Neuropsychological studies on lead workers in Singapore

The neuropsychological performance of a group of 49 workers occupationally exposed to lead was compared with a matched control group of 36 non-exposed workers. The psychometric measurements were composed of tests covering a broad range of different neuropsychological functions, particular emphasis being given to perceptual motor ability and attention concentration functioning. A questionnaire to assess subjective symptoms in mood, sleep disturbance, poor concentration and forgetfulness, somatic complaints, and social passivity was also included in the battery of tests. Compared with the controls, the performance of the lead workers was found to be significantly poorer for digit symbol, Bourdon-Wiersma, trail making test (part A), Santa Ana test, flicker fusion, and simple reaction time. In terms of subjective symptoms the exposed group also reported significantly more complaints of anxiety and depressed mood, poor concentration and forgetfulness, and other somatic complaints. These differences were observed among lead workers with a mean blood lead value of 2.35 mumol/l (SD 0.7).     

Neuropsychological test results and symptoms among workers with well-defined long-term exposure to lead.

Lead intoxication is a classical environmental hazard that can cause encephalopathy. During recent years several studies have suggested poor performances in psychological tests and increased numbers of subjective symptoms among workers with comparatively low blood lead concentrations. Forty-nine long-term lead-exposed male workers with time-weighted average blood lead concentrations between 1.3 and 3.3 mumol/l calculated from at least seven years' results have been compared with a referent group of 27 male industrial workers with normal blood lead concentrations and comparable intellectual backgrounds. Several indices of exposure were used. Both groups were examined with neuropsychological tests and a questionnaire covering neuropsychiatric symptoms. The exposed group performed less well in 11 of 14 non-verbal tests, and there were significant differences in tests of memory and reaction time. A non-linear dose-effect trend was indicated. The results are in accordance with those found in similar studies, and it is concluded that the blood lead concentration should be below 2.5 mumol/l to avoid the effects shown in this study.     

Objective neuropsychological test performance of professional divers reporting a subjective complaint of "forgetfulness or loss of concentration"

OBJECTIVE: This study attempted to determine whether the higher prevalence of reported "forgetfulness or loss of concentration" among professional divers can be confirmed using objective neuropsychological tests. Secondary aims were to qualify the functional nature of the complaints and to ascertain whether reduced performance was linked to diving history. METHODS: In a case-control study, the neuropsychological test performance of divers complaining of moderate or severe "forgetfulness or loss of concentration" was compared with two age-matched control groups reporting no or slight "forgetfulness or loss of concentration" ("nonforgetful" divers and "nonforgetful" nondivers). The group differences were analyzed using a multivariate analysis of co-variance, followed by canonical discriminant function analysis. Altogether 102 divers with a complaint, 100 nonforgetful divers, and 100 nonforgetful nondivers completed the study. RESULTS: The overall neuropsychological performance differed significantly between the groups [Pillai's trace: F(24,484)=2.04, P=0.003]. Verbal memory (Logical Memory and the California Verbal Learning Test), current intelligence (Wechsler Abbreviated Scale of Intelligence), and sustained attention (rapid visual processing) were poorer among the divers with a complaint than among the nonforgetful divers or the nonforgetful nondivers. The tests of memory, but not those of executive function, differentiated the divers with complaints from the two control groups. Mixed gas bounce diving and surface oxygen decompression diving, but not other techniques, were negatively associated with memory performance. CONCLUSIONS: A cognitive complaint of divers was confirmed using objective tests of neuropsychological performance. Memory, rather than executive function, was affected at the group level, but only to a mild degree. The relationships between diving experience and neuropsychological test performance were small and only seen with diving techniques used in the offshore oil and gas industry.     

Neurobehavioural evaluation of Venezuelan workers exposed to inorganic lead.

OBJECTIVES--To assess neurobehavioural effects of low exposure to lead, 43 workers from a lead smelter and 45 workers from a glass factory were evaluated with the World Health Organisation neurobehavioural core test battery (NCTB) in a cross sectional study. METHODS--The NCTB comprises a questionnaire and seven tests that measure simple reaction time, short-term memory (digit span, Benton), mood (profile of mood states), eye-hand coordination (Santa Ana pegboard, pursuit aiming II), and perceptual speed (digit-symbol). RESULTS--Smelter workers were employed on average for four years, and had a mean blood lead concentration of 2.0 mumol/l (42 micrograms/dl). Glass factory workers had a mean of 0.72 mumol/l (15 micrograms/dl). Historical blood lead concentrations were used to classify exposure based on current, peak, and time weighted average. Although the exposed workers performed less well than the non-exposed in 10 of 14 response variables, only profile of mood states tension-anxiety, hostility, and depression mood scales showed a significantly poorer dose-response relation with blood lead concentration in multiple linear regression models that included age, education, and alcohol intake as covariates. The frequency of symptoms of anger, depression, fatigue, and joint pain were also significantly increased in the exposed group. CONCLUSION--This study is consistent with the larger body of neurobehavioural research of low occupational exposure to lead. The small effects found in this study occurred at blood lead concentrations slightly lower than those reported in several previous studies.     

Neurological effects in workers exposed to manganese

The purpose of this study was to examine the effects on the nervous system in enamels-production workers who have low levels of and long exposure to manganese (Mn). The study included 138 Mn-exposed workers and 137 controls who received questionnaires on symptoms, a battery of psychological tests, and assessments of blood concentrations of metal. The exposure levels to airborne Mn concentrations were determined by personal and stationary samplings. The mean duration exposure to Mn was 19.87 years (SD +/- 9). The workers exposed to Mn reported more nonspecific subjective complaints than the control group. No effect of Mn exposure was indicated by the results of any of the neuropsychological tests. The Mn workers did not have higher concentrations of Mn in blood than the controls. Exposures of workers currently working with Mn averaged 57 micrograms/m3 respirable (personal samplings) and 12 g/m3 (stationary samplings). In conclusion, long exposure to low levels of Mn (approximately 200 micrograms/m3), as induced in our study, showed no significant disturbance of neurological performance.     

Longitudinal study to explore chronic neuropsychologic effects on solvent exposed workers

AIM: The aim of the study was to examine possible neurotoxic effects on the central nervous system (CNS) in relation to a chronic solvent exposure at the workplace. METHOD: The collective included 127 workers exposed to solvent mixtures, such as spray painters and printers. They were examined twice by means of a physical examination, neuropsychological testbattery, biological and air monitoring. RESULTS: Major component of the solvents were white spirits in concentrations up to 127 ppm in air and 2,666 microg/l in blood. Single substances were mainly toluene and xylenes in concentrations below current threshold values at the workplace. During the 2 yr interval, the concentrations of solvents decreased, and no significant associations between the neuropsychological tests and the solvent exposure were found. Regarding the whole working history of each participant, we found a significant reduction on information processing velocity and performance in the trailmaking test, as well as more complaints of workers with higher solvent exposure in the past. CONCLUSIONS: A slight increase of subjective complaints and a deteriorated power of concentration seems to be associated with chronic solvent exposure.     

Behavioral indicators of lead neurotoxicity: Results of a clinical field survey

Summary Central nervous system dysfunction in workers occupationally exposed to lead was investigated by means of performance tests. The test scores of lead-exposed workers were compared with those of control groups (steel workers, papermill workers and farmers). It was found that secondary lead smelter workers showed significantly poorer performance scores than the nonexposed, control groups. The group differences between steel workers and lead workers in test scores were not attributable to differences in age or education. In the lead-exposed workers correlations between test scores and indicators of lead absorption (particularly blood lead and zinc protophyrin levels) were analyzed. Increases in zinc protoporphyrin levels were found to be highly correlated with decreases in test scores. Lower performance test scores were consistent with a sizeable prevalence of central nervous system symptoms among secondary lead smelter workers. Moreover, lead workers without central nervous system symptoms also showed decrements in performance test scores which were also correlated with elevated zinc protoporphyrin levels. The data indicate that certain behavioral tests might be important tools for studying subclinical central nervous system dysfunction due to lead toxicity; significant correlations between zinc protoporphyrin levels and behavioral test scores are considered to be consistent with an etiologic relationship between decrement in performance scores and lead effects on the central nervous system.     

A neuropsychotoxicological assessment of workers in a sodium azide production plant

OBJECTIVE: Despite its known toxicity and extensive current industrial use, the occupational neuropsychotoxicology of sodium azide has not yet been investigated. METHOD: Neuropsychological and psychological tests, a symptom self-report questionnaire and haematological and cardiac measurements were gathered from 41 exposed workers and 42 unexposed workers in a chemical production plant yearly for 3 years. RESULTS: The exposed workers presented significantly more acute symptoms of exposure (headache, vertigo, nausea, fatigue, cardiac palpitations, irritated or red eyes) than did the unexposed workers. However, only one chronic symptom was repeatedly and more significantly reported, namely trembling of the hands. No psychological or neuropsychological tests (reaction time, psychomotor, cognitive, chromatopsia, Profile of Mood States) differentiated the two groups. However, acute effects of exposure on plasma creatinine and on systolic pressure were noted. Low creatinine levels in the plasma of exposed workers correlated significantly with impairment of mood on the Profile of Mood States test, but not with any other measure. We recommend that workers exposed to sodium azide be assessed with tremometry, clinically and in a future field study.     

Effects of occupational exposure to mercury vapour on the central nervous system.

Possible effects of mercury on the central nervous system (CNS) were examined in a group of chloralkali workers exposed to mercury (n = 89) and compared with a control group (n = 75), by registration of subjective symptoms, personality changes, forearm tremor, and performance on six computerised psychometric tests in the two groups. The groups were similar in age, education, verbal comprehension, and work tasks. In the chloralkali group, median blood mercury concentration (B-Hg) was 55 nmol/l, serum mercury concentration (S-Hg) 45 nmol/l, and urine mercury concentration (U-Hg) 14.3 nmol/mmol creatinine (25.4 micrograms/g creatinine). Corresponding concentrations in the control group were 15 nmol/l, 4 nmol/l, and 1.1 nmol/mmol creatinine (1.9 micrograms/g creatinine) respectively. The number of self reported symptoms, the scores for tiredness and confusion in the profile of mood states (POMS), and the degree of neuroticism in the Eysenck personality inventory (EPI), were significantly higher in the mercury exposed group compared with the controls. Performance on the psychometric tests and tremor frequency spectra did not differ significantly between the two groups. Dose-response calculations showed weak but statistically significant relations between symptom prevalence and current mercury concentrations in both blood and urine. The performance on three of the psychometric tests was negatively correlated with earlier peak exposures. The findings indicate a slight mercury induced effect on the CNS among the chloralkali workers.     

Effects of occupational exposure to mercury vapour on the central nervous system.

Possible effects of mercury on the central nervous system (CNS) were examined in a group of chloralkali workers exposed to mercury (n = 89) and compared with a control group (n = 75), by registration of subjective symptoms, personality changes, forearm tremor, and performance on six computerised psychometric tests in the two groups. The groups were similar in age, education, verbal comprehension, and work tasks. In the chloralkali group, median blood mercury concentration (B-Hg) was 55 nmol/l, serum mercury concentration (S-Hg) 45 nmol/l, and urine mercury concentration (U-Hg) 14.3 nmol/mmol creatinine (25.4 micrograms/g creatinine). Corresponding concentrations in the control group were 15 nmol/l, 4 nmol/l, and 1.1 nmol/mmol creatinine (1.9 micrograms/g creatinine) respectively. The number of self reported symptoms, the scores for tiredness and confusion in the profile of mood states (POMS), and the degree of neuroticism in the Eysenck personality inventory (EPI), were significantly higher in the mercury exposed group compared with the controls. Performance on the psychometric tests and tremor frequency spectra did not differ significantly between the two groups. Dose-response calculations showed weak but statistically significant relations between symptom prevalence and current mercury concentrations in both blood and urine. The performance on three of the psychometric tests was negatively correlated with earlier peak exposures. The findings indicate a slight mercury induced effect on the CNS among the chloralkali workers.     

职业性铅作业工人神经行为学研究

用WHO神经行为学核心成套测试方法对某铅熔炼厂39名铅作业工人进行了神经行为学检查，结果表明，接触组情感状态、简单反应时、数字广度、数字译码、视觉保留、目标追踪及圣他·安那提转敏捷度测试成绩与对照组比较均有显著改变，提示长期低浓度铅接触可致高级神经功能紊乱。多元回归分析提示接触组工人部分神经行为功能改变与空气铅浓度及工人血铅有关，说明控制作业场所空气铅浓度是减少工人神经行为功能损害的重要途径。     

Comparison of neurobehavioral function in workers exposed to a mixture of organic and inorganic lead and in workers exposed to solvents

The neurobehavioral effects of lead (organic and inorganic) and organic solvents were compared in 386 U.S. workers (52 reference, 190 lead, and 144 solvent workers). The association between neurobehavioral test performance and duration of exposure to lead or solvents was also examined and compared. The neurobehavioral test battery consisted of examiner and computer-administered neurobehavioral tests, a test of olfactory function, and questionnaires that assessed neuropsychiatric symptoms. Adjusted mean differences on the neurobehavioral test scores were estimated by comparing the exposed group to the referent group using linear regression and adjusting for premorbid intellectual ability, age, and race. Both lead and solvents were associated with diminished neurobehavioral performance in all neurobehavioral areas tested. Specifically, while lead and solvent exposure had the same magnitude of adverse effects on tests of manual dexterity, lead exposure was associated with greater adverse effects on memory and learning tests but with less adverse effects on executive/motor tests and on a test of olfaction than solvent exposure. An elevated number of neuropsychiatric symptoms was reported by 7% of the referent group, 43% of the lead group, and 15% of the solvent group. For exposure duration of ?10 years, more neurobehavioral decrements were found in the solvent group relative to the lead group. However, for exposure duration of ?18 years, the lead group showed more decrements than the solvent group. Overall, these data suggest differences in neurobehavioral functioning between the lead (organic and inorganic) and solvent exposed workers examined in this study.     

Neurobehavioural changes and persistence of complaints in workers exposed to styrene in a polyester boat building plant: influence of exposure characteristics and microsomal epoxide hydrolase phenotype

OBJECTIVES—To investigate neurobehavioural effects and the persistence of complaints in workers exposed to styrene relative to exposure characteristics and the enzyme microsomal epoxide hydrolase (mEH) activity.
METHODS—A cross sectional study was performed in a retrospective cohort of workers of a polyester boat building plant 3 years after the main activity shut down in 1989. Workers still currently exposed to a much lower concentration of styrene in air than before (n=27) and formerly exposed workers (n=90) were compared with matched control workers (n=64). Currently and formerly exposed workers laminated 4700 and 3610 hours on average at mean exposure to styrene concentrations of 148 and 157 mg/m³ respectively. A structured neurological anamnesis into former and present complaints, the NSC-60 questionnaire, and computer assisted neurobehavioural tests (NES) were administered. The mEH phenotype activity was measured in lymphocytes with a novel gas chromatography-mass spectroscopy (GC-MS) method.
RESULTS—For the period before 1989, currently and formerly exposed workers reported more complaints than control workers which related well with the mean exposure to airborn styrene concentration (p=0.03). Most complaints disappeared after the end of exposure, although the chest, equilibrium, and somatic category scores of NSC-60 and the number of workers reporting diminished sense of smell remained increased in formerly exposed workers (p0.05). Symbol-digit substitution and digit span forwards test results were worse in currently and formerly exposed workers (p0.01). In the combined group of currently and formerly exposed workers, the symbol-digit substitution and colour-word vigilance results related well to duration of exposure (p<0.01 and p=0.03) and mEH phenotype activity (p=0.01 and p=0.05), whereas the digit span forwards results only showed associations of borderline significance (duration of exposure (p=0.08) and mEH phenotype activity (p=0.08)).
CONCLUSION—Most subjective symptoms were reversible but some persisted after the end of exposure to styrene, whereas dysfunction of visuomotor performance and perceptual speed seemed to persist. Duration of exposure at lamination tasks and the interaction, duration of exposure×concentration of exposure, were found to be the best predictors of worsening visuomotor and perceptual speed performances. Activity of the mEH phenotype may play a modulating part in styrene neurotoxicity. The results suggested that less than 10 years of exposure to atmospheric styrene at an average concentration of 155 mg/m³ may result in persistent neurotoxic effects.


Keywords: styrene; neurobehavioural performance; neurotoxicity; microsomal epoxide hydrolase     

Neurobehavioural effects of occupational exposure to lead

A set of neurobehavioural tests selected on the basis of information processing theory was used to study the effect of low level occupational lead exposure on 59 lead workers compared with a matched control group of the same number. Only one of the lead exposed group had a blood lead concentration above the current threshold limit value of 3.81 mumol/l at the time of testing (mean 2.36 mumol/l, range 1.19-3.92 mumol/l) and none had been detected above that level in the previous three years. Nevertheless, most neurobehavioural functions tested showed some impairment in the lead workers. Visual sensory function was affected and, perhaps as a consequence, sustained attention and psychomotor tasks were performed more slowly by the lead exposed group. Cognitive functions were also impaired, with sensory store memory, short term memory, and learning abilities all showing deficits in lead workers. Such cognitive deficits may also be partly due to initial degradation of the visual input. Long term memory performance compared equally with control levels possibly because of development of a compensatory strategy such as rehearsal by the lead exposed subjects. Multiple linear regression analysis relating to lead workers test performance and their lead exposure showed that performance on the sensory store memory test alone was significantly related to exposure. This was probably due to the homogeneity of the lead exposed group with regard to blood lead concentrations and the use of blood lead as a measure of chronic lead exposure.     

Psychological performance of workers with blood-lead concentration below the current threshold limit value

Summary The effects of lead exposure on psychological test performance and subjective feelings of well-being were investigated in 40 exposed workers whose PbB levels had never exceeded 60 g/100 ml and in 20 controls matched for sex, age and educational level. The exposed workers were divided into two groups of 20, with recent PbB levels in the range 45–60 g/100 ml or below 35 g/100 ml. The group of workers with the higher PbB levels showed significantly poorer performance and reported more physical symptoms than the other two groups. These differences were unrelated to socio-demographic and personality characteristics. A principal component analysis suggested that the poorer performance was mainly due to an impairment of general functioning and only to some extent to a deterioration in specific functions, such as verbal reasoning and abstraction. Higher lead concentrations were correlated with poorer performance and a higher number of physical complaints. These results indicate that in exposed workers the threshold for impaired performance lies below the blood-lead concentration of 60 g/100 ml, which is the current threshold limit value (TLV).This study was supported by the Consiglio Nazionale delle Ricerche (CNR, Roma), Gruppo Nazionale Scienze del Comportamento (Grant no. 81.00083.04 and no. 82.02117.04)     

Neurobehavioural effects of occupational exposure to lead.

A set of neurobehavioural tests selected on the basis of information processing theory was used to study the effect of low level occupational lead exposure on 59 lead workers compared with a matched control group of the same number. Only one of the lead exposed group had a blood lead concentration above the current threshold limit value of 3.81 mumol/l at the time of testing (mean 2.36 mumol/l, range 1.19-3.92 mumol/l) and none had been detected above that level in the previous three years. Nevertheless, most neurobehavioural functions tested showed some impairment in the lead workers. Visual sensory function was affected and, perhaps as a consequence, sustained attention and psychomotor tasks were performed more slowly by the lead exposed group. Cognitive functions were also impaired, with sensory store memory, short term memory, and learning abilities all showing deficits in lead workers. Such cognitive deficits may also be partly due to initial degradation of the visual input. Long term memory performance compared equally with control levels possibly because of development of a compensatory strategy such as rehearsal by the lead exposed subjects. Multiple linear regression analysis relating to lead workers test performance and their lead exposure showed that performance on the sensory store memory test alone was significantly related to exposure. This was probably due to the homogeneity of the lead exposed group with regard to blood lead concentrations and the use of blood lead as a measure of chronic lead exposure.     

Long-term use of organophosphates and neuropsychological performance

This study evaluated neuropsychological effects due to chronic organophosphate use among farmers with no history of acute poisoning. Fifty-seven male tree fruit farmers (exposed) were compared with 42 age-matched male cranberry/blueberry growers and hardware store owners (unexposed). Univariate analyses of covariance (reading test as covariate) comparing exposed and unexposed subjects revealed significantly slower reaction time. No other significant differences were noted on tests of concentration, visuomotor skills, memory, expressive language, or mood. Based on an exposure metric derived from detailed exposure histories, farmers were divided into high exposure (n = 40) and low exposure (n = 59) groups, and their neuropsychological performance was compared. Analysis of covariance with age and reading test score as covariates revealed that the high exposure group had significantly slower reaction time, dominant hand. Long-term use of organophosphates without evidence of an acute poisoning episode appears to produce, at most, subtle changes in neuropsychological performance. Am. J. Ind. Med. 32:487–496, 1997. © 1997 Wiley-Liss, Inc.     

Neuropsychological function in Gulf War veterans: relationships to self-reported toxicant exposures.

BACKGROUND: The present study was aimed at (1) exploring evidence of central nervous system (CNS) dysfunction among Gulf War (GW) veterans on neuropsychological tests and (2) examining whether performance on neuropsychological tests was related to specific neurotoxicant exposures experienced in the Gulf. METHODS: The GW-deployed groups were selected using stratified random sampling methods from two distinct cohorts of GW veterans. A comparison group that had been called up for GW service but deployed to Germany rather than the Gulf also was examined. Neuropsychological function was assessed using a pre-determined battery chosen to include tests known to be highly sensitive to the behavioral effects of the neurotoxicants thought to have been present in the Gulf. RESULTS: Self-reported exposures were related to neuropsychological test performance controlling for post-traumatic stress disorder, major depression, and other known covariates of neuropsychological test performance. Results showed that GW-deployed veterans performed more poorly than the Germany-deployed veterans on several specific neuropsychological tests, but after adjustment for multiple comparisons, only the differences in mood complaints remained significant. Within the GW-deployed group, self-reported exposure to chemical warfare agents was associated with poorer performance on cognitive tests involving specific functional domains. CONCLUSIONS: Results provide evidence that there are subtle differences in CNS function among GW-deployed veterans who report chemical warfare agent exposure while in the GW theater.     

Neurobehavioural effects of repeated occupational exposure to toluene and paint solvents.

In studies of two workforces 44 men exposed to paint solvents and 52 men working with toluene were compared with age matched comparison groups of non-exposed workers. Scores on a series of performance tests were examined, the solvent exposed in each study functioning less well than their comparison group. The apparent deficit among the paint exposed workers was substantial, but this was reduced after allowance for estimated intellectual capacity. No deficit was apparent on rematching with a second comparison group of more appropriate measured capacity. No evidence was found of impaired nerve conduction in the ulnar or median nerves, and few clinical signs of neurological damage were apparent. Nevertheless, in an associated inquiry of neuropsychological symptoms among 236 painters and 128 non-exposed workers a highly significant excess of symptoms was found among those exposed to paint solvents.     

Evaluation of neuropsychological symptoms and exposure to benzene, toluene and xylene among two different furniture worker groups in Izmir

This study was conducted to determine whether there was any exposure to toluene, xylene and benzene and to assess the health impact of these solvents on workers in furniture enterprises in Karabaglar, Izmir. This cross-sectional study covered furniture enterprises in Karabaglar, Izmir. This study was comprised of an exposed group consisting of workers engaged in painting and varnishing and therefore exposed either directly or indirectly toluene, xylene and benzene in the workplace and the non-exposed group engaged in other aspects of production. While a total of 261 individuals completed questionnaires, 210 workers agreed to provide blood samples. Blood solvents levels were determined using gas chromatograph at Ege University, Intoxication Research and Application Centre. The modified EUROQUEST questionnaire was used to assess neuropsychological symptoms and neurological and general examination were performed. Occupational and exposure history, demographic and work-related information was collected. In this study of workers, blood toluene and benzene levels were found to be significantly higher among those engaged in painting and varnishing compared to those who perform other tasks. The average blood toluene and benzene concentrations among exposed workers were 6.95 times and 1.64 times respectively higher than those in the nonexposed groups. Smokers and participants who worked in excess of 8 hours/day had higher blood toluene and benzene levels. The most frequently work-related health complaints were back pain, allergies and asthma. No differences were found in the average scores in the neuropsychological symptoms questionnaire between exposed and non-exposed groups. Neurological examination of two individuals with these complaints revealed a loss of reflexes. The workers were unaware that they were being exposed to solvents at work. Tobacco smoke is a major source of internal exposure to benzene. Improving working conditions in furniture work places is a priority.