Dietary lead intakes for mother/child pairs and relevance to pharmacokinetic models.

Blood and environmental samples, including a quarterly 6-day duplicate diet, for nine mother/child pairs from Eastern Europe have been monitored for 12 to >24 months with high precision stable lead isotope analysis to evaluate the changes that occur when the subjects moved from one environment (Eastern Europe) to another with different stable lead isotopes (Australia). The children were between 6 and 11 years of age and the mothers were between 29 and 37 years of age. These data were compared with an Australian control mother/child pair, aged 31 and 6 years, respectively. A rationale for undertaking this study of mother/child pairs was to evaluate if there were differences in the patterns and clearance rates of lead from blood in children compared with their mothers. Blood lead concentrations ranged from 2.1 to 3.9 microg/dl in the children and between 1.8 and 4.5 microg/dl in the mothers, but the mean of differences between each mother and her child did not differ significantly from zero. Duplicate diets contained from 2.4 to 31.8 microg Pb/kg diet; the mean+/- standard deviation was 5.5 +/- 2.1 microg Pb/kg and total daily dietary intakes ranged from 1.6 to 21.3 microg/day. Mean daily dietary intakes relative to body weight showed that the intake for children was approximately double that for the mothers (0.218 vs. 0. 113 microg Pb/kg body weight/day). The correlations between blood lead concentration and mean daily dietary intake either relative to body weight or total dietary intake did not reach statistical significance (p>0.05). Estimation of the lead coming from skeletal (endogenous) sources relative to the contribution from environmental (exogenous) sources ranges from 8 to 70% for the mothers and 12 to 66% for the children. The difference between mothers and children is not statistically significant (p = 0.28). The children do not appear to achieve the Australian lead isotopic profile at a faster rate than their mothers. These data provide evidence that the absorption or uptake of lead from dietary sources is similar in adult females and children of the age in this study. In spite of lower bone lead and faster bone remodeling and recycling in children compared with adult females, we see no differences between the mothers and their children in overall contribution of tissue lead to blood lead. Results from this study suggest that fractional absorption of ingested lead by children 6-11 years of age is comparable with absorption patterns observed among adult females in the 29-37-year-old age range. Because pharmacokinetic models apply a 40-50% absorption even for 7-year-old children, further investigations on fractional absorption of ingested lead by young children are warranted. Further investigations are especially needed in younger children than those who were subjects in the current study, particularly children in the 1-3-year-old age range. In addition, the effect of nutritional status and patterns of food intake on children's lead absorption require investigation, particularly given the increased prevalence of marginal nutritional status among low-income populations that are at increased risk of elevated blood lead levels.

precision stable lead isotope analysis to evaluate the changes that occur when the subjects moved from one environment (Eastern Europe) to another with different stable lead isotopes (Austa). The children were between 6 and 11 years of age and the mothers were between 29 and 37 years of age. These data were compared with an Ausrlian control motherchild pair, aged 31 and 6 years, respectively. A rationale for undertaldg this study of mother/child pairs was to evaluate if there were differences in the patterns and rates of lead fiom blood in ciden compared with their mothers. Blood lead coneiraion ran om 2.1 to 3.9 pvdl in the children and between 1.8 and 4.5 pg/dl in the mothers, but the mean of differences between each mother and her child did not differ sgnific from zero. Duplicate diets contained from 2.4 to 31.8 pg Pb/kg diet; the mean ± stndard deviation was 5.5 ± 2.1 pg Pb/kg and tol dly dietay intakes ranged from 1.6 to 21.3 pg/day. Mean daily dietay intakes relative to body weight showed that the intake for children was aproxima double that foir the mothers (0.218 vs. 0.113 pg Pb/kg body weig/day). The correlations between blood lea concentration and mean daily dietary intake either reative to body weight or total dietary intake did not reach statcal siificance (0.05). E ion of the lead coming fiom skeletal (endogenous) soure relative to the contribution from environmental(exgnous) uc ire fom 8 to 70% for the mothers and 12 to66% for the dren. The difference between mothers and children is not statistically significant (p = 0.28). The childirn do not appear to achieve the Ausalin lead isotopic profile at a fastr rate dt their mothers. These data provide evience that the absorption or uptake of lead from dietar'ysources is iir in ult females and children of the -ag in this study. In spite of lower bone led and fase bone remodeling and recyclg in children compared with adult females, we see no r between the mothers and their children i overall contribution of tissue lead to blood lead. Results from this study sugst that fractioxia absorption of ingested lead by child 6-11 years of age is cmpable with absorption patterns observed among adult females in the 29-37-year-old age rang. Because p kinetic models apply a 40-50% absorpion even for 7-year-old children, firther iniions on fractional absotption of ingested lead by young children are warnted. Further investigaons aree ally needed in younger children than those who were subjects in the current study, particuarl idren in the 1-3-year-old age range. In addition, the effect of nutritional status and patterin of food intake on children's lead absrpton requaire inestigdton, par ly the increased prevalence of marginal nutrtional status among low-income populations that are at increased risk of elevated blood lead levels. Key rnk-: child, diet, lead isotopes, models, mother.

En
Hal Perspect 105:13341342 (1997). htpl/ebi.nxiehs.nib.gov Blood lead (PbB) levels decreased in developed countries between the late 1970s and the late 1980s to mid-1990s (1)(2)(3) as a result of decreased lead exposure from leaded gasoline, lead-soldered food cans, and other changes in manufacturing by the food industry. Consequently, lead from dietary sources has become progressively less important for the majority of children in the general population, especially for children having PbB concentrations less than 5 pg/dl. For example, the EPA and the Food and Drug Administration (FDA) estimated that over the period [1986][1987][1988][1989][1990] the contribution of lead from dietary sources for a 2-year-old child decreased from 47 to 16% (4). These large decreases in the percentage contribution of dietary lead to overall lead ingestion are partly attributable to the belated recognition of the major contribution of dust and soil to PbB in young children (5). The contribution of dust to PbB is, however, most critical for children aged 1-3 years, typically the age group with the highest PbB levels (6) and greatest hand-to-mouth activity (7). In individuals older than 4 years, hand-to-mouth activity is much less predominant and diet assumes a greater importance as a source of lead. For example, for a female of child-bearing age the FDA estimates the contribution from diet is 65%, most of this coming from food (43%) and water (22%) (4).
All pharmacokinetic models for lead in humans differentiate between a lower absorption rate (uptake from the gastrointestinal tract) of 5-15% for adult male subjects versus 40-50% for children (8)(9)(10)(11). In the EPA Integrated Exposure Uptake Biokinetic (IEUBK) model (9), the higher absorption values among adult males are applied to children up to 7 years old. The adult values for gastrointestinal lead uptake are fairly well validated using long-term mass balance studies (12,13), radioactive tracers (14)(15)(16)(17)(18)(19), and stable isotope tracers (20,21). Most adult subjects were males. James et al. (19) determined the gastrointestinal absorption of tracer doses of 203Pb in a group consisting of 12 women and 11 men at 26-77 years of age. The study primarily evaluated the influence of foods and beverages on lead absorption. Unfortunately, the report provided no discussion of whether or not the retention of 203Pb differed between male and female subjects.
Uptake rates for children are much less well established and are based essentially on two mass balance studies with small numbers of children. Alexander et al. (22) conducted 11 balance studies with eight subjects ranging in age from 3 months to 8 years. Intakes averaged 10.6 pg Pb/kg body weight (bw)/day (range, 5-17 pg Pb/kg bw/day), with absorption averaging 53% of intake and retention averaging 18% of intake. In their investigation of 61 metabolic balance studies Articles * Dietary lead with 12 infants ranging in age from 14 to 746 days and whose lead intakes were greater than 5 pg Pb/kg bw/day, Ziegler et al. (23) reported an average absorption of 41.5% and net retention of 31.7% of intake. Ziegler et al. (23) suggested that there was a higher absorption and retention of lead in younger infants compared with older children. The Glasgow Duplicate Diet study (24) is also cited as a data source for absorption of lead by young children. This study, largely aimed at evaluating the impact of drinking water on PbB in 131 mothers and infants, the age of the latter being up to 3 months (24), does not provide information on absorption of lead from food.
We have monitored a cohort of mother/child pairs as part of an investigation to compare the contribution of environmental and endogenous sources of lead to blood lead among female adults and children who immigrated to Australia. Gulson et al. (25) showed that there were significant differences in the isotopic composition of biological samples between Australian subjects and those from other countries. The isotopic composition in blood and urine of female adults migrating to Australia from Eastern Europe changed rapidly over a 3to 4month period towards Australian isotopic values. The rapid change is related to the approximately 120-day life of erythrocytes, the main store of lead in blood (26). Thereafter, an equilibrium was reached between skeletal lead and the Australian environmental lead with 41-73% of lead in blood derived from skeletal sources even after 12 months of residence in Australia.
We have monitored 10 mother/child pairs for up to 24 months to evaluate the impact of absorption of dietary lead during middle childhood compared with adults' absorption and to determine its impact on the lead burden of children versus adults. If there are significant differences in absorption rates in adults and children, the children's blood isotopic profile should be different than the maternal profile following establishment of an equilibrium with the Australian environment. Methods Nine of these mother/child pairs immigrated from Eastern Europe, with seven from the former Soviet Union, one from Poland, and one from Bosnia (Table 1). Their data are compared with an Australian control pair (referred to by their subject numbers 1044 and 2044). The ages of the children ranged from 6 to 11 years and the mother/child pairs were monitored from 12 to longer than 24 months. An age of 12 years was chosen as the cut-off limit because after this age the skeleton is considered to be in a relatively Food sampling involved collection of a 6-day duplicate diet to coincide with the quarterly biological and environmental sampling. The diets for the mothers and children were collected and analyzed separately. Each daily sampling was blended in a cleansed blender. Several equal portions were then taken from each day's blended diet and composited in a single 6-day sample. Several food samples were analyzed in duplicate to determine the efficiency of homogenization of the blending. Venous blood samples were collected following the protocol described by Gulson et al. (27). Fully flushed drinking water was collected from the kitchen faucet after an additional 30-sec flush. Dust was collected as dust fall accumulation using petri dishes placed in at least two locations in the residence for 3 months (28). The methods for sample preparation and analysis for blood and environmental samples have been reported previously (25,27). An aliquot of the blended food was analyzed by Australian Government Analytical Laboratory personnel (who perform the analyses of the Australian National Market Basket Survey) for concentrations of Ca, Mg, K, Na, Ba, Sr, Hg, Cd, Cu, Pb, and Zn.
Statistical calculations were performed using the S-Plus (Statistical Sciences, Seattle, WA) and Microsoft Excel Version 7.0 (Microsoft, Redmond, WA) packages.  Figure 1. Notched box plots showing the 206pb/204Pb in 6-day duplicate diets (n = 54), lead loading in house dust (n = 134), and tap water (n = 147). The upper and lower ends of the boxes (the rectangular areas) are the upper and lower quartiles. The distance between these two values (the interquartile range) is a measure of the spread of the distribution. The relative distances of the upper and lower quartiles from the median (the white rectangle at the notch) give information about the shape of the distribution of the data. (if one distance is much bigger than the other, the distribution is skewed.) The notches surrounding the median provide a measure of the rough significance of differences between the values. Specifically, if the notches about two medians do not overlap in the plots, the medians are roughly significantly different at about a 95% confidence level. The dashed appendages of the box plot encode the adjacent values, given by the following relationships. If r is the interquartile range, the upper adjacent value is the largest observation that is less than or equal to the upper quartile plus 1.5r. The lower adjacent value is the smallest observation that is greater than or equal to the lower quartile minus 1.5r. The horizontal lines are outliers.

Results
The data for the important environmental samples of drinking water, house dust, and 6-day duplicate diet are summarized in notched box plots in Figures    Daily-intake (pg/kg/day) 7 (continued, neox as part of the 6-day diet. Dust collected as lumber quarterly dust fall accumulation (28) in -umber both residences and school classrooms generally have low lead loadings and 9 206Pb/204Pb ratios <17.0 (Fig. 2).
Information obtained from parents and children indicated that, except for school consumption, diet of the children was gen- 10 erally similar to the adults in the same fami-lQ ly ( Table 2). In testing the methods, several food samples were analyzed in duplicate. 8 Even with complete digestion of the sample $ by the microwave, the reproducibility of results compared with that expected for 8 other samples, such as blood, is poor (Table   8 3 Mother/child bloods. The PbB concen-* trations in all subjects were <5 pg/dl. In 7 out of 10 cases, the mean PbB of the child 8a was greater than that of the mother (Table 1)  8 and the pooled mean PbB for the mothers and children had a p-value of 0.07 (Table 4).
Correlation between the repeated measure-5 ments for mother/child bloods was examined 5 by taking the differences between the mother and the child. Each component of the covariance of these differences was then plot-4 ted against the time interval between the readings (not shown). For most pairs, there 5 was litdle pattern evident in the plots, which 5 showed random scatter about the zero line. However there was a downward trend evident in the 207Pb/206Pb and 206Pb/204Pb isotope ratios for subjects 1023 and 2023. By 6 assuming the time intervals were equally spaced, these plots were checked by plots of 5S the autocorrelation for each series. These plots confirmed the correlation between repeated measures was not statistically significant (with the exception of the 1023/2023 5 pair). Similarly, the correlations between the i5 paired blood and food repeated measures were examined. No evidence of correlation was found. We therefore omitted the data for the 1023/2023 pair and felt it was plausible to treat the remainder of the data as sets 3s of independent observations. For 8 out of 10 3 mother/child pairs, there was a statistically 3 significant positive correlation using the Kendall's Tau measure of rank correlation between the mother and her child's blood for the isotopic ratios.  Representative time-series plots of isotopic compositions expressed as the 206Pb/204Pb ratio and PbB concentrations Table 3 2.15 Russia for a holiday (Fig. 5) 2.14 essary for the variance of these adjacent dif-a1 and 2 indicate duplicate analysis of a single sampli ferences to be similar for all mother/child bAl, A2, B1, etc., indicate duplicate analysis of four s; pairs. Unfortunately this was not the case. Biokinetics of Lead in Human Pregnancy. It is therefore not possible to perform a statistical test to confirm or deny parallelism. Table 5. Statistical parameters for blood and diet ol The data are relatively uniform over time (as shown by the means and standard 207pb/206Pb deviations in Table 1). If anything, the data for each mother exhibited larger variations Parameter/identifier No.
Tau p-Value than for the corresponding child. However, Blood from mother/child F-tests on the variances for the isotopic pairs (isotopic raisshowed thtnone of temother/child composition) ratios showed that none of the mother/child 1015/2015 12 0.49 0.01 pairs attained significance (     Figure 5. Time-series plotfor 206Pb/M"Pb and blood lead (PbB) for mother/child pair Figure 6. Time-series plot for 206Pb/204Pb and blood lead (PbB) for 1023/2023. The time at which the mother and child returned for a visit to Russia is mother/child pair 1044/2044. indicated. than 17.0 (27). The larger isotopic variations (Table 2), and this range applied for subject mother/child pairs, the daily intake was also and increasing 206Pb/2 Pb ratios in the 6-2031. significantly different in six of the nine pairs day diets over time are probably a reflection The mean daily intake of lead for the (Table 4). There did not appear to be any of the desire to consume food from the children was 0.21 ± 0.11 pg Pb/kg bw/day relationship between child/mother daily country of origin of the subjects and global-compared with 0.11 ± 0.06 pg Pb/kg bw/day intake and PbB and isotopic composition. ization of the food market.
for the mothers. The mean daily intake of Pb Except for subjects 1015, 1044, and The 6-day averaged daily weight of con-for the children was overall approximately 2046, the correlations of individual mother sumed dietary material varied from a low twice that of the mothers; the ratio of dietary blood-food and individual child blood-food 338 g in subject 2031 to 1,929 g for subject intake for child/mother was from 1.20 to for isotopic composition failed to reach sta-1046. The daily weights were relatively con-6.11 jig/kg bw/day ( Table 4). The combined tistical significance (p>0.05). There was not a sistent for each subject over the period of data for mothers and children showed that statistically significant (p>0.05) association monitoring. The 6-day averaged daily lead there were significant differences in mean between blood lead and food lead concentraintake varied from 1.5 to 21.3 pg Pb/day daily intake (p<0.001; Table 4). For matched tions. When the data were pooled (Table 5) there was a statistically significant correlation for mother blood-food in isotopic composition (p<0.01 for 206Pb/204Pb and 207Pb/206Pb) but not for the child blood-food data (p 0.2). The lack of statistical significance is obvious when the data are plotted in various ways. For example, the blood and diet isotopic data for subjects 1015 and 2015 are plotted in Figures 8 and 9 compared with the PbB and 6-day averaged dietary intake. In both mother and child for the May 1996 sampling, there was a marked increase in dietary intake, but totally contrasting isotopic compositions in the diet; yet, the PbB showed very little change and, for the child 2015, even the isotopic composition showed little change. The isotopic composition of the mother 1015 showed a decrease. In the case of mother/child pair number 1029/2029, there was a marked increase in dietary intake in the middle of the monitoring, but minimal effect was observed in the blood isotopic composition or concentration ( Fig. 10 and  11). Variability in either isotopic composition of the diet and/or dietary intake but with minimal change in blood isotopic composition or blood was observed in most of the other mother/child pairs (Fig. 3, 5, 6).
Blood lead concentrations and, commonly, the isotopic composition exhibited very little variation over time, even when the isotopic composition of diet was markedly different from the blood isotopic composition and the dietary intake was >10 pg Pb/day, as shown for 1029/2029 in Figures 10 and 11 and summarized for all subjects in Figure 7.
As expected, the 6-day diets show considerable variation in the elements such as Ca, Mg, Sr, Ba, etc., but at this stage there does not appear to be any systematic trends between mothers or children.

Discussion
Clearance rate of lead from blood and skeletal contribution to blood lead. This study evaluates differences in the patterns and clearance rates of lead from blood in children compared with their mothers. Gulson et al. (25) showed that there was an exponential decrease in the 206Pb/204Pb ratio over a 3-to-4-month period in female adults migrating from Eastern Europe to Australia, which was related to the mean life of lead in the red blood cell. That is, the European lead in blood was exchanging with Australian lead. Furthermore, after equilibrium with the Australian environment was attained after 3 to 4 months, about 41-73% of lead in the blood derived from endogenous (predominantly skeletal) tissues. In most cases it was not possible to evaluate the clearance rates of lead from  Figure 7. Summary of time-series plots for all subjects for 206Pb/204Pb in food and blood, lead daily intake (pg/kg body weight), and blood lead (pg/dl). blood in the children in the present study because they were usually recruited at least 1 month or longer after the mother had been recruited. The similar blood lead isotopic and concentration trends shown in Figures 3 through 6 and summarized in Figure 7 for the mother/child pairs indicates that the nine clearance rates for lead from blood are similar for the children and their mothers. Further evidence for this hypothesis comes from the subjects 1023/2023 who visited Russia for 3 months and then returned to Australia. The trends in both isotopic composition and pre-and post-Russia are identical and would suggest that the clearance rate of lead from blood is similar for both mother and child (Fig. 5). When equilibrium was reached between skeletal lead and Australian lead, the skeletal contribution to PbB for the mothers ranged from 16 to 70% and for children varied from 26 to 64% (Table 6). There was no consistency between mothers and children as to whether or not body stores contributed more than environmental sources to PbB. Three of nine mother/child pairs showed a higher contribution of skeletal lead to blood lead for the mother compared with the corresponding child, two pairs had the same, and four mother/child pairs showed the child having a larger contribution than the mother. Absorption rates. The PbB concentrations in these subjects are low; hence, any changes in blood lead due to diet should be more easily discernible than among subjects with elevated body stores of lead (e.g., persons having PbB levels over 10 pg/dl). If there was a 40-50% absorption for a child Environmental Health Perspectives * Volume 105, Number 12 December 1997  Figure 9. Time-series plots for 206Pb/204Pb in blood and 6-day duplicate diet for blood lead (PbB; pg/dl)and daily dietary intake (pg/day/kg bw) for mother and for blood lead (PbB;pg/dl) and daily dietary intake(pg/day/kg bw) for  Figure 10. Time-series plots for 206Pb/204Pb in blood and 6-day duplicate diet . Figure 11. Time-series plots for 206Pb/204Pb in blood and 6-day duplicate diet and for blood lead (PbB; pg/dl) and daily dietary intake (pg/day/kg bw) for mothand for blood lead (PbB; pg/dl) and daily dietary intake (pg/day/kg bw) for child er 1029. The scale for daily dietary intake is the same as for PbB. 2029. The scale for daily dietary intake is the same as for PbB. and if the isotopic composition in the diet two times the rate (i.e., daily intake Pb per composition of blood are simslar for mothers changes markedly, this should be reflected kilogram body weight) compared with their and chbldren ( Fig. 4-7) or the change is in by a more rapid change in the child's blood mothers; and 3) the children have lower the opposite direction to the change in isoisotopic composition towards the Australian body lead stores than adults (30,31) so that topic composition of the diet (Fig. 7, 9, 10). values. This more rapid change in the chil-they have less lead of European origin to The above data indicate that the lead dren's blood isotopic composition does not counter the input of dietary lead of absorption from the gastrointestinal tract in occur in spite of 1) a greater intake of Australian isotopic composition. Increased these children is essentially the same as for Australian lead from lunches consumed bone turnover in the children (32) as an the adult females. That is, the absorption away from home, and potentially a greater argument also fails to explain the cases in rate is around 10-15% rather than 40-50%. intake of lead from dust/dirt with the which the diet shows an increase in both Our interpretations are supported by data of Australian isotopic composition compared intake and isotopic composition, such as for Angle et al. (33) in which they suggested that with adult women; 2) the children are subjects 2015 (Fig. 9)