Probability estimates for the unique childhood leukemia cluster in Fallon, Nevada, and risks near other U.S. Military aviation facilities

A Historical Survey of Key Epidemiological Studies of Ionizing Radiation Exposure

In this article we review the history of key epidemiological studies of populations exposed to ionizing radiation. We highlight historical and recent findings regarding radiation-associated risks for incidence and mortality of cancer and non-cancer outcomes with emphasis on study design and methods of exposure assessment and dose estimation along with brief consideration of sources of bias for a few of the more important studies. We examine the findings from the epidemiological studies of the Japanese atomic bomb survivors, persons exposed to radiation for diagnostic or therapeutic purposes, those exposed to environmental sources including Chornobyl and other reactor accidents, and occupationally exposed cohorts. We also summarize results of pooled studies. These summaries are necessarily brief, but we provide references to more detailed information. We discuss possible future directions of study, to include assessment of susceptible populations, and possible new populations, data sources, study designs and methods of analysis.

Review of the risk of cancer following low and moderate doses of sparsely ionising radiation received in early life in groups with individually estimated doses

BACKGROUND

The detrimental health effects associated with the receipt of moderate (0.1-1 Gy) and high (>1 Gy) acute doses of sparsely ionising radiation are well established from human epidemiological studies. There is accumulating direct evidence of excess risk of cancer in a number of populations exposed at lower acute doses or doses received over a protracted period. There is evidence that relative risks are generally higher after radiation exposures in utero or in childhood.

METHODS AND FINDINGS

We reviewed and summarised evidence from 60 studies of cancer or benign neoplasms following low- or moderate-level exposure in utero or in childhood from medical and environmental sources. In most of the populations studied the exposure was predominantly to sparsely ionising radiation, such as X-rays and gamma-rays. There were significant (p < 0.001) excess risks for all cancers, and particularly large excess relative risks were observed for brain/CNS tumours, thyroid cancer (including nodules) and leukaemia.

CONCLUSIONS

Overall, the totality of this large body of data relating to in utero and childhood exposure provides support for the existence of excess cancer and benign neoplasm risk associated with radiation doses < 0.1 Gy, and for certain groups exposed to natural background radiation, to fallout and medical X-rays in utero, at about 0.02 Gy.

Infectious triggers and novel therapeutic opportunities in childhood B cell leukaemia

B cell acute lymphoblastic leukaemia (B-ALL) is the most common form of childhood cancer. Although treatment has advanced remarkably in the past 50 years, it still fails in ~20% of patients. Recent studies revealed that more than 5% of healthy newborns carry preleukaemic clones that originate in utero, but only a small percentage of these carriers will progress to overt B-ALL. The drivers of progression are unclear, but B-ALL incidence seems to be increasing in parallel with the adoption of modern lifestyles. Emerging evidence shows that a major driver for the conversion from the preleukaemic state to the B-ALL state is exposure to immune stressors, such as infection. Here, we discuss our current understanding of the environmental triggers and genetic predispositions that may lead to B-ALL, highlighting lessons from epidemiology, the clinic and animal models, and identifying priority areas for future research.

Origin of tungsten and geochemical controls on its occurrence and mobilization in shallow sediments from Fallon, Nevada, USA

Tungsten (W) occurrence and speciation was investigated in sediments collected from Fallon, Nevada where previous studies have linked elevated W levels in human body fluids to an unusual cluster of childhood leukemia cases. The speciation of sedimentary W was determined by μ-XRF mapping and μ-XANES. The W content of the analyzed surface sediments ranged between 81 and 25,908 mg/kg, which is significantly higher than the W content in deeper sediments which ranged from 37 to 373 mg/kg at 30 cm depth. The μ-XANES findings reveal that approximately 20-50% of the total W in the shallow sediment occurs in the metallic form (W⁰); the rest occurs in the oxide form (W^VIO₃). Because W⁰ does not occur naturally, its elevated concentrations in surface sediments point toward a possible local anthropogenic origin. The oxidation of metallic W⁰ with meteoric waters likely leads to the formation of W^VIO₃. The chief water-soluble W species was identified as WO₄^2- by chromatographic separation and speciation modeling. These results led us to postulate that W⁰ particles from a currently unknown but local source(s) is (are) deposited onto the soils and/or surface sediments. The W⁰ in interaction with meteoric water is oxidized to W^VIO₃, and as these sediment-water interactions progress, WO₄^2- is formed in the water at pH ∼7. Under pH < 7, and sufficient W concentrations, tungstate tends to polymerize, and polymerized species are less likely to adsorb onto sediments. Polymerized species have lower affinity than monomers, which leads to enhanced mobility of W.

Structural Evidence of Programmed Cell Death Induction by Tungsten in Root Tip Cells of Pisum sativum

Previous studies have shown that excess tungsten (W), a rare heavy metal, is toxic to plant cells and may induce a kind of programmed cell death (PCD). In the present study we used transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM) to investigate the subcellular malformations caused by W, supplied as 200 mg/L sodium tungstate (Na₂WO₄) for 12 or 24 h, in root tip cells of Pisum sativum (pea), The objective was to provide additional evidence in support of the notion of PCD induction and the presumed involvement of reactive oxygen species (ROS). It is shown ultrastructurally that W inhibited seedling growth, deranged root tip morphology, induced the collapse and deformation of vacuoles, degraded Golgi bodies, increased the incidence of multivesicular and multilamellar bodies, and caused the detachment of the plasma membrane from the cell walls. Plastids and mitochondria were also affected. By TEM, the endoplasmic reticulum appeared in aggregations of straight, curved or concentric cisternae, frequently enclosing cytoplasmic organelles, while by CLSM it appeared in bright ring-like aggregations and was severely disrupted in mitotic cells. However, no evidence of ROS increase was obtained. Overall, these findings support the view of a W-induced vacuolar destructive PCD without ROS enhancement.

The Krümmel (Germany) Childhood Leukaemia Cluster: a review and update

The debate surrounding possible adverse health effects from the civil use of nuclear power under normal operating conditions has been on-going since its introduction. It was particularly intensified by the detection of three leukaemia clusters near nuclear installations, i.e. near the reprocessing plants in Sellafield and Dounreay, UK, and near the Krümmel nuclear power plant, Germany, the last of which commenced between 1990 and 1991 and was first described in 1992; it continued until 2003, and an elevated risk up to 2005 has been reported in the literature. A number of expert commissions and working groups were set up by the governments of the German federal states of Lower Saxony and Schleswig-Holstein to investigate the possible causes of the cluster. An overview of the many risk factors that were investigated as a possible explanation of the Krümmel cluster is given here, focussing on radiation, but also including other risk factors. Further, results from related epidemiological and cytogenetic studies are described. In summary, the cause of the occurrence of the Krümmel cluster has to be considered as unknown. Further research on the causes of childhood leukaemia is needed, focussing on epigenetics and on gene-environment interaction. An update of the leukaemia incidence around the Krümmel site shows that the incidence rates are now comparable to the average rate in Germany.

High-resolution measurement and mapping of tungstate in waters, soils and sediments using the low-disturbance DGT sampling technique

Increasing tungsten (W) use for industrial and military applications has resulted in greater W discharge into natural waters, soils and sediments. Risk modeling of W transport and fate in the environment relies on measurement of the release/mobilization flux of W in the bulk media and the interfaces between matrix compartments. Diffusive gradients in thin-films (DGT) is a promising passive sampling technique to acquire such information. DGT devices equipped with the newly developed high-resolution binding gels (precipitated zirconia, PZ, or ferrihydrite, PF, gels) or classic/conventional ferrihydrite slurry gel were comprehensively assessed for measuring W in waters. (Ferrihydrite)DGT can measure W at various ionic strengths (0.001-0.5molL(-1) NaNO3) and pH (4-8), while (PZ)DGT can operate across slightly wider environmental conditions. The three DGT configurations gave comparable results for soil W measurement, showing that typically W resupply is relatively poorly sustained. 1D and 2D high-resolution W profiling across sediment-water and hotspot-bulk media interfaces from Lake Taihu were obtained using (PZ)DGT coupled with laser ablation ICP-MS measurement, and the apparent diffusion fluxes across the interfaces were calculated using a numerical model.

Geographic Variation in Cancer Incidence among Children and Adolescents in Taiwan (1995-2009)

BACKGROUND

Evidence from our recent study suggested that the overall trend for cancer incidence in children and adolescents has been increasing in Taiwan.

METHODS

To analyze geographic variations in this trend, cancer frequencies and incidence rates of disease groups were quantified according to geographic areas among 12,633 patients aged <20 years during 1995-2009 by using the population-based Taiwan Cancer Registry. Three geographic levels were defined, namely county or city, region (Northern, Central, Southern, and Eastern Taiwan), and local administrative area (special municipality, provincial city, county-administered city, township, and aboriginal area).

RESULTS

Of the regions, Northern Taiwan had the highest incidence rate at 139.6 per million person-years, followed by Central (132.8), Southern (131.8), and Eastern (128.4) Taiwan. Significantly higher standardized rate ratios (SRRs) were observed in Northern Taiwan (SRR = 1.06, 95% confidence interval [CI] = 1.02-1.10) and at the township level (SRR = 1.07, 95% CI = 1.03-1.11). Of the cities or counties, New Taipei City yielded the highest SRR (1.08), followed by Taipei City (SRR = 1.07). A comparison of the rates in the four regions and the remainder of Taiwan according to cancer type revealed that only the rate of neuroblastomas in Eastern Taiwan was significantly low. Trend analysis showed that the most significant increase in incidence rate was observed at the township level, with an annual percent change of 1.8% during the 15-year study period.

CONCLUSIONS

The high rate of childhood cancer in Northern Taiwan and at the township level deserves further attention. The potential impacts of environmental factors on the upward trend of childhood cancer incidence rate in townships warrant further investigation.

Childhood leukaemia risks: from unexplained findings near nuclear installations to recommendations for future research

Recent findings related to childhood leukaemia incidence near nuclear installations have raised questions which can be answered neither by current knowledge on radiation risk nor by other established risk factors. In 2012, a workshop was organised on this topic with two objectives: (a) review of results and discussion of methodological limitations of studies near nuclear installations; (b) identification of directions for future research into the causes and pathogenesis of childhood leukaemia. The workshop gathered 42 participants from different disciplines, extending widely outside of the radiation protection field. Regarding the proximity of nuclear installations, the need for continuous surveillance of childhood leukaemia incidence was highlighted, including a better characterisation of the local population. The creation of collaborative working groups was recommended for consistency in methodologies and the possibility of combining data for future analyses. Regarding the causes of childhood leukaemia, major fields of research were discussed (environmental risk factors, genetics, infections, immunity, stem cells, experimental research). The need for multidisciplinary collaboration in developing research activities was underlined, including the prevalence of potential predisposition markers and investigating further the infectious aetiology hypothesis. Animal studies and genetic/epigenetic approaches appear of great interest. Routes for future research were pointed out.

Tungsten distribution in soil and rice in the vicinity of the world's largest and longest-operating tungsten mine in China

The objective of this study is to investigate tungsten (W) contamination in soil and its enrichment in rice in the area of the world's largest and longest-operating W mines in China. Root zone soil and rice plants were sampled at 15 sites in the agricultural field adjacent to W mines and analyzed for Al, Fe, Mn, Sc, and W contents and W chemical forms in the soil samples and W contents in the rice root, stem, leaf, and grain samples. Results showed that W content in the soil ranged from 3.99 to 43.7 mg kg(-1), with more than 90% of W in the residual fraction, showing its low mobility and bioavailability. Average W contents in the rice root, stem, leaf, and grain were 7.06, 2.34, 4.76, 0.17 mg kg(-1), respectively. In addition, they were linearly independent of W content and chemical forms in the soil. Average enrichment factor values were 0.39, 0.13, 0.28, and 0.01 for the root, stem, leaf, and grain, respectively. In can be concluded that W mining activity in the Dayu county contaminated the nearby agricultural soil and led to W bioaccumulation in the rice. This may pose a health risk to residents via food and soil ingestion, which should be a focus of scrutiny.

Cancer cluster investigations: review of the past and proposals for the future

Residential clusters of non-communicable diseases are a source of enduring public concern, and at times, controversy. Many clusters reported to public health agencies by concerned citizens are accompanied by expectations that investigations will uncover a cause of disease. While goals, methods and conclusions of cluster studies are debated in the scientific literature and popular press, investigations of reported residential clusters rarely provide definitive answers about disease etiology. Further, it is inherently difficult to study a cluster for diseases with complex etiology and long latency (e.g., most cancers). Regardless, cluster investigations remain an important function of local, state and federal public health agencies. Challenges limiting the ability of cluster investigations to uncover causes for disease include the need to consider long latency, low statistical power of most analyses, uncertain definitions of cluster boundaries and population of interest, and in- and out-migration. A multi-disciplinary Workshop was held to discuss innovative and/or under-explored approaches to investigate cancer clusters. Several potentially fruitful paths forward are described, including modern methods of reconstructing residential history, improved approaches to analyzing spatial data, improved utilization of electronic data sources, advances using biomarkers of carcinogenesis, novel concepts for grouping cases, investigations of infectious etiology of cancer, and "omics" approaches.

Tungstate adsorption onto oxisols in the vicinity of the world's largest and longest-operating tungsten mine in China

Tungstate adsorption in soils is critical to understand tungstate mobility and bioavailability, but study of this is lacking.

The risk of childhood leukaemia following exposure to ionising radiation--a review

Since the early years of follow-up of the Japanese atomic-bomb survivors, it has been apparent that childhood leukaemia has a particular sensitivity to induction by ionising radiation, the excess relative risk (ERR) being expressed as a temporal wave with time since exposure. This pattern has been generally confirmed by studies of children treated with radiotherapy. Case-control studies of childhood leukaemia and antenatal exposure to diagnostic x-rays, a recent large cohort study of leukaemia following CT examinations of young people, and a recent large case-control study of natural background γ-radiation and childhood leukaemia have found evidence of raised risks following low-level exposure. These findings indicate that an ERR/Sv for childhood leukaemia of ~50, which may be derived from risk models based upon the Japanese atomic-bomb survivors, is broadly applicable to low dose or low dose-rate exposure circumstances.

Tungsten Toxicity in Plants

Tungsten (W) is a rare heavy metal, widely used in a range of industrial, military and household applications due to its unique physical properties. These activities inevitably have accounted for local W accumulation at high concentrations, raising concerns about its effects for living organisms. In plants, W has primarily been used as an inhibitor of the molybdoenzymes, since it antagonizes molybdenum (Mo) for the Mo-cofactor (MoCo) of these enzymes. However, recent advances indicate that, beyond Mo-enzyme inhibition, W has toxic attributes similar with those of other heavy metals. These include hindering of seedling growth, reduction of root and shoot biomass, ultrastructural malformations of cell components, aberration of cell cycle, disruption of the cytoskeleton and deregulation of gene expression related with programmed cell death (PCD). In this article, the recent available information on W toxicity in plants and plant cells is reviewed, and the knowledge gaps and the most pertinent research directions are outlined.

An examination, with a meta-analysis, of studies of childhood leukaemia in relation to population mixing

Background:

Marked influxes of people into rural areas, termed rural population mixing (PM), have been associated with excesses of childhood leukaemia (CL), consistent with mini-epidemics of a mainly immunising, subclinical infection to which CL is a rare response. For such situations of rural PM would promote contacts between infected and susceptible individuals, the latter tending to have a higher than average prevalence in rural or isolated areas. Confusion has arisen from some workers applying the term PM to non-rural situations lacking known recent change.

Methods:

Available PM studies using the original definition of influxes were examined, a meta-analysis carried out of studies of CL in relation to exposure to high levels of rural PM, and also a detailed analysis by age group.

Results:

The meta-analysis of 17 studies shows a significant CL excess in association with rural PM: overall relative risk (RR) at ages 0–14: 1.57; 95% confidence interval 1.44–1.72; at 0–4 years 1.72 (1.54–1.91). This contrasts with the absence of an excess of CL in similarly exposed urban areas (RR 1.00; 0.93–1.07), pointing to a high level of immunity there. The mixed results of studies using other definitions of PM were summarised. The excess associated with rural PM below age 2 years (RR 1.51; 1.17, 1.92) was not appreciably different from that at later childhood ages.

Conclusion:

Much of the inconsistency among studies ostensibly about CL and PM reflects the use of definitions other than that originally proposed. The broad similarity of the CL excess below age 2 with that at older childhood ages is inconsistent with the Greaves’ delayed infection hypothesis, since any infection underlying the former is difficult to consider as delayed.

Comparison of size and geography of airborne tungsten particles in Fallon, Nevada, and Sweet Home, Oregon, with implications for public health

To improve understanding of possible connections between airborne tungsten and public health, size and geography of airborne tungsten particles collected in Fallon, Nevada, and Sweet Home, Oregon, were compared. Both towns have industrial tungsten facilities, but only Fallon has experienced a cluster of childhood leukemia. Fallon and Sweet Home are similar to one another by their particles of airborne tungsten being generally small in size. Meteorologically, much, if not most, of residential Fallon is downwind of its hard metal facility for at least some fraction of time at the annual scale, whereas little of residential Sweet Home is downwind of its tungsten facility. Geographically, most Fallon residents potentially spend time daily within an environment containing elevated levels of airborne tungsten. In contrast, few Sweet Home residents potentially spend time daily within an airborne environment with elevated levels of airborne tungsten. Although it cannot be concluded from environmental data alone that elevated airborne tungsten causes childhood leukemia, the lack of excessive cancer in Sweet Home cannot logically be used to dismiss the possibility of airborne tungsten as a factor in the cluster of childhood leukemia in Fallon. Detailed modeling of all variables affecting airborne loadings of heavy metals would be needed to legitimately compare human exposures to airborne tungsten in Fallon and Sweet Home.

Review of the Churchill County, NV ALL cluster, 1997-2004

Between 1997 and 2002, 16 cases of acute childhood leukemia were diagnosed in children who either lived in Churchill County, Nevada at the time of diagnosis or had lived in the county before their diagnosis. The cases were characterized as a cluster of like illnesses and the probability of having such a cluster occur by chance was estimated to be very small (approximately one in 2.33×10(8)). This suggested that the cluster could be linked to one or more physical, limnological, chemical, or biological agents. This review discusses the setting in which the cluster took place, the epidemiological investigations carried out by the Nevada Bureau of Health Protection Services, the National Center for Environmental Health Centers for Disease Control and Prevention and the Agency for Toxic Substances and Disease Registry, and subsequent investigations supported by a special allocation of federal funds through the US Environmental Protection Agency's Region IX office in San Francisco, CA. This review is meant as background for the papers in this special issue that report results from multi- and interdisciplinary research into environmental and biological factors potentially related to the Churchill County leukemia cluster.

Unusual space-time patterning of the Fallon, Nevada leukemia cluster: Evidence of an infectious etiology

The town of Fallon within Churchill County, Nevada exhibited an unusually high incidence of childhood leukemia during the years 1997-2003. We examined the temporal and spatial patterning of the leukemia case homes in comparison to the distribution of the general population at risk, other cancer incidence, and features of land use. Leukemia cases were predominantly diagnosed during the early to mid summer, exhibiting a seasonal bias. Leukemia cases lived outside of the "developed/urban" area of Fallon, predominantly in the "agriculture/pasture" region of Churchill County, circumscribing downtown Fallon. This pattern was different from the distribution of the underlying population (p-value<0.01) and different from the distribution of other cancers, which were evenly distributed when compared to the population (p-value=0.74). The unusual space-time patterning of childhood leukemia is consistent with the involvement of an infectious disease. A possible mode of transmission for such an infectious disease is by means of a vector, and mosquitoes are abundant in Churchill County outside of the urban area of Fallon. This region harbors a US Navy base, and a temporally concordant increase in military wide childhood leukemia rates suggests the base a possible source of the virus. Taken together, our current understanding of the etiology of childhood leukemia, the rural structure combined with temporal and geospatial patterning of these leukemia cases, and the high degree of population mixing in Fallon, suggest a possible infectious cause.

The ‘delayed infection’ (aka ‘hygiene’) hypothesis for childhood leukaemia

The common variant of childhood acute lymphoblastic leukaemia (cALL) is the most frequent paediatric cancer subtype. Its incidence rate appears to have increased substantially in Western societies during the mid-20th century and continues to increase at ∼1%/year. Worldwide cALL appears to track with affluence of societies. The ‘delayed infection’ hypothesis, first formulated in 1988, parallels the hygiene hypothesis and has an evolutionary foundation in the concept of a mismatch between prior genetic selection and programming (of the immune system) and contemporary social circumstances. In essence, the hypothesis predicts that ALL is triggered by an abnormal immune response to one or more common microbial infections and that the abnormality arises for two reasons: (i) infectious exposures being delayed beyond the immunologically anticipated period of infancy; (ii) some degree of inherited genetic susceptibility via, for example, allelic variation in genes involved in the MHC and/or immune response network. The hypothesis also has a framework in the underlying cell and molecular biology of ALL and its natural history. Epidemiological studies of social contacts in infancy (as a proxy for common infections) and risk of ALL provide indirect but strong support for the hypothesis. The idea still requires mechanistic and genetic endorsement and the appropriate studies are in progress.

Increased childhood liver cancer mortality and arsenic in drinking water in northern Chile

Arsenic in drinking water is an established cause of lung, bladder, and skin cancers in adults and may also cause adult kidney and liver cancers. Some evidence for these effects originated from region II of Chile, which had a period of elevated arsenic levels in drinking water, in particular from 1958 to 1970. This unique exposure scenario provides a rare opportunity to investigate the effects of early-life arsenic exposure on childhood mortality; to our knowledge, this is the first study of childhood cancer mortality and high concentrations of arsenic in drinking water. In this article, we compare cancer mortality rates under the age of 20 in region II during 1950 to 2000 with those of unexposed region V, dividing subjects into those born before, during, or after the peak exposure period. Mortality from the most common childhood cancers, leukemia and brain cancer, was not increased in the exposed population. However, we found that childhood liver cancer mortality occurred at higher rates than expected. For those exposed as young children, liver cancer mortality between ages 0 and 19 was especially high: the relative risk (RR) for males born during this period was 8.9 [95% confidence interval (95% CI), 1.7-45.8; P = 0.009]; for females, the corresponding RR was 14.1 (95% CI, 1.6-126; P = 0.018); and for males and females pooled, the RR was 10.6 (95% CI, 2.9-39.2; P < 0.001). These findings suggest that exposure to arsenic in drinking water during early childhood may result in an increase in childhood liver cancer mortality.

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.

Heavy metals in water of the San Pedro River in Chihuahua, Mexico and its potential health risk

The objective of this study was to determine the seasonal and downstream water quality variations of the San Pedro River in Chihuahua, Mexico. Water samples were collected monthly from October 2005 to August 2006 in triplicate, totaling 165 water samples. The five sampling locations were: below the Francisco I. Madero dam (LP); between Rosales and Delicias (RD); Meoqui (M); El Torreon (ET), and Julimes (LJ). The levels of As, Be, Ca, Cd, Co, Cu, Cr, Fe, Li, Mg, Mn, Mo, Ni, Pb, Sb, Se, Sr, Ti, Ta, V and Zn were measured using an Inductively Coupled Plasma- Optical Emission Spectrometry (ICP-OES) Perkin Elmer 2100. In addition, temperature, pH, electrical conductivity and total and fecal coliformes were determined. The statistical analysis considered a factorial treatment design; where factor A was the location point and factor B was sampling date. In addition, a multivariate technique looking for principal components was performed. The results indicated that some samples exceeded Mexican standards for As, Be, Ca, Cd, Co, Cr, Fe, Mn, Ni, Pb, Sb, Se, Sr and Zn. The As level must be considered for a red flag to the communities along the Rio San Pedro because both the monthly average level (0.10 mg L-1) and location (0.10 mg L-1) exceeded the Mexican and International norms. The multivariate analysis showed a predominant aggregation at the LP location, meaning that there was a predominance of As, Sr, Fe and Li. At the rest of the locations the elements did not present a tendency for aggregation. Statistics applied to sampling month showed that December, January, March and April were aggregated in a negative quadrant of component 1 indicating a predominance of V, Ni, Be, Fe and As. Overall, the results confirmed that this stretch of the San Pedro River is contaminated with heavy metals and other contaminants that might affect human health as well as the health of the ecosystem.

Cancer incidence among children and adolescents in the United States, 2001-2003

OBJECTIVE

Our goal was to describe current childhood cancer incidence in the United States and identify demographic and geographic variation among children and adolescents with cancer.

METHODS

We examined data from 39 National Program of Cancer Registries and 5 Surveillance, Epidemiology, and End Results statewide registries (representing >90% of the US population) to identify cancers diagnosed among persons aged 0 to 19 from 2001-2003. Diagnosed cancers were grouped by the third version of the International Childhood Cancer Classification. Analyses were stratified according to gender, age, race, ethnicity, and US census region. A multivariable negative binomial regression model was used to evaluate demographic and geographic differences in incidence for all cancers combined.

RESULTS

We identified 36446 cases of childhood cancer with an age-adjusted incidence rate of 165.92 per million. Stratified analyses showed that, for all cancers combined, boys had a significantly higher rate than girls; children (aged 0-14 years) had a significantly lower rate than adolescents (aged 15-19 years); and white children had the highest incidence rate among all races. Young people living in the Northeast had the highest incidence rate among all US census regions, which may be partially attributed to significantly higher incidence rates for central nervous system neoplasms and lymphomas in this region compared with other US census regions. Negative binomial regression analysis demonstrated that the childhood cancer-incidence rate varied significantly according to gender, age, race, ethnicity, and geography.

CONCLUSIONS

This study is the first to demonstrate substantial regional differences in the incidence of childhood cancer. It also shows that incidence varies according to gender, age, race, and ethnicity. Our research findings are useful for prioritizing future childhood cancer research needs.

Spatial patterns of tungsten and cobalt in surface dust of Fallon, Nevada

Spatial patterns of tungsten and cobalt are described for surface dust of Fallon, Nevada, where a cluster of childhood leukemia has been ongoing since 1997. In earlier research, airborne tungsten and cobalt was shown to be elevated in total suspended particulates in Fallon. To fine-tune the spatial patterns of tungsten and cobalt deposition in Fallon, surface dust was collected in a grid pattern within as well as outside of Fallon to establish background concentrations of metals. In surface dust, tungsten and cobalt show sharp peaks (934 ppm and 98 ppm, respectively) within Fallon just north of highway 50 and west of highway 95. These two peaks overlap spatially, and given the grid pattern used for collecting surface dust, the source area of these two airborne metals can be pinpointed to the vicinity of hard-metal industry located north of highway 50 and west of highway 95. Fallon is distinctive in west central Nevada because of high airborne tungsten and cobalt particulates, and given its cluster of childhood leukemia, it stands to reason that additional biomedical research is in order to test directly the leukogenicity of combined airborne tungsten and cobalt particulates.

Morphological and chemical characteristics of airborne tungsten particles of Fallon, Nevada

Morphological and chemical characteristics were determined for airborne tungsten particles in Fallon, Nevada, a town that is distinguishable environmentally by elevated airborne tungsten and cobalt. From samples of airborne dust collected previously at six different places in Fallon, tungsten-rich dust particles were isolated and analyzed with automated electron microprobe and wavelength-dispersive spectrometry. Representative W particles were further analyzed using transmission electron microscopy. Morphologically, Fallon W particles are angular and small, with minimum and maximum sizes of < or = 1 microm and 5.9 microm in diameter, respectively. The number and size of tungsten-rich particles decrease in Fallon with distance from a hard-metal facility located near the center of town. Chemically, Fallon airborne W particles include mixtures of tungsten with cobalt plus other metals such as chromium, iron, and copper. No W-rich particles were identifiable as CaWO4 (scheelite) or MnWO4 (huebnerite). From d-spacings, Fallon particles are most consistent with identification as tungsten carbide. Based on these multiple lines of evidence, airborne W particles in Fallon are anthropogenic in origin, not natural. The hard-metal facility in Fallon processes finely powdered W and W-Co, and further investigation using tracer particles is recommended to definitively identify the source of Fallon's airborne tungsten.

Using lichen chemistry to assess airborne tungsten and cobalt in Fallon, Nevada

This paper describes the use of lichen chemistry to assess airborne tungsten and cobalt in Fallon, Nevada, where a cluster of childhood leukemia has been on going since 1997. Lichens and their rock substrates were collected from Rattlesnake Hill within Fallon as well as from four different rock outcrops located north, east, south, and west of Fallon and at least 20 km away from the town center. In the lichens themselves, W and Co are significantly higher within Fallon than in the combined control site outside of Fallon. In the rock substrates of the lichens, no differences exist in W and Co. The W and Co differences in lichens cannot be attributed to substrate geochemistry. Fallon is distinctive in west central Nevada for high airborne W and Co, and given its cluster of childhood leukemia, it stands to reason that additional biomedical research is in order to test directly the leukogenicity of combined airborne W and Co.

Temporal variability of tungsten and cobalt in Fallon, Nevada

BACKGROUND

Since 1997, Fallon, Nevada, has experienced a cluster of childhood leukemia that has been declared "one of the most unique clusters of childhood cancer ever reported." Multiple environmental studies have shown airborne tungsten and cobalt to be elevated within Fallon, but the question remains: Have these metals changed through time in correspondence with the onset of the leukemia cluster?

METHODS

We used dendrochemistry, the study of element concentrations through time in tree rings, in Fallon to assess temporal variability of airborne tungsten and cobalt since the late 1980s. The techniques used in Fallon were also tested in a different town (Sweet Home, OR) that has airborne tungsten from a known source.

RESULTS

The Sweet Home test case confirms the accuracy of dendrochemistry for showing temporal variability of environmental tungsten. Given that dendrochemistry works for tungsten, tree-ring chemistry shows that tungsten increased in Fallon relative to nearby comparison towns beginning by the mid-1990s, slightly before the onset of the cluster, and cobalt has been high throughout the last approximately 15 years. Other metals do not show trends through time in Fallon.

DISCUSSION

Results in Fallon suggest a temporal correspondence between the onset of excessive childhood leukemia and elevated levels of tungsten and cobalt. Although environmental data alone cannot directly link childhood leukemia with exposure to metals, research by others has shown that combined exposure to tungsten and cobalt can be carcinogenic to humans.

CONCLUSION

Continued biomedical research is warranted to directly test for linkage between childhood leukemia and tungsten and cobalt.

Investigating childhood leukemia in Churchill County, Nevada

BACKGROUND

Sixteen children diagnosed with acute leukemia between 1997 and 2002 lived in Churchill County, Nevada, at the time of or before their illness. Considering the county population and statewide cancer rate, fewer than two cases would be expected.

OBJECTIVES

In March 2001, the Centers for Disease Control and Prevention led federal, state, and local agencies in a cross-sectional, case-comparison study to determine if ongoing environmental exposures posed a health risk to residents and to compare levels of contaminants in environmental and biologic samples collected from participating families.

METHODS

Surveys with more than 500 variables were administered to 205 people in 69 families. Blood, urine, and cheek cell samples were collected and analyzed for 139 chemicals, eight viral markers, and several genetic polymorphisms. Air, water, soil, and dust samples were collected from almost 80 homes to measure more than 200 chemicals.

RESULTS

The scope of this cancer cluster investigation exceeded any previous study of pediatric leukemia. Nonetheless, no exposure consistent with leukemia risk was identified. Overall, tungsten and arsenic levels in urine and water samples were significantly higher than national comparison values; however, levels were similar among case and comparison groups.

CONCLUSIONS

Although the cases in this cancer cluster may in fact have a common etiology, their small number and the length of time between diagnosis and our exposure assessment lessen the ability to find an association between leukemia and environmental exposures. Given the limitations of individual cancer cluster investigations, it may prove more efficient to pool laboratory and questionnaire data from similar leukemia clusters.

Genetic studies of a cluster of acute lymphoblastic leukemia cases in Churchill County, Nevada

OBJECTIVE

In a study to identify exposures associated with 15 cases of childhood leukemia, we found levels of tungsten, arsenic, and dichlorodiphenyldichloroethylene in participants to be higher than mean values reported in the National Report on Human Exposure to Environmental Chemicals. Because case and comparison families had similar levels of these contaminants, we conducted genetic studies to identify gene polymorphisms that might have made case children more susceptible than comparison children to effects of the exposures.

DESIGN

We compared case with comparison children to determine whether differences existed in the frequency of polymorphic genes, including genes that code for enzymes in the folate and purine pathways. We also included discovery of polymorphic forms of genes that code for enzymes that are inhibited by tungsten: xanthine dehydrogenase, sulfite oxidase (SUOXgene), and aldehyde oxidase.

PARTICIPANTS

Eleven case children were age- and sex-matched with 42 community comparison children for genetic analyses. Twenty parents of case children also contributed to the analyses.

RESULTS

One bilalleleic gene locus in SUOX was significantly associated with either case or comparison status, depending on which alleles the child carried (without adjusting for multiple comparisons).

CONCLUSIONS

Although genetic studies did not provide evidence that a common agent or genetic susceptibility factor caused the leukemias, the association between a SUOXgene locus and disease status in the presence of high tungsten and arsenic levels warrants further investigation.

RELEVANCE

Although analyses of community clusters of cancer have rarely identified causes, these findings have generated hypotheses to be tested in subsequent studies.

Infection, immune responses and the aetiology of childhood leukaemia

Childhood leukaemia is the principal subtype of paediatric cancer and, despite success in treatment, its causes remain enigmatic. A plethora of candidate environmental exposures have been proposed, but most lack a biological rationale or consistent epidemiological evidence. Although there might not be a single or exclusive cause, an abnormal immune response to common infection(s) has emerged as a plausible aetiological mechanism.

Community clusters of childhood leukemia and lymphoma: evidence of infection?

Information suggesting that infection may be an underlying cause of childhood leukemia and lymphoma includes the occasional appearance of cases in time-space clusters within communities and increased incidence after communities experience marked population influxes (population mixing). Among 50 clusters involving cases of childhood leukemia and lymphoma investigated in the United States in 1961-1977, eight showed suggestive evidence of underlying infectious causation. In seven of the eight communities, case occurrence was associated with the attendance of patients or their siblings at particular schools or with family participation in particular church groups. In five, rapid population growth had occurred. Other findings included the possible association of cases with unusual patterns of infectious disease (rheumatic illness in one community, chickenpox in another) and with other childhood diseases, including other forms of childhood cancer. In one community, two cases of Burkitt's lymphoma occurred at the same time, and a third case arose 3 years later in boys living in a newly developing neighborhood. Such community observations support the need for continued biologic research regarding the possible role of infectious agents in childhood leukemia and lymphoma.