S.C. Foo

Chronic neurobehavioural effects of elemental mercury in dentists.

Neurobehavioural tests were performed by 98 dentists (mean age 32, range 24-49) exposed to elemental mercury vapour and 54 controls (mean age 34, range 23-50) with no history of occupational exposure to mercury. The dentists were exposed to an average personal air concentration time weighted average (TWA) of 0.014 (range 0.0007-0.042) mg/m3 for a mean period of 5.5 (range 0.7-24) years and had a mean blood mercury concentration of 9.8 (range 0.6-57) micrograms/l. In neurobehavioural tests measuring motor speed (finger tapping), visual scanning (trail making), visuomotor coordination and concentration (digit symbol), verbal memory (digit span, logical memory delayed recall), visual memory (visual reproduction, immediate and delayed recall), and visuomotor coordination speed (bender-gestalt time), the performance of the dentists was significantly worse than that of the controls. The dentists scored 3.9 to 38.9% (mean 13.9%) worse in these tests. In trail making, digit span, logical memory delayed recall, visual reproduction delayed recall, and bender-gestalt time test scores were more than 10% poorer. In each of the tests in which significant differences were found and in the block design time, the performance decreased as the exposed dose (product of the TWA of air mercury concentrations and the years of exposure) increased. These results raise the question as to whether the current threshold limit value of 0.050 mg/m3 (TWA) provides adequate protection against adverse effects of mercury.

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.

Chronic neurobehavioural effects of toluene

Neurobehavioural tests were undertaken by 30 female workers exposed to toluene and matched controls with low occupational exposure to toluene. The environmental air levels (TWA) of toluene was 88 ppm for the exposed workers and 13 ppm for the controls. The toluene in blood concentrations for the exposed workers was 1.25 mg/l and for the controls 0.16 mg/l. Statistically significant differences between workers exposed to toluene and controls in neurobehavioural tests measuring manual dexterity (grooved peg board), visual scanning (trail making, visual reproduction, Benton visual retention, and digit symbol), and verbal memory (digit span) were observed. Further, the performance at each of these tests was related to time weighted average exposure concentrations of air toluene. The workers exposed to toluene had no clinical symptoms or signs. The question arises as to whether these impairments in neurobehavioural tests are reversible or whether they could be a forerunner of more severe damage.

Elements in the hair of South-East Asian islanders

Mercury (Hg), lead (Pb), cadmium (Cd) and copper (Cu) in hair samples from Singapore island (85 samples) and two islands off Batam, Indonesia (68 samples) were analysed to assess the environmental uptake of elements. Hair samples were washed with 0.1% Triton X-100 solution for 20 min in an ultrasonic bath, rinsed five times with de-ionized water and air dried. Ten to 20 mg of hair samples were digested with 1 ml of ultra-pure concentrated nitric acid in Parr bombs at 120 degrees C for 2 h. Hair digests were analysed by atomic absorption spectrophotometry (AAS). Hg was determined by the cold vapour AAS method and Pb, Cd and Cu by the electro-thermal graphite furnace AAS method. For Singapore hair, the contents of Cd (in microgram/g) averaged 0.17 (range 0.02-1.81); Cu 13.2 (range 3.1-70.1); Hg 5.92 (range 1.14-35.52); and Pb 6.74 (range 0.06-107.8). For the islands off Batam, Cd was 0.32 (range 0.06-1.80); Cu 21.1 (range 3.8-143.6); Hg 5.59 (range 0.78-60.86); and Pb 15.1 (range 0.13-116.6). Statistically significant differences in Cd, Pb and Hg contents were observed between the hair samples from Singapore and those of the islands off Batam in cumulative logit analysis. Hair from Singapore contained more Hg, but less Cd and Pb compared to hair from the islands off Batam. For Pb in hair, significant differences were also observed between the two islands off Batam (island 1, 18.9; and island 2, 10.2). These differences in hair metal contents are due to differences in community lifestyle (dietary, environmental or occupational intake).

Concentrations of heavy metals in maternal and umbilical cord blood

Concentrations of lead, cadmium, methylmercury and total mercury were measured in maternal and umbilical cord blood using graphite atomic absorption spectrometry. Two essential metals, copper and zinc, were also determined using ion chromatography. Lead, copper and zinc were found to be lower in the cord blood, whereas methylmercury and total mercury were higher in cord blood than in maternal blood. Little differences were noted for cadmium in maternal and cord blood. Significant positive correlations were observed between the concentrations in maternal and cord blood with regard to lead (correlation coefficient, r = 0.44), copper (r = 0.34), zinc (r = 0.29), methylmercury (r = 0.44) and total mercury (r = 0.58). These results suggest that, like essential metals, most heavy metals can move rather freely across the human placenta. The potential health effects of heavy metal transfer from mothers to young infants cannot be discounted.

Toluene in Blood after Exposure to Toluene

Analysis of the postshift toluene levels in the blood of 50 assembly line workers indicates that toluene levels in blood were correlated with the time-weighted average (TWA) exposure levels of the same day (r = 0.90). Toluene concentrations in 10 laboratory technicians not exposed to toluene at their work gave an average level of 0.002 microgram/mL of blood. Significant levels of residual toluene were found in the preshift blood of workers exposed to 57 to 146 ppm of toluene as compared to the unexposed. The blood toluene values determined from capillary blood taken from finger tips are higher than the reported values from venous blood. The method described is useful for large-scale screening and epidemiological surveys.

Mercury in scalp hair of healthy Singapore residents.

Two hundred and twenty-five hair samples (150 Chinese, 44 Malays and 31 Indians) from healthy residents not occupationally exposed to mercury were analyzed by cold vapour atomic absorption spectrophotometry to determine their total, inorganic and organic mercury levels. The arithmetic means of total mercury levels in hair were 6.1, 5.2 and 5.4 ppm for the Chinese, Malays and Indians, respectively. Factors contributing to the amount of mercury in hair, including consumption of fish and marine products, use of traditional ethnic medicines, artificial hair waving, age, sex and ethnicity were analyzed. Fish consumption, sex and ethnicity are factors found to contribute significantly (p less than 0.05) to mercury levels in hair.

Postural stability of workers exposed to lead.

OBJECTIVE--To detect, with a computerised postural sway measurement system, any significant deviation of postural sway parameters among lead workers compared with a control group. METHODS--Postural stability was investigated with a computerised postural sway measurement system in 60 workers exposed to lead with a duration of exposure of 84 (range 3-366) months and 60 controls. Sway parameter data were collected with an Advanced Mechanical Technology computerised biomechanics platform system. RESULTS--The mean current blood lead concentration was 36.0 (range 6.4 to 64.5) micrograms/dl for the exposed workers and 6.3 (range 3.1 to 10.9) micrograms/dl for the 14 controls. There was no significant difference between the groups for the postural sway parameters obtained when the eyes were open. Significant differences were found for Xs, Ys (SDs of the coordinates of the centre of pressure); Xm, Ym (mean deviation of the coordinates of the centre of pressure); Rm (average displacement of Xi, Yi, from Xo, Yo); L (length of sway path); Vel (mean velocity of the centre of pressure along its path); Ao (area included within the path of the centre of pressure); Ae (95% confidence elliptical area). The Romberg ratios (the relation between eyes closed and open) for the Vel, L, Ao and Ae of the exposed workers were also significantly different from the controls. CONCLUSION--The study showed that workers exposed to lead had significantly poorer postural stability than the controls. Lead may affect certain parts of the whole sensory neural axis resulting in postural instability when the visual input is cut off. Based on current blood lead concentrations, we were not able to obtain any significant association with the postural sway parameters.

Benzene pollution from gasoline usage

Local gasolines contain benzene ranging from 1.8 to 3.7% and their use can lead to significant exposure to benzene. Gasoline station attendants were found to be exposed to short-term exposure levels (STEL) of 0.064-179 ppm. Their 8-h time-weighted averaged (TWA) exposure ranged from 0.028 to 0.71 ppm. For motorcar service mechanics, TWA exposure levels ranged from 0.014 to 1.7 ppm. The exposure of drivers of gasoline delivery tankers ranged from 0.08 to 2.37 ppm for personal TWA exposure over the whole workshift. For local people not occupationally exposed to gasoline or other benzene-containing volatile chemicals, exposure from the ambient environment ranged from 0.0023 to 0.027 ppm. Gasoline usage also contributed to the contamination of surface water with benzene. Benzene levels in water samples taken from drains leading from gasoline stations were between 1.1 and 40.4 micrograms l-1.

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.