Effects of chronic occupational exposure to measured concentrations of benzene.

All ten employees have a history of exposure to benzene which exceeded a 25 ppm, eight-hour TWA for several years. For five of these employees this exposure level started over 20 years ago. One employee's high exposure level started over 35 years ago. All ten employees had their initial high exposure to benzene more than 16 years ago. At one period (late 1963 and early 1964) all ten employees had alterations in their peripheral blood studies, evidenced by an increase in MCV. Some of the employees had slight reduction of hemoglobin levels. No other significant blood or bone marrow abnormalities were evident. A mortality study, for the years 1940 to 1973, of 594 employees chronically exposed to benzene at the Midland, Mich., Dow location has recently been accepted for publication. This study was followed by a morbidity study of 282 employees, which were a subset of the employees in the mortality study. The morbidity study was based on health data obtained between 1967 and 1974. The ten employees described in this article were included in both the mortality study population of 594 employees and the morbidity study of the 282 employees.