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Metal concentrations in blood and hair in pregnant females in southern Sweden.

Introduction

The risk that mercury (Hg), lead (Pb) and cadmium (Cd) exposure during pregnancy will lead to adverse childhood outcomes is modulated by, e.g., hereditary factors, diet, nutritional status, and alcohol and tobacco intake.

Mercury

A recent study of a non-fish-eating population in Sweden (N = 27; Lindberg, Ask-Bjornberg, Vahter, & Berglund, 2004) showed low concentrations of total Hg in whole blood (median B-Hg [blood mercury] 0.28 [micro]g/L; range 0.11-1.4 [micro]g/L). Fish consumption has been positively associated with hair-Hg levels in several studies. In a study of 127 pregnant females from the Uppsala and Osthammar communities in the middle of Sweden, the median intake of fish and shellfish was about 25 g/ day (Berglund et al., 2001). During pregnancy the intake decreased. The median concentrations of methylmercury (MeHg) and inorganic Hg in cord blood at delivery were 1.3 and 0.2 [micro]g/L, respectively. A similar study from the west coast of Sweden (Rodstrom, Barregard, Lundh, & Sallsten, 2004) showed median B-Hg concentrations of 1.2 [micro]g/L in the total population (coastal community: 1.2 [micro]g/L; city of Gothenburg: 1.5 [micro]g/L; samples collected during pregnancy weeks 6-8).

Lead and Cadmium

Smoking as well as environmental tobacco smoke may increase B-Pb (blood lead) levels in pregnant subjects as well as other Pb sources such as special food, eyeliner, and substandard housing with old lead painting. Smoking, low iron stores, and low B-Cu (blood copper) levels may increase the B-Cd (blood cadmium) concentrations in pregnant women.

The aim of the present study was to determine the concentrations of Hg, Pb, and Cd in whole blood and Hg in hair in pregnant females in an inland and a coastline city in southern Sweden. Furthermore, another goal of the study described here was to evaluate possible regional differences in Sweden.

Materials and Methods

The study was comprised of 50 pregnant females from the city of Hassleholm in the middle of the county of Skane in southern Sweden and 50 pregnant females from the city of Simrishamn on the east coast of Skane. At the first visit to the prenatal care clinic (pregnancy weeks 6-8) each participant had a structured interview (questions about work history, fish consumption, amalgam fillings, smoking habits, and the use of chewing gum) and left a blood sample. The midwife then registered the number and the location of amalgam fillings in a standardized manner. The vials from the prenatal care clinics were mailed to the laboratory at the department of Occupational and Environmental Medicine, Lund University Hospital, Sweden, and stored at --20[degrees]C until analysis.

At the last visit at the prenatal care clinic (about pregnancy week 32), a hair sample (thickness comparable to a match; length approximately 9 cm) was collected from the neck of each participant with a pair of scissors. The hair samples were kept in separate envelopes in a box at the respective prenatal care clinic until the end of the collection period and then brought to the laboratory at the department of Occupational and Environmental Medicine, Lund University Hospital, Sweden, for analysis.

Metal Analysis

Analytical Methods

The concentration of B-Pb and B-Cd was determined by inductively coupled plasmamass spectrometry. The samples were prepared and analyzed according to Barany and co-authors (1997). The limit of detection (LOD), calculated as three times the standard deviation (SD) for the blank were for Cd, 0.02 [micro]g/L, and for Pb, 0.11 [micro]g/L.

The determinations of total Hg in hair (Hair-Hg) and B-Hg were made in acid-digested samples by cold vapor atomic fluorescence spectrometry (Sandborgh-Englund, Elinder, Langworth, Schutz, & Ekstrand, 1998). In the analysis of B-Hg, duplicate subsamples of 0.2 mL blood were treated with 1 mL mixture of nitric and perchloric acid in the proportions 5:1, at 70[degrees]C for 16 hours. After cooling, 12 mL of water and 0.15 mL of tributyl phosphate (antifoaming agent) were added to the samples. By use of an auto sampler, samples were pumped into a reaction vessel whereupon stannous chloride was added as a reducing agent. Hair samples of approximately 30 mg were mixed with 2 mL acid mixture, and then treated by the same procedure as for the determination of B-Hg in blood. The LOD calculated as three times SD for the blanks was 0.26 [micro]g/L for B-Hg. The LOD for Hair-Hg was 9.0 ng/g. In the total material, 14 females (10 from the city of Hassleholm, four from the city of Simrishamn) showed B-Hg levels below the LOD. They were excluded from the correlation and regression calculations in the results section and also from the B-Hg presentation in Table 2. All subjects had Hair-Hg levels exceeding the LOD.

Quality Control

To ensure the accuracy of the analytical methods and results, quality control (QC) samples were analyzed along with the collected samples. In the analysis of B-Hg, B-Pb, and B-Cd, Seronorm trace elements in whole blood with recommended values were used. Also, certified QC blood samples from Centre de Toxicologie du Quebec, International Comparison Program, Canada (QTC) were used in the analysis of B-Hg. As QC for Hair-Hg, the certified reference material GBW 09101-CRM from Shanghai Institute of Nuclear Research Academia, Sinicia, China, was used. The obtained values for the QC samples showed good agreement with the recommended and certified concentrations (Table 1).

Statistics

The variables showed a skewed distribution (checked by normal probability plots). Thus, nonparametric statistical processing was applied (Mann-Whitney U-test; Spearman's correlation coefficient [[r.sub.s]]). P-values less than .05 were regarded as statistically significant (two-tailed tests). We also wanted to obtain more information from the data, using the flexibility and power of parametric methods. Multiple regression was utilized to elucidate the impact of different predictors on the variation in the mercury concentrations in blood. The p-values used to include or exclude the variables in the stepwise process were .05 and .10, respectively. Model fits were checked by means of residual analyses. Calculations were performed using the Statistical Package for the Social Sciences (SPSS version 15.0, 2008).

Results

Median and ranges for age; number of amalgam fillings; Cd, Pb, and Hg concentrations in whole blood; and Hg concentrations in hair are presented in Table 2. Interview data about occupational exposure to mercury, fish consumption, amalgam restoration, amalgam fillings, smoking habits, and the use of chewing gum are shown in Table 3.

The females from the coastal city of Simrishamn had significantly higher whole blood concentrations of B-Cd (p = .004) and B-Hg (p = .005), as well as higher Hair-Hg levels (p = .015) as compared with the group from the inland city of Hassleholm. The other variables did not differ significantly between the groups.

In the total material, 86 females had B-Hg levels exceeding the LOD. In this subpopulation, the subjects consuming sea fish and freshwater fish the last six months (n = 9) showed approximately the same concentrations of B-Hg and Hair-Hg as subjects solely consuming fish from the sea (n = 72). The median consumption of fish in the total material was about one fish meal per week during the last six months. Subjects with B-Hg at least at LOD consuming crab during the same period (n = 13) showed somewhat higher B-Hg concentrations (p = .055) as compared with those who did not eat crab (n = 73).

Correlation Coefficients

In the total material, the number of occlusal as well as the total number of amalgam fillings increased with age, [r.sub.s] = 0.51 (p < .001) and [r.sub.s] = 0.45 (p < .001), respectively. Strong positive correlations were observed between the concentrations of Hair-Hg and B-Hg ([r.sub.s] = 0.40; p < .001), especially in the inland city of Hassleholm ([r.sub.s] = 0.77; p < .001), while the correlation was not significant in the coastal City of simrishamn ([r.sub.s] = 0.16; NS). Also, the concentrations of B-Pb and B-Cd showed a weak positive relationship ([r.sub.s] = 0.21; p = .034).

Regression Analysis

In a linear regression model, B-Hg (dependent variable) was related to the number of fish meals per week (no FM/w), the number of occlusal amalgam fillings (no OAF), crab intake, and age, giving the equation: Total B-Hg = 0.20 + 0.23 x no FM/w + 0.04 x no OAF (multiple r = 0.51; p < .001; 95% CI [beta]1 0.13-0.33; [beta]2 0.02-0.06).

Discussion

Hair Mercury Levels

Me-Hg is strongly accumulated in hair (blood to hair ratio 1:250; hair growth rate about 1 cm/month). As the hair samples collected had a length of about 9 cm, the Hair-Hg levels represent the median Hg level during the female's nine-month pregnancy period. The Hair-Hg levels were slightly lower (total material: median 0.22 [micro]g/g; range 0.04-0.83 [micro]g/g) than values from recent, similar studies in Sweden (west coast: median 0.43 [micro]g/g, Rodstrom et al., 2004; county of Uppsala: median 0.35 [micro]g/g, Berglund et al., 2001). Females from the coastal city had significantly higher Hair-Hg levels as compared with females from the inland city of Hassleholm. All Hair-Hg levels, however, were far below the reference dose presented by the U.S. Environmental Protection Agency (based on a daily intake of 0.1 [micro]g MeHg/kg body weight), which corresponds to 1.2 [micro]g/g total mercury in hair. In a study of 779 mother-infant pairs from the Republic of Seychelles (mean consumption 12 ocean fish meals per week), the prenatal MeHg exposure was estimated from the mothers' hair MeHg concentrations (mean 6.9 [micro]g/g), which is about 30 times higher than in our study. No adverse neurodevelopmental effects of MeHg exposure from fish consumption was detected in this cohort (Myers et al., 2003). In the Faroe Islands, however, MeHg exposure from intake of pilot whale meat was higher (average total mercury concentration 3.3 [micro]g/g; half of which was MeHg). Adverse findings in neuropsychological tests were observed in children whose mothers had Hair-Hg concentrations between 10 and 20 [micro]g/g, as compared with children with an exposure below 3 [micro]g/g. The findings were most striking for domains related to motor function, language, and memory (Grandjean et al., 1997).

Mercury Concentrations in Whole Blood

The concentrations of B-Hg in our study were considerably lower (median 0.7 [micro]g/L; 0.3-2.1 [micro]g/L) as compared with corresponding values from previous studies on the west coast of Sweden (1.2, 0.4-5.6 [micro]g/L; Rodstrom, et al., 2004). All these values in pregnant Swedish females, however, are far below the neurobehavioral dysfunction reference limit of 24 [micro]g Hg/L in blood, which corresponds to maternal mercury concentrations in hair exceeding 6 [micro]g/g (Grandjean, Weihe, & Nielsen, 1994).

No significant differences in B-Hg were noted between females consuming sea fish as compared with females consuming sea fish and freshwater fish. Subjects consuming crab during the last six months showed somewhat higher levels of B-Hg as compared with subjects not eating crabs.

In occupationally unexposed populations, Hg intake from amalgam fillings is generally the dominant Hg source. The contribution of each amalgam filling to urinary Hg excretion has been estimated to be about 0.08 [micro]g/L (Soleo et al., 1998). In our study, both the number of occlusal (median 3; range 0-14) as well as of total amalgam surfaces (7; 0-48) increased with age. In a multiple linear regression model, mercury concentrations in whole blood were related both to the number of fish meals per week, and to the total number of occlusal amalgam fillings. Similar findings have been reported by other authors (Lindberg, Ask Bjornberg, Vahter, & Berglund, 2004; Carta et al., 2003). In the latter study, the studied regular tuna fish eaters had an intake of MeHg that gave concentrations in whole blood (median 42 [micro]g/L), which were about 60 times higher than the B-Hg concentrations in our study (median 0.70 [micro]g/L).

Concentrations of Lead and Cadmium in Whole Blood

The levels of B-Pb and B-Cd in whole blood were low (Table 2) and did not indicate any risks of adverse health effects. Smokers (n = 10) had significantly higher (p < .001) B-Cd levels (median 1.15 [micro]g/L; range 0.5-2.7 [micro]g/L) than nonsmokers (0.28; 0.05-4.8; n = 89). Higher values have been reported from other studies of the general population, e.g., in Italy (B-Cd 1.1 and 0.5 [micro]g/L in smokers and non smokers, respectively) (dell'Omo et al., 1999). In a Polish study of five towns with no large industrial lead-emitting plants, geometric mean B-Pb concentrations ranged from 24 to 48 [micro]g/L in females (Jakubowski, Trzcinka-Ochocka, Razniewska, Christensen, & Starek, 1996). In a study of 473 occupationally unexposed subjects in Sweden (Elinder, Friberg, Lind, & Jawaid, 1983) the median B-Cd concentration in nonsmoking females was 0.3 [micro]g/L, the same level that was observed in our study, while smoking females showed a median B-Cd level of 1.2 [micro]g/L. Median B-Pb concentrations in 1980 (69 [micro]g/L for current smokers; 57 [micro]g/L for nonsmokers) in Swedish females, however, were considerably higher as compared to our study (13 [micro]g/L for smokers; 10 [micro]g/L for nonsmokers), probably mainly depending on the change from leaded to unleaded gasoline in the early 1990s. The highest observed B-Pb level in our study was 79 [micro]g/L, which can be compared to the current biological exposure limit in nonpregnant lead exposed females in Sweden, i.e., 166 [micro]g/L.

Conclusion

The concentrations of B-Hg and Hair-Hg were lower in the studied pregnant females from southern Sweden than in recently published studies from the west coast and the middle part of Sweden. All levels were below suggested biological reference limits. Also, the concentrations of B-Pb and B-Cd were lower than suggested biological reference intervals. Thus, there seemed to be no risk of adverse health effects from Hg, Cd, and Pb exposure among the pregnant females.

Disclaimer: Financial support from the Swedish Environmental Protection Agency is gratefully acknowledged. The study was conducted in accordance with national and institutional guidelines for the protection of human subjects. The study was approved by the Ethical Committee of Lund University, Sweden.

Corresponding Author: Lars Gerhardsson, Occupational and Environmental Medicine, Sahlgrenska Academy and University Hospital, Box 414, SE-405 30 Goteborg, Sweden. E-mail: lars.gerhardsson@amm.gu.se.

Pre-published digitally November 2009, National Environmental Health Association.

References

Barany, E., Bergdahl, I.A., Schutz, A., Skerfving, S., & Oskarsson, A. (1997). Inductively coupled plasma mass spectrometry for direct multi-element analysis of diluted human blood and serum. Journal of Analytical Atomic Spectrometry, 12, 1005-1009.

Berglund, M., Ask, K., Palm, B., Petersson-Grawe, K., Bjors, U., & Vahter, M. (2001). Investigation of mercury exposure in pregnant females in the county of Uppsala, Sweden. Report to Swedish Environmental Protection Agency (in Swedish).

Carta, P., Flore, C., Alinovi, R., Ibba, A., Tocco, M.G., Aru, G., Carta, R., Girei, E., Mutti, A., Lucchini, R., & Randaccio, F.S. (2003). Sub-clinical neurobehavioral abnormalities associated with low level of mercury exposure through fish consumption. Neurotoxicology, 24(4-5), 617-623.

dell'Omo, M., Muzi, G., Piccinini, R., Gambelunghe, A., Morucci, P., Fiordi, T., Ambrogi, M., & Abbritti, G. (1999). Blood cadmium concentrations in the general population of Umbria, central Italy. Science of the Total Environment, 226(1), 57-64.

Elinder, C.G., Friberg, L., Lind, B., & Jawaid, M. (1983). Lead and cadmium levels in blood samples from the general population of Sweden. Environmental Research, 30(1), 233-253.

Grandjean, P., Weihe, P., & Nielsen, J.B. (1994). Methylmercury: Significance of intrauterine and postnatal exposures. Clinical Chemistry, 40(7[2]), 1395-1400.

Grandjean, P., Weihe, P., White, R.F., Debes, F., Araki, S., Yokoyama, K., Murata, K., Sorensen, N., Dahl, R., & Jorgensen, P.J. (1997). Cognitive deficit in 7-year-old children with prenatal exposure to methylmercury. Neurotoxicology and Teratology, 19(6), 417-428.

Jakubowski, M., Trzcinka-Ochocka, M., Razniewska, G., Christensen, J.M., & Starek, A. (1996). Blood lead in the general population in Poland. International Archives of Occupational and Environmental Health, 68(3), 193-198.

Lindberg, A., Ask Bjornberg, K., Vahter, M., & Berglund, M. (2004). Exposure to methylmercury in non-fish-eating people in Sweden. Environmental Research, 96(1), 28-33.

Myers, G.J., Davidson, P.W., Cox, C., Shamlaye, C.F., Palumbo, D., Cernichiari, E., Sloane-Reeves, J., Wilding, G.E., Kost, J., Huang, L.S., & Clarkson, T.W. (2003). Prenatal methylmercury exposure from ocean fish consumption in the Seychelles child development study. Lancet, 361(9370), 1686-1692.

Rodstrom, A., Barregard, L., Lundh, T., & Sallsten, G. (2004). Mercury in hair and blood in pregnant females on the west coast of Sweden. Report to Swedish Environmental Protection Agency (in Swedish).

Sandborgh-Englund, G., Elinder, C.G., Langworth, S., Schutz, A., & Ekstrand, J. (1998). Mercury in biological fluids after amalgam removal. Journal of Dental Research, 77(4), 615-624.

Soleo, L., Pesola, G., Vimercati, L., Elia, G., Michelazzi, M., Gagliardi, T., Drago, I., & Lasorsa, G. (1998). Dental amalgams and urine elimination of mercury in workers exposed to low concentrations of inorganic mercury. Medicina del Lavoro, 89(3), 232-241 (in Italian).

LARS GERHARDSSON, MD

THOMAS LUNDH, PHD
TABLE 1
Results from analytical Quality control of cadmium, Lead, and
total Mercury

Quality Control        Batch        Analyte       Reference Value
Material                                           ([micro]g/L)

Seronorm               OK0336          Cd                0.73
                       OK0336          Pb                 33
                       MR9067          Cd                5.4
                       MR9067          Pb                395
Seronorm               OK0336         B-Hg               2.1
QTC                   M-02-18         B-Hg               6.0
Hair-QC            GBW 09101-CRM     Hair-Hg     2.16 [+ or -] 0.21 *

Quality Control      Obtained Value Mean          n
Material           [+ or -] SD ([micro]g/L)

Seronorm              073 [+ or -] 0.07          29
                       30 [+ or -] 1.1           29
                      6.3 [+ or -] 0.24          28
                       390 [+ or -] 15           27
Seronorm              1.7 [+ or -] 0.18          24
QTC                   5.9 [+ or -] 0.32           8
Hair-QC              1.9 [+ or -] 0.08 *          8

* [micro]g/g.

TABLE 2
Median and Ranges for Age, Number of Amalgam Fillings,
and Metal Concentrations in Blood and Hair

Variables                           All Females         Hassleholm
                                     (N = 100)           (n = 50)

Age (y)                              30 (19-44)         31 (23-40)
No. of occlusal fillings              3 (0-14)          4.5 (0-13)
No. of total fillings                 7 (0-48)           7 (0-36)
B-Cd ([micro]g/L)                 0.30 (0.05-4.8)    0.26 (0.11-2.7)
B-Pb ([micro]g/L)                  11.0 (4.2-79)     11.0 (5.2-22.8)
B-Hg total ([micro]g/L; n = 86)   0.70 (0.27-2.1)    0.62 (0.27-1.7)
Hair-Hg ([micro]g/g)              0.22 (0.04-0.83)   0.20 (0.04-0.55)

Variables                            Simrishamn
                                      (n = 50)

Age (y)                              30 (19-44)
No. of occlusal fillings             2.5 (0-14)
No. of total fillings                 6 (0-48)
B-Cd ([micro]g/L)                 0.37 (0.05-4.8)
B-Pb ([micro]g/L)                  10.7 (4.2-79)
B-Hg total ([micro]g/L; n = 86)   0.82 (0.27-2.1)
Hair-Hg ([micro]g/g)              0.31 (0.04-0.83)

TABLE 3
Interview Data from Pregnant Females in Hassleholm
and Simrishamn

Variables         Alternatives      All       Hassleholm   Simrishamn
                                  Females      (n = 50)     (n = 50)
                                 (N = 100)

Work exposure         Yes             2            0            2
to Hg                  No            97           50           47

Fish meals           Never            3            3            0
per week               <1            46           24           22
                       ~1            36           16           20
                      1-2            11            6            5
                       ~2             2            1            1
                       >2             1            0            1

Sea fish              Yes            80           39           41

Sea fish and          Yes             9            3            6
freshwater fish

Crab eating           Yes            14            6            8
                       No            85           44           41

Amalgam               Yes             5            2            3
restoration            No            94           48           46

Amalgam               Yes            84           46           38
fillings               No            14            4           10

Smoking               Yes            10            3            7
                       No            89           47           42

Nicotine              Yes             1            0            1
chewing gum            No            98           50           48

Ordinary              Yes            27           12           15
chewing gum            No            72           38           34
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Article Details
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Title Annotation:INTERNATIONAL PERSPECTIVES
Author:Gerhardsson, Lars; Lundh, Thomas
Publication:Journal of Environmental Health
Article Type:Report
Geographic Code:4EUSW
Date:Jan 1, 2010
Words:3293
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