A blood lead benchmark for assessing risks from childhood lead exposure

Abstract

Lead exposure is an insidious problem, causing subtle effects in children at low exposure levels where clinical signs are not apparent. Although a target blood lead concentration (Pb_B) of ten micrograms per deciliter (10 μg/dL) has been used as the basis for environmental decision-making in California for nearly two decades, recent epidemiologic evidence suggests a relationship between cognitive deficits and Pb_B at concentrations < 10 μg/dL. Based on a published meta-analysis of children's IQ scores and their blood lead concentrations, we developed a new blood lead benchmark: an incremental increase in blood lead concentration (ΔPb_B) of 1 μg/dL, an increase that we estimate could decrease the IQ score in an average school child in California by up to one point. Although there is no evidence to date for a threshold for the neurobehavioral effects of lead, a one-point IQ decrement was chosen to represent a de minimus change. To safeguard the intellectual potential of all children, additional efforts to reduce or eliminate multiple-source exposures to lead are warranted.

Keywords:

• Lead
• toxicity
• children
• behavior
• neurodevelopment
• cognition
• IQ
• slope
• risk assessment

Acknowledgments

Dr. Dowling received partial salary support from a Fulbright Senior Scholar award.

The authors gratefully acknowledge the manuscript reviewers and helpful suggestions of Dr. Richard Hornung and Dr. Herbert Needleman.

Notes

∗Source: U.S. Environmental Protection Agency.^{[ 27 ]}

^a Slope estimates are the relationship between IQ and concurrent blood lead levels, except Bellinger & Needleman,^{[ 71 ]} used 24-month blood lead levels; Baghurst et al.^{[ 77 ]} used lifetime average blood lead levels; and Wasserman et al.^{[ 75 ]} used lifetime cumulative blood lead levels.

^b The pooled analysis by Lanphear et al.^{[ 31 ]} included data from seven individual studies, including Baghurst et al.,^{[ 77 ]} Bellinger et al.,^{[ 79 ]} Canfield et al.,^{[ 49 ]} Dietrich et al.,^{[ 72 ]} and Wasserman et al.^{[ 75 ]}

^c In Al-Saleh et al.,^{[ 76 ]} 69% (n = 368) of the children had blood lead levels < 10 μg/dL. The estimated slope for blood lead levels < 10 μg/dL is based on the model for the entire sample population.