The Auditory & Non-Auditory Effects of Noise Pollution:An Occupational Health Study

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1. Introduction: The present study was planned as a prospective, longitudinal and panel-type of a study with the documentation of the health effects of noise exposure as its primary objective. Noise as a health hazard has been studied extensively in the last decade and a substantial amount of dose-response information on NIHL and its risk factors has been documented. However most of these studies were of noise as an individual stressor. In field situations noise does not occur as the sole stressor, but exists in combination with multiple other stressors like vibration, heat, illumination etc. Insufficient data on health effects of noise exposure when it occurs in combination with other pollutants raises considerable barriers in the formulation and implementation of hearing conservation interventions.

With a view of addressing this aspect, the present study was not planned to be a traditional controlled study of noise pollution as a sole environmental stressor. Instead, it attempted a study of health effects caused with an exposure to noise in combination with multiple stressors routinely present in the occupational environments of India.

2. Research Methodology: Subjects matched on sex and age, from two occupational environments viz the power loom industry & an internal office, were recruited for the study. Maintaining noise as an independent variable, the study focused on its health effects. It is well known and has been amply proved, that health effects of noise are expansive, affecting the human body physiologically as well as psychologically. Hence the parameters selected for the present study were hearing sensitivity, anxiety-state, anxiety-trait, blood pressure (systolic & diastolic) and pulse rate. Each subject of the study was studied on the above parameters for one year. The study levels were designated as Level 1 at the beginning of the study period, Level 2 six months after Level 1, and Level 3 six months after Level 2 & one year after Level 1. Descriptive statistics like means, medians and standard deviations of study parameters were then calculated, to describe their central tendencies. The two-group’t’ test and the non-parametric, Mann Whitney test were used to compute the significance of differences found in the study parameters, as they occurred in the control and experimental groups.

3. Results & Discussion: The arithmetic mean of noise levels to which the subjects (N=120) from the control (indoor office) group were exposed to was 92dB(A) while subjects (N=120) from the experimental (power loom) group were exposed to a mean noise level of 102 dB (A).

3.1. Hearing Loss: The prevalence of hearing loss in the control group was 23% as compared to a prevalence of 77% in the experimental group. This statistic assumes additional significance as the subjects of the control and experimental groups were matched for sex and stratified for age. They did not vary in any way on hearing risk factors other than different levels of occupational noise exposure. Hence the researcher concluded that this differential noise exposure was an important causal factor in the high hearing loss prevalence observed in the experimental group. In spite of the match on sex and age in the study subjects, their mean hearing thresholds varied substantially. However the researcher could not draw any conclusions on the general trends of these hearing thresholds.

3.2. Systolic & Diastolic Blood Pressure: The grouped “t”- test and the Mann Whitney non-parametric test were applied to the differences in blood pressures of the control and experimental group. No statistically significant difference in systolic (P=0.1768) and diastolic (P= 0.2630) blood pressures between the two groups was found. This finding is supported by multiple other studies on noise-induced blood pressure changes. In spite of using a variety of research methodologies, most studies concluded that the extreme variability in blood pressure levels and their multiple confounders make blood pressure predictions complicated. However blood pressure, as a dependant variable is highly plausible and hence warrants further study. Some studies even suggested a documentation of study results so as to create a large national occupation-specific blood pressure database with detailed information on its multiple confounders, which might be able to aid blood pressure predictions in future.

3.3. Pulse Rate: The t-test and the Mann Whitney non-parametric test of significance were applied to the differences in average pulse rates between the two study groups. The P statistic (P=0.2781) and the chi square statistic indicated no significant difference. However the Fishers statistic (0.1831) was low and seemed to tend towards significance.

3.4. Post-Work Increases in Blood Pressure (Systolic, Diastolic) and Pulse Rate: In addition to higher blood pressure and pulse rate values in the experimental group as compared to the control group, the researcher had hypothesized a higher prevalence of increased post-work systolic and diastolic blood pressures and pulse rates in the experimental group as compared to the control group. Tests for significance were applied to the differences between the study groups in the post-work increases of systolic, diastolic blood pressures and pulse rates. The chi square (0.0236), P (0.8779) and Fishers tests (0.5000) concluded that there was no significant difference between groups in the systolic blood pressure increases, while the proportion of increase in the diastolic blood pressures were the same in the control and experimental groups. When prevalence of pulse rate increases in the study groups were tested for significance, the P statistic (0.2781) and the chi square statistic indicated no significant difference. However the Fisher’s statistic (0.1831) was low and seemed to tend towards significance.

3.5. Anxiety-State: The difference in the mean STAI-State scores was tested for significance with the application of the t-test and the Mann Whitney non-parametric test, yielding results of the difference being highly significant (P= 0.0064, Mann Whitney Statistic =8664.0000). The researcher on the basis of the above significance postulated that the high ambient noise levels in the power-loom occupational environment as compared to the lower ambient noise levels in the indoor office is responsible for the increased state-anxiety observed in the experimental group. The control group is exposed to comparatively lower ambient noise levels at work, causing a lower level of the anxiety-state and hence exhibit lower STAI-state scores as compared to the experimental group.

3.6. Anxiety-Trait: The difference between STAI-Trait scores were as hypothesized, not significant (P=0.4166, Mann Whitney Statistic= 6763.5000).

3.7. Subject Profile: In addition to monitoring subjects of the control and experimental groups on the study parameters, the present study with the use of an exhaustive questionnaire, constructed a profile of the subjects from the control and experimental group. On analysis, the questionnaire generated prevalence information of various aspects of the study subjects like their lifestyle, social habits and common health complaints. The study found that 33% of the experimental group had sleeplessness as compared to a prevalence of 8% in the control group, 32% of the experimental group complained of recruitment as compared to 14% in the control group, tinnitus had a prevalence of 30% in experimental group as compared to 4% in control group, 57% of subjects in the experimental group imbibed alcohol as against 36% in the control group, while tobacco was utilized by 48% in experimental group and 19% in control group.18% of the subjects in the experimental group complained of post-work irritability as compared to 1% in the control group.

4. Conclusion: The conclusions of the present study are supported by the conclusions Melamed (2001) drew from his study. Melamed stated that it was inappropriate to study occupational noise exposure as the sole modifier of parameters like blood pressure and anxiety-state. In his study of high-noise exposed workers, he observed that those with complex jobs showed increases in BP that were more than double as those shown by simple jobs. Paradoxically, under low noise exposure there was a small increase in BP for workers with complex jobs but about a 3-fold increase in workers with simple jobs. This clearly indicated, Melamed further stated, that the presence of some unknown variable in the occupational environment was acting to influence the health effects of high ambient noise levels. For his study Melamed postulated that the level of cognition required for a job was the missing or third variable. He stated, that when a job demands a lower level of cognition, ambient noise would create an arousal effect on the subjects and improve their performance while a complex job would be negatively impacted by high noise levels. Applying the above rationale to the present study, the researcher postulates that a lower level of cognition required by the weaving job, led to ambient noise creating an arousal effect on some weavers. These weavers hence, were not negatively affected by the noise and did not exhibit any increase in blood pressures and anxiety-states. This finding demonstrates, that the health effects of noise exposure vary in accordance with the cognitive requirement of a job. This complicates substantially, attempts by researchers to draw clear-cut conclusions with reference to the prevalence and trends of noise-induced health effects.

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