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10 secondary references because these new regulations do not bus and tramway drivers in Copenhagen, a negative associ- change this factor. ation between lung cancer and increased years of employment The National Institute for Occupational Safety and Health was found (Soll-Johanning 2003). Finally, a meta-analysis of (NIOSH) document of April 2004, Overtime and Extended 29 studies addressing occupational exposure to diesel exhaust Work Shifts: Recent Findings on Illnesses, Injuries, and Health and lung cancer showed that 21 of the 23 studies meeting the Behaviors, is not included in this review. This document inclusion criteria observed relative risk estimates greater than reviewed the literature and was consistent with this review one. A positive duration response was noted in all studies but did not add any new insight to the articles already gath- quantifying exposure (Bhatia 1998). ered on those issues. Several additional articles showing an association between exposure to diesel exhaust and lung cancer were found and listed in the secondary references. Three articles on lung can- REVIEW OF PRIMARY SOURCES cer referenced in the notice of proposed rulemaking draft of December 17, 2004, as sent to Office of Management and Bud- The summaries are divided into the following subsections get, are not included here because they did not address HOS cardiovascular disease, lung cancer, bladder cancer, WBV or cumulative exposure; they were surveillance/prevalence effects, musculoskeletal disorders, GI disorders, noise-induced studies. hearing loss, reproductive effects, effects of long work hours, effects of disruption of circadian rhythm, and effects of length of sleep. Bladder Cancer Several articles indicating an association between truck Cardiovascular Disease driving and bladder cancer were found. The most recent arti- Two articles addressed the issue of hours of work and dura- cle was selected for summary. The others can be found in the tion of exposure. A case-control study of the risk of myocar- secondary references. dial infarction (MI) from exposure to motor exhaust found a Three articles addressed the association between duration positive association, although results were not significant of exposure to diesel exhaust and bladder cancer. A popula- (Gustavsson Mar 2001). A case-control study of the risk of tion based case-control study in New Hampshire found a pos- MI from long working hours found a U-shaped relationship itive association between bladder cancer and tractor-trailer with mean working hours of 11 hr compared with working driving as well as a positive trend with duration of employ- 9 to 11 hr with a trend toward increasing risk with increasing ment (Colt 2004). A large retrospective cohort in Finland hours (Sokejima 1998). found increased standard incidence ratios for 6 types of can- Numerous articles were found on the association of cardio- cer in truck drivers. Cumulative exposure to diesel exhaust vascular disease and professional driving. These are included was negatively associated with all cancers except ovarian in the secondary references. cancer in women with high cumulative exposure (Guo 2004). A meta-analysis of 29 studies on bladder cancer and truck driv- ing found an overall significant association between high Lung Cancer exposure to diesel exhaust and bladder cancer as well as a dose- response trend. The authors concluded that diesel exhaust There are numerous articles reporting on an association exposure may result in bladder cancer, but the effects of mis- between lung cancer and work in occupations where there is classification, publication bias, and confounding could not be exposure to diesel exhaust and other combustion particles. fully taken into account (Boffetta Jan. 2001). Diesel exhaust is considered to be a probable lung carcino- gen by the U.S. EPA, the World Health Organization, and U.S. Department of Health and Human Services National WBV Effects Toxicology Program. In this review, four articles addressed the issue of hours of work and duration of exposure. As to objective findings of vertebral pathology, Heliovaara A large case-control study in Germany found a significant reported in 1987 on a case-control study of patients followed association between lung cancer and employment as a profes- for 11 years after completing a normal physical exam. Those sional driver, as well as evidence of a dose-response relation- discharged from a hospital with the diagnosis of herniated ship by years of exposure to diesel exhaust (Bruske-Hohlfeld lumbar intervertebral disc or sciatica were compared with 4 1999). An exposure-response analysis and risk assessment of controls each. In men, the risk of being hospitalized due to lung cancer and diesel exhaust found a significant increase in herniated lumbar disc or sciatica was lowest in professional lung cancer risk with increasing estimated cumulative expo- and related occupations, significantly higher in all other sure to diesel exhaust among workers in the trucking indus- groups, and highest in blue-collar workers in industry and try based on an historical extrapolation of elemental carbon motor vehicle drivers. The variation in the risk between occu- levels (Steenland Sept 1998). In a large case-control study of pational groups of women proved less but was nevertheless
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11 still apparent. In contrast, a Finnish case-controlled study of tected ears is 90 dBA limited to 8 hr per day. FMCSA has monozygotic twins published in 2002 did not find any sig- adopted a 90 dBA noise standard. nificant differences in vertebral degeneration between drivers In 1995, the Office of Motor Carriers conducted a study of and nondrivers over thousands of hours of estimated driving noise in CMVs (Robinson et al. 1997). The results of this time (Battie 2002). study showed that noise levels in CMV cabs as reported over A study of Danish professional drivers in 1996 found that the last 25 years (1970 to 1995) have decreased. Other envi- almost all men in occupations involving professional driving ronmental studies confirm that overall cab noise levels have had statistically significant elevated risks of being hospital- declined over this period as documented by several studies ized with prolapsed cervical intervertebral disc (Jensen 1996). and reported in Robinson (1997). This information was secured by following all economically This study found that the overall broadband sound pressure active men in Denmark, identified on January 1, 1981, and fol- level for the nine trucks evaluated was 89.1 dBA for eight lowed for first hospitalization with prolapsed cervical inter- conditions of highway driving. The truck-cab average of 89.1 vertebral disc until December 31, 1990. dBA was very close to the FMCSA permissible exposure Finally, based on these and other studies, a review done for limit of 90 dBA based on the OSHA 8-hr day TWA standard. the British Columbia Workers' Compensation Board in 1999 This study measured the noise exposure of 10 truck drivers concluded that "The data support a causal link between back during normal commercial runs of 8 to 18 hr. The noise was disorders and both driving occupations and whole body vibra- measured with rest breaks, meal breaks, and refueling breaks tion" (Teschke 1999). included, so they represented realistic projections of actual driver exposure. In a more recent study of a variety of models, makes, and Musculoskeletal Disorders age of tractors as well as routes that covered different types of Canadian terrain, noise exposure was measured (more than Studies addressing musculoskeletal disorders in truck driv- 400 measurements) under several conditions. The noise level ers by and large evaluate the effects of WBV and are included recorded ranged from 78 to 89 dBA, with a mean of 82.7 in that section. A questionnaire survey of Japanese truck dBA. Trucks with cabs mounted over the engine were quieter drivers found short resting time and irregular duty time to be than other trucks by about 2.6 dBA. When the radio was on significant risk factors for LBP. It also found positive but and the side window open the levels were regularly 85 dBA insignificant associations with long driving time in a day and in and in 10% of the cases above 90 dBA (Seshagiri 1998). a week but the hours were not quantified (Miyamoto 2000). A study of knee pain in taxi drivers found a significantly increased Reproductive Effects risk of knee pain in workers with >10 hr of daily driving. A sig- nificant dose-response trend was also seen (Chen April 2004). Two studies were reviewed that addressed years of driving and male reproductive function. Because this exposure dura- tion does not relate to daily or weekly driving hours, these GI Disorders articles are secondary references. A questionnaire study of auto workers in the Midwest found that schedule variability, evening shift, and number of hours Effects of Long Work Hours worked per week were significantly associated with adverse GI outcomes (Caruso Dec. 2004). In a study on employees from 45 companies in the Nether- lands, need for recovery scores (subjective measure of the self-perceived need to rest) were significantly elevated in Noise-Induced Hearing Loss those working 9 to 10 hr per day, >40 hr per week with fre- quent overtime (Jansen 2003). A literature review of recent The American College of Occupational and Environmen- empirical research on extended work hours and health con- tal Medicine in its 2002 statement on noise-induced hearing firms findings from studies on cardiovascular diseases, ill- loss noted the following: nesses leading to disability retirement, and subjectively reported ill health (van der Hulst 2003). . . . the risk of noise-induced hearing loss is considered to A review document published by NIOSH in April 2004 increase significantly with chronic exposures above 85 dBA titled "Overtime and Extended Work Shifts: Recent Findings for an 8-hr time-weighted average (TWA). In general, con- tinuous noise exposure over the years is more damaging than on Illnesses, Injuries, and Health Behaviors" (Publication interrupted exposure to noise which permits the ear to have a No. 2004-143), documents the lack of data on general health rest period. effects and even when looking at fatigue and accidents iden- tifying "differences between 8-hr and 12-hr shifts are difficult The Occupational Safety and Health Administration because of the inconsistencies in the types of work schedules (OSHA) noise exposure standard for the workplace for unpro- examined across studies. Work schedules differed by the time
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12 of day (i.e., day, evening, night), fixed versus rotating sched- In a thorough review of the literature on shift work and ules, speed of rotation, direction of rotation, number of hours health up to 1999 appearing as a chapter in a hardbound text worked per week, number of consecutive days worked, num- (Scott 2000), the author concludes that GI, cardiovascular ber of rest days, and number of weekends off." disease, and reproductive dysfunctions are more common in shift workers and that these effects may be due to shift work factors such as rotating or fixed shifts, number of nights Effects of Disruption of Circadian Rhythm worked consecutively, predictability of schedule, and length Two studies using experimental conditions to evaluate the of shift and starting time. Exacerbation of medical conditions effect of circadian rhythm disruption on insulin secretion such as diabetes, epilepsy, psychiatric disorders as well as the found increased insulin resistance and glucose response asso- diseases noted above may occur due to sleep deprivation and ciated with a longer sleep-wake cycle such as that which might circadian rhythm disruption. be found with rotating shift work (Morgan 1998). Two-hundred sixty-one shift workers completed the stan- Effects of Length of Sleep dard shift work index in an investigation of health and well- being (Barton 1994). Workers on an advancing system were No articles were found that demonstrated a clear health more likely to complain of digestive and cardiovascular (CV) impact of increasing sleep time during the work week from disorders then those on a delayed rotating system. Authors con- 6 hr (reflecting the sleep time that could occur with 8 hr off cluded that the combination of direction of rotation and length work allowing for travel time) to 8 hr (reflecting the sleep of break when changing from one shift to another may be a crit- time that could occur under the new regulations with 10 hr ical factor in the health and well-being of shift workers. off work).