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Mercury levels in dental surgeries and dental personnel in Slovenia
Chemosphere, Vol.24, No.12, pp 1731-1743, 1992 Printed in Great Britain
0045-6535/92 $5.00 + 0 00 Pergamon Press Ltd.
MERCURYLEVELS IN DENTALSURGERIESAND DENTAL PERSONNELIN SLOVENIA
Franek Klemenc,I Mirjana ~kreblin2., Milena Horvat2 and Peter Stegnar2
IDepartment for Dental Diseases, University Dental Clinic 2Department of Nuclear Chemistry, "J. Stefan" Institute University of Ljubljana, Slovenia
ABSTRACT The level of mercury exposure in Slovenian dental practice was studied by measurement of air mercuw leyels in 63 surgeries and by analysis of the mercury content in blood and urine samples of professionally exposed and control groups (total of 77 participants). The mean ambiental mercury concentration for all investigated surgeries was 2.8 ug Hg/m3 (range: 0.4-8.2), which is considerably below the health-based occupational exposure l i m i t of 25 ug/m3. No significant relationships between age or type of surgeries, or the time during the working day and the air mercury levels were found. The mean value for mercury in blood was 3.0 ng Hg/g (range: 0.9-7.7), which can be considered as the normal range for the general population. The occupational profile of the workers, years in the profession, as well as sex, showed a nonsignificant effect on blood mercury. Urinary mercury levels were also low. Only 3 of 44 values exceeded 15 ng Hg/g. No influence of sex or occupational p r o f i l e was found; however, a significant negative linear relationship (r=-0.473; PffiO.O012) was observed between the concentration of mercury in urine and years in the profession. The data indicate good mercury hygiene in Slovenian dentistry.
1731
1732
INTRODUCTION
Dental amalgam is
extensively used as a f i l l i n g material
and i t s potential
health hazard as a source of
in dental restoration
mercury vapour exposure for
dental personnel who handle the amalgam, has provoked numerous and extensive surveys on mercury contamination
in dental
practice
throughout the
world
(DeFreitas, 1981). With the exception of a few sporadic measurements (Ga~per~ic et a l . , 1973), there has been no similar report in Slovenia so far.
Hence, the
purpose of this study was to check mercury hygiene in Slovenian dental surgeries by measuring the level of
mercury in
ambiental a i r as well as the
blood and
urine mercury levels in some groups of professional dental workers. The results obtained were s t a t i s t i c a l l y analysed concerning different aspects of the ambiental (age and type of surgeries, period of the working day), as well as the biological
parameters (sex and occupational profile
of workers, years in
profession).
MATERIALS AND METHODS Mercury vapour monitoring of the surgeries In the ambiental mercury study 63 dental surgeries (45 of general practice and 18 children's)
from different
parts of Slovenia were included.
visited had no previous notice of
intended monitoring.
samples for mercury analysis were taken under similar
In all
Each surgery cases, the air
condition; they were
collected during March, approximately from the same position (near the dental chair ] m above the floor and away from the amalgam preparation area) and in the same manner. Using a vacuum pump, a i r was drawn for 2 min at a flow rate of 30 I/h through succesively connected quartz tubes; the f i r s t one was f i l l e d with quartz wool and s i l i c a as traps for dust and moisture, and the second was f i l l e d with a g~Id trap for mercury. collected
was later
The procedure was repeated twice.
determined in
amalgamation AAS technique.
the
The mercury
analytical laboratory using the
gold
The detection l i m i t of the procedure was 0.04 ug/m3
(Horvat et a l . , ]987). For each surgery data relating session were collected. measurements of a i r
to the
age, type
and the
time of
treatment
In addition to the investigations described above, some
mercury in
a student,s
training
laboratory during
the
1733
preparation of amalgam by the included in the study.
hand mixing
procedure, were also
performed and
Bioloqical monitorina of dental oersonnel In the biological study a total of 77 participants were included; 67 of them were from the University Dental Clinic, Ljubljana, (20 students, 22 dentists and 25 dental nurses), and the remaining subjects were anamnestically unexposed inhabitants, who represented the control group. The blood samples, collected from all participants, were taken from a cubital vein, placed in quartz ampoules and immediately frozen in liquid nitrogen and then stored deep - frozen until analysis. Urine samples were taken from dental personnel and the control group. Early morning and evening urine were both collected in tightly closed glass containers and refrigerated for stability until analysis was completed. Mercury in blood was estimated using the neutron activation procedure according to Byrne and Kosta (1974), which is recommended as a reference method for total mercury analysis (WHO, ]ggo). Urinary mercury was determined by means of flameless atomic absorption spectroscopy, after the aliquots of urine had been weighed and wet digested in tightly closed quartz tubes (May and Stoeppler, 1984). Ultratra~e levels (down to 0.1 ng/g) of mercury could be determined and urine with the applied analytical methods.
in blood
Data analysis Variability of air mercury concentrations was analysed with respect to the age and type of surgery, as well as regarding the time during the working day. The data on the blood and urine mercury levels of dental workers were compared to the control group and analysed with respect to sex, the profile of the workers and their years of employment in the profession. Statistical significance between groups was determined using the procedure for a one - way analysis of variance (ANOVA). The logarithmic transformation of urine data was performed to meet the assumption of homogeneity of variances for the ANOVA test. Correlation analysis was done using Pearson's coefficient.
1734
RESULTS Surqeries The mean and the median values for a l l tested calculated
separately for
those in
surgeries) are presented in Table I. no significant
surgeries (including the results
general practice
and for
children's
Regarding the different type of surgeries,
differences were found for
mean and median values
of mercury
concentrations in ambiental air. TABLE 1. Ambiental mercury levels (ug/m3)
n
min
max
mean +_ stdev,
median
General practice
45
0.4
8.2
2.7 -+ 1.9
2.5
Children's
18
0.4
8.0
2.9 + 2.6
2.1
63
0.4
8.2
2.8 ± 2.2
2.4
SURGERIES
Total [,
,,
Individual measurements of ambiental mercury concentrations coresponding each of 63 dental surgeries ordered according to in a sequence data plot in Fig. 40 r
.........
35
>-
age in increasing years, are presented
i. 40
age of s u r g e r i e s ambiental mercury
35.-.
30
30
25
35 v
2O
20
15
15
10
i0
5
5
~o
0
'
|
1
8
16
|
24 32 40 Observations
i
i
48
56
o
63
Fig. h Sequence data plot: monitoring of air mercury concentrations in 63 dental surgeries ordered in increasing age in years.
1735
Correlation analysis showed no significant tendency for mercury concentrations to follow the increasing age of surgeries. To test i f there are any significant differences between groups, regarding age, all surgeries were grouped in six sets, each increasing by five years, and a l-way ANOVA test was performed. No significant differences among the groups were found. Fig. 2. shows variations in ambiental mercury levels during the working day, from 8 to 15 hours, including both types of surgeries. A nonsignificant F was observed for the whole data set.
5 ~4
2
8
9
I0
11 12 13 14 15 Time (hours) mean st. dev.
Fig. 2: Variations in ambiental mercury levels during the working day. Mean values represent 5 - 12 surgeries.
Table 2. presents somemeasurements of ambiental air in the student,s training laboratory during the preparation of amalgam by hand mixing. TABLE 2. Ambiental mercury vapour levels in dental student's training laboratory i
Procedure
D~tance
Student
ug Hg/m3 a~
J
amalgam condensation of a second class preparation
preparation of amalgam by hand mixing
15 cm away from mouth
A
69.5
B
86.9
15 cm away from centre at the breathing zone
158.0
C
95.6
1736
Bioloqical study Blood mercury levels
as well as the
of the exposed groups,
control group, are
presented in Table 3. TABLE 3. Blood m e r c u r y levels (ng/g)
PARTICIPANTS
BLOOD
Hg L E V E L S ( n g / g )
PROFILE
n
YEAP~IN PROFESSION
rain
max
meaa~ + st. d e v .
Students
20
3-5 years of study
1.6
5.9
2.9±1.1
2.6
Dentists
22
6-26 (mean 19)
1.6
7.7
3.6±1,5
3.7
Dental nurses
25
3-38 (mean 19)
0.9
5.4
2.8±1.t
2.7
Control group
lO
/
1.0
4.B
2.7 ± 1.2
2.5
dentists.
However, no
The highest mean value of 3.6 ng Hg/g was observed for
median
significant difference was found in comparison to the control group, which had a mean value of 2.7 ng Hg/g.
An overall ANOVAtest gave a nonsignificant F, thus
indicating that the p r o f i l e of workers had no significant effect on the level of mercury in blood. In order to evaluate the influence of on the
the years of employment in the profession
blood mercury level, both groups
subdivided with
respect to the
- dentists and dental nurses
meannumber of
total years in
- were
dental practice
(19); however, no significant differences were found between the subsets. Sex dependence of blood mercury level was also found to be nonsignificant. For urinary mercury, tests of significance were performed on the logarithmically transformed
data; therefore,
the means with
95 % confidence intervals
were
reported for urinary mercury levels in dental personnel and in the control group (Table 4). the
control
The mean urinary mercury values for the dentists, dental nurses and group were 4.1,
6.7
and 3.0
differences between them were observed.
ng/g;
however, no
significant
1737
TABLE4. Urinary mercury levels (ng/g)
PARTICIPANTS
mean with 95 Z confidence intervals
Dentists
21
4.1
(2.B
Dental nurses
23
6.7
(4.6 9.6)
Control group
1o
3.o
(L7 s.3)
-
5.9)
-
-
Urinary mercury levels in dentists and dental nurses, regarding sex and years in the profession, are presented in Fig. 3.
14
40
.)
• t~0
r = -0.473 P = 0.0012
30 t b)
~10 "~
"" 8
/
: 20b
.-= 6
•
•
t~
== 4
d ~op
~2
I
"
•
~10
Den Hsls
l~urse~
~ 8
~2 o
.'~O'
•
"
1
P = 0.005
LOll 81-
4[-
1
_
y <[]2 0
y
l
.
y_>20
.&
N.S.
I
40
T
Den/ists
Profile / Sex
•
NUFSeS
I d) DenHsls
[4~
[2[-
4
•
16,
c)
14
.-= 6
•
10 20 30 Years in profession
Sex
16
"
:22o
i
Profile / Years in profession
Fig.3: Urinary mercury levels in dental personnel, presented with respect to sex (a), years in profession (b) and profile of workers adjusted for sex (c) and the mean number of years in profession (d). The means with 95Z confidence intervals are presented for different groups. P = level of significance; N.S. = nonsignificant
1738
For the female group (dentists and dental nurses), higher i f compared to the male group (dentists only) (Fig. with a similar pattern
values were observed
3c), which is in accordance
for both sexes regardless of
the p r o f i l e
(Fig.
However, nonsignificant differences were observed for the different
3a).
sexes, as
well as for the three groups from Fig. 3c. There was a significant linear relationship between urinary mercury levels (including a l l dental workers) and the number of years spent in the profession (r=-0.473; P=0.0012) (Fig.
3b).
The influence of years in the
the urinary mercury levels appeared in dental nurses too (Fig.
3d).
profession on
the same pattern among dentist and among
Both of the
"profile" groups consisted
of two
subgrouPs - one having less than 20 years in the profession and the other one having 20 or the
more. An overall ANOVAtest found a significant difference among
groups from Fig.
nurses having less
3d
(P=O.OOS).
A multimean comparison revaled
than 20, and dentists
profession, as the groups with the
having 20 or
dental
more years in
maximal and minimal levels of
the
mercury in
urine, which d i f f e r significantly.
DISCUSSION
For all from 0.4
the investigated surgeries, the air to
occupational
8.2
ug/m3
concentrations of
(median 2.4), which is
exposure l i m i t
(TLV) of
well
50 ug Hg/m3 and is also
recommended health-based occupational exposure l i m i t of ensure a reasonable degree of symptoms (WHO, 1980).
protection against
Thus, our
results indicate
hygiene in Slovenian dentistry. mercury levels (Temmerman et
mercury ranged
below the
threshold below the
25 ug/m3 which would
mercury-induced nonspecific very satisfactory mercury
However, by comparison with
the data
for
in the general atmosphere, which are t y p i c a l l y below 20 ng/m3 a l . , 1990), the air
in the dental office
with mercury vapour. Our results
for the
was s t i l l contaminated
air mercury levels were comparable
with the ones obtained in Sweden (Nilsson and Nilsson, 1986) where median values for public and private dental care were 1.5 ug/m3 and 3.6 ug/m3, respectively, and were lower than those reported by other investigators DeFreitas, 1981).
(Nixon et a l . , 1981;
The mode of amalgam preparation is
one of the
affect the level of a i r mercury.
our study, of the all surgeries tested, 94
In
principal factors
which could
% use preencapsulated amalgam (Vivadent almacap), and the remaining use dentomat. However, hand mixing of amalgamwas s t i l l in use in the student training course of a week ( once per year). During the preparation of amalgam by this method, high levels of a i r mercury, exceeding the
TLV can be observed.
Although such excessive levels are momentary in nature, precautionary measures must be taken to minimize mercury exposure. The use of means of personal protection, as well as maintaining a safe working environment in accordance with
1739
the educational practices advanced, are of prime importance. Of a l l the
surgeries tested, the most recently occupied were no more than one
year old, and the oldest was 40 years old; ambiental mercury level was found.
however, no
influence of
age on
Regarding the d i f f e r e n t time point during the working day, an overall ANOVA test showed that However, an
there were no significant increasing trend of rising
differences
between the
sets.
data
a i r mercury concentrations up to 13 h,
followed by a rapid drop at 14 h, can be observed (Fig. 2). This probably reflects the usual dental practice that after 13 h acceptance of patients is complete and surgeries are then well ventilated. Although the source
level of atmospheric
of mercury
hygienic
exposure of
habits of
workers,
mercury in the
dental surgery is
the prime
dental personnel
as a group, the
different
as well
mercury, can cause great variation in persons working exposure cannot
in the
as the
individual
background level
of
individual mercury body burdens, even for
same conditions.
However, the r i s k
of
be s a t i s f a c t o r i l y evaluated either from blood or
mercury levels, and only monitoring of the
individual from urinary
body burden on a group basis shows a
correlation with the level of exposure (WHO, 1980; Kobal, 199]). In this study, low a i r levels of
mercury in surgeries were reflected in the low For the following discussion, blood
body burden of mercury in dental personnel. and urine mercury
concentrations (from
Tables 3 and 4)
specific gravity of 1.06 for blood and 1.02 for urine Thus, the mean value
for blood
mercury concentrations (including
dental nurses and students) was 3.2 ng Hg/ml. the hygienic threshold blood and the
were corrected
to a
(Reference Han ICRP 23). dentists,
According to a WHO report (1976),
l i m i t for professionally exposed workers is
reference values for the mean concentrations
blood in non-exposed populations is about 8 ng Hg/ml.
35 ng Hg/ml
of total mercury in
However, i t is recognised
that mercury level in blood may be highly influenced by food intake, especially by fish consumption, so no value for the threshold l i m i t of mercury in blood was recommended
in the
exposed people,
newer publication of
WHO (]980).
with moderate consumption of fish,
reported to be 10 - 20 ng/ml (WHO, ]980). are reported 1990) and, i f elemental
to release mercury vapour present,
mercury
they
air
nonoccupationally levels were
In addition, dental mercury f i l l i n g s into the oral
represent the
vapour through
For
blood mercury
cavity (Weiner et a l . ,
dominant source
inhalation
in the
of exposure to
general
population
(Clarkson et a l . , 1988). In this connection i t is interesting to mention the paper of Stortebecker (1989), who discussed the danger of direct nose-brain transport of mercury from dental amalgam f i l l i n g s . In our study there was no detailed information on fish intake habits number of amalgam f i l l i n g s of
the dental
and the
personnel; however, a l l values
of
mercury in blood were in the range from 0.95 to 8.2 (mean and median around 3) ng/ml, which can be considered as normal values for an unexposed population.
1740
For comparison, twenty years ago, mercury levels in a small group of Slovenian dentists
were found to be increased with
ranged from 3.3
respect to
the control
32.1 (mean around 10) ng/ml (Ga~per~i¢ at a l . ,
-
present results for those obtained in
blood mercury in dentists (median 3.9 Danish dentists
confirmed observations
(median 4.0
group, and 1973). Our
ng/ml) were close to
ng/ml), and at the
sametime
of decreased mercury exposure in dentistry in
the last
10-15 years (Moller-Madsen et a l . , 1988). None of
the parameters examined (profile of
workers, age in
showed a s t a t i s t i c a l l y significant effect on blood mercury. (Moller-Madsen et
a l . , 1988), the
profession, sex) In a similar study
relationship between blood level
of mercury
and the d a t a concerning age, sex, main occupation, number of amalgam restorations performed per day, last amalgam f i l l i n g and frequency of fish meals was investigated and only the last factor was shown to be significant. the blood mercury level is influenced and is a useful index of actual
In fact,
by recent exposure (Cherian et a l . , 1978)
short-term exposure (Kobal, 1991), and hence i t
is less useful as an index of periodical long-term occupational exposure. Mercury in blood
is interrelated to mercury in urine;
however, the
rate of
excretion of mercury through urine is a more time-averaged process. From'this reason the urinary mercury level
is accepted as a valuable parameter for
assessing chronic mercury exposure (Calder et
al.,
1984). The recommended
health - based occupational exposure l i m i t for mercury in urine WHO (1980), and according to a recent evaluation of selected the reference
median value for mercury in urine for the
of 44 values exceeded 15 ng Hg/ml, indicating the personnel.
These results
are
l i t e r a t u r e data,
general population is
4.3 ng/ml (range: 0.1 to 20) (lyengar and Woittiez, 1988). dental
is 50 ng Hg/ml
In our study, only 3
low exposure of investigated
comparable with
that
obtained
for
Scandinavian dental personnel (Verschoor et a l . , 1988; Nilsson et a l . , 1990) and are of the same order of magnitude as for the general population as a whole. Three higher values were observed in dental nurses; however, no significant difference was found between dentists and the nurses. In similar studies, with on the
regard to the effect of the
urinary mercury level,
profile of dental workers
different and also opposite findings
have been
found (Verschoor et a l . , 1988; Huberlant et a l . , 1983). Generally higher nurses) than in nonsignificant. A significant
levels of urinary mercury were found in women (dentists and men (dentists), but the influence of sex was found to be
negative
linear
relationship
(r=-0.473;
P=0.0012) was found
between concentrations of mercury in urine and the years the dental workers had spent in practice. After correcting for different profiles, lower mean values of urinary mercury were observed in the
dentists as well as in
the nurses who
had 20 or more years in the profession than in those having less than 20 years. Similar findings, a reduction of urinary mercury levels over the years, were observed by Nixon et ai.(1981). Battistone et al. (1976) observed that a
1741
greater percentage of dentists in practice less than 5 years have mercury blood values above 10 ng/ml than dentists in practice 5-10 years; after about 20 years in practice, a decrease in mercury uptake has been found. The reasons for this decreasing trend may be the increased experienceof older workers, as well as improved hygienic measures in dental practices (Verschoor et al., 1988); however, the presence of physiological factors cannot be excluded. In monitoring the level of exposure of 4272 US dentist, the following factors were found to contribute significantly to the level of mercury in urine: type of practice; years in practice, in surgery and in speciality; hours of practice per week; number of restorations performed; method of amalgam preparation and mercury expression; type of amalgamcapsule used; and type of heating and cooling system (Naleway e t a ] . , ]985). Although there has been great progress in recognising the potential hazard of mercury exposure in dental practice, more investigations are needed to find and explain the relationship betweenthe level of exposure, and the body burden of mercury expressed by different indexes of exposure.
REFERENCES
Battistone, G.C., J.J. Hefferren, R.A. Miller and D.E. Cutright (1976). Mercury: its relation to the dentist,s health and dental practice characteristics. JADA, 92:1182-1188. Byrne, A.R. and L. Kosta (1974). Simultaneous neutron activation determination of selenium and mercury in biological samples by volatilization. Talanta, 21:1083-1090. Calder, I. M., G.R. Kelman and H. Mason (1984). mercury excretion. HumanToxicol., 3:463-467
Diurnal variations in urinary
Cherian, M.G., J.B. Hursh, T.W. Clarkson, and J. Allen (1978). Radioactive mercury distribution in biological fluids and excretion in human subjects after inhalation of mercury vapour. Arch. Environ. Health, 33: 10g-114. Clarkson, T.W., L. Friberg, J.B. Hursh and M. Nylander (1988). The prediction of intake of mercury vapor from amalgams. In Biological Monitoring of Toxic Metals, edited by Clarkson, T.W., L. Frieberg, G.F. Nordberg and P.R. Sager, Plenum Press, London, pp. 247-263. DeFreitas, J.F. (1981). Mercury in the dental work-place: An assessment of the health hazard and safeguards. Austral. D.J., 26:156-161 Ga~per~iC, D., P.Stegnar and C. Ravnik (1973). Mercury uptake and its distribution in some tissues from workers in dental surgeries. ZobV, 28:5-11.
1742
Horvat, M., E. Nanut, T. ZvonariC, A. R. Byrne and P. Stegnar (1987). Determination of mercury in air by gold amalgamation atomic absorption spectrometry. Paper presented at 4th Symposium "Spectroscopy in theory and practice", Kranjska gora, 1987. Huberlant,
J.M., H.
Roels, J.P.
Buchet, A.
Bernard, R. Lauwerys (1983).
Evaluation de l,exposition au mercure et des ses repercussions eventuelles sur la sante du personnel d,une trentaire de cabinets dentaires. Cab. Med.Trav., 206:109-127. lyengar, G.V. and J.W.R. Woittez (IgB8). Trace elements in human clinical specimens: evaluation of literature data to identify reference values. Clin. Chem., 34:474-481. Kobal, A. B. (1991). Occupational exposure to elemental mercury and its influence on mercury content in blood, erythrocytes, plasma, exhaled breath, and urine, and catalase activity in erythrocytes. Ph D. thesis, University of Ljubljana, 1991 (in Slovene). May, K. and M. Stoeppler (1984). Pretreatment studies with biological and environmental materials. IV. Complete wet digestion in partly and completely closed quartz vessels for subsequent trace and ultratrace mercury determination. Fresenius Z. Anal. Chem., 317:248-251. Moller-Madsen, B., J.C. Hansen and J. Kragstrup (1988). Mercury concentrations in blood from Danish dentists. Scand. J. Dent. Res., 96:56-59. Naleway, C., R. Sakaguchi, E.Mitchell, T. Muller, W.A. Ayer and J.J. (1985). Urinary mercury levels in US dentists, 1975-1983: review assessment program. JADA, 111:37-42.
Hefferren of health
Nilsson, B. and B.Nilsson (1986). Mercury in dental practice. I. The working environment of dental personnel and their exposure to mercury vapour. Swed. Dent. J., 10:1-14. Nilsson, B., L. Gerhardsson, G.F. Nordberg (1990). Urine mercury levels and associated symptoms in dental personnel. Sci. Tot. Environ., 94:179-185. Nixon, G.S., C . A . Whittle, A.Woodfin (1981). Mercury levels surgeries and dental personnel. Brit. Dent. J., 151:149-154.
in
dental
Reference Man ICRP 23 (1974). Report of the task group on reference man. International commission on radiological protection, Pergamon press, Oxford
1743
Stortebecker, P. (198g). Direct transport of mercury from the oronasal cavity to the cranial cavity as a cause of dental amalgam poisoning. Swed. J. Biol. Med., 3:8-21.
Temmerman, E., C. Vandecasteele, G. Vermeir, R. Leyman, R. Dams (Iggo). Sensitive determination of gaseous mercury in air by cold vapour atomic fluorescence spectrometry after amalgamation. Anal. Chim. Acta, 236:371-376. Verschoor, M;A., R.M.F. Herber, R.L. Zielhuis (1988). Urinary mercury levels and early changes in kidney function in dentists and dental assistants. Community Dent. Oral Epidemio1., 16:148-152.
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Exposure to Heavy
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(Receivedin Germany 15 Apfil1992;accep~d25May 1992)
amalgam
Geneva, World
0045-6535/92 $5.00 + 0 00 Pergamon Press Ltd.
MERCURYLEVELS IN DENTALSURGERIESAND DENTAL PERSONNELIN SLOVENIA
Franek Klemenc,I Mirjana ~kreblin2., Milena Horvat2 and Peter Stegnar2
IDepartment for Dental Diseases, University Dental Clinic 2Department of Nuclear Chemistry, "J. Stefan" Institute University of Ljubljana, Slovenia
ABSTRACT The level of mercury exposure in Slovenian dental practice was studied by measurement of air mercuw leyels in 63 surgeries and by analysis of the mercury content in blood and urine samples of professionally exposed and control groups (total of 77 participants). The mean ambiental mercury concentration for all investigated surgeries was 2.8 ug Hg/m3 (range: 0.4-8.2), which is considerably below the health-based occupational exposure l i m i t of 25 ug/m3. No significant relationships between age or type of surgeries, or the time during the working day and the air mercury levels were found. The mean value for mercury in blood was 3.0 ng Hg/g (range: 0.9-7.7), which can be considered as the normal range for the general population. The occupational profile of the workers, years in the profession, as well as sex, showed a nonsignificant effect on blood mercury. Urinary mercury levels were also low. Only 3 of 44 values exceeded 15 ng Hg/g. No influence of sex or occupational p r o f i l e was found; however, a significant negative linear relationship (r=-0.473; PffiO.O012) was observed between the concentration of mercury in urine and years in the profession. The data indicate good mercury hygiene in Slovenian dentistry.
1731
1732
INTRODUCTION
Dental amalgam is
extensively used as a f i l l i n g material
and i t s potential
health hazard as a source of
in dental restoration
mercury vapour exposure for
dental personnel who handle the amalgam, has provoked numerous and extensive surveys on mercury contamination
in dental
practice
throughout the
world
(DeFreitas, 1981). With the exception of a few sporadic measurements (Ga~per~ic et a l . , 1973), there has been no similar report in Slovenia so far.
Hence, the
purpose of this study was to check mercury hygiene in Slovenian dental surgeries by measuring the level of
mercury in
ambiental a i r as well as the
blood and
urine mercury levels in some groups of professional dental workers. The results obtained were s t a t i s t i c a l l y analysed concerning different aspects of the ambiental (age and type of surgeries, period of the working day), as well as the biological
parameters (sex and occupational profile
of workers, years in
profession).
MATERIALS AND METHODS Mercury vapour monitoring of the surgeries In the ambiental mercury study 63 dental surgeries (45 of general practice and 18 children's)
from different
parts of Slovenia were included.
visited had no previous notice of
intended monitoring.
samples for mercury analysis were taken under similar
In all
Each surgery cases, the air
condition; they were
collected during March, approximately from the same position (near the dental chair ] m above the floor and away from the amalgam preparation area) and in the same manner. Using a vacuum pump, a i r was drawn for 2 min at a flow rate of 30 I/h through succesively connected quartz tubes; the f i r s t one was f i l l e d with quartz wool and s i l i c a as traps for dust and moisture, and the second was f i l l e d with a g~Id trap for mercury. collected
was later
The procedure was repeated twice.
determined in
amalgamation AAS technique.
the
The mercury
analytical laboratory using the
gold
The detection l i m i t of the procedure was 0.04 ug/m3
(Horvat et a l . , ]987). For each surgery data relating session were collected. measurements of a i r
to the
age, type
and the
time of
treatment
In addition to the investigations described above, some
mercury in
a student,s
training
laboratory during
the
1733
preparation of amalgam by the included in the study.
hand mixing
procedure, were also
performed and
Bioloqical monitorina of dental oersonnel In the biological study a total of 77 participants were included; 67 of them were from the University Dental Clinic, Ljubljana, (20 students, 22 dentists and 25 dental nurses), and the remaining subjects were anamnestically unexposed inhabitants, who represented the control group. The blood samples, collected from all participants, were taken from a cubital vein, placed in quartz ampoules and immediately frozen in liquid nitrogen and then stored deep - frozen until analysis. Urine samples were taken from dental personnel and the control group. Early morning and evening urine were both collected in tightly closed glass containers and refrigerated for stability until analysis was completed. Mercury in blood was estimated using the neutron activation procedure according to Byrne and Kosta (1974), which is recommended as a reference method for total mercury analysis (WHO, ]ggo). Urinary mercury was determined by means of flameless atomic absorption spectroscopy, after the aliquots of urine had been weighed and wet digested in tightly closed quartz tubes (May and Stoeppler, 1984). Ultratra~e levels (down to 0.1 ng/g) of mercury could be determined and urine with the applied analytical methods.
in blood
Data analysis Variability of air mercury concentrations was analysed with respect to the age and type of surgery, as well as regarding the time during the working day. The data on the blood and urine mercury levels of dental workers were compared to the control group and analysed with respect to sex, the profile of the workers and their years of employment in the profession. Statistical significance between groups was determined using the procedure for a one - way analysis of variance (ANOVA). The logarithmic transformation of urine data was performed to meet the assumption of homogeneity of variances for the ANOVA test. Correlation analysis was done using Pearson's coefficient.
1734
RESULTS Surqeries The mean and the median values for a l l tested calculated
separately for
those in
surgeries) are presented in Table I. no significant
surgeries (including the results
general practice
and for
children's
Regarding the different type of surgeries,
differences were found for
mean and median values
of mercury
concentrations in ambiental air. TABLE 1. Ambiental mercury levels (ug/m3)
n
min
max
mean +_ stdev,
median
General practice
45
0.4
8.2
2.7 -+ 1.9
2.5
Children's
18
0.4
8.0
2.9 + 2.6
2.1
63
0.4
8.2
2.8 ± 2.2
2.4
SURGERIES
Total [,
,,
Individual measurements of ambiental mercury concentrations coresponding each of 63 dental surgeries ordered according to in a sequence data plot in Fig. 40 r
.........
35
>-
age in increasing years, are presented
i. 40
age of s u r g e r i e s ambiental mercury
35.-.
30
30
25
35 v
2O
20
15
15
10
i0
5
5
~o
0
'
|
1
8
16
|
24 32 40 Observations
i
i
48
56
o
63
Fig. h Sequence data plot: monitoring of air mercury concentrations in 63 dental surgeries ordered in increasing age in years.
1735
Correlation analysis showed no significant tendency for mercury concentrations to follow the increasing age of surgeries. To test i f there are any significant differences between groups, regarding age, all surgeries were grouped in six sets, each increasing by five years, and a l-way ANOVA test was performed. No significant differences among the groups were found. Fig. 2. shows variations in ambiental mercury levels during the working day, from 8 to 15 hours, including both types of surgeries. A nonsignificant F was observed for the whole data set.
5 ~4
2
8
9
I0
11 12 13 14 15 Time (hours) mean st. dev.
Fig. 2: Variations in ambiental mercury levels during the working day. Mean values represent 5 - 12 surgeries.
Table 2. presents somemeasurements of ambiental air in the student,s training laboratory during the preparation of amalgam by hand mixing. TABLE 2. Ambiental mercury vapour levels in dental student's training laboratory i
Procedure
D~tance
Student
ug Hg/m3 a~
J
amalgam condensation of a second class preparation
preparation of amalgam by hand mixing
15 cm away from mouth
A
69.5
B
86.9
15 cm away from centre at the breathing zone
158.0
C
95.6
1736
Bioloqical study Blood mercury levels
as well as the
of the exposed groups,
control group, are
presented in Table 3. TABLE 3. Blood m e r c u r y levels (ng/g)
PARTICIPANTS
BLOOD
Hg L E V E L S ( n g / g )
PROFILE
n
YEAP~IN PROFESSION
rain
max
meaa~ + st. d e v .
Students
20
3-5 years of study
1.6
5.9
2.9±1.1
2.6
Dentists
22
6-26 (mean 19)
1.6
7.7
3.6±1,5
3.7
Dental nurses
25
3-38 (mean 19)
0.9
5.4
2.8±1.t
2.7
Control group
lO
/
1.0
4.B
2.7 ± 1.2
2.5
dentists.
However, no
The highest mean value of 3.6 ng Hg/g was observed for
median
significant difference was found in comparison to the control group, which had a mean value of 2.7 ng Hg/g.
An overall ANOVAtest gave a nonsignificant F, thus
indicating that the p r o f i l e of workers had no significant effect on the level of mercury in blood. In order to evaluate the influence of on the
the years of employment in the profession
blood mercury level, both groups
subdivided with
respect to the
- dentists and dental nurses
meannumber of
total years in
- were
dental practice
(19); however, no significant differences were found between the subsets. Sex dependence of blood mercury level was also found to be nonsignificant. For urinary mercury, tests of significance were performed on the logarithmically transformed
data; therefore,
the means with
95 % confidence intervals
were
reported for urinary mercury levels in dental personnel and in the control group (Table 4). the
control
The mean urinary mercury values for the dentists, dental nurses and group were 4.1,
6.7
and 3.0
differences between them were observed.
ng/g;
however, no
significant
1737
TABLE4. Urinary mercury levels (ng/g)
PARTICIPANTS
mean with 95 Z confidence intervals
Dentists
21
4.1
(2.B
Dental nurses
23
6.7
(4.6 9.6)
Control group
1o
3.o
(L7 s.3)
-
5.9)
-
-
Urinary mercury levels in dentists and dental nurses, regarding sex and years in the profession, are presented in Fig. 3.
14
40
.)
• t~0
r = -0.473 P = 0.0012
30 t b)
~10 "~
"" 8
/
: 20b
.-= 6
•
•
t~
== 4
d ~op
~2
I
"
•
~10
Den Hsls
l~urse~
~ 8
~2 o
.'~O'
•
"
1
P = 0.005
LOll 81-
4[-
1
_
y <[]2 0
y
l
.
y_>20
.&
N.S.
I
40
T
Den/ists
Profile / Sex
•
NUFSeS
I d) DenHsls
[4~
[2[-
4
•
16,
c)
14
.-= 6
•
10 20 30 Years in profession
Sex
16
"
:22o
i
Profile / Years in profession
Fig.3: Urinary mercury levels in dental personnel, presented with respect to sex (a), years in profession (b) and profile of workers adjusted for sex (c) and the mean number of years in profession (d). The means with 95Z confidence intervals are presented for different groups. P = level of significance; N.S. = nonsignificant
1738
For the female group (dentists and dental nurses), higher i f compared to the male group (dentists only) (Fig. with a similar pattern
values were observed
3c), which is in accordance
for both sexes regardless of
the p r o f i l e
(Fig.
However, nonsignificant differences were observed for the different
3a).
sexes, as
well as for the three groups from Fig. 3c. There was a significant linear relationship between urinary mercury levels (including a l l dental workers) and the number of years spent in the profession (r=-0.473; P=0.0012) (Fig.
3b).
The influence of years in the
the urinary mercury levels appeared in dental nurses too (Fig.
3d).
profession on
the same pattern among dentist and among
Both of the
"profile" groups consisted
of two
subgrouPs - one having less than 20 years in the profession and the other one having 20 or the
more. An overall ANOVAtest found a significant difference among
groups from Fig.
nurses having less
3d
(P=O.OOS).
A multimean comparison revaled
than 20, and dentists
profession, as the groups with the
having 20 or
dental
more years in
maximal and minimal levels of
the
mercury in
urine, which d i f f e r significantly.
DISCUSSION
For all from 0.4
the investigated surgeries, the air to
occupational
8.2
ug/m3
concentrations of
(median 2.4), which is
exposure l i m i t
(TLV) of
well
50 ug Hg/m3 and is also
recommended health-based occupational exposure l i m i t of ensure a reasonable degree of symptoms (WHO, 1980).
protection against
Thus, our
results indicate
hygiene in Slovenian dentistry. mercury levels (Temmerman et
mercury ranged
below the
threshold below the
25 ug/m3 which would
mercury-induced nonspecific very satisfactory mercury
However, by comparison with
the data
for
in the general atmosphere, which are t y p i c a l l y below 20 ng/m3 a l . , 1990), the air
in the dental office
with mercury vapour. Our results
for the
was s t i l l contaminated
air mercury levels were comparable
with the ones obtained in Sweden (Nilsson and Nilsson, 1986) where median values for public and private dental care were 1.5 ug/m3 and 3.6 ug/m3, respectively, and were lower than those reported by other investigators DeFreitas, 1981).
(Nixon et a l . , 1981;
The mode of amalgam preparation is
one of the
affect the level of a i r mercury.
our study, of the all surgeries tested, 94
In
principal factors
which could
% use preencapsulated amalgam (Vivadent almacap), and the remaining use dentomat. However, hand mixing of amalgamwas s t i l l in use in the student training course of a week ( once per year). During the preparation of amalgam by this method, high levels of a i r mercury, exceeding the
TLV can be observed.
Although such excessive levels are momentary in nature, precautionary measures must be taken to minimize mercury exposure. The use of means of personal protection, as well as maintaining a safe working environment in accordance with
1739
the educational practices advanced, are of prime importance. Of a l l the
surgeries tested, the most recently occupied were no more than one
year old, and the oldest was 40 years old; ambiental mercury level was found.
however, no
influence of
age on
Regarding the d i f f e r e n t time point during the working day, an overall ANOVA test showed that However, an
there were no significant increasing trend of rising
differences
between the
sets.
data
a i r mercury concentrations up to 13 h,
followed by a rapid drop at 14 h, can be observed (Fig. 2). This probably reflects the usual dental practice that after 13 h acceptance of patients is complete and surgeries are then well ventilated. Although the source
level of atmospheric
of mercury
hygienic
exposure of
habits of
workers,
mercury in the
dental surgery is
the prime
dental personnel
as a group, the
different
as well
mercury, can cause great variation in persons working exposure cannot
in the
as the
individual
background level
of
individual mercury body burdens, even for
same conditions.
However, the r i s k
of
be s a t i s f a c t o r i l y evaluated either from blood or
mercury levels, and only monitoring of the
individual from urinary
body burden on a group basis shows a
correlation with the level of exposure (WHO, 1980; Kobal, 199]). In this study, low a i r levels of
mercury in surgeries were reflected in the low For the following discussion, blood
body burden of mercury in dental personnel. and urine mercury
concentrations (from
Tables 3 and 4)
specific gravity of 1.06 for blood and 1.02 for urine Thus, the mean value
for blood
mercury concentrations (including
dental nurses and students) was 3.2 ng Hg/ml. the hygienic threshold blood and the
were corrected
to a
(Reference Han ICRP 23). dentists,
According to a WHO report (1976),
l i m i t for professionally exposed workers is
reference values for the mean concentrations
blood in non-exposed populations is about 8 ng Hg/ml.
35 ng Hg/ml
of total mercury in
However, i t is recognised
that mercury level in blood may be highly influenced by food intake, especially by fish consumption, so no value for the threshold l i m i t of mercury in blood was recommended
in the
exposed people,
newer publication of
WHO (]980).
with moderate consumption of fish,
reported to be 10 - 20 ng/ml (WHO, ]980). are reported 1990) and, i f elemental
to release mercury vapour present,
mercury
they
air
nonoccupationally levels were
In addition, dental mercury f i l l i n g s into the oral
represent the
vapour through
For
blood mercury
cavity (Weiner et a l . ,
dominant source
inhalation
in the
of exposure to
general
population
(Clarkson et a l . , 1988). In this connection i t is interesting to mention the paper of Stortebecker (1989), who discussed the danger of direct nose-brain transport of mercury from dental amalgam f i l l i n g s . In our study there was no detailed information on fish intake habits number of amalgam f i l l i n g s of
the dental
and the
personnel; however, a l l values
of
mercury in blood were in the range from 0.95 to 8.2 (mean and median around 3) ng/ml, which can be considered as normal values for an unexposed population.
1740
For comparison, twenty years ago, mercury levels in a small group of Slovenian dentists
were found to be increased with
ranged from 3.3
respect to
the control
32.1 (mean around 10) ng/ml (Ga~per~i¢ at a l . ,
-
present results for those obtained in
blood mercury in dentists (median 3.9 Danish dentists
confirmed observations
(median 4.0
group, and 1973). Our
ng/ml) were close to
ng/ml), and at the
sametime
of decreased mercury exposure in dentistry in
the last
10-15 years (Moller-Madsen et a l . , 1988). None of
the parameters examined (profile of
workers, age in
showed a s t a t i s t i c a l l y significant effect on blood mercury. (Moller-Madsen et
a l . , 1988), the
profession, sex) In a similar study
relationship between blood level
of mercury
and the d a t a concerning age, sex, main occupation, number of amalgam restorations performed per day, last amalgam f i l l i n g and frequency of fish meals was investigated and only the last factor was shown to be significant. the blood mercury level is influenced and is a useful index of actual
In fact,
by recent exposure (Cherian et a l . , 1978)
short-term exposure (Kobal, 1991), and hence i t
is less useful as an index of periodical long-term occupational exposure. Mercury in blood
is interrelated to mercury in urine;
however, the
rate of
excretion of mercury through urine is a more time-averaged process. From'this reason the urinary mercury level
is accepted as a valuable parameter for
assessing chronic mercury exposure (Calder et
al.,
1984). The recommended
health - based occupational exposure l i m i t for mercury in urine WHO (1980), and according to a recent evaluation of selected the reference
median value for mercury in urine for the
of 44 values exceeded 15 ng Hg/ml, indicating the personnel.
These results
are
l i t e r a t u r e data,
general population is
4.3 ng/ml (range: 0.1 to 20) (lyengar and Woittiez, 1988). dental
is 50 ng Hg/ml
In our study, only 3
low exposure of investigated
comparable with
that
obtained
for
Scandinavian dental personnel (Verschoor et a l . , 1988; Nilsson et a l . , 1990) and are of the same order of magnitude as for the general population as a whole. Three higher values were observed in dental nurses; however, no significant difference was found between dentists and the nurses. In similar studies, with on the
regard to the effect of the
urinary mercury level,
profile of dental workers
different and also opposite findings
have been
found (Verschoor et a l . , 1988; Huberlant et a l . , 1983). Generally higher nurses) than in nonsignificant. A significant
levels of urinary mercury were found in women (dentists and men (dentists), but the influence of sex was found to be
negative
linear
relationship
(r=-0.473;
P=0.0012) was found
between concentrations of mercury in urine and the years the dental workers had spent in practice. After correcting for different profiles, lower mean values of urinary mercury were observed in the
dentists as well as in
the nurses who
had 20 or more years in the profession than in those having less than 20 years. Similar findings, a reduction of urinary mercury levels over the years, were observed by Nixon et ai.(1981). Battistone et al. (1976) observed that a
1741
greater percentage of dentists in practice less than 5 years have mercury blood values above 10 ng/ml than dentists in practice 5-10 years; after about 20 years in practice, a decrease in mercury uptake has been found. The reasons for this decreasing trend may be the increased experienceof older workers, as well as improved hygienic measures in dental practices (Verschoor et al., 1988); however, the presence of physiological factors cannot be excluded. In monitoring the level of exposure of 4272 US dentist, the following factors were found to contribute significantly to the level of mercury in urine: type of practice; years in practice, in surgery and in speciality; hours of practice per week; number of restorations performed; method of amalgam preparation and mercury expression; type of amalgamcapsule used; and type of heating and cooling system (Naleway e t a ] . , ]985). Although there has been great progress in recognising the potential hazard of mercury exposure in dental practice, more investigations are needed to find and explain the relationship betweenthe level of exposure, and the body burden of mercury expressed by different indexes of exposure.
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amalgam
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