Mamoru Hirata

Correlation between lead in plasma and other indicators of lead exposure among lead-exposed workers.

In order to clarify the bioavailability of lead in plasma (PbP), we performed a study on five workers in a Japanese factory manufacturing lead glass-based paints. Blood and urine samples were obtained over a period of 15 months, during which time the workers took it in turns to perform sifting work (with the highest level of lead exposure) for 1-month periods. A total of 75 sets of blood and urine samples were thus obtained. We determined whole blood lead (PbB), PbP, Urinary coproporphyrin (CPU), urinary δ-aminolevulinic acid (ALAU), urinary lead (PbU) and ALA in plasma (ALAP). In the 15 sets of samples obtained at the end of the period with a high level of lead exposure, PbP correlated significantly with ALAU, CPU, PbU and ALAP, but PbB correlated significantly only with PbU. In the 60 sets of samples obtained following a low level of lead exposure, correlation coefficients between the concentrations of PbP and of ALAU, CPU and PbU exceeded those between the concentrations of PbB and of ALAU, CPU and PbU. These findings indicate that PbP is a better dose indicator of lead biochemically available for heme synthesis and that PbU has a closer correlation with PbP than with PbB.

A cross-sectional study on the brainstem auditory evoked potential among workers exposed to carbon disulfide.

SummaryIn order to clarify the chronic effect of carbon disulfide (CS2) on the central nervous system (CNS), the brainstem auditory evoked potential (BAEP) was measured in spinning workers exposed to CS2 in a viscose rayon manufacturing factory and unexposed workers in Japan. Workers exposed to CS2 were divided into three groups according to length of exposure: current spinning workers with an exposure duration of more than 240 months (L group, n = 34), current spinning workers with an exposure duration of 24–84 months (S group, n = 25), and former spinning workers with an exposure duration of more than 120 months (R group, n = 16). Unexposed controls were selected from workers in a nylon filament factory using the same criteria (N group; n = 40). BAEP records were analyzed based on the latencies of three main components (I, III, V) and interpeak latencies (I–III IPL, III–V IPL, I–V IPL). Latencies of component V, III–V IPL, and I–V IPL in the L group were significantly greater (P < 0.01, P < 0.05, P < 0.05, respectively). The significantly, higher III–V IPL in the L group suggested that in humans, chronic exposure to CS2 involves the auditory ascending tract in the brainstem. Recovery from this neurotoxic effect is apparently possible, as the BAEP parameters in the R group were not significantly higher than those of the N group despite the long previous CS2 exposure of the R group.

Work schedule differences in sleep problems of nursing home caregivers

Nursing home caregivers (n=775; 604 women; mean age 33.6 years) were studied to examine how work schedules affect their sleep. The shift group (n=536) worked under a rotating two-shift system (n=365), a rotating three-shift system (n=66), or other types of shifts (n=78). The non-shift group included 222 caregivers. Participants completed a questionnaire about working conditions, sleep problems, health, lifestyle, and demographic factors. The two-shift caregivers reported the highest levels of difficulty initiating sleep (DIS, 37.6%), insomnia symptoms (43.0%), and poor quality of sleep (24.9%) among the groups. Adjusted odds ratios for these problems were significantly greater for the two-shift caregivers than for non-shift counterparts: DIS (odds ratio 2.86, 95% confidence interval 1.57-5.20), insomnia symptoms (2.33, 1.36-4.02), and poor sleep quality (2.15, 1.09-4.22). Our data suggest that working under a rotating two-shift system, which has a longer night shift, is associated with an elevated risk of sleep problems for nursing home caregivers.

Musculoskeletal pain and night-shift naps in nursing home care workers

BACKGROUND Care workers in nursing homes are at high risk of developing musculoskeletal disorders (MSDs). Many care workers work in shifts, which may compromise both the quality of care they give and their working life. Taking a nap during night shifts has been proposed to ameliorate shift work-related problems, but its relationship with MSDs is not clear. AIMS To explore how MSD pain differs according to frequency of night-shift naps. METHODS A questionnaire study was conducted on 111 care workers at three nursing homes. Of 98 respondents, data from 66 shift workers (54 women) were analysed. Data on self-rated pain in multiple sites (neck, shoulder, arm, leg and low back), naps during night shifts and relevant variables were collected. Participants were categorized into three groups on the basis of frequency of night-shift naps taken during the previous month: non-nappers, <50% nappers and >or =50% nappers. RESULTS Pain at all sites, with the exception of low back pain, differed significantly among the three groups. Pain scores were lowest at the arm and leg for the > or =50% nappers. Neck and shoulder pain was lower for the > or =50% nappers and the non-nappers compared to the <50% nappers. CONCLUSIONS Reduced pain in the arm and leg was associated with taking a nap at least once every two night shifts among the nursing home care workers. No association was found between low back pain and night-shift naps in this sample.

Changes in auditory brainstem response in rats chronically exposed to carbon disulfide

The chronic effect of carbon disulfide (CS2) on the central nervous system (CNS) was studied by examining auditory brainstem responses (ABRs) in female rats (Jcl Wistar) exposed to 200 ppm or 800 ppm CS2 by inhalation, 6 h a day, 5 days a week, for 15 weeks. Two modes of ABRs evoked by clicks at 61 and 96 dB sound pressure levels (61 dB-ABR and 96 dB-ABR) were recorded during the exposure and for 6 weeks afterwards. Three main components (I, III and V) of ABRs were analyzed from the latencies and differences between latencies of them (interpeak latencies, IPL I–III, IPL III–V and IPL I–V). The latencies of the three components and IPLs of 96 dB-ABR in rats group exposed to 800 ppm of CS2 were significantly delayed during the exposure period. The delay of latency of component V and IPL III–V and I–V tended to increase with exposure time. At 61 dB-ABR, the changes in the latency of component V, IPL III–V and I–V resembled those at 96 dB-ABR. For the rats group exposed to 200 ppm CS2, the latency of component I, IPL III–V and I–V at 96 dB-ABR were delayed significantly but transiently during the exposure period. For both groups, recovery from the latencies of the three components and IPLs of ABR was observed by the end of the recovery period. The delayed latencies of ABR observed in rats exposed to 800 ppm CS2 suggested a conduction dysfunction in the brainstem due to CS2 exposure. The transient delay of the parameters in the rats group exposed to 200 ppm CS2 was considered to represent a slight conduction dysfunction.

Involvement of the central nervous system in vibration syndrome

In order to clarify the involvement of the central nervous system (CNS) in vibration syndrome (VS), patients with VS and age-matched controls were given a questionnaire and neurophysiological tests on auditory brainstem response (ABR), event-related potential (P300), short-latency somatosensory evoked potentials (SLSEP), and blink reflex (BR). Twenty-eight patients with a mean age of 56.3 (SD = 3.01, range 48–65) years from western Japan were examined. They had been on sick leave for an average of 6.13 (SD = 3.2, range 1–13) years at the time of the testing. Almost all were experiencing Raynauds phenomenon in the winter of 1990–1991. They were not suffering from diseases or injuries which might have affected the CNS function. These patients were divided into two subgroups, one with more symptoms related to the CNS, especially memory and judgment (n = 13, group A), and the other with fewer symptoms (n = 15, group B). Normal controls with an average age of 55.8 (SD = 4.8, 48–65) years were people from the same area who met similar criteria. The ABR parameters of the patients were slightly, but not significantly, delayed compared with those of the controls. The SLSEP and BR parameters of the patients were not delayed. The latencies of P300 in group A were significantly delayed compared with those in the controls. The findings suggest that VS involves the cognitive and attention functions of the cerebral higher function, but not the conduction function in the auditory and somatosensory ascending tract and facial nerve reflex tract in the brainstem.

A new HPLC fluorimetric method to monitor urinary delta-aminolevulinic acid (ALA-U) levels in workers exposed to lead

SummaryA new sensitive HPLC method for the determination of urinary delta-aminolevulinic acid (ALA-U) was used to evaluate the relationship between blood-lead (Pb-B) and ALA-U levels in male workers exposed to lead. The differences between the ALA-U levels determined by this method (ALAU-HP) and by a colorimetric method (ALA-U-CL) are discussed. The HPLC method gave values similar to the ALA-U-CL values at high ALA-U level. However, at low blood-lead levels (58 ± 22 μg/l, n = 23), the mean ALA-U-HP level corrected by urinary creatinine level was one-third of the corrected ALA-UCL level (0.83 ± 0.14 and 2.4 ± 0.5 mg/g creatinine, respectively). A significant increase of the mean corrected ALA-U-HP level was observed at 162 ± 22 μg/l Pb-B (P < 0.05, n = 26), while that of ALA-UCL was observed at 245 ± 30 μg/l Pb-B (P < 0.01, n = 37). The regression equation based on the logistic model fitted well to the relationship data between the Pb-B level and the percentage of the subjects with corrected ALA-U-HP above the cut-off point (1.12 mg/g creatinine) and the expected Pb-B level for 50% response was 270 μg/l Pb-B, while it did not fit well to the relationship data between Pb-B level and the percentage of the subjects with corrected ALAU-CL above the cut-off point (3.5 mg/g creatinine). The maximum responses for the two sets of corrected ALA-U levels were both observed at 625 ± 25 μg/l. The corrected ALA-U level by HPLC method seems to be a useful indicator for biological monitoring of exposure to lead at low levels (< 400 μg/l Pb-B = health-based biological limit, WHO) as well as high ones.

Comparison between the fluorometric HPLC method and the conventional method for determining urinary δ-aminolevulinic acid and coproporphyrin as indices of lead exposure

SummaryFluorometric methods for determining δ-aminolevulinic acid (ALA) and coproporphyrin (CP) in urine have been recently developed by using high-performance liquid chromatography (HPLC). In the present study, urinary ALA and CP in lead-exposed workers were determined with these fluorometric HPLC methods and the conventional methods, and the results obtained were compared. In lead workers with a urinary ALA ≥ 5 mg/l, the values obtained with the fluorometric HPLC method corresponded well with those measured with the conventional colorimetric method. In contrast, in lead workers with ALA < 5 mg/l, ALA values obtained with the fluorometric HPLC method were lower than those measured with the conventional method, suggesting the possibility of matrix interference in urine. The urinary CP values obtained with the conventional method of Rimington (1971) were higher than those measured with the fluorometric HPLC method, though the correlation was good.

Relationships between Lifestyle-Related Factors and Immune Parameters in Middle-Aged Male Workers.

Relationships between Lifestyle‐Related Factors and Immune Parameters in Middle‐Aged Male Workers: Yumiko Nakano et al. Division of Industrial Health, Osaka Prefectural Institute of Public Health—Recent studies have demonstrated that unhealthy lifestyles and stress act as risk factors for various cardiovascular diseases, cerebrovascular disorders and cancer. The present study was carried out to investigate the effect of individual lifestyle and comprehensive lifestyle practices on T cell function in peripheral blood lymphocytes in 291 middle‐aged male workers belonged to 4 occupational groups: self employed men (I), employees of a television station (II), local civil servants (III) and workers in a manufacturing factory (IV). The proliferative responsiveness of the lymphocytes to phytohemagglutinin (PHA) was measured by the incorporation of radiolabeled thymidine by stimulated lymphocytes in vitro. lnterferonγ(IFNγ T helper type 1 cytokine) and interleukin‐4 (IL‐4; T helper type 2 cytokine) production from the stimulated lymphocytes were measured by quantitative sandwich enzyme immunoassay. Interviews by means of questionnaires including 19 items related to lifestyles, work stress, life event and health condition were performed. Subjects were classified into groups reporting healthy and unhealthy lifestyles according to their responses to the individual questionnaire. Then, the relationships between these lifestyle practices and the immune parameters were analyzed at the level of the occupational groups and the pooled subjects. The average number of unhealthy practices differed significantly among occupational groups, i.e., higher in the order of I, II, III and IV. Significantly negative correlations were observed between the number of unhealthy lifestyle practices and the PHA responses both at the level of the occupational groups and the pooled subjects. In contrast, there was no significant difference in IFN‐y production among occupational groups, though the group I showed a somewhat low tendency. The levels of IL‐4 in group I were noticeably higher than that in the other groups. It may be possible that severe suppression of cell‐mediated immunity changes the balance of T cell subsets from T helper type 1 to T helper type 2. For each lifestyle practice, subjects reporting “healthy” practices on 7 items showed significantly greater proliferative response to PHA than those reporting unhealthy practices. Subjects reporting “healthy” practices on two items showed significantly lower levels of IL‐4 compared with those reporting unhealthy practices. A 1.5‐yr follow up study performed in the subjects with low PHA responses showed that the reduction of unhealthy lifestyle practices significantly improved the PHA responses. Consequently, the present study suggests that the individual unhealthy lifestyle practices may act on the immune system cumulatively, and the measurement of PHA response may be used to evaluate the lifestyle practices of middle‐aged male workers at both the individual and the occupational group level.

Study on measurement of δ-aminolevulinic acid in plasma by high-performance liquid chromatography

A method for the determination of δ-aminolevulinic acid in plasma of lead-exposed workers by high-performance liquid chromatography with fluorescence detection of a fluorescent δ-aminolevulinic acid derivative (2-methylidineamino-3,5-diacetyl-4,6-dimethylpropionic acid) was established. The detection limit of δ-aminolevulinic acid in plasma was 0.01 μg/ml at a signal-to-noise ratio of 5:1. A linear correlation was obtained between the amounts of δ-aminolevulinic acid injected from 0.01 to 0.5 μg/ml (r = 0.999). The recovery of 0.05 and 0.1 μg/ml of δ-aminolevulinic acid added to plasma with various concentrations of δ-aminolevulinic acid in plasma ranged from 80.0 to 100.8%. This method, combined with the use of an automatic sampler, should facilitate the routine measurement of δ-aminolevulinic acid in plasma.