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Year : 2005  |  Volume : 7  |  Issue : 29  |  Page : 7--11

Audiometric findings in petrochemical workers exposed to noise and chemical agents

MC De Barba1, AL Jurkiewicz1, BS Zeigelboim1, LA de Oliveira2, A Pompermayer Belle2,  
1 Department of Audiology, Universidade Tuiuti do Paran�, Curitiba, Brazil, USA
2 Department of Occupational Health and Hygiene, Rio Grande do Sul, Brazil, USA

Correspondence Address:
B S Zeigelboim
Rua Gutemberg, n� 99/9� floor, Bairro Batel - 80420-030, Curitiba/PR, Brazil


This study investigated the occurrence of hearing loss among workers of a petrochemical industry during a period of five years. The records of environmental noise and solvents measurements and the results of annual audiometry performed by the company were examined. The audiometric results of workers from olefin operational areas 1 and 2 and aromatic plant areas exposed to solvents and noise and utility area workers exposed only to noise were analyzed for the standard threshold shift (STS). Despite the low exposures to solvents and a moderate exposure to noise, 45.3% of workers had hearing losses and 29.6% had STS.

How to cite this article:
De Barba M C, Jurkiewicz A L, Zeigelboim B S, de Oliveira L A, Belle A P. Audiometric findings in petrochemical workers exposed to noise and chemical agents.Noise Health 2005;7:7-11

How to cite this URL:
De Barba M C, Jurkiewicz A L, Zeigelboim B S, de Oliveira L A, Belle A P. Audiometric findings in petrochemical workers exposed to noise and chemical agents. Noise Health [serial online] 2005 [cited 2023 Sep 30 ];7:7-11
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It is known that many solvents used in industry are toxic in a wide range of levels and potentially harmful to health if their use is not controlled. The potential risks depend on several factors such as the manner in which solvents are used, the route of exposure, duration of exposure and vapor concentrations in the work environment. There are certain medical drugs and chemical compounds that may damage the structure of the inner ear, cochlear and/or the vestibular apparatus, temporarily or permanently. Several studies have demonstrated that chemical compounds like metal fumes (lead, mercury, manganese, cobalt and arsenic), asphyxiant gases (carbon monoxide, nitrate of butyl and tetrachloride of carbon) and organic solvents (toluene, xylene, styrene, n-hexane, tetrachloroethylene and disulfide of carbon) may cause hearing loss, either acting alone or when interacting with noise. [1]

The objective of the present study was to verify the factors that have influence over the occurrence of hearing loss on petrochemical workers.

 Materials and Methods

This study was conducted at a petrochemical company, in the state of Rio Grande do Sul (Brazil). The main industrial process of that company is to turn naphtha into a mixture of simpler compounds through thermal processes. The major units of the productive process are olefins (unit 1 and 2), aromatics and utilities. The aim of the study was to evaluate the occurrence of standard threshold shift (STS) as defined by the National Institute for Occupational Safety and Health, NIOSH (1998) which is a shift of 15 dB or greater at any test frequency from 500Hz to 6000 Hz from the audiometric exams in relation to the previous exams (reference). Annual audiograms were examined for this purpose. The occurrence of hearing losses was calculated. One hundred and seventy two individuals were studied, all male, ages ranging from 25 to 57 years with a mean age of 44.3 years, divided in to four groups, according to the plants of the company studied. The plants have different chemical processes and the workers are in contact with different chemical agents. [Table 1] summarizes the results of noise and solvent measurements performed by the company.

The inclusion criteria were at least five years of exposure to chemical compounds and/or noise and the availability of a minimum of two pure-tone audiograms from 1998 to 2002. Workers who had conductive hearing loss were excluded from the study. The workers' mean hearing thresholds in the frequency range of 250Hz to 8000 Hz in the year 2002 were compared with a control group (unexposed) of the same age as the workers.

The data were obtained from a database owned by the company. It contained the identification number, birth date, admission date, department and threshold for pure-tone audiometry. The annual noise and solvents measurement results were obtained from reports of the Program for the Prevention of Environmental Risks, prepared by the safety technicians, following Brazilian regulations and FUNDACENTRO technical standards, Decree 3214/78 NR 15 and respective annexes.

 Pure-Tone Audiometry

The company routinely performs audiometric tests at admission and/or periodic exams according to the Brazilian Law NR 7, Decree 19/1998. Otoscopy and air conduction pure-tone audiometry is performed in the frequency range of 250 to 8000 Hz and in the frequencies of 500 to 4000 Hz for bone conduction. The majority of the pure-tone audiometry was performed in the company, inside an audiometric booth, using an audiometer SD 25 SIEMENS, earphones TDH 39, calibrated according to the ISO 8253 - 1, IEC 645 and ISO 389. Some employees underwent pure-tone audiometric testing at a clinic that uses the AC 30, AD 27 and AD 229 Interacoustics audiometer and TDH 39 earphones.


The mean audiograms obtained in the year 2002 by plant including the control group are displayed in [Figure 1],[Figure 2].

At the significance level of 5% ( P = 0,05) the Chi-square test shows that there is no linear tendency between age and STS.

[Table 2] shows the number of workers who had a STS in 2002 in relation to 1998, according to the exposure time in the company, in years.

At the significance level of 5% ( P = 0.05) the Chi-square test shows that there is no dependence between exposure time and number of workers with STS [Table 3].

[Table 4] presents the percentage of workers who have a STS in their respective workplaces.

At the significance level of 5% ( P = 0.05), the test of difference between two proportions shows that there is a significant difference among the workers from the utility and olefin 2 plants, regarding STS percentages.

In [Table 5],[Table 6], the frequency of the STS in each ear, is displayed according to the operational plant.

At the significance level of 5% (P= 0.05) the test for difference of proportions shows that there is no significant difference among the plants in the frequencies of 4000, 6000 and 8000 Hz.

At the significance level of 5% ( P = 0.05) the test for difference of proportions shows that there is no significant difference among the plants in the frequencies of 4.000, 6.000 and 8.000 Hz.

The percentage of workers who have normal hearing and those who have hearing loss in the frequency range of 3000 to 8000 Hz in 2002, is shown in [Table 7].

At the significance level of 5% (a = 0.05) the test for difference of proportions shows that there only exists a significant difference of hearing loss among workers of olefin 2 and aromatic plants ( P = 0.0491).


Previous studies have shown that solvents can contribute to the deterioration of the cochlear function. Vestibular and hearing disorders have been reported in individuals exposed only to organic solvents. [2] Chemical agents may cause hearing loss when acting alone or in interaction with the noise. [3] Several studies have recommended the evaluation of the effects of chemical exposures on hearing. [4],[5],[6],[7],[8]

This study investigated the occurrence of STS in petrochemical industry workers. The participants of this study were exposed to noise and solvents in concentrations within the Brazilian exposure limits. NIOSH [9] considers as a STS a difference of 15 dB or greater compared to that at the baseline audiometric exam in relation to subsequent exams, in any of the test frequencies from 500 to 6000 Hz. The occurrence of 5% or higher STS may be a signal that the hearing conservation program is not being effective. Since Sliwinska-Kowalska et al , [8] have shown solvents may also affect 8000 Hz, this frequency was also considered in this analysis. Significant differences among the groups occurred in 6000 and 8000 Hz. The difference in 6000 Hz is certainly associated with noise exposure, but the difference of 8000 Hz may suggest another type of hearing damage caused by the solvent exposure.

Though this study analyzed STS per frequency, it is similar to the study by Sliwinska-Kowaslka et al , [8] that reported the effects of occupational exposure to styrene and noise on hearing. The authors found a significant increase in thresholds in all subgroups exposed in frequency in the range of 2000 to 8000 Hz, where the subgroup exposed to styrene and noise did not differ from the subgroup exposed only to noise, except for the frequency of 8000 Hz.

In the present study, regardless of the workplace, the workers' exposure time was not an important variable, where there was not dependence between the exposure time and the number of STS workers ( P = 0.652) at a significance level.

The analysis of the percentage of workers, who have STS, in relation to the operational plants, evidences a high occurrence of hearing loss in all groups. Morata et al , [6] also found high percentage of high frequency hearing losses in workers exposed to aromatic solvents and noise at an oil refinery. Chen and Tsai [10] described workers from an oil refinery in Taiwan with hearing loss which increased from low to high frequencies. Still, the results of environmental measurements for both noise and solvents were low in other studies conducted in refineries. [6],[10] How can these elevated rates of hearing loss be explained? It is possible that these measurement results do not accurately reflect the environmental conditions of the companies.

Another hypothesis to explain the results found is that other chemicals, in spite of the low exposure, could be contributing for the progression of hearing loss caused by noise exposure, requiring further investigation.

The employees of the company receive instructions and training about the use of hearing protection devices when they are hired, but their use may not be effective. The olefin 1 and the utility plants present the higher percentage of STS (30.7% and 36.8%) and have higher exposure to noise (77.8 to 88.8 dBA and 74.4 to 91.8 dBA, respectively), thus noise is likely to be associated with the hearing losses in those workers.


This study suggests the necessity for reviewing the preventive measurements adopted by the company studied for eliminating the occurrence of hearing losses and standard threshold shift.

It is most likely that the traditional measurements for hearing conservation are not meeting the needs of several populations of workers. The inclusion of 8000 Hz frequency in this study contributed to a high percentage of STS and it might help differentiate the effect of noise from the ones from solvents.

Reducing exposures and training on how to use personal protective equipment on an individual basis for every area of exposure could prevent future standard threshold shifts.


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