The third study in 1978 was conducted in the four mills visited in the second study. Combining the three studies yields questionnaire data on 444 participants. Analysis of demographic factors and distributions among dust exposure categories (similar to that detailed for the second study) indicated that the participants formed a representative subset of the target population. Eleven of the 444 participants (2.5 percent) reported symptoms defining byssinosis.
Accumulated lung function data showed a significantly larger decline in FEVX and FEF25-75 among workers on the evening shift. This decline was not explained by differences in demographic, exposure, or host variables; in the analyses that follow, average changes over shift are based on data from only the day and night shift workers.
The second cross-sectional study was carried out in three of the four mills originally studied, and a larger mill substituted for the smallest The target population of this study consisted of all 334 employees of the four mills. Personnel records showed that 98 percent were men and 66 percent were black; the mean age was 38.7 years, and the mean length of mill employment was 9.8 years. Thirty-five employees did not work on the day of testing, and four were excluded because they had worked the day before. This left 295 potential participants, and 256 (87 percent) of these were interviewed This group was 97 percent men and 63 percent black, with mean age 38.1 years, and mean length of mill employment 9.9 years. The interviewed employees thus constituted a representative subset of the target population.
This presentation summarizes our experience in three cross-sectional studies of respiratory health in cottonseed crushing mills. These studies were done in 1975, 1977, and 1978. Three milk were visited on all three occasions, another twice, and another once. In the course of these studies, health data were collected on a total of 444 subjects in the five mills.
In the United States, crushing mills receive cottonseed directly from the gins, with fibrous linters firmly adherent to each seed. This fibrous portion is contaminated with bracts, stems, dirt, and other contaminants similar to those of baled cotton fiber. The major steps in production include storage, removal from storage, cleaning with mechanical shakers, delinting with circular saws, hull removal with mechanical knives, cooking of meats, oil extraction by press or solvent extraction, and production of cake or meal from the meat residue. Linters, hulls, oil, cake, and meal are all of commercial value and are processed for storage and shipment.