The Relationship between Early Childhood Blood Lead Levels and Performance on End-of-Grade Tests

Although much progress has been made, childhood lead poisoning remains a critical environmental health concern. Since the late 1970s, mounting research demonstrates that lead causes irreversible, asymptomatic effects far below levels previously considered safe. Thus, the Centers for Disease Control and Prevention (CDC) lowered incrementally its intervention threshold for lead levels considered dangerous in children by 88% from 60 to 10 μg/dL over the last 40 years (CDC 2006). The 2003–2004 National Health and Nutrition Examination Survey (NHANES) survey data reveal blood lead levels at or above the CDC blood lead action level of 10 μg/dL in 2.3% of 1- to 5-year-olds in the United States, with children tested having an overall geometric mean blood lead level of 2.1 μg/dL (National Center for Health Statistics 2006). These data indicate that > 500,000 children < 6 years of age currently experience blood lead levels at or above the CDC blood lead action level of 10 μg/dL (U.S. Census Bureau 2002). Low-level lead exposure, including prena-tal exposure, has been linked to decreased performance on standardized IQ tests for school-age children (Bellinger et al. 1992; Canfield et al. 2003; Chiodo et al. 2004; Dietrich et al. 1993; Schnaas et al. 2006; Tong et al. 1996). A meta-analysis conducted by Schwartz (1994) estimated that a 10-μg/dL increase in blood lead causes a 2.6-point decrease in IQ level. Dudek and Merecz (1997) observed a statistically significant relationship between blood lead and IQ in a population of 380 children with an average blood lead level of 10.2 μg/dL. The analysis finds that the most severe declines occur in children with blood lead levels between 5 and 10 μg/dL. Not only is there a correlation between blood lead levels and a decrease in IQ, but the slope of the IQ–lead regression is steeper at the lowest levels (Lanphear et al. 2005; Needleman and Landrigan 2004; Schnaas et al. 2006; Schwartz 1993). Needleman and Landrigan (2004) state that this indicates that significant damage occurs at the lowest levels of exposure. Another study examining repeated blood lead levels in children followed from < 1 to 5 years of age detected steeper declines in cognitive abilities in children whose maximum blood lead level never reached 10 μg/dL (Canfield et al. 2003). Linear modeling incorporating the full range of data indicates a 0.46-point decrease in IQ for every 1-μg/dL rise in blood lead level (Canfield et al. 2003). However, linear modeling restricted to blood lead levels < 10 μg/dL indicates a 1.37-point decrease in IQ for every 1-μg/dL rise in blood lead level (Canfield et al. 2003). Nonlinear modeling indicated a 7.4-point decrease in IQ as lifetime average blood lead levels rise from 1 to 10 μg/dL and a 2.5-point decrease in IQ as lifetime average blood lead levels rise from 10 μg/dL to 30 μg/dL (Canfield et al. 2003). Although the shifts in IQ are relatively small, the shifts are both important on a population scale and could be an indicator for other adverse neurologic effects in the individual (Rogan and Ware 2003). Thus, research suggests that significant adverse health effects occur at blood lead levels below the current CDC blood lead action level, leading several researchers to call for its lowering. Learning and behavioral deficits may occur at blood lead levels < 5 μg/dL (Canfield et al. 2003; Chiodo et al. 2004; Lanphear et al. 2000; Schnaas et al. 2006). Meta-analysis and reviews suggest that any level of exposure is potentially detrimental (Gatsonis and Needleman 1992; Lanphear et al. 2005; Schwartz 1993, 1994). In a recent review article, Gilbert and Weiss (2006) called for reducing the CDC blood lead action level to 2 μg/dL. Linking blood lead surveillance data with end-of-grade testing data for several counties in North Carolina, this study explores the potential relationship between early childhood lead exposure and educational achievement in elementary school. The objective of the current study is to determine whether blood lead levels in early childhood are related to educational achievement in early elementary school as measured by performance on end-of-grade testing. In undertaking this study, we link two large databases generated by two different offices of the State of North Carolina in the same populations but at different time periods.