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Biomedical subjects

D Mergler

Publications and source records attributed to D Mergler.

At least 37 records · Page 2Linked to original sources
PubMed1998

Neurotoxic effects of low-level methylmercury contamination in the Amazonian Basin.

Many studies have demonstrated mercury contamination in the Amazonian ecosystem, particularly in fish, a dietary mainstay of populations in this region. The present study focused on potential health effects of this low-level methylmercury exposure. The study was carried out in a village on the Tapajós River, a tributary of the Amazon, on 91 adults inhabitants (15-81 years), whose hair mercury levels were inferior to 50 mu/g. Performance on a neurofunctional test battery and clinical manifestations of nervous system dysfunction were examined in relation to hair mercury concentrations. Near visual contrast sensitivity and manual dexterity, adjusted for age, decreased significantly with hair mercury levels (P < 0.05), while there was a tendency for muscular fatigue to increase and muscular strength to decrease in women. For the most part, clinical examinations were normal, however, hair mercury levels were significantly higher (P < 0.05) for persons who presented disorganized movements on an alternating movement task and for persons with restricted visual fields. These results suggest dose-dependent nervous system alterations at hair mercury levels below 50 micrograms/g, previously considered a threshold for clinical effects. The profile of dysfunction in this adult population is consistent with the current knowledge on methyl-mercury poisoning. The long-term implications of these findings are unknown and need to be addressed.

Adolescent↗
PubMed1997

Early manifestations of manganese neurotoxicity in humans: an update.

It is possible to detect early signs of neurotoxic dysfunction associated with occupational and environmental exposure to manganese; neurophysiologic and neurobehavioral tests can be used in the absence of clinical manifestations. Although outcomes from individual studies vary, they collectively show a pattern of slowing motor functions, increased tremor, reduced response speed, enhanced olfactory sense, possible memory and intellectual deficits, and mood changes. This overall portrait is consistent with the action of manganese on the central nervous system. In reports to date, there is little consistency in dose-effect relationships between internal parameters of manganese exposure (blood manganese, urinary manganese, hair manganese) and external measures and neurologic outcomes. Several studies suggest the existence of dose-effect relationships, but additional clarification is needed.

Environmental Exposure↗
PubMed1997

Peripheral markers of catecholaminergic dysfunction and symptoms of neurotoxicity among styrene-exposed workers.

AIM: A cross-sectional investigation was carried out to assess possible relations between styrene-induced changes in three peripheral markers of catecholaminergic dysfunction and self-reported symptoms of neurotoxicity. SUBJECTS: Male workers (n = 46) aged 14-60 (mean 29.5) years who had been exposed to styrene for an average of 6 (0.2-29) years were recruited in glassfiber reinforced plastics plants. A control group of 30 blue-collar workers aged 22-52 (mean 35) years and with no history of exposure to chemicals was recruited from local industries. Styrene exposure ranged from 5 to 120 ppm (8 h-TWA), the median level being relatively low (25 ppm, 8 h-TWA). Styrene metabolites, mandelic and phenylglycoxylic acids (MAPGA) in the "next morning" urine spot samples ranged from 32.0 to 931.1 mg/g creatinine (median 186.5). METHODS: Platelet monoamine oxidases B (MAO B) and dopamine beta-hydroxylase (DBH) activities were assessed using methods based on HPLC and electrochemical detection. Plasma prolactin (PRL) was measured by a commercially available immunoassay. Questionnaire 16 (Q16) was used to survey self-reported symptoms. RESULTS: Although there was no difference in DBH activity between exposed workers and controls, the most highly exposed workers had significantly lower activity than control subjects. A tendency to lower platelet MAO B activity in exposed than in control subjects was observed. The prevalence of plasma DBH and platelet MAO B values below the lower reference limit was similar in the two groups. PRL values exceeding the upper reference limit were higher (14/46 vs 2/30) among styrene-exposed workers, who also exhibited significantly higher median levels (10.0 vs 5.7 micrograms/l) than control subjects. Although the number of reported symptoms was similar among exposed and control subjects, in the exposed group it was positively associated with urinary MAPGA (Rho = 0.30, P = 0.04). Of the three peripheral markers of catecholaminergic dysfunction, plasma DBH was the only parameter negatively related to both urinary MAPGA (F = 9.56, P = 0.003) and the number of reported symptoms (Rho = 0.23, P = 0.05). CONCLUSIONS: Plasma PRL appears to be a sensitive marker of styrene-induced tubero-infundibular dopaminergic dysfunction in male subjects. DBH in plasma and MAO B in platelets seem to be less suitable markers for biomonitoring effect at the individual level, although DBH was related to the number of reported symptoms and to internal dose. Further studies on a larger and more exposed population are necessary to clarify the significance of these markers for health and their predictive value with regard to both subjective disturbances and concurrently administered performance tests.

Adolescent↗
PubMed1996

Evidence of early nervous system dysfunction in Amazonian populations exposed to low-levels of methylmercury.

There is increasing concern about the potential neurotoxic effects of exposure to methylmercury in Amazonian populations due to mercury (Hg) release from gold-mining activities. A preliminary study was undertaken in two villages on the Tapajos River, an effluent of the Amazon, situated over 200 km downstream from the extraction areas. The study population included 29 young adults (< or = 35 years), 14 women and 15 men, randomly chosen from a previous survey. Hair analyses were conducted with cold vapor atomic fluorescence spectrophotometry. Total hair Hg (THg) varied between 5.6 micrograms/g and 38.4 micrograms/gl, with MeHg levels from 72.2% to 93.3% of the THg. A quantitative behavioural neurophysiological test battery, designed for use under standard conditions, in an area without electricity and for persons with minimal education was administered to all participants. The results of visual testing showed that although all participants had good near and far visual acuity, color discrimination capacity (Lanthony D-15 desaturated panel) decreased with increasing THg (F = 4.1; p = 0.05); near visual contrast sensitivity profiles (Vistech 6000) and peripheral visual field profiles (Goldman Perimetry with Targets I and V) were reduced for those with the highest levels of THg. For the women, manual dexterity (Santa Ana, Helsinki version) decreased with increasing THg (F = 16.7; p < 0.01); this was not the case for the men. Although the women showed a tendency towards reduced grip strength, muscular fatigue did not vary with THg for either sex. The findings of this study demonstrate that it is possible, using a sensitive test battery, to detect alterations in nervous system functions, consistent with knowledge on Hg toxicity, at levels below the currently recognized threshold of 50 micrograms/g THg.

Adolescent↗
PubMed1996

[Mental health deterioration in workers exposed to styrene].

Emotional instability which might be an early symptom of more severe disorders, is one of the first manifestations of chronic exposure to organic solvents. The present study measures the association between exposure to styrene and mood states of active workers. A total of 128 workers (85% of the total population) from 3 factories where styrene is used, participated on a voluntary basis. They filled out the following self-administered questionnaires: Profile of Mood States (POMS), Psychiatric Symptom Index and Well-being Index. The results indicate a significant relationship between post work-shift urinary mandelic acid (biological indicator of styrene exposure) and the scores obtained on the POMS scales of tension-anxiety (Spearman's rank correlation rho = 0.30; p < 0.01), anger-hostility (rho = 0.29; p < 0.01), fatigue-inertie (rho = 0.34; p < 0.01), and confusion-bewilderment (rho = 0.23; p = 0.04), as well as the Psychological Distress Index (rho = 0.30; p < 0.01). All scores were adjusted for the effects of 4 potentially confounding variables: age, schooling, alcohol and cigarette consumption. These indicators of mood states do not constitute a diagnosis of mental disease but reveal progressive deterioration of well being associated with neurotoxic exposure in the workplace.

Adult↗
PubMed1996

Color vision loss among styrene-exposed workers neurotoxicological threshold assessment.

Styrene represents nowadays one of the most used organic solvent. The current exposure limit proposed for this chemical differs significantly from country to country: the Threshold Limit Value-Time Weighted Average (TLV-TWA) proposed by the American Conference of Governmental Industrial Hygienists (ACGIH) is 50 ppm while the German, Finnish and Swedish occupational exposure limit is 20 ppm. Nevertheless, effects on the nervous system were recently reported in workers exposed at TWA styrene levels below the current TLV. Neuro-optic pathways have been shown to be particularly vulnerable to organic solvent exposure. Analysis and measurements of visual functions can provide important information on early neurotoxic effects. Previous studies support the hypothesis that styrene exposure can induce a dose-dependent color vision loss. The aim of this study is to assess a threshold level below which no detectable effect occurs for color vision. We applied a sub-application of the change point problem in two-phase regression considering one phase as a constant line. In accordance with this model the maximum-likelihood technique was used as a method to examine the dose- effect relationship between external styrene exposure and chromatic discrimination. The present article presents a joint analysis of data from two previously published studies, one carried out in Canada and the other in Italy. The age and seniority of the workers from both countries were remarkably similar, as were the process type, the chemicals used and the work-tasks of exposed subjects. The mathematical method presented here shows the existence of a statistically significant threshold. This finding shows that, in fiberglass-reinforced plastics industry, visual color impairment could be significantly detected above 4 ppm (upper limit of the confidence interval at 5% = 26 ppm). The exact clinical meaning of this effect, and also the progress of the impairment in exposed workers, is still to be assessed in further studies. The results of our study support the need of a reduction of the occupational limits for styrene in workplaces to values close to or lower than German, Finnish or Swedish exposure limits.

Adult↗
PubMed1995

Peripheral markers of catecholamine metabolism among workers occupationally exposed to manganese (Mn).

In a preliminary study of 11 men randomly selected in a ferro-alloy plant and of 15 control subjects, platelet monoamine oxidase (MAO) and serum dopamine beta-hydroxylase (DBH) activities were measured. A tendency towards lower MAO-B activity in the exposed workers as compared to control subjects (t = 1.95; P = 0.06) was found whereas DBH activity was similar. In the exposed group, a dose-effect relationship was noted between a manganese (Mn) cumulative exposure index (CEI) and DBH activity (R2 = 0.40, P < 0.05). Since DBH is an expression of catecholamine release, the relative increase in such activity could be envisaged as a compensatory mechanism to a reduced turnover rate as reflected by MAO-B activity. Owing to the limited sample size, these findings should be confirmed by further epidemiological and experimental studies.

Adult↗
PubMed1995

Visual dysfunction among styrene-exposed workers.

OBJECTIVES: The present study was undertaken to examine the relation between visual functions and occupational exposure to styrene. METHODS: A total of 128 workers (85% of the total population), from three glass-reinforced plastics plants in Canada, agreed to participate in the study. Environmental and biological measures were made on the day(s) prior to the assessment of near visual acuity (National Optical Visual Chart), chromatic discrimination (Lanthony D-15 desaturated panel), and near contrast sensitivity (Vistech 6000). The analyses were performed on 81 workers with near visual acuity of at least 1 min of arc at 0.5 m. RESULTS: The subjects were relatively young [29 (SD 8) years], with little seniority [5 (SD 4) years]. Styrene exposure for 8 h ranged from 6 to 937 (first quartile 21 mg.m-3, third quartile 303 mg.m-3), depending on the job site. The end-shift concentrations of urinary mandelic acid ranged from nondetectable to 1.90 mmol.mmol creatinine-1. Significant positive relations were found between the internal and external styrene exposure measurements and color vision loss adjusted for age, alcohol consumption, and seniority in a multiple regression analysis. The multiple regression analysis is also showed that the end-shift concentration of urinary mandelic acid was inversely related to contrast sensitivity at 6 and 12 cycles.degree-1. Logistic multiple regression models indicated that the end-shift concentration of urinary mandelic acid was related to the prevalences of blurred vision, tearing, and eye irritation. CONCLUSIONS: These findings suggest that there is a positive relation between styrene exposure and early color and contrast vision dysfunction.

Adult↗
PubMed1995

[Monitoring neurotoxic effects among laboratory personnel working with organic solvents].

The relationship between organic solvent exposure and central nervous disorders make early detection of neurophysiologic et neuropsychologic alterations in organic solvent exposed workers a priority. Moreover, the variability in the frequency of exposure and the numerous organic solvents encountered in scientific laboratories render the environmental and biological measurements used in medical surveys almost impossible. The present study was undertaken to appreciate the potential neurotoxic effects of organic solvents handling in laboratory employees. Neurophysiological and neuropsychological tests batteries were used with each worker and data were adjusted for potential confounding factors (age and education level). A Principal Components Analysis were performed to reduce the information and the first five factors corresponded to: mood states, speed coding, contrast vision in high frequencies, manual dexterity and contrast vision in low frequencies. These five factors were compared between the daily manipulators of at least one solvent (n = 75) and the non or occasional solvent users (n = 35). The results from this study showed that subjects directly in contact with solvents had a poorer mood state than those who were not or rarely exposed (p < 0.01) and that independently of the "work activity". Mood state impairment in chronic solvent exposed workers has been shown by many authors, with or without psychomotor alteration, and may reflect possible over-exposure. Detection of this instability may lead to early neurophysiologic alteration in exposed workers and permit health services to intervene before the development of irreversible effects.

Adult↗
PubMed1994

Nervous system dysfunction among workers with long-term exposure to manganese.

Neurological disorders, bearing many similarities to Parkinson's disease, have been associated with environmental and occupational exposure to manganese (Mn). To document early nervous system dysfunction associated with long-term exposure to Mn, a battery of neurofunctional tests was administered to workers employed in Mn alloy production. Study participation was 95% (n = 115). A matched pair design was used; actively working men, with no history of workplace exposure to neurotoxins, were recruited from the region as referents. Matching was done on the variables: age (+/- 3 years), educational level (+/- 2 years), smoking status, and number of children. Stationary environmental sampling indicated that Mn levels varied widely (geometric means: Mn dust, 0.89 mg/m3; respirable Mn, 0.04 mg/m3). The alloy workers had significantly higher levels of whole blood Mn (geometric mean: 1.03 microgram/100 ml vs 0.68 microgram/100 ml); no differences were observed for urinary Mn. Univariate analysis (paired t test, Signed Rank and McNemar) and multivariate analysis of variance (Hotelling-Lawley statistic) revealed that the pairs differed on symptom reporting, emotional state, motor functions, cognitive flexibility, and olfactory perception threshold; verbal fluency, basic mathematics, reading capability, and attentional capacity were similar. These findings are consistent with current knowledge on brain Mn activity and suggest that manifestations of early manganism can be observed in well designed population studies, using sensitive testing methods.

Adult↗
PubMed1994

Psychological, psychosocial, and psychophysiological sequelae in a community affected by a railroad chemical disaster.

Psychological, psychosocial, and psychophysiological sequelae were studied in a community which had experienced a railroad chemical spill of 19,000 gallons of the toxic pesticide metam sodium. Two hundred twenty exposed residents were compared to 114 controls and paired on age, education, gender, race, and number of children. A clinical interview and physiological measurements (blood pressure, pulse, and cortisol level) were taken, the MMPI-2, IES Scale, Mood Scale, Environmental Worry, Perceived Social Support, and Perceived Control Scale and a questionnaire were administered. Results indicated greater levels of depression, anxiety, and somatic symptoms in the spill residents in addition to greater environmental worry and lower perceived social support. Spill residents had higher blood pressure and less fluctuation of cortisol levels than controls. No difference on litigation status was obtained except on the IES, Intrusion and the POMS scales. Chemical disasters are associated with a wide variety of psychological, psychosocial, and physiological distress.

Acute Disease↗
PubMed1994

Olfactory adaptation, threshold shift and recovery at low levels of exposure to methyl isobutyl ketone (MIBK).

The anatomic position of olfactory receptors renders them vulnerable to airborne pollutants. Chamber inhalation studies have shown dose-dependent olfactory adaptation and temporary olfactory threshold perception shift for particular inhaled substances. The present study was undertaken to examine olfactory perception threshold (OPT) and adaptation of healthy subjects exposed for 7h to MIBK. Volunteers (n = 4) were exposed in an inhalation chamber to MIBK at concentrations of 20 ppm and 40 ppm. For each of 6 exposure days, OPT for MIBK and PM-Carbinol were determined once before exposure and at 3 successive intervals following exit. Exhaled air samples were taken at regular intervals during and after exposure. Perceived odor intensity and symptoms were ascertained through a questionnaire filled out hourly. On all days, post-exposure OPT-MIBK at chamber exit was significantly higher than pre-exposure, representing a ninefold increase in concentration; recovery was dose-dependent and not complete 95 min. after exit. No threshold shift was observed for OPT-PM-Carbinol. Perceived odor intensity was high when entering the chamber, but diminished with time, stabilizing after approximately 2 hours. Symptoms of nose, eye or throat irritation and headache were present in some subjects. The findings of this study suggest that at these levels of MIBK, there is olfactory adaptation during exposure and a transient OPT shift for the inhaled substance. Persons exposed professionally or environmentally to certain organic solvents may suffer temporary smell loss which hinders odor detection.

Adaptation, Physiological↗
PubMed1994

Diadochokinesimetry: a study of patients with Parkinson's disease and manganese exposed workers.

Diadochokinesia, the ability to perform rapid alternating movements is often impaired in patients with extrapyramidal disease. It is a common sign among patients with Parkinsonism or manganism. In the present study we compare patients with Parkinson's disease (n = 11), workers formerly exposed to manganese (n = 10) and control subjects (n = 11) performing rapid alternating hand movements for 5 s under four conditions repeated twice (natural cadence and maximal speed with one or two hands). Data recorded using a diadochokinesimeter built in our laboratory and connected to a 486/33 microcomputer were digitized in real time while subjects rotated back and forth hand held foam spheres connected to flexible rods articulated with optical encoders. Significant differences were found between control subjects and patients with Parkinson's disease, but not with manganese exposed workers, in most variables examined. However, trajectory length (a combination of movement amplitude and velocity) indicated that manganese exposed workers and patients with Parkinson's disease were significantly different from the controls in functional asymmetries between right and left hand. In addition, workers and patients tend to have marked differences between the performance of right and left hands. Improved quantitative measurement of rapid alternating movements may prove to be an important tool in early and differential diagnosis of Parkinson's disease and manganese exposure.

Humans↗
PubMed1994

Aftermath of a chemical spill: psychological and physiological sequelae.

Psychological, and psychophysiological sequelae were studied in a community which had experienced a railroad chemical spill of 19,000 gallons of the toxic pesticide metam sodium. Information was collected on 350 persons living in the area of the spill (spill residents) and 114 nonexposed controls, recruited using a randomized sampling strategy, from a nearby similar, but unexposed control town. Psychological measures used were the MMPI-2, POMS, IES Scale, Environmental Worry, Perceived Social Support and Perceived Control Scale. Physiological measurements were two measurements of blood pressure, pulse, and salivary cortisol level, taken both at the beginning and the conclusion of the study. Demographic and medical information was asked in a Questionnaire. Results indicate greater levels of depression, anxiety, and somatic symptoms in the spill residents in addition to greater environmental worry and lower perceived social support. Spill odor perception was related to increased psychological and physiological sequelae. The spill residents had higher blood pressure and less fluctuation of cortisol levels than the controls. Comparison of spill residents who were litigants and those who were not, indicates no differences for blood pressure, pulse, and cortisol, MMPI-2, Environmental Worry and the Control Scale. Litigants scored slightly higher on the IES, Intrusion and the POMS scales. No dose/response relationship between distance to the river and evacuation status was obtained. The chemical spills was associated with a wide variety of psychological and physiological reactions.

Adult↗
PubMed1993

Comparison of performance from three continents on the WHO-Recommended Neurobehavioral Core Test Battery.

To address the need for standardized test batteries, an expert group convened by the World Health Organization (WHO) and the U.S. National Institute for Occupational Safety and Health during 1983 proposed the Neurobehavioral Core Test Battery (NCTB) to identify nervous system effects of chemical exposures in human populations worldwide. To determine the feasibility of using the NCTB in varied cultures, a cross-cultural assessment was conducted under WHO auspices. Data were collected in 10 countries of Europe, North and Central America, and Asia from over 2300 males and females who were not exposed to chemicals at work, within five age ranges between 16 and 65. Results suggest that performance on two NCTB tests (Simple Reaction Time, Benton Visual Retention) is very similar in a broad range of countries and that performance on four other NCTB tests (Santa Ana, Digit Symbol, Digit Span, Aiming) is relatively more variable from country to country, in both males and females. However, data collected from very poorly educated males in one country revealed very low performance levels suggesting that the NCTB may not provide an adequate reference group for identifying (behavioral) neurotoxic effects in such populations. More research is thus needed on evaluating neurotoxicity in poorly educated subjects.

Adult↗
PubMed1992

Stability of psychological impairment: two year follow-up of former microelectronics workers' affective and personality disturbance.

For the past twenty years women's complaints in the microelectronics industry have often been diagnosed as mass psychogenic illness, despite evidence of potential exposure to organic solvents, which have been associated with affect and mood changes. In the present study, the standard version of the Minnesota Multiphasic Personality Inventory (MMPI) was used to evaluate affective and personality disturbance among 63 former microelectronics workers (56 women and 7 men) over a two-year period of time. In both 1986 and 1988, the former workers obtained mean scale score elevations beyond two standard deviations above the normative sample (T = greater than 70) on the MMPI clinical scales of schizophrenia, hypochondriasis, psychasthenia, depression and hysteria. For most scales, 86-88 mean score differences did not attain the 0.05 significance level (two-tailed paired t-test) and no significant differences were observed for 86-88 comparison scale scores = greater than 70 (McNemar paired statistic). Although there were too few men to perform gender comparisons, men scored higher than women on 5 scales and all of the men had scores = greater than 70 on hypochondriasis, depression, hysteria, psychasthenia and schizophrenia. These findings reveal that these former microelectronics workers manifested affective and personality disturbances, consistent with organic solvent toxicity, which persisted over a two year period, indicating that they were not reactive, transient hysterical neurosis.

Adult↗