Pre- and Postnatal Low-Level Lead Exposure and Children′s Dysfunction in School

Abstract

The contributions of pre- and postnatal low-level lead exposures to the risk of learning problems were evaluated among 1923 children who were born in one Boston hospital in 1979–1980 and followed to age 8 years. In this relatively privileged group, more than 20% of the children had a mother with some formal postgraduate education. Prenatal lead exposure was estimated with a measurement of umbilical cord blood lead content, and postnatal lead exposure was approximated with measurement of lead in the dentin of an exfoliated deciduous tooth. Information about potential confounders and effect modifiers was obtained from maternal interview shortly after delivery and from a mailed questionnaire completed and returned when the child was approximately 6 years old. An assessment of each child"s function in school was provided by the teacher, who completed a questionnaire near the end of the school year in which the child reached the age of 8 years. We considered a learning problem to be related to lead exposure if its adjusted prevalence increased with each log e increase in lead, and if the adjusted prevalence was elevated among children with high levels (i.e., approximating the highest decile) of umbilical cord blood lead (i.e., ≥l0 μg/dl) or dentin lead (i.e., ≥5 μg/g). Girls with elevated umbilical cord blood lead levels were more likely than their peers to be dependent and impersistent and to display an inflexible and inappropriate approach to tasks (defined as the "tasks" cluster). Boys with elevated umbilical cord blood lead levels were more likely than others to have difficulty with both simple directions and sequences of directions. Among girls, elevated deciduous tooth dentin lead content was associated with reading and spelling difficulties, the tasks cluster, and with "not functioning as well as peers." Elevated dentin lead levels were not overrepresented among boys with any of the assessed learning clusters. These findings are consistent with the inference that lead levels still prevalent among children (i.e., blood < 15 μg/dI) are associated with some learning problems in girls.