Increased Blood Lead and Decreased Calcium Levels during Pregnancy: ,A Prospective Study of Swedish :Women Living near a Smelter

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Bitgitta Json Lagerk-vist, MD, PhD, Sven Ekesrvdh, MD, Vagn Englvst, MD, Gunnar F. Nordberg, MD, PhD, Hanis-Ake Soderberg, MD, and

Dan-Eric Wikhind, MD, PhD

Introduction

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In recent ycars, incrcasing attention has been given to possiblc adverse effects on the neuropsychological devclopment of childrcn of exposurc in utero and earlv childhood to relatively low levels of lead.'-~Blood lead levels associated with poorer performance in various mental developmcnt index tests have been as low as 10 to 25 .tg/dL. Adverse effects (e.g., reduced gestational age. decrease in birthweight, and miscarriage) have also been reported.4 Lcad crosses the placenta, and umbilical cord blood lead levcls havc been reported to be about 85`' to 90% of those of the mothcr.''' The present study was part of a survcy monitoring the levels of heavy and trace metals in mothers and infants living in the vicinitv of R6nnskirsverken, a coppcr and lead smeltcr in northcrn Sweden."-- The control subjects were mothers and infants from a community 120 km south of the smclter. The two areas are similar with regard to both the size of the population and social and economic background. The control area was chosen as being clearly outside any influence from the smelter's emissions.

::- Methods Studv Area anid Study Popuilation Emissions of lead to the ambient air from the smelter had gradually decreased from 500 tons per year in the late 1960s to 51 tons in 1989, when this study began. In 1983 and 1990. the deposition of metals was surveyed by analyzing the levels of lead and other metals in moss (Plewvoziurn schrebern) taken from 74 locations up to

100 km from the smelter. After drying, representative samples (mean age of plants = 3 years) were analyzed with inductively-coupled plasma cmission. Moss lead levels followed a gradient. decrcasing with increasing distance from the smelter emissions, and these levels decreased by 50% to 90% between 1983 and 1990. In 1990. the highcst value w as 54 mg kg d.w.. and levels above background wcre found only within 30 km of the smelter. The emissions were then purified to 97c. At the most distant location, 85 to 95 km from the smelter and 25 to 35 km north of the control area, the moss lead level was 8 mg/kg d.w. (Institute of Water and Air Research. unpublished data, 1984.

1992). The women participating in the study were recruitcd on thcir first visit to a primarv health care unit for antcnatal carc during a 2-ycar period, February 1989 to February 1991. Eighty-five pcrcent (n = 290) of the women from the smeltcr area and 90%'C (n = 194) of the women from the reference arca agrecd to participate in the study. Seventeen of the cnvironmentally exposed womcn were Birgitta Json Lagerkvist and Gunnar F. Nordberg are with the Department of Environmental Medicine, Ume'a Universit, Umea'. Sweden. Sven Ekesrvdh is with the Primary Health Care Unit. Holmsmund. Sweden. Vagn Englvst is with the Companny Health Care Unit, Boliden Mineral AB, Skelleftehamn Sweden. Hans-Ake S6derberg is writh the Primary Health Care Unit, Skelleftehamn. Dan-Eric Wiklund is with the Department of Obstetrics and Gvnaecology. University Hospital. Umeza. Requests for reprints should be sent to

Birgitta Json Lagerkvist, MD. PhD. Department of Environmental Medicine. Umea Universitv, S-901 87 Umezi, Sweden. This paper was accepted April 4. 1996. American Journial of Public

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TABLE 1-Characteristics of the Women in the Smelter and Reference Area Groups at the First Visit for Antenatal Care: Northern Sweden, 1989 to 1991

Maternal age, y 21 Lead accumulates in the skeleton, and about 95% of the body burden of lead is sequestered in bone.22 Release of bone lead to blood has been documented in retired workers (e.g., see Nilsson et al.23). Experimental studies have reported mobilization of lead from body stores during pregnancy and lactation.2425 Human studies on blood lead levels during pregnancy have not produced consistent results. Decreased postpartum blood lead concentrations have been reported in two case studies,26'27 and it was suggested that the results supported the hypothesis of mobilization of bone lead during pregnancy. However, some studies have reported unchanged or decreased mean blood lead concentrations during preg-

nancy.19,283() Three of the studies just mentioned were cross sectional, and blood lead levels in different groups of women were analyzed at different stages of pregnancy. 19'28'3 In the study conducted by McMichael et al., blood samples were collected during weeks 14 through 20 and around week 32

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of gestation and at delivery.29 Mean blood lead values did not vary systematically with gestational stage, although there was a tendency for them to increase with the duration of pregnancy. This study clearly indicates that blood lead levels do increase during pregnancy, whereas serum calcium concentrations decrease. This may be due to the mobilization of bone lead, together with the marked change in calcium metabolism during pregnancy (see Silbergeld5). The significant decrease in serum calcium and blood lead levels between weeks 10 and 32 found in our study may be a consequence of the increased blood volume and increased transfer of calcium (and possibly lead) to the fetus. The significant increase in blood lead during late pregnancy may be associated with the increased calcium requirements of the fetus during the last trimester. The concomitant increase of maternal serum calcium may be due to mobilization of bone calcium and/or an increased uptake. An increased dietary absorption of lead may also contribute to increased blood lead levels in late pregnancy. If the mother's dietary intake of calcium is insufficient, demineralization of maternal bone will occur, and bone lead may be mobilized.5 That the fetus' need for calcium is met, whatever the maternal sources are, is supported by the fact that mean cord serum calcium is above the normal reference value of the laboratory. In a subgroup of the study, blood lead levels in women in the smelter area had decreased 6 weeks after delivery and were not statistically different from those of the control subjects. Milk lead levels were, however, higher in the case than in the control women (0.09 vs 0.05 ,ug blood lead/dL). Thus, lead may be excreted in breast milk, which may consequently be a source of exposure for breast-fed infants.31 In conclusion, blood lead concentrations were found to be low in this group of pregnant women in Sweden. However, levels increased during pregnancy, despite the increase in blood volume and unchanged or decreasing environmental lead levels. Also, serum calcium concentrations decreased. The mobilization of lead from bone during pregnancy and lactation is thus a possibility. In view of the adverse effects reported on the intellectual and neurobehavioral development of children exposed to lead in utero and early childhood, all possible measures should be taken to reduce environmental lead exposure. Pregnant women should be

encouraged to stop or at least decrease their consumption of wine and cigarettes, especially when environmental exposures are high. (Counseling of pregnant women conceming tobacco and alcohol is probably already routine in many areas because of the known adverse effects of these substances on pregnancy outcome [e.g., increased prematurity and decreased birthweight as a result of smoking and fetal alcohol syndrome as a result of heavy alcohol consumption].32'33) It is also crucial that maternal calcium intake is sufficient. DG

Acknowledgments This work was supported by the County Council of Vasterbotten, the Work Environment Fund, and the Boliden Mineral Co Ltd, Skelleftehamn, Sweden. Lars Jonsson and Susanne Sandberg are acknowledged for skillful technical assistance. Klas Lundbergh of the Boliden Mineral Co Ltd provided valuable information concerning the emissions from the smelter and their environmental impact. We are grateful to the participating women; to the staff at the health care centers in Skelleftehamn, Burea, and Holmsund-Obbola; and to the obstetric clinics in Skellefte'a and Umea. Stefan Marklund and the staff of the Department of Clinical Chemistry at University Hospital are acknowledged for the serum calcium analyses.

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(hsest Thomas, PhD, SpecialIssue tofUealthB. bytheAssociationfortheStephen

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