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Biomedical subjects

W H Phoon

Publications and source records attributed to W H Phoon.

At least 37 records · Page 2Linked to original sources
PubMed1991

Biological monitoring of occupational exposure to tetrahydrofuran.

Occupational exposure to tetrahydrofuran (THF) was studied by analysis of environmental air, blood, alveolar air, and urine from 58 workers in a video tape manufacturing plant. Head space gas chromatography (GC) with an FID detector was used for determination of THF concentration in alveolar air, urine, and blood. Environmental exposure to THF was measured by personal sampling with a carbon felt passive dosimeter. When the end of shift urinary THF concentrations were compared with environmental time weighted average (TWA) values, urinary THF concentration corrected for specific gravity correlated well with THF concentration in air (r = 0.88), and uncorrected urinary THF concentration gave a similar result (r = 0.86). Correction for creatinine in urine weakened the correlation (r = 0.56). For exposure at the TWA concentration of 200 ppm the extrapolated concentration of THF was 33 mumol/l in blood and 111.9 mumol/l (61 mumol/g creatinine) or 109 mumol/l at a specific gravity of 1.018 in urine. The correlation between exposure to THF and its concentration in exhaled breath and blood was low (r = 0.61 and 0.68 respectively). Laboratory methodological considerations together with the good correlation between urinary THF concentration and the environmental concentration suggest that THF concentration in urine is a useful biological indicator of occupational exposure to THF.

Adult↗
PubMed1991

Monitoring of exposure to cyclohexanone through the analysis of breath and urine.

Occupational exposure to cyclohexanone was studied for 59 workers through the analysis of environmental air, alveolar air, and urinary cyclohexanol. Environmental cyclohexanone exposure was measured by personal sampling with a carbon-felt passive dosimeter. Cyclohexanone in alveolar air and cyclohexanol in urine were determined with gas chromatography with a flame ionization detector. The end-of-shift urinary cyclohexanol levels correlated well with the time-weighted average environmental cyclohexanone values (r = 0.66). Urinary cyclohexanol corrected for creatinine correlated best with cyclohexanone in air (r = 0.77); when corrected for specific gravity, it gave a similar correlation coefficient (r = 0.73). When the time-weighted average of the exposure was 25 ppm, the corresponding calculated concentration for urinary cyclohexanol was 54.5 mg/1, 23.3 mg/g of creatinine, or 43.5 mg/l at a specific gravity of 1.018. The relationship between cyclohexanone exposure and its concentration in exhaled breath was found to be poorer than that for cyclohexanone exposure and the urinary metabolite (r = 0.51).

Adolescent↗
PubMed1991

Silicosis and lung cancer among Chinese granite workers.

Of the 184 cases of silicosis registered between 1 January 1970 and 31 December 1984 in Singapore, all the relevant information was available for 159, which were linked to the population-based National Cancer Register for lung cancer. Nine cases of lung cancer were found. The standardized incidence ratio (SIR) was computed with the age- and calendar-specific incidence of lung cancer rates of Chinese males in Singapore as a basis. Excess risk of lung cancer was found (SIR 2.01, 95% confidence interval 0.92-3.81). Adjustment for smoking showed that it alone could not account for the excess lung cancer risk. There was an increasing, but not significant, trend with increasing severity of silicosis and exposure duration. The results suggest that the severity of silicosis and possibly exposure to free silica may have contributed to the excess of lung cancer among the cases of silicosis studied.

Cohort Studies↗
PubMed1991

Pulmonary effects of polyvinyl chloride dust exposure on compounding workers.

Spirometry, chest radiography, environmental measurements, and a questionnaire on respiratory symptoms were used to evaluate the effects of exposure to polyvinyl chloride (PVC) dust on 171 Chinese and Malay PVC compounding workers in comparison with an unexposed reference group. Workers with high cumulative PVC dust exposure had a lower forced expiratory volume in 1 s and forced vital capacity, and a higher prevalence of radiological profusion of small opacities. Wheezing or chest tightness was also significantly more frequent in this group. Unlike previous studies, the PVC compounding workers in this study were exposed to only negligible amounts, if any, of vinyl chloride monomer or thermal degradation products of PVC such as hydrogen chloride, phosgene, or chlorine. The conclusion was drawn that a low grade of pneumoconiosis and a small degree of lung function impairment is associated with PVC dust exposure. Reversible airways obstruction is also likely and warrants further investigation.

Adult↗
PubMed1991

Occupational asthma in Singapore--a review of cases from 1983 to 1990.

One of the newer occupational diseases in Singapore is occupational asthma. As on 31 December 1990 there were 35 confirmed cases of occupational asthma in the official statistics on occupational disease. We report in this paper our observations and experience based on these cases. The problem of under-reporting and the importance of early diagnosis are discussed.

Adolescent↗
PubMed1991

Diurnal variation in peak expiratory flow rate among polyvinylchloride compounding workers.

The diurnal variation in peak expiratory flow rate (PEFR) was studied in 24 mixers and 24 non-mixers in three polyvinylchloride (PVC) compounding plants and 24 non-PVC controls from a marine police workshop. The three groups (all men) were matched for age, race, and smoking. The mean respirable dust concentration (essentially PVC dust) was 1.6 mg/m3 for mixers and 0.4 mg/m3 for nonmixers. The mean diurnal variation in PEFR of the mixers was 6.5%. This was significantly higher than the 4.8% for non-mixers and 4.3% for the non-PVC controls. Six mixers had a diurnal variation of more than 15% on at least one day compared with none among the other two groups. Twenty nine per cent of mixers complained of wheezing compared with 4% of non-mixers and none among non-PVC workers. These differences were significant. Forced expiratory volume in one second (FEV1) for the mixers was 10% below the predicted values whereas that of non-PVC workers was 2% below predicted values. The study indicates a significant acute airway constriction from occupational exposure to PVC dust.

Adult↗
PubMed1990

Statutory medical examinations and designated factory doctors in Singapore.

This paper describes the system of statutory medical examinations introduced in Singapore since 1985 and the role of designated factory doctors, as well as the progress of the system, problems and issues involved. The basic objective of the system is to ensure that workers in special risk occupations are fit for such work. Factory workers exposed to any of 14 prescribed hazards must undergo specific medical examinations and tests by designated factory doctors who are trained and registered with the Labour Ministry. Abnormal work-related cases are notified to the Ministry for further investigation. Currently there are 330 designated factory doctors and each year, over 38,000 workers are examined, 88 per cent for noise exposure. The system provides opportunities for early detection of both occupational and non work-related abnormalities, individual counselling and timely preventive action. It also complements industrial hygiene monitoring activities in the evaluation of health hazards and promotes self-regulation. To enhance the effectiveness of the system, the doctors must be properly trained and some degree of supervision is needed, particularly with regard to accuracy and interpretation of laboratory results, emphasis on counselling and re-orientation and updating of knowledge.

Environmental Exposure↗
PubMed1990

Occupational asthma due to isocyanates in Singapore.

Nine cases of occupational asthma due to isocyanates are described. The isocyanates involved included toluene diisocyanate (TDI), diphenyl-methane diisocyanate (MDI) and polyisocyanates. The importance of asking the occupational history in a patient with asthma is illustrated. The importance of early diagnosis and removal from further exposure is also discussed.

Adolescent↗
PubMed1990

Biological monitoring of workers exposed to inorganic lead in Singapore.

Medical surveillance of workers exposed to a lead hazard is a common practice in many countries. In Singapore, legislation on periodic medical examinations for lead exposed workers in factories was introduced in 1985. This paper discusses the results of the laboratory tests in workers exposed to inorganic lead in 1987. The WHO recommended that the health-based limit for lead absorption be 40 micrograms/dL for adult male workers. Taking this level, we could divide the factories into a "higher risk" category and a "lower risk" one, the latter not having a single result of blood lead of 40 micrograms/dL or above. The former category included factories manufacturing PVC and lead storage batteries, with the highest level of 79.6 micrograms/dL found in PVC manufacture. Of the 3 main races in Singapore, the Chinese have the lowest blood lead levels after adjusting for the type of industry, age and duration of exposure to lead. Age was correlated with the duration of lead exposure. The higher blood lead levels in Malays and Indians may have been contributed to by eating habits (eating with hands). The higher prevalence of smoking among Malays may also be contributory. The results in this study, while reassuring that no worker was found with blood lead above 80 micrograms/dL, also indicated that workers in some factories were still exposed to a health risk.

Adult↗
PubMed1989

Sleep-wake patterns and subjective sleep quality of day and night workers: interaction between napping and main sleep episodes.

Five hundred and ninety-three women electronics workers were studied to determine if there was any association between their subjective sleep quality and their sleep patterns. They were 108 day workers, 107 permanent night workers, 216 workers on weekly phase-advance (night/afternoon/morning), and 162 workers on two-weekly phase-delay (morning/afternoon/night) rotating shift schedules. The study was part of a larger survey on night workers involving a self-administered questionnaire. The proportion of nappers was higher in night workers than in day, morning, and afternoon shift workers. Nappers had shorter main sleep, but their total sleep duration was generally the same as that of nonnappers. Compared to nonnappers, a higher proportion of day and morning shift workers who napped did not sleep well. Permanent night workers, with the highest proportion of nappers, had more workers sleeping well than rotating night workers. Subjects who slept well were those with longer total and main sleep and generally started the main sleep earlier. The results indicate a relationship between subjective sleep quality, sleep length, main sleep start, and napping behavior. Whether this relationship is causal is difficult to establish as sleep quality may also reflect the general health status, and this may result in differences in sleep behavior.

Adult↗
PubMed1984

Stevens-Johnson syndrome associated with occupational exposure to trichloroethylene.

Reports on cases of Stevens-Johnson syndrome (erythema multiforme major) have seldom related it to occupational exposure to chemicals. Serious liver involvement is also uncommon. This report describes 5 cases of the syndrome who had been occupationally exposed to trichloroethylene. The circumstantial evidence suggested that the chemical might have been a causative factor in the disease. The liver was involved in all and in 3 it was serious, with one death. The degree of exposure to trichloroethylene varied. The duration of exposure ranged from 2 to 5 weeks. It seemed likely that there was a hypersensitive reaction to trichloroethylene in these cases.

Adolescent↗
PubMed1984

Five cases of arsine poisoning.

Arsine is one of the most potent haemolytic agents found in industry. Four workers presented with abdominal pain, jaundice and passing tea-coloured urine. A fifth worker also passed dark urine but had no other symptoms. Investigation revealed that all five workers were from a tin smelting plant where they were involved in mixing tin ore with dross. They were exposed to arsine gas after mixing a particularly large quantity of dross with tin ore which was wet because of rain. Three of the cases developed renal impairment and also a mild sensory neuropathy. All survived with proper management in hospital which included exchange blood transfusions, and peritoneal dialysis where indicated. Prevention of such poisoning includes keeping dross away from all moisture, good ventilation in work areas, and adding dross directly to the furnace.

Acute Kidney Injury↗