The behavior and routes of lead exposure in pregrasping infants

Understanding the routes of lead exposure in a very young infant is an essential precursor to identifying effective strategies for minimizing blood-lead (PbB) levels throughout infancy. The present study integrated observational data, lead-loading data, and household airborne particulate levels <10 mu m (PM10) to understand the broad patterns of lead exposure in infants from Port Pirie, South Australia. Seven, 2 - 19-week-old infants were observed between three and six times, for 3 - 9 h per visit, at intervals of 1 - 9 weeks. Household lead-loading and PM10 data were collected for five of the families. Eight objects were observed in an infant's mouth, but only the infant's fingers, pacifier, and nipple of the mother's breast or teat of a bottle were observed in an infant's mouth for an average of more than 1% of an observation day. The objects most frequently put in an infant's mouth were their own fingers or their pacifier. Synthesizing our data on behavioral frequency, lead loading, and the surface area of contact, and using estimates of dose response, and sampling, transfer, and absorption efficiencies, the results suggest that a 4-month-old infant could absorb up to 4 mu g of lead a day (equivalent to a PbB level of up to about 2.4 mu g/dl) by mouthing their fingers, about two-thirds of all exposure routes identified in this study. Estimates also suggest that lead uptake via inhalation accounts for about 0.5 - 3% of an infant's PbB at 5 mg/dl. If our estimates reflect real routes and values, the majority of the average PbB level of 6-month-old infants in Port Pirie during 2002 could potentially be accounted for by the normal infant and family behaviors observed in this study. While the current level of concern is 10 mu g/dl, recent studies indicate no safe threshold for Pb exposure, and so interventions for reducing chronic low-level exposure are useful. We suggest that home-based interventions for reducing Pb exposure should focus on maintaining low Pb loadings on objects that are directly associated with an infant, and outside objects that have few transfer steps to the infant.