of all leukemia [rate ratio (RR) = 1.37; 95% confidence interval (CI), 1.05, 1.78]. This association was higher for acute myeloid leukemia (AML) (RR = 2.02; 95% CI, 1.03-3.96) than for acute lymphocytic leukemia (ALL) (RR = 1.24; 95% CI, 0.92-1.66). Among census tracts with the highest 1,3-butadiene levels, we observed RRs of 1.40 (95% CI, 1.07-1.81), 1.68 (95% CI, 0.84-3.35), and 1.32 (95% CI, 0.98-1.77) for all leukemia, AML, and ALL, respectively. We detected no associations between benzene or 1,3-butadiene levels and lymphoma incidence. Results that examined joint exposure to benzene and 1,3-butadiene were similar to those that examined each pollutant separately.

CONCLUSIONS

Our ecologic analysis suggests an association between childhood leukemia and hazardous air pollution; further research using more sophisticated methodology is warranted.

Residential traffic density and childhood leukemia risk

BACKGROUND

Exposures to carcinogenic compounds from vehicle exhaust may increase childhood leukemia risk, and the timing of this exposure may be important.

METHODS

We examined the association between traffic density and childhood leukemia risk for three time periods: birth, time of diagnosis, and lifetime average, based on complete residential history in a case-control study. Cases were rapidly ascertained from participating hospitals in northern and central California between 1995 and 2002. Controls were selected from birth records, individually matched on age, sex, race, and Hispanic ethnicity. Traffic density was calculated by estimating total vehicle miles traveled per square mile within a 500-foot (152 meter) radius area around each address. We used conditional logistic regression analyses to account for matching factors and to adjust for household income.

RESULTS

We included 310 cases of acute lymphocytic leukemias (ALL) and 396 controls in our analysis. The odds ratio for ALL and residential traffic density above the 75th percentile, compared with subjects with zero traffic density, was 1.17 [95% confidence interval (95% CI), 0.76-1.81] for residence at diagnosis and 1.11 (95% CI, 0.70-1.78) for the residence at birth. For average lifetime traffic density, the odds ratio was 1.24 (95% CI, 0.74-2.08) for the highest exposure category.

CONCLUSIONS

Living in areas of high traffic density during any of the exposure time periods was not associated with increased risk of childhood ALL in this study.

The Epidemiology of Childhood Leukemia with a Focus on Birth Weight and Diet

Leukemia is the most common childhood cancer and a major source of morbidity and mortality. The etiology of childhood leukemia remains largely unknown. Cytogenetic abnormalities determine disease subtypes, prognosis, clinical presentation, and course and may help in discovering etiological factors. Epidemiologic investigations of leukemia are complicated by many factors, including the rarity of the disease, necessitating careful study design. Two emerging areas of interest in leukemia etiology are birth weight and diet. High birth weight has been associated with increased risk of childhood leukemia. The biological mechanism behind this association may involve insulin-like growth factor I (IGF-I), which is associated with high birth weight. IGF-I may act by increasing the absolute number of stem cells available for transformation, stimulating the growth of cells that are already transformed, or a combination of effects. Diet has been linked with leukemia. Maternal dietary DNA topoisomerase II (DNAt2) inhibitor intake is associated with infant acute myeloid leukemia (AML) with the MLL gene translocation. Increased intake of fruits and vegetables has been associated with decreased leukemia risk and, relatedly, lack of maternal folate supplementation has been associated with increased childhood leukemia risk, possibly by causing DNA hypomethylation and increased DNA strand breaks. Methylenetetrahydrofolate reductase (MTHFR) gene polymorphisms modify this risk.

Geographic risk modeling of childhood cancer relative to county-level crops, hazardous air pollutants and population density characteristics in Texas

BACKGROUND

Childhood cancer has been linked to a variety of environmental factors, including agricultural activities, industrial pollutants and population mixing, but etiologic studies have often been inconclusive or inconsistent when considering specific cancer types. More specific exposure assessments are needed. It would be helpful to optimize future studies to incorporate knowledge of high-risk locations or geographic risk patterns. The objective of this study was to evaluate potential geographic risk patterns in Texas accounting for the possibility that multiple cancers may have similar geographic risks patterns.

METHODS

A spatio-temporal risk modeling approach was used, whereby 19 childhood cancer types were modeled as potentially correlated within county-years. The standard morbidity ratios were modeled as functions of intensive crop production, intensive release of hazardous air pollutants, population density, and rapid population growth.

RESULTS

There was supportive evidence for elevated risks for germ cell tumors and "other" gliomas in areas of intense cropping and for hepatic tumors in areas of intense release of hazardous air pollutants. The risk for Hodgkin lymphoma appeared to be reduced in areas of rapidly growing population. Elevated spatial risks included four cancer histotypes, "other" leukemias, Central Nervous System (CNS) embryonal tumors, CNS other gliomas and hepatic tumors with greater than 95% likelihood of elevated risks in at least one county.

CONCLUSION

The Bayesian implementation of the Multivariate Conditional Autoregressive model provided a flexible approach to the spatial modeling of multiple childhood cancer histotypes. The current study identified geographic factors supporting more focused studies of germ cell tumors and "other" gliomas in areas of intense cropping, hepatic cancer near Hazardous Air Pollutant (HAP) release facilities and specific locations with increased risks for CNS embryonal tumors and for "other" leukemias. Further study should be performed to evaluate potentially lower risk for Hodgkin lymphoma and malignant bone tumors in counties with rapidly growing population.

Epidemiologic evidence of relationships between reproductive and child health outcomes and environmental chemical contaminants

This review summarizes the level of epidemiologic evidence for relationships between prenatal and/or early life exposure to environmental chemical contaminants and fetal, child, and adult health. Discussion focuses on fetal loss, intrauterine growth restriction, preterm birth, birth defects, respiratory and other childhood diseases, neuropsychological deficits, premature or delayed sexual maturation, and certain adult cancers linked to fetal or childhood exposures. Environmental exposures considered here include chemical toxicants in air, water, soil/house dust and foods (including human breast milk), and consumer products. Reports reviewed here included original epidemiologic studies (with at least basic descriptions of methods and results), literature reviews, expert group reports, meta-analyses, and pooled analyses. Levels of evidence for causal relationships were categorized as sufficient, limited, or inadequate according to predefined criteria. There was sufficient epidemiological evidence for causal relationships between several adverse pregnancy or child health outcomes and prenatal or childhood exposure to environmental chemical contaminants. These included prenatal high-level methylmercury (CH(3)Hg) exposure (delayed developmental milestones and cognitive, motor, auditory, and visual deficits), high-level prenatal exposure to polychlorinated biphenyls (PCBs), polychlorinated dibenzofurans (PCDFs), and related toxicants (neonatal tooth abnormalities, cognitive and motor deficits), maternal active smoking (delayed conception, preterm birth, fetal growth deficit [FGD] and sudden infant death syndrome [SIDS]) and prenatal environmental tobacco smoke (ETS) exposure (preterm birth), low-level childhood lead exposure (cognitive deficits and renal tubular damage), high-level childhood CH(3)Hg exposure (visual deficits), high-level childhood exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (chloracne), childhood ETS exposure (SIDS, new-onset asthma, increased asthma severity, lung and middle ear infections, and adult breast and lung cancer), childhood exposure to biomass smoke (lung infections), and childhood exposure to outdoor air pollutants (increased asthma severity). Evidence for some proven relationships came from investigation of relatively small numbers of children with high-dose prenatal or early childhood exposures, e.g., CH(3)Hg poisoning episodes in Japan and Iraq. In contrast, consensus on a causal relationship between incident asthma and ETS exposure came only recently after many studies and prolonged debate. There were many relationships supported by limited epidemiologic evidence, ranging from several studies with fairly consistent findings and evidence of dose-response relationships to those where 20 or more studies provided inconsistent or otherwise less than convincing evidence of an association. The latter included childhood cancer and parental or childhood exposures to pesticides. In most cases, relationships supported by inadequate epidemiologic evidence reflect scarcity of evidence as opposed to strong evidence of no effect. This summary points to three main needs: (1) Where relationships between child health and environmental exposures are supported by sufficient evidence of causal relationships, there is a need for (a) policies and programs to minimize population exposures and (b) population-based biomonitoring to track exposure levels, i.e., through ongoing or periodic surveys with measurements of contaminant levels in blood, urine and other samples. (2) For relationships supported by limited evidence, there is a need for targeted research and policy options ranging from ongoing evaluation of evidence to proactive actions. (3) There is a great need for population-based, multidisciplinary and collaborative research on the many relationships supported by inadequate evidence, as these represent major knowledge gaps. Expert groups faced with evaluating epidemiologic evidence of potential causal relationships repeatedly encounter problems in summarizing the available data. A major driver for undertaking such summaries is the need to compensate for the limited sample sizes of individual epidemiologic studies. Sample size limitations are major obstacles to exploration of prenatal, paternal, and childhood exposures during specific time windows, exposure intensity, exposure-exposure or exposure-gene interactions, and relatively rare health outcomes such as childhood cancer. Such research needs call for investments in research infrastructure, including human resources and methods development (standardized protocols, biomarker research, validated exposure metrics, reference analytic laboratories). These are needed to generate research findings that can be compared and subjected to pooled analyses aimed at knowledge synthesis.

Association of childhood leukemia with residential exposure to petrochemical air pollution in taiwan

To investigate the relationship between petrochemical air pollution and childhood leukemia (19 yr of age or younger), the authors conducted a matched case-control study using childhood deaths that occurred in Taiwan from 1995 through 2005. Data on all eligible childhood leukemia deaths were obtained from the Bureau of Vital Statistics of the Taiwan Provincial Department of Health. The control group consisted of children who died from causes other than neoplasms or diseases that were not 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. The proportion of a municipality's total population employed in the petrochemical industry in a municipality was used as an indicator of a resident's exposure to air emissions from the petrochemical industry. The subjects were divided into three levels (< or =25th percentile; 25th-75th percentile; > 75th percentile) according to the levels of the index just described. After controlling for possible confounders, results showed that children who lived in the group of municipalities characterized by the highest levels of petrochemical air pollution had a statistically significant higher risk of developing leukemia than the group that lived in municipalities with the lowest petrochemical air pollution levels. The results of this study shed important light on the relationship between the Taiwan petrochemical industry and human health risks.