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ARTICLE Table of Contents   
Year : 2007  |  Volume : 9  |  Issue : 36  |  Page : 75-77
Hearing impairment among mill workers in small scale enterprises in southwest Nigeria

1 Department of Community Medicine, University College Hospital, Ibadan, Nigeria
2 Department of Otorhinolaryngology, University College Hospital, Ibadan, Nigeria

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  Abstract 

This cross-sectional study was conducted among mill workers in a large market in Ibadan, southwest Nigeria. These workers are engaged in small scale businesses with little or no regulation of work exposures. Questionnaires administered to mill workers sought information on personal characteristics, length of time engaged in the job, type of milling done and symptoms of hearing impairment. Noise exposure and hearing impairment were assessed among 85 mill workers. Audiometry was done on mill workers and 45 controls with no known exposure to noise and no history of aural disease. Noise levels at work stations ranged from 88-90dB for small mills and 101-105 for larger mills. None of the workers used hearing protection. Analysis based on total number of ears showed that 56% of the workers had hearing impairment ranging from mild (49%) moderate (6.4%) to severe (0.6%) whilst 33% of the controls had hearing impairment which was mild (26%), moderate (7%) and no severe losses, P = 0.001. There was no association between age and hearing impairment but prevalence of hearing impairment was highest among those who had been engaged in the trade for more than 20 years. There is a need for regulation of small scale enterprises to protect the health of workers. Health education and provision of low cost ear plugs will reduce the occurrence and severity of hearing impairment among these low income workers.

Keywords: Audiometry, hearing impairment, mill workers, occupational noise, small scale enterprises

How to cite this article:
Omokhodion FO, Adeosun A A, Fajola A A. Hearing impairment among mill workers in small scale enterprises in southwest Nigeria. Noise Health 2007;9:75-7

How to cite this URL:
Omokhodion FO, Adeosun A A, Fajola A A. Hearing impairment among mill workers in small scale enterprises in southwest Nigeria. Noise Health [serial online] 2007 [cited 2018 Nov 18];9:75-7. Available from: http://www.noiseandhealth.org/text.asp?2007/9/36/75/36983
The majority of the working population in Nigeria are engaged in small scale enterprises. Many of these workers are self-employed and work in unregulated premises. There are several reports of poor work conditions in these enterprises [1],[2] but few studies have reported adverse effects on workers. Small scale enterprises operating wet and dry mills used for processing vegetables and food grains are located in markets or residential areas in many Nigerian cities. Noise is the predominant hazard produced by the operation of these mills. Whereas several studies have reported hearing problems among workers exposed to noise in organized workplaces in Nigeria, [3],[4],[5] there are very few reports, if any, on hearing problems among workers in the informal sector. Here, lack of regulation means that allowable limits of noise exposure may be exceeded and hearing protection may not be worn. This study was designed to determine the prevalence of hearing impairment among workers engaged in this trade.


  Materials and Methods Top


The study was conducted in a large market in Ibadan, Southwest Nigeria. Bodija market is one of the largest food markets in the Southwest. There are about 3,596 designated stalls and several unauthorized stalls. Mill workers engaged in milling of vegetables such as pepper, onions and tomatoes (wet milling) or dry foods like corn, millet and yam (dry milling) are located in designated areas of the market and are organized as a trade union. Permission to conduct the study was obtained from the trade union. Workers were informed about the purpose and procedures involved in the study during a routine meeting of the union. Participation in the study was voluntary. Control subjects were volunteers recruited from among adults in a community with similar socioeconomic characteristics as the mill workers. They had no occupational exposure to noise and no history of aural disease. A questionnaire was administered to each participant by trained interviewers. It sought information on personal characteristics of the worker, the type of work done, length of time spent at work and any presence of symptoms of hearing impairment. The noise level at each work station was measured using a type 2 digital integrating sound level meter CEL 269 (CEL Instruments U.K) set for A weighting.

It was not possible to convince workers to come to the hospital in order to attain standard conditions for audiometry. Hence, audiograms were done on all consenting workers and controls in a quiet office across the road from the market with a background noise level of 35-40 dB. Audiograms were done before workers started the day's work, at least 14 hours after exposure to noise. Ear examination was done before audiometric assessment to rule out any existing disease of the outer or middle ear. A diagnostic audiometer (Kamplex KLD 21) was used. Pure tone audiometry was done in 5 dBA steps at frequencies of 250, 500, 1000, 2000 and 4000 Hz in both ears.

Hearing impairment was calculated using the pure tone average of frequencies of 500, 1000, 2000 and 4000 Hz. Hearing impairment was classified according to the WHO definition; [6] normal hearing < 25 dB hearing threshold level (HTL), mild hearing impairment = 26-40 dB HTL, moderate hearing impairment = 41-60 dB HTL and severe hearing impairment = 61-80 dB HTL.


  Results Top


Eighty-five mill workers, 46 (54%) males and 39 (46%) females aged 18-65 years, participated in the study. Nineteen (23%) had no education, two (2%) had Islamic education, 32 (38%) had primary education, 19 (23%) had secondary education and 11 (13%) had post-secondary education. Forty-nine (58%) had worked in the mills for ten years or less, 18 (21%) for 11-20 years, 14 (16%) for more than 20 years and four (5%) did not reveal the length of their work history at the mills.

Twenty-three (27%) were engaged in wet-milling and 60 (72%) were engaged in dry-milling. They worked for a mean of 10.5 hours a day, range 5-13 hours. Forty-five control subjects were recruited. They were aged between 12 and 55 years and consisted of 22 males and 23 females. Five (11%) had no education, two (4%) had Islamic education, ten (22%) had primary education, 19 (42%) had secondary education and nine (20%) had post-secondary education.

Noise levels at work stations ranged from 88-90 dB for smaller machines and 101-105 dB for larger machines. Workers did not use any form of hearing protection.

Twenty (24%) mill workers gave a history of hearing problems. This was mostly tinnitus affecting 19 workers. Twenty-five workers (29%) had normal hearing in both ears with 60 (71%) recording impairment in one or both ears. For the worse ear, 50 (59%) had mild hearing impairment, nine (11%) had moderate hearing impairment and one (1%) had severe hearing impairment. For the better ear, 50 (59%) had normal hearing, 33 (39%) had mild hearing impairment and two (2%) had moderate hearing impairment. Among the controls, 24 (53%) had normal hearing in both ears with 21 (47%) recording hearing impairment in one or both ears. For the worse ear, 16 (36%) had mild hearing impairment and five (11%) had moderate hearing impairment. For the better ear, 37 (82%) had normal hearing, seven (16%) had mild hearing impairment and one (2%) had moderate hearing Impairment. The difference in hearing impairment in the worse ear and better ear of study group and controls was significant ( P = 0.022). Analysis based on total number of ears, showed that 56% of mill workers and 33% of controls had hearing impairment ( P = 0.001), [Table - 1]. Bilateral hearing impairment was recorded among 33 mill workers (39%) and eight controls (18%, P = 0.014). There was no association between age and hearing impairment. However, the prevalence of hearing impairment was highest among those who had been engaged in the trade for more than 20 years.

All 20 workers who complained of hearing problems had hearing impairment; 16 mild and four moderate. Forty workers with hearing impairment reported no symptoms. Of these, 34 had mild hearing impairment, five moderate and one had severe impairment in one ear.


  Discussion Top


Noise levels in the work stations of mill workers in this study exceeded the acceptable noise limits of 85 dB for an eight hour day. The prevalence of hearing loss in either ear of 71% among workers in this trade is not surprising and is due to unregulated exposure to noise and nonuse of hearing protection. However, the majority of these workers had mild hearing impairment and would benefit from hearing conservation measures. The prevalence of hearing impairment in this study is similar to levels recorded among workers in heavy industries in the organized sector. A prevalence of 65% was reported among laundry workers in Lagos, [3] 79.8% among textile workers [5] and 28% among Nigerian steel-rolling mill workers exposed to noise levels of 49-93 dB. [7] Reports from other developing countries indicate similar situations. [8],[9] Hearing loss was highest among those who had been engaged in the trade for 20 years or more. Similar findings were reported in a textile mill in Jordan where the occurrence of hearing loss was highest among those with more than 25 years of exposure. [8]

Awareness about noise hazard is high among Nigerian workers with reports of adverse effects such as hearing loss, tinnitus and headaches. [10] In spite of the fact that 24% of the workers in this study complained of hearing problems and most of these complained of tinnitus, none of them used any form of hearing protection. Ignorance about sources or suppliers of hearing protection devices and the low financial resources characteristic of the informal sector may be responsible for this attitude.

This study highlights the need for regulation of small scale enterprises in the informal sector in order to protect the health of workers, a situation that constitutes a continuing challenge to Occupational Health and Safety authorities in Nigeria. Health education and provision of low-cost ear plugs to reduce hearing impairment will be a useful intervention package for this group of low-income workers.


  Acknowledgment Top


The study was supported by a grant from the Dreyfus Health Foundation, New York, U.S.A.

 
  References Top

1.Asogwa SE. A survey of working conditions in small scale industries in Nigeria. J Occup Med 1981;23:775-7.  Back to cited text no. 1  [PUBMED]    
2.Jinadu MK. Occupational health problems of motor vehicle mechanics, welders and painters in Nigeria. Roy Soc Health 1982;102:130-2.  Back to cited text no. 2      
3.Elias SO, Ijaduola GT, Sofola OA. Noise induced hearing loss in laundry workers in Lagos. Nigerian Med Pract 2003;44:3-6.  Back to cited text no. 3      
4.Odusanya OO, Nwalolo CC, Ademuson EO, Akinola DO. Disabling hearing loss in two industries in Lagos, Nigeria. Niger J Clin Pract 2004;7:4-7.  Back to cited text no. 4      
5.Oshibogun A, Igweze IA, Adeniran LO. Noise-induced hearing loss among textile workers in Lagos metropolis. Niger Postgrad Med J 2000;7:104-11.  Back to cited text no. 5      
6.World Health Organization. Report of the Informal Working Group on Prevention of Deafness and Hearing Impairment, Programme Planning, WHO/PDH/91.1: Geneva; June 1991. p. 18-21.  Back to cited text no. 6      
7.Ologe FE, Akande TM, Olajide TG. Occupational noise exposure and sensorineural hearing loss among workers of a steel rolling mill. Eur Arch Otorhinolaryngol 2006;263:618-21.  Back to cited text no. 7  [PUBMED]  [FULLTEXT]  
8.Shakhatreh FM, Abdul-Baqi KJ, Turk MM. Hearing loss in a textile factory. Saudi Med J 2000;21:58-60.  Back to cited text no. 8  [PUBMED]    
9.Minja BM, Moshi NH, Riwa P. Noise induced hearing loss among industrial workers in Dar es Salaam. East Afr Med J 2003;80:298-302.  Back to cited text no. 9  [PUBMED]    
10.Ologe FE, Akande TM, Olajide TG. Noise exposure, awareness, attitudes and use of hearing protection in a steel rolling mill in Nigeria. Occup Med (Lond) 2005;55:487-9.  Back to cited text no. 10  [PUBMED]    

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Correspondence Address:
Folashade O Omokhodion
Department of Community Medicine, University College Hospital, Ibadan
Nigeria
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/1463-1741.36983

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