The mean (± standard deviation) age of the cohort with any outcome data (n = 49,266) on September 11, 2001, was 38.3 ± 8.8 years. Incident ear pain occurred younger (ear pain mean age 48.5 ± 9.2) than hearing loss (mean age 53.4 ± 9.4) and tinnitus (52.1 ± 9.1 years old) (Table 2). Those experiencing incident hearing loss were younger than those not experiencing hearing loss (mean age 55.2 ± 9.6), although they were older than those without hearing loss on September 11, 2001, and at their last visit. The average observation time (last vs first visit) was longer for cases than noncases (hearing loss: 12.1 ± 6.1 vs 7.9 ± 6.7 years; tinnitus: 10.6 ± 6.6 vs 7.8 ± 6.7 years; and ear pain: 11.4 ± 6.4 vs 7.8 ± 6.7 years, all P ≤ 0.001). However, the average follow-up time from the first day worked on the WTC effort until the event (cases) or until last visit (noncases) was 11.9 ± 4.6 years and 18.2 ± 5.3 years for members with and without persistent hearing loss, 14.8 ± 5.6 years and 17.9 ± 5.5 years with and without persistent tinnitus, and 14.6 ± 6.7 years and 18.4 ± 5.2 years with and without persistent ear pain (all P ≤ 0.001). Forty percent of the cohort experienced one of the three outcomes, with substantial intersection among the three (Fig. 1). Of those studied, 12,479 (25.4%) reported persistent hearing loss, 12,379 (25.1%) reported persistent tinnitus, and 7490 (15.2%) reported persistent ear pain (Fig. 3). Another 17.4% reported short term hearing loss (duration of <10 months) after their participation in the WTC work effort (data not shown).

Most of the sociodemographic and BMI characteristic distributions were statistically significantly different between those with and without persistent hearing loss, yet, except for smoking cigarettes, the magnitude of the differences were generally small (Table 2). Members engaged in occupations other than protective services (including ~1% military) on September 10, 2001, had higher risks of hearing loss, tinnitus, and ear pain (Tables 3–5).

Without considering other measures of WTC exposure, exposure to noise while working on the WTC effort increased the risk of incident hearing loss (adjusted relative risk [ARR] 1.23 [1.18, 1.27]), tinnitus (ARR 1.17 [1.13, 1.22]), and ear pain (ARR 1.33 [1.26, 1.41]). However, the combined effects of WTC noise and other measures of WTC exposure revealed dose-response relationships where members who experienced noise while working on the WTC effort consistently had higher risk of hearing loss (Table 3, Fig. 2), tinnitus (Table 4), and ear pain (Table 5).

Compared with members with the lowest Exp4 level without WTC noise exposure, the risk of hearing loss increased with higher exposure among those who did not have WTC noise exposure, except in the group with very high Exp4, which had a small sample size (n = 103) and unstable risk estimate (Table 3, Table 6). While significantly higher risk of hearing loss was associated with ever working on the WTC debris pile and with the number of days worked on the WTC effort, those risks were only similar to the range of Exp4 risk through intermediate exposure with WTC noise. Similar patterns, but lower risk of tinnitus than hearing loss, were associated with Exp4, EverPile and DaysWTC (Table 4). Similar patterns, but higher risk of ear pain, were observed with Exp4, ever working on the debris pile and number of days worked on the WTC site (Table 5). Cox proportional hazards sensitivity analyses accounting for time-to-event produced stronger results (Table 7), similar to the odds ratios from logistic analyses of WTC exposures and noise (Table 8). The log binomial regression analyses produced more conservative (lower) estimates than the logistic regression analyses (Table 8). The sensitivity analyses limited to members with two or more monitoring visits produced similar results to the analyses including members with a single monitoring visit (data not shown). For example, the association of persistent hearing loss and intermediate Exp4 without WTC noise exposure was ARR 1.10 (1.01, 1.19 when limited to members with ≥2 visits; the full sample was ARR 1.11 [1.02, 1.21]). For very high Exp4 with WTC noise exposure, members with ≥2 visits had ARR 1.52 (1.38, 1.69; the full sample had ARR 1.58 [1.43, 1.76]). Sensitivity analyses using multiple imputation of missing values for covariates also produced almost identical results as the main analyses assigning the missing values to the mode value for the all outcomes (data not shown). For example, the adjusted risk ratio for the association of persistent hearing loss and intermediate (Exp4) without noise was ARR 1.12 (1.09, 1.15) and for very high Exp4 with WTC noise exposure was ARR 1.59 (1.54, 1.65).

Compared with members engaged in protective services the day before the attack, all members reporting other occupations, particularly those engaged in construction work or who reported being unemployed or retired, had higher risk of hearing loss (Table 2), tinnitus (Table 4) and ear pain (Table 5). The results of primary outcome sensitivity analyses excluding occupational status (data not shown) were almost identical (for hearing loss, intermediate Exp4 without WTC noise ARR 1.12 [1.03, 1.22], and very high Exp4 with WTC noise ARR 1.51 [1.36, 1.68]).

This study found GRC members with more intense WTC exposures and WTC noise exposure had significantly elevated risk of persistent, post-September 11, 2001, incident hearing loss, tinnitus, and ear pain. The results of our sensitivity analyses were similar. Our results in GRC members without WTC noise exposure are also consistent with the direction and magnitude of the associations observed in studies of people who had WTC exposures, including FDNY firefighters and EMS workers, disaster-affected area nonresponders, as well as WTC Health Registry rescue and recovery workers.^28–32 Among the GRC sample, the risk was greatest for those with high and very high WTC exposure who were also exposed to noise while working on the WTC effort. Similarly, for the WTC Health Registry studies, the highest rates of hearing impairment were found in those who had dust cloud exposure during which they reported being unable to hear.^29,30 The shorter observation time between first and last visits in members without hearing impairment does not reflect underidentification among them as their retrospective reporting period began from their date of birth (per the questions “have you ever had”). Case follow-up time-to-event was substantially shorter than the follow-up times of members without hearing impairment, so follow-up duration was unlikely to meaningfully bias the results, as reflected in the proportional hazards results.

Evidence suggests that noise exposure increases the risk of hearing impairment and exacerbates the effects of other environmental exposures.^8,14,15 Members employed in construction, telecommunications, and other installation and repair and in transportation and material moving before the attack may also have had past occupational exposure to noise and hand-arm vibration that contributed to their hearing impairment; however, excluding occupation on September 10, 2001, from the log binomial analyses did not meaningfully change the associations.^15,40 These members had elevated risks of hearing loss compared with members occupied in protective services. While military service has been associated with increased risk of hearing loss, very few members who were engaged in protective services were in jobs directly related to the military on September 10, 2001.¹² Some evidence suggests exposure to air pollution and solvents such as those present in the WTC collapse are also associated with hearing impairment.^8,16 Thus, the associations observed between WTC exposures and hearing impairment are coherent with biologic mechanisms leading to hearing impairment.

The study strengths include a 22-year cohort of nearly 50,000 members. The data are captured by five clinical centers that serve WTC responders in the New York—New Jersey—Connecticut tristate area. The cohort sample size supported the assessment of the adjusted log binomial regression analyses producing reasonably tight confidence limits. The only WTC exposure ARRs to cross the null value for the associations of WTC exposure with hearing loss, tinnitus, and ear pain was the sparse category of GRC members who had very high Exp4 but no WTC noise. The strength of the associations was similar for hearing loss and ear pain, with weaker associations observed for tinnitus. However, consistent dose-response patterns of level and duration with WTC noise exposures were evident across all analyses. We believe that our results are generalizable to the full GRC as 92% attending monitoring visits between July 1, 2002, and June 30, 2024, consented to their data being used for research, with 89% included in these analyses and results.

The study weaknesses include the use of self-reported outcomes, possible underadjustment of potential confounders, and lack of direct evidence to explain the mechanisms of hearing impairment. Most of the evidence regarding the associations of WTC exposures and hearing problems is based upon self-reported outcomes.^28–31 While agreement between self-reported and audiometric assessment of hearing loss varies somewhat by age, sex, and race, it is a more objective measure than self-reported status with an accuracy generally above 70%.⁴¹ One study conducted in FDNY firefighters and EMS workers compared the results of examinations, conducted in sound booths within 2 years of WTC exposure and the last examination before September 11, 2001, of pure-tone audiograms using supra-aural earphones.³² That study found smaller associations of short-term low and high frequency hearing loss than we observed with Exp4 and WTC noise, similar to those we observed with Exp4 in GRC without WTC noise exposure. The consistency of the associations of WTC exposures with both self-reported and examination-based hearing loss and the stronger joint associations of WTC noise and other WTC exposures also supports the validity of our self-reported outcomes and results.

Our analyses adjusted for occupation on September 10, 2001, as a surrogate measure of occupational exposures. The analyses did not adjust for comorbidities other than having overweight or obese status at the members’ first monitoring visit. The Exp4 WTC noise associations from our unadjusted models were somewhat suppressed by the adjusted analyses confounder variables. Nevertheless, our data were insufficiently sound to adjust for other occupational exposures and head injury, and we did not have information regarding risk factors such as genetic susceptibility or premature birth.

Noise can mechanically, ischemically and/or metabolically damage the inner ear sensory hair cells and cause permanent or temporary hearing impairment.⁷ The fact that exposure to WTC noise systematically increased the risk of hearing impairment above and beyond that of level and duration of WTC exposures suggests some increased risk may be due to acceleration of sensorineural impairment. Our data cannot directly test the mechanisms leading to hearing loss in the GRC.

Current evidence indicates that the level of GRC on-site WTC work and WTC-related noise exposures is associated with increased risk and incidence of hearing loss. Twenty-five percent of GRC reported persistent hearing loss and 40% reported some persistent hearing impairment. The associations for WTC exposure and increased risk of hearing loss, with its broad health and social consequences, are consistent across the general responders, FDNY firefighters and EMS workers, and the WTC Health Registry members. This study clarifies the importance of WTC-noise exposure when evaluating the effects of WTC exposures on hearing loss.

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