Brain cancer risk and electromagnetic fields (EMFs): assessing the geomagnetic component.

Cancer cluster studies in North Carolina identified several communities in which there existed an elevated risk of brain cancer. These findings prompted a series of case-control studies. The current article, which originated from the results of the 3rd of such studies, is focused on inclusion of the earth's own geomagnetic fields that interact with electromagnetic fields generated from distribution power lines. This article also contains an assessment of the contribution of confounding by residential (e.g., urban, rural) and case characteristics (e.g., age, race, gender). Newly diagnosed brain cancer cases were identified for a 4-county region of central North Carolina, which the authors chose on the basis of the results of earlier observations. A 3:1 matched series of cancer cases from the same hospitals in which the cases were diagnosed served as the comparison group. Extensive geographic information was collected and was based on an exact place of residence at the time of cancer diagnosis, thus providing several strategic geophysical elements for assessment. The model for this assessment was based on the effects of these two sources of electromagnetic fields for an ion cyclotron resonance mechanism of disease risk. The authors used logistic regression models that contained the predicted value for the parallel component of the earth's magnetic field; these models were somewhat erratic, and the elements were not merged productively into a single statistical model. Interpretation of these values was difficult; therefore, the modeled values for the model elements, at progressive distances from the nearest power-line segments, are provided. The results of this study demonstrate the merits of using large, population-based databases, as well as using rigorous Geographic Information System techniques, for the assessment of ecologic environmental risks. The results also suggest promise for exposure classification that is compatible with the theoretical biological mechanisms posited for electromagnetic fields.

Accuracy of industry and occupation on death certificates of electric utility workers: implications for epidemiologic studies of magnetic fields and cancer.

A substantial epidemiologic literature has relied on occupation and industry information from death certificates to make inferences about the association of electric and magnetic field exposure with cancer, but the validity of the occupational data on death certificates is questionable. We compared occupation and industry information from death certificates to company work histories for 793 electric utility workers who died from brain cancer (n=143), leukemia (n=156), lung cancer (n=246, randomly sampled), and non-cancer causes (n=248, randomly sampled). Nearly 75% of death certificates correctly indicated utility industry employment and of those, 48% matched the longest held occupation derived from company work histories. Hence, only 36% matched on both industry and occupation. We computed odds ratios relating occupations involving magnetic field exposure to brain cancer and leukemia both for the occupation listed on the death certificate and for the longest-held occupation based on company records in order to examine the impact of exposure misclassification based on reliance on the death certificate information. For brain cancer, the odds ratio was 1.2 based on death certificates and 1.7 based on company work history, suggesting some attenuation due to misclassification. For leukemia, death certificate information yielded an odds ratio of 0.9, whereas company work histories yielded an odds ratio of 1.3. Although work histories are limited to the period of employment in a specific company, these data suggest that there is substantial misclassification in use of death certificate information on industry and occupation of utility workers, as found in other industries. The limited quality of occupation and industry information on death certificates argues against relying on such information to evaluate modest associations with mortality.

Review of epidemiologic evidence on benzene and lymphatic and hematopoietic cancers.

Exposure to benzene is generally accepted as a cause of acute myeloid leukemia (AML), but the association with other cell types of leukemia and other lymphatic and hematopoietic cancers is controversial. We compiled epidemiologic research on benzene and lymphatic and hematopoietic cancers in order to assess the pattern of associations. Eighteen relevant community-based and 16 industry-based studies were located. Four of seven studies of lymphatic and hematopoietic cancer in the aggregate identified relative risks of 1.8 or more, and eight of 14 total leukemia studies yielded relative risks in that range. The few available studies of specific histologic types of leukemia do not indicate larger or more consistent elevations in risk for AML compared to other leukemia cell types. Sporadic reports have linked benzene to non-Hodgkin's lymphoma and multiple myeloma, but most studies do not indicate a positive association. Limitations in study quality, particularly exposure assessment, pervade all of the studies reviewed, and the distinction between studies addressing benzene and those addressing jobs in industries that use benzene is somewhat arbitrary. Nonetheless, the epidemiologic evidence linking benzene to leukemia in the aggregate, as well as for subtypes other than AML, is no less persuasive than that for AML alone.

Drinking water and pregnancy outcome in central North Carolina: source, amount, and trihalomethane levels.

In spite of the recognition of potentially toxic chemicals in chlorinated drinking water, few studies have evaluated reproductive health consequences of such exposure. Using data from a case-control study of miscarriage, preterm delivery, and low birth weight in central North Carolina, we evaluated risk associated with water source, amount, and trihalomethane (THM) concentration. Water source was not related to any of those pregnancy outcomes, but an increasing amount of ingested water was associated with decreased risks of all three outcomes (odds ratios around 1.5 for 0 glasses per day relative to 1-3 glasses per day, falling to 0.8 for 4+ glasses per day). THM concentration and dose (concentration x amount) were not related to pregnancy outcome, with the possible exception of an increased risk of miscarriage in the highest sextile of THM concentration (adjusted odds ratio = 2.8, 95% confidence interval = 1.1-2.7), which was not part of an overall dose-response gradient. These data do not indicate a strong association between chlorination by-products and adverse pregnancy outcome, but given the limited quality of our exposure assessment and the increased miscarriage risk in the highest exposure group, more refined evaluation is warranted.

Occupation and cervical cancer.

Data collected for a multicenter case-control study of invasive cervical cancer and carcinoma in situ of the cervix were analyzed with regard to occupation. Odds ratios comparing 481 invasive cases and 293 carcinoma in situ cases to 801 controls were calculated and adjusted for potential confounding factors. Working women and homemakers had a similar risk of invasive cervical cancer, with several groups of service and industrial workers showing elevated risks (particularly maids, cleaners, and cooks). Risk of carcinoma in situ was slightly increased for working women, but no occupational groups had notable associations. The principal strengths of this analysis were the ability to address both invasive cervical cancer and carcinoma in situ and to control for multiple potential confounding factors. However, occupational information was limited and risk estimates for women in specific occupations were imprecise.

Prenatal lead exposure in relation to gestational age and birth weight: a review of epidemiologic studies.

Although the adverse effect on pregnancy outcomes at high levels of lead exposure in the workplace has been recognized for years, there is uncertainty regarding the impact of exposure at the lower community exposure levels commonly encountered today. This review summarizes the epidemiologic literature and discusses pertinent methodologic issues and possible sources of interstudy variation. The authors conclude that prenatal lead exposure is unlikely to increase the risk of premature membrane rupture but does appear to increase the risk of preterm delivery. Whether prenatal lead exposure decreases gestational age in terms of infants is unclear. Prenatal lead exposure also appears to be associated with reduced birth weight, but results vary in relation to study design and degree of control for confounding. Adjustment for gestational age, a possible confounder of the birth weight-lead exposure association, did not yield clearer results.

Simplified method for determination of total dietary fiber in foods.

A simplified method, based on the same principles as the AOAC enzymatic-gravimetric method for determining total dietary fiber (TDF) (43.A14-43.A20), has been tested on 12 food samples which had been used in other collaborative studies. TDF values obtained in our laboratory for these 2 methods were in good agreement (y = 0.96x + 0.39; r = 0.999). The simplified method uses a single incubation period and only 1 enzyme (amyloglucosidase), and thus yields smaller blank and ash corrections but a higher protein correction.