Adjusted for age and sex, the estimated risk of NHL in “petrochemical workers” (“chemical workers” were reported on separately) was somewhat increased (RR 1.83, 95% CI 0.87–3.84).

Blair et al. (1993) assembled white, male NHL cases diagnosed in 1980–1983 from the Iowa State Health Registry and from a surveillance network of hospitals in Minnesota. They interviewed 622 of them (or next of kin of 13% who were deceased) and 820 population controls (or next of kin) who were free of lymphohematopoietic cancer and matched by state, age, and year of death. With adjustment for age, state, smoking, family history of lymphoproliferative diseases, exposure to agricultural pesticides, hair-dye use, and response by next of kin, the risk associated with having worked in the petroleum-refining industry for at least 1 year was questionable (SIR 1.6, 95% CI 0.5–5.8).

Combustion Products

Table 4.41 presents the most relevant findings considered by the committee in drawing its conclusion on the possibility of an association between exposure to combustion products and NHL, presented in reverse chronologic order within type of study design.

Cohort Study

Boffetta et al. (1988) tracked the vital status of participants in the ACS II prospective cohort 2 years after enrollment, when detailed information that included a detailed occupational history had been gathered. With adjustment for age, smoking, and other occupational exposure, lymphomas considered together (ICD-9 200–202) showed no increase in risk (RR 0.92) associated with self-reported exposure to diesel-engine exhaust in men 40–79 years old at the time of enrollment.

Case-Control Studies

An early occupational case-control study was constructed by reviewing medical records of patients in 1956–1965 at Roswell Park Memorial Institute (Decoufle and Stanislawczyk 1977; Viadana et al. 1976). When all lymphomas were considered together, locomotive engineer or fireman was the only exhaust-related occupation that showed an intensified (but still imprecise) risk when limited to those with at least 5 years of exposure (RR 2.13).

The Montreal multicancer case-control study’s analysis of 206 men who had NHL showed only a modest increased risk posed by exposure to jet-fuel exhaust (OR 1.7, 95% CI 0.5–5.2) on the basis of four exposed cases (Siemiatycki et al. 1988).

The case-control study of NHL in Iowa and Minnesota (Blair et al. 1993) focused on agricultural exposure, but it also reported on some exposures related to combustion products derived by application of a JEM to each subject’s work history. The risk estimates for NHL associated with exposure to gasoline or diesel exhaust, to asphalt or creosote, or to oils or greases showed little deviation from unity; for each of these, the risk was slightly greater for high-intensity exposure.

Using the NECSS, Mao et al. (2000) identified histologically confirmed cases of NHL diagnosed in eight Canadian provinces in 1994–1997. Completed mailed questionnaires were received from 764 male cases, 705 female cases, and 5,073 cancer-free population controls that were frequency-matched for age and sex. The analyses of the self-reported exposures were adjusted for age, province, and BMI. Both the men (OR 1.2, 95% CI 0.9–1.5) and the women (OR 1.3, 95% CI 0.7–2.3) had somewhat increased estimated risks of NHL in association with

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