P.B. Hammond

Evolution of efficient methods to sample lead sources, such as house dust and hand dust, in the homes of children

Efficient sampling methods to recover lead-containing house dust and hand dust have been evolved so that sufficient lead is collected for analysis, and to ensure that correlational analyses linking these two parameters to blood lead are not dependent on the efficiency of sampling. Precise collection of loose house dust from a 1-unit area (484 cm2) with a Tygon or stainless steel sampling tube connected to a portable sampling pump (1.2 to 2.5 liters/min) required repetitive sampling (three times). The Tygon tube sampling technique for loose house dust less than 177 microns in diameter was around 72% efficient with respect to dust weight and lead collection. A representative house dust contained 81% of its total weight in this fraction. A single handwipe for applied loose hand dust was not acceptably efficient or precise, and at least three wipes were necessary to achieve recoveries of greater than 80% of the lead applied. House dusts of different particle sizes less than 246 microns adhered equally well to hands. Analysis of lead-containing material usually required at least three digestions/decantations using hot plate or microwave techniques to allow at least 90% of the lead to be recovered. It was recommended that other investigators validate their handwiping, house dust sampling, and digestion techniques to facilitate comparison of results across studies. The final methodology for the Cincinnati longitudinal study was three sampling passes for surface dust using a stainless steel sampling tube; three microwave digestions/decantations for analysis of dust and paint; and three wipes with handwipes with one digestion/decantation for the analysis of six handwipes together.

Toxic effects of lead and lead compounds on human health, aquatic life, wildlife plants, and livestock.

In order to recommend the levels of lead concentration in fresh water which will not adversely affect various water uses, a literature survey was carried out on the toxic effects of lead and lead compounds on human health, laboratory animals, aquatic life, terrestrial plants and livestock. The information is summarized in this paper.

Condition and type of housing as an indicator of potential environmental lead exposure and pediatric blood lead levels

Environmental evaluations in a prospective behavioral study of children with blood lead levels up to about 50 micrograms/dl were performed by an intensive environmental survey and by exterior visual evaluation of housing quality. Serial blood lead values for infants in the study were compared to exterior housing type and quality, which itself was also compared with results of the intensive environmental evaluation. Five housing condition and type categories were defined: public housing; private housing (satisfactory, deteriorated, and dilapidated); and rehabilitated private housing. In this interim report on the first subset of available data, the housing categories were found to differ in paint and environment dust lead levels, with public and rehabilitated housing having lowest values. Blood lead concentrations of children differed across housing categories as early as 6 months of age, with children residing in public housing having lowest levels, followed by those in rehabilitated housing. The spread in mean blood lead concentrations among the housing quality categories increased with increasing age of the children. Housing category accounted for over one-half of the blood lead variability in 18-month-old children.

THE INFLUENCE OF SOCIAL AND ENVIRONMENTAL FACTORS ON DUST LEAD, HAND LEAD AND BLOOD LEAD LEVELS IN YOUNG CHILDREN

The roles of environmental and behavioral factors in determining blood levels were studied in a cohort of young children living in an urban environment. The subjects were observed at 3-month intervals from birth to 24 months of age. Repeated measurements were made of the childrens blood lead levels, environmental levels of lead in house dust, and in the dust found on the childrens hands. A qualitative rating of the residence and of the socioeconomic status of the family was obtained. Interviews and direct observation of parent and child at home were used to evaluate various aspects of caretaker-child interactions. Data analysis consisted of a comparison of results obtained by simple correlational analysis, multiple regression analysis, and structural equations analysis. The results demonstrated that structural equation modeling offers a useful approach to unraveling the complex interactions present in the data set. In this preliminary analysis, the suspected relationship between the levels of lead in house dust and on hands and the blood lead level was clearly demonstrated. Furthermore, the analyses indicated an important interplay between environmental sources and social factors in the determination of hand lead and blood lead levels in very young children.

The Cincinnati prospective study of low-level lead exposure and its effects on child development: Protocol and status report☆

This project attempts to integrate information on exposure history, cognitive and behavioral development, and health and social functioning in order to delineate the association between chronic, low-level lead exposure and behavioral development. A dose-response analysis will be made seeking to relate the frequency with which effects occur to degree of lead exposure.

Lead Exposure in Early Life: Health Consequences

Until very recently it has been considered that of the many manifestations of lead toxicity, those involving the elaboration and function of hemoproteins occur at lower levels of lead exposure than any others. The critical target seems to be the enzyme heme synthetase, which is essential for the insertion of iron into the precursor, protoporphyrin IX. The major consequences of this effect, which have been evaluated in both adults and children, are reduction of circulating levels of hemoglobin and cytochrome P-450-dependent Phase I drug metabolism. Lead clearly inhibits normal hemoprotein function in both respects. The threshold level of lead exposure for these effects seems to be at a circulating lead concentration (PbB) of approximately 30 to 40 micrograms/dL. A growing body of evidence suggests, however, that the functional integrity of the central nervous system is compromised at substantially lower levels of lead exposure, particularly in the human fetus and young child. Early postnatal neurobehavioral development is compromised at maternal or cord PbB of somewhat less than approximately 10 micrograms/dL, a level of lead exposure not uncommon in the general population. Results of more recent cross-sectional and prospective studies indicate that postnatal lead exposure resulting in PbBs as low as 25 micrograms/dL, and probably lower, also are associated with deficits in intellectual attainment, achievement, and behavior. The long-term consequences of these effects remain to be fully evaluated. Little is known concerning basic mechanisms that are responsible for these effects. They may be manifestations of a more basic common effect of lead on cell proliferation and differentiation.

Dose-effect and dose-response relationships of blood lead to erythrocytic protoporphyrin in young children

Dose-effect and dose-response relationships were analyzed for blood lead concentration (PbB) vs blood protoporphyrin concentration using multiple data points from 165 children, ages 3-36 months. Protoporphyrin concentrations were measured using a front-face fluorometer designed to measure zinc protoporphyrin (ZPP) and an extraction method designed to measure total protoporphyrin as the free base (FEP). Estimations were made of the threshold for PbB effects on FEP and ZPP, as well as the slopes of the PbB-FEP and PbB-ZPP interactions. There was essentially no difference in thresholds estimated using ZPP vs FEP as the effect parameter. There was no apparent effect of age on threshold. However, the slope for PbB vs ZPP was less steep than the slope for PbB vs FEP. Moreover, the average ratio FEP:ZPP was markedly elevated at 3 months (1.84:1) and decreased slowly, attaining unity at 33 months. The possible reasons for this discrepancy are discussed, as well as the implications for interpretation of lead screening program data.

Mechanisms by which lead depresses linear and ponderal growth in weanling rats

Lead is known to reduce linear and ponderal growth in children, even at levels of exposure common in the general population. The mechanism involved is not known. The present study was conducted in order to establish the role of food consumption and insulin-like growth factor (IGFI), also commonly known as somatomedin C (SmC), in lead-induced reduction in growth in weanling rats. A further purpose was to test the hypothesis that depressed growth could be prevented by administration of growth hormone and thyroxine, a procedure which prevents arrested growth due to hypophysectomy. Treatment with growth hormone in combination with thyroxine had no effect on depressed growth or food consumption. The reduction in linear and ponderal growth due to lead (approximately 17%) could be largely though not completely accounted for on the basis of reduced food consumption, apparently by a mechanism not involving growth hormone or thyroxine (see above). Plasma SmC was reduced in proportion to reduced food intake, regardless of whether due to Pb or to restriction of food intake in a pair-feeding experiment thereby ruling out an effect of lead on SmC synthesis or activity other than through reduced food consumption. The experiments leading to these conclusions all involved administration of lead in the drinking water, suggesting the possibility that reduced food consumption was peripherally mediated as a result of contact of lead with appetite-depressant receptors in the gastrointestinal tract, e.g., taste receptors. An additional experiment therefore was conducted comparing food consumption and growth resulting from oral lead administration to subcutaneous administration. Similar depressant effects on food consumption and growth resulted at similar concentrations of lead and zinc protoporphyrin in blood. These effects were significantly greater following oral administration, however, suggesting that lead depresses appetite by both a systemic mechanism and one operating at the level of the gastrointestinal tract.

Effect of lead exposure on patterns of food intake in weanling rats.

The reduction in growth resulting from lead (PB) exposure in weanling rats is consistent with a lowering of the biological set-point for food intake. In this study the effects of lead on the patterns of food intake were examined. For 10 days (from ages 26 to 36 days), female rats were provided with drinking water containing 250 ppm lead as the acetate (n = 6) or equivalent acetate as sodium acetate (n = 6). A computerized system was used to monitor daily food intake at 5-min intervals over 10 successive 23-h periods (each period consisting of 12 h dark, 11 h light). Control rats consumed approximately 75% to 85% of their food intake during the dark phase. Exposure to lead resulted in decreased body weight, tail length, and cumulative food intake. Decreased food intake associated with lead during the first 6 days of exposure was due to a decrease in the size of each meal during the dark phase, which reflected a decrease in the duration of each meal. These results suggest that lead, at least initially, was affecting food-satiety signals to produce a premature termination of food intake during a meal. After 6 days, the lead-exposed rats appear to have adjusted their meal size and meal duration to approximately control values. However, this compensation appears to have occurred at the expense of the daily (nocturnal) number of meals, which decreased slightly (although not significantly) in lead-exposed animals. Thus, the total daily intake of food in lead-treated animals remained depressed relative to control animals.

The renal handling of δ-aminolevulinic acid in the rat and in the human

Abstract Renal mechanisms for handling δ-aminolevulinic acid (ALA) were investigated in control and lead-exposed rat and human populations. Elevated plasma ALA levels consequent to lead exposure permitted study of these mechanisms under conditions of heavy load. Reabsorption was observed in both species. The reabsorption mechanism appears to be saturable in the human and exists in parallel with a secretory process of smaller capacity. Reabsorption in the rat has a much larger capacity than in the human but appears also to be saturable. No secretory mechanism was apparent in the rat.