| The Paducah Gaseous Diffusion Plant was located in western Kentucky. In response to concern about past and present radiation and chemical exposures, NIOSH funded a collaborative study by the Universities of Louisville, Kentucky, and Cincinnati to conduct an occupational cohort mortality study titled “Health effects of occupational exposures in PGDP workers.” The purpose of the study was to determine if PGDP workers had mortality patterns that differed from the general U.S. population and to investigate if mortality patterns were associated with job title or workplace exposures. |
| A retrospective occupational cohort mortality study was conducted on 6,759 workers. Standardized mortality ratio analyses compared the cohort to the referent U.S. population. Internal comparisons producing standardized rate ratios were conducted by job title, metal exposure, and cumulative internal and external radiation exposures. |
| Demographic (PGDPSA02_d1), work history (PGDPSA02_d4), and vital status (PGDPSA02_d6) data were collected on 6,820 workers. Inclusion criteria required workers to have been employed at the PGDP for at least 30 days from the start of plant operations in September 1952 through the end of study, December 2003. Analyses were conducted using LTAS, which requires three files for each analysis: a person file, an outcome file, and a history file. Separate file sets were prepared for investigation of the cohort by job title, radiation exposure, metals exposure, and TCE exposure; although all analyses used the same outcome file and some used the same person or history file. The data file set used for the job title analysis was also used to characterize the cohort as a whole. LTAS is available from NIOSH at http://cdc.gov/niosh/ltas/. The data file set contains 6 files. |
| Each person file contains 6,820 records and gives gender, race, vital status, birth date, employment start date, and death or end of study date for each employee. In addition, the person file for the metals analysis also includes the category for the highest exposure to five metals during employment (low, medium, or high exposure); the radiation person file also contains variables that indicate the quartile of exposure for external and internal radiation exposure. |
| The history files (PGDPSA02_d3 and PGDPSA02_d5) have 119,474 records and contain multiple records for each employee. Each record represents a time period in the worker’s employment history. Many workers changed job positions during their employment tenure, and therefore their exposures changed. The history files document these changes and exposures, allowing calculation of person years at risk for an exposure. All of the history files contain an ID variable, a begin date for a time period, and the date last observed, which gives the date of death or end of study. The history file used for the general, grouped job title, and radiation analyses contains information on grouped job title held through the use of ever/never variables. For each grouped job title, a variable is created that indicates if an employee ever or never held that position. The history file for the metals analysis contains variables indicating the relative rank of exposure (range 0 to 5) for the metals arsenic, beryllium, chromium, nickel, and uranium. These ranks were determined by limited measurements and interviews with long-time employees and management. The metals history file also contains ever/never variables for each metal for high exposure, which indicates whether an employee has been exposed to a metal with a 4 or 5 rank. |
| The outcome file (PGDPSA02_d2) is the same for all analyses. It contains 1,639 records, one for each deceased employee. It gives the date and cause of death. |
| A total of 1,674 deaths were identified out of 6,820 workers in the cohort. Because of incomplete history and outcome data, 61 workers were eliminated, resulting in analyses on 6,759 workers and 1,638 deaths. |
| Known exposures at the facility included metals (arsenic, beryllium, chromium, nickel, and uranium) and both internal and external radiation exposure. For metals, certain positions in the plant were known to have higher exposures compared with other positions. Because measurements for exposures were inconsistent throughout the plant’s history, a job exposure matrix was developed that ranked exposures based on the position within the plant and the time period worked. These ranks are relative exposure amounts and are based on few measurements. The ranks allowed the comparison of workers who were employed in positions with higher exposures to be compared with workers who held positions thought to have less exposure. The job exposure matrix gave ranks on a scale of 0 (no exposure) to 5 (highest exposure). In the analysis of exposures, these ranks were condensed into low (0-1), medium (2-3), and high (4-5) exposure groups. |
| For internal and external radiation exposure, the ranges of measurements for external radiation exposure and internal radiation exposure were broken into quartiles. Standardized rate ratios were generated, comparing higher quartiles with the lowest exposure quartile. |
