An outbreak of N-hexane induced polyneuropathy among press proofing workers in Taipei

[Neuropathy in n-hexane poisoning]

N-Hexane is a solvent widely used in manufacturing as a cleaner, degreaser and component of rubber cement. Chronic exposure to n-hexane either through contact with unprotected skin or inhalation can lead to the development of clinical symptoms and electrophysiological changes similar to those of inflammatory demyelinating polyneuropathy which requires careful differential diagnosis. This article presents three cases of severe predominantly motor polyneuropathy with demyelinating features in 15- and 16-year-old adolescents. The results of laboratory tests were within normal limits; electroneuromyography revealed symmetrical involvement of sensory and motor fibers of the nerves of the legs and arms with a decrease in the speed of propagation of excitation and conduction blocks. Sural nerve biopsy revealed intraneural and perineural swelling without any signs of inflammation or fibrosis confirming the genesis of the neuropathy. Despite a relatively favorable prognosis there is no specific therapy for hexane poisoning and the recovery period can last up to several years.

The Role of Protein Adduction in Toxic Neuropathies of Exogenous and Endogenous Origin

The peripheral (axonal) neuropathy associated with repeated exposure to aliphatic and aromatic solvents that form protein-reactive γ-diketones shares some clinical and neuropathological features with certain metabolic neuropathies, including type-II diabetic neuropathy and uremic neuropathy, and with the largely sub-clinical nerve damage associated with old age. These conditions may be linked by metabolites that adduct and cross-link neuroproteins required for the maintenance of axonal transport and nerve fiber integrity in the peripheral and central nervous system.

n-Hexane intoxication in a Chinese medicine pharmaceutical plant: a case report

BACKGROUND

n-Hexane is a well-known neurotoxicant. Polyneuropathy due to occupational n-hexane exposure has been reported worldwide, however, our case is the first report in the Chinese herb industry.

CASE PRESENTATION

A 25-year-old Asian man experienced progressive weakness and numbness in his hands and feet after working as an operator in a Chinese medicine pharmaceutical plant for the manufacture of Chinese herbal pain relief patches for 10 months. Electrophysiological studies indicated a reduction in nerve conduction velocity, prolongation of distal latencies, mildly positive sharp waves, and reduced recruitment with polyphasic potentials, particularly at distal sites. Demyelination with axonal degeneration caused by occupational n-hexane exposure was strongly suspected. Through investigation of our patient's workplace, the ambient n-hexane concentration in air was found to considerably exceed the permissible exposure limit/time-weighted average for n-hexane in Taiwan. His symptoms were gradually relieved after 4 months of cessation of exposure to n-hexane. He was then confirmed as a case of occupational n-hexane intoxication. Further effective control measures should be implemented as soon as possible to prevent exposure of workers to n-hexane.

CONCLUSIONS

Despite a typical clinical presentation, his exposure at workplace was appropriately investigated. Chemical exposure in Chinese medicine pharmaceutical plants could be an emerging issue that may affect workers' health. The lack of knowledge and management of solvents could endanger the health of workers. This case has profound educational implications for occupational health and is worthy of further follow-up for improving hazards control.

Occupational neurotoxic diseases in taiwan

Occupational neurotoxic diseases have become increasingly common in Taiwan due to industrialization. Over the past 40 years, Taiwan has transformed from an agricultural society to an industrial society. The most common neurotoxic diseases also changed from organophosphate poisoning to heavy metal intoxication, and then to organic solvent and semiconductor agent poisoning. The nervous system is particularly vulnerable to toxic agents because of its high metabolic rate. Neurological manifestations may be transient or permanent, and may range from cognitive dysfunction, cerebellar ataxia, Parkinsonism, sensorimotor neuropathy and autonomic dysfunction to neuromuscular junction disorders. This study attempts to provide a review of the major outbreaks of occupational neurotoxins from 1968 to 2012. A total of 16 occupational neurotoxins, including organophosphates, toxic gases, heavy metals, organic solvents, and other toxic chemicals, were reviewed. Peer-reviewed articles related to the electrophysiology, neuroimaging, treatment and long-term follow up of these neurotoxic diseases were also obtained. The heavy metals involved consisted of lead, manganese, organic tin, mercury, arsenic, and thallium. The organic solvents included n-hexane, toluene, mixed solvents and carbon disulfide. Toxic gases such as carbon monoxide, and hydrogen sulfide were also included, along with toxic chemicals including polychlorinated biphenyls, tetramethylammonium hydroxide, organophosphates, and dimethylamine borane. In addition we attempted to correlate these events to the timeline of industrial development in Taiwan. By researching this topic, the hope is that it may help other developing countries to improve industrial hygiene and promote occupational safety and health care during the process of industrialization.

Association between metabolic gene polymorphisms and susceptibility to peripheral nerve damage in workers exposed ton-hexane: A preliminary study

Chronic exposure to n-hexane may result in peripheral neuropathy. 2,5-Hexanedione (2,5-HD) has been identified as a toxic metabolite of n-hexane. The CYP2E1, CYP1A1 and GST genes are involved in the formation of 2,5-hexanedione from n-hexane as well as the elimination of 2,5-HD-formed electrophile, and these genes are highly polymorphic in the general population. A nested case-control study in an industrial cohort was conducted to evaluate the associations between polymorphisms in these metabolic genes and n-hexane-induced peripheral nerve damage. The study subjects included 22 cases, who worked in a printing factory with symptoms of peripheral nerve damage, and 163 controls, who came from the same factory of cases. DNA was extracted from blood samples and genotyping was conducted for CYP2E1 Pst, CYP2E1 Dra, CYP2E1 Ins96, CYP1A1 Msp, GSTT1 null, GSTM1 null and GSTP1 105V. Unconditional logistic regression was applied to estimate the odds ratio and 95% confidence intervals. There were no significant differences between the two groups regarding age, sex, smoking and alcohol status. A significant association between Dra polymorphism and peripheral nerve damage was found. The frequency of CYP2E1 Dra homozygous mutation in the case group (18.2%) was higher than that in the control group (3.7%, p=0.015). Individuals with homozygote genotype (CC) of CYP2E1 Dra had a significantly higher risk of peripheral nerve damage compared with those with DD genotype (adjusted OR=?.58, 95% CI=1.32-23.65) after n-hexane exposure duration, sex, age, smoking and alcohol status were adjusted. No significant association was found that CYP2E1 Pst, CYP2E1 Ins96, CYP1A1 Msp, GSTT1, GSTM1, GSTP gene polymorphisms associated with the susceptibility of peripheral nerve damage. These findings suggested that CYP2E1 gene might increase the susceptibility to n-hexane-induced peripheral damage.

Worker exposure to volatile organic compounds in the vehicle repair industry

This study evaluated exposures among vehicle repair technicians to hexane, acetone, toluene, and total volatile organic compounds (VOCs). On randomly selected workdays, we observed a characteristic pattern of solvent use among 36 technicians employed in 10 repair shops, each of which used an aerosol solvent product. We obtained quantitative exposure measurements from a subset of nine technicians (employed in three of these shops) who used an aerosol product containing hexane (25-35%), acetone (45-55%), and toluene (5-10%). The time-weighted average (TWA) exposure concentration for task-length breathing zone (BZ) samples (n = 23) was 36 mg/m(3) for hexane, 50 mg/m(3) for acetone, and 10 mg/m(3) for toluene. The TWA area concentrations (n = 49) obtained contemporaneously with BZ samples ranged from 25% to 35% of the BZ concentrations. The solvent emission rate (grams emitted/task time) was correlated with the total VOC exposure concentration (R(2) = 0.45). The proportions of VOCs in the BZ samples were highly correlated (r = 0.89 to 0.95) and were similar to those of the bulk product. Continuous exposure measurements for total VOCs (n = 1238) during 26 tasks produced a mean BZ VOC "pulse" of 394 mg/m(3) within 1 min following initiation of solvent spraying. The geometric mean air speed was 5.2 meters/min in the work areas (n = 870) and was associated with 0.8 air changes per minute in the BZ. The findings suggest that vehicle repair technicians who use aerosol solvent products experience episodic, inhalation exposures to the VOCs contained in these products, and the proportions of VOCs in the breathing zone are similar to those of the bulk product. Because acetone appears to amplify the severity and duration of the neurotoxic effects of n-hexane, products formulated with both hexane and acetone should be avoided. Further evaluation of exposures to VOCs is needed in this industry, along with information on effective alternatives to aerosol solvent products.

Are sperm parameters the best indicator of 2,5-hexanedione reproductive toxicity in male rats?

In this study on 40 male Wistar rats of approximately 3-weeks-old, the effects of 2,5-hexanedione on sperm principal parameters were examined by subcutaneously administering 100, 200 and 400 mg/(kgday) for 12 weeks. Other indicators of 2,5-hexanedione intoxication were examined: testes, epididymides, body weight, limb paralysis and histology. The sperm motility was adversely affected in all of the three treatment groups. No sperm motility at all was observed in the 200 and 400 mg/(kgday) treatment groups and rapid progressive motility was significantly reduced in the 100 mg/(kgday) group (P<0.05). The sperm concentration and morphology, testes, epididymides and body weight were significantly affected in the 200 and 400 mg/(kgday) groups but not in the 100 mg/(kgday) group (P<0.05). All the rats in the 400 mg/(kgday) group could not move due to leg paralysis, whereas only 50% of the rats in the 200mg/(kgday) group and none in the 100 mg/(kgday) were affected. Histological examination of the testes in the 400, 200 and 100 mg/(kgday) groups revealed Sertoli cell-only syndrome in 70, 30 and 0% of the rats, respectively. In conclusion, this study has shown that sperm motility was the most significantly sensitive indicator of 2,5-hexanedione intoxication in all the treatment groups.

Trichloroethylene--a review of the literature from a health effects perspective

This report reviews the literature on the impact of exposure to trichloroethylene (TCE) on human health. Special emphasis is given to the health effects reported in excess of national norms by participants in the TCE Subregistry of the Volatile Organic Compounds Registry of the National Exposure Registries--persons with documented exposure to TCE through drinking and use of contaminated water. The health effects reported in excess by some or all of the sex and age groups studied were speech and hearing impairments, effects of stroke, liver problems, anemia and other blood disorders, diabetes, kidney disease, urinary tract disorders, and skin rashes.

An investigation of the association between exposure to styrene and hearing loss

The importance of the association between advancing age and hearing loss is well recognized. Further, prolonged significant noise exposures are also known to result in permanent hearing loss. However, little is known of the contribution of industrial chemical exposures to hearing loss. Information available, from both animal and human studies, raises the possibility that certain aromatic hydrocarbons are ototoxic. The purpose of this study was to assess whether occupational styrene exposure causes hearing loss in a group of workers in the fiber-reinforced plastics manufacturing industry. The hearing acuity of 299 subjects was determined, using pure-tone screening audiometry, at the beginning of a single workshift and again at the end of the shift. On the same day, the personal, time-weighted average exposures of each subject to both styrene and noise were measured. In addition, information on the following factors was obtained from each participant: previous work history, including exposures to noise and chemicals; use of personal protective equipment for noise or solvents; personal and family history of hearing problems; and smoking history. Current exposures together with work histories were used to construct lifetime noise and styrene exposure indices. No conclusive evidence was found for a chronic styrene-induced effect on hearing acuity, when both noise and styrene lifetime exposures were taken into account. As expected, age and noise exposures were highly important variables, both positively associated with hearing loss. In addition, the detrimental effect of noise exposure on hearing acuity was found to be strengthened with increased age. Noise and styrene exposures were highly correlated, clearly illustrating the importance of considering all associated variables in analysis of such data. No evidence was found for a relationship between smoking, recreational noise, solvent exposures, and hearing loss.

Effect of exposure to 2,5-hexanediol in light or darkness on the retina of albino and pigmented rats. II. Electrophysiology

Albino (Sprague-Dawley) and pigmented (Norwegian Brown) male rats were exposed to 2,5-hexanediol (H; 1%) in their drinking water for 5 or 8 weeks, respectively. Half of the rats of each strain were housed in light (average 30 cd/cm2 inside cage, 12 h/day); the other half was kept in constant darkness. Control groups were studied in parallel under identical conditions but without H. Electrophysiological recordings were made 2-5 days and 13 weeks after the end of the exposure to H. Alterations in the visual system, as measured by electroretinography and visual evoked response, were found in groups of albino rats exposed to H and/or light. The pupillary diameter was enlarged in the albino group exposed to both H and light. Among the pigmented rats, alterations were recorded only in the visual evoked response of the H exposed groups. The results demonstrate that simultaneous exposure to H and light can lead to alterations in visual function that are more severe than those induced by each agent alone, and may exceed a simple summation.

N-hexane neuropathy in offset printers

In an offset printing factory with 56 workers, 20 (36%) developed symptomatic peripheral neuropathy due to exposure to n-hexane. Another 26 workers (46%) were found to have subclinical neuropathy. The initial change in the nerve conduction study was reduced amplitude of the sensory action potentials, followed by reduced amplitude of the motor action potentials, reduction in motor conduction velocities and increase in distal latencies. These changes indicate primary axonal degeneration with secondary demyelination. Sural nerve biopsy in a severe case showed giant axonal swellings due to accumulation of 10nm neurofilaments, myelin sheath attenuation and widening of nodal gaps. The development of neuropathy bore no direct relationship to the duration of exposure, hence factors such as individual susceptibility may be important. Optic neuropathy and CNS involvement were uncommon and autonomic neuropathy was not encountered.

Biological monitoring of occupational exposure to n-hexane by measurement of urinary 2,5-hexanedione

Occupational exposure to n-hexane in shoe factory workers was monitored by measuring urinary 2,5-hexanedione, the major metabolite of this solvent and the probable cause of peripheral neuropathy in exposed workers. Solvent pollution was monitored in the work environments of 189 employees, of whom 123 (65%) worked in Alicante, Spain, and 66 (35%) in Veneto, Italy. 2,5-Hexanedione was measured in spot urine samples collected from workers at the end of the shift. Information on working conditions was obtained from a previous study. A significant linear correlation was found between mean environmental concentration of n-hexane and urinary concentration of 2,5-hexanedione. The variability in the correlation may have been due to the variable use of protective clothing (gloves), and to variations in exposure during the working week. In numerous workers, percutaneous absorption of n-hexane represented as much as 50% of the total absorbed dose. Urinary concentrations of 2,5-hexanedione tended to increase during the working week. Simultaneous exposure to n-hexane and toluene tended to reduce urinary excretion of 2,5-hexanedione, whereas exposure to n-hexane and methyl ethyl ketone tended to increase excretion of the metabolite.

Autonomic and peripheral nervous system dysfunction in workers exposed to mixed organic solvents

To assess possible solvent-induced dysfunction of the autonomic and peripheral nervous systems, 11 solvent-exposed workers and 11 age-matched unexposed controls were examined using the coefficient of variation in electrocardiographic R-R intervals (CVRR) and the distribution of nerve conduction velocities (DCV). Two components of CVRR, i.e., the C-CVRSA and C-CVMWSA, were also examined, which are considered to reflect parasympathetic and sympathetic activities, respectively. The workers had been occupationally exposed to toluene and/or solvent mixtures such as thinners, for 35-360 months. In the solvent-exposed workers, the CVRR and C-CVRSA were significantly reduced compared with unexposed controls. Similarly, the faster velocities of the DCV and median nerve conduction velocities were significantly slowed. The reduction in the CVRR was significantly correlated with duration of exposure in the solvent-exposed workers. These data, despite the small sample size and the variety of organic solvents, suggest that organic solvents may affect both the faster myelinated nerve fibers and autonomic nervous activity (principally, parasympathetic component).

From conjecture and refutation to the documentation of occupational diseases in Taiwan

The documentation of occupational diseases in a developing country like Taiwan is a challenge to an occupational physician. For lack of a system including material safety data sheet (MSDS), workers are usually not aware of what chemicals they are exposed to. Since many occupational diseases have long latencies and do not show any specific symptoms and signs, recognition and identification of the occupational origin are often very difficult. Using databases which provide a relatively complete list of industrial chemicals and a set of specific signs and/or symptoms, combined with the epidemiologic approach of conjectures and refutations--i.e., considering and ruling out all possible alternative explanations--we have documented eight kinds of occupational diseases and an outbreak of botulism. We recommend that a similar approach be applied to any other country with a similar situation, and that a system involving an identification sheet (e.g., MSDS) for each chemical be advocated and implemented in such countries as one means to enable prompt recognition and prevention of occupational diseases.

The method of choice for the determination of 2,5-hexanedione as an indicator of occupational exposure to n-hexane

To identify the method of choice for analysis of urine for 2,5-hexanedione (2,5-HD) as an indicator of occupational exposure to n-hexane, the end-of-shift urine samples of 36 n-hexane exposed male workers and 30 non-exposed male workers were analyzed for 2,5-HD under three conditions of hydrolysis, i.e. enzymic hydrolysis at pH 4.8, acid hydrolysis at pH 0.5, and without hydrolysis. The 2,5-HD concentrations thus determined were examined for correlation with 8-h, time-weighted average exposure concentrations of n-hexane measured by diffusive sampling. The regression analysis showed that the 2,5-HD concentrations without any hydrolysis correlated best with the intensity of exposure to n-hexane. No 2,5-HD was detected in the urine of the non-exposed subjects under the analytical conditions with no hydrolysis. Thus, the analysis without hydrolysis was considered to be the method of choice from the viewpoint of simplicity in analytical procedures, sensitive separation of the exposed from the non-exposed, and quantitative increase in the amount of 2,5-HD after n-hexane exposure.

Patients with n-hexane induced polyneuropathy: a clinical follow up

The prognosis of hexacarbon induced polyneuropathy is usually good, though its clinical course after the cessation of exposure has not been described in detail. Eleven patients with moderate to severe n-hexane induced polyneuropathy due to occupational exposure were regularly followed up for a period of four years at the neurological department of the National Taiwan University Hospital. Sensorimotor neuropathy was diagnosed in nine patients and motor neuropathy in two. All were removed from further exposure to n-hexane after aetiological confirmation, but motor disturbance continued to worsen in five cases. Sensory functions were regained earlier than motor functions. All the patients, including one who was tetraplegic and confined to a wheelchair in the early stages, regained their full motor capabilities within one to four years. Three patients with severe neuropathy had residual muscle atrophy in the intrinsic foot and hand muscles. Signs of damage to the central nervous system, including increased tendon reflexes in two patients and leg tightness in six patients, emerged as muscle power was nearing complete recovery. The tightness of the legs gradually disappeared, but muscle cramps of the calves developed and these were still present at the end of follow up. Two patients had mild abnormal colour vision, and the abnormality was still detectable four years later. It is concluded that n-hexane induced neuropathy has a good prognosis, and that spasticity due to damage to the central nervous system is functionally reversible; muscle cramps and dyschromatopsia persist much longer.

Evoked potentials in chronic n-hexane intoxication

Somatosensory, brainstem auditory and pattern-reversal visual evoked potentials (SEP, BAEP and PVEP) were studied in 5 patients with n-hexane polyneuropathy to determine if the CNS was affected. In SEPs, the median central conduction (N13-to-N20) was normal but the tibial central conduction (N22-to-P40) was delayed. The central conduction time (I-to-V interval) of the BAEP was also prolonged. However, the P100 latency of the PVEP was normal. The present data indicate that the spinal cord and the brainstem are primarily affected in chronic n-hexane intoxication.

Neurophysiological approaches to the detection of early neurotoxicity in humans

Various neurophysiological methods, including electroencephalography, electromyography, nerve conduction velocities, and evoked potential techniques, have been used to detect early signs of neurotoxicity in humans. These methods have been applied to groups of occupationally exposed workers and their referents in epidemiologic studies, to patients with suspected or proven diseases after long-term work in toxic environment, and to human subjects during or after experimental exposure. The main body of knowledge arises from epidemiologic studies of occupationally exposed subjects, and several chemicals widely used in industry have been shown to be neurotoxic. Of these, e.g., lead causing peripheral neuropathy, some solvents like carbon disulfide, n-hexane, and methyl n-butyl ketone also causing neuropathy and at times central nervous system effects as well as acryl amide have been studied using neurophysiological approaches. Several other solvents including toluene, xylene, and various mixtures of organic solvents have been suspected to be neurotoxic, and nervous system effects have been ascribed to those in several neurophysiological studies. Some studies have elucidated acute nervous system effects of ethyl alcohol or industrial solvents in experimental situations applying, for example, evoked potential techniques or electroencephalography.

Neurotoxic effects of n-hexane on the human central nervous system: evoked potential abnormalities in n-hexane polyneuropathy

An outbreak of n-hexane polyneuropathy as a result of industrial exposure occurred in printing factories in Taipei area from December 1983 to February 1985. Multimodality evoked potentials study was performed on 22 of the polyneuropathy cases, five of the subclinical cases, and seven of the unaffected workers. The absolute and interpeak latencies of patterned visual evoked potential (pVEP) in both the polyneuropathy and subclinical groups were longer than in the normal controls. The pVEP interpeak amplitude was also decreased in the polyneuropathy cases. Brainstem auditory evoked potentials (BAEP), showed no difference of wave I latency between factory workers and normal controls, but prolongation of the wave I-V interpeak latencies was noted, corresponding with the severity of the polyneuropathy. In somatosensory evoked potentials (SEPs), both the absolute latencies and central conduction time (CCT) were longer in subclinical and polyneuropathy cases than in the unaffected workers and normal controls. From this evoked potentials study, chronic toxic effects of n-hexane on the central nervous system were shown.