neurobehavioral performance in aluminum welders

AMERICAN JOURNAL OF INDUSTRIAL MEDICINE 37:184±192 (2000)

Neurobehavioral Performance inAluminum Welders

Rita Bast-Pettersen, PsyD,� Vidar Skaug, MD,2 Dag Ellingsen, MD, PhD,1

and Yngvar Thomassen, MSc1

Methods Twenty aluminum welders (mean age 33 years; range 21±52), who had beenexposed to aluminum for an average of 8.1 years (range 2±21), were tested for tremorand reaction time and screened for neuropsychiatric symptoms in a cross-sectional study.The welders' median urinary aluminum concentration was 1.5�mol/L (range 0.7±4.8).Aluminum in air, measured inside the respiratory protection, was 0.9 mg/m3 (range 0.6±3.8). The welders were compared with twenty construction workers matched for age.Results Welders reported more symptoms than referents did (median 2 vs. 1; P� 0.047).Although the welders as a group performed better than the referents on a tremor test,years of exposure, but not age, was predictive of poorer performance. The welders'reaction times were rapid by clinical standards (mean simple reaction time (SRT): 221milliseconds; mean continuous performance test (CPT): 364 milliseconds). Although, asa group, they performed better than the referents, there was a statistically signi®cantrelation between longer reaction times and aluminum in air (air-Al).Conclusions The relations between hand steadiness and years exposed, and betweenreaction time and air-Al, could indicate slight effects from exposure to aluminum. Thepossibility of selection of workers with high manual skills into welding work and apossible job-related training effect, might partly serve to explain the good performanceamong the welders. Am. J. Ind. Med. 37:184±192, 2000. ß 2000 Wiley-Liss, Inc.

KEY WORDS: aluminum; aluminum welders; neurobehavioral performance;neuromotor function; neuropsychometric tests; neuropsychiatric symptoms

INTRODUCTION

Research on effects on the human central nervous

system (CNS) of exposure to aluminum (Al) originated

partly from the study of dialysis dementia. Alfrey et al.

[1976] showed elevated brain aluminum levels in patients

who had died of dialysis encephalopathy. Aluminum

deposition in the brain has also been associated with the

development of neurodegenerative diseases, particularly

Alzheimer's disease, but the existing evidence is insuf®cient

to provide a conclusive answer to this question. [Doll,

1993; Savory et al., 1996; Armstrong et al., 1996;

Edwardson and Candy, 1989]. The most important sources

of aluminum in occupationally unexposed humans are food,

drinking water, health-care products and pharmaceuticals

[Nieboer et al., 1995]. Data on Al in drinking water are

relatively easily available, and most epidemiological studies

have focused on this source of exposure. However,

aluminum in drinking water recounts for only a fraction

of the total amount of aluminum ingested orally [Savory

et al., 1996].

Few epidemiological studies have focused on nervous

system effects in occupationally exposed workers. Canadian

miners who inhaled `̀ McIntyre powder'' as a prophylactic

against silicosis showed poorer cognitive function than the

controls [Rifat et al., 1990]. Aluminum foundry workers

1National Institute of Occupational Health, Oslo, Norway2ABB-StrÖmmen A/S, StrÖmmen, NorwayContract grant sponsor: Working Environment Fund of the Confederation of Norwegian

Business and Industry.*Correspondence to: Rita Bast-Pettersen, Department of Occupational Medicine, National

Institute of Occupational Health, P.O. Box 8149 Dep., N-0033 Oslo, Norway.

Accepted 2 September1999

ß 2000Wiley-Liss, Inc.

were reported to have slightly impaired cognitive function

[Hosovski et al., 1990], and Bast-Pettersen et al. [1994]

found slightly more neuropsychiatric symptoms among

elderly foundry and potroom workers than among the

controls, and a slight tremor among the potroom workers.

More neuropsychiatric and neurological symptoms and

neurological signs were found among aluminum potroom

workers compared to referents [Sim et al., 1997]. No CNS-

effects were observed in a recent study of foundry and

primary smelter workers with low exposure to aluminum

[Iregren et al., 1997]. In addition to these epidemiological

studies, a study of 25 selected patients showed neurological

symptoms and impaired cognitive function [White et al.,

1992].

Only few studies have been conducted on the CNS in

aluminum welders. SjoÈgren et al. [1990] have reported more

neuropsychiatric symptoms among 65 aluminum welders

than among railroad track welders. HaÈnninen et al. [1994]

found an association between urinary aluminum (U-Al) and

poorer performance on memory tests and a signi®cant

relation between higher variability of reaction times and

serum aluminum concentrations in 17 aluminum welders.

Thirty-eight aluminum welders reported more symptoms

related to the nervous system than railroad track welders

did. Decreased motor function was found in ®ve tests

[SjoÈgren et al., 1996].

Several studies have demonstrated elevated concentra-

tions of aluminum in serum and urine in workers exposed

to aluminum [SjoÈgren et al., 1983; SjoÈgren et al., 1985;

Ljunggren et al., 1991], thus con®rming absorption of alu-

minum into the body from occupational exposure. However,

little is known about the toxicokinetics of aluminum in the

CNS, and the mechanism of how aluminum gains access to

the CNS by crossing the blood-brain barrier has not been

clearly established [Armstrong et al., 1996]. It has been

suggested that aluminum binds to transferrin as Al3� [Jong

et al., 1995], and crosses the blood-brain barrier via the iron-

transport system [Edwardson and Candy, 1989].

The aim of this study was to investigate possible

neurobehavioral/neuromotor effects in aluminum welders

employed in a railroad wagon production factory. The test

methods were selected on the basis of ®ndings from

previous studies among aluminum-exposed workers, where

the main ®ndings include neuropsychiatric symptoms,

impaired motor function and longer reaction times [Bast-

Pettersen et al., 1994; Sim et al., 1997; SjoÈgren et al., 1990;

HaÈnninen et al., 1994; SjoÈgren et al., 1996].

SUBJECTS AND METHODS

Subjects

The aluminum welders were employed in a railroad

wagon production factory. In this cross-sectional study, the

same inclusion and exclusion criteria were de®ned for both

the exposed group and the control group. Inclusion criteria

were at least one year of employment and being currently at

work. Exclusion criteria were exposure to solvents and

diseases which could affect the CNS, including cancer,

cerebrovascular diseases, neurological diseases, and dia-

betes. Workers who reported mild head injury/mild brain

concussion were included in the study, but in the statistical

analysis, the occurrence of head trauma was regarded as a

possible confounder. The investigation was restricted to men

only.

Altogether 21 workers were identi®ed as aluminum

welders at the time when the study was conducted. They all

met the inclusion criteria and were invited to participate.

Twenty subjects accepted and attended the examinations

(response rate 95%). Construction workers employed by a

contracting company in the vicinity of the railroad wagon

factory were asked to serve as referents. They worked a

`̀ long day shift'' (from 6 a.m. to 6 p.m., of which 10.5 h

were spent on active work) for two weeks, and had the

following week off. Thirty-four workers were asked to serve

as referents in this study and in another study [Bast-

Pettersen, 1999]. Two workers declined, thus giving a list

of 32 male construction workers willing to serve as

referents, a participation rate of 94%. From this list of 32

male construction workers, 20 workers were chosen at

random, based on frequency matching for age. Referents

were tested the second or third day at work, after having one

week off.

None of the eligible subjects were excluded because of

the exclusion criteria. All subjects underwent a structured

interview focusing on education, occupational history,

accidents, and illnesses. Their current alcohol consumption

was calculated (liters of pure alcohol/year), based on the

volume and frequency of consumption of beer, wine, and

distilled spirits, as reported in an interview based on a

standardized questionnaire [Hauge et al., 1987].

Table I shows some background variables for the 20

aluminum welders and the 20 referents. The two groups

were comparable with respect to educational background

and mild head injuries, but current alcohol consumption was

slightly (not signi®cantly) higher among the referents. All

the examined workers volunteered to participate in the

study, and their written informed consent was obtained.

Exposure

During the traditional Metal Inert Gas (MIG) and

pulsed Metal Active Gas (MAG)-welding operations, the

electrodes are consumed under a protected layer of

argon/carbon dioxide shielding gas. The welding aerosol

contains mainly respirable aluminum-containing particles.

Chemical characterization of the welding aerosol and

mass balance consideration show that aluminum is fully

Neurobehavioral Study of Aluminum Welders 185

oxidized. Nitrogen oxides and ozone are also emitted.

Many of the welding operations involved dif®cult working

positions, making local ventilation dif®cult to apply.

Personal respiratory protection devices (positive pressure

supplied air respirators) were introduced at the factory

about four years prior to this study. The welders were

directly engaged in welding for more than 50% of a working

week.

Past exposure in terms of years exposed was assessed at

the interview. Current aluminum exposure at the time of the

examinations was assessed by environmental and biological

monitoring.

Air sampling and biological monitoring

The aerosol sampling equipment used in this study was

the three piece 25 mm Millipore cassette (Millipore, Bed-

ford, MA, U.S.A.) con®gured in its closed face mode and

battery powered Cassella AFC 123 personal pumps operated

at 2 L/min (Casella Ltd., London, UK). All ®lters used were

of the Millipore 0.8 mm cellulose ester type AAWP02500.

The welders wore this equipment during eight hour work

shifts, with the aerosol sampler placed inside the welding

protection helmet close to the breathing zone.

The welders were instructed to void the ®rst morning

urine at home, and the ®rst post-shift urine after changing to

their own clothes. The urine samples were collected directly

into 25 mL screw-capped plastic containers (Universal

Container, NUNC, Denmark) tested free of aluminum

(<1 mg/L). The urine specimens were kept frozen at

ÿ20�C until analysis.

Measurements of aluminum in urine andaerosol ®lters

To prevent the risk of laboratory acquired infections

and to dissolve urine precipitates, all urine samples were

heated for one hour at 95�C prior to analysis. U-Al was

measured by electrothermal atomic absorption spectro-

metry, using a Perkin-Elmer Model 5100 PC/HGA-600

instrument equipped with a Zeeman based background cor-

rection system under STPF-conditions. Calibrations were

made against urine matched standard solutions. Human

urine SeronormTM (Sero Ltd, Asker, Norway) trace element

quality control materials (Batch No. 108) were used

throughout to monitor the accuracy and reproducibility of

the measurements. The day-to-day variation in the alumi-

num measured in the quality control materials was typically

� 6% and the aluminum concentrations measured in the

quality control urine samples were consistent with the value

recommended by the producer (� 5%). The detection limit

of the method was 1.5 mg/L of aluminum (3� standard

deviation). U-Al was corrected for dilution of the urine by

measuring the urinary creatinine concentration (Jaffe's

method). The number of collected urine samples was 189.

The mean number of urine samples was 9.5 (range 4±10)

for each exposed subject. The median U-Al concentration

for each individual was used for further statistical calcula-

tions.

Aluminum in the air inside the respiratory protection

was measured for 17 of the welders. Each worker wore his

equipment for an average of four (range 2±5) days. Sixty-

nine measurements were made, and the concentrations of

TABLE I. BackgroundData for 20Norwegian AluminumWelders and 20Referents, and Exposure-Related Variables for 20AluminumWelders

Aluminumwelders Referents

Mean Median Range Mean Median Range

Sociodemographic data

Age (years) 32.7 28.0 21^52 33.8 30.5 22^53Years of education 10.5 10.3 9^12 10.6 10.5 9^13Self-reported alcohol consumption (L/year) 6.5 3.5 0.8^32.0 8.7 6.9 0^23.2Prevalence of self-reported earlier mild brain concussions (%) 20 20

Exposure

Number of years aswelder 12 8.5 3.5^29Number of yearswith aluminumwelding 8.1 7 2^21Aluminum in urine (mmol/L) 1.86 1.54 0.7^4.8Aluminum in urine (mmol Al/mmol creatinine) 0.18 0.15 0.06^0.46Aluminum in air (mg/m3) (inside respiratory protection)a 1.18 0.91 0.57^3.77

aN� 17.

186 Bast-Pettersen et al.

air-Al presented here are based on the individual median

concentrations. All air ®lters were dissolved in a mixture

of 2 mL aqua regia and 0.2 mL hydro¯uoric acid in

te¯on autoclaves with microwave assisted digestion. The

material collected on the inside surfaces of the aerosol

cassette was also recovered by extraction with 2 mL of

0.5% Triton X-100 in 15% nitric acid water and was added

to the ®lter fraction before digestion. A Perkin-Elmer

Optima Model 3000 inductively coupled plasma atomic

emission spectrometer was used to measure aluminum in

the solutions. In-house commercially available reference air

®lter material was also analyzed for aluminum. The

measured aluminum concentration coincided well with

the recommended value (� 5%) and the day-to-day

variation for aluminum in air ®lters was typically � 5%.

The exposure-related variables for the 20 aluminum welders

are shown in Table I.

Two years prior to this study, ®ve of the included

workers had been monitored for aluminum in urine and in

air. Their average measured U-Al had decreased from

3.48 mmol/L (94 mg/L) to 2.48 mmol/L (67 mg/L). The cor-

responding average air-Al had decreased from 2.05 to

1.46 mg/m3.

Neurobehavioral methods

Both groups under study were tested during their

working day in the of®ces of the occupational health

services, in premises close to their worksite.

Subjective symptoms were recorded by means of the

self-administered questionnaire Q16, containing 16 items

referring to neurological symptoms, and memory and

concentration dif®culties [Lundberg et al., 1997]. The

subject is required to answer yes or no to each question.

The measure is the total number of symptoms.

Hand steadiness was measured by the Klùve±Matthews

Static Steadiness Test (SST) (Klùve±Matthews Motor

Steadiness Battery, Lafayette Instruments Co., Lafayette,

IN) [Matthews and Klùve, 1964] which is a stylus-and-hole

apparatus. The stylus and base plate are connected

electrically, to record each contact between stylus and base

plate. Sitting at a table, the subject is required to insert the

stylus into successively smaller holes. The aim is to hold the

stylus in each of nine holes for 15 seconds without it

touching the sides. The measures are number and duration

of contacts between stylus and base plate.

Reaction times were measured by means of two

computerized tests from the Neurobehavioral Evaluation

System (NES2) [Baker et al., 1985; Letz et al., 1996]. In the

Simple reaction time (SRT) test, the subject is asked to press

a button as quickly as possible when a large square appears

on a computer screen. The inter-trial interval is varied

randomly to reduce the effects of stimulus anticipation. If

the subject does not respond within 1 second, the screen is

cleared and a new trial is started. Ninety reaction times are

recorded. The ®rst 10 are regarded as practice, and are

discarded. An initial mean and standard deviation (SD) are

calculated by using all trials between 100 and 1000

milliseconds. The ®nal mean and SD are calculated by

using all trials between 100 milliseconds and 3 SDs above

the initial mean. This ®nal mean reaction time (RT) is

presented.

The Continuous Performance Test (CPT) measures

sustained visual attention as well as reaction time [Letz

et al., 1996]. Different large letters are ¯ashed brie¯y on

the screen for about 50 milliseconds, at a rate of one per

second for ®ve minutes. The subject is required to press a

button only when a large letter `̀ S'' and not any other letter,

is projected on the computer screen. The sequence of

stimulus letters is randomly selected. The number of RTs

collected is 60. The ®rst 12 RTs are regarded as practice,

and are discarded. Latencies longer than 1000 milliseconds

are not included when calculating mean reaction time

and SD.

Statistics

Continuous variables were inspected visually and tested

for normal distribution (Shapiro±Wilk's test). They were

log-transformed when not normally distributed (Static

Steadiness and air-Al) to achieve normalization of the

distributions prior to statistical analysis.

Students t-test was used to assess differences between

the groups. However, owing to the skewed distribution and

the fact that many of the respondents had zero symptoms,

the number of symptoms (Q16) was analyzed with a non-

parametric test (Mann±Whitney). Analysis of covariance

was used to assess the in¯uence of potential confounders

on the difference between the groups. Age, education

(number of years), alcohol consumption (liter pure alcohol/

year), and history of mild head injury (yes/no) were

included as covariates in the analysis. Because of the

limited number of subjects, the potential confounders were

entered separately.

For the exposed subjects, multiple linear regression

analysis was used to assess the statistical relations between

the neuropsychometric test results, potential confounders

and exposure-related variables (U-Al, air-Al, and years

exposed). Because of the limited number of subjects in the

study, only two independent variables were entered

simultaneously. Since no satisfactory age-related norms

were available for the outcome variables [Bast-Pettersen,

1999], the ®nal models included age in addition to the

exposure-related variables. The level of signi®cance was

set at 0.05 (two-tailed). The statistical analyses were

carried out on a personal computer using SPSS 6.1 for

Windows1.


RESULTS

Symptoms

Both groups reported a few neuropsychiatric symp-

toms, but the welders reported more symptoms than the

referents did. The difference was statistically signi®cant

(Table II). No statistically signi®cant relations were found

between number of symptoms and the applied exposure

estimates. Further, none of the covariates was signi®cantly

related to number of symptoms.

Hand Steadiness

Table III shows the results of the Steadiness Test (total

number and duration of contacts between the stylus and the

base-plate). As a group, the aluminum exposed workers

performed statistically signi®cant better than the referents.

Introducing the covariates did not change the overall pattern.

However, when the results of the exposed group were

analyzed separately, a signi®cant correlation was found

among the exposed subjects between poorer performance

and duration of exposure in years (Table IV). Years of

exposure was signi®cantly associated with number of

contacts between stylus and base-plate (Figures 1 and 2),

while a weaker correlation was found (signi®cant only for

the non-dominant hand) between years of exposure and

duration of these contacts. Performance in the Static

Steadiness Test was not associated with any of the potential

confounders in the exposed group.

No association was found between the steadiness

measures and either U-Al or air-Al. No clinically signi®cant

tremor was observed in any of the groups.

Reaction Time

Table V presents the results of the reaction time tests. In

general, the welders performed better than the referents, but

the difference was not statistically signi®cant. A correlation

between the occurrence of a history of head injury with

concomitant unconsciousness and prolongation of the SRT

(P� 0.02) was found in the analysis of covariance, but

without signi®cantly in¯uencing the overall difference

between the groups.

Among the exposed subjects, increasing air-Al was

predictive of longer SRT (P� 0.04). Since the SRT was not

associated with any of the potential confounders in the

exposed group, this statistically signi®cant relation between

longer SRT and air-Al could not be explained by age, as

illustrated in Table IV.

DISCUSSION

With regard to comparability, the two groups studied,

workers and referents were similar in terms of age,

educational background, and prevalence of self-reported

mild head injuries. The referents, however, had some-

what higher self-reported current consumption of alcohol.

The participation rate was high, both for the exposed

workers (95%) and for the referents (94%). None of the

subjects worked on night-shift. However, the referents

worked through long days for two weeks and had the

following week off. They were tested two or three days

after they had had one week off, to exclude bias due to

more fatigue among the referents, since their working

hours were longer than those of the welders. The simi-

larity in the distribution of the background variables

TABLE II. Neuropsychiatric Symptoms,Q16, in 20Norwegian AluminumWelders, and 20Referents


Mean Median Range Mean Median Range P-value

Number of symptoms 2.5 2 0^10 1.6 1.0 0^8 0.047

TABLE III. Results of the Static SteadinessTest for 20Norwegian AluminumWelders and 20Referents.Higher Score IndicatesWeaker Performancea


Mean Median Range Mean Median Range P

Dominant hand, number 57 57 13^139 119 107 53^241 < 0.001Dominant hand, duration in sec 2.6 2.3 0.6^6.3 6.9 6.7 2.1^14.2 < 0.001Non-dominant hand, number 71 58 15^168 135 120 40^319 < 0.001Non-dominant hand, duration in sec 4.0 3.3 0.5^12.3 8.2 7.5 2.1^17.8 0.001

aLog transformed values used in the statistical analyses.


TABLEIV. ResultsofLinearMultipleRegressionAnalysisofOutcomeVariables forNorwegianAluminumWelders,with Indices forAluminumExposureandAgeas IndependentVariables

Dependent variable Independent variables B Standard error P r2 Multiple r

Simple ReactionTime (SRT)a Constant 229.39 21.20 0.000 0.26 0.51Age ÿ0.27 0.63 0.678Aluminum in air; (log) 65.72 29.63 0.044

Steadinessb

Dominant hand, number of contacts (log) Constant 1.55 0.21 0.000 0.28 0.53Age ÿ0.01 0.01 0.497Years of aluminumwelding 0.04 0.02 0.035

Dominant hand, duration in seconds (log) Constant 0.37 0.21 0.094 0.12 0.36Age ÿ0.01 0.01 0.377Years of aluminumwelding 0.02 0.02 0.144

Non-dominant hand, numberof contacts (log) Constant 1.61 0.19 0.000 0.35 0.59Age ÿ0.01 0.01 0.494Years of aluminumwelding 0.04 0.02 0.016

Non-dominant hand, duration in seconds (log) Constant 0.53 0.23 0.034 0.23 0.48Age ÿ0.01 0.01 0.242Years of aluminumwelding 0.04 0.02 0.042

aN� 17.bN� 20.

FIGURE 1. Relation between years of exposure to aluminum and number of contacts

between stylus and base-plate (dominant hand) on the Static Steadiness test for 20

Norwegian aluminumwelders.

FIGURE 2. Relation between years of exposure to aluminum and number of contacts

between stylus and base-plate (non-dominant hand) on the Static Steadiness test for 20

Norwegian aluminumwelders.


indicates that the construction workers were suitable as

referents.

Exposure

The mean U-Al concentration of the welders at the time

of examination was 1.86 mmol/L (50.3 mg/L) (median

1.54 mmol/L or 41.5 mg/L), which is between the levels

reported in other neurobehavioral studies of aluminum

welders: SjoÈgren et al. [1996] reported median U-Al of

0.81 mmol/L (22 mg/L) and HaÈnninen et al. [1994]

2.4 mmol/L (65 mg/L). A mean U-Al between 5.9 and

54 mg/L has been reported in aluminum production workers

[Iregren et al., 1997; Hosovski et al., 1990; Bast-Pettersen

et al., 1994]. The air-Al measured inside the respiratory

protection (mean 1.18 mg/m3; median 0.91 mg/m3) was

higher than reported in two neurobehavioral studies on

aluminum production workers, where ambient air-Al was

found to be 0.48 mg/m3 [Bast-Pettersen et al., 1994] and

0.5 mg/m3 [Sim et al., 1997].

The exposed subjects had worked as aluminum welders

for an average of 8.1 years. In the study by HaÈnninen

et al. [1994], the aluminum welders had been exposed for

about four years. Other studies have reported a median

exposure duration of at least 10 years [Rifat et al., 1990;

SjoÈgren et al., 1990; Hosovski et al., 1990; Bast-Pettersen

et al., 1994].

To sum up, in the present study the duration of exposure

was shorter than in other studies on the neurobehavioral

effects of aluminum exposure, but the level of exposure,

as assessed by aluminum in air and urine, is higher than in

most other neurobehavioral studies among Al-exposed

workers.

Neuropsychiatric Symptoms

The exposed welders reported more subjective symp-

toms than the referents did, but few symptoms by clinical

standards. None of the applied exposure measures was

associated with the number of symptoms among the

exposed subjects. A higher prevalence of subjective

symptoms related to CNS functions has also been reported

in other studies in workers exposed to aluminum [Bast-

Pettersen et al., 1994; Sim et al., 1997]. In a study among

Al-welders, SjoÈgren et al. [1990] found that long-term

exposed aluminum welders had higher risk of three or more

symptoms on the Q16. This ®nding was not con®rmed,

however, in the present study. In a later study, SjoÈgren et al.

[1996], reported signi®cantly more subjective symptoms in

38 aluminum welders than in the referents. This disagrees

with the ®ndings of HaÈnninen et al. [1994], who reported a

signi®cant negative correlation between serum aluminum

(S-Al) and subjective symptoms.

HAND STEADINESS

No clinically signi®cant tremor was observed in either

of the groups. The welders' performance was excellent on

the Steadiness Test; in fact they performed better than the

referents. Their performance was also better than that of

subjects examined in other Norwegian studies; e.g., of 32

younger Norwegian students at a divers school (mean age 24

years), who were tested before starting their career as divers

[Bast-Pettersen, 1999], and a group of wood processing

workers aged 40.5 years who had not been exposed to

neurotoxicants and were used as control group in another

study [Bast-Pettersen et al., 1998]. The results of our control

group, on the other hand, were similar to those of the wood

processing workers [Bast-Pettersen et al., 1998], whose

results on the tremor test (mean� SD) were 123 (� 117)

(number) and 6.8 (� 4.4) (time in seconds) for the dominant

hand, and 120 (� 91) (number) and 7.9 (� 5.1) (time in

seconds) for the non-dominant hand. Thus, the results of the

control group are within the range observed in other studies

of industrial workers in Norway.

The excellent performance of the welders on the

steadiness test could indicate a selection of workers with

good steadiness of hand to the aluminum welding profes-

sion, or it could indicate a job-related training effect. Since

none of the welders showed signi®cantly reduced perfor-

mance in clinical terms in the Steadiness Test, the ®nding in

the multiple regression analysis that years exposed is a

statistically signi®cant predictor of the performance in the

steadiness test (Table IV), should be interpreted with

caution. It might be a random ®nding, but the possibility

cannot be ruled out that cumulative exposure may have a

slight effect in a highly selected population. The perfor-

mance in the Steadiness Test was not associated with any of

TABLE V. Results of the ReactionTimeTests for 20Norwegian AluminumWelders and 20 Referents.Higher Score IndicatesWeaker Performance


Mean (SD) Median Range Mean (SD) Median Range P-value

Simple ReactionTime (SRT), msec 221 (27) 216 187^282 228 (16) 231 189^264 0.314Continuous PerformanceTest (CPT),msec 364 (26) 362 321^416 382 (29) 381 320^427 0.054


the potential confounders in the exposed group, thus, as

illustrated in Table IV, the relation between poorer

performance and duration of exposure cannot be explained

by age. It is worth noting in this connection that elderly

workers employed in the potroom of an aluminum plant

[Bast-Pettersen et al., 1994] performed less well than the

referents did on the same SST.

In disagreement with the results of this study is the

work by Sim et al. [1997], who did not observe increased

tremor among aluminum workers. Their reference group,

however, included aluminum foundry (cast house)

workers, who probably were exposed to aluminum,

although at lower levels, and this may have confounded

the results.

Reaction Time

Reaction times were faster among the welders than

among the referents, but the difference was non-signi®cant.

Both groups under study had, by clinical standards, good

reaction times. The welders' fast RTs were comparable to

those of the above-mentioned younger Norwegian diver

students (mean SRT� SD; 219� 20 milliseconds, and

mean CPT� SD; 371� 31 milliseconds) [Bast-Pettersen,

1999]. Performance on RT tasks may be sensitive to

motivational factors, and the exposed welders could have

been more motivated to perform well, since they were more

concerned about a possible effect from welding on the

nervous system.

The ®nding in the multiple regression analysis of air-Al

as a predictor of SRT (Table IV) may agree with reports

from another study on aluminum welders of a signi®cant

relation between S-Al and variability of RT [HaÈnninen et al.,

1994]. Both measures of exposure are probably related to

current exposure, and could suggest an acute effect of

exposure. However, both studies are small, and do not

provide ®rm evidence of an association between current

exposure to aluminum and reaction time.

This study may indicate a slight exposure-related effect

on the studied parameters, i.e., reaction time, steadiness of

hand, and neuropsychiatric symptoms in aluminum welders.

However, the presented results indicate that these welders

were not clinically impaired in terms of steadiness of hand

or RT.

A positive selection of workers with high manual skills

into welding work, and a possible job-related training effect

on hand steadiness, may be the possible explanations of the

good steadiness among the welders.

ACKNOWLEDGMENTS

We acknowledge the contribution of Siri Hetland, MSc,

for the data on air-Al. We also thank Mary Bjñrum, BSc, for

revising the English.

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neurobehavioral performance in aluminum welders

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