Date of Award
Doctor of Philosophy
Interdisciplinary Health Sciences
Background and Significance: Despite the many historical efforts by the U.S. to reduce lead (Pb) in the environment, childhood Pb poisoning continues to be a public health issue today. Pb has been identified as a child hazard because children are highly vulnerable to the effects even at lower levels of exposure (blood lead levels (BLLs) < 10 μg/dL), and these effects can be physical, cognitive, and behavioral. Current state and federal blood lead level screening guidelines for identifying exposed children are based on assumptions that BLLs < 10 μg/dL will remain stable or decline over time (with age); disregard the effects of lowest-range Pb exposure; and disregard Pb levels in children older than approximately age 6. We have observed in past clinical studies that in one U.S./Mexico border community, children in high-risk neighborhoods experienced substantially higher proportions of elevated blood lead levels (CDC reference level of ≥ 5 μg/dL) than the rest of the U.S., and a large proportion of children had detectable blood lead levels. To test current policy assumptions regarding child blood lead level screening, this study examined whether time and/or other possible factors over time, predicted child blood lead levels in children with chronic low-level Pb absorption. Whether time was a significant predictor was examined, and also whether age, sex, and living in families with incomes below the U.S. poverty line, living in an older home, and living near industries predicted child blood lead levels.
Aims and Objectives: Changes in current policy must be evidence-based. The over-arching goal of this study was to test current assumptions that one blood lead level test is sufficient to rule out child lead exposure, and that lead exposure and risk of lead exposure, reliably diminishes as children age. The hypotheses also tested other possible factors that may influence children’s BLLs, accounting for time. Specifically, this study determined: 1) the blood lead levels of children living in high-risk neighborhoods of El Paso County; 2) the numbers of children with blood lead levels exceeding the current CDC reference level for “elevated” of 5 μg/dL; 3) whether blood lead levels change predictably with time, during a period of approximately 18 months (across three time points); and 4) factors other than time that predicted children’s low blood lead levels (< 10 μg/dL).
Hypotheses: H1): There will be significant differences in child BLLs across three time points; H2): Time as a factor will predict changes in child BLLs across three time points (that exceed within child variability of BLL); H3): Whether a child lived below the U.S. 2020 poverty threshold will influence whether child BLLs change significantly over time; H4): Whether a child lived in an older home (built before 1986) will influence whether child BLLs change significantly over time; H5): Whether a child lived near industry will influence whether child BLLs change significantly over time.
Methods: This was a prospective longitudinal study of child blood Pb levels in 206 children ages 6 months to 16 years living in high-risk neighborhoods in El Paso County. The children were a convenience sample, recruited through school events, community health fairs, and door- to-door invitations. Child BLLs were determined from finger-stick blood samples analyzed using inductively coupled plasma mass spectrometry (ICP-MS) and were tested every 3 through 6 months approximately over 18 months. Children included were those tested for blood lead and with BLLs from not detectable to 10 μg/dL. All data for this study were collected in the community and data collection was stopped in March 2020 by COVID-19 shutdown orders. As of March 2020, the base sample included 193 children with one (N = 193), two (N = 86), or three (N = 29) BLL screenings. Family demographics, child medical history, and household characteristics were collected from parents, and child blood lead levels were collected in children’s homes. Multiple imputation simulated missing data, yielding 193 children with three time points. All individual growth curve (linear mixed) models were performed for datasets N = 29 and N = 193.
Results: Blood lead mean values for children were below the CDC reference value of elevated blood lead levels ≥ 5.0 μg/dL at every test point. The proportion of children with elevated BLLs however were 4.7%, 7.0%, and 3.4%, at Time 1, Time 2, and Time 3 respectively, which were substantially higher than the expected national percentage of 2.5% for children ages 1 through 5 years across the three-time points. Individual growth curve (linear mixed models) showed that child BLLs changed significantly within children, and that time was not a significant predictor of BLL. Also, age and sex, living with a family income below the poverty line, and living in an older home were not significant predictors of child BLL. The age by sex interaction and living near an industry predicted child blood lead levels controlling for time as a repeated measure in the N =193 multiple imputation dataset. Children living near an industry had higher blood lead levels regardless of age and sex, with an average 0.22 μg/dL increase. Pre- and adolescent females had higher blood lead levels than males of the same age.
Conclusion: Time is not a significant predictor of child BLLs, and policy regarding BLL child screenings must be changed to require ongoing monitoring of child BLLs for children and adolescents living in high-risk neighborhoods. Also, as suggested by previous literature, other factors created special risk of lead exposure for children, including living below the poverty line, and living in an older home. Very interestingly, the age and sex interaction was significant for female pre-and adolescent children suggesting that puberty may play a critical role in lead absorption in this age group. Living near an industry predicted a significant proportion of variance in child blood lead levels but the estimate was not very precise (relatively broad confidence interval). This finding suggested that all children living near polluting industries require ongoing BLL monitoring. The remaining unexplained variance in the model suggested that other factors not explored in this study are contributing to variability in child blood lead levels in these children with chronic low-level lead absorption.
Recommendations: Children in high-risk communities must be continually monitored. One BLL test in early childhood is not sufficient to rule out chronic lead exposure in children. Additional studies are needed to identify other possible sources of lead contamination, that may exist in the soil, air, and water. Comprehensive community education must be provided on an ongoing basis in these high-risk neighborhoods, to help families identify lead sources typical lead hazard sources by neighborhood; limit consumption of foods and use of products that may cause lead exposure; increase nutrition; and safely renovate lead-paint sources in the home.
Recieved from ProQuest
Michelle Del Rio
Del Rio, Michelle, "Stability Of Blood Lead Levels In Children With Chronic Low-Level Lead Absorption" (2021). Open Access Theses & Dissertations. 3239.