Results
Of the 298 landfill waste landfill workers, all of them completed the questionnaire for demographic
information; 2 (0.7%) of them did not finish the questionnaire for work history; 49
(16.4%) of them were not administrated audiometric testing; 2 (0.7%) of them suffered from
significant hearing loss due to ototoxic drug use. No workers claimed any genetic risk for hearing
loss. The 2 workers without work history did not finish audiometric testing neither; therefore,
the 298 potential study subjects were reduced to 247 with a participant rate of 82.9%.
Proportion of male workers for the 298 workers and the selected 247 workers were 81.0% and
80.6%, respectively; while the median age for the two populations were 39.0 and 38.0 years, respectively.
Distributions and differences among subjects of selected characteristics were shown
in Table 1. There were no female workers in group 3, and significantly more male workers in
group 2 compared to group 1 (P < 0.05). Ratios of regularly smoking and drinking were significantly
higher in group 3, compared to both group 1 and group 2 (P < 0.05). The education
level of workers in group 3 was significantly lower than that in group 1 and group 2 (P < 0.05).
These descriptive statistics and comparisons did not change materially for male workers only.
Table 2 shows the noise levels by work sites of different groups of the workers. The mean
noise level for 4 landfills was 66.1 dB with a range of 43.3 to 89.2 dB. The noise level at worksites
of group 3 was significantly higher than that of group 1 and group 2 (P < 0.05), though
there was no significant difference between group 1 and group 2. Of the 56 noise samples, 3
(5.4%) of them were over 85 dB, all of which were from group 3 (8.8%). The mean time-weighted
noise exposure of bulldozer drivers and compacting machine operators were 95.1 dB and
91.1 dB, respectively. As shown in Table 3, we found significantly higher TVOCs level at worksites
of group 3, compared to that of group 1 and group 2 (P < 0.05).
Table 4 show the hearing thresholds of different groups of workers by frequencies of 2000,
3000 and 4000 Hz that were used in the evaluation of occupational hearing loss. For all frequencies,
there was no significant difference for hearing thresholds between workers from
group 1 and group 2 (P > 0.05); however, the hearing thresholds of group 3 was significantly
higher than that of both group 1 and group 2 (P < 0.05). Similarly, the mean combined value
of hearing thresholds at 2000, 3000 and 4000 Hz for workers from group 3 was significantly
higher than that from group 1 and group 2 (P < 0.05).