The uptake of lead by children in differing environments.

Balance studies have been performed for lead upon eight healthy children in three different home environments and upon eight children with inborn errors of metabolism in hospital (consuming two different types of synthetic diet). The balances were for 3 days and involved the use of metal-free diapers where indicated. The concentration of lead in all the samples was determined by atomic absorption spectroscopy after suitable sample preparation. In addition, the total population of children under the age of 16 living in a working class area exposed to undue amounts of lead was examined in an attempt to determine whether their mental development had been affected. Blood lead levels, general intelligence, reading ability, and rate of behavior disorder were measured. The results of the balances showed that the mean daily intake of lead in both groups of children was lower than previously recorded figures, being lowest of all in the breastfed infant. The healthy group absorbed a mean value of 53% and retained 18% of the dietary intake and there was no relationship to age or month of the year of study. The children with inborn errors showed a significantly lower percentage absorption of lead. The preliminary results of the population survey showed that distance from the polluting lead source was related to blood lead level, but no relationship could be found between blood lead level and any measure of mental function.


Introduction
There is increasing evidence that children, and the young of most species, are more prone to lead intoxication than adults (1,2). Barltrop (3) has suggested that this may be due to the oral exploration by children of their environment. Pentschew and Garro (4) considered that there was an increase in susceptibility to lead of the young animal. Kostial, Simmonovic, and Pisonic (5) showed that the uptake of lead from the intestine of new born rats was fifty times that of the adult rat.
We have performed 11 balance studies on eight healthy children in their different home environments and eitht children with inborn errors of metabolism living in hospi-*The Hospital for Sick Children, Great Ormond Street, London, England. tal. Although the balances were carried out to determine the requirements for trace metals of the children on synthetic diets, this provided us with an opportunity to assess the intake and excretion of lead by children in different environments.
In addition, there are suggestions that low-level lead intoxication leads to subtle changes in behaviour and mental development in young children. David et al. (6) showed evidence of a greater lead load in overactive children as compared with controls from the same population. Also Burde and Choate (7) reported poor fine motor control in children with pica and evidence of mild lead intoxication. However, Kotak (8) was unable to demonstrate any relationship between behavioral or intellectual disturbances and lead ingestion.
We have been associated with a unique study in a population exposed to varying amounts of lead in the environment emitted from a smelting factory (9). In this study the place of residence (past and present), blood lead levels, intelligence, reading ability, and behavior were all examined for possible relationships.

Subjects
Group A constituted A control group of eight healthy children whose ages ranged from 3 months to 81/2 years. Three children were at one of our homes, two at another and the other three in an institution; all were on a free diet. The youngest was breast fed at the time of the balance.
Group B was a group of six patients with inborn errors of metabolism on aminogram (Allen and Hanbury Ltd.) and mineral supplements (ages 3 months to 81/2 years).
Group C comprised two neonates with phenylketonu?ia (PKU) on Minafen (Cow and Gate).

Method
Three day balances were performed between markers, "metal-free" diapers being used, where necessary, as described by Alexander and Delves (10). Samples were collected, homogenized, and analyzed by atomic absorption spectrometry as described previously (10).

Environmental Study
Blood was collected by finger-prick from 476 children in the area, 119 of whom were over 5 years of age, and the lead level determined by the micro-technique devised by Delves (11). Children at school received standard tests of intelligence (according to Wechsler) and the Burt graded word reading test. They were also assessed by school teachers as to behavior according to a valid questionnaire.

Results
Balances Figure 1 shows the daily uptake of lead  represented as histograms in Figu drawn according to the conventions by Albright et al. (12). The healthy dren (group A) appear on the top li chronological order; group C is the two histograms on the lower line, ti mainder represent group B. The mean intake, excretion, absorption and ret of lead by the other groups are list Table 1.
The daily intake of lead increased age from 40 jug in the breast-fed i to 210 jig at 81/2 years (Fig. 1). TI take by -children on synthetic diets higher (90 jg at 1 month to 240 jg X years) but did not differ significantly the healthy controls. Again, there w significant difference between the g when intake per kilogram was plotted al excretion (Fig. 2). The individual bh histograms (Fig. 3) show that lead i per unit weight was highest in the n( and that absorption and retention ol were also higher in the younger chi with the exception of the breast-fed c (Wl) and one of the PKU childr Minafen (CM).
These observations are confirmed mean daily values for the three groups (  Figure 4.

Infant
The relationship between distance from infant the works and intelligence and behavior he inis shown in Figures 5 and 6 Figure 4 shows that the nearer the child lived to the source of lead, the higher the blood lead level. There was a significant dif-  Blood level (pg/00ml)  Table 2 that there was no significant correlation between intelligence and behavior and either lead level or current address in the first 2 years of life. Indeed, those children who had moved into the area after the ears second year of life appeared to be of lower chimney intelligence and have a higher degree of behavior disorder.

Discussion
The very low intake of lead by the breastfed infant has been reported previously (3) and may be explained bya natural filter mechanism. The daily intake of lead by all the children studied increases linearly with age but never reaches the value of 300 Kg reported by Kehoe (13) and presumed by Barltrop (3) to be the maximum daily intake for children.
The significantly higher fecal excretion by the children in group B is responsible for their significantly lower absorption and is probably related to a difference in the constitution of the diets. We have reported elsewhere (14) that the calcium/phosphorus ratio in the diets of group B is significantly higher than that of control diets (1.14 for group B; 0.76 for group A). The healthy controls in our series absorbed 53% of the ingested lead. This figure is very much higher than previous reports by Kehoe, for adults, of zero (13) and 5%o% (15), but is of the same order as the absorption of lead of 55% by newborn rats reported by Kostial et al.

(5).
This finding may go some way to explain the increased susceptibility of young children to exposure to lead and should be taken into account when calculating safety limits for children.
In the environmental study the positive correlation between blood lead levels and proximity to the smelting works was expected. Even though 43 out of the 257 school children (17%o) had blood lead levels greater than 40 there was no correlation with lower intelligence or deviant behavior. It may be that the methods of testing were not sufficiently sensitive to detect more subtle deviations of intelligence or behavior. There is also some anecdotal evidence that the children who moved into the periphery of the field of study belonged to families with greater social problems. Nevertheless, these preliminary results suggest that mild exposure to lead does not produce detectable, adverse mental effects.