Hearing Loss in Agricultural Workers

Dr. James Lankford, College of Health and Human Sciences, Northern Illinois University, DeKalb, IL, Sue Zurales, Vice President, Mobilear Inc., Lisle, IL, Barbara Garrett, Audiologist, Longmont, CO, and Joseph Delorier Supervisor, Speech and Hearing Clinic, Northern Illinois University, DeKalb, IL

It is somewhat paradoxical that a peaceful rural farm can be the same environment where periods of high-intensity noise may result in hearing loss among agricultural workers. Our 10-year study of farmers shows that many audiologists see workers who have varying concerns about hearing loss prevention and identification.

After a decade of studying the farming population and analyzing the results of audiometric and survey data, it is apparent, and not surprising, that noise-induced hearing loss (NIHL) is a very large part of the personal lives of most farmers. Because of this, we suggest that annual hearing tests should begin in rural farming communities at the age of 10 and be mandated throughout the person's life. In addition, hearing protection must be made available to all those in the farming community, and educational programs should motivate farmers to wear hearing protective devices (HPDs) during exposure to all high-intensity noises.

More than 5,000 hearing evaluations were conducted over a 10-year period. Of those, 4,170 (2,695 males and 1,475 females) were analyzed and summarized. Farmers came from 34 states and four foreign countries, with the majority residing in Illinois, Indiana and Iowa. The data reflect an age range of 7-89, with an average of 54 years.

The increased spread of hearing loss from high frequencies through low frequencies with age and noise exposure is common for this population. Hearing loss of farmers is very characteristic of a sensorineural, bilateral sloping configuration resulting from both noise and aging. When age group data were compared to the 1983 hearing sensitivity values of the U.S. Occupational Safety and Health Administration (OSHA), all farmer populations, ages 20-60, showed dramatically more hearing loss than the comparison group. This also was true when the data were compared to the International Organization for Standardization (ISO) 1990 data.

Analysis of the audiometric results showed approximately a 3 dB difference between ears of males, with the right ear better than the left. Although relatively small, this difference in hearing ability is mentioned consistently in the farming literature. Most of the explanations for this phenomenon relate to more noise arriving at the left ear than the right. This may happen on a tractor when the farmer looks back over his right shoulder or due to the doorway being on the left side of a tractor or combine with a cab. Some have suggested there may be physiological reasons due to an ear dominance effect.

The primary vehicle for providing information and services to and gathering data from the farming community for the purposes of this study was the annual Farm Progress Show, which rotates among Illinois, Indiana and Iowa. The 3-day show in late September attracts more than 250,000 visitors each year.

Sources of Noise

A summary of answers to the 10 survey questions provided a profile of the average farmer. It was not surprising that 92% of farmers reported being exposed to very loud noise while involved in farming activities. When asked to rank the loudest noise sources on the farm, they listed tractors, grain dryers, combines, chain saws, grain grinding and animals (see Table 1).

Table 1: Typical Sound Levels on the Farm

In addition, 58% reported exposure to noise outside the farming environment. Firearm noise proved to be one of the most common sources that may reduce hearing ability in farmers, as 84% indicated this type of exposure. It may be another reason for the differential in hearing ability between ears, with more muzzle blast from a rifle or shotgun getting to the left ear of a right-handed shooter. Fortunately, hearing protection usage did increase over the 10 years that the study was conducted, from 30% to 44%; but many farmers are not using HPDs on a regular basis.

Seventy-eight percent of males believed they had a hearing loss, and 81% partially attributed the loss to noise on the farm. When asked if they would wear a hearing aid if they knew they had a significant hearing loss, 91% of farmers affirmed they would; yet only 4% were wearing hearing aids. Forty-three percent had never had a hearing test.

Hearing test results across the audiometric frequency range for all male subjects yielded a consistent pattern for both ears that progressed with age and showed significant decreases at 3000, 4000, 6000 and 8000 Hz). For the decade group aged 10 to 19 years, a 6000 Hz notch is the first apparent indication of noise-induced hearing loss. The progression of that notch and inclusion of frequencies such as 4000, 3000 and 2000 Hz is apparent from ages 10-70 and older.

Presence of Presbycusis

The rapid decrease of hearing sensitivity at 8000 Hz tends to obscure the notch configuration and probably reflects the presence of presbycusis for that higher frequency. Hearing loss at 4000 Hz seems to progress rapidly up through age 60. This is true for 3000 Hz as well. At 2000 Hz the hearing loss begins and progresses more rapidly from age 40 through 89. For 500 Hz the hearing loss appears to begin at approximately 60 years and increase through age 89.

HPD Use Studied

Another study investigated use of the devices and whether they were reducing the amount of hearing loss among farmers. Fifty individuals who consistently used HPDs were paired with a group of non-users, and the results showed that significantly less hearing loss occurred among farmers who had worn protectors.

One project examined the hearing sensitivity of females in the farming community. Results indicated that hearing loss due to noise does occur among some women and may start as early as 10 years of age.

The noise notch at 6000 Hz progressed through age 60, and hearing loss at the higher frequencies continued, which for some may relate more to aging than to noise exposure. Seventy-five percent of female respondents indicated they had been exposed to high-intensity noise from farm machinery; and there was a trend noted that the duration of noise exposure was increasing. This may reflect the increased involvement of women in noisy, work-related activities on the farm. However, a fairly good percentage of women (78%) were using HPDs in noisy environments.

One last study relating to the agricultural workers concerned noise levels for crop dusters, or agricultural aerial spraying service personnel. This investigation tested the hearing of 12 pilots, six from Illinois and six from Colorado. Results indicated substantially high levels of noise for this population and greater hearing loss among the pilots than a non-exposed group. The findings suggest that agri-pilots should be included in a hearing conservation program that includes annual audiometry and the utilization of HPDs.

In accordance with current literature, it is recommended that educational programs for hearing loss prevention start in elementary school and continue through the 12th grade. Hearing tests should be provided by audiologists at farm shows and other farm events as a way of identifying individuals with potential hearing loss or those at risk for noise-induced hearing impairment. In addition, hearing protectors can decrease the amount of hearing loss due to noise and therefore reduce the amount of communicative difficulties in the everyday lives of farmers.

(This article originally ran on the Web site of ADVANCE for Audiologists magazine, at www.advanceforaud.com on July 29, 2002. ADVANCE for Audiologists is a bimonthly publication offering strategies for growth and profitability to nearly 20,000 hearing health care professionals.) Source: http://www.nsc.org/issues/agri/hearingloss.htm