A conceptual framework provides the possibility to identify factors determining the effects of whole-body vibration (WBV) on the spine and the internal stress-strain relationships. Epidemiological studies were critically evaluated with respect to their significance for the derivation of quantitative exposure-effect relationships. The approach of deriving such relationships from a comparison with self-generated accelerations during daily activities was considered as unsuited. Trunk muscle activity and control with apparently identical accelerations of body parts during self-generated and forced motions differ widely. Simple biodynamic models coupled with experimental in vivo and in vitro data permitted a preliminary deduction of quantitative relationships between WBV and spinal health with the consideration of individual factors and exposure conditions. Examples of anatomy-based verified finite element models and their application are provided. Such models are considered as a very promising instrument. They can be used to assess quantitatively preventive measures and design. Future research needs concern the examination of (1) the nonlinearity of biodynamics, (2) the effects of WBV in x- and y-axes, (3) the strength of the spine for shear, (4) the contact parameters between the seat and man, (5) the significance of postures and muscle activity, and (6) material properties of spinal structures.
Exposure to whole-body vibration is a risk factor for the development of low back pain. In order to develop a fuller understanding of the response of the seated person to vibration, experiments have been conducted in the laboratory investigating the biomechanics of the seated person. Some of these methods are based on the driving force and acceleration at the seat and are reported in the literature as apparent mass, driving point mechanical impedance or absorbed power. This paper introduces the background behind such impedance methods, the theory and application of the methods. It presents example data showing typical responses of the seated human to whole-body vibration in the vertical, fore-and-aft and lateral directions. It also highlights problems that researchers might encounter in performing, analysing and interpreting human impedance data.
Researches into the relationship between the physical quantity of vibration and the subjectively perceived quantity become important in designs for the vibration environment. Subjective experimental methods to obtain the relationship between the physical quantity of vibration and the subjectively perceived quantity are different depending on the design objectives which consider the human sense of vibration characteristic. In this review, the following are outlined: (i) fundamental methods for obtaining the design objectives for vibration environments; (ii) reported findings on the physical quantity of vibration environments and the human characteristics of sense vibration; and (iii) problems with and limits of the ISO 2631-1 standard, which defines the subjective response of the ride comfort in public transportation. Finally, the directions of research into the subjective experimental methods for obtaining design objectives in the vibration environment considering of the human characteristics of sense vibration are described.
The U.S. Army Aeromedical Research Laboratory conducted a research program to develop a new methodology for health hazard assessment of tactical ground vehicle rides. This paper describes the new method and compares the health risk prediction using the new multiple shocks standard International Standards Organization (ISO 2631-5) to predictions by the current whole-body vibration (WBV) standard (ISO 2631-1). This article also describes the software tool developed to implement both parts of ISO 2631, as well as Army Regulation 40-10. The comparison shows the new standard to be more sensitive to cross-country terrain than other standards. Data analysis demonstrates the applicability of the new ISO 2631-5 standard to tactical ground vehicles, especially in the vertical axis.
Occupational exposure to whole-body vibration is often combined with a requirement to perform twisting actions. This paper reports a study where the effect of twisting on the biomechanical response of the seated person was investigated. Twelve male subjects were exposed to vertical random whole-body vibration at 0.4 m/s2 r.m.s. Each subject sat in four different postures: ‘back-on’, ‘back-off’, ‘twist’ (where subjects were required to twist the torso by 90°) and ‘move’ (where subjects were required to performing a moving task with extended arms). Similar apparent masses were measured for the ‘back-on’, ‘back-off’ and ‘twist’ conditions, where a peak occurred at about 6 Hz. For the ‘move’ condition, the peak in the apparent mass was attenuated indicating a different biomechanical response in this posture. The 6 Hz peak in fore-and-aft cross-axis apparent mass was eliminated in the ‘move’ condition. It is suggested that the change in biomechanical response is due to either the extended arms acting as a passive vibration absorber or that the twisting action interferes with the usual acceleration-muscle feedback system. Further work will be required to test these hypotheses.
The response characteristics of seated human subjects exposed to fore-aft (x-axis) and lateral (y-axis) vibration are investigated through measurements of dynamic interactions between the seated body and the seat pan, and the upper body and the seat backrest. The experiments involved: (i) three different back support conditions (no back support, and upper body supported against a vertical and an inclined backrest); (ii) three different seat pan heights (425, 390 and 350 mm); and three different magnitudes (0.25, 0.5 and 1.0 m/s2 rms acceleration) of band limited random excitations in the 0.5-10 Hz frequency range, applied independently along the fore-aft and lateral directions in an uncoupled manner. The body force responses, measured at the seat pan and the backrest along the direction of motion, are applied to characterize the total body apparent mass (APMS) reflected on the seat pan, and those of the upper body reflected on the backrest. Unlike the widely reported responses of seated occupants under vertical vibration, the responses to horizontal vibration show strong effect of excitation magnitude. The large displacements at lower frequencies cause considerable rotations of the upper body, and the knees and ankles, particularly when seated without a back support, which encouraged the occupants to continually shift larger portion of the body weight towards their feet. This together with the strong dependence on the excitation magnitude resulted in considerable inter-subject variability of the data. The addition of a back support causes stiffening of the body to limit the low frequency rocking motion of the upper body under x-axis motion, while considerable dynamic interactions with the backrest occur. The mean apparent mass (APMS) responses measured at the seat pan and the backrest suggest strong contributions due to the back support condition, and the direction and magnitude of horizontal vibration, while the role of seat height is important only in the vicinity of the resonant frequencies. In the absence of a back support, the seat pan responses predominate at a lower frequency (near 0.7 Hz) under both directions of motion, while two secondary peaks in the magnitude also occur at relatively higher frequencies. The addition of back support causes the seat pan response to converge mostly to a single primary peak, resulting in a single-degree-of-freedom like behavior, with peak occurring in the 2.7-5.4 Hz range under x-axis, and 0.9-2.1 Hz range under y-axis motions, depending upon the excitation magnitude and the back support condition. This can be attributed to the stiffening of the body in the presence of the constraints imposed by the backrest. A relaxed posture with an inclined backrest, however, causes a softening effect, when compared to an erect posture with a vertical backrest. The backrest, however, serves as another source of vibration to the seated occupant, which tends to cause considerably higher magnitude responses. The considerable magnitudes of the apparent mass response measured at the seat back under fore-aft motions suggest strong interactions with the backrest. Such interactions along the side-to-side motions, however, are relatively small. The results suggest that the biodynamic characterization of seated occupants exposed to horizontal vibration requires appropriate considerations of the interactions with the backrest.
Objective: The purpose of this study was to investigate the apparent mass of the sitting human body and to compare it with current experimental data and the ISO 5982 standard impedance model. Method: The apparent mass of the seated human body in the vertical direction was measured. Twelve male subjects were exposed to random whole-body vibration of frequency range (1-20 Hz), with a vibration excitation level of 1.0 m/s2 r.m.s. The body posture was upright with no backrest contact. Results: The obtained apparent masses were compared to the International Standard, (ISO 5982). The biodynamic response of the seated Japanese subjects peaked in the 4-6.5 Hz frequency range, which is little bit higher than the reported range of fundamental frequencies (4.5-5 Hz) in most other studies which used different experimental conditions. The outcomes show a clear difference between apparent mass of Japanese subjects and ISO 5982 data. Conclusion: It is not sufficient to apply the ISO 5982 standard to Japanese vehicle design or dummy design.
In vehicle systems occupational drivers might expose themselves to vibration for a long time. This may cause illness of the spine such as chronic lumbago or low back pain. Therefore, it is necessary to evaluate the influence of vibration to the spinal column and to make up appropriate guidelines or counter plans. In ISO2631-1 or ISO2631-5 assessment of vibration effects to human in the view of adverse-health effect was already presented. However, it is necessary to carry out further research to understand the effect of vibration to human body to examine their validity and to prepare for the future revision. This paper shows the detail measurement of human response to vibration, and the modelling of the seated human body for the assessment of the vibration risk. The vibration transmissibilities from the seat surface to the spinal column and to the head are measured during the exposure to vertical excitation. The modal paramters of seated subject are extracted in order to understand the dominant natural modes. For the evaluation of adverse-health effect the multi-body modelling of the spinal column is introduced. A simplified model having 10 DOFs is counstructed so that the transmissibilities of the model fit to those of experiment. The transient response analysis is illustrated when a half-sine input is applied. The relative displacements of vertebrae are evaluated, which can be a basis for the assessment of vibration risk. It is suggested that the multi-body dynamic model is used to evaluate the vibration effect to the spinal column for seated subjects.
The biodynamics of human hand-arm system is one of the most important foundations for the measurement, evaluation, and risk assessment of hand-transmitted vibration (HTV) exposure. This paper presents a new conceptual model relating factors influencing cause-effect relationships for HTV exposure, a new study strategy, and a comprehensive review of the recent advances in the biodynamics closely associated with HTV exposure. The review covers the following five aspects: theoretical modeling of biodynamic responses, vibration transmissibility, driving-point biodynamic responses, evaluation of anti-vibration gloves, and applied forces. This review finds that some significant advances in each of these aspects have been achieved in the recent years. Several important issues and problems in the biodynamic measurement have been identified and resolved, which has significantly helped improve the reliability and accuracy of the experimental data. The results reported in recent years suggest that, from the point of view of biodynamics, the frequency weighting specified in ISO 5349-1 (2001) overestimates the low frequency effect but underestimates the high frequency effect on the fingers and hand. The major problems, issues, and topics for further studies are also outlined in this paper. It is anticipated that the further studies of the biodynamics of the system will eventually lead to establishment of a robust vibration exposure theory. Although this review focuses on the biodynamics of the hand-arm system, the fundamental concepts and some methodologies reviewed in this paper may also be applicable for the study of whole-body vibration exposure.
The European Union adopted a Directive in 2002 on minimum requirements for the health and safety of workers exposed to vibration. This is known as the Physical Agents (Vibration) Directive. It builds on existing general employers' duties to manage risks to health and safety, and introduces exposure action and limit values for both hand-arm vibration and whole-body vibration, setting minimum standards for the control of vibration risks across Europe. New Regulations on Vibration at Work will be introduced in Great Britain on 6 July 2005 to implement the Directive. These Regulations should serve to strengthen the continuing work of the Health and Safety Executive (HSE) to reduce exposures to hand-arm vibration in British industry. Implementation of the Directive for whole-body vibration presents a different challenge and the HSE is currently preparing appropriate guidance to accompany the Regulations. This will form part of an holistic approach to back pain in professional drivers, setting vibration in context with other risk factors, particularly postural concerns and manual handling operations.
To review the main achievement and problems of study on hand-arm vibration syndrome in China. The epidemiological and clinical study indicate that HAVS was reported from almost provinces in China, the prevalence of VWF ranges from 2.5% to 82.8% in the workers with vibrating tool use. The exposure-response relationship between prevalence of VWF and intensity and duration of exposed to hand-transmitted vibration has confirmed. Diagnostic criteria of HAVS has been established and performed by Chinese government in 1985, and it was revised by government as a national standard for occupational health in 2002. The “hygienic standard for hand-transmitted vibration in workplace” as a national standard and the “methods of measurement and assessment for hand-transmitted vibration” as a recommend standard were published by government also. The limited value of exposed to hand-arm vibration was 5.0 m/s2 that is energy equivalent frequency-weighted acceleration for a period of 4 h (ahw(4)). There are some problems in this field of China need to further study in the future.
The hand-tool coupling force in the operation of a vibrating tool is generally composed of applied force (AF) and biodynamic force (BF). There is wide interest in quantifying the coupling force. The objectives of this study are to develop an effective method for estimating the BF and to investigate its fundamental characteristics. Using the biodynamic response of the hand-arm system, such as apparent mass or mechanical impedance, and the acceleration that can be measured on vibrating tools, this study proposed an indirect method for the BF estimation. The BFs distributed on the fingers and the palm of the hand along the forearm direction (zh-axis) in the operations of eighteen types of tool were estimated and used to identify the distributed BF characteristics. The results indicate that the BFs depend on both the tool vibration spectrum and the biodynamic properties of the hand-arm system. The dominant BF frequency component is usually at the same frequency as the dominant vibration frequency of each tool. The BF distributed on the palm (2-98 N) is much higher than that distributed on the fingers (1-30 N) at frequencies less than 100 Hz, but these biodynamic forces (2-22 N) are comparable at higher frequencies. The palm BF on several tools with relatively low dominant frequencies (≤40 Hz), especially in the resonant frequency range (16-40 Hz), is comparable with the applied palm force (50-100 N). Since the resonant frequency of the palm BF is also in the range of the dominant vibration frequencies of many percussive tools, the palm BF may be related to the disorders in the wrist-arm system. The BF on the fingers is likely to be closely related to the dynamic stresses and deformations in the fingers and it may thus be used to quantify the finger vibration exposure.
The biodynamic responses of the hand-arm system under xh-axis vibration are investigated in terms of the driving point mechanical impedance (DPMI) and absorbed power in a laboratory study. For this purpose, seven healthy male subjects are exposed to two levels of random vibration in the 8-1,000 Hz frequency range, using three instrumented cylindrical handles of different diameters (30, 40 and 50 mm), and different combinations of grip (10, 30 and 50 N) and push (0, 25 and 50 N) forces. The experiments involve grasping the handle while adopting two different postures, involving elbow flexion of 90° and 180°, with wrist in the neutral position for both postures. The analyses of the results revealed peak DPMI magnitude and absorbed power responses near 25 Hz and 150 Hz, for majority of the test conditions considered. The frequency corresponding to the peak response increased with increasing hand forces. Unlike the absorbed power, the DPMI response was mostly observed to be insensitive to variations in the excitation magnitude. The handle diameter revealed obvious effects on the DPMI magnitude, specifically at frequencies above 250 Hz, which was not evident in the absorbed power due to relatively low velocity at higher frequencies. The influence of hand forces was also evident on the DPMI magnitude response particularly at frequencies above 100 Hz, while the effect of hand-arm posture on the DPMI magnitude was nearly negligible. The magnitude of power absorbed within the hand and arm was observed to be strongly dependent upon the excitation level over the entire frequency range, while the influence of hand-arm posture on the total absorbed power was observed to be important. The effect of variations in the hand forces on the absorbed power was relatively small for the bent elbow posture, while an increase in either the grip or the push force coupled with the extended arm posture resulted in considerably higher energy absorption. The results suggested that the handle size, hand-arm posture and hand forces, produce coupled effect on the biodynamic response of the hand-arm system.
A new frequency weighting method to assess hand-arm vibration exposure is proposed in this paper. The influence of frequency components was first estimated using the method of multivariate analysis, then a simple form of the weighting curve was introduced. Compared with the frequency weighting in the current ISO 5349-1 (2001), the proposed weighting can better explain the relationship between rates of symptoms and vibration exposure among vibrating tool users. Although this new weighting is derived from limited data, it suggests that the current weighting in ISO 5349-1 should be changed to give more weight to the high frequency range and less weight to the low frequency range.
The frequency weighting for assessing hand-transmitted vibration exposure is critical to obtaining a true dose-response relationship. Any valid weighting must have a solid theoretical foundation. The objectives of this study are to examine the biodynamic foundation for assessing the vibration exposure and to develop a set of biodynamic methods to formulate the frequency weightings for different anatomical locations of the fingers-hand-arm system. The vibration transmissibility measured on the fingers, hand, wrist, elbow, shoulder, and head was used to define the transmitted acceleration-based (TAB) frequency weighting. The apparent masses measured at the fingers and the palm of the hand were used to construct the biodynamic force-based (BFB) weightings. These weightings were compared with the ISO weighting specified in ISO 5349-1 (2001). The results of this study suggest that the frequency weightings for the vibration-induced problems at different anatomical locations of the hand-arm system can be basically divided into three groups: (a) the weighting for the fingers and hand, (b) the weighting for the wrist, elbow, and shoulder, and (c) the weighting for the head. The ISO weighting is highly correlated with the weighting for the second group but not with the first and third groups. The TAB and BFB finger weightings are quite different at frequencies lower than 100 Hz, but they show similar trends at higher frequencies. Both TAB and BFB finger weightings at frequencies higher than 20 Hz are greater than the ISO weighting.
In the United Kingdom the diagnosis of Hand-arm Vibration Syndrome varies depending on the purpose of that diagnosis. The criteria differ in three situations. More than 100,000 miners and ex-miners with claims for HAVS have been examined using a Medical Assessment Process which included the use of standardised tests. This contract is unique but it has had significant effects on the two other processes. The Industrial Injuries Disablement Benefit Scheme provides a benefit that can be paid to an employed earner because of an accident or Prescribed Disease. New recommendations have been published to remove the anomalies in the present format for assessing HAVS. If implemented the new scheme will recognise the Stockholm Workshop Scales and workers with neurological problems will also be compensated. The Health and Safety Executive will issue new guidance in the near future on the hazards of hand-arm vibration. Health surveillance in the workplace will be fundamental and the HSE propose a tiered approach with levels 1 to 5. Specialist occupational nurses and doctors with training in the diagnosis and assessment of HAVS will be needed for levels 3 and 4. Only at this level may a diagnosis of HAVS be made. The Medical Assessment Process has demonstrated that it is possible to examine a large number of claimants in a standardised manner. The IIAC and HSE recommendations contain very important improvements on the existing positions in the UK and it must be hoped that they will be implemented in the near future.
Objectives: The measurement of vibrotactile perception thresholds (VPTs) at fingertips in workers belongs in Poland among obligatory methods used to diagnose hand-arm vibration syndrome. The aim of the study was to compare vibrotactile perception threshold (VPT) values for healthy subjects using two different types of measuring equipment, i.e. a system designed according to the requirements of the ISO 13091-1 standard and a system that had so far been in use in Poland. Materials and Methods: 59 men and 22 women aged on average 40.4 years old participated in the study. The VPT measurements were carried out using a new pallesthesiometer P8 (EMSON-MAT, Poland), developed according to the ISO 13091-1 standard and a vibrotactile meter MCW 2K that had so far been used in Poland. Measurements were taken for the index, middle and ring fingers of both hands using the frequencies of 4, 25, 31.5, 63, 125, 250, 400 and 500 Hz for the ISO method and 63, 125, 250, 400 and 500 Hz for the Polish method. Results: The mean vibrotactile perception threshold values determined with the ISO 13091-1 method were significantly higher in comparison with the values obtained when the method used in Poland was employed. The differences between vibrotactile threshold levels were almost the same at the compared frequencies. Conclusions: The results of the VPT measurements obtained employing the standard method adopted in Poland may be used in further diagnostic examinations carried out with the ISO 13091-1 method only if an appropriate correction value is calculated in order to determine the difference in the VPT levels at a selected frequency.
Manual dexterity and hand functional difficulties in daily life in hand-arm vibration syndrome (HAVS) were investigated in 29 male patients with HAVS and 30 male controls without occupational exposure to hand-arm vibration. Manual dexterity was assessed by measuring the performance time of picking up and transferring 30 red beans, one by one, from one plate to another. Vibrotactile perception thresholds at 125 Hz and grip strength were also examined. Hand functional difficulties in daily life were surveyed with a questionnaire. The HAVS patients had an increased vibrotactile threshold, decreased grip strength, and low performance in transferring beans. Low performances with transfer times over 53 s (2SD from the mean in the controls) were found in 66% of the HAVS patients and 3% of the controls. Bean transfer times in the patients were correlated with an increasing vibrotactile threshold and decreasing grip strength. The transfer times of the patients were also associated with hand functional difficulties such as picking up coins, turning the pages of a newspaper, buttoning clothes, and pouring from a teapot. The patients with a prolonged transfer time over 60 s (3SD from the mean in the controls) were most likely to have hand functional difficulties. The present findings suggest that measurement of the bean transfer time will serve to assess manual dexterity among HAVS patients, and that impaired manual dexterity in patients may be associated with impaired sensory feedback and muscular dysfunction in the fingers and hands.
Measurements of changes in finger skin blood flow with laser Doppler perfusion imaging (LDPI) in response to cold provocation test (10°C, 10 min) were performed in 12 men suffering from vibration induced white finger (VWF) and 13 exposed controls. The mean perfusion values in both groups reduced markedly as a result of immersion of the hand in cold water. In the controls, however, the mean value increased gradually until the end of the cold provocation, while that in the VWF subjects remained at the lowest level. After removal of the hand from the cold water, the skin blood perfusion in the controls recovered rapidly and nearly reached the baseline value. In the VWF subjects, it had a slight increase immediately following the cold immersion but no tendency to rise as the time span increased. Analysis of covariance controlling for possible confounders revealed that the VWF subjects had significantly lower perfusion values compared to the controls in the last several minutes of the cold provocation and the following recovery. These findings suggest that the LDPI technique enables visualizing and quantifying the peripheral vascular effects of cold water immersion on the finger skin blood perfusion and thus has the potential of providing more detailed and accurate information that may help detect the peripheral circulatory impairment in the fingers of vibration-exposed workers.
Effects of modifying the palm adapter geometry on ISO 10819 antivibration glove test results were investigated. 30 rigid acrylic adapters were designed, fabricated, and evaluated. The length of the adapters that met ISO 10819 requirements covered 70-80% of the width of the palm. The upper curvatures of the adaptors were greater than or equal to the radius specified in ISO 10819:1996. Glove vibration transmissibility tests were conducted using a constant velocity vibration input with a value of 0.01 m/s in each third octave frequency band from 16-1,600 Hz (F spectrum). Glove vibration transmissibility results obtained using the M (16-400 Hz) and H (100-1,600 Hz) spectra specified in ISO 10819:1996 were compared to similar results using the constant velocity spectrum. The results obtained from the constant velocity spectrum, when divided into the M and H frequency ranges, were nearly the same as those obtained from the ISO 10819 M and H spectra. Test subject training was required to ensure reliable glove vibration transmissibility results. The measured transmissibility values obtained with the M, H, and F spectra were all higher at the beginning of the test program. The transmissibility values decreased and approached lower limiting values as the test subjects became more experienced.
This study aims to evaluate the effect of occupational exposure to noise and organic solvents on hearing loss in the aviation industry. The study population comprised 542 male workers, who worked in avionics jobs in Kimhae, Korea, who kept records of work environment evaluations and medical examinations. The Cumulative Exposure Index (CEI) was constructed to assess the lifetime cumulative exposure of the workers, and pure tone audiometry (PTA) data of the workers from their biannual medical surveillance was used to assess hearing loss. The prevalence of hearing loss found in the group exposed to noise and mixed solvents simultaneously (54.9%) was higher than those in the other groups (6.0% in the unexposed, 17.1% in the noise-only, and 27.8% in the exposed to only a solvents mixture). The relative risks, adjusted for age, were estimated to be 4.3 (95% CI 1.7-10.8) for the noise-only group, 8.1 (95% CI 2.0-32.5) for the noise and solvents group, and 2.6 (95% CI 0.6-10.3) for the solvents-mixture group. These suggest that chronic exposure to mixed solvents had a toxic effect on the auditory system. This raises the issue of whether hearing conservation regulations should be applied to all workers exposed to solvents.
Co and Ni are essential but relatively rare elements as to organisms. In the mammalian membrane, these metals are transported by the same carrier proteins. The aim of this study was to investigate the direct effects of CoCl2 and NiCl2 on citrate uptake by rat renal brush border membrane vesicles (BBMV). BBMV were prepared by the divalent cation precipitation methods, and citrate uptake was measured by the Millipore rapid membrane filtration technique. The time course of citrate uptake during 120-min of incubation with 1 mM CoCl2 and NiCl2 showed a rapid significant inhibition at the early phase and a slight recover at the late phase. Incubation for 1 min of BBMV with 1, 5 and 25 mM CoCl2 and NiCl2, respectively, significantly inhibited citrate uptake in a concentration-dependent manner compared with that of 0 mM. We discuss these findings from the point of view that Co and Ni are located in Group VIII of the periodic table.
Human body surface vibrations induced by high-level low-frequency pure tones were measured at the chest and the abdomen. At the same time, the subject rated the unpleasantness that he had just perceived during the exposure to low-frequency noise stimulus. Examining the relationship between the measured vibration and the rating score of the unpleasantness revealed that the unpleasantness was in close correlation with the vibration acceleration level (VAL) of the vibration measured. Taking previous results into account, this finding suggests that noise-induced vibrations primarily induce vibratory sensations and through the vibratory sensation or together with some other factors, secondarily contribute to the unpleasantness. The present results suggest that in evaluating high-level low-frequency noise, the effect of vibration should be taken into account.
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 μg/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.
Subchronic toxicity of 1,4-dichloro-2-nitrobenzene (DCNB) was examined by feeding F344 rats and BDF1 mice of both sexes a diet containing 1,481, 2,222, 3,333, 5,000 or 7,500 ppm DCNB (w/w) for 13 wk. Oral administration of DCNB in feed to rats and mice retarded growth rates and induced subchronic toxicity affecting the liver, kidney, testes and blood. Liver and kidney were most responsive to DCNB. BMDL10 values for relative liver weight were 12.0 and 22.6 mg/kg/d for male and female rats, respectively, and 88.7 and 94.4 mg/kg/d for male and female mice, respectively. Increased liver weights and centrilobular hypertrophy of hepatocytes were observed in the DCNB-fed rats and mice of both sexes. Both increased serum activities of AST and ALT and liver necrosis occurred in the DCNB-fed mice. Increased incidences of hyaline droplets and granular casts in the proximal renal tubules were observed only in the DCNB-fed male rats, indicating α2υ-globulin nephropathy. Eosinophilic droplets in the renal tubular cells and increased BUN concentrations occurred in the DCNB-fed female rats. DCNB-induced testicular and hematologic changes were noted in rats and mice. On the basis of these results, the highest dose level for the 2-yr bioassay study of rodent carcinogenicity was determined to be 2,000 ppm.
This cases report compared the short-term changes of BLL with medical removal intervention and follow-up the long-term changes of BLL afterward. During a physical examination in October 1992, a 44-year old shipyard welder was discovered to have a blood lead level (BLL) of 54.1 μg/dl. It was recommended that the shipyard remove this worker from his workplace. In 1993 the BLLs checked for this worker were 36.7 μg/dl in March and 32.0 μg/dl in April. After six months of medical removal, he returned to initial welding work. In 2002, we collected two blood samples from this worker for analysis in May and October. The results were 30.4 μg/dl and 31.6 μg/dl, respectively. Meanwhile, two other welding workers (case 2 and case 3) with BLLs over 40 μg/dl in the survey conducted at the same shipyard in 1992. It took 4 yr to let BLLs downed to less than 40 μg/dl. However, after the blood lead concentration drops to below 40 μg/dl, 10 yr long-term observation indicates that BLLs reduction level off and do not continue to go down in these three cases.