Use of sequentially administered stable lead isotopes to investigate changes in blood lead during pregnancy in a nonhuman primate (Macaca fascicularis)

Bone manganese is a sensitive biomarker of ongoing elevated manganese exposure, but does not accumulate across the lifespan

Studies have established associations between environmental and occupational manganese (Mn) exposure and executive and motor function deficits in children, adolescents, and adults. These health risks from elevated Mn exposure underscore the need for effective exposure biomarkers to improve exposure classification and help detect/diagnose Mn-related impairments. Here, neonate rats were orally exposed to 0, 25, or 50 mg Mn/kg/day during early life (PND 1-21) or lifelong through ∼ PND 500 to determine the relationship between oral Mn exposure and blood, brain, and bone Mn levels over the lifespan, whether Mn accumulates in bone, and whether elevated bone Mn altered the local atomic and mineral structure of bone, or its biomechanical properties. Additionally, we assessed levels of bone Mn compared to bone lead (Pb) in aged humans (age 41-91) living in regions impacted by historic industrial ferromanganese activity. The animal studies show that blood, brain, and bone Mn levels naturally decrease across the lifespan without elevated Mn exposure. With elevated exposure, bone Mn levels were strongly associated with blood Mn levels, bone Mn was more sensitive to elevated exposures than blood or brain Mn, and Mn did not accumulate with lifelong elevated exposure. Elevated early life Mn exposure caused some changes in bone mineral properties, including altered local atomic structure of hydroxyapatite, along with some biomechanical changes in bone stiffness in weanlings or young adult animals. In aged humans, blood Mn ranged from 5.4 to 23.5 ng/mL; bone Mn was universally low, and decreased with age, but did not vary based on sex or female parity history. Unlike Pb, bone Mn showed no evidence of accumulation over the lifespan, and may not be a biomarker of cumulative long-term exposure. Thus, bone may be a useful biomarker of recent ongoing Mn exposure in humans, and may be a relatively minor target of elevated exposure.

Teeth reveal juvenile diet, health and neurotoxicant exposure retrospectively: What biological rhythms and chemical records tell us

Integrated developmental and elemental information in teeth provide a unique framework for documenting breastfeeding histories, physiological disruptions, and neurotoxicant exposure in humans and our primate relatives, including ancient hominins. Here we detail our method for detecting the consumption of mothers' milk and exploring health history through the use of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) mapping of sectioned nonhuman primate teeth. Calcium-normalized barium and lead concentrations in tooth enamel and dentine may reflect milk and formula consumption with minimal modification during subsequent tooth mineralization, particularly in dentine. However, skeletal resorption during severe illness, and bioavailable metals in nonmilk foods, can complicate interpretations of nursing behavior. We show that explorations of the patterning of multiple elements may aid in the distinction of these important etiologies. Targeted studies of skeletal chemistry, gastrointestinal maturation, and the dietary bioavailability of metals are needed to optimize these unique records of human health and behavior.

A pharmacokinetic model of lead absorption and calcium competitive dynamics

Lead is a naturally-occurring element. It has been known to man for a long time, and it is one of the longest established poisons. The current consensus is that no level of lead exposure should be deemed "safe". New evidence regarding the blood levels at which morbidities occur has prompted the CDC to reduce the screening guideline of 10 μg/dl to 2 μg/dl. Measurable cognitive decline (reduced IQ, academic deficits) have been found to occur at levels below 10 μg/dl, especially in children. Knowledge of lead pharmacology allows us to better understand its absorption and metabolization, mechanisms that produce its medical consequences. Based upon an original and very simplified compartmental model of Rabinowitz (1973) with only three major compartments (blood, bone and soft tissue), extensive biophysical models sprouted over the following two decades. However, none of these models have been specifically designed to use new knowledge of lead molecular dynamics to understand its deleterious effects on the brain. We build and analyze a compartmental model of lead pharmacokinetics, focused specifically on addressing neurotoxicity. We use traditional phase space methods, parameter sensitivity analysis and bifurcation theory to study the transitions in the system's behavior in response to various physiological parameters. We conclude that modeling the complex interaction of lead and calcium along their dynamic trajectory may successfully explain counter-intuitive effects on systemic function and neural behavior which could not be addressed by existing linear models. Our results encourage further efforts towards using nonlinear phenomenology in conjunction with empirically driven system parameters, to obtain a biophysical model able to provide clinical assessments and predictions.

Bone remodeling during pregnancy and post-partum assessed by metal lead levels and isotopic concentrations

Bone remodeling is normally evaluated using bone turnover markers/indices as indicators of bone resorption and formation. However, during pregnancy and post-partum, there have been inconsistent results between and within biomarkers for bone formation and resorption. These differences may relate to pregnancy-related changes in metabolism and/or hemodilution altering measured marker levels. An alternative approach to evaluating bone remodeling is to use the metal lead (Pb) concentrations and Pb isotopic compositions in blood. These measurements can also provide information on the amount of Pb that is mobilized from the maternal skeleton. Despite some similarities with accepted bone turnover markers, the Pb data demonstrate increased bone resorption throughout pregnancy that further continues post-partum independent of length of breast-feeding, dietary intake and resumption of menses. Furthermore the isotopic measurements are not affected by hemodilution. These data confirm calcium balance studies that indicate increased bone resorption throughout pregnancy and lactation. They also indicate potentially major public health implications of the transfer of maternal Pb burden to the fetus and new born.

High bone matrix turnover predicts blood levels of lead among perimenopausal women

Skeletal bone is the primary endogenous source of lead in circulating blood, particularly under conditions of accelerated bone turnover and mineral loss, such as pregnancy and postmenopausal osteoporosis. We studied the influence of bone turnover rate on the release of lead from bone in 1225 female farmers from 5 districts in Japan. We collected peripheral blood and urine samples and medical nutritional information, and measured forearm bone mineral density (BMD). We found that blood lead levels in perimenopausal women were highest among all groups studied. Analysis of data for subjects grouped by level of markers of bone metabolism suggested that, in perimenopausal women, blood lead levels were higher in groups with high levels of N-telopeptide cross-linked collagen type I (NTx) and high levels of bone-specific alkaline phosphates (BALP) or osteocalcin (OC) compared with groups with low NTx and low BALP or OC levels. Linear multivariate models showed that markers of bone turnover were significantly positively related to blood lead levels. These results provide evidence that high bone turnover rates increase the release of lead stored in bone into the circulation. It is likely that markers of bone metabolism can be used to predict blood lead levels.

Stable lead isotopes in environmental health with emphasis on human investigations

There has been widespread use of stable lead isotopes in the earth sciences for more than 40 years focussed on the origin and age of rocks and minerals with lesser application in environmental investigations where the emphasis has been directed typically to the source of lead in environmental media such as air, water and soils. In contrast, the number of environmental health investigations focussed on humans (and primates) is limited in spite of the demonstrated utility of the approach in pioneering studies in the early 1970's. This paper reviews the status of lead isotopes in human investigations especially over the past 2 decades, the period over which most activity has taken place. Following a brief introduction to the method, examples are provided illustrating the use of lead isotopes in a wide spectrum of activities including sources and pathways of lead in diverse environments from urban to mining communities, various applications associated with pregnancy, the contribution of bone lead to blood lead including in the elderly, the half-life of lead in blood, and lead in bones and other media. A brief outline of critical research on non-human primates is also given. The lead isotope method is a powerful technique for tracing lead and could be employed more widely in human investigations.

Stable isotopic tracing-a way forward for nanotechnology

Numerous publications and reports have expressed health and safety concerns about the production and use of nanoparticles, especially in areas of exposure monitoring, personal use, and environmental fate and transport. We suggest that stable isotopic tracers, which have been used widely in the earth sciences and in metabolic and other health-related studies for several decades, could be used to address many of these issues. One such example we are pursuing is the use of stable isotopes to monitor dermal absorption of zinc and titanium oxides in sunscreen preparations and other personal care products. Other potential applications of this tracing approach are discussed.

Parental exposure to lead and small for gestational age births

BACKGROUND

Previous studies about the effect of lead exposure on adverse birth outcomes are still inconsistent and few studies estimate the relationship between parental lead exposure and small for gestational age (SGA) infants. An occupational cohort study to assess whether parental lead exposure would be related to decreased birth weight and shortened gestational ages of their offspring was conducted. Whether higher lead exposure doses would increase risks of low birth weight (LBW), preterm delivery, and SGA births was also investigated.

METHODS

A Program to Reduce Exposure by Surveillance System-Blood Lead Levels (Press-BLLS) was established in Taiwan in July 1993. The names of workers exposed to lead was collected from this occupational blood-lead notification database. The birth outcomes of their offspring were determined by linking to the Taiwan birth registration database from 1993 to 1997. Only singleton births whose parental blood-lead concentrations were tested during pregnancy or prior to conception, or within a 1-year span before these two periods were included.

RESULTS

Among 1,611 eligible births, 72 births were LBW, 74 were preterm deliveries, and 135 were SGA. Maternal blood-lead concentrations (PbBs) equal to or more than 20 microg/dl had a higher risk of mothering a SGA child (risk ratio (RR) = 2.15; 95% confidence interval (CI), 1.15-3.83).

CONCLUSIONS

Additional evidence of the effects of lead on adverse birth outcomes, especially for SGA births is reported. Maternal exposure to lead plays a more important role in the adverse effect on birth outcome than does paternal exposure.

Are there sex and gender differences in acute exposure to chemicals in the same setting?

We have little understanding of the influence that sex and gender may have on exposure to and measurement of occupational chemicals. If men and women are in the same physical environment, whether that be an occupational or an environmental setting, researchers need to question whether their acute exposure, as measured by administered and/or biologically effective dose, is the same. Not doing so may result in incorrect inferences being made about the risks associated with that exposure. Three critical questions arise specifically, do men and women differ in (1) their personal environments (immediate physical environments and personal attributes), (2) their absorption of the substance across the various biological barriers, and (3) the amount of active substance that reaches the target sites? Both contextual (e.g., smoking habits, diet, use of personal care products and jewellery, hobbies, stress, and use of medications) and biological (e.g., endocrine status) factors should be considered in answering these questions. Examples from the literature are provided to show that, depending on the chemical compound, there may be sex and gender differences in exposure to chemicals which can be manifested in sex differences in absorption, distribution, metabolism, storage, and excretion. An argument is developed to support the need to make information available, such as pharmacokinetic modeling studies in both men and women including appropriate age groups representing the spectrum of life stages and reproductive status.

Pb enamel biomarker: deposition of pre- and postnatal Pb isotope injection in reconstructed time points along rat enamel transect

Exposure to lead (Pb) as well as other heavy metals in the environment is still a matter of public health concern. The development of the enamel biomarker for heavy metal exposure assessment is designed to improve studies of dose-effect relationships to developmental anomalies, particularly embryonic dysfunctions, and to provide a time-specific recount of past exposures. The work presented in this paper demonstrates maternal transfer across the placental barrier of the enriched isotope (206)Pb tracer to the enamel of the rat pup. Likewise, injections of (204)Pb-enriched tracer in the neonate rat resulted in deposition of the tracer in the enamel histology as measured by secondary ion microprobe spectrometry. Through enamel, we were able to observe biological removal and assimilation of prenatal and postnatal tracers, respectively. This research demonstrates that enamel can be used as a biomarker of exposure to Pb and may illustrate the toxicokinetics of incorporating Pb into fetal and neonatal steady-state system processes. The biomarker technique, when completely developed, may be applied to cross-sectional and longitudinal epidemiological research.

Blood lead changes during pregnancy and postpartum with calcium supplementation

Pregnancy and lactation are times of physiologic stress during which bone turnover is accelerated. Previous studies have demonstrated that there is increased mobilization of lead from the maternal skeleton at this time and that calcium supplementation may have a protective effect. Ten immigrants to Australia were provided with either calcium carbonate or a complex calcium supplement (approximately 1 g/day) during pregnancy and for 6 months postpartum. Two immigrant subjects who did not conceive acted as controls. Sampling involved monthly venous blood samples throughout pregnancy and every 2 months postpartum, and quarterly environmental samples and 6-day duplicate diets. The geometric mean blood lead at the time of first sampling was 2.4 microg/dL (range, 1.4-6.5). Increases in blood lead during the third trimester, corrected for hematocrit, compared with the minimum value observed, varied from 10 to 50%, with a geometric mean of 25%. The increases generally occurred at 6-8 months gestation, in contrast with that found for a previous cohort, characterized by very low calcium intakes, where the increases occurred at 3-6 months. Large increases in blood lead concentration were found during the postpartum period compared with those during pregnancy; blood lead concentrations increased by between 30 and 95% (geometric mean 65%; n = 8) from the minimum value observed during late pregnancy. From late pregnancy through postpartum, there were significant increases in the lead isotopic ratios from the minimum value observed during late pregnancy for 3 of 8 subjects (p < 0.01). The observed changes are considered to reflect increases in mobilization of lead from the skeleton despite calcium supplementation. The identical isotopic ratios in maternal and cord blood provide further confirmation of placental transfer of lead. The extra flux released from bone during late pregnancy and postpartum varies from 50 to 380 microg lead (geometric mean, 145 microg lead) compared with 330 microg lead in the previous cohort. For subjects replete in calcium, the delay in increase in blood lead and halving of the extra flux released from bone during late pregnancy and postpartum may provide less lead exposure to the developing fetus and newly born infant. Nevertheless, as shown in several other studies on calcium relationships with bone turnover, calcium supplementation appears to provide limited benefit for lead toxicity during lactation.

Identification of sources of lead in children in a primary zinc-lead smelter environment

We compared high-precision lead isotopic ratios in deciduous teeth and environmental samples to evaluate sources of lead in 10 children from six houses in a primary zinc-lead smelter community at North Lake Macquarie, New South Wales, Australia. Teeth were sectioned to allow identification of lead exposure in utero and in early childhood. Blood lead levels in the children ranged from 10 to 42 micro g/dL and remained elevated for a number of years. For most children, only a small contribution to tooth lead can be attributed to gasoline and paint sources. In one child with a blood lead concentration of 19.7 microg/dL, paint could account for about 45% of lead in her blood. Comparison of isotopic ratios of tooth lead levels with those from vacuum cleaner dust, dust-fall accumulation, surface wipes, ceiling (attic) dust, and an estimation of the smelter emissions indicates that from approximately 55 to 100% of lead could be derived from the smelter. For a blood sample from another child, > 90% of lead could be derived from the smelter. We found varying amounts of in utero-derived lead in the teeth. Despite the contaminated environment and high blood lead concentrations in the children, the levels of lead in the teeth are surprisingly low compared with those measured in children from other lead mining and smelting communities.

Release of lead from bone in pregnancy and lactation

Concentrations and isotope ratios of lead in blood, urine, 24-h duplicate diets, and hand wipes were measured for 12 women from the second trimester of pregnancy until at least 8 months after delivery. Six bottle fed and six breast fed their infants. One bottle feeder fell pregnant for a second time, as did a breast feeder, and each was followed semicontinuously for totals of 44 and 54 months, respectively. Bone resorption rather than dietary absorption controls changes in blood lead, but in pregnancy the resorption of trabecular and cortical bone are decoupled. In early pregnancy, only trabecular bone (presumably of low lead content) is resorbed, causing blood leads to fall more than expected from hemodilution alone. In late pregnancy, the sites of resorption move to cortical bone of higher lead content and blood leads rise. In bottle feeders, the cortical bone contribution ceases immediately after delivery, but any tendency for blood leads to fall may be compensated by the effect of hemoconcentration produced by the postpartum loss of plasma volume. In lactation, the whole skeleton undergoes resorption and the blood leads of nursing mothers continue to rise, reaching a maximum 6-8 months after delivery. Blood leads fall from pregnancy to pregnancy, implying that the greatest risk of lead toxicity lies with first pregnancies.

Mobilization of lead from human bone tissue during pregnancy and lactation--a summary of long-term research

The skeleton is potential endogenous source of lead during pregnancy and lactation. We have undertaken a longitudinal investigation into the mobilization of lead from the human maternal skeleton to determine whether lead is mobilized from the maternal skeleton during pregnancy and lactation, and if so, when and how much is released. Subjects in the study were migrants to Australia (n=15) whose skeletal lead isotopic composition (endogenous lead) was different to that prevailing in the Australian environment (exogenous lead). This migrant cohort was compared with 6 multi-generational Australian controls. Biological and environmental samples were taken pre-pregnancy where possible, throughout pregnancy and postpartum for at least 6 months. Newly-born infants of the migrant and Australian mothers were monitored for 6 months. Blood lead concentrations for the migrant mothers ranged from 1.5 to 20 microg/dl (geometric mean 2.8) and for Australian mothers ranged from 1.9 to 4.3 microg/dl (geometric mean 2.9). There was minimal change in lead isotopic composition of the Australian pregnant controls although there were increases of approximately 40% in blood lead concentration in 3 of 6 cases during the postpartum period and from 0 to 12% in the other 3. In the migrant pregnant subjects, the geometric mean skeletal lead contribution to blood lead using the isotopic composition was approximately 33% (range 10-88%) for 14 subjects using a revised estimate for exogenous lead. Skeletal contribution to blood lead during the postpartum period was significantly greater than during pregnancy (P<0.001). The skeletal contributions to blood lead are higher and the changes are more consistent in those subjects who conceived within 100 days of arrival in Australia compared with those who conceived longer than 100 days. In the migrant subjects, changes in blood lead concentration during pregnancy and postpartum varied from subject to subject with an overall 20% increase; the increases during the postpartum period were greater than during pregnancy (P<0.001). It was estimated that the amount of maternal skeletal lead mobilized during pregnancy and transferred to the infant via cord blood averaged approximately 79%. The increased skeletal contribution to blood lead is attributed to a low daily calcium intake of approximately 500 mgCa/day, a condition which was present in both migrant and Australian subjects. An ongoing clinical trial is providing a new cohort with calcium supplements. A summary of other aspects of the study is included and covers: additional flux released from the skeleton during pregnancy and postpartum; XRF bone lead results; urinary excretion of lead during pregnancy and postpartum; dietary contribution to blood lead in female adults and children; comparison of rates of exchange of lead in blood of newly-born infants and mothers; relationships of lead in breast milk to lead in blood, urine and diet of the infant and mother; changes in blood lead after cessation of breastfeeding; urinary lead isotopes during pregnancy and postpartum indicate no preferential partitioning of endogenous lead into plasma; a comparison of some aspects of the nonhuman primate and human pregnancy studies.

Bioaccumulation and damaging action of polymetal industrial dust on laboratory mice Mus musculus alba. I. Analysis of Zn, Cu, Pb, and Cd disposition and mathematical model for Zn and Cd bioaccumulations

The concentrations of Zn, Cu, Pb, and Cd in the liver, kidneys, spleen, bones, and carcass of laboratory mice BALB/cy were observed in toxicological experiments. Polymetal industrial dust containing these metals was given to experimental animals at 1% concentration mixed with conventional animal food. Samples for analyses were taken on Days 15, 40, 60, 90, and 120 posttreatment. The experimental data clearly support the established antagonistic interactions among cadmium, zinc, copper, and lead. A mathematical model was proposed to study the main tendencies of heavy metal bioaccumulation under conditions of metal interaction and excessive exposure. The experimental results were assessed on the basis of the model. A rate constant of renal excretion greater than that of hepatic excretion was obtained, which agrees with the observed inversion of cadmium kidney/liver ratio in the conditions of very high exposure.

Effect of maternal bone lead on length and head circumference of newborns and 1-month-old infants

The authors evaluated the effects that maternal bone lead stores have in anthropometry at birth in 223 mother-infant pairs. The participants were recruited between April and November 1994. Anthropometric data were collected within the first 12 hr following delivery. Maternal information was obtained 1 mo after delivery occurred. Bone lead burden was determined with in-vivo K-x-ray fluorescence of the tibia (cortical bone) and the patella (trabecular bone). The authors transformed anthropometric measurements to an ordinal 5-category scale, and the association of measurements with other factors was evaluated with ordinal logistic-regression models. Mean bone lead levels were 9.8 microgram/gm bone mineral and 14.4 microgram/gm bone mineral for the tibia and patella, respectively. Birth length of newborns decreased as tibia lead levels increased. Compared with women in the lower quintiles of the distribution of tibia lead, those in the upper quintile had a 79% increase in risk of having a lower birth length newborn (odds ratio = 1.79; 95% confidence interval = 1.10, 3.22). The authors adjusted by birth weight, and the effect was attenuated--but nonetheless significant. Patella lead was positively and significantly related to the risk of a low head circumference score; this score remained unaffected by inclusion of birth weight. The authors estimated the increased risk to be 1.02 per microgram lead/gm bone mineral (95% confidence interval = 1.01, 1.04 per microgram lead/gm bone mineral). Odds ratios did not vary substantially after the authors adjusted for birth weight and other important determinants of head circumference.

Longitudinal study of daily intake and excretion of lead in newly born infants

As an adjunct to a study of lead mobilization during pregnancy and lactation, we have obtained estimates of the daily lead intake and excretion/intake for 15 newly born infants monitored for at least 6 months postpartum. The longitudinal data presented reflect the far lower levels of environmental contribution to lead in blood in the 1990's than that in the earlier studies from the 1970's and early 1980's, the last period for which such dietary information is available in newly born infants. Infants were breast-fed or formula-fed or both and, in the second quarter, were usually fed solid foods (beikost). Lead concentrations were as follows: lead in breast milk, ranged from 0.09 to 3.1 microg/kg with a geometric mean of 0.55 microg/kg, lead in infant formula ranged from 0.07 to 11.4 microg/kg with a geometric mean of 1.6 microg/kg, and lead in beikost ranged from 1.1 to 27 microg/kg with a geometric mean of 2.9 microg/kg. Daily lead intakes ranged from 0.04 to 0.83 microg/kg body weight/day with a geometric mean of 0.23 microg Pb/kg body weight/day, and excretion/intake ranged from 0.7 to 22 with a geometric mean of 2.6. There was no significant difference at the 5% level in lead concentration in daily intakes and excretion/intake for the first quarter versus the second quarter for this small number of subjects. Assuming that there was no contribution from environmental samples such as house dust and ambient air, the contribution of diet to blood has been estimated from lead isotopic measurements with the following ranges: for breast milk only as the dietary source, 40 to 65%; for breast milk and infant formula as the dietary sources, 15 to 70%; and for infant formula and beikost, 20 to 80%. The geometric mean value of the dietary contribution to blood over the 6-month period of approximately 35% is consistent with earlier estimates of uptake of lead in blood in newly born infants when environmental lead concentrations were much higher. Other sources such as air, soil, and dust are considered to contribute minimally to blood lead in these infants because of the low 206Pb/204Pb ratios in environmental media. Thus, we consider that the increased excretion over intake, along with other evidence, reflects mobilization of infant tissues arising especially from rapid bone turnover at this stage of life; the tissue lead has been identified isotopically in urine.

Urinary lead isotopes during pregnancy and postpartum indicate no preferential partitioning of endogenous lead into plasma

We have compared lead isotopic ratios and lead concentrations in 51 matched blood and spot urine samples from 13 subjects covering the interval from before pregnancy through 180 days postpartum to evaluate whether mobilization of lead from the maternal skeleton is preferentially partitioned into plasma; we have used urine as an isotopic proxy for plasma. There was no statistically significant difference in the lead 206/lead 204 and lead 207/lead 206 ratios over pregnancy. The urine data for the postpartum period are in the opposite relationships to that predicted for a preferential partitioning hypothesis. These data provide no support for the hypothesis that lead released from the skeleton is preferentially partitioned into plasma.

Estimation of cumulative lead releases (lead flux) from the maternal skeleton during pregnancy and lactation

Recent longitudinal studies with human subjects and nonhuman primates using high-precision stable lead isotopes show that lead is mobilized from the maternal skeleton during pregnancy and the postpartum period. We have now calculated the cumulative lead release (lead flux in micrograms) mobilized from the skeleton during these periods by means of analysis of monthly PbB samples from recent immigrants to Australia. Results included a statistically significant inverse relationship (P = .006) between the lead flux and the time of conception after the arrival of the subjects in Australia. By using an area-under-the-curve approach to determine the added lead inputs to blood during pregnancy and nursing versus a baseline value, the net lead release to blood varied from 0.9 to 10.1 microg/d, which is equivalent to 0.3 to 4.03 mg of lead. With group PbB concentrations usually less than 3 microg/dL, the observed releases imply a high skeletal turnover of greater than 10% and possibly greater than 30% in some subjects during pregnancy and the postpartum period. These elevated rates in some subjects may partly arise from low daily calcium intakes, being one half to two thirds of that of recommended daily requirements. The lead flux calculated from a cumulative approach was compared with other approaches: first-order kinetics, bone turnover, bone x-ray fluorescence measurements, and the International Commission for Radiological Protection lead pharmacokinetic model. Calculated lead releases and remaining bone lead concentrations would likely not be detectable by current x-ray fluorescence methods.

Intrauterine lead exposure and preterm birth

The objective of this study was to determine the risk of preterm birth in relation to umbilical cord blood lead levels (UCL) among primiparous and multiparous women. A case-cohort study was performed in Mexico City during 1995. A total of 459 full-term births was compared with 161 preterm births (before 37 gestational weeks). Mothers were interviewed before the delivery about their reproductive histories and other related factors of preterm birth. Lead was determined by atomic absorption spectrophotometry. Lead levels were higher in primiparous women who had a preterm birth than in primiparous women with a full-term birth (9.77+/-2.0 microgram/dl vs 8.24+/-2.15 microgram/dl); this difference was marginally significant. After adjusting for other known preterm birth risk factors, the frequency of preterm birth was almost three times higher among women who had UCL levels greater or equal to 5.1 microgram/dl compared to those who had UCL levels lower than 5.1 microgram/dl. This difference was not observed among multiparous women. Our results suggest that intrauterine lead exposure may be associated with preterm birth in first deliveries but not in subsequent ones.

Comparison of the rates of exchange of lead in the blood of newly born infants and their mothers with lead from their current environment

Newly born infants (n = 15) were monitored for 6 months after birth or for longer periods to evaluate the changes in isotopic composition and lead concentration in infants as compared with that in women from the same population groups and to determine the clearance rates of lead from blood in the infants. These data represent the first published results for serial blood sampling in a relatively large cohort of newly born infants. Blood lead concentrations decrease from the cord to samples taken at 60 to 90 days and then increase by amounts varying from negligible to 166%. In spite of concern about individual susceptibility to lead pharmacokinetics, changes in isotopic ratio followed a smooth decrease over time for 9 of the 11 infants born to migrant parents, and the patterns of variation were quite reproducible. Data for 2 of 4 infants born to multigenerational Australian parents exhibited little change in isotopic ratio over time, and in the other two cases, the changes were attributed to diet. The rate of exchange (t1/2) for the migrant infants of lead in blood derived from the mother during pregnancy and the lead from the current environment was calculated by using a linear function and ranged from 65 to 131 (91+/-19, mean+/-SD) days. The half-lives for the exchange of skeletal and environmental lead for 7 of the 8 women before significant mobilization of lead from the maternal skeleton ranged from 50 to 66 (59+/-6) days. One explanation for the longer half-lives for infants as compared with the mothers may be the proportionally higher contribution of current environmental (Australian) lead in the infants at parturition. Exchanges of lead in infants are more complex than for the adults, reflecting inputs from sources such as maternal skeletal lead during breast feeding.