The long term effects of exposure to low doses of lead in childhood have been examined in 132 of 270 young adults who had initially been studied as primary school children in 1975-1978 and the results of an 11 year follow-up are reported from the School of Medicine, University of Pittsburgh; Boston University; and the Neuroepidemiology Unit, Children’s Hospital and Harvard Medical School, Boston, MA. Neurobehavioral functioning in the earlier study of school children was found to be inversely related to dentin lead levels. In the subjects reexamined as adults, impairment in neurobehavioral function was still related to the lead content of teeth shed at the ages of six and seven. The persistent toxicity of lead was seen to result in significant and serious impairment of academic success, specifically a sevenfold increase in failure to graduate from high school, lower class standing, greater absenteeism, impairment of reading skills, and deficits in vocabulary, fine motor skills, reaction time, and hand-eye coordination. A dose response relation was demonstrated between exposure and numerous outcome variables. Young people with dentin lead levels greater than 20 PPM had a markedly higher risk of dropping out of high school and of having a reading disability as compared with those with dentin lead levels less than 10 PPM. [1]

COMMENT. Exposure to lead even in children who remain asymptomatic may have an important and enduring effect on brain function and learning. Since 16% of children in the United States are reported to have elevated blood lead levels (greater than 15 mcg/dl), the early detection and attention to lead in the environment might prevent school failure in a significant number of children in the USA. The agency for Toxic Substances and Disease Registry has defined the threshold for neurobehavioral toxicity for lead as 10-15 mcg/dl. The mean blood level among the subjects reported with high tooth lead levels was 34 mcg/dl.

In the Sydney Lead Study, a prospective investigation of the relationship between low level lead exposure and neurobehavioral development during the first five years of life, average blood lead levels at the fourth year were approximately 10 mcg/dl and this degree of lead exposure was not associated with mental or motor deficits [2]. A meta-analysis of 24 modern studies of childhood exposures to lead in relationship to IQ inferred that low dose lead exposure is closely associated with deficits in psychometric intelligence [3]. The level of lead exposure in these studies may have been higher than that in the Sydney Lead Study.

In another current study of lead exposure in preschool children, the calcium status of 64 black urban children aged 18-47 months was evaluated in relation to blood lead levels and behavior, particularly pica. Children with blood levels less than 30 mcg/dl were compared with a group having blood levels greater than 30 mcg/dl. The study verified the positive association between blood lead levels and pica, an association recognized for many years. Decreased calcium intake and three other calcium measures were not related to blood lead levels and calcium intake was not associated with pica scores [4]. Pica has been emphasized as a common prelude to plumbism [5] and should prompt the early diagnosis of lead exposure and prevention of neurobehavioral deficits. The identification of children with lead poisoning in need of chelation is possible using unstimulated urinary lead excretion without the necessity of the CaNa₂EDTA provocative test. [6]