Jerry Jeyaratnam

Metals in hair as biological indices for exposure

SummaryHair samples from three groups of occupationally exposed subjects were analyzed for their lead (Pb), manganese (Mn) and mercury (Hg) contents. For lead (number of subjects, n=209), the hair Pb ranged from 0.93 to 3527 μg/g (geometric mean, GM=641) and blood Pb from 33.3 to 774 μg/l (GM=341); for manganese (n=38), the hair Mn ranged from 0.20 to 52.97 μg/g (GM=2.66) and urine Mn ranged from 1.70 to 17.9 μg/l (GM=5.56); and for mercury (n=85), the hair Hg from 1.79 to 12.8 μg/g (GM=5.09) and the blood Hg from 0.63 to 57.3 μg/l (GM=10.9). The hair Pb was significantly (P<0.0001) correlated to blood Pb (r=0.85); the hair Mn to urinary Mn (r=0.45); and the hair Hg to blood Hg (r=0.53). The average metal content at the distal end was not significantly (P>0.05) different from that of proximal end. The GM levels for the distal end were 223 μg/g (95% CI 152–347) and 2.26 (95% CI 0.97–5.29); and those for the proximal end were 186 (95% CI 97–261) and 1.18 (95% CI 0.54–2.58) for Pb and Mn respectively. However, linear regression analysis of hair metal levels in the proximal end with respect to those in the distal end after logarithmic transformation showed that hair Pb in the proximal end was related to hair Pb in the distal end with a slope of 0.95 (95% Cl 0.89–1.01) whereas hair Mn in the proximal end was related to that of the distal end with a slope of only 0.52 (95% CI 0.13–0.91), reflecting the relatively constant Pb exposure as compared to the dropping Mn exposure in recent years. Metals in hair are suitable biological indicators for exposure and the distribution along the different segments of hair strands reflects the time history of exposure.

Urinary N-acetyl-beta-D-glucosaminidase activity in workers exposed to inorganic lead.

Urinary N-acetyl-beta-D-glucosaminidase (NAG) had been shown to be a useful early marker of renal injury. In workers exposed to lead it seems to be the only early marker but the dose response and dose effect relations are weak. Furthermore, the significance and underlying mechanism of increased urinary NAG activity is far from clear. By studying the isoenzyme profiles of urinary NAG, the significance and underlying mechanism may be further clarified. The heat labile (NAG-A) and heat stable (NAG-B) isoenzyme profiles of 128 workers exposed to lead from a lead stabiliser factory were analysed. NAG activity was expressed as total NAG, NAG-A, and NAG-B activity as well as ratios (NAG-B/total NAG and NAG-B/NAG-A). Exposure indices included the recent concentration of blood lead (BPb), a cumulative blood lead index (TBPb), and the recent change in concentration of blood lead (CBPb). The NAG indices correlated best with CBPb. Nearly 50% of the variation in NAG-B activity could be explained by the combination of all three exposure indices but only the CBPb was highly significant. When these exposure indices were entered separately into the regression equation, CBPb accounted for 36.3% of the variation in NAG-B activity, 5.7% was accounted for by TBPb and 2.7% by BPb. There was also no dose-effect or dose-response relation between the NAG variables and BPb or TBPb groups. With CBPb, there were dose-effect and dose-response relations. With CBPb, there was an increase in NAG variables in the group with more than 25% increase in blood lead over the past six months. The increase in NAG activity in this study is likely to be due to a recent increase in concentration of blood lead and hence presumably a recent rise in renal burden of inorganic lead. This suggests that the increase in urinary NAG activity is a form of acute response to a sharp increase in renal burden of lead, rather than to a cumulative dose. Heat stable NAG is part of the lysosomal membrane and is present in the urine when there is breakdown of lysosomes. Our data therefore contradict suggestions that the increase in urinary NAG activity is due to exocytosis.

Effects of 2-ethoxyethylacetate menstrual patterns of workers exposed to low levels of 2-ethoxyethylacetate (EGEEA)

The objectives of this study were to determine the exposure levels among workers who handle 2-ethoxyethylacetate (EGEEA) in the liquid crystal display (LCD) manufacturing industry and to study the menstrual patterns among the exposed workers compared to a referent group of workers. A total of 52 female exposed workers and 55 referents was studied. Detailed menstrual histories were obtained by personal interview using a structured questionnaire. All the exposed had individual 8-hour personal monitoring for EGEEA in the environment and start-of-shift and end-of-shift urine analysis for EGEEA concentration. The geometric mean end-of-shift urine EGEEA concentration was 0.16 mg/g creatinine. End-of-shift urine EGEEA was well correlated with the air concentration; r = 0.81 [p < 0.0001]. No significant differences were observed between the exposed and referent groups for duration of each menstrual cycle (period), duration (days) of the menses, and the amount of flow, even after adjusting for possible confounders viz. age, years of education, use of oral contraceptive pills, age at menarche, gravidity, and race. The workers in the LCD manufacturing industry were exposed to a mean TWA of 0.51 ppm of EGEEA. At this concentration, the findings did not reveal any significant difference between the menstrual patterns of the exposed and referent subjects.

Kinetics of styrene urinary metabolites: a study in a low-level occupational exposure setting in Singapore.

SummaryBiological monitoring of styrene exposure commonly involves measurement of styrene metabolites, mainly mandelic acid (MA) and phenylglyoxylic acid (PGA), in the urine of exposed subjects. Previous studies on the kinetics of styrene metabolites in urine were mostly conducted in a controlled environment on subjects exposed to high concentrations of styrene. In this study, we examined subjects exposed to low levels of styrene in a fiber-reinforced plastics (FRP) plant to see whether the excretion kinetics of styrene metabolites are similar under field conditions. Eight healthy Chinese male volunteers were exposed to styrene for 4 h with a mean environmental concentration of 11 ppm. Urine samples were collected continuously for 20 h after termination of the exposure and concentrations of urinary MA and PCA were determined. The results showed that MA was rapidly excreted in urine after the exposure, with a half-life of 2.1 h or 1.9 h when corrected with urine creatinine. The excretion of PGA followed that of MA and the half-life was 8.1 h or 5.1 h after correction with creatinine. The half-lives are considerably shorter compared to those in previous reports, suggesting that environmental factors, exposure conditions, or ethnic differences may affect the excretion kinetics of styrene metabolites. The fast excretion of styrene metabolites is also consistent with the observation that urine MA and PGA levels correlated better with the half-day time-weighted average (TWA) concentration of environmental styrene than with the whole-day TWA concentration. Our findings thus underscore the need for information on excretion kinetics in order to develop an appropriate biological monitoring scheme for specific exposure settings and subjects.

Textbook of occupational medicine practice

Part 1 Clinical occupational medicine: work and health, D. Koh and J. Jeyaratnam renal disorders, K.S. Chia and E.J.C. Lee cardiovascular disorders, W.O. Phoon respiratory disorders, H.S. Lee and C.B.E. Chee skin disorders, D. Koh and C.L. Goh haematological disorders, K.S. Chia and R. Suri neurological disorders, S.E. Chia and P.N. Chong mental health, E.K. Ung and E.H. Kua reproductive disorders, S.E. Chia musculoskeletal disorders, E.H. Lee and H.K. Wong hepatobiliary and gastrointestinal disorders, T.C. Aw and M. Harrington auditory disorders, K.G. Rampal and N.H. Ismail eye injuries and other disorders. T.Y. Wong and V. Balakrishnan occupational infections, T.C. Aw. Part 2 Special issues in occupational medicine: occupational cancers, K.S. Chia and H.P. Lee health screening and periodic medical examinations, C.S. Lai and S.M. Lee medical disaster planning and response, M.K. Lim and V. Anantharaman assessment of disability for compensation, W.H. Phoon et al shiftwork and health, A. Spurgeon and J.M. Harrington health of corporate travellers, M.K. Lim health promotion at the workplace, I.R. Gardner prevention of occupational diseases, D. Koh et al occupational safety and health legislation, M. Chan et al.

Continuing Education in Occupational Medicine for Physicians

Continuing education (CE) in occupational medicine is necessary in Singapore in view of the existing deficiencies and in order to maintain and enhance professional competence. CE should be designed with three categories in mind: physicians not practising occupational medicine, occupational medicine specialists and designated factory doctors. If CE is to be made mandatory there will be a need for a substantial increase in the existing manpower and financial resources. Furthermore, provider units will have to be institutionalised and have the active support of the health care system.

Health and Safety Ethics for Management

AH employers are ethically required to provide a safe and healthy workplace for their employees. Health and safety professionals (HSP) may of ten be employed either full-time or part-time to achieve this end. The HSP should be viewed as a non-partisan provider of safety and health services at the workplace. He is equally on the side of management and worker in discharging his duties. His primary goal is to achieve a safe and healthy workplace and to improve the health of the workforce. Ethical dilemmas may surface in the course of the HSPs work largely because there may be occasions when there are conflicts of interest and loyalty derived from the different roles of the HSP. The best way to resolve such dilemmas is to prevent them from arising. However, when this is not possible, managements understanding of the professional ethical considerations of the HSP will help to improve the working relationship and professional results of these staff. Several aspects in the HSPs work require managements understanding. These include subjects such as communicating information on staff medical examinations to management, and the disclosure of commercially confidential information to assess related health risks. Management should also be aware that guidelines have been developed by a number of professional health and safety organizations for their members. In the instances when answers to ethical questions cannot be resolved, these guidelines can be consulted, in conjunction with discussions with senior HSP colleagues.

Factors Influencing the Assessment and Control of Occupational Hazards in Developing Countries1

The principles of occupational health may be the same in the developed and developing countries. However, there can be a wide diversity in practice. The exposure to chemicals at the workplace in developing countries is usually of a different nature, and the level of exposure is generally of a higher magnitude. The leading occupational diseases in developing countries are also very different to those reported in industrialized nations. For hazard evaluation in developing countries, more factors need to be considered. Problems are usually more complicated as most workplaces are subjected to many factors which typify small-scale industries. Low capital investment often culminates in cutbacks on necessary expenses, especially on occupational or environmental health activities. Thus the health, safety, and welfare of the workers are usually overlooked. This situation helps only to promote greater risks to the workers. Furthermore, many workers in the developing countries suffer from poor nutrition, endemic diseases, and other debilitating conditions. For these reasons, it is possible that currently recommended occupational exposure limits could allow injury to workers in the developing nations. When carrying out health assessment, careful attention must be paid to cultural practices, genetic components, working conditions, and other predisposing factors. This paper reviews some of the current techniques commonly used for the monitoring of toxic substances and an in-depth discussion on various problems facing the developing countries concerning the usage of these techniques.

Neurobehavioral Effects in Occupational Chemical Exposure1

Neurobehavioral effects in 30 female workers (aged 18–41, mean 25.6) exposed to an average of 341 mg/m3 (SD 100) toluene for an average of 5.7 years (SD 3.3) compared with 30 matched controls (aged 18–48, mean 25.1), 24 male workers (aged 18–32, mean 24.7) exposed to 268 mg/m3 (SD 185) toluene equivalent of mixed solvent (82.2% toluene, 12.3% ethyl acetate, and 5.5% methyl ethyl ketone) for 2.3 years (SD 3.0) compared with 24 matched controls (aged 17–31, mean 24.3), and 94 dentists (aged 24–49, mean 31.7) exposed to 0.017 mg/m3 (SD 0.009) of elemental mercury for 7.4 years (SD 5.3) compared with 54 referents (aged 23–50, mean 33.6) were studied. The Z score (made up of Digit Span, Symbols Digit, and Grooved Peg Board) for the workers exposed to toluene was 0.79, for workers exposed to mixed solvents was 0.38, and for the dentists exposed to mercury was 0.42. The Z score for each group of exposed subjects was statistically poorer than that for its controls. Neurobehavioral performance was statistically related to exposure intensity for the toluene-exposed workers and to years of exposure or dose (exposure intensity x years of exposure) for mixed solvent- and mercury-exposed subjects. The type of chemical species and pattern of exposure appear to influence whether the adverse effects will be cumulative.