A 25-Year Record of Childhood Blood Lead Exposure and Its Relationship to Environmental Sources

Abstract

Listen

Translate article

Background: Broken Hill, the oldest silver (Ag) –zinc (Zn) –lead (Pb) mining community in Australia, has an ongoing and legacy problem of environmental Pb exposure that began as early as 1893. To reduce Pb exposure risks, identifying potential exposure pathways and related factors is a critical first step. Methods: This study examined PbB levels of children ≤ 60 months old (n = 24,106 samples), along with corresponding soil (n = 10,160 samples), petri-dish dust (n = 106 houses) and ceiling dust (n = 80 houses) Pb concentrations at homes over a 25-year period from 1991-2015. Regression analysis was used to identify potential factors driving blood Pb exposures as well as the relationship between environmental Pb sources and children’s blood lead (PbB) outcomes. Findings: Analysis of the dataset showed there were multiple statistically significant (p<0.01) independent predictors of PbB including age, gender, ethnicity, socio-economic status and age of housing. The presence of multiple co-variates renders the identification of a single primary cause of elevated PbB as implausible. Nevertheless, the data reveal the relative role of different variables in driving PbB levels. Aboriginal children in Broken Hill had geometric mean PbB of 7.4 μg/dL (95% CI: 6.7-7.4) being significantly higher (p<0.01) than non-Aboriginal children (PbB 6.2 μg/dL, 95% CI: 6.2-6.3) for all years between 1991-2015. Children at the age of 24-36 months had a higher PbB compared with other age groups. Higher PbB levels were also statistically associated with lower socio-economic status and for children living in houses built before 1940 (p<0.01). Blood Pb was also significantly correlated with both soil Pb and indoor petri-dish dust Pb loadings, confirming that these are important pathways for PbB exposure in Broken Hill. A 100 mg/kg increase in soil Pb was associated with a 0.12 μg/dL increase in childhood PbB. In addition, PbB concentrations increased with higher indoor petri-dish dust Pb loadings (i.e., 0.08 μg/dL per 100 μg/m2/30 days). Spatial analysis of PbB exposures over the 25-year period shows that children living adjacent to the mining leases frequently report with levels ≥ 10 µg/dL, the primary level of concern during the sample period. Interpretation: The 25-year data paint a stark picture of persistent exposures with children of all ages presenting with a ≥ 10 µg/dL across the whole city area. In other words, the risk of exposure at > 10 µg/dL was seemingly unavoidable irrespective of residential address. In terms of moving forward and mitigating harmful early-life Pb exposures, the data show that children aged 24–36 months and Aboriginal children should be prioritised for feasible intervention practices. The primary intervention must focus on mitigating contemporary ongoing dust emissions from the mining operations and the associated mine-lease areas followed by household soil remediation, to help prevent recontamination of homes. Additional practices of dust cleaning using wet mopping and wiping techniques, vacuuming of carpets and furnishings, ongoing monitoring of children and household dust remain important short-lived abatement strategies, but the key aim should be to eliminate risk by removing contamination in the wider environment as well as in individual homes. Funding Statement: C. Dong was funded via an International Macquarie University Research Excellence Scholarship (iMQRES No. 2014098). He received technical and practical support from the Broken Hill Environmental Lead Program (BHELP) as part of a Macquarie University-BHELP collaboration agreement, which included funding support from NSW EPA to MP Taylor. Declaration of Interests: The authors declare no competing financial interests. M.P. Taylor has completed an independent Review of the New South Wales Environment Protection Authority’s Management of Contaminated Sites for the NSW Minister for the Environment (available at: http://www.epa.nsw.gov.au/resources/epa/Contaminated-Sites-Review-2016.pdf) and is also an occasional advisor to the NSW EPA’s Broken Hill Environmental Lead Program. M.P. Taylor is also the lead author of an independent review (in progress) of the scientific evidence related to PbB exposures and sources for the NSW EPA’s Broken Hill Environmental Lead Program. B. Gulson has been nominated as an independent reviewer of that report. Ethics Approval Statement: Data access and its subsequent analysis were subject to ethics approval from NSW Health and Macquarie University.