Occupational cancer epidemiology in the coming decades

Occupational studies have identified many of the established chemical carcinogens. Studies in the next millennium will be needed to identify the hazardous agents in occupations known to have high cancer rates, to assess human risks from animal carcinogens that have not been well evaluated epidemiologically, to provide information on women and minorities, to evaluate interactions with genetic factors and other risk factors, to contribute to our understanding of risks from the spread of chemicals from the workplace to the general environment, and to identify mechanisms of cancer. The traditional retrospective cohort design will be insufficient to meet these needs. Population-based case-control, nested case-control, prospective cohorts, and cross-sectional designs will assume more important roles because of the need to collect information on nonoccupational risk factors and biological tissues. Improvement in the assessment of quantitative exposures is needed for the efficient evaluation of interactions between occupational exposures, genetic factors, and nonoccupational exposures.

Oxidized low density lipoprotein displaces endothelial nitric-oxide synthase (eNOS) from plasmalemmal caveolae and impairs eNOS activation

Hypercholesterolemia-induced vascular disease and atherosclerosis are characterized by a decrease in the bioavailability of endothelium-derived nitric oxide. Endothelial nitric-oxide synthase (eNOS) associates with caveolae and is directly regulated by the caveola protein, caveolin. In the present study, we examined the effects of oxidized low density lipoprotein (oxLDL) on the subcellular location of eNOS, on eNOS activation, and on caveola cholesterol in endothelial cells. We found that treatment with 10 microgram/ml oxLDL for 60 min caused greater than 90% of eNOS and caveolin to leave caveolae. Treatment with oxLDL also inhibited acetylcholine-induced activation of eNOS but not prostacyclin production. oxLDL did not affect total cellular eNOS abundance. Oxidized LDL also did not affect the palmitoylation, myristoylation or phosphorylation of eNOS. Oxidized LDL, but not native LDL, or HDL depleted caveolae of cholesterol by serving as an acceptor for cholesterol. Cyclodextrin also depleted caveolae of cholesterol and caused eNOS and caveolin to translocate from caveolae. Furthermore, removal of oxLDL allowed eNOS and caveolin to return to caveolae. We conclude that oxLDL-induced depletion of caveola cholesterol causes eNOS to leave caveolae and inhibits acetylcholine-induced activation of the enzyme. This process may be an important mechanism in the early pathogenesis of atherosclerosis.

Quality control (Part 2). Communication: implementation of the Resident Assessment Instrument (RAI): the benefits of a structured communication plan

Following a government mandate to use the assessment portion of the Resident Assessment Instrument, S&WCHSC began to integrate the RAI into the care of its Aging Program residents. S&WCHSC have used this as an opportunity to provide a structure for assessment and care planning within the existing philosophy of Patient Focused Care. Implementation of the RAI required the development and implementation of a Communication Plan. An adaptation of a framework, "Effective Strategic Planning for Communications" provided guidelines for assessment of key stakeholders' communication needs.

The adipose tissue to serum dichlorodiphenyldichloroethane (DDE) ratio: some methodological considerations

Dichlorodiphenyldichloroethane (DDE) adipose tissue level has been regarded as a preferred indicator of accumulated human exposure to DDT; however, blood sera are more feasible to obtain and analyze than adipose tissue samples. Inconsistent and scarce information exists in relation to the adipose tissue/serum DDE ratio. As a part of a hospital-based case-control study performed in Mexico City from 1994 to 1996, 198 paired serum and adipose tissue samples were obtained from 72 women with histologically confirmed breast cancer and 126 women with benign breast disease. Both adipose tissue and serum DDE levels were determined by gas-liquid chromatography and reported as ppb lipid weight (ng/g) as well as wet basis (ng/ml). Results showed that the adipose tissue/serum DDE ratio (ADSE) varies according to the type of information (lipid vs wet basis, arithmetic vs geometric means) used for its estimation. ADSE gets a value near 1 (1.1) only when the geometric DDE levels in lipid basis are used for its estimation. The correlation between DDE serum and adipose tissue levels was found (r=0.364, P<0.001). The ADSE did not vary by disease status, nor was it altered by parity, history of breast-feeding, and other reproductive characteristics. We endorse the use of venipuncture instead of biopsy as a way to estimate DDT body burden levels in further research.

Occupational cancer among women: research status and methodologic considerations

Occupational causes of cancer have not been well-evaluated among women. An increase in the number of women in the work force in jobs with potentially hazardous exposures during the past few decades raises the question as to whether there is a need to enhance our efforts in this area. The inability to evaluate occupational causes of female gynecologic tumors in studies of men, plus the potential for variation in outcome responses between men and women because of gender-based exposure and susceptibility differences, underscore the need for investigations specifically focused on women. Investigations of occupational exposures and cancer risk among women may require design considerations that differ somewhat from studies of men. Issues to consider include the impact of studying outcomes with high survival (e.g., breast cancer), gender-specific exposure patterns and toxicokinetic processing of some chemicals, special limitations in the use of the general population as the referent, and the need to control for established risk factors for gynecologic tumors.

Expression of HOX genes, HOX cofactors, and MLL in phenotypically and functionally defined subpopulations of leukemic and normal human hematopoietic cells

To explore the possibility that deregulated HOX gene expression might commonly occur during leukemic hematopoiesis, we compared the relative levels of expression of these and related genes in phenotypically and functionally defined subpopulations of AML blasts and normal hematopoietic cells. Initially, a semi-quantitative RT-PCR technique was used to amplify total cDNA from total leukemic blast cell populations from 20 AML patients and light density cells from four normal bone marrows. Expression of HOX genes (A9, A10, B3 and B4), MEIS1 and MLL was easily detected in the majority of AML samples with the exception of two samples from patients with AML subtype M3 (which expressed only MLL). Low levels of HOXA9 and A10 but not B3 or B4 were seen in normal marrow while MLL was easily detected. PBX1a was difficult to detect in any AML sample but was seen in three of four normal marrows. Cells from nine AML patients and five normal bone marrows were FACS-sorted into CD34+CD38-, CD34+CD38+ and CD34-subpopulations, analyzed for their functional properties in long-term culture (LTC) and colony assays, and for gene expression using RT-PCR. 93 +/- 14% of AML LTC-initiating cells, 92 +/- 14% AML colony-forming cells, and >99% of normal LTC-IC and CFC were CD34+. The relative level of expression of the four HOX genes in amplified cDNA from CD34- as compared to CD34+CD38- normal cells was reduced >10-fold. However, in AML samples this down-regulation in HOX expression in CD34- as compared to CD34+CD38- cells was not seen (P < 0.05 for comparison between AML and normal). A similar difference between normal and AML subpopulations was seen when the relative levels of expression of MEIS1, and to a lesser extent MLL, were compared in CD34+ and CD34- cells (P < 0.05). In contrast, while some evidence of down-regulation of PBX1a was found in comparing CD34- to CD34+ normal cells it was difficult to detect expression of this gene in any subpopulation from most AML samples. Thus, the down-regulation of HOX, MEIS1 and to some extent MLL which occurs with normal hematopoietic differentiation is not seen in AML cells with similar functional and phenotypic properties.

Occupational physical activity and non-Hodgkin's lymphoma

PURPOSE

The purpose of this study was to evaluate the role of physical activity in the development of non-Hodgkin's lymphoma (NHL).

METHODS

Incident NHL cases and population-based controls were identified from three case-control studies conducted in four midwestern states: Iowa, Kansas, Minnesota, and Nebraska. A total of 1177 cases (993 men, 184 women) and 3625 controls (2918 men, 707 women) were interviewed. Usual occupation (all states) and lifetime occupational histories (Iowa and Minnesota only), obtained from interviews, were classified for energy expenditure (EE) and sitting time. Odds ratios (OR) and 95% confidence intervals were calculated comparing moderate and high activity levels with sedentary levels.

RESULTS

There was no evidence of an association between NHL and occupational physical activity measured either by EE or sitting time. Among men, the OR associated with usual occupation moderate and high EE were 1.1 and 1.0, respectively. For sitting time, the OR were also 1.1 and 1.0 for moderate and high activity, respectively. Among women, slight nonsignificant elevations in risk of NHL were observed among the high energy level and high activity sitting categories. The trends were not significant. There was no evidence of confounding or effect modification by vital status, hair dye use, or solvent exposure. Among subjects with lifetime occupational histories, there were no significant increases or trends for cumulative or average EE or sitting time. There was no association between occupational physical activity and NHL.

CONCLUSION

Research on nonoccupational physical activity, which in the U.S. is likely the more important component of daily activity than occupational activity, may still be warranted given the laboratory evidence linking physical activity and immune function, an important factor in the etiology of NHL.

Exposure received from application of animal insecticides

Part of an investigation of data collection methods in epidemiologic studies of farmers evaluated exposures received by farmers from the application of insecticides to animals. Twenty farmers were monitored during a normal application using a fluorescent dye surrogate for the active ingredient (AI). Two exposure measures were estimated, AI concentration and the time-weighted average for the application period (TWAa). Four application methods were used: high- (n = 5) and low-pressure (n = 3) spraying, backpack (n = 2) and pour-on (n = 10). The two farmers using a backpack sprayer had nondetectable levels of dye. Only two of the farmers using the pour-on method had detectable dye levels, but these levels were high. All of the low- and high-pressure sprayers had detectable amounts of dye. Multiple layers of clothing, gloves, and boots (n = 10) were associated with a low mean AI concentration for the exposed farmers (18 micrograms) and more than two-thirds of the farmers wearing this amount of clothing had nondetectable exposures. In contrast, clothing providing little or no protection was associated with a significantly higher (p < 0.01) average AI concentration (4420 micrograms), and less than a third of the farmers with this degree of protection had nondetectable exposures. Poor work practices (leaking equipment, contact with wet animals or fences, and back splash) were associated with statistically higher exposure levels (p < 0.01) than the absence of such practices. There was a moderate statistically significant association between AI concentration and TWAa with total volume of the AI/dye/water mixture using the Spearman coefficient. Time was significantly inversely proportional to the two exposure measures. The association between the two exposure measures and AI volume was not significant.

Characteristics of pesticide use in a pesticide applicator cohort: the Agricultural Health Study

Data on recent and historic pesticide use, pesticide application methods, and farm characteristics were collected from 35,879 restricted-use pesticide applicators in the first 2 years of the Agricultural Health Study, a prospective study of a large cohort of private and commercial licensed pesticide applicators that is being conducted in Iowa and North Carolina. (In Iowa, applicators are actually "certified," while in North Carolina they are "licensed"; for ease of reference the term license will be used for both states in this paper.) Commercial applicators (studied in Iowa only) apply pesticides more days per year than private applicators in either state. When the types of pesticides being used by different groups are compared using the Spearman coefficient of determination (r2), we find that Iowa private and Iowa commercial applicators tend to use the same type of pesticides (r2=0.88). White and nonwhite private applicators tended to use the same type of pesticides (North Carolina r2=0.89), as did male and female private applicators (Iowa r2=0.85 and North Carolina r2=0.84). There was less similarity (r2=0. 50) between the types of pesticides being used by Iowa and North Carolina private applicators. A greater portion of Iowa private applicators use personal protective equipment than do North Carolina private applicators, and pesticide application methods varied by state. This heterogeneity in potential exposures to pesticides between states should be useful for subsequent epidemiologic analyses using internal comparison groups.

Risk of premenopausal breast cancer and patterns of established breast cancer risk factors among teachers and nurses

BACKGROUND

Contrasting results have been published regarding the risk of breast cancer among teachers and nurses. Confounding by reproductive factors may explain the increased risk observed among women in these occupations as information on those factors were not available in most studies.

METHODS

We examined the risk of premenopausal breast cancer among teachers and nurses using occupational histories in a case-control study where information on established risk factors was available.

RESULTS

Having ever held a teaching job was not related to breast cancer (OR = 0.74, 95% CI = 0.44-1.28) and women who worked for 10 years or less in this occupation had a non-significant deficit of risk (OR = 0.52, 95% CI = 0.27-1.02). No elevation in risk was found in association with having ever been a nurse (OR = 0.85, 95% CI = 0.45-1.61) or with duration of nursing. Although direct comparison of established risk factors among teachers and nurses and other women in the study showed some evidence of differential distribution, especially when comparing teachers to other women, adjustment for reproductive variables and other breast cancer risk factors did not change the results of this study.

CONCLUSION

These findings suggest that teachers and nurses are not at an increased risk of breast cancer. This study also suggests that established risk factors for premenopausal breast cancer may not explain the elevation of risk found in other studies of teachers and nurses. However, this conclusion is limited by the fact that in the present study teachers and nurses had lower than expected breast cancer risk with or without adjustment for established risk factors. Limitations of this study such as low response rates and limited statistical power should be considered in the interpretation of these findings.

Characteristics of persons who self-reported a high pesticide exposure event in the Agricultural Health Study

Characteristics of persons who report high pesticide exposure events (HPEE) were studied in a large cohort of licensed pesticide applicators from Iowa and North Carolina who enrolled in the Agricultural Health Study between December 1993 and December 1995. Fourteen percent reported having "an incident or experience while using any pesticide which caused an unusually high personal exposure. " After taking into account total number of applications made and education, females (OR=0.76), applicators from NC (OR=0.65), and privately licensed applicators (OR=0.65) were less likely to have reported an HPEE. Work practices more common among both private and commercial applicators with an HPEE included delay in changing clothing or washing after pesticide application, mixing pesticide application clothing with the family wash, washing up inside the house after application, applying pesticides within 50 yards of their well, and storing pesticides in the home. Job characteristics more common among those with an HPEE included self-repair of application equipment and first pesticide use more than 10 years in the past. These job characteristics explained much of the difference in reported HPEE between males and females, but not between IA and NC subjects or between commercial or private applicators.

Exposure of farmers to phosmet, a swine insecticide

OBJECTIVES

The goal of this study was to measure dermal and inhalation exposures to phosmet during application to animals and to identify what determinants of exposure influence the exposure levels.

METHODS

Ten farmers were monitored using dermal patches, gloves, and air sampling media during normal activities of applying phosmet to pigs for insect control. Exposures were measured on the clothing (outer), under the clothing (inner), on the hands, and in the air. Possible exposure determinants were identified, and a questionnaire on work practices was administered.

RESULTS

The geometric mean of the outer exposure measurements was 79 microg/h, whereas the geometric mean of the inner exposure measurements was 6 microg/h. The geometric mean for hand exposure was 534 microg/h, and the mean air concentration was 0.2 microg/m3. Glove use was associated with the hand and total dermal exposure levels, but no other determinant was associated with any of the exposure measures. The average penetration through the clothing was 54%, which dropped to 8% when the farmers wearing short sleeves were excluded. The farmers reported an average of 40 hours a year performing insecticide-related tasks.

CONCLUSIONS

Farmers who applied phosmet to animals had measurable exposures, but the levels were lower than what has been seen in other pesticide applications. Inhalation exposures were insignificant when compared with dermal exposures, which came primarily from the hands. Clothing, particularly gloves, provided substantial protection from exposures. No other exposure determinant was identified.

Occupation and pancreatic cancer risk in Shanghai, China

BACKGROUND

Any association between occupation and pancreatic cancer risk has not been conclusively demonstrated. A population-based case-control study was conducted to examine occupational risks of pancreatic cancer in Shanghai, China.

METHODS

The study included 451 pancreatic cancer patients newly diagnosed in 1990-1993 and 1,552 controls randomly selected from Shanghai residents. Information on a lifetime job history and other factors was obtained in a face-to-face interview.

RESULTS

Among men, an increased risk of pancreatic cancer was associated with employment as an electrician (OR = 7.5, CI = 2.6-21.8), and a positive trend in risk with increasing duration of employment was apparent (P for trend = 0.0003). Exposure to electric magnetic fields (EMF) as measured by a job exposure matrix also was associated with an increased risk among electricians. Threefold risks were observed for men with the highest level of intensity and for those with the highest probability of EMF exposure, although women with heavy EMF exposure did not experience increased risk. Among men, elevated risks also were found for metal workers (OR = 2.1, CI = 1.0-4.8); toolmakers (OR = 3.4, CI = 14-7.1); plumbers and welders (OR = 3.0, CI = 1.2-7.5); and glass manufacturers, potters, painters, and construction workers (OR = 2.6, CI = 1.1-6.3). Among women, textile workers experienced an increased risk (OR = 1.4, CI = 0.8-2.6).

CONCLUSIONS

Our results suggest that occupations associated with exposures to metal and textile dusts or certain chemicals may increase the risk of pancreatic cancer. The elevated risk among electricians may warrant further study to evaluate the possible role of EMF or other exposures.

Most acute myeloid leukemia progenitor cells with long-term proliferative ability in vitro and in vivo have the phenotype CD34(+)/CD71(-)/HLA-DR-

Acute myeloid leukemia (AML) occurs as the result of malignant transformation in a hematopoietic progenitor cell, which proliferates to form an accumulation of AML blasts. Only a minority of these AML cells are capable of proliferation in vitro, suggesting that AML cells may be organized in a hierarchy, with only the most primitive of these cells capable of maintaining the leukemic clone. To further investigate this hypothesis, we have evaluated a strategy for purifying these primitive cells based on surface antigen expression. As an in vitro endpoint, we have determined the phenotype of AML progenitor cells which are capable of producing AML colony-forming cells (CFU) for up to 8 weeks in suspension culture (SC) and compared the phenotype with that of cells which reproduce AML in nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice. AML cells were fluorescence-activated cell sorted (FACS) for coexpression of CD34 and CD71, CD38, and/or HLA-DR and the subfractions were assayed in vitro and in vivo at various cell doses to estimate purification. While the majority of primary AML CFU lacked expression of CD34, most cells capable of producing CFU after 2 to 8 weeks in SC were CD34(+)/CD71(-). HLA-DR expression was heterogeneous on cells producing CFU after 2 to 4 weeks. However, after 6 to 8 weeks in SC, the majority of CFU were derived from CD34(+)/HLA-DR- cells. Similarly, the majority of cells capable of long-term CFU production from SC were CD34(+)/CD38(-). Most cells that were capable of engrafting NOD/SCID mice were also CD34(+)/CD71(-) and CD34(+)/HLA-DR-. Engraftment was not achieved with CD34(+)/CD71(+) or HLA-DR+ subfractions, however, in two patients, both the CD34(+) and CD34(-) subfractions were capable of engrafting the NOD/SCID mice. A three-color sorting strategy combining these antigens allowed approximately a 2-log purification of these NOD/SCID leukemia initiating cells, with engraftment achieved using as few as 400 cells in one experiment. Phenotyping studies suggest even higher purification could be achieved by combining lack of CD38 expression with the CD34(+)/CD71(-) or CD34(+)/HLA DR- phenotype. These results suggest that most AML cells capable of long-term proliferation in vitro and in vivo share the CD34(+)/CD71(-)/HLA-DR- phenotype with normal stem cells. Our data suggests that in this group of patients the leukemic transformation has occurred in a primitive progenitor, as defined by phenotype, with some degree of subsequent differentiation as defined by functional assays.

Use of a life events calendar approach to elicit occupational history from farmers

BACKGROUND

Precise and valid exposure assessment is generally the primary challenge in retrospective occupational epidemiology studies, particularly when the only available method for exposure characterization is a personal interview. Agricultural workers may represent a particular challenge; for example, whereas many farmers have worked from childhood at the same location, raising the same crops and animals, they may have used different equipment, chemicals, and protective gear over time. One method to assist in recall is the "life events calendar," a cognitive tool based on the subject's own life history to help anchor occupational activities in time.

METHODS

Unstructured interviews of farmers, focus groups, and pilot interviews among rural men, primarily African-Americans, were conducted to create a questionnaire for obtaining farm history information within the context of personal life events.

RESULTS

Farmers used both personal events and national events (as well as events relating directly to farming) to recall their activities. These subjects had extensive history of farming (10-75 years) and chemical use (median lifetime chemicals = 13).

CONCLUSION

The life events calendar provided a useful tool to facilitate the recall of a lifetime of agricultural activity. Life events calendars are useful additions to the tools available for retrospective occupational exposure assessment.

Risk for prostate cancer by occupation and industry: a 24-state death certificate study

Current knowledge of the etiology of prostate cancer is limited. Numerous studies have suggested that certain occupations and industries may be associated with the occurrence of prostate cancer. Information on occupation and industry on death certificates from 24 states gathered from 1984 to 1993 was used in case control study on prostate cancer. A total of 60,878 men with prostate cancer as underlying cause of death was selected and matched with controls who died of all other causes except cancer. Similar to the findings of our parallel large case control study of prostate cancer, we observed excess risks in some white-collar occupations, such as administrators, managers, teachers, engineers, and sales occupations. However, some blue-collar occupations, such as power plant operators and stationary engineers, brickmasons, machinery maintenance workers, airplane pilots, longshoreman, railroad industry workers, and other occupations with potential exposure to PAH also showed risk of excess prostate cancer. Risk was significantly decreased for blue-collar occupations, including farm workers, commercial fishermen, mechanics and repairers, structural metal workers, mining, printing, winding, dry cleaning, textile machine operators, cooks, bakers, and bartenders. Although we observed excess risks of prostate cancer among some low socioeconomic status (SES) occupations, the overall results suggest that the effects of higher SES cannot be ruled out in associations between occupational factors and the risk of prostate cancer.

The proliferative status of haematopoietic progenitor cells in the developing murine liver and adult bone marrow

A class of primitive progenitor cells with high proliferative potential in vitro (HPP-CFC), has been identified in fetal liver and adult bone marrow both in murine and human systems. The kinetic properties of HPP-CFC2 and the more mature granulocyte-macrophage colony forming units (CFU-GM) derived from murine fetal liver on d13, d15 and d19 of gestation, newborn liver and neonatal liver on d3 and d8 postpartum have been evaluated and compared with the kinetic properties of these progenitor cell populations derived from adult bone marrow. The frequency of HPP-CFC2 in fetal liver was found to be greatest on d15 of gestation then subsequently declined in newborn and neonatal liver. Similarly, the highest proportion of HPP-CFC2 engaged in DNA synthesis (53+/-3%) was detected in d15 fetal liver. This proportion decreased to 13+/-2% in the liver 1 wk after birth, which is comparable to the number of HPP-CFC2 derived from adult BM which were in S-phase (10+/-1%). Production of CFU-GM was found to be greater in adult bone marrow than in either fetal or newborn liver. While the proportion of CFU-GM in S-phase was high all 3 tissue samples, the greatest proportion of cycling CFU-GM (50+/-2%) was detected in d15 fetal liver. These results suggest that HPP-CFC2 derived from fetal liver are actively cycling while HPP-CFC2 derived from adult bone marrow are relatively quiescent. In contrast, a high proportion of CFU-GM derived from fetal, newborn liver and adult bone marrow are engaged in DNA synthesis.

Mortality of industrial workers exposed to acrylonitrile

OBJECTIVES

This study was designed to evaluate the relationship between occupational exposure to acrylonitrile and cancer mortality.

MATERIALS AND METHODS

Workers (18079 white men, 4293 white women, 2191 nonwhite men, and 897 nonwhite women) employed in acrylonitrile production or use in the 1950s through 1983 were followed through 1989 for vital status and cause of death. Exposure-response relationships were evaluated from quantitative estimates of historical exposures. Tobacco use was determined for a sample of workers to assess potential confounding. Mortality rates between the exposed and unexposed workers in the cohort were compared using the Poisson regression.

RESULTS

Analyses by cumulative, average, peak, intensity, duration, and lagged exposure revealed no elevated risk of cancers of the stomach, brain, breast, prostate or lymphatic and hematopoietic systems. Mortality from lung cancer was elevated for the highest quintile of cumulative exposure. When the decile categories were used, the relative risk did not continue to increase at higher levels. Adjustment for cigarette use reduced the risk for lung cancer only slightly. Separate analyses for wage and salaried workers, long-term and short-term workers, fiber and nonfiber plants, and individual plants revealed no clear exposure-response patterns.

CONCLUSIONS

The results indicate that exposure to acrylonitrile at the levels studied is not associated with an increased relative risk for most cancers of a priori interest. The excess of lung cancer in the highest quintile of cumulative exposure may indicate carcinogenic activity at the highest levels of exposure, but analyses of exposure-response do not provide strong or consistent evidence for a causal association.

Exposure assessment for a study of workers exposed to acrylonitrile

Procedures used to develop estimates of exposure to acrylonitrile for a cohort study (>25000 workers in 8 monomer, fiber, and resin companies from 1952 to 1983) are presented. Visits to the companies were made, interviews of workers were conducted, historical records were made, and measurements were taken. On the basis of similar tasks, locations, other exposures, and a similar distribution of exposures to acrylonitrile, 3600 exposure groups were formed. Special procedures were used to reduce the misclassification of workers performing tasks that varied in time but that were inadequately reflected in the job title. A software program organized and retained all exposure information on each exposure group. Quantitative estimates of acrylonitrile exposure were developed using a hierarchical approach in a software program that documented the derivation of each estimate and facilitated data review. Two of the estimation methods were evaluated in a comparison with measurement data.

Agricultural use of DDT and risk of non-Hodgkin's lymphoma: pooled analysis of three case-control studies in the United States

OBJECTIVES

The objective of this pooled analysis was to examine whether exposure to DDT was associated with the risk of non-Hodgkin's lymphoma among male farmers.

METHODS

Data from three case-control studies from four midwestern states in the United States (Nebraska, Iowa, Minnesota, Kansas) were pooled to carry out analyses of 993 cases and 2918 controls. Information on use of agricultural pesticides and other risk factors was based on interviews. Non-farmers (people who had never lived or worked on a farm) were used as a reference category.

RESULTS

There were 161 cases and 340 controls who reported use of DDT on animals or crops, or on both, yielding an odds ratio (OR) of 1.2 (95% confidence intervals (95% CI) 1.0 to 1.6). Farmers who had used DDT for > or = 15 years had an OR of 1.5 (95% CI 1.0 to 2.3). Adjustment for respondent status and use of other pesticides resulted in slightly reduced ORs. Analyses by the number of days of use a year was limited to the Nebraska data. The most notable increase was found among farmers who used DDT for > or = 5 days a year (OR 2.6, 95% CI 1.1 to 5.9); however, additional adjustment for use of organophosphates, phenoxyacetic acids, and the individual pesticides lindane, malathion, and atrazine reduced the ORs to 1.0, 0.9, 1.1, 1.6, and 1.9 respectively.

CONCLUSIONS

No strong consistent evidence was found for an association between exposure to DDT and risk of non-Hodgkin's lymphoma. It seems that the excess risk initially found may be explained by use of other pesticides.

Factors associated with self-reported, pesticide-related visits to health care providers in the agricultural health study

To investigate factors associated with pesticide-related visits to health care providers (i.e., doctor or hospital visits), responses to self-administered questionnaires received from 35,879 licensed restricted-use pesticide applicators participating in the Agricultural Health Study were analyzed. (In Iowa, applicators are actually certified, whereas in North Carolina they are licensed; for ease of reference, the term license will be used for both states in this paper.) The cohort reported a total of more than 10.9 million pesticide-application days. These applications were associated with one or more pesticide-related health care visits by 2,214 applicators (7.0% of the applicator cohort for whom health care visit data were available). The odds of a pesticide-related health care visit were increased for commercial applicators compared to private applicators [odds ratio (OR = 1.77; 95% confidence interval (CI), 1.52-2.06) and for applicators who used insecticides 70 times or more in their lifetime compared to those who used insecticides less frequently (OR = 1.43; CI, 1.26-1.63). After adjusting for the number of applications in a logistic regression model, significantly higher odds of health care visits were observed among North Carolina applicators compared to Iowa applicators (OR = 1.35; CI, 1.17-1.52), among applicators who mixed their own pesticides (OR = 1.65; CI, 1. 22-2.23), and among applicators who personally repaired their pesticide application equipment at least once per year (OR = 1.12; CI, 1.06-1.25). Significantly lower odds were found among female versus male applicators (OR = 0.68; CI, 0.46-0.99) and among applicators who graduated from high school versus those who did not (OR = 0.82; CI, 0.71-0.94 for high school graduates and OR = 0.79; CI, 0.68-0.91 for those with at least some college). Several methods of pesticide application to crops, seed, or stored grain were also associated with significantly elevated odds ratios of health care visits. These observations suggest that several steps can be taken to reduce the number of health care visits resulting from occupational exposure to pesticides. The implications of this pattern of pesticide-related health care visits may have etiologic implications for cancer and other chronic diseases.

The impact of initial job assignment on formaldehyde exposure among African-American and white formaldehyde industry workers

We compared initial job assignments of African-American and white employees at eight worksites that used formaldehyde between 1940 and 1979. Unexposed workers were excluded. Median, ambient air formaldehyde, 8-hour, time-weighted average (TWA8) exposure estimates were determined for each worksite. Job assignments with TWAs above the worksite's median TWA8 were called high formaldehyde exposed (HFE). Job assignments with TWAs less than or equal to the worksite's median TWA8 for the same period were called lower formaldehyde exposed (LFE). Two worksites assigned black workers to HFE jobs in significantly higher proportions than white workers in some decades. One worksite assigned white workers in significantly higher proportions than black workers to HFE jobs in some decades. One worksite assigned racial groups in nearly equal proportions from 1940 to 1969. The remaining sites showed insignificant assignment disproportions (alpha = 0.05; Chi-square < or = 3.841, 1 degree of freedom) for any period. No major trend was apparent across all plants and decades.

Parental occupational exposures and risk of childhood cancer

Occupational exposures of parents might be related to cancer in their offspring. Forty-eight published studies on this topic have reported relative risks for over 1000 specific occupation/cancer combinations. Virtually all of the studies employed the case-control design. Occupations and exposures of fathers were investigated much more frequently than those of the mother. Information about parental occupations was derived through interviews or from birth certificates and other administrative records. Specific exposures were typically estimated by industrial hygienists or were self-reported. The studies have several limitations related to the quality of the exposure assessment, small numbers of exposed cases, multiple comparisons, and possible bias toward the reporting of positive results. Despite these limitations, they provide evidence that certain parental exposures may be harmful to children and deserve further study. The strongest evidence is for childhood leukemia and paternal exposure to solvents, paints, and employment in motor vehicle-related occupations; and childhood nervous system cancers and paternal exposure to paints. To more clearly evaluate the importance of these and other exposures in future investigations, we need improvements in four areas: a) more careful attention must be paid to maternal exposures; b) studies should employ more sophisticated exposure assessment techniques; c) careful attention must be paid to the postulated mechanism, timing, and route of exposure; and d) if postnatal exposures are evaluated, studies should provide evidence that the exposure is actually transferred from the workplace to the child's environment.