Childhood leukemia and road traffic: A population-based case-control study

Examining the relationship between land use and childhood leukemia and lymphoma in Tehran

We conducted a hospital-based case-control study to explore the association between proximity to various land use types and childhood leukemia and lymphoma. This research involved 428 cases of childhood leukemia and lymphoma (2016-2021), along with a control group of 428 children aged 1-15 in Tehran. We analyzed the risk of childhood cancer associated with land use by employing logistic regression adjusted for confounding factors such as parental smoking and family history. The odds ratio (OR) for children with leukemia and lymphoma residing within 100 m of the nearest highway was 1.87 (95% CI = 1.00-3.49) and 1.71 (95% CI = 1.00-2.93), respectively, in comparison to those living at a distance of 1000 m or more from a highway. The OR for leukemia with exposure to petrol stations within 100 m was 2.15 (95% CI = 1.00-4.63), and for lymphoma it was 1.09 (95% CI = 0.47-2.50). A significant association was observed near power lines (OR = 3.05; 95% CI = 0.97-9.55) within < 100 m for leukemia. However, no significant association was observed between power lines and the incidence of childhood lymphoma. There was no association between bus stations, major road class 2, and the incidence of childhood leukemia and lymphoma. In conclusion, our results suggest a possible association between the incidence of childhood leukemia and proximity to different urban land uses (i.e., highways and petrol stations). This study is the first step in understanding how urban land use affects childhood leukemia and lymphoma in Tehran. However, comprehensive studies considering individual-level data and specific pollutants are essential for a more nuanced understanding of these associations.

Residential proximity to oil and gas production sites and hematologic malignancies: A case-control study

BACKGROUND

We investigated the association between residential proximity to oil and gas production sites and hematologic malignancies, due to a cancer cluster in the German state of Lower Saxony.

METHODS

A registry-based case-control study was conducted including 3978 cases of hematologic malignancies diagnosed within 2013-2016 and 15,912 frequency-matched controls randomly drawn by population registries. Residential proximity to 5333 oil and gas production sites at the time of diagnosis was calculated. Unconditional logistic regression models were used to estimate the association between living within 1 km of any exposure site and developing a hematologic malignancy. Models were adjusted for matching variables sex, age group, district, and year of diagnosis as well as for proximity to main streets and to agricultural land.

RESULTS

We found no association between the development of hematologic malignancies and the proximity to all oil and gas production sites (odds ratio: 0.97; 95% confidence interval: 0.85, 1.11). Focusing on gas production sites increased the odds of developing hematologic cancer (odds ratio: 1.19; 95% confidence interval: 0.97, 1.45). In stratified analyses, associations were stronger in women and for acute myeloblastic leukemia. We also found an association in the district where the initial cluster occurred.

CONCLUSIONS

Our results suggest that residential proximity to oil and gas production is not a risk factor for all hematologic malignancies in general. Sporadic and past exposures are the most likely scenarios for mechanisms involving oil and gas production, leading to increased risk for certain subtypes of cancer in certain populations.

Health effects of exposure to indoor volatile organic compounds from 1980 to 2017: A systematic review and meta-analysis

Exposure to volatile organic compounds (VOCs) indoors is thought to be associated with several adverse health effects. However, we still lack concentration-response (C-R) relationships between VOC levels in civil buildings and various health outcomes. For this paper, we conducted a systematic review and meta-analysis of observational studies to summarize related associations and C-R relationships. Four databases were searched to collect all relevant studies published between January 1980 and December 2017. A total of 39 studies were identified in the systematic review, and 32 of these were included in the meta-analysis. We found that the pooled relative risk (RR) for leukemia was 1.03 (95% CI: 1.01-1.05) per 1 μg/m³ increase of benzene and 1.25 (95%CI: 1.14-1.37) per 0.1 μg/m³ increase of butadiene. The pooled RRs for asthma were 1.08 (95% CI: 1.02-1.14), 1.02 (95% CI: 1.00-1.04), and 1.04 (95% CI: 1.02-1.06) per 1 μg/m³ increase of benzene, toluene, and p-dichlorobenzene, respectively. The pooled RR for low birth weight was 1.12 (95% CI: 1.05-1.19) per 1 μg/m³ increase of benzene. Our findings provide robust evidence for associations between benzene and leukemia, asthma, and low birth weight, as well as for health effects of some other VOCs.

1,3-Butadiene: a ubiquitous environmental mutagen and its associations with diseases

1,3-Butadiene (BD) is a petrochemical manufactured in high volumes. It is a human carcinogen and can induce lymphohematopoietic cancers, particularly leukemia, in occupationally-exposed workers. BD is an air pollutant with the major environmental sources being automobile exhaust and tobacco smoke. It is one of the major constituents and is considered the most carcinogenic compound in cigarette smoke. The BD concentrations in urban areas usually vary between 0.01 and 3.3 μg/m³ but can be significantly higher in some microenvironments. For BD exposure of the general population, microenvironments, particularly indoor microenvironments, are the primary determinant and environmental tobacco smoke is the main contributor. BD has high cancer risk and has been ranked the second or the third in the environmental pollutants monitored in most urban areas, with the cancer risks exceeding 10^-5. Mutagenicity/carcinogenicity of BD is mediated by its genotoxic metabolites but the specific metabolite(s) responsible for the effects in humans have not been determined. BD can be bioactivated to yield three mutagenic epoxide metabolites by cytochrome P450 enzymes, or potentially be biotransformed into a mutagenic chlorohydrin by myeloperoxidase, a peroxidase almost specifically present in neutrophils and monocytes. Several urinary BD biomarkers have been developed, among which N-acetyl-S-(4-hydroxy-2-buten-1-yl)-L-cysteine is the most sensitive and is suitable for biomonitoring BD exposure in the general population. Exposure to BD has been associated with leukemia, cardiovascular disease, and possibly reproductive effects, and may be associated with several cancers, autism, and asthma in children. Collectively, BD is a ubiquitous pollutant that has been associated with a range of adverse health effects and diseases with children being a subpopulation with potentially greater susceptibility. Its adverse effects on human health may have been underestimated and more studies are needed.

Exposure to outdoor air pollution at different periods and the risk of leukemia: a meta-analysis

The causes of leukemia remain largely unknown; our aims were to examine the association between the exposure to outdoor air pollution and leukemia risk and to explore the effect of this exposure during different periods of pregnancy and early life. We searched for all case-control and cohort studies published before February 20, 2021, which measured the risk of leukemia in relation to exposure to the air pollutants: particulate matter, benzene, nitrogen dioxide (NO₂), and nitrogen oxides (NO_x). We then carried out a meta-analysis and calculated the summary relative risks (RRs) of leukemia by using a random-effects model. The potential dose-response relationship was further explored. The results showed that the highest exposure to benzene (RR: 1.20, 95%CI: 1.06-1.35) and NO₂ (RR: 1.04, 95%CI; 1.02-1.08) were positively correlated with leukemia risk when compared to the lowest exposure categories for each air pollutant. During pregnancy, exposure to benzene in the third trimester, as well as exposure to NO₂ in the second trimester and entire pregnancy, could also increase the risk of leukemia. In the dose-response analysis, benzene exposure and NO₂ exposure were linearly associated with the risk of leukemia. Other air pollutants did not have a statistical correlation with leukemia risk. There was a certain degree of publication bias in studies on benzene. Overall, our results support a link between outdoor air pollution and leukemia risk, particularly due to benzene and NO₂. Prospero Registration Number: PROSPERO CRD42020207025.

DNA Damage and Perturbed Topoisomerase IIα as a Target of 1,4-Benzoquinone Toxicity in Murine Fetal Liver Cells

Benzene is a ubiquitous environmental pollutant. Recent studies have shown a link between the development of childhood leukemias and maternal benzene exposure, suggesting that these leukemias may be initiated in utero. Benzene crosses the placental barrier however the mechanisms behind in utero benzene toxicity have not been well elucidated. This study is the first to show that the benzene metabolite, benzoquinone (BQ), perturbs fetal topoisomerase IIα (Topo IIα), an enzyme essential for DNA repair. Using cultured murine CD-1 fetal liver cells, this study shows that Topo IIα activity decreases following 24 hours of exposure to BQ (12.5 and 15.625 µM), with the 12.5 µM confirmed to disrupt the c-kit+Lin-Sca-1-Il7rα- population of cells in culture. Pre-treatment with the antioxidant, N-acetylcysteine did not prevent the inhibtion of Topo IIα by BQ. An increase in Topo IIα-DNA covalent adducts was detected following 24-hour exposures to BQ (12.5 and 50 µM). Interestingly, BQ (12.5 µM) exposure did not significantly increase levels of 4-hydroxynonenal (4-HNE), a marker of oxidative stress after 24 hours. However, increased levels of the double-stranded DNA break marker γH2AX were detected following 24 hours of BQ exposure, confirming that Topo IIα-induced breaks are increased in BQ treated cells. This study shows that fetal Topo IIα is perturbed by BQ and suggests that this protein is a target of benzene and may be implicated with in utero benzene toxicity.

Predictors of residential mobility and its impact on air pollution exposure among children diagnosed with early childhood leukemia

Epidemiology studies relying on one address to assign exposures over time share common methodological limitations in failing to account for mobility that may introduce potential exposure misclassification. Using Texas birth certificate and cancer registry data, we identified predictors of residential mobility among mothers of children diagnosed with early childhood leukemia in Texas from 1995 to 2011. We used U.S. Environmental Protection Agency (EPA) National Air Toxics Assessment data to estimate residential levels of benzene and 1,3-butadiene based on addresses at birth and diagnosis and applied mixed-effects ordinal logistic regression models to evaluate differences in exposure classification between the two time periods. In total, 55% of children moved from time of birth to diagnosis, although they generally did not move far (median distance moved was 8 km). Predictors of mobility, at delivery, included younger age, being unmarried and living in neighborhoods with high benzene levels, and, at diagnosis, increasing child's age and living in neighborhoods with low poverty rates. We observed that the odds of being assigned to a higher exposure quartile at diagnosis relative to the time of birth decreased by 31% for 1,3-butadiene (OR = 0.69, 95% CI 0.59-0.82) and by 12% for benzene (OR = 0.88, 95% CI 0.75, 1.05).

A Meta-analysis of Traffic-related Air Pollution and Risk of Childhood Leukemia

BACKGROUND

Many studies have analyzed the association between traffic-related air pollution and risk of childhood leukemia, but the results are inconsistent. Therefore, we performed this meta-analysis to investigate the association between traffic-related air pollution and risk of childhood leukemia.

METHODS

PubMed, Cochrane, and Embase databases were searched by the index words to identify eligible case-control studies, and relevant literature sources were also searched. The latest research was performed in September 2017. Odds ratio (OR) along with 95% confidence interval (95% CI) were used to analyzed the main outcomes.

RESULTS

Twenty-one case-control studies were included in the meta-analysis. The results indicated that in the studies of overall traffic density (OR: 1.01, 95% CI: 0.98-1.04), high traffic density (OR: 1.04, 95% CI: 0.91-1.17), moderate exposure to NO2 (OR: 1.02, 95% CI: 0.93-1.10), and benzene (OR: 1.04, 95% CI: 0.71-1.37), the risks of childhood leukemia incidence were higher in the case group than the control group, but no significant difference was found. In other analysis, no significant difference was observed in the risk of childhood leukemia in the 2 groups.

CONCLUSIONS

Current evidence suggests that childhood leukemia is associated with traffic density, and moderate exposure to NO2 and benzene. However, more high-quality studies are required to confirm the conclusions.

Association between Outdoor Air Pollution and Childhood Leukemia: A Systematic Review and Dose-Response Meta-Analysis

BACKGROUND

A causal link between outdoor air pollution and childhood leukemia has been proposed, but some older studies suffer from methodological drawbacks. To the best of our knowledge, no systematic reviews have summarized the most recently published evidence and no analyses have examined the dose-response relation.

OBJECTIVE

We investigated the extent to which outdoor air pollution, especially as resulting from traffic-related contaminants, affects the risk of childhood leukemia.

METHODS

We searched all case-control and cohort studies that have investigated the risk of childhood leukemia in relation to exposure either to motorized traffic and related contaminants, based on various traffic-related metrics (number of vehicles in the closest roads, road density, and distance from major roads), or to measured or modeled levels of air contaminants such as benzene, nitrogen dioxide, 1,3-butadiene, and particulate matter. We carried out a meta-analysis of all eligible studies, including nine studies published since the last systematic review and, when possible, we fit a dose-response curve using a restricted cubic spline regression model.

RESULTS

We found 29 studies eligible to be included in our review. In the dose-response analysis, we found little association between disease risk and traffic indicators near the child's residence for most of the exposure range, with an indication of a possible excess risk only at the highest levels. In contrast, benzene exposure was positively and approximately linearly associated with risk of childhood leukemia, particularly for acute myeloid leukemia, among children under 6 y of age, and when exposure assessment at the time of diagnosis was used. Exposure to nitrogen dioxide showed little association with leukemia risk except at the highest levels.

DISCUSSION

Overall, the epidemiologic literature appears to support an association between benzene and childhood leukemia risk, with no indication of any threshold effect. A role for other measured and unmeasured pollutants from motorized traffic is also possible. https://doi.org/10.1289/EHP4381.

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.

Maternal exposure to gasoline and exhaust increases the risk of childhood leukaemia in offspring - a prospective study in the Norwegian Mother and Child Cohort Study

Background

In the prospective population-based Norwegian Mother and Child Cohort Study (MoBa), comprising 113 754 offspring, we investigated the association between parental exposure to “gasoline or exhaust”, as a proxy for benzene exposure, and childhood leukaemia.

Methods

Around gestational week 17, mothers and fathers responded to a questionnaire on exposure to various agents during the last 6 months and 6 months  pre-conception, respectively. Benzene exposure was assessed through self-reported exposure to “gasoline or exhaust”. Cases of childhood leukaemia (n = 70) were identified through linkage with the Cancer Registry of Norway. Risk was estimated by hazard ratios (HRs) with 95% confidence intervals (95%CI), comparing offspring from exposed and unexposed parents using a Cox regression model.

Results

Maternal exposure to "gasoline or exhaust" was associated with an increased risk of childhood leukaemia (HR = 2.59; 95%CI: 1.03, 6.48) and acute lymphatic leukaemia (HR = 2.71; 95%CI: 0.97, 7.58). There was an increasing risk for higher exposure (p value for trend = 0.032 and 0.027). The association did not change after adjustment for maternal smoking.

Conclusion

In spite of rather few cases, the findings in this prospective study, with the exposure metric defined a priori, support previous observations relating maternal exposure to benzene from gasoline and other petroleum-derived sources and the subsequent development of childhood leukaemia in the offspring.

Comprehensive Proteomic Characterization of Ontogenic Changes in Hematopoietic Stem and Progenitor Cells

Hematopoietic stem and progenitor cells (HSPCs) in the fetus and adult possess distinct molecular landscapes that regulate cell fate and change their susceptibility to initiation and progression of hematopoietic malignancies. Here, we applied in-depth quantitative proteomics to comprehensively describe and compare the proteome of fetal and adult HSPCs. Our data uncover a striking difference in complexity of the cellular proteomes, with more diverse adult-specific HSPC proteomic signatures. The differential protein content in fetal and adult HSPCs indicate distinct metabolic profiles and protein complex stoichiometries. Additionally, adult characteristics include an arsenal of proteins linked to viral and bacterial defense, as well as protection against ROS-induced protein oxidation. Further analyses show that interferon α, as well as Neutrophil elastase, has distinct functional effects in fetal and adult HSPCs. This study provides a rich resource aimed toward an enhanced mechanistic understanding of normal and malignant hematopoiesis during fetal and adult life.

Ambient benzene at the residence and risk for subtypes of childhood leukemia, lymphoma and CNS tumor

Exposure to benzene increases the risk for acute myeloid leukemia and possibly other types of cancer in adults. For children, only limited evidence about benzene and cancer exists. A few studies have indicated that benzene may increase risk for some subtypes of childhood cancer but not for others. We aimed to investigate if outdoor levels of benzene at the residence increase the risk for subtypes of leukemia, lymphoma and CNS tumor in children. We identified 1,989 children diagnosed with leukemia, lymphoma or CNS tumor during 1968-1991 in the Danish Cancer Registry and randomly selected 5,506 control children from the Danish population, matched on sex, age and calendar time. We traced residential history of all children from 9 months before birth to time of diagnosis, calculated outdoor benzene concentration at all addresses and summarized cumulative exposure over fetal and childhood periods separately. We used conditional logistic regression for the statistical analyses. Benzene exposure during childhood above the 90th percentile was associated with relative risks for acute lymphocytic leukemia (ALL) and acute myeloid leukemia (AML) of 1.0 (95% confidence intervals (CI): 0.6-1.7) and 1.9 (95% CI: 0.3-11.1), respectively, when compared with exposure levels below the median. For CNS tumors, there was a tendency of lower risk for ependymoma and higher risk for medulloblastoma in association with higher exposure. In conclusion, benzene was associated with higher risk for childhood AML, but not ALL, which is consistent with the few previous studies.

Diallyl trisulfide (DATS) suppresses benzene-induced cytopenia by modulating haematopoietic cell apoptosis

Benzene is a well-known occupational and environmental toxicant associated with cytopenia, which is characterized by a disorder in the peripheral blood cell counts. However, no effective preventive strategy has been developed yet to tackle the exposure to benzene in daily life. The aim of this study was to evaluate the protective effects of diallyl trisulfide (DATS) on benzene-induced haematopoietic damage and to reveal its potential mechanisms of action. In our study, male Sprague-Dawley rats were divided into six groups. Rats were administered with benzene (1.3 g/kg BW by gavage) to establish the benzene poisoning model, while the DATS treatment groups were treated with benzene plus DATS (15 mg/kg, 30 mg/kg, 45 mg/kg, respectively, by gavage) for 28 days. Our results demonstrated that the counts of peripheral blood WBC and RBC decreased to 31.0% and 79.2%, respectively, in the benzene poisoning model group compared to the control. However, blood cell counts were restored by DATS treatment (30 mg/kg, 45 mg/kg). The apoptosis rates of peripheral blood mononuclear cells (PBMCs) and bone marrow cells (BMCs) were increased to 274% and 284%, respectively, following benzene exposure. Furthermore, expression levels of Bcl-2, PI3K and p-Akt were downregulated and those of Bax were upregulated in both cell types. Moreover, the oxidative parameters (oxygen species, malonaldehyde) were significantly increased, while the non-enzymatic GSH/GSSG ratios and the activities of enzymatic antioxidants (superoxide dismutase, glutathione peroxidase and catalase) were decreased. Interestingly, DATS treatment can restore the WBC number by 267.1% and 304.8% while RBC number by 108.6% and 117.7% in 30,45 mg/k DATS treated groups. In summary, we demonstrated that benzene-induced cytopenia was related to the apoptosis of PBMCs and BMCs, and DATS treatment could prevent benzene-induced cytopenia by suppressing oxidative stress-mediated cell apoptosis via the PI3K/Akt pathway.

Benzene and childhood acute leukemia in Oklahoma

BACKGROUND

Although childhood cancer is a leading cause of childhood mortality in the US, evidence regarding the etiology is lacking. The goal of this study was to evaluate the association between benzene, a known carcinogen, and childhood acute leukemia.

METHODS

We conducted a case-control study including cases diagnosed with acute leukemia between 1997 and 2012 (n = 307) from the Oklahoma Central Cancer Registry and controls matched on week of birth from birth certificates (n = 1013). We used conditional logistic regression to evaluate the association between benzene, measured with the 2005 National-Scale Air Toxics Assessment (NATA) at census tract of the birth residence, and childhood acute leukemia.

RESULTS

We observed no differences in benzene exposure overall between cases and controls. However, when stratified by year of birth, cases born from 2005 to 2010 had a three-fold increased unadjusted odds of elevated exposure compared to controls born in this same time period (4th Quartile OR: 3.53, 95% CI: 1.35, 9.27). Furthermore, the estimates for children with acute myeloid leukemia (AML) were stronger than those with acute lymphoid leukemia, though not statistically significant.

CONCLUSIONS

While we did not observe an association between benzene and childhood leukemia overall, our results suggest that acute leukemia is associated with increased benzene exposure among more recent births, and children with AML may have increased benzene exposure at birth. Using the NATA estimates allowed us to assess a specific pollutant at the census tract level, providing an advantage over monitor or point source data. Our study, however, cannot rule out the possibility that benzene may be a marker of other traffic-related exposures and temporal misclassification may explain the lack of an association among earlier births.

Childhood cancer in small geographical areas and proximity to air-polluting industries

AIM

Pediatric cancer has been associated with exposure to certain environmental carcinogens. The purpose of this work is to analyse the relationship between environmental pollution and pediatric cancer risk.

METHOD

We analysed all incidences of pediatric cancer (<15) diagnosed in a Spanish region during the period 1998-2015. The place of residence of each patient and the exact geographical coordinates of main industrial facilities was codified in order to analyse the spatial distribution of cases of cancer in relation to industrial areas. Focal tests and focused Scan methodology were used for the identification of high-incidence-rate spatial clusters around the main industrial pollution foci.

RESULTS

The crude rate for the period was 148.0 cases per 1,000,0000 children. The incidence of pediatric cancer increased significantly along the period of study. With respect to spatial distribution, results showed significant high incidence around some industrial pollution foci group and the Scan methodology identify spatial clustering. We observe a global major incidence of non Hodgkin lymphomas (NHL) considering all foci, and high incidence of Sympathetic Nervous System Tumour (SNST) around Energy and Electric and organic and inorganic chemical industries foci group. In the analysis foci to foci, the focused Scan test identifies several significant spatial clusters. Particularly, three significant clusters were identified: the first of SNST was around energy-generating chemical industries (2 cases versus the expected 0.26), another of NHL was around residue-valorisation plants (5 cases versus the expected 0.91) and finally one cluster of Hodgkin lymphoma around building materials (3 cases versus the expected 2.2) CONCLUSION: Results suggest a possible association between proximity to certain industries and pediatric cancer risk. More evidences are necessary before establishing the relationship between industrial pollution and pediatric cancer incidence.

Residential Proximity to Gasoline Stations and Risk of Childhood Leukemia

Significant elevations in the risk of childhood leukemia have been associated with environmental exposure to gasoline; aromatic hydrocarbons from refinery pollution, petroleum waste sites, and mobile sources (automobile exhaust); paints, paint products, and thinners; and secondary cigarette smoke in the home. These higher risks have also been associated with parental exposure to benzene, gasoline, motor vehicle-related jobs, painting, and rubber solvents. These exposures and jobs have 1 common chemical exposure-benzene, a recognized cause of acute leukemia in adults-and raise the question of whether children represent a subpopulation in which a higher risk of leukemia is associated with very low level exposure to environmental benzene.

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.

Traffic-related air pollution and childhood acute leukemia in Oklahoma

BACKGROUND

While many studies have evaluated the association between acute childhood leukemia and environmental factors, knowledge is limited. Ambient air pollution has been classified as a Group 1 carcinogen, but studies have not established whether traffic-related air pollution is associated with leukemia. The goal of our study was to determine if children with acute leukemia had higher odds of exposure to traffic-related air pollution at birth compared to controls.

METHODS

We conducted a case-control study using the Oklahoma Central Cancer Registry to identify cases of acute leukemia in children diagnosed before 20 years of age between 1997 and 2012 (n=307). Controls were selected from birth certificates and matched to cases on week of birth (n=1013). Using a novel satellite-based land-use regression model of nitrogen dioxide (NO2) and estimating road density based on the 2010 US Census, we evaluated the association between traffic-related air pollution and childhood leukemia using conditional logistic regression.

RESULTS

The odds of exposure to the fourth quartile of NO2 (11.19-19.89ppb) were similar in cases compared to controls after adjustment for maternal education (OR: 1.08, 95% CI: 0.75, 1.55). These estimates were stronger among children with acute myeloid leukemia (AML) than acute lymphoid leukemia, with a positive association observed among urban children with AML (4th quartile odds ratio: 5.25, 95% confidence interval: 1.09, 25.26). While we observed no significant association with road density, male cases had an elevated odds of exposure to roads at 500m from the birth residence compared to controls (OR: 1.39, 95% CI: 0.93, 2.10), which was slightly attenuated at 750m.

CONCLUSIONS

Although we observed no association overall between NO2 or road density, this was the first study to observe an elevated odds of exposure to NO2 among children with AML compared to controls suggesting further exploration of traffic-related air pollution and AML is warranted.

Air toxics and early childhood acute lymphocytic leukemia in Texas, a population based case control study

BACKGROUND

Traffic exhaust, refineries and industrial facilities are major sources of air toxics identified by the U.S. Environmental Protection Agency (U.S. EPA) for their potential risk to human health. In utero and early life exposures to air toxics such as benzene and 1,3-butadiene, which are known leukemogens in adults, may play an etiologic role in childhood leukemia that comprises the majority of pediatric cancers. We conducted a population based case-control study to examine individual effects of benzene, 1,3-butadiene and polycyclic organic matter (POM) in ambient residential air on acute lymphocytic leukemia (ALL) diagnosed in children under age 5 years in Texas from 1995-2011.

METHODS

Texas Cancer Registry cases were linked to birth records and then were frequency matched by birth month and year to 10 population-based controls. Maternal and infant characteristics from birth certificates were abstracted to obtain information about potential confounders. Modelled estimates of benzene, 1,3-butadiene and POM exposures at the census tract level were assigned by linking geocoded maternal addresses from birth certificates to U.S. EPA National-Scale Air Toxics Assessment data for single and co-pollutant statistical analyses. Mixed-effects logistic regression models were applied to evaluate associations between air toxics and childhood leukemia.

RESULTS

In adjusted single pollutant models, odds of childhood leukemia among mothers with the highest ambient air exposures compared to those in the lowest quartile were 1.11 (95 % CI: 0.94-1.32) for POM, 1.17 (95 % CI: 0.98-1.39) for benzene and 1.29 (95 % CI: 1.08-1.52) for 1,3-butadiene. In co-pollutant models, odds ratios for childhood leukemia remained elevated for 1,3-butadiene but were close to the null value for benzene and POM.

CONCLUSIONS

We observed positive associations between 1,3-butadiene and childhood leukemia in single and co-pollutant models whereas effect estimates from single pollutant models were diminished for benzene and POM in co-pollutant models. Early life exposure to 1,3-butadiene rather than benzene or POM appears to increase early childhood risk of acute lymphocytic leukemia.

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.

Progression and inflammation of human myeloid leukemia induced by ambient PM2.5 exposure

PM2.5 (aerodynamic diameter ≤2.5 μm) has been a dominating and ubiquitous air pollutant and has become a global concern. Emerging evidences suggest a positive correlation between PM2.5 and leukemia, but the underlying molecular mechanisms remain unclear and need to be elucidated. Here, we assessed the impacts of PM2.5 on the progression and inflammation of human myeloid leukemia at lower environmental doses and explored the possible pathway. We showed that PM2.5 exposure significantly induced the leukemia cell growth and enhanced the release of inflammatory mediators in both in vitro and in vivo models. Additionally, NF-κB p65 and p-STAT3 were activated in PM2.5-treated leukemia cells, with a concomitant increase in both ROS formation and NADPH oxidase expressions. Strikingly, the supplement of inhibitors, including NAC (ROS), PDTC (NF-κB), or WP1066 (STAT3), contributed to a decline in leukemia cell growth. Furthermore, enhanced expressions of inflammatory cytokines were attenuated by the addition of NAC or PDTC, but not affected by WP1066. This study demonstrates that PM2.5 promotes leukemia progression, identifies a potential intervention target, and provides further understanding of the detrimental effect of PM2.5 exposure on human health.

Residential Proximity to Heavy-Traffic Roads, Benzene Exposure, and Childhood Leukemia-The GEOCAP Study, 2002-2007

Childhood leukemia may be associated with traffic-related environmental exposure to benzene, and additional data are needed. The Géolocalisation des Cancers Pédiatriques (GEOCAP) Study, a nationwide French case-control study, was designed to avoid selection bias due to differential participation and misclassification. The study compared the 2,760 childhood leukemia cases diagnosed in France between 2002 and 2007 (including 2,275 cases of acute lymphoblastic leukemia (ALL) and 418 cases of acute myeloblastic leukemia (AML)) with 30,000 contemporaneous child population controls. The residence addresses were precisely geocoded, and 3 indicators of residential proximity to traffic were considered. Estimates of benzene concentrations were also available for the Île-de-France region (including Paris). A 300-m increase in major road length within 150 m of the geocoded address was significantly associated with AML (odds ratio = 1.2, 95% confidence interval: 1.0, 1.4) but not with ALL (odds ratio = 1.0, 95% confidence interval: 0.9, 1.1), and the association was reinforced in the Île-de-France region when this indicator was combined with benzene estimates. These results, which were free from any participation bias and based on objectively determined indices of exposure, showed an increased incidence of AML associated with heavy-traffic road density near a child's home. The results support a role for traffic-related benzene exposure in the etiology of childhood AML.

Traffic-related air pollution and the incidence of childhood central nervous system tumors: Texas, 2001-2009

BACKGROUND

Due to increasing concerns regarding air pollution and childhood cancer, we conducted a population-based study evaluating the association between traffic-related hazardous air pollutants (1,3-butadiene, benzene, diesel particulate matter [DPM]) and the incidence of childhood central nervous system (CNS) tumors.

PROCEDURE

Information on children diagnosed with a CNS tumor at <15 years of age, in Texas, for the period of 2001-2009 (n = 1,949) was obtained from the Texas Cancer Registry. Information on the corresponding at-risk population was obtained from the United States (U.S.) Census. Annual census tract-level pollutant concentrations, estimated by the U.S. Environmental Protection Agency, were categorized based on quartiles (low, medium, medium-high, and high) of the statewide distribution. Multivariable Poisson regression was used to calculate adjusted incidence rate ratios (aIRR). Juvenile pilocytic astrocytomas (JPAs) (n = 384), other astrocytomas (n = 372), ependymomas (n = 142), medulloblastomas (n = 235), and primitive neuroectodermal tumors (PNET) (n = 47) were evaluated.

RESULTS

Census tracts with medium and medium-high 1,3-butadiene concentrations had higher astrocytoma incidence rates (aIRR [95% confidence interval (CI)]: 1.46 [1.05-2.01] and 1.69 [1.22-2.33], respectively) compared with low concentrations. Census tracts with medium DPM concentrations had higher astrocytoma (aIRR [95%CI]: 1.42 [1.05-1.94]) and medulloblastoma (aIRR [95%CI]: 1.46 [1.01-2.12]) incidence rates compared with low concentrations. Increased concentrations of 1,3-butadiene and benzene were strongly associated with increased PNET incidence rates, but were not statistically significant. No associations were detected with JPA or ependymoma incidence.

CONCLUSIONS

In one of the largest studies of its kind, our results suggest positive associations between hazardous air pollutants and incidence of astrocytoma (1,3-butadiene and DPM) and medulloblastoma (DPM).

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 leukemia and residential proximity to industrial and urban sites

BACKGROUND

Few risk factors for the childhood leukemia are well established. While a small fraction of cases of childhood leukemia might be partially attributable to some diseases or ionizing radiation exposure, the role of industrial and urban pollution also needs to be assessed.

OBJECTIVES

To ascertain the possible effect of residential proximity to both industrial and urban areas on childhood leukemia, taking into account industrial groups and toxic substances released.

METHODS

We conducted a population-based case-control study of childhood leukemia in Spain, covering 638 incident cases gathered from the Spanish Registry of Childhood Tumors and for those Autonomous Regions with 100% coverage (period 1990-2011), and 13,188 controls, individually matched by year of birth, sex, and autonomous region of residence. Distances were computed from the respective subject's residences to the 1068 industries and the 157 urban areas with ≥10,000 inhabitants, located in the study area. Using logistic regression, odds ratios (ORs) and 95% confidence intervals (95%CIs) for categories of distance to industrial and urban pollution sources were calculated, with adjustment for matching variables.

RESULTS

Excess risk of childhood leukemia was observed for children living near (≤2.5 km) industries (OR=1.31; 95%CI=1.03-1.67) - particularly glass and mineral fibers (OR=2.42; 95%CI=1.49-3.92), surface treatment using organic solvents (OR=1.87; 95%CI=1.24-2.83), galvanization (OR=1.86; 95%CI=1.07-3.21), production and processing of metals (OR=1.69; 95%CI=1.22-2.34), and surface treatment of metals (OR=1.62; 95%CI=1.22-2.15) - , and urban areas (OR=1.36; 95%CI=1.02-1.80).

CONCLUSIONS

Our study furnishes some evidence that living in the proximity of industrial and urban sites may be a risk factor for childhood leukemia.

Socioeconomic Status and Childhood Leukemia Incidence in Switzerland

Socioeconomic status (SES) discrepancies exist for child and adult cancer morbidity and are a major public health concern. In this Swiss population-based matched case–control study on the etiology of childhood leukemia, we selected the cases from the Swiss Childhood Cancer Registry diagnosed since 1991 and the controls randomly from census. We assigned eight controls per case from the 1990 and 2000 census and matched them by the year of birth and gender. SES information for both cases and controls was obtained from census records by probabilistic record linkage. We investigated the association of SES with childhood leukemia in Switzerland, and explored whether it varied with different definitions of socioeconomic status (parental education, living condition, area-based SES), time period, and age. In conditional logistic regression analyses of 565 leukemia cases and 4433 controls, we found no consistent evidence for an association between SES and childhood leukemia. The odds ratio comparing the highest with the lowest SES category ranged from 0.95 (95% CI: 0.71–1.26; P_trend = 0.73) for paternal education to 1.37 (1.00–1.89; P_trend = 0.064) for maternal education. No effect modification was found for time period and age at diagnosis. Based on this population-based study, which avoided participation and reporting bias, we assume the potential association of socioeconomic status and childhood leukemia if existing to be small. This study did not find evidence that socioeconomic status, of Switzerland or comparable countries, is a relevant risk factor or strong confounder in etiological investigations on childhood leukemia.

Heck J, Malagoli C, Del Giovane C, Vinceti M. A review and meta-analysis of outdoor air pollution and risk of childhood leukemia

Leukemia is the most frequent malignant disease affecting children. To date, the etiology of childhood leukemia remains largely unknown. Few risk factors (genetic susceptibility, infections, ionizing radiation, etc.) have been clearly identified, but they appear to explain only a small proportion of cases. Considerably more uncertain is the role of other environmental risk factors, such as indoor and outdoor air pollution. We sought to summarize and quantify the association between traffic-related air pollution and risk of childhood leukemia, and further examined results according to method of exposure assessment, study quality, leukemia subtype, time period, and continent where studies took place. After a literature search yielded 6 ecologic and 20 case-control studies, we scored the studies based on the Newcastle-Ottawa Scale. The studies assessed residential exposure to pollutants from motorized traffic by computing traffic density in the neighboring roads or vicinity to petrol stations, or by using measured or modeled nitrogen dioxide and benzene outdoor air levels. Because heterogeneity across studies was observed, random-effects summary odds ratios (OR) and 95% confidence intervals (CI) were reported. Whenever possible we additionally conducted stratified analyses comparing acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML). Limiting the analysis to high-quality studies (Newcastle-Ottawa Scale ≥ 7), those using traffic density as the exposure assessment metric showed an increase in childhood leukemia risk in the highest exposure category (OR = 1.07, 95% CI 0.93-1.24). However, we observed evidence of publication bias. Results for NO2 exposure and benzene showed an OR of 1.21 (95% CI 0.97-1.52) and 1.64 (95% CI 0.91-2.95) respectively. When stratifying by leukemia type, the results based upon NO2 were 1.21 (95% CI 1.04-1.41) for ALL and 1.06 (95% CI 0.51-2.21) for AML; based upon benzene were 1.09 (95% CI 0.67-1.77) for ALL and 2.28 (95% CI 1.09-4.75) for AML. Estimates were generally higher for exposures in the postnatal period compared to the prenatal period, and for European studies compared to North American studies. Overall, our results support a link between ambient exposure to traffic pollution and childhood leukemia risk, particularly due to benzene.

Residential traffic exposure and childhood leukemia: a systematic review and meta-analysis

CONTEXT

Exposure to elevated concentrations of traffic-related air pollutants in the near-road environment is associated with numerous adverse human health effects, including childhood cancer, which has been increasing since 1975. Results of individual epidemiologic studies have been inconsistent. Therefore, a meta-analysis was performed to examine the association between residential traffic exposure and childhood cancer.

EVIDENCE ACQUISITION

Studies published between January 1980 and July 2011 were retrieved from a systematic search of 18 bibliographic databases. Nine studies meeting the inclusion criteria were identified. Weighted summary ORs were calculated using a random effects model for outcomes with four or more studies. Subgroup and sensitivity analyses were performed.

EVIDENCE SYNTHESIS

Childhood leukemia was positively associated (summary OR=1.53, 95% CI=1.12, 2.10) with residential traffic exposure among seven studies using a postnatal exposure window (e.g., childhood period or diagnosis address) and there was no association (summary OR=0.92, 95% CI=0.78, 1.09) among four studies using a prenatal exposure window (e.g., pregnancy period or birth address). There were too few studies to analyze other childhood cancer outcomes.

CONCLUSIONS

Current evidence suggests that childhood leukemia is associated with residential traffic exposure during the postnatal period, but not during the prenatal period. Additional well-designed epidemiologic studies that use complete residential history to estimate traffic exposure, examine leukemia subtypes, and control for potential confounding factors are needed to confirm these findings. As many people reside near busy roads, especially in urban areas, precautionary public health messages and interventions designed to reduce population exposure to traffic might be warranted.

Quantitative assessments of indoor air pollution and the risk of childhood acute leukemia in Shanghai

We investigated the association between indoor air pollutants and childhood acute leukemia (AL). A total of 105 newly diagnosed cases and 105 1:1 gender-, age-, and hospital-matched controls were included. Measurements of indoor pollutants (including nitrogen dioxide (NO2) and 17 types of volatile organic compounds (VOCs)) were taken with diffusive samplers for 64 pairs of cases and controls. Higher concentrations of NO2 and almost half of VOCs were observed in the cases than in the controls and were associated with the increased risk of childhood AL. The use of synthetic materials for wall decoration and furniture in bedroom was related to the risk of childhood AL. Renovating the house in the last 5 years, changing furniture in the last 5 years, closing the doors and windows overnight in the winter and/or summer, paternal smoking history and outdoor pollutants affected VOC concentrations. Our results support the association between childhood AL and indoor air pollution.

Risk of leukemia in relation to exposure to ambient air toxics in pregnancy and early childhood

There are few established causes of leukemia, the most common type of cancer in children. Studies in adults suggest a role for specific environmental agents, but little is known about any effect from exposures in pregnancy to toxics in ambient air. In our case-control study, we ascertained 69 cases of acute lymphoblastic leukemia (ALL) and 46 cases of acute myeloid leukemia (AML) from California Cancer Registry records of children <age 6, and 19,209 controls from California birth records within 2 km (1.3 miles) (ALL) and 6 km (3.8 miles) (AML) of an air toxics monitoring station between 1990 and 2007. Information on air toxics exposures was taken from community air monitors. We used logistic regression to estimate the risk of leukemia associated with one interquartile range increase in air toxic exposure. Risk of ALL was elevated with 3(rd) trimester exposure to polycyclic aromatic hydrocarbons (OR=1.16, 95% CI 1.04, 1.29), arsenic (OR=1.33, 95% CI 1.02, 1.73), benzene (OR=1.50, 95% CI 1.08, 2.09), and three other toxics related to fuel combustion. Risk of AML was increased with 3rd trimester exposure to chloroform (OR=1.30, 95% CI 1.00, 1.69), benzene (1.75, 95% CI 1.04, 2.93), and two other traffic-related toxics. During the child's first year, exposure to butadiene, ortho-xylene, and toluene increased risk for AML and exposure to selenium increased risk for ALL. Benzene is an established cause of leukemia in adults; this study supports that ambient exposures to this and other chemicals in pregnancy and early life may also increase leukemia risk in children.

Childhood cancer and traffic-related air pollution exposure in pregnancy and early life

BACKGROUND

The literature on traffic-related air pollution and childhood cancers is inconclusive, and little is known on rarer cancer types.

OBJECTIVES

We sought to examine associations between childhood cancers and traffic-related pollution exposure.

METHODS

The present study included children < 6 years of age identified in the California Cancer Registry (born 1998-2007) who could be linked to a California birth certificate (n = 3,590). Controls were selected at random from California birthrolls (n = 80,224). CAlifornia LINE Source Dispersion Modeling, version 4 (CALINE4) was used to generate estimates of local traffic exposures for each trimester of pregnancy and in the first year of life at the address indicated on the birth certificate. We checked our findings by additionally examining associations with particulate matter (≤ 2.5 μm in aerodynamic diameter; PM2.5) pollution measured by community-based air pollution monitors, and with a simple measure of traffic density.

RESULTS

With unconditional logistic regression, a per interquartile range increase in exposure to traffic-related pollution during the first trimester (0.0538 ppm carbon monoxide, estimated using CALINE4) was associated with acute lymphoblastic leukemia [ALL; first trimester odds ratio (OR) = 1.05; 95% CI: 1.01, 1.10]; germ cell tumors (OR = 1.16; 95% CI: 1.04, 1.29), particularly teratomas (OR = 1.26; 95% CI: 1.12, 1.41); and retinoblastoma (OR = 1.11; 95% CI: 1.01, 1.21), particularly bilateral retinoblastoma (OR = 1.16; 95% CI: 1.02, 1.33). Retinoblastoma was also associated with average PM2.5 concentrations during pregnancy, and ALL and teratomas were associated with traffic density near the child's residence at birth.

CONCLUSIONS

We estimated weak associations between early exposure to traffic pollution and several childhood cancers. Because this is the first study to report on traffic pollution in relation to retinoblastoma or germ cell tumors, and both cancers are rare, these findings require replication in other studies.

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.

Exposure to benzene and childhood leukaemia: a pilot case-control study

OBJECTIVES

Main purpose To evaluate the feasibility of a measurement-based assessment of benzene exposure in case-control studies of paediatric cancer; Additional aims To identify the sources of exposure variability; to assess the performance of two benzene biomarkers; to verify the occurrence of participation bias; to check whether exposures to benzene and to 50 Hz magnetic fields were correlated, and might exert reciprocal confounding effects.

DESIGN

Pilot case-control study of childhood leukaemia and exposure to benzene assessed by repeated seasonal weekly measurements in breathing zone air samples and outside the children's dwellings, with concurrent determinations of cotinine, t-t-muconic acid (MA) and sulfo-phenylmercapturic acid (S-PMA) in urine.

PARTICIPANTS

108 cases and 194 controls were eligible for inclusion.

RESULTS

Full-participation was obtained from 46 cases and 60 controls, with low dropout rates before four repeats (11% and 17%); an additional 23 cases and 80 controls allowed the collection of outdoor air samples only. The average benzene concentration in personal and outdoor air samples was 3 μg/m(3) (SD 1.45) and 2.7 μg/m(3) (SD 1.41), respectively. Personal exposure was strongly influenced by outdoor benzene concentrations, higher in the cold seasons than in warm seasons, and not affected by gender, age, area of residence or caseness. Urinary excretion of S-PMA and personal benzene exposure were well correlated. Outdoor benzene levels were lower among participant controls compared with non-participants, but did not differ between participant and non-participant cases; the direction of the bias was found to depend on the cut-point chosen to distinguish exposed and unexposed. Exposures to benzene and extremely low-frequency magnetic fields were positively correlated.

CONCLUSIONS

Repeated individual measurements are needed to account for the seasonal variability in benzene exposure, and they have the additional advantage of increasing the study power. Measurement-based assessment of benzene exposure in studies of childhood leukaemia appears feasible, although it is financially and logistically demanding.

Leukemia risk in children exposed to benzene and PM10 from vehicular traffic: a case-control study in an Italian population

Benzene, a recognized occupational leukemogen in adults, has been hypothesized to also increase the risk of childhood leukemia. We carried out a population-based case–control study in a northern Italy community involving 83 cases with acute childhood leukemia diagnosed in the years 1998–2009 and 332 matched controls. We assessed residential exposure to benzene and to particulate matter ≤10 μm (PM₁₀) from motorized traffic using geocoded residences and detailed emission and dispersion modeling. Exposure to benzene, and to a lesser extent to PM₁₀, appeared to be independently associated with an excess leukemia risk. When we stratified the study population by age and by leukemia subtype, the relative risk associated with benzene exposure was higher among children aged less than 5 years, and despite small numbers this relation appeared to be considerably stronger for acute myeloid leukemia than for acute lymphoblastic leukemia. Overall, these findings suggest that exposure to low levels of benzene released from motorized traffic may increase the risk of childhood leukemia, and suggest a possible independent effect of PM₁₀, although unmeasured confounding due to other pollutants cannot be ruled out.

Polycyclic aromatic hydrocarbon burden in ambient air in selected Niger Delta communities in Nigeria

The Niger Delta area in Nigeria has major oil producing and refining centers that characterized enormous industrial activities, especially in the petroleum sector. These industrial processes release different kinds of atmospheric pollutants, of which there is paucity of information on their levels and health implications. The objective of this study was to determine the ambient levels of polycyclic aromatic hydrocarbons (PAHs) in communities of a local government area (Eleme) where oil wells, petrochemical installations, a refinery, and a fertilizer complex are located. Respirable particulate matter (PM) in air were collected using Anderson high-volume sampler with PM with aerodynamic diameter > 10 microm (PM10) inlet for collecting filterable, particle-bound PAHs according to standard methods. PAHs were analyzed following standard methods for the 16 World Health Organization (WHO) prioritized components. The results were compared against the levels in another local government area (Ahoada East) with low industrial presence. The average total PAH concentration in Eleme of 9.2 microg/m3 was among the highest in the world; by contrast, the average concentration in Ahoada East was only 0.17 ng/m3. The most prominent PAHs at Eleme were those known to be carcinogenic and included benzo(a)pyrene (1.6 x 10(4) ng/m3 at bubu), benzo(k)fluoranthene (2.4 x 10(4) ng/m3 at Akpajo where a petrochemical is located), pyrene (3.1 x 10(3) ng/m3 at Ogale), and indeno(1,2,3-cd)pyrene (9.1 x 10(3) ng/m3 at Akpajo). Data from this study emphasize the need for a comprehensive source apportionment study and an assessment of the health effects of oil production on local communities of Nigeria where no such information currently exists.

Refuelling of vehicles, the use of wood burners and the risk of acute lymphoblastic leukaemia in childhood

It is plausible that exposure of the parents before birth or of the child to sources of benzene increases the risk of childhood acute lymphoblastic leukaemia (ALL). The aim of this analysis was to investigate whether refuelling a vehicle with petrol before birth or burning wood to heat the home before or after the child's birth increased the risk of childhood ALL. Data from 389 cases and 876 frequency-matched controls were analysed using unconditional logistic regression, adjusting for study matching factors and potential confounders. The odds ratio (OR) for the mother ever refuelling a vehicle with petrol for non-occupational purposes before or during the pregnancy was 0.97 [95% confidence interval (CI) 0.69, 1.38]. The OR for the father for this exposure in the year before conception was 0.88 [95% CI 0.52, 1.48]. The OR for use of a closed wood burner to heat the home in the year before or during pregnancy was 1.41 [95% CI 1.02, 1.94] and 1.25 [95% CI 0.92, 1.70] after birth. We found no evidence that non-occupational refuelling a vehicle with petrol in the year before or during pregnancy increased the risk of ALL in the offspring. There was weak evidence that burning wood in a closed burner to heat the home increased the risk, but there was no dose-response relationship and chance could explain the finding.

Expression and methylation analysis of p15 and p16 in mouse bone marrow cells exposed to 1,4-benzoquinone

Benzene is an important industrial chemical. It is also an environmental pollutant recognized as a human carcinogen. Both prenatal and adult exposures to benzene are associated with the development of leukemia. To understand the mechanism of benzene-induced epigenetic variations, we investigated the expression and methylation patterns of CpG (phosphodiester bond between cytosine and guanine) islands in p15 and p16 promoter regions in 1,4-benzoquinone (1,4-BQ)-treated primary cultivated C57BL/6J mouse bone marrow cells in vitro. The cell toxicity of 1,4-BQ was evaluated by cell viability test, real-time PCR was used to measure the mRNA expression levels, and bisulfite sequencing PCR (BSP) was used to look into the methylation patterns. The cell viability test indicates that 1,4-BQ exhibited a dose-dependent toxicity to mouse bone marrow cells. After a 24-h exposure to 1,4-BQ at final concentrations of 0, 0.1, 1, and 10 μmol/L, the mRNA expression of p15 and p16 decreased with the increase in 1,4-BQ concentration. The BSP results gathered from the exposure and the control groups were the same. In summary, despite the observation that short-term exposure to 1,4-BQ primary cultivated mouse bone marrow cells decreased the p15 and p16 transcripts, with no influence by their gene promoter methylation.

Residential proximity to environmental hazards and adverse health outcomes

How living near environmental hazards contributes to poorer health and disproportionate health outcomes is an ongoing concern. We conducted a substantive review and critique of the literature regarding residential proximity to environmental hazards and adverse pregnancy outcomes, childhood cancer, cardiovascular and respiratory illnesses, end-stage renal disease, and diabetes. Several studies have found that living near hazardous wastes sites, industrial sites, cropland with pesticide applications, highly trafficked roads, nuclear power plants, and gas stations or repair shops is related to an increased risk of adverse health outcomes. Government agencies should consider these findings in establishing rules and permitting and enforcement procedures to reduce pollution from environmentally burdensome facilities and land uses.

The role of residence near hazardous waste sites containing benzene in the development of hematologic cancers in upstate New York

OBJECTIVES

Epidemiologic studies suggest an association between environmental exposure to benzene and hematologic cancers, but the relationship is not firmly established. The aim of this study was to assess the potential association between residence near hazardous waste sites containing benzene and hospitalization discharge rates for persons having hematologic cancers.

MATERIALS AND METHODS

We determined the number of hospital discharges of people with hematologic cancers in New York State except for New York City for the years 1993 to 2008.Descriptive statistics and negative binomial regression models were used to compare the rates of hospitalization of residents in zip codes containing hazardous waste sites containing benzene to the rates of discharges from residents in zip codes without waste sites.

RESULTS

When adjusting for potential confounders we found a 15% increase in the rate of hospitalization for chronic lymphatic leukemia (CLL) [rate ratio (RR): 1.15; 95% confidence interval (CI): 1.00-1.33], a 22% increase in the rate of discharges for total leukemia (RR: 1.22; 95% CI: 1.04-1.43) and a 17% increase in the rate of discharges for total lymphoma (RR: 1.17; 95% CI: 1.02-1.35) in the benzene exposed sites. We found greater effects of exposure in African Americans compared to Caucasians, females compared to males and people with higher socioeconomic status (SES) compared to those with lower SES for several of the diseases studied.

CONCLUSIONS

After controlling for major confounders we found statistically significant increases in discharge rates for several hematologic cancers in persons residing in zip codes containing benzene waste sites. These results provide additional support for a relationship between environmental exposure to benzene and risk of hematologic cancers.

Road traffic and childhood leukemia: the ESCALE study (SFCE)

BACKGROUND

Traffic is a source of environmental exposures, including benzene, which may be related to childhood leukemia.

OBJECTIVES

A national registry-based case-control study [ESCALE (Etude Sur les Cancers et les Leucémies de l'Enfant, Study on Environmental and Genetic Risk Factors of Childhood Cancers and Leukemia)] carried out in France was used to assess the effect of exposure to road traffic exhaust fumes on the risk of childhood leukemia.

METHODS

Over the study period, 2003-2004, 763 cases and 1,681 controls < 15 years old were included, and the controls were frequency matched with the cases on age and sex. The ESCALE data were collected by a standardized telephone interview of the mothers. Various indicators of exposure to traffic and pollution were determined using the geocoded addresses at the time of diagnosis for the cases and of interview for the controls. Indicators of the distance from, and density of, main roads and traffic nitrogen dioxide (NO(2)) concentrations derived from traffic emission data were used. Odds ratios (ORs) were estimated using unconditional regression models adjusted for potential confounders.

RESULTS

Acute leukemia (AL) was significantly associated with estimates of traffic NO(2) concentration at the place of residence > 27.7 µg/m(3) compared with NO(2) concentration < 21.9 µg/m(3) [OR=1.2; confidence interval (CI), 1.0-1.5] and with the presence of a heavy-traffic road within 500 m compared with the absence of a heavy-traffic road in the same area (OR=2.0; 95% CI, 1.0-3.6). There was a significant association between AL and a high density of heavy-traffic roads within 500 m compared with the reference category with no heavy-traffic road within 500 m (OR=2.2; 95% CI, 1.1-4.2), with a significant positive linear trend of the association of AL with the total length of heavy-traffic road within 500 m.

CONCLUSION

This study supports the hypothesis that living close to heavy-traffic roads may increase the risk of childhood leukemia.

Elemental and organic carbon in aerosols over urbanized coastal region (southern Baltic Sea, Gdynia)

Studies on PM 10, total particulate matter (TSP), elemental carbon (EC) and organic carbon (OC) concentrations were carried out in the Polish coastal zone of the Baltic Sea, in urbanized Gdynia. The interaction between the land, the air and the sea was clearly observed. The highest concentrations of PM 10, TSP and both carbon fractions were noted in the air masses moving from southern and western Poland and Europe. The EC was generally of primary origin and its contribution to TSP and PM 10 mass was on average 2.3% and 3.7% respectively. Under low wind speed conditions local sources (traffic and industry) influenced increases in elemental carbon and PM 10 concentrations in Gdynia. Elemental carbon demonstrated a pronounced weekly cycle, yielding minimum values at the weekend and maximum values on Thursdays. The role of harbors and ship yards in creating high EC concentrations was clearly observed. Concentration of organic carbon was ten times higher than that of elemental carbon, and the average OC contribution to PM 10 mass was very high (31.6%). An inverse situation was observed when air masses were transported from over the Atlantic Ocean, the North Sea and the Baltic Sea. These clean air masses were characterized by the lowest concentrations of all analysed compounds. Obtained results for organic and elemental carbon fluxes showed that atmospheric aerosols can be treated, along with water run-off, as a carbon source for the coastal waters of the Baltic Sea. The enrichment of surface water was more effective in the case of organic carbon (0.27+/-0.19 mmol m(-2) d(-1)). Elemental carbon fluxes were one order of magnitude smaller, on average 0.03+/-0.04 mmol m(-2) d(-1). We suggest that in some situations atmospheric carbon input can explain up to 18% of total carbon fluxes into the Baltic coastal waters.

A biomarker approach to estimate the daily intake of benzene in non-smoking and smoking individuals in Germany

Owing to its carcinogenic properties, benzene is one of the most important environmental air pollutants. We have applied a simple pharmacokinetic model to estimate the individual daily exposure of persons of the general population to benzene using their urinary excretion of S-phenylmercapturic acid as biomarker of exposure. On the basis of a non-representative convenience sample of the general population, spontaneous urine samples of 43 non-smoking persons, 13 persons with exposure to environmental tobacco smoke (ETS) (as determined by urinary cotinine) and 72 smokers were analyzed for S-phenylmercapturic acid, and benzene exposure was back calculated on the basis of the results. The pharmacokinetic model was based either on estimated daily urinary volume or creatinine excretion. Median daily exposure of non-smokers was calculated to be 47 microg/day (volume-based model) and 63 microg benzene/day (creatinine-based model). ETS-exposed persons had a slightly higher median daily exposure of 65 microg/day (volume-based model) and 72 microg benzene/day (creatinine-based model). The daily exposure of smokers was significantly higher with median values of 491 microg benzene/day (volume-based model) and 693 microg benzene/day (creatinine-based model). Our biomarker-based model gave plausible results for daily benzene exposure that were in good agreement with exposure estimations published earlier. As it is purely based on the determination of individual internal dose, our model provides a powerful tool for the risk assessment of environmental benzene.

Aetiology of childhood leukaemia

The acute leukaemias account for about 30% of all malignancy seen in childhood across the Western world. A peak incidence of precursor B cell ALL has emerged as socio-economic conditions have improved in countries worldwide. From twin studies and the use of neonatal blood spots it has been possible to back track the first initiating genetic events within critical haemopoietic cells to foetal development in utero for most precursor B cell ALL and some cases of AML. These events may occur as part of normal foetal development. Whether other factors (environmental or constitutional) are involved to increase the chance of these first genetic changes happening is unclear. For some leukaemias (e.g. infant MLL positive ALL) the first event appears adequate to create a malignant clone but for the majority of ALL and AML further 'genetic' changes are required, probably postnatal. Many environmental factors have been proposed as causative for leukaemia but only ionising irradiation and certain chemicals, e.g. benzene and cytotoxics (alkylators and topoisomerase II inhibitors) have been confirmed and then principally for acute myeloid leukaemia. It appears increasingly likely that delayed, dysregulated responses to 'common' infectious agents play a major part in the conversion of pre-leukaemic clones into overt precursor B cell ALL, the most common form of childhood leukaemia. Constitutional polymorphic alleleic variants in immune response genes (especially the HLA Class II proteins) and cytokines may play a role in determining the type of immune response. High penetrance germ-line mutations are involved in only about 5% of childhood leukaemias (more in AML than ALL). There is little evidence to support any role of viral transformation in causation, unlike in animals. Other environmental factors for which some evidence exists include non-ionising electromagnetic radiation and electric fields, although their mode of action in leukaemogenesis remains unclear. There is no single cause for childhood leukaemia and for most individuals a combination of factors appears to be necessary; all involving gene-environment interactions. To date few clear preventative measures have emerged, except the complete avoidance of first trimester X-rays in pregnancy; a healthy diet with adequate oral folic acid intake both preconception and early in pregnancy; and the early exposure of children to other children outside the home to facilitate stimulation and maturation of the natural immune system. Here then are clear echoes of the "hygiene hypothesis" regarding the initiation of allergies, autoimmune disease and type I diabetes mellitus in children and young people.