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Biological monitoring of mercury vapour exposure by scalp hair analysis in comparison to blood and urine
Toxicology Letters Toxicology Letters 88 (1996) 221-226
Biological rnonitoring of mercury vapour exposure by scalp hair analysis in comparison to blood and urine Michael Wilhelm *a, Frank Miillerb, Helga Idel” Dfsseldorf; P. 0. Box IO IO 07, D-40001 Dukeldorf; Germany bDepartment of Dentistry, Heinrich-Heine-University Dukeldorl; P, 0. Box 10 IO 07, D-40001 Dtikseldorf; Germany
“Institute of Hygiene, Heinrich-Heine-University
Abstract The reliability of human scalp hair as an indicator of mercury vapour exposure is contentious. In this study mercury concentratilons in hair were compared with those in blood and urine of 20 dental students during their first “occupational)) exposure to mercury vapour. Samples were collected before, at the end of the technical course of operating dentistry which lasted 6 weeks, and 3 months later. Mercury was measured by cold vapour atomic absorption spectrometry. In all biological media studied, mercury levels significantly (P c 0.05) reflected exposure to mercury vapour. After the time period without exposure mercury content decreased. Hair mercury levels were correlated to those in erythrocytes at sampling times 1 and 3 (r = 0.686 and r = 0.492) and to the frequency of fish consumption at sampling time 1. It is concluded that hair may be used as an indicator of internal uptake of mercury provided that it was not externally exposed to mercury vapour. In cases of occupational exposure to mercury vapour, hair is an ulseful tool for monitoring external exposure. Keywords:
Biological monitoring;
Mercury vapour exposure; Hair; Erythrocytes; Plasma; Urine
1. Introduction Elemental
mercury
vapour
released
from den-
tal amalgam surfaces into the mouth is the predominant source of human exposure to mercury in the general population with low frequency of fish consumption [l]. Depending on the number of amalgam fillings, daily intake of mercury vapour amounts to 4-21 pg. In contrast, dietary intake of inorganic mercury compounds is about 4 &day and, recently, for German children a dietary mercury intake of only 0.4 pg was found on days without fish consumption [2]. In view of *Corresponding authlor.
the complex toxicokinetics of mercury vapour, there is at present no suitable indicator specimen for biological monitoring that will reflect the mercury content in critical organs such as the brain and kidneys [l]. Mercury in blood probably reflects recent mercury intake, while urine mercury concentrations may correlate with longterm exposure. The usefulness of scalp hair is questioned; however, mercury levels in hair indicate the dietary intake of methylmercury via fish
C3l In general, the reliability of human scalp hair as an indicator of exposure to metals is contentious. Besides advantages such as non-invasive collection of samples, relative stability of speci-
0378-4274/96/s] 5.00 $J 1996 Elsevier Ireland Ltd. All rights reserved PII SO378-4274(96)03’7411
222
M. Wilhelm et ul. I Toxicology Letters 88 (1996) 221-226
men and providing a lasting record of the average intake over some weeks, hair analysis is impaired firstly by difficulties in differentiating between exogenous metal contamination from water, air, or cosmetic treatment and the metal deposited endogenously, and secondly by the lack of information on the mechanisms and kinetics by which endogenous trace elements are incorporated into the hair [4,5]. We studied mercury concentrations in hair in relation to those in erythrocytes, plasma and urine of dental students during their first occupational exposure to mercury vapour by handling dental amalgam.
2. Materials and methods Twenty students from the University of Diisseldorf took part. Mean age was 24 f (SD.) 2.4 years.‘Six were female, 14 were male. They had no dentists in their family, they had not been exposed occupationally to mercury vapour before and they did not use special cosmetic hair treatment. Median frequency of fish consumption was 2 per month (range O-7 per month). No fish was eaten 4 weeks before and during the study period. Fifteen subjects had amalgam fillings. The median number of amalgam surfaces was 10 (range O-48). No amalgam replacement or removal was done at least 8 months before and during the study period. Hair, blood and spot urine samples were collected at three different times: firstly before, secondly at the end of the technical course of operating dentistry which lasted 6 weeks, and thirdly 3 months later. During the last time period the students did not handle dental amalgam. Additionally, morning urine samples were collected weekly during the course. Blood was collected by venipuncture in heparinized Vacutainers tubes (Becton Dickinson, Rutherford, NJ). Whole blood was stored at 4°C and plasma after separation from blood cells at -20°C until analyzed. in polypropylene tubes. Mercury concentrations in red cells were calculated from the levels in whole blood and plasma with reference to the hematocrit. Acidi-
fied urine samples were stored in acid-washed polypropylene vessels at - 20°C. Maximum storage period was 6 months. Urine concentrations were adjusted to the creatinine excretion. Creatinine was measured using a test kit (Merckotest no. 3385, Merck, Darmstadt) which is based on the Jaffe reaction. Hair samples were obtained from symmetrical occipital regions. Only the first 2 cm of the proximal end was used for analysis, thus reflecting the average intake over the past 2 months. Hair samples (approximately 20 mg) were digested in 30 ml quartz vessels with 2 ml HNO, (65%) and 100 ~1 H,SO, in a pressure controlled microwave oven (PMD 2, Kiirner, Rosenheim, FRG) for 7 min at power step 6. After cooling for 10 min the solution was diluted to 10 ml with H,SO, (0.4%). Mercury analysis was performed by cold vapour atomic absorption spectrometry after enrichment on a gold-platinum net as described elsewhere [6]. A PerkinElmer model 1100 B equipped with a mercury hydride system MHS 20 was used. The detection limits were 0.15 pg/l for urine, 0.3 pg,il for whole blood, 0.15 ,&I for plasma and 0.15 pg/g (20 mg sample) for hair. The day-to-day precisions were as follows: urine 3.6% (3.3 pg/l; n = 49), whole blood 5.6% (3.2 pg/l; n = 8) and hair 5.9% (0.54 pg/g; n = 20). Quality control was carried out with different reference materials (urine no. 115 with 35 pg Hg/l, whole blood no. 010010 with 3.3-5.1 pg Hg/l, both Seronorm, Nycomed, Oslo, Norway; CRM no. 397 human hair with 12.3 pg Hg/g BCR, Brussels, Belgium; GBW 09101 human hair with 2.16 pg/g, Shanghai Institute of Nuclear Research, China). Statistical comparison between different groups was undertaken by the Wilcoxon matched pairs signed rank test. Correlation between selected variables was tested by the Spearman rank order correlation.
3. Results and discussion Fig. 1 shows the results of mercury analysis in urine. Daily mercury excretion in urine expressed as pg/g creatinine (median) before the course was fairly constant and in the range of other data
223
M. Wilhelm er al. I Toxicology Letters 88 (19%) 221-226
Mg
Hg/g creatinine ,..
1.4 -
P < 0.001
1.2 -
0.6 Period of Hg vapour exposure
q 1
I
I
I
2
3
4
I,
II
I 123456
I
I
I
I
,I
II
I 20
Fig. 1. Hg levels in urine (median) of 20 dental students during their first “occupational” exposure (technical course of operative dentistry) to mercury vapour from dental amalgam.
reported for Germany [7,8]. During the course there was a steady increase of mercury concentrations in urine, reflecting an absorption of mercury vapour as a result of the first “occupational” exposure. The salme observation has been reported by other authors [9]. Three months later values had decreased but were still higher than the initial levels. Since absorbed mercury vapour is principally eliminated in the inorganic form of mercury, this may reflect the long whole body half-life of inorganic mercury which is about 60 days [l]. Alterations of mercury levels in erythroctyes and plasma were quite similar. In erythrocytes initial median m’ercury concentration was 1.47 pg/l (Fig. 2). The: increase following 6 weeks of intense mercury vapour exposure amounted to approximately 60%. After 3 months the values had decreased and there was no difference compared with those at the beginning of the study. Median plasma mercury levels rose from 0.45 to 0.82 and decreased to 0.6 pg/l at the end of the
study, but like in urine were still higher than the first values (Fig. 3). The erythrocyte-plasma ratios of mercury were about 3:l and showed only minor alterations during the study period. These findings indicate that after absorption through the pulmonary membranes mercury vapours dissolve in the circulating blood. This circulatory mercury is partitioned between packed cells and plasma. Furthermore, it can be assumed that no biotransformation of mercury vapour to organomercury occurred, since within blood the latter compound is concentrated in red cells. Unlike other suggestions, our results show that not only blood but also urine analysis can be used to assess recent exposure to mercury vapour [lo]. Assuming a continual exposure and in the absence of steady state conditions, our results indicate that the participants would reach the critical mercury level (level which may be associated with adverse effects) of 50 fig/g creatinine after approximately 8 years. However, studies
224
M. Wilheh et al. I Toxicology Letters 88 (1994) 221-226
yg He/l erythrocytes
4.0.
.
I I
3.2 .
P ( 0.01
................. .. .
I
-LL
............. ...... ..............
1
1
P ( 0.01
.
.................... ........................
T
2
3
Fig. 2. Box-and-whisker plot of Hg concentrations in erythrocytes of 20 dental students before (I), immediately at the end of a 6 week technical course (2) and 3 months after first “occupational” exposure to mercury vapour.
pg Hg/l
plasma
P ( 0.05 x x 1.5 ...................f.... ....... P”(“.~;I1’ .........................~‘p ( o,05 .. ... .....I.................
i l .O.
. . . . . . . . . . . . . . .&.._
’
II l. . . . . . . . . . . . . . . . . . . . . . . . . . . ..@
1 * . . . . . . . . . . . . . . . . . . . . .. .. . . .. .
B
.
.
.
.
.
.
.
.
.
0.5. .... ... ...... . ... . .... .... ... .. ... .. . . ....... ...... ......................... .. .... ..... .. .. ..........
I
1,
1
L
2
3
Fig. 3. Box-and-whisker plot of Hg concentrations in plasma of 20 dental students before (l), immediately at the end of a 6 week technical course (2) and 3 months after first “occupational” exposure to mercury vapour.
M. Wilhelm et al I Toxicology Letters 88 (1996) 221-226
225
yg Hg/g hair 3.0s
2_j_ . . . . . . . . ..__...___.......................
p..~.t)‘.~
. . . . *...................... ............................
.
I -L ‘1.8. ....................................................... ..................... ........................................ I
1.2. ..................................!...c!!.!i r
0.6.
.. . . . . . . . . . . . . . .
x . ...... .........!...v?:.!.! -IL.
’ . .. . ..... . .. .. .... .. . ..
. .. .
. .. .
..... ...
..
45
E? x 0.0. 1
2
3
Fig. 4. Box-and-whisker plot of Hg concentrations in hair of 20 dental students before (I), immediately at the end of a 6 week technical course (2) and 3 months after first “occupational” exposure to mercury vapour.
workers exposed to mercury vapour suggest that steady state is reached after 4 months of exposure [ 111. Hair mercury concentrations also reflected the exposure of the students during their technical course (Fig. 4). However, of all specimens studied hair analysis reve:aled the most striking alterations. Values increased from 0.47 to 1.05 ,ug/g, which corresponds, to an increase of 125%. At the end of the study hair mercury levels were quite similar to the initial values. The distribution pattern of the hair data obviously varied considerably. The range between the lower and upper quartiles of mercury concentrations in hair which was collected immediately at the end of the technical course was much wider compared with the other results. Thus it is likely that the mercury levels in hair of our students reflected to some unknown e:xtent adsorption of mercury vapour from the (atmosphere. Recently, in vitro experiments also showed a significant external contamination of human hair even at low levels of metallic mercury in the air [5]. Additionally, removal of mercury from hair by different washing procedures was found to be ineffective, suggesting a strong binding of external mercury contamination to functional groups of the hair structure. with
Correlation analysis of data also confirmed a significant influence of external contamination of hair samples. Table 1 summarizes correlation coefficients of mercury levels in hair in relation to those in other specimens, to the frequency of fish consumption and to the number of amalgam surfaces at the three different times of sample collection. For samples taken before and 3 months after the course there was a close relationship between mercury contents in hair and erythrocytes. Additionally, hair mercury concentrations were related to the frequency of fish consumption at the first sampling period. No other significant relationships of hair mercury were observed. Thus we conclude that at steady state conditions and without increased mercury vapour exposure from the atmosphere, mercury levels in hair and erythyrocytes provide a lasting record of the average mercury intake of the last 2-3 months, probably mainly from dietary intake even at low frequency of, or without, fish consumption. In summary, the results show that mercury levels in hair, erythrocytes, plasma and urine reflected the first ‘occupational” exposure to mercury vapour of dental students in a similar pattern. Increased mercury hair levels at the end of the first occupational exposure indicated adsorp-
226
M. Wilhelm et al. I Toxicology Letters 88 (1996) 221-226
Table 1 Hg levels in hair in relation (Spearman’s rank order correlation coefficient) to Hg in erthyrocytes, plasma, mine; to frequency of fish consumption; and to number of amalgam surfaces of 20 dental students before (l), immediately at the end (2) and 3 months after first “occupational” exposure to mercury vapour 1 Erythrocytes (pg Hg/l) Plasma @g HgjI) Urine (pg Hg/g creatinine) Fish consumption/month Number of amalgam surfaces
2
3
0.686** -0.063 0.492* -0.090 -0.059 -0.326 -0.281 -0.208 -0.278 0.448* 0.194 0.325 -0.074 0.032 -0.253
*P < 005: ** P < 0.001.
tion of mercury vapour from the atmosphere. At steady state conditions and in the absence of increased mercury air levels, hair mercury is related to erythrocyte mercury concentration even at low frequency of, or without, fish consumption.
Cl1 WHO PI
(1991) Inorganic Mercury, Environmental Health Criteria 118, WHO, Geneva. Wilhelm, M., Lombeck, I., Kouros, B., Wuthe, J. and Ohnesorge, F.K. (1995) Duplicate study on the dietary intake of some metals/metalloids by German children, Part I: Arsenic and Mercury. Zbl. Hyg. 197, 345-356.
c31 Airey, D. (1983) Total mercury concentrations in human hair from 13 countries in relation to fish consumg tion and location. Sci. Total Environ. 31, 157-180. c41 Wilhelm, M., Ohnesorge, F.K., Lombeck, I. and Hafner, D. (1989) Uptake of aluminum, cadmium, copper, lead, and zinc by human scalp hair and elution of the adsorbed metals. J. Anal. Toxicol. 13, 17-21. 151 Hat, E. and Krechniak, J. (1993) Mercury concentrations in hair exposed in vitro to mercury vapour. Biol. Trace Elem. Res. 39, 109- 115. LX1Schierling, P. and Schaller, K.H. (1981) Einfache und zuverlhsige Methoden zur absorptionsspektrometristhen Bestimmung von Quecksilber in Blut und Urin. Arbeitsmed. Sozialmed. PrHventivmed. 16, 57-61. c71 Zander, D., Ewers, U., Freuer, I., Westerweller, S., Jermann, E. and Brockhaus, A. (1990) Untersuchung zur Quecksilberbelastung der Bevolkerung. I. Quecksilberkonzentrationen im Urin bei Normalpersonen. Zbl. Hyg. 190,315-324. PI Herrmann, M. and Schweinsberg, F. (1993) Biomonitoring zur Beurteilung einer Quecksilberbelastung aus Amalgamfullungen. Quecksilberbestimmung in Urin vor und nach oraler Gabe von 2,3-Dimercapto-l-propansulfonshre (DMPS) und in Haaren. Zbl. Hyg. 194, 271-291. c91 Pieper, K., V&r, H., Isemann, M. and Stalder, K. (1989) Eine prospektive Untersuchung iiber die Quecksilberbelastung von Zahnmedizinstudenten. Teil 1 Anstieg der Hg-Ausscheidung im Verlauf des Phantomkurses. Dtsch. Zahniirztl. Z. 44,714-716. Cl01 Barregard, L. (1993) Biological monitoring of exposure to mercury vapour. Stand. J. Work Environ. Health 19, suppl. 1, 45-49. Cl11 Ishihara, N. and Urushiyama, K. (1994) Longitudinal study of workers exposed to mercury vapour at low concentrations: time course of inorganic and organic mercury concentrations in urine, blood, and hair. Occup. Environ. Med. 51, 660-662.
Biological rnonitoring of mercury vapour exposure by scalp hair analysis in comparison to blood and urine Michael Wilhelm *a, Frank Miillerb, Helga Idel” Dfsseldorf; P. 0. Box IO IO 07, D-40001 Dukeldorf; Germany bDepartment of Dentistry, Heinrich-Heine-University Dukeldorl; P, 0. Box 10 IO 07, D-40001 Dtikseldorf; Germany
“Institute of Hygiene, Heinrich-Heine-University
Abstract The reliability of human scalp hair as an indicator of mercury vapour exposure is contentious. In this study mercury concentratilons in hair were compared with those in blood and urine of 20 dental students during their first “occupational)) exposure to mercury vapour. Samples were collected before, at the end of the technical course of operating dentistry which lasted 6 weeks, and 3 months later. Mercury was measured by cold vapour atomic absorption spectrometry. In all biological media studied, mercury levels significantly (P c 0.05) reflected exposure to mercury vapour. After the time period without exposure mercury content decreased. Hair mercury levels were correlated to those in erythrocytes at sampling times 1 and 3 (r = 0.686 and r = 0.492) and to the frequency of fish consumption at sampling time 1. It is concluded that hair may be used as an indicator of internal uptake of mercury provided that it was not externally exposed to mercury vapour. In cases of occupational exposure to mercury vapour, hair is an ulseful tool for monitoring external exposure. Keywords:
Biological monitoring;
Mercury vapour exposure; Hair; Erythrocytes; Plasma; Urine
1. Introduction Elemental
mercury
vapour
released
from den-
tal amalgam surfaces into the mouth is the predominant source of human exposure to mercury in the general population with low frequency of fish consumption [l]. Depending on the number of amalgam fillings, daily intake of mercury vapour amounts to 4-21 pg. In contrast, dietary intake of inorganic mercury compounds is about 4 &day and, recently, for German children a dietary mercury intake of only 0.4 pg was found on days without fish consumption [2]. In view of *Corresponding authlor.
the complex toxicokinetics of mercury vapour, there is at present no suitable indicator specimen for biological monitoring that will reflect the mercury content in critical organs such as the brain and kidneys [l]. Mercury in blood probably reflects recent mercury intake, while urine mercury concentrations may correlate with longterm exposure. The usefulness of scalp hair is questioned; however, mercury levels in hair indicate the dietary intake of methylmercury via fish
C3l In general, the reliability of human scalp hair as an indicator of exposure to metals is contentious. Besides advantages such as non-invasive collection of samples, relative stability of speci-
0378-4274/96/s] 5.00 $J 1996 Elsevier Ireland Ltd. All rights reserved PII SO378-4274(96)03’7411
222
M. Wilhelm et ul. I Toxicology Letters 88 (1996) 221-226
men and providing a lasting record of the average intake over some weeks, hair analysis is impaired firstly by difficulties in differentiating between exogenous metal contamination from water, air, or cosmetic treatment and the metal deposited endogenously, and secondly by the lack of information on the mechanisms and kinetics by which endogenous trace elements are incorporated into the hair [4,5]. We studied mercury concentrations in hair in relation to those in erythrocytes, plasma and urine of dental students during their first occupational exposure to mercury vapour by handling dental amalgam.
2. Materials and methods Twenty students from the University of Diisseldorf took part. Mean age was 24 f (SD.) 2.4 years.‘Six were female, 14 were male. They had no dentists in their family, they had not been exposed occupationally to mercury vapour before and they did not use special cosmetic hair treatment. Median frequency of fish consumption was 2 per month (range O-7 per month). No fish was eaten 4 weeks before and during the study period. Fifteen subjects had amalgam fillings. The median number of amalgam surfaces was 10 (range O-48). No amalgam replacement or removal was done at least 8 months before and during the study period. Hair, blood and spot urine samples were collected at three different times: firstly before, secondly at the end of the technical course of operating dentistry which lasted 6 weeks, and thirdly 3 months later. During the last time period the students did not handle dental amalgam. Additionally, morning urine samples were collected weekly during the course. Blood was collected by venipuncture in heparinized Vacutainers tubes (Becton Dickinson, Rutherford, NJ). Whole blood was stored at 4°C and plasma after separation from blood cells at -20°C until analyzed. in polypropylene tubes. Mercury concentrations in red cells were calculated from the levels in whole blood and plasma with reference to the hematocrit. Acidi-
fied urine samples were stored in acid-washed polypropylene vessels at - 20°C. Maximum storage period was 6 months. Urine concentrations were adjusted to the creatinine excretion. Creatinine was measured using a test kit (Merckotest no. 3385, Merck, Darmstadt) which is based on the Jaffe reaction. Hair samples were obtained from symmetrical occipital regions. Only the first 2 cm of the proximal end was used for analysis, thus reflecting the average intake over the past 2 months. Hair samples (approximately 20 mg) were digested in 30 ml quartz vessels with 2 ml HNO, (65%) and 100 ~1 H,SO, in a pressure controlled microwave oven (PMD 2, Kiirner, Rosenheim, FRG) for 7 min at power step 6. After cooling for 10 min the solution was diluted to 10 ml with H,SO, (0.4%). Mercury analysis was performed by cold vapour atomic absorption spectrometry after enrichment on a gold-platinum net as described elsewhere [6]. A PerkinElmer model 1100 B equipped with a mercury hydride system MHS 20 was used. The detection limits were 0.15 pg/l for urine, 0.3 pg,il for whole blood, 0.15 ,&I for plasma and 0.15 pg/g (20 mg sample) for hair. The day-to-day precisions were as follows: urine 3.6% (3.3 pg/l; n = 49), whole blood 5.6% (3.2 pg/l; n = 8) and hair 5.9% (0.54 pg/g; n = 20). Quality control was carried out with different reference materials (urine no. 115 with 35 pg Hg/l, whole blood no. 010010 with 3.3-5.1 pg Hg/l, both Seronorm, Nycomed, Oslo, Norway; CRM no. 397 human hair with 12.3 pg Hg/g BCR, Brussels, Belgium; GBW 09101 human hair with 2.16 pg/g, Shanghai Institute of Nuclear Research, China). Statistical comparison between different groups was undertaken by the Wilcoxon matched pairs signed rank test. Correlation between selected variables was tested by the Spearman rank order correlation.
3. Results and discussion Fig. 1 shows the results of mercury analysis in urine. Daily mercury excretion in urine expressed as pg/g creatinine (median) before the course was fairly constant and in the range of other data
223
M. Wilhelm er al. I Toxicology Letters 88 (19%) 221-226
Mg
Hg/g creatinine ,..
1.4 -
P < 0.001
1.2 -
0.6 Period of Hg vapour exposure
q 1
I
I
I
2
3
4
I,
II
I 123456
I
I
I
I
,I
II
I 20
Fig. 1. Hg levels in urine (median) of 20 dental students during their first “occupational” exposure (technical course of operative dentistry) to mercury vapour from dental amalgam.
reported for Germany [7,8]. During the course there was a steady increase of mercury concentrations in urine, reflecting an absorption of mercury vapour as a result of the first “occupational” exposure. The salme observation has been reported by other authors [9]. Three months later values had decreased but were still higher than the initial levels. Since absorbed mercury vapour is principally eliminated in the inorganic form of mercury, this may reflect the long whole body half-life of inorganic mercury which is about 60 days [l]. Alterations of mercury levels in erythroctyes and plasma were quite similar. In erythrocytes initial median m’ercury concentration was 1.47 pg/l (Fig. 2). The: increase following 6 weeks of intense mercury vapour exposure amounted to approximately 60%. After 3 months the values had decreased and there was no difference compared with those at the beginning of the study. Median plasma mercury levels rose from 0.45 to 0.82 and decreased to 0.6 pg/l at the end of the
study, but like in urine were still higher than the first values (Fig. 3). The erythrocyte-plasma ratios of mercury were about 3:l and showed only minor alterations during the study period. These findings indicate that after absorption through the pulmonary membranes mercury vapours dissolve in the circulating blood. This circulatory mercury is partitioned between packed cells and plasma. Furthermore, it can be assumed that no biotransformation of mercury vapour to organomercury occurred, since within blood the latter compound is concentrated in red cells. Unlike other suggestions, our results show that not only blood but also urine analysis can be used to assess recent exposure to mercury vapour [lo]. Assuming a continual exposure and in the absence of steady state conditions, our results indicate that the participants would reach the critical mercury level (level which may be associated with adverse effects) of 50 fig/g creatinine after approximately 8 years. However, studies
224
M. Wilheh et al. I Toxicology Letters 88 (1994) 221-226
yg He/l erythrocytes
4.0.
.
I I
3.2 .
P ( 0.01
................. .. .
I
-LL
............. ...... ..............
1
1
P ( 0.01
.
.................... ........................
T
2
3
Fig. 2. Box-and-whisker plot of Hg concentrations in erythrocytes of 20 dental students before (I), immediately at the end of a 6 week technical course (2) and 3 months after first “occupational” exposure to mercury vapour.
pg Hg/l
plasma
P ( 0.05 x x 1.5 ...................f.... ....... P”(“.~;I1’ .........................~‘p ( o,05 .. ... .....I.................
i l .O.
. . . . . . . . . . . . . . .&.._
’
II l. . . . . . . . . . . . . . . . . . . . . . . . . . . ..@
1 * . . . . . . . . . . . . . . . . . . . . .. .. . . .. .
B
.
.
.
.
.
.
.
.
.
0.5. .... ... ...... . ... . .... .... ... .. ... .. . . ....... ...... ......................... .. .... ..... .. .. ..........
I
1,
1
L
2
3
Fig. 3. Box-and-whisker plot of Hg concentrations in plasma of 20 dental students before (l), immediately at the end of a 6 week technical course (2) and 3 months after first “occupational” exposure to mercury vapour.
M. Wilhelm et al I Toxicology Letters 88 (1996) 221-226
225
yg Hg/g hair 3.0s
2_j_ . . . . . . . . ..__...___.......................
p..~.t)‘.~
. . . . *...................... ............................
.
I -L ‘1.8. ....................................................... ..................... ........................................ I
1.2. ..................................!...c!!.!i r
0.6.
.. . . . . . . . . . . . . . .
x . ...... .........!...v?:.!.! -IL.
’ . .. . ..... . .. .. .... .. . ..
. .. .
. .. .
..... ...
..
45
E? x 0.0. 1
2
3
Fig. 4. Box-and-whisker plot of Hg concentrations in hair of 20 dental students before (I), immediately at the end of a 6 week technical course (2) and 3 months after first “occupational” exposure to mercury vapour.
workers exposed to mercury vapour suggest that steady state is reached after 4 months of exposure [ 111. Hair mercury concentrations also reflected the exposure of the students during their technical course (Fig. 4). However, of all specimens studied hair analysis reve:aled the most striking alterations. Values increased from 0.47 to 1.05 ,ug/g, which corresponds, to an increase of 125%. At the end of the study hair mercury levels were quite similar to the initial values. The distribution pattern of the hair data obviously varied considerably. The range between the lower and upper quartiles of mercury concentrations in hair which was collected immediately at the end of the technical course was much wider compared with the other results. Thus it is likely that the mercury levels in hair of our students reflected to some unknown e:xtent adsorption of mercury vapour from the (atmosphere. Recently, in vitro experiments also showed a significant external contamination of human hair even at low levels of metallic mercury in the air [5]. Additionally, removal of mercury from hair by different washing procedures was found to be ineffective, suggesting a strong binding of external mercury contamination to functional groups of the hair structure. with
Correlation analysis of data also confirmed a significant influence of external contamination of hair samples. Table 1 summarizes correlation coefficients of mercury levels in hair in relation to those in other specimens, to the frequency of fish consumption and to the number of amalgam surfaces at the three different times of sample collection. For samples taken before and 3 months after the course there was a close relationship between mercury contents in hair and erythrocytes. Additionally, hair mercury concentrations were related to the frequency of fish consumption at the first sampling period. No other significant relationships of hair mercury were observed. Thus we conclude that at steady state conditions and without increased mercury vapour exposure from the atmosphere, mercury levels in hair and erythyrocytes provide a lasting record of the average mercury intake of the last 2-3 months, probably mainly from dietary intake even at low frequency of, or without, fish consumption. In summary, the results show that mercury levels in hair, erythrocytes, plasma and urine reflected the first ‘occupational” exposure to mercury vapour of dental students in a similar pattern. Increased mercury hair levels at the end of the first occupational exposure indicated adsorp-
226
M. Wilhelm et al. I Toxicology Letters 88 (1996) 221-226
Table 1 Hg levels in hair in relation (Spearman’s rank order correlation coefficient) to Hg in erthyrocytes, plasma, mine; to frequency of fish consumption; and to number of amalgam surfaces of 20 dental students before (l), immediately at the end (2) and 3 months after first “occupational” exposure to mercury vapour 1 Erythrocytes (pg Hg/l) Plasma @g HgjI) Urine (pg Hg/g creatinine) Fish consumption/month Number of amalgam surfaces
2
3
0.686** -0.063 0.492* -0.090 -0.059 -0.326 -0.281 -0.208 -0.278 0.448* 0.194 0.325 -0.074 0.032 -0.253
*P < 005: ** P < 0.001.
tion of mercury vapour from the atmosphere. At steady state conditions and in the absence of increased mercury air levels, hair mercury is related to erythrocyte mercury concentration even at low frequency of, or without, fish consumption.
Cl1 WHO PI
(1991) Inorganic Mercury, Environmental Health Criteria 118, WHO, Geneva. Wilhelm, M., Lombeck, I., Kouros, B., Wuthe, J. and Ohnesorge, F.K. (1995) Duplicate study on the dietary intake of some metals/metalloids by German children, Part I: Arsenic and Mercury. Zbl. Hyg. 197, 345-356.
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