Occupational Exposures

Some of the most intensive epidemiological studies of adult leukemias have focused on specific occupations and occupational exposures. In particular, benzene is considered an established risk factor for adult AML.

Benzene Workers

Since the first case report, benzene has been extensively described as a known leukemogen for AML in several case-control and cohort studies of occupational^ exposed workers in the shoe, rubber, leather, and chemical manufacturing indus-tries.107,108 There is strong evidence of a dose-response effect; workers with higher or longer exposure to benzene are at the highest risk of developing AML.109 In one of the most recent cohort studies of approximately 75,000 Chinese workers exposed to benzene from 1972 through 1987, individuals exposed to average levels less than 10 parts per million had a relative risk (compared to unexposed workers) for AML of 3.2 (95 percent CI = 1.0 to 10.1), whereas workers exposed to levels of 25 ppm or higher had a relative risk of 7.1 (95 percent CI = 2.1 to 23.7).110 Other occupational groups that have had higher rates of AML include painters, petroleum refinery workers, and pressmen, all of which could be related to benzene exposure since it is found in most of the products used by these groups.108 The observed relative risks in these studies range from about a fourfold increased risk to nearly tenfold. It is important to note, however, that these occupational groups likely account for a very small proportion of the adult AML cases. Epidemiologists often use a formula to calculate the population attributable risk to describe the contribution of a particular exposure to the risk of a specific disease.111 This formula is based on estimates of the relative risk associated with the exposure and the proportion of the population likely exposed. Assuming that less than 1 percent of individuals work in occupations that include exposure to benzene,112 and given relative risks of between 4 and 10, the population attributable risk of benzene to leukemia development would be between 3 and 8 percent.

Other Occupations

The risk of leukemia has been explored in other industries that may have potential low-dose benzene and other solvent exposure including diesel exhaust workers, gas station attendants, pilots, dry cleaners, chemists, furniture manufacturers, embalmers, painters, auto manufacturing machinists, auto mechanics, professional drivers, and seamen on tankers.113-122 Although several of these studies found an increased risk of leukemia overall, AML, or AML mortality, others have found no increased risk. It is important to note that many of these studies observed small numbers of leukemia deaths among these workers and compared this number to the number of deaths that would be expected in the general population. In many instances, other factors that may also be associated with an increased risk (i.e., smoking) were not controlled for.

A number of studies have demonstrated positive associations between leukemia and farming, while other studies have found no elevated risk.108 However, an increased risk of leukemia has also been reported with exposure to certain chemicals used in farming including crop and animal insecticides, herbicides, and fertilizers.123-125

Other occupations potentially associated with an increased risk of leukemia include veterinarians and abattoir workers (both of which could be consistent with a viral etiology), nurses, barbers and hairdressers, and firefighters.108,126,127 With the exception of occupational exposure to benzene, however, the majority of these associations have either been observed in only a limited number of studies, or have been inconsistent among studies.

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