Date of Degree
PhD (Doctor of Philosophy)
Occupational and Environmental Health
Wayne T. Sanderson
Kelley J. Donham
Hazardous noise exposures and hearing loss have been documented among farmers and farm workers for many years. However, little is known about the noise exposures during specific agricultural work tasks and their effect on hearing loss. The objective of this dissertation was to assess the effects of specific agricultural tasks on hearing loss and their contribution to total noise exposures.
Three studies were conducted to accomplish this objective. The first study examined associations between hearing sensitivity among rural residents (nfarmer = 960, nnon-farmers = 608) and self-reported years of participation in 12 agricultural tasks. Logistic regression analysis was used to examine associations between agricultural activities and hearing loss >25dB. Linear regression analysis was used to examine associations between agricultural tasks and mean decibels of hearing loss. The results indicated farmers have greater hearing loss than non-farmers. However years of participation in specific agricultural tasks was poorly associated with hearing loss. This result suggests that self-reported years engaging in specific agricultural activities may be a poor surrogate for true noise exposure
In the second study noise exposures (personal dosimetry) and corresponding task data (direct observation) were collected on 18 grain farms, and mean noise exposures (dBA) were calculated for specific agricultural tasks. Noise exposures ranged from 78.6 dBA to 99.0 dBA across all tasks. The noise exposures for each task varied greatly (large standard deviation and maximum exposure) with most of the variability within the farms. Although specific tasks with intense noise exposures were identified, most comparisons of mean noise exposures from one task to another were not statistically different and intense exposures were present for nearly all tasks. Therefore, controlling noise only for those tasks with the greatest mean noise exposures may not completely eliminate hazardous exposures or the hearing loss risk.
For the third study, estimates of 8-hr time-weighted-average (TWA) noise exposures were calculated using time-at-task observations from one population of farmers and prior dosimeter measured mean task-based noise exposures from an independent population of farmers. Additionally, dosimeter measured daily noise exposures from the independent population of farmers were also analyzed to identify significant determinants of noise exposure. Simple linear regression analysis was used to compare estimated and actual dosimeter-measured 8-hr TWA noise exposures. The noise exposure determinants were identified by conducting multivariable linear mixed-effects regression analysis on the one-minute noise measurements from the dosimeter measured daily noise exposures. The results indicated the estimated and measured 8-hr TWA noise exposures varied considerably. Therefore, the estimates were not considered reliable. Furthermore, task, number of noise sources and work area were found to have a statistically significant association with noise exposure.
In summary, hearing loss and noise exposures among agricultural populations are complex and cannot be completely explained by examining agricultural tasks only. More detailed evaluations of tasks are needed to increase the understanding of hearing loss and noise exposure in this dynamic work environment.
Copyright 2011 Michael Jerome Humann
Humann, Michael Jerome. "Hearing loss and task-based noise exposures among agricultural populations." doctoral dissertation, University of Iowa, 2011.