LAW-LEVEL LEAD-EXPOSURE AND BEHAVIOR IN EARLY-CHILDHOOD

Objective. To assess whether small elevations in blood lead level were associated with measurable behavioral changes in a group of poor chil dren between 1 and 3 years old. Methods. The study population consiste d of children presenting for routine well-child care to the pediatric clinic at Bellevue Hospital Center, a large urban public hospital. The following inclusion criteria were used for entry into the study: age 12 to 36 months; capillary lead screening result <1.21 mu mol/L (25 mu g/dL); no known prior history either of blood lead level >1.21 mu mol /L (25 mu g/dL) or lead exposure requiring chelation therapy; Latino o r African-American; English or Spanish spoken in the home; biological mother as primary caretaker; child not presently attending day care; f ull-term, singleton gestation; birth weight at least 2500 g; no known neurologic or developmental disorder; and no severe chronic disease, i ncluding human immunodeficiency virus infection. Study enrollment was simultaneously stratified by capillary lead level and age. All childre n between 12 and 36 months attending the pediatric clinic during the s tudy period received screening capillary blood measures of lead level following the recommendations of the Centers for Disease Control and P revention and the American Academy of Pediatrics as part of routine pr imary care. During periods of enrollment, consecutive lead measurement s performed in the pediatric clinic were reviewed by one of the resear chers. For those children meeting entry criteria based on lead level a nd age, further eligibility based on the remainder of the inclusion cr iteria was determined through parental interview and review of the med ical record. Lead exposure was assessed with a single capillary blood specimen, using atomic absorption spectrophotometry. Subjects were con sidered to be lead-exposed if their lead level was between 0.48 and 1. 20 mu mol/L (10 and 24.9 mu g/dL) and nonexposed if their lead level w as between 0 and 0.48 mu mol/L (0 and 9.9 mu g/dL). Behavior was asses sed using the Behavior Rating Scale (BRS) of the Bayley Scales of Infa nt Development, second edition. The BRS in this age group consists of three components: an Emotional Regulation Factor that measures hyperac tive/distractible/easy-frustration behaviors; an Orientation-Engagemen t Factor that measures fear/withdrawal/disinterest behaviors; and a Mo tor Quality Factor that assesses the appropriateness of movement and t one. The BRS is scored as a percentile; lower scores reflect more prob lematic behaviors. Researchers performing the BRS were blinded to capi llary lead results. Information was collected concerning factors that might confound the relationship between lead and behavior. Demographic factors were collected, including: child's age, gender, and country o f origin; mother's age, marital status, parity, country of origin, and primary language spoken; parental education, and occupation and recei pt of public assistance. Socioeconomic status was determined using the Hollingshead Two-Factor Inner of Social Position. Maternal verbal IQ was assessed using the Peabody Picture Vocabulary Test-Revised. Matern al depression was assessed using the Center for Epidemiologic Studies- Depression Scale. Cognitive stimulation provided in the home was asses sed using a new office-based instrument, the StimQ, which measures the quantity and quality of play materials and parent-toddler activities in the child's home. To assess the child for iron deficiency, we perfo rmed a hematocrit and mean corpuscular volume at the time of the capil lary lead evaluation. A presumptive diagnosis of iron deficiency was m ade if the child was either anemic (defined as a hematocrit <32) or ha d a mean corpuscular volume <72. Results. The study sample consisted o f 72 children. Children in the lead-exposed group (n = 41) had a mean BRS behavior score that was 15.8 points lower than that of children in the nonexposed group (n = 31), which was significant by the Student's t test. For the emotional regulation factor measuring hyperactive/imp ulsive/easy-frustration behaviors, children in the exposed group had a mean score that was 14.6 points lower than that of the nonexposed gro up, which was significant by the Student's t test. For the orientation -engagement factor measuring fear/withdrawal/disinterest behaviors, ch ildren in the exposed group had a mean score that was 14.1 points lowe r, significant by the Student's t test. Multiple linear regression ana lyses were used to examine the independent relationship between BRS (t otal and factor scores) and lead group, after adjusting for potential confounders. Six variables were related to either lead group or BRS be havior score in unadjusted analysis and were, therefore, included as p otential confounders in each of the multiple regressions: child's age and gender, and mother's age, verbal IQ, depression score, and provisi on of cognitive stimulation. In the analysis of the relationship betwe en the BRS total score and lead group, the adjusted mean BRS behavior score in the exposed group was 17.3 points (95% confidence [CI]: 3.3, 31.3) lower than that of children in the nonexposed group (sr = -0.27) . In the analysis of the relationship between the emotional regulation factor and lead group, the adjusted mean factor score in the exposed group was 16.6 points (95% CI: 2.1, 31.2) lower than that for the none xposed group (sr = -0.25). In the analysis of the relationship between the orientation-engagement factor and lead group, the exposed group h ad an adjusted mean score that was 14.2 points (95% CI: -2.1, 30.5) lo wer than that for the nonexposed group (sr = -0.20). In these multiple regression analyses, mother's depression score was significantly asso ciated with a lower total BRS score (sr = -0.25) and with lower emotio nal regulation factor (sr = -0.23). Older children had higher BRS scor es (sr = 0.20), and had significantly higher emotional regulation fact or scores (sr = 0.22). A relationship was observed between male gender and lower emotional regulation scores that did not reach significance (sr = -0.21). Iron deficiency, cognitive stimulation provided in the home and mother's verbal IQ were not related to any measures of behavi or. Conclusions. Low-level lead exposure is associated with adverse be havioral changes in very young preschool children. This association ma y be particularly important for poor children, who are also at risk fo r behavior problems on the basis of other environmental fact