The hearing of rural workers exposed to noise and pesticides.

n work environments, different physical and chemical agents that may pose a risk to workers' hearing health coexist. In this context, occupational hearing loss stands out. It has mostly been attributed to only noise exposure, although there are other agents, that is, pesticides that might contribute to occupational hearing loss. In this report, two cases will be presented that consider rural workers exposed to pesticides and intense noise generated by an adapted rudimentary vehicle. The noise measured in this vehicle was 88.3 dBA up to 93.4 dBA. Pure-tone audiometry, distortion product otoacoustic emissions, and high-frequency audiometry tests were performed. This report is unusual because of the short time of exposure to noise and pesticides and the hearing loss found, indicating a synergy between those agents.

Introduction

Workers exposed to pesticides may exhibit loss in overall health and the quality of life, and it is believed that hearing loss may be an early symptom of poisoning by these agents. Pesticides are ototoxic agents that can cause damage to the auditory system, especially the cochlea and the auditory nerve, in addition to causing changes in the vestibular system and the central nervous system.[12345678910]

Noise is a harmful agent present in the daily lives of people and is found in traffic, at work, during leisure time, and in different locations. It is estimated that about 16% of the population is exposed to noise that can cause disease. In addition, noise-induced hearing loss (NIHL) is now the work-related injury with the highest incidence; it is believed that 25% of workers exposed to noise may have changes in hearing.[1112] In a family involved in agriculture, it is common for the work to be performed manually through weeding, soil preparation, cultivation, and harvesting.[1314] The high cost of specialized agricultural machinery can often force the rural worker to use various dangerous adaptations of existing machines.

Case History

The “Jackal”

It is a rudimentary motor vehicle used for the transport of products and also of workers. It has an adapted structure on the chassis of another vehicle that was already deteriorated, whose steering wheel, seat and compartment charges were welded onto the old. It has four wheels and slick used tires. It had its engine amateurishly adapted for use with cooking gas, that is, liquefied petroleum gas (LPG), as its fuel.[13] It is used illegally in some farms and ranches, thereby making its monitoring by competent authorities difficult [Figure 1].

Figure 1

The vehicle with LPG tank in detail

The vehicle’s noise was measured twice a month during the first year. The meter used to measure the sound level was the Instrutherm model DEC 490, IEC type II, which had a range of 30–130 dB, with balancing of circuit “A,” slow integration time, 0.1 dB resolution, and coupled to a wind shield. In addition, according to Brazilian labor law, the sound meter’s microphone was held next to the driver’s ear. The intermittent noise was measured to be 88.3 dBA with the vehicle in neutral and to be 93.4 dBA when accelerated (average values for one workday).

The Hearing Health of the Rural Worker

Two workers belonging to families working on farm were atended: a 26-year-old male (Case 1) and a 24-year-old male (Case 2). Both reported driving the “Jackal” for about 3 h a day, 6 days a week. Only the participant of Case 2 reported regular and concurrent exposure to several pesticides, including glyphosate, pyrethroid, and organochlorine. Both of them had worked in a rural setting for 12 years; however, they had worked with the “Jackal” only for the past 2 years.

They did not report any previous otologic disease, the use of ototoxic medication, surgery or head trauma, social exposure to intense noise, and the regular use of alcohol, tobacco, or drugs. Both workers had normal otoscopies.

The tests were performed at the following three different moments: baseline, after 12 months, and after 24 months. Responses on the Distortion Product OtoAcoustic Emissions (DPOAE), which assess the hair cells of the cochlea, were considered normal when the criterion for pass/fail response recorded in 2000–8000 Hz frequencies was equal to or greater than −5 dB, and the signal-to-noise ratio was equal to or greater than 6 dB in all the tested frequencies.

Pure-tone air audiometry was performed on the two participants at the frequencies of 0.5, 1, 2, 3, 4, 6, and 8 kHz and high-frequency audiometry (HFA) at 9, 10, 11, 12.5, 14, 16, 18, and 20 kHz in compliance with the environment according to ISO 8253-1. Thresholds were considered normal if they were equal to or better than 25 dB in both the ears.

The results of initial tests and tests in the first year were normal, that is, Distortion Product OtoAcoustic Emissions (DPOAE) present, conventional audiometry was close to normal and HFA revealed similar configuration between both cases. Throughout the study, the subjects showed no changes in their health, which were worthy of note, or otologic complications. They were subjected to the same tests during the years. The tests results were normal in both ears, except for HFA in Case 2, who had concomitant exposure to pesticides, and in whom, worsening in thresholds 11, 12.5, 14, 16, 18 and 20 kHz in the second year was observed [Figure 2].

Figure 2

Audiometry comparison between different moments and participants

Discussion

The work activities in rural areas usually revolved around families on small farms. The impacts on health can be enhanced by early exposure to occupational risk agents.[1516] In our cases, a history of child labor was identified, because the activities that the participants were involved in the field started around 13 years of age, although exposure to noise, effectively, only started 2 years prior to the study.

Noise alone can cause many health problems. In work environments it can coexist with combined exposures to other agents, which can also be harmful to human hearing. Furthermore, working agriculture-related areas poses risks to workers when they are routinely exposed to pesticides. It has been noted that alterations to the vestibulocochlear system could be caused by an exposure to pesticides. However the useage of a mixture of various products of different toxicities in agriculture, as reported by the participant of Case 2, could hinder the identification of individual concentrations of all the toxic agents involved.[2341718]

Brazilian and international labor legislation asserts that audiological monitoring is mandatory for occupationally exposed workers; however, it is related only to the physical risk as a result of noise agents.[1920] There are no legal parameters regarding hearing for cases of exposure to chemical agents. However, since 2003, the European Union recommends that prevention programs also operate, whereby workers exposed to chemical agents are constantly monitored.

Studies have linked hearing loss at higher frequencies (above 8 kHz) to tinnitus, exposure to intense noise, and ototoxic agents.[212223] However, currently, there are no studies investigating the association between pesticides and noise, as well as its effect on hearing loss. Comparing the cases investigated, we observed that only the results obtained by HFA were different between the participants, which reinforces the theory that pesticides may have ototoxic effects sooner than noise itself.

The invariable results in DPOAE in both the cases surveyed are in line with authors who found no significant difference between DPOAE and biomarkers in students exposed to pesticides.[8] It is believed that, similar to conventional audiometry, this frequency range did not suffer damage from ototoxic agents, in a period of 2 years, as noted.The hearing damages caused by loud noise are recognized, and the studies that associate noise exposure with the use of HFA endorse the importance of this tool in the evaluation and monitoring of NIHL.[24252627]

The synergistic effect between noise and toxic agents may potentiate hearing loss.[28] In addition, the results obtained from the participant in Case 2, in whom there was a change at high frequencies, supposedly related to the different types of pesticides handled routinely by the participant, give a hint that pesticides may be an ototoxic agent.

Conclusion

In the assessment of the cases presented, HFA was considered a sensitive instrument to detect hearing impairment in workers exposed to noise and pesticides.

It is noteworthy that the lack of obligation, as prescribed by law, for the monitoring of hearing among workers exposed to chemical agents, requires a critical stand by researchers, health professionals, and work-safety organizations to contribute positively to change this scenario.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.