ASSESSMENT OF NOISE-INDUCED HEARING LOSS OF THE MINE WORKERS OF CHROMITE MINES AT SUKINDA, ODISHA, INDIA

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1 ASSESSMENT OF NOISE-INDUCED HEARING LOSS OF THE MINE WORKERS OF CHROMITE MINES AT SUKINDA, ODISHA, INDIA S. Kerketta *, R. Gartia and S. Bagh Ministry of Environment, Forest & Climate Change, Eastern Regional Office, Bhubaneswar, Odisha, India Department of Statistics, Sambalpur University, Odisha, India 1 2 *For Correspondence: suna1466@rediffmail.com ABSTRACT In this study, an attempt has been made to evaluate the hearing loss of workmen (subjects) in opencast Chromite mines with respect to age, working experience, and workstations. The age group years is found to be the biggest age group suffering a significant hearing loss in both the ears. Also, the work zone area is found to be the most significant area affecting hearing loss on both the ears. However, the subjects working for nearly and years have the most significant hearing loss on left and right ears, respectively. Also, there is no significant difference of hearing loss exhibited by the subjects on both the ears of the age group of years and to the subjects working in the work zone area. Keywords: Dip, Notch, High fence, Low fence, Asymmetry hearing loss. INTRODUCTION Auditory effects or any other health effects may develop to any person at any frequency level depending upon the individual exposure to noise situation. Low-frequency noise Schust 2004 up to 100 Hz may cause non-aural physiological and psychological effects below the individual hearing threshold Leventhal et al., 2003 also emphasized that Hz frequency noise is an environmental noise sensitive to people in their homes and offices. This is the group which generates many complaints and is generally seen to the people of middle age. It may also occur to the subjects working in the industry but generally found at levels well above threshold. Similarly, low-frequency noise Nakashima et al., 2007 produced by the armoured vehicle also causes negative effects on reaction time to the normal hearing subjects Pal et al., 2000 have investigated that dozer, dumper, screen plant and pit exhaust fan generate noise in the alarming frequency range of Hz. Similarly, haulage machine generates noise at dominating frequency of 1.6 khz. When spectral noise level of 50 db SPL is applied at the midfrequencies, viz., 1 and 3 khz to the exposed subjects, auditory sensitivity loss increases with the decrease of loss of frequency selectivity linearly Pal et al., 2000; Mahmood et al., 2004 studied that there is an increase in systolic and diastolic blood pressure to the young adults exposed to the noise level of 90 dba at 4 khz. Subjects working in a Hydroelectric Power Plant generally exposed to the noise levels in the range of dba at 2-8 khz and hearing loss occurs within the first 10 years of exposure to noise and a dip found at 4 khz (Celik et al., 1998). The subjects exposed to the high level of noise produced by aircraft and heavy machinery exhibited notch at 6 khz (McBridge et al., 2001). Similarly, road traffic noise contributes high-frequency noise level of 70 dba which causes listening interference equivalent to 3 db (Satish et al., 2008). investigated that intense low-frequency noise may cause maximal loss over the khz range and intense high-frequency noise 60 ENVIS Centre on Himalayan Ecology

2 loss at 6 or 8 khz (McBridge et al., 2001). Therefore, the present work aimed at to study the hearing loss of the workman of chromite mines with the following objectives: (i) To estimate the hearing loss of subjects with respect to age, experience and workstations, (ii) To test if there exists a significant difference of the hearing loss on both the ears at high fence with respect to the different age groups, (iii) To test if there exists a significant difference of the hearing loss on both the ears at high fence with respect to the different working experience, (iv) To test if there exists a significant difference of the hearing loss on both the ears at high fence with respect to the different area of workstations, (v) To determine the most influential age group, working experience group and area of workstations which exhibit the hearing loss significantly on both the ears and (vi) To test if there exists any significant difference of hearing loss for the most influential age group on both the ears of the subjects and also for working experiences and the work stations and the working experience. SUBJECTS AND METHODS In the present study, audiometric data for a group of 500 subjects (481 males and 19 females) have been taken for the period of an open cast chromite mining complex in Sukinda Valley area in the state of Odisha (India). The retrospective data have been used to evaluate the possibility of a dip or notch at high fence i.e., 4, 6 and 8 khz due to exposure to different levels of noise by the subjects. The subjects were divided into 4 age groups, 8 experience groups and 5 workstations as depicted in (Table 1. a, b & c). The age of the whole subjects vary between the range 29 to 59 years and the experiences vary from 4 to 37 years. The descriptive statistics for both the ears at different frequency levels have been depicted in (Table 2. a & b). The audiometric data have been used for evaluation of hearing loss as per the ISO guidelines. To meet the research objectives, the data so obtained are analyzed through SPSS (16.0) package under Window XP environment. Generalized Linear Model ANOVA, Post hoc analysis, Gabriel Multiple comparisons for mean difference, Student's t-test and Paired t-test were used as statistical tools to meet the objectives of the present work. RESULTS Table 1. Audiometric data for a sample of 500 subjects. (a) Descriptive statistics for age (b) Descriptive statistics for working experience and (c) Descriptive statistics for different Workstations. Sl. No. (a) Descriptive statistics for age Age (yr) Male Female Total (N) Age Nos. % Nos. % Mean SD Mean SD Total (b) Descriptive statistics for working experience Sl. No. (yr) Male Female Total (N) Age Nos. % Nos. % Mean SD Mean SD ENVIS Bulletin Himalayan Ecology, Vol 24,

3 > (c) Descriptive statistics for different Workstations NB: W: Work zone, A: Industrial Area, B: Commercial Area, C: Residential and D: Silence zone Table 2. Descriptive statistics of hearing the loss of the whole subjects. (a) Left ear (b) Right ear (a) Hearing 4 khz 6 khz 8 khz level (db) n % Mean SD n % Mean SD n % Mean SD > (b) Area category Male Female Total (N) Hearing 4 khz 6 khz 8 khz level (db) n % Mean SD n % Mean SD n % Mean SD > Age Sl. No. Nos. % Nos. % Mean SD Mean SD 1. W A B C D Assuming the null hypothesis that there is no significant difference between the left and right ears with regard to hearing loss, a two-tailed t-test was conducted for the whole subjects and found that both the ears do not exhibit any significant difference at 4 khz, p=0.728 (p>0.05), 6 khz p=0.796 (p>0.05) and 8 khz, p=0.416 (p>0.05). Thus, the asymmetric hearing loss may be attributed either in the left or the right ear at 4 khz, 6 khz or 8 khz. To test if there exists a significant difference among the different age groups, experience groups, and workstations with regard to hearing loss on both the ears, ANOVA was performed for age, experience, and workstations. The most influential age group, experience group, and workstation were determined by Gabriel multiple comparisons of the mean difference. The audiometry data of the subjects in respect of the age group, experience, and workstations have been exhibited in Table 3 (a, b & c). 62 ENVIS Centre on Himalayan Ecology

4 Table 3. Audiometry data with respect to age, experience, and workstations. (a) Hearing level (db) at different age and frequency Range (year) 4.0 khz 6 khz 8.0 khz Right Left Right Left Right Left Hypothesis: Various age groups are independent for hearing loss at the high fence.the hypothesis is rejected at 1% level of significance as p=0.000 (p<0.01) Table 3. Audiometry data with respect to age, experience, and workstations. (b) Hearing level (db) at different years of experience and frequency (year) 4.0 khz 6.0 khz 8.0 khz 4.0 khz 6.0 khz 8.0 khz Right Left Right Left Right Left (year) Right Left Right Left Right Left < > Hypothesis: Different years of experience are homogeneous for hearing loss at the high fence. The hypothesis is rejected at 1% level of significance as p=0.000 (p<0.01). Table 3. Audiometry data with respect to age, experience, and workstations. (c) Hearing loss (db) with different workstations and frequency Work station 4.0 khz 6.0 khz 8.0 khz Right Left Right Left Right Left Work Zone Industrial Area Commercial area Residential area Sensitive Area Hypothesis: Various workstations are homogeneous for hearing loss at high fence The hypothesis is rejected at 1% level of significance as p=0.000 (p<0.01). ENVIS Bulletin Himalayan Ecology, Vol 24,

5 Table 4. The most influential test frequency and the subgroups Right ear Left ear Sl. No. Group Most significant Most significant Frequency khz p Subgroup (Years) p Frequency, khz p Subgroup (Years) p 1. Age Work Location Work Zone Work Zone 0.00 As exhibited in Table 4, the Post hoc analysis of multiple comparisons of means by Gabriel method reveals that the test frequencies 4 and 6 khz are found to be the most significant test frequencies for right and left ears, respectively, indicative of noiseinduced hearing loss at 1% level of significance with respect to age and workstation. Similarly, the Post hoc analysis of multiple comparisons of means by Gabriel method reveals that the test frequency 4 khz is found to be the most influential for both the ears, indicative of noise-induced hearing loss at 1% level of significance with respect to experience.fig.1 exhibits the variation of mean hearing loss of the whole subjects with respect to all the test frequencies (0.5, 1, 2, 4, 6 and 8 khz). The audiogram indicates a bilateral, no hearing loss below low fence (0.5, 1 and 2 khz) and then moderate flat sloping mild hearing loss from 2 to 6 khz, a notch at 6 khz and then slight recovery at 8 khz. The significance with respect to experience audiogram does not exhibit any notch at 4 khz that is generally found due to noise induced hearing loss but shows little dip at 6 khz. Thus, the asymmetric hearing loss may be attributed in either of the ears thesubjects group year does not show any sign of a dip or notch at 6 khz for the left ear. Figure-4: Hearing Level Vs. Work Place (Right ear) Frequency, khz Hearing level, db Work Zone Industrial Commercial Residential Sensitive ENVIS Centre on Himalayan Ecology

6 However, this does not mean that there is no notch or no subjects have a hearing impairment. On examining, 35 subjects (7.0% of total subjects) fall between the hearing loss range of db and 4 subjects (2.0% of total subjects) exceed the hearing loss>40 db for the left ear. As shown in Fig. 10, the audiogram of the subjects working in the work zone does not show sign of a dip As exhibited in Fig. 9, the audiogram for the subjects group of (right ear) and (left ear) years experience does not show any sign of a dip or notch at 4 khz for both ears. However, this does not imply that no subjects in the group have a hearing impairment. On examining, 7 subjects (1.4% of total subjects) fall between the hearing loss range of db for the right ear and 7 subjects (1.4% of total subjects) fall between the hearing loss range of db and 1 subject (0.2% of total subjects) exceeds the hearing loss of >40 db for the left ear. DISCUSSION The Post hoc analysis of multiple comparisons of means by Gabriel method reveals that the age group of years is the most significant age group affected hearing loss at the high fence on both left and right ears separately (Table 3a). Ertem et al., 1998 identified the first hearing loss at the age of 45 years or more to the textile workers. However, Kim et al., 2000 found that the hearing loss attributed to age starts after 65 years of age or more. But, the present work found the age group year as the ENVIS Bulletin Himalayan Ecology, Vol 24,

7 most significant group at the test frequency of 4 and 6 khz and may be assigned these values as the occurrence of a dip or notch and attributed to the possibility of the sensitivity of both the ears at the earlier stage. This asymmetry Backus 2009 may be caused due to the presence of a subgroup (operators of the HEMMs) that generally exposed to higher noise level i.e. more acoustic energy of the sound reaching in the left ear than to the right ear (Satish et al., 2008; McBridge et al., 2001; Royster et al., 1991). This asymmetric hearing loss may also be exhibiting in the left ear because 21.4% of total subjects fall between the hearing range loss of db with mean hearing loss of db and SD=3.84 at 6 khz as compared to only 14.6% of total subjects with mean hearing loss of db and SD=3.64 at 4 khz. Frank 1996 investigated that 90% of workers attained hearing loss by the age of 50 years as confirmed by the present study. Similarly, Johansson et al., 2002 found that hearing threshold levels start more rapidly in the 50 year age group for frequencies more than 3 khz. It is found that working experience of years is the most significant for the right ear and that of years of experience is the most significant for the left ear affected by the hearing loss at a different level of frequencies (Table 3b). Yildirim et al., 2007 found in their study that hearing loss begins to all the textile workers within the first 8 years of noise exposure and more evident could be ascertained between 5-8 years and then the hearing loss showed a slight increase in the later period of service. In the present study, the most significant group was found to be the subjects having working experience of and years at the test frequency of 4 khz for the right ear and left ear, respectively. This asymmetric behavior may be attributed to the acoustic energy of the sound reaching both the ears is not equal (Scheiblechner 1947; Fernandes SV 2010). It may be inferred that there could be variation between the two ears with regard to response and recovery. Like in earlier studies, the worse ear is not equated to the better ear in the present study and considered separately so that respond to sound is not happening in the same manner (Backus et al., 2009; McBridge et al., 2001; Scheiblechner et al., 1947; Coles et al., 1983; McDermott et al., 2010). Therefore, both ears have assumed equally sensitive to any loudness strength and offer the same level of speech recognition on that particular bandwidth. Similarly, from Table 3(c), it is found that there exists a significant difference among the various workstations and the work zone is the most significant workstation to have hearing loss at different frequency levels at 1% level of significance. Since the most significant frequency is 4 khz for both right and left ears, Paired t-test was conducted to evaluate whether there is any significant difference exists between the right and left ears of the subjects with reference to experience. With Paired t-test (twotailed), the p-value is found to be (p>0.05) and it may be said that there is no significant difference in hearing loss for both the ears at 4 khz at 1% level of significance. From the above findings, the hearing loss is found to be dependent on age, experience and working stations. It has been found that 6 khz is the frequency of influence to the left ear for the older subjects i.e. the age group years (7.8% subjects having hearing loss of >25 db with mean hearing loss of 35 db) and also for the subjects working in the work zone area (9.8% subjects having hearing loss of >25 db with mean hearing loss of db). The frequency of influence to the right ear is 4 khz and is the most sensitive to the age group years, the experience group years and the group working in the work zone area. Thus, it is to infer that any subjects beginning their service at the age of 30 years in the work zone area of an open cast chromite mines then the noise-induced hearing loss may be the most significant after working for more than 25 years. So, the following points are outlined for the chromite mining complex to abate noise impairment of the workmen: (i) The hearing loss is found to be at 6 khz, thus the working areas of the subjects working at work zone should be regularly rotated in less noisy areas to reduce the exposure time. (ii) The high frequency noise protective device should be advocated among all the subjects in general and HEMMs operators in particulars. (iii) Regular audiometry test of all the subjects should be 66 ENVIS Centre on Himalayan Ecology

8 performed to identify the hearing loss of the subjects occurring at 6 khz. (iv) It is essential to perform periodic maintenance of all the HEMMs to keep all the vehicles in good condition that are generating noise at dominating frequency of 4 and 6 khz. REFERENCES Atchariyasathian V, Chayarpham S, Saekhow S (2008). Evaluation of Noise-Induced Hearing Loss with Audiometer and Distortion Product Otoacoustic Emissions. J Med Asso Thailand 9: Backus, BC, Williamon A (2009). Evidence of noiseinduced hearing loss among orchestral musicians. International Symposium on Performance Science, Published by the AEC, Celik O, Yalcin S, Ozturk A (1998). Hearing parameters in noise-exposed industrial workers. Auris Nasus Larynx 25: Coles RRA, Burns W, King PF (1983). Assessment of hearing disability: Discussion paper. J Royal Soc Med 76: Denes PB (1963). On the Statistics of Spoken English. Acoust Soc Am J 35: Ertem M, Ilcin E, Meric F (1998). Noise Induced Hearing Loss among Cotton Textile and Carpet Mill Workers. Turkish J Med Sci 28: Fernandes SV (2010). The asymmetric hearing loss in industry. ANZ J Surgery 80: Frank JR (1996). Analysis of audiograms of a large cohort of noise-exposed mines. Internal Report National Institute for Occupational Safety and Health, Cincinnati, OH 3-8. French NR, Steinberg JC (1947). Factors governing the intelligibility of speech sounds. J Acoust Soc Am 19: Ishiyama T, Hashimoto T, (2000). The impact of sound quality on annoyance caused by road traffic noise: An influence of frequency spectra on annoyance. Japan Society of Automotive Engineers Review 21: Johansson M, Arlinger S (2004). Reference data for evaluation of occupationally noise-induced hearing loss. Noise Health 6: Kim H-N, Kim SG, Lee H-K, Ohrr H, Moon S-K, Chi J, Lee EK, Park K, Park DJ, Lee J-H, Yi S-W (2000). The incidence of Presbycusis of Korean Populations in Seoul, Kyunggi and Kangwon provinces. J Korean Med, Sci 15: Krishnamurti S (2009). Sensorineural Hearing Loss Associated with Occupational Noise Exposure: Effects of Age-Corrections. Int J Environ Res Pub Health 6: Laroche C, Hetu R, Quoc HT, Josserand B, Glasberg B (1992). Frequency selectivity in workers with noise-induced hearing loss. Hearing Research 64: Leventhal G, Pelmear P, Benton S (2003). A review of published research on low frequency noise effects: A report. Published by the Department for Environment, Food and Rural Affairs. Mahmood R, Khan GJ, Alam S, Safi AJ, Salahuddin, Amin-ul-Haq (2004). Effects of 90-decibel noise of 4000 hertz on blood pressure in young adults. J Ayub Med Coll Abbottabad 16: McBridge DI, Williams S (2001). Audiometric notch as a sign of noise induced hearing loss. J Occup Environ Med 58: McBridge DI, Williams S (2001). Audiometric notch as a sign of noise induced hearing loss. J Occup Environ Med 58: ENVIS Bulletin Himalayan Ecology, Vol 24,

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