Occupational exposures to nitrous oxide (N20) were measured in numerous dental operatories. In all cases, the National Institute of Occupational Safety and Health (NIOSH) recommended time-weighted average (for one operation) of 25 ppm was exceeded by wide margins (NIOSH considers 50 ppm to be attainable in dental operatories). However, a new risk assessment is necessary to determine appropriate exposure limits. Many of the operatories were not equipped with scavenging systems and none of them used a scavenging device in combination with a local exhaust ventilation system. Scavenging devices and local exhaust ventilation should be used to control nitrous oxide exposures. Leaks in N20 delivery systems, which were found to be commonplace, should also be controlled. Research and development efforts are needed to improve upon the already existing scavenging devices, and provision for local exhaust ventilation needs to be included in the design of dental operatories.
Although nitrous oxide (N2O) has been widely used since 1844, in recent years it has been implicated in a number of serious health hazards such as reproductive, nerve, liver, and kidney disorders. The National Institute of Safety and Health (NIOSH) recommends a limit of 25 ppm for chronic exposure to N2O in the dental office. Our study monitored ambient N2O levels in the dental office. N2O levels were compared for procedures performed in open clinics and private operatories as well as with and without a gas-scavenging system. Measurements were taken in the Dental Breathing Zone (DBZ) and Dental Chair Foot (DCF) at regular intervals. A four- to eightfold increase in average N2O levels was noted in the DBZ for unscavenged versus scavenged procedures. A three- to fourfold increase for unscavenged versus scavenged procedures was similarly noted in the DCF. N2O were significantly higher in private operatories than in open clinics, due to limited room volumes and in the DBZ over the DCF, due to mask leakage and increased oral exhalation. Scavenged N2O levels for both operatory types did not meet NIOSH guidelines. In contrast to previous studies using any form of gas removal, our study shows a significant decrease in N2O level achieved with an adequate scavenger system. With only four states regulating the use of N2O, and with concern over its deleterious effects growing, additional states and the federal government are expected to enact legislation regulating the use of N2O in the near future.
This paper presents the successful design and implementation of several exhaust ventilation systems in a paint manufacturing factory. The ventilation systems were designed based on American Conference of Governmental Industrial Hygienists recommendations. The duct works, fans, and other parts were made and mounted by local manufacturers. The concentrations of toluene and xylene as the common solvents used in paint mixing factories were measured to evaluate the role of ventilation systems in controlling the organic solvents. Occupational exposure to toluene and xylene as the major pollutants was assessed with and without applying ventilation systems. For this purpose, samples were taken from breathing zone of exposed workers using personal samples. The samples were analyzed using Occupational Safety and Health Administration analytical method No.12. The samples were quantified using gas chromatography. The results showed that the ventilation systems successfully controlled toluene and xylene vapors in workplace, air well below the recommended threshold limit value of Iran (44.49 and 97.73 ppm, respectively). It was also discovered that benzene concentration in workplace air was higher than its allowable concentrations. This could be from solvents impurities that require more investigations.
Exhaust ventilation systems; occupational exposure; paint manufacturing; ventilation standard
The exposure of midwives to nitrous oxide in four hospitals was measured with personal samplers. In three of the four hospitals the average exposure was not significantly less than 100 parts per million (ppm). In one hospital the average exposure was 360 ppm; this was reduced by a factor of about 2.5 when a trial scavenging system was used. Differences in working practices and in the layout, size, and ventilation of the labour suites contributed to the observed differences in average exposure. Midwives and other staff working in the labour room are potentially at risk from excessive occupational exposure to nitrous oxide.
Aims: To compare environmental and biological monitoring of midwives for nitrous oxide in a delivery suite environment.
Methods: Environmental samples were taken over a period of four hours using passive diffusion tubes. Urine measurements were taken at the start of the shift and after four hours.
Results: Environmental levels exceeded the legal occupational exposure standards for nitrous oxide (100 ppm over an 8 hour time weighted average) in 35 of 46 midwife shifts monitored. There was a high correlation between personal environmental concentrations and biological uptake of nitrous oxide for those midwives with no body burden of nitrous oxide at the start of a shift, but not for others.
Conclusions: Greater engineering control measures are needed to reduce daily exposure to midwives to below the occupational exposure standard. Further investigation of the toxicokinetics of nitrous oxide is needed.
A number of tasks in construction generate worker overexposures to respirable crystalline silica dust, which is a significant contributor to occupational mortality and morbidity. This study evaluated the performance of commercially available engineering controls used in dusty construction tasks commonly performed by bricklayers.
Local exhaust ventilation (LEV) controls for a portable abrasive cutter and for tuckpointing grinders were examined at a bricklayers' training center, as were two stationary wet saws. Personal breathing zone air samples were collected with and without the use of LEV or water suppression during simulated concrete block cutting, brick cutting, and tuckpointing.
Compared with the use of no exposure control during block and brick cutting, the portable LEV unit significantly reduced mean respirable quartz exposures by 96% for block cutting and 91% for brick cutting (p<0.01). The use of stationary wet saws was also associated with 91% reductions in exposure (p<0.01). For tuckpointing, the reductions in mean respirable quartz concentrations were between 91% and 93% with the LEV controls (p<0.05).
Reductions of up to 96% in mean respirable quartz concentration were observed between control and no-control scenarios. These reductions with commercially available off-the-shelf tools demonstrate the effectiveness of engineering control interventions to reduce crystalline silica exposures in construction. Strategies to further improve control performance and approaches for increasing control interventions in construction are needed.
Nitrous oxide (N2O) is the oldest anesthetic in routine clinical use and its occupational exposure is under regulation by many countries. As studies are lacking to demonstrate the status of nitrous oxide levels in operating and recovery rooms of Iranian hospitals, we aimed to study its level in teaching hospitals of Tehran University of Medical Sciences.
During a 6-month period, we have measured the shift-long time weighted average concentration of N2O in 43 operating and 12 recovery rooms of teaching hospitals of Tehran University of Medical Sciences.
The results show that the level of nitrous oxide in all hospitals is higher than the limits set by different countries and anesthetists are at higher risk of exposure. In addition, it was shown that installation of air ventilation could reduce not only the overall exposure level, but also the level of exposure of anesthetists in comparison with other personnel.
The high nitrous oxide level in Iranian hospitals necessitates improvement of waste gas evacuation systems and regular monitoring to bring the concentration of this gas into the safe level.
Nitrous oxide occupational health; Ventilation; Environmental monitoring; Iran
Healthy young and elderly males were administered sedative concentrations of nitrous oxide/oxygen (N2O/O2) under a protocol designed to mimic that used in a dental operatory. Samples of end-tidal expired gas were taken at the end of 30-minutes inhalation of, and periodically for 70 minutes after withdrawal from, nitrous oxide/oxygen. Samples were analyzed to monitor the decline of alveolar nitrous oxide levels and any changes in alveolar carbon dioxide levels, to determine if there were any age-related differences. The fall in alveolar N2O following cessation of administration was rapid, and in a double-exponental manner as was expected. No age-related difference in N2O decline was observed. Alveolar carbon dioxide (CO2) levels were lower and more variable in the elderly group. Both groups exhibited elevated CO2 levels at the end of the N2O period, and an unexplained rise in CO2 at approximately 30 min post N2O.
The morphology of the bone marrow of 21 dentists who habitually used nitrous oxide in their surgeries was investigated. Exposure to nitrous oxide was measured with an atmospheric sampling device, and each dentist was invited to fill in a questionnaire giving details of medical history, diet, and intake of alcohol. During the trial a full neurological and haematological investigation was carried out and a bone marrow aspirate was examined both morphologically and by the deoxyuridine suppression test. Mean exposures to nitrous oxide ranged from 159 to 4600 parts per million. In all subjects serum vitamin B12 and folate concentrations were within normal limits. Abnormal results of deoxyuridine suppression tests were obtained in three of the 20 dentists tested; two of these three had abnormal white cells in their peripheral blood films. This study provides direct evidence that occupational exposure to nitrous oxide may cause depression of vitamin B12 activity resulting in measurable changes in bone marrow secondary to impaired synthesis of deoxyribonucleic acid.
The occupational exposure of hospital staff to inhaled anaesthetics was investigated using a personal sampling device that provides a measure of the average concentrations breathed by a person over a period of time, as distinct from the spot sampling in the general environment. The anaesthetist's average exposure to nitrous oxide and halothane during complete operating sessions was twice that expected from simple dilution of the escaping gases by the operating room ventilation. The sampling technique was also used to evaluate the effect of (1) redirection of the waste gas outflow; (2) active scavenging connected to the piped vacuum system. Short-period studies under controlled conditions in the operating theatres and anaesthesia induction rooms showed that the anaesthetist's exposure could be reduced two- or fourfold by redirecting the outflow and another four- to sixfold by active scavenging. Exposures during complete operating sessions were reduced two- to seven-fold by scavenging.
Health care workers (HCW) are exposed to ribavirin aerosol during therapy of infants with respiratory syncytial virus infections. To assess the degree of HCW exposure, we analyzed air samples from patient rooms and HCW personal breathing zones during ribavirin aerosol delivery by ventilator (two samples), oxygen hood (two samples), and a new vacuum exhaust hood (four samples). HCW exposure to ribavirin during aerosol delivery by ventilator or vacuum exhaust hood system was substantially lower than HCW exposure during aerosol delivery by oxygen hood in rooms with adequate ventilation.
Phenol is not reliable as a biomarker for exposure to benzene at concentrations below 5 ppm (8-hr time-weighted average [TWA]). S-Phenylmercapturic acid (S-PMA) and trans-trans-muconic acid (tt-MA), two minor urinary metabolites of benzene, have been proposed as biomarkers for low-level exposures. The aim of this study was to compare their suitability as biomarkers. S-PMA and tt-MA were determined in 434 urine samples collected from 188 workers in various settings in the petrochemical industry and from 52 control workers with no occupational exposure to benzene. Benzene concentrations in the breathing zone of the potentially exposed workers were assessed by personal air monitoring. Strong correlations were found between S-PMA and tt-MA concentrations in end-of-shift samples and between either of these parameters and airborne benzene concentrations. Exposure to 1 ppm benzene (8-hr TWA) leads to an average concentration in end-of-shift samples of 21 mol S-PMA and 1.5 mmol tt-MA per mol creatinine. Of an inhaled dose of benzene, on average 0.11% (range 0.05-0.26%) was excreted as S-PMA with an apparent elimination half-life of 9.1 (standard error [SE] 0.7) hr and 3.9% (range 1.9-7.3%) as tt-MA with a half-life of 5.0 (SE 0.5) hr. Due to its longer elimination half-life, S-PMA proved a more reliable biomarker than tt-MA for benzene exposures during 12-hr shifts. Specificity of S-PMA, but not tt-MA, was sufficient to discriminate between the 14 moderate smokers and the 38 nonsmokers from the control group. The mean urinary S-PMA was 1.71 (SE 0.27) in smokers and 0.94 (SE 0.15) mol/mol creatinine in nonsmokers (p = 0.013). The mean urinary tt-MA was 0.046 (SE 0.010) in smokers and 0.029 (SE 0.013) mmol/mol creatinine in nonsmokers (p = 0.436). The inferior specificity of tt-MA was due to relatively high background values of up to 0.56 mmol/mol creatinine, which may be found in nonexposed individuals and limits the use of tt-MA to concentrations of benzene over 1 ppm (8-hr TWA). We conclude that S-PMA is superior to tt-MA as a biomarker for low-level benzene exposures because it is more specific, enabling reliable determination of benzene exposures down to 0.3 ppm (8-hr TWA), and because its longer half-life makes it more suited for biological monitoring of operators working in shifts longer than 8 hr.
Acrolein is a common air pollutant that is present in high concentrations in wood, cotton, and tobacco smoke, automobile exhaust and industrial waste and emissions. Exposure to acrolein containing environmental pollutants such as tobacco smoke and automobile exhaust has been linked to the activation of the coagulation and hemostasis pathways and thereby to the predisposition of thrombotic events in human. To examine the effects of acrolein on platelets, adult male C57Bl/6 mice were subjected acute (5 ppm for 6 h) or sub-chronic (1 ppm, 6h/day for 4 days) acrolein inhalation exposures. The acute exposure to acrolein did not cause pulmonary inflammation and oxidative stress, dyslipidemia or induce liver damage or muscle injury. Platelet GSH levels in acrolein-exposed mice were comparable to controls, but acrolein-exposure increased the abundance of protein-acrolein adducts in platelets. Platelets isolated from mice, exposed to both acute and sub-chronic acrolein levels, showed increased ADP-induced platelet aggregation. Exposure to acrolein also led to an increase in the indices of platelet activation such as the formation of platelet-leukocyte aggregates in the blood, plasma PF4 levels, and increased platelet-fibrinogen binding. The bleeding time was decreased in acrolein exposed mice. Plasma levels of PF4 were also increased in mice exposed to environmental tobacco smoke. Similar to inhalation exposure, acrolein feeding to mice also increased platelet activation and established a pro-thrombotic state in mice. Together, our data suggest that acrolein is an important contributing factor to the pro-thrombotic risk in human exposure to pollutants such as tobacco smoke or automobile exhaust, or through dietary consumption.
Acrolein; Platelets; Platelet Factor 4; fibrinogen binding
This study was conducted to determine the impact of diesel exhaust inhalation on the fetus. Seventy-two pregnant rats and 18 nonpregnant rats were divided into three groups: a group exposed to total diesel engine exhaust containing 5.63 mg/m(3) particulate matter, 4.10 ppm nitrogen dioxide, and 8.10 ppm nitrogen oxide; a group exposed to filtered exhaust without particulate matter; and a group exposed to clean air. The exposure period was from day 7 until day 20 of pregnancy. In addition, 15 pregnant rats were treated with aromatase inhibitors or testosterone to clarify the process by which diesel exhaust exerts its toxicity. The anogenital distance was significantly longer in male and female fetuses from both exhaust-exposed groups than in those of the control. Differentiation of the testis, ovary, and thymus was delayed and disturbed. Maternal testosterone and progesterone levels, which increased due to pregnancy whether or not the rats were exposed, were significantly higher and lower, respectively, in the pregnant rats exposed to total exhaust and filtered exhaust. The serum adrenocorticotropic hormone (ACTH) level and urinary excretion of 17-hydroxycorticosteroids (OHCS) did not differ among the pregnant groups. These results indicate that elevated testosterone did not result from elevated maternal adrenal function. The feto-placental-ovarian unit and inhibition of aromatase activity and synthesis caused by diesel exhaust inhalation might have played an essential role in the accumulation of testosterone. Since both exhaust-exposed groups showed almost the same reactions toward the inhalation, the gaseous phase must have included the relevant toxicants.
Recent adoption by the American Conference of Governmental Industrial Hygienists of a Threshold Limit Value of 50 ppm for an 8-hour average exposure to nitrous oxide (N2O) increases the likelihood for its regulation by state and federal occupational health agencies. This review outlines current information on the health risks of N2O inhalation to provide a basis from which safe and reasonably attainable exposure limits can be proposed. Although N2O was for many years believed to have no toxicity other than that associated with its anesthetic action, bone marrow depression in patients administered N2O for extended periods of time and neurological abnormalities in health care workers who inhaled N2O recreationally have disproved this notion. Retrospective surveys of dental and medical personnel have also linked occupational exposure to N2O with a number of health problems and reproductive derangements. Nitrous oxide reacts with the reduced form of vitamin B12, thereby inhibiting the action of methionine synthase, an enzyme that indirectly supports methylation reactions and nucleic acid synthesis. Many, if not all, of the nonanesthetic-related adverse effects of N2O may be ascribed to this action. Animal and human studies indicate that the toxic effects of N2O are concentration- and time-dependent. It is suggested that a time-weighted average of 100 ppm for an 8-hour workday and/or a time-weighted average of 400 ppm per anesthetic administration would provide adequate protection of dental personnel and be achievable with existing pollution control methods.
The results are given of environmental and clinical investigations in four card rooms where one of the latest systems of exhaust ventilation to control dust has been installed. The concentration of air-borne coarse dust particles, larger than 2 mm., was reduced by between 80% and 90% around the carding engines. The card rooms consequently looked less dusty. However, the concentrations of medium and fine sized dust particles were not always reduced and were actually increased in some places. In one mill, when the new control system had been running for three years, there was found to be no reduction in the prevalence of non-specific chest symptoms, and there was an increase in the number of those with chest tightness on Mondays, a symptom characteristic of byssinosis. Evidence is given of a similar failure to reduce the dust sufficiently in three other mills where the same exhaust system is installed.
There is an urgent need to extend the limited investigations reported here to a larger number of mills. Meanwhile there is a continuing morbidity and mortality from byssinosis. Until work in card rooms has been made safe and proved to be so, it is necessary to have regular measurement of dust conditions and for the workers to have periodical medical examinations to enable managements to be advised about the hazards in their mills and advice to be given to the individuals affected by the dust.
The National Institute for Occupational Safety and Health (NIOSH) in early 1974 began industrial hygiene studies of vinyl chloride exposed workers. Three VC monomer plants, three VC polymerization plants, and seven PVC fabrication plants were surveyed. V polymerization plant workers and workers in one job category in VC monomer plants were exposed to average levels above 1 ppm. The highest average exposure was 22 ppm. NIOSH health hazard evaluation studies since these initial surveys have primarily shown nondetectable levels of vinyl chloride. A NIOSH control technology study in 1977 showed that exposure levels in VC polymerization plants had been drastically reduced but exposure levels above 1 ppm were still found in several cases.
The mercury (Hg) content of dental-operatory wastewater has become an issue in many localities, and Hg removal is rapidly becoming a matter of concern for all dental clinics. This preliminary study tested the efficacy of polymers for the removal of Hg contaminants from the dental-unit wastewater stream. Two commercially available polymers were used to treat dental-operatory wastewater. Used separately, each polymer removed from 74.9% to 88.4% of the Hg from dental-wastewater supernatant. The polymers used in combination, within the recommended pH range, removed up to 99.9% of the total Hg from dental-wastewater supernatant. The estimated optimal concentration of the two polymers is approximately 2.33 ml of each per liter of waste, and more than 90% of the Hg may be removed with 0.13 ml/l. Results indicate that a combination of the two polymers may sufficiently reduce Hg levels to allow discharge of clarified supernatants into public sewer systems.
Extended tunnelled roadways requiring ventilation via exhaust stacks are an increasingly common solution to traffic congestion around the world. In response to community concerns about adverse health effects associated with emissions from a new road tunnel exhaust stack, despite no demonstrable change in local ambient air quality, we conducted a cross sectional study to test for an association between exposure to the exhaust stack emissions and the presence of eye, nose and throat symptoms.
Stack emissions were modelled and categorised into areas of high, medium and low levels of exposure to emissions. A telephone interview survey was conducted in these three zones. Multivariate analysis was undertaken using Cox Proportional Hazards modelling to estimate prevalence ratios between zones for eye, nose and throat symptoms.
The prevalence of eye, nose and throat symptoms in the study area were 50 percent, 67 percent and 33 percent respectively and did not differ between the exposure zones. The presence of these symptoms was associated with a measure of reported "environmental worry".
The study did not demonstrate a community wide health impact associated with modelled emissions but is unable to exclude the possibility of sensitive individuals being adversely affected.
This study is the first to measure exposure to waste nitrous oxide (N2O) in the dental work setting in a broad geographical region (25 states), with passive dosimeters, and for dental hygienists. Thirty-five dental hygienists who reported that they administered N2O and 20 dental hygienists who reported that they never administered N2O constituted the sample. The former (n = 35) received both a 40-hr dosimeter, which measured exposure during administration of N2O, and a 168-hr dosimeter, which measured exposure during all work hours. The latter (n = 20) received only the 168-hr dosimeter. Exposure was measured during 2 wk in April 1990. For all work hours, the mean ppm-hr was 3,636 and the mean time-weighted average (TWA) was 78 ppm. The corresponding means during administration were 2,754 ppm-hr and 842 ppm TWA. The data for dental hygienists with passive dosimeters were similar to previously reported findings for dentists as measured by infrared spectrophotometry and gas chromatography. Hygienists who worked in dental settings with scavenging equipment received higher average levels of exposure to N2O than did hygienists who worked in settings without scavenging.
Numerous potential problems have been associated with long term or occupational exposure to both nitrous oxide and halothane. Despite the lack of firmly established cause-and-effect relationships, particularly in humans, it would seem prudent to use techniques that minimize operator exposure. With this in mind, a scavenging system for use in both conscious sedation and general anesthetic techniques was developed which fulfills the requirements of both general dentists as well as those administering general anesthesia. This paper describes this system and its adaptation to the commonly used Magill circuit. It also briefly reviews the factors involved in potential toxicity caused by long term exposure to nitrous oxide and halothane.
Exposure to ultrafine particles (UFPs) from vehicle exhaust has been related to risk of cardiovascular and pulmonary disease and cancer, even though exposure assessment is difficult. We studied personal exposure in terms of number concentrations of UFPs in the breathing zone, using portable instruments in six 18-hr periods in 15 healthy nonsmoking subjects. Exposure contrasts of outdoor pollution were achieved by bicycling in traffic for 5 days and in the laboratory for 1 day. Oxidative DNA damage was assessed as strand breaks and oxidized purines in mononuclear cells isolated from venous blood the morning after exposure measurement. Cumulated outdoor and cumulated indoor exposures to UFPs each were independent significant predictors of the level of purine oxidation in DNA but not of strand breaks. Ambient air concentrations of particulate matter with an aero-dynamic diameter of ≤10 μm (PM10), nitrous oxide, nitrogen dioxide, carbon monoxide, and/or number concentration of UFPs at urban background or busy street monitoring stations was not a significant predictor of DNA damage, although personal UFP exposure was correlated with urban background concentrations of CO and NO2, particularly during bicycling in traffic. The results indicate that biologic effects of UFPs occur at modest exposure, such as that occurring in traffic, which supports the relationship of UFPs and the adverse health effects of air pollution.
comet assay; exposure; oxidative DNA damage; personal; traffic; ultrafine particles
BACKGROUND--Dental technician's pneumoconiosis is a dust-induced fibrotic lung disease of fairly recent origin. This study was carried out to estimate its occurrence in Sweden. METHODS--Thirty seven dental technicians in central and south eastern Sweden with at least five years of exposure to dust from cobalt chromium molybdenum (CoCrMo) alloys, identified by postal survey, agreed to undergo chest radiography and assessment of lung function and exposure to inorganic dust. RESULTS--Six subjects (16%; 95% confidence interval 6% to 23%) showed radiological evidence of dental technician's pneumoconiosis. The lung function of the study group was reduced compared with historical reference material. With local exhaust ventilation dust levels were generally low, whereas in dental laboratories without such equipment high levels of dust, particularly cobalt, were found. CONCLUSIONS--Pneumoconiosis may result from exposure to inorganic dust in the manufacturing of CoCrMo-based dental constructions. It is possible to reduce this hazard substantially by local exhaust ventilation.
To examine the effects of installing a mechanical ventilation system at a riding-school stable on indoor air quality and human and horse airways.
The intervention was the installation of mechanical ventilation in a riding-school stable. Carbon dioxide (CO2), ammonia, particles, horse allergen, microorganisms and endotoxins were measured in the stable. The stable-workers and riding-students completed a questionnaire and underwent the following tests: analysis of nasal lavage for inflammation biomarkers; levels of exhaled nitrogen oxide (NO); measurements of daily peak-expiratory flow (PEF). The horses were examined clinically by airway endoscopy and bronchoalveolar lavage (BAL) and were analysed for cytology and biomarkers.
Levels of CO2 were nearly halved and airborne horse allergen levels were markedly reduced (5–0.8 kU/m3) after the intervention. A decreased level of ultrafine particles was observed (8000–5400 particles/cm3) after the intervention, while total and respirable dust levels were mainly unchanged (200 and 130 μg/m3). Levels of microorganisms in surface samples decreased following the intervention, whereas airborne microorganisms and endotoxin increased. There was no significant change in human symptoms, PEF-variability, exhaled NO or inflammatory biomarkers in the nasal lavage. In horses, the mean score of lower airway mucus was significantly reduced together with the mean level of expression of interleukin-6 mRNA in BAL cells after the intervention.
The installation of a mechanical ventilation system resulted in an increased air exchange rate, as demonstrated by reduced levels of CO2, ammonia, ultrafine particles and horse allergen. There was no significant clinical effect on human airways, but there was a tendency for reduced inflammation markers. The results on the horses may indicate less impact on their airways after the intervention.
Airways; Biomarker; Horse; Human; Indoor air quality
OBJECTIVES: To examine the effect of occupational exposure to cyclohexane on the peripheral nervous system. METHODS: A nerve conduction study was performed on 18 workers exposed to cyclohexane in a luggage factory and on age and sex matched occupationally unexposed controls. 12 workers had been exposed to n-hexane (median 2.8 years) before the start of exposure to cyclohexane. To confirm the effect of exposure, a follow up study was performed on nine workers one year after the first study. The mean exposure to cyclohexane was 1.2 years in the first study. A symptom survey was performed. The exposure was measured by air sampling of the breathing zone of each worker. The urinary metabolite cyclohexanol was also monitored. RESULTS: The concentration of airborne cyclohexane ranged from 5 to 211 ppm. The urinary concentration of cyclohexanol ranged from 0.12 to 1.51 mg/l. There was a strong correlation between the cyclohexane exposure in personal air and urinary cyclohexanol. No differences were found in nerve conduction velocities (NCV) between workers exposed to cyclohexane and age and sex matched controls. The results of the follow up study showed significant improvements in peroneal motor NCV (P < 0.01) and sural sensory NCV (P < 0.05) and in ulnar motor distal latency (MDL, P < 0.05) and peroneal MDL (P < 0.05) compared with the first study. Although the past n-hexane exposure affected the first neurophysiological study, the effect had disappeared in the second study, one year later. CONCLUSION: Occupational exposure to the concentrations of cyclohexane experienced in this study had no adverse effects on the peripheral nervous system.