Effect of teeth amalgam on mercury levels in the ... - Springer Link

Environ Monit Assess (2012) 184:375–380 DOI 10.1007/s10661-011-1974-1

Effect of teeth amalgam on mercury levels in the colostrums human milk in Lenjan Elaheh Norouzi · Nader Bahramifar · Seyed Mahmoud Ghasempouri

Received: 9 June 2010 / Accepted: 24 February 2011 / Published online: 15 April 2011 © Springer Science+Business Media B.V. 2011

Abstract Human milk is usually the only source of food for infants during the first 4 to 5 months of their life. Maternal environmental mercury exposure is directly related to fish consumption or amalgam filling. In this research, 38 human milk samples were collected from mothers of Lenjan area who were not occupationally exposed with mercury. Mercury concentration in human milk was determined by AMA254 Mercury Analyzer. A level of mercury was examined in relation to somatometric, demographic and dental amalgam parameters. Obtained results showed that only dental amalgam significantly increased the mercury level in human milk ( p < 0.001). The mean mercury concentrations in milk of mothers without teeth fillings (n = 13), with one to three teeth fillings (n = 10), and four to eight teeth fillings (n = 15) were 2.87, 5.47, and 13.33 μg/l, respectively. The result of this study also showed a positive correlation of mercury milk levels with the number of teeth fillings

E. Norouzi · N. Bahramifar · S. M. Ghasempouri Department of Environmental Sciences, Faculty of Natural Resources and Marine Sciences, Tarbiat Modares University, Noor, Mazandran, Iran N. Bahramifar (B) Department of Chemistry, Payame Noor University (PNU), Sari, Iran e-mail: [email protected]

of the mother ( p < 0.05, r = 0.755). The estimated weekly intake of mercury of a breastfed infant in this study was, in some cases, higher than provisional tolerance weekly intake recommended by FAO/WHO, which pose a threat to their health. Keywords Mercury · Breast milk · Dental amalgam · Lenjan Isfahan

Introduction Nowadays, mercury, as a pollutant, is scattered around a wide area of atmospheres and oceans. This means that even countries with minimal pollution which are far from industrial factories may be affected by this pollutant substance. Considering mounting amount of pollution in water ecosystems, the effect of these pollutants (especially mercury) on human health is considerable. Since mercury concentrates in fish, fish consumption can be a major route for entrance of mercury to the human body (Harakeh et al. 2003). Ordinary people who are not professionally exposed to mercury may be affected by tooth amalgam or fish consumption and in those people with low fish consumption; tooth amalgam can be the only way that they can be exposed to mercury (Drasch et al. 1998; Drexler and Schaller 1998; Oskarsson et al. 1996).

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Environ Monit Assess (2012) 184:375–380

More commonly, maternal environmental mercury exposure is directly related to fish consumption (MMeHg) or amalgam filling (In–Hg). Infant methylmercury exposure during fetal development and breast-feeding is strongly related to maternal mercury burden (Barbosa and Dorea 1998). The transfer of mercury from the mother to the fetus is through the placenta (Unuvar et al. 2007) and occurs at different rates, depending on the source of mercury (amalgam fillings or fish eating). Two factors are considered to be mainly responsible for increased mercury concentrations in breast milk: the uptake of organic mercury (methylmercury) primarily via fish consumption, and the uptake of inorganic mercury through dental amalgam (Oskarsson et al. 1996; Vahter et al. 2000). Methylmercury is strongly bound to erythrocytes. A small quantity of methylmercury passes into breast milk and is easily absorbed by the suckling infant. Inorganic mercury is readily transferred into breast milk, but is not well absorbed by infants (Dorea and Donangelo 2006). It is well established that amalgam mercury exposure constitutes the largest non-occupational exposure source for the general population, and is greater than mercury exposure from all other environmental sources combined, including food. Estimates of amalgam mercury daily dose in humans have varied from 1.2 to 27 μg Hg/day, with a present consensus of approx 10–12 μg absorbed/day for the average person with eight colossally involved fillings (Lorscheider et al. 1995; Vimy et al. 1997). Results indicate that In–Hg is the favored form of transfer from maternal plasma to milk. It has been estimated that 50% to 80% of mercury in human milk is in the inorganic form (Oskarsson et al. 1996; Skerfving 1988). Thus, recent exposure to methylmercury from fish consumption is reflected in mercury levels in maternal blood but

Table 1 Characteristics of the study population

not in milk. In milk, an average of 51% of total mercury was found to be In–Hg, whereas in blood, only 26% was present in the inorganic form (Oskarsson et al. 1996). Dental amalgam f illings Amalgam placement and removal and mercury exposure during preand postnatal periods have been studied. Vimy et al. (1997) have suggested that the placement and removal of amalgam in pregnant and lactating mothers could subject fetuses and neonates to exposure risks. Lindow et al. (2003) reported that fetal hair-Hg was significantly higher in babies when their mothers had amalgam restoration procedures performed before or during pregnancy.

Material and methods During a 1-year period (August 2007–August 2008), human breast milk samples were obtained from 38 healthy women living in the Lenjan area at least for 2 years before pregnancy; none of them were occupationally exposed to mercury. Mothers filled out a questionnaire on demographic, somatometric, and environmental factors such as: number of amalgam-filled teeth (it was checked by medical staff and that all filled teeth had amalgam), the level of dietary fish consumption, maternal age, maternal weight, and infant weight (Table 1). Breast milk samples (10–20 ml) were collected on the fourth day postpartum. Collection was accomplished in the morning, 2 h after the previous breast-feeding. The hands and breast to be milked were thoroughly washed with deionized water. Milk was expressed by hand into polyethylene (Universal 50 ml) tubes previously incubated in nitric acid 10% v/v for one day and well rinsed with deionized water; frozen at −20◦ C until ana-

Parameter

Range

Median

Mean ± SE

Number

Mother’s age Mother’s weight(kg) Newborn’s birth weight(g) Number amalgam filling

38–20 45–102 2,450–3,900 0–8

25 65 3,000 2

26.15 ± 0.70 65.22 ± 2.24 3080 ± 52.98 –

64 58 60 56

Environ Monit Assess (2012) 184:375–380 Table 2 Mercury concentration in breast milk according to country

377

Reference

Country

Mean(μgl−1 )

Comment

Klemann et al. (1990) Drasch et al. (1998)

Germany Germany

Vimy et al. (1997)

Canada

1.9 0.2 0.57 0.50 2.11 0.24 0.15

No correlation with amalgam filling No amalgam filling One to four amalgam fillings Four to seven amalgam fillings Over seven amalgam fillings Amalgam filling No amalgam filling

lyzed. They were transferred to the environmental laboratory of Faculty of Natural Resources and Marine Sciences. To prepare these samples for mercury level measurement, an amount of milk was poured in nickel pipes washed with acetone and deionized water. Then, they were kept at 60 C for 6 h. Then, dried samples were weighed and finally mercury concentrations were measured by mercury analyzer device. A mercury analyzer device model 254 made by LECO Company according to ASTM D-6722 standard was used in this study. Using standard reference materials (SRM1633b), quality control was performed to evaluate the result. By using standard reference materials five times, a range of 98% to 103% of recovery was calculated which confirmed the accuracy of the results. The first data analyzed with Kolmogrov– Smirnov test was abnormal, thus we used nonparametric test for comparisons of mercury levels in milk. Mann–Whitney U and Kruskal–Wallis H tests were applied to compare between the mercury concentration with various socioeconomic and demographic factors. The relation between the numbers of amalgam-filled teeth and other factors with mother milk mercury level was assessed by Spearman correlation coefficient. The level of confidence was chosen to be 95% (SPSS V11.5 Inc., USA).

Table 3 Mean mercury concentration in breast milk

Std. error of mean

Result and discussion In the WHO/IAEA collaborative study, the median milk mercury levels in the six participating countries ranged from 1.29–25.53 μg/L. The mean concentration of mercury in all tested breast milk samples in this study was 7.57 ± 1.08 μg/L. In the present study, the mean value of mercury is within the range of median value of mercury in WHO/IAEA collaborative study (FAO/WHO 1978, 1993). The level of mercury varies widely in human milk samples around the world. Levels difference depending on sampling place, time, and exposure levels of the mothers. Our result of mercury milk levels are compared with data from the literature; the mercury levels found in breast milk in the present study are quite high, and higher than those found in Germany by (Drasch et al. Drasch et al. (1998)), Vimy et al. (1997) and Klemann et al. (1990); Table 2. In this area, fish consumption diet was low enough to be ignored. We evaluated only the effect of amalgam, maternal age, maternal weight and infant weight on mother’s milk mercury level. There were 13 mothers without amalgam-filled teeth, 10 mothers with one to three amalgamfilled teeth, and fifteen mothers with four to eight amalgam-filled teeth in this study. As it is presented in Table 3 and Fig. 1, our results confirmed the presents of significant differences in mother’s

Mean (μgl−1 )

N

Group

0.33

2.89

13

1.33

5.47

10

1.84

13.33

15

Mothers without amalgam-filled teeth Mothers with one to three amalgam-filled teeth Mothers with four to eight amalgam-filled teeth

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Fig. 1 Mean concentration of mercury in breast milk

milk mercury level between these three groups. Also, there was a significant positive correlation between mother’s milk mercury level and the number of amalgam-filled teeth ( p < 0.05, r = 0.755). These results were in a great extent compatible with other studies. Vimy et al. (1997), Oskarsson et al. (1996), Drasch et al. (1998), Klemann et al. (1990), Langworth et al. (1991) and Ursinyova and Masanova (2005) detected significant differences in mothers milk mercury levels between mothers with and without amalgam-filled teeth. Also, Drasch et al. (1998) and Ursinyova and Masanova (2005) confirmed the presence of significant differences in mother’s milk mercury level in mothers with different number of amalgamfilled teeth. Vimy et al. (1997), Oskarsson et al. (1996), and Drasch et al. (1998) found a significant positive correlation between mother’s milk mercury level and the number of amalgam-filled teeth were detected in different study. Klemann et al. (1990) detected an insignificant positive correla-

Table 4 Mean mercury concentration in breast milk between groups of somatometric characteristics of the study population

Parameter Mother’s age 0.05). Saleh et al. (2003) and Ursinyova and Masanova (2005) did not find statistically significant differences in the mean levels

Number

Hg(μgl−1 ) Mean ± SE

p value

18 21

6.83 ± 1.151 8.15 ± 1.08

0.05

18 18

7.33 ± 1.58 8.53 ± 1.70

0.05

18 19

6.62 ± 1.53 7.60 ± 1.60

0.05


of mercury between groups with different birth weights. Mercury intakes were calculated based on the actual infant birth weights and the daily milk intake which was considered equivalent to one sixth of the infant weight. The median intakes of mercury were 4.47 (range 0.46–27.38) μg/kg/week. In our study, 35.13% of infants had weekly mercury intakes, which are more than provisional tolerable weekly intake of 5 μg/kg/week, proposed by FAO/WHO (1978, 1993). Although, human milk should be considered as the most important food source for infants due to its unique nutritional and immunological characteristics, the risk of heavy metal exposure should be carefully considered.

Conclusions As we showed, the number of amalgamfilled teeth in breast-feeding mothers strongly influences the mercury level in their milk. Take it into consideration that maternal milk is the only source of nutrition during the first few months after birth, attention to its pollutant source is inevitable. The results of this study, in combination with descriptive data of questionnaire filled by mothers, support the effect of tooth amalgam on the dangerous pollution of mercury in mother’s milk. Acknowledgements The authors wish to thank Dr. Soleimani and Dr. Ghiasi for their sincere help in performing technical parts of the project. The authors are also grateful to shohadae Lenjan Hospital and Hygiene and Treatment Center of Lenjan for assistance in sampling.

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