Alan Nye, PhD | Principal Toxicologist, Director of Risk Assessment
The United States Centers for Disease Control and Prevention (CDC) has established a new “reference value” for managing the human health effects of lead of 5 micrograms of lead per deciliter of blood (5 ug/dL). We believe that the 5 ug/dL reference value will replace the 10 ug/dL target blood lead level currently used by the United States Environmental Protection Agency (USEPA) and other regulatory agencies. This change will likely result in lower cleanup levels for lead in soil and other environmental media and reduce permissible lead concentrations in consumer products.
Beginning in the 1990s, lead cleanups of residential soil and dust were based on a target blood lead level (BLL) of 10 micrograms per deciliter. In developing its remedial standards for lead in residential soil and dust, the USEPA allowed a probability not greater than 5% that a child would exceed a BLL of 10 ug/dL. The USEPA targeted a BLL of 10 ug/dL in keeping with policy implemented by the CDC in 1991. As presented in the Table 1, CDC-derived BLLs of concern declined from 40 ug/dL in 1970 to 10 ug/dL in 1991.
Table 1.0 Timeline of Centers for Disease Control (CDC)
Blood Lead Levels of Concern/Blood Lead Reference Values
Since the 1990s, the protectiveness of 10 ug/dL as a BLL of concern has been considered controversial, with some scientists and health professionals arguing for lower BLLs of concern. In January 2012, the Advisory Committee on Childhood Lead Poisoning Prevention (ACCLPP) recommended that the CDC eliminate the term “level of concern” as applied to BLLs since:
“Effects at BLLs < 10 µ g/dL are also reported for other behavioral domains, particularly attention- related behaviors and academic achievement. New findings suggest that the adverse health effects of BLLs less than 10 µ g/dL in children extend beyond cognitive function to include cardiovascular, immunological, and endocrine effects. Additionally, such effects do not appear to be confined to lower socioeconomic status populations. Therefore, the absence of an identified BLL without deleterious effects combined with the evidence that these effects, in the absence of other interventions, appear to be irreversible, underscores the critical importance of primary prevention. (ACCLP, 2012)”
Instead of a 10 µ g/dL BLL of concern, the ACCLPP recommended that the CDC adopt a “reference value” for blood lead of 5 ug/dL. The reference value is based on the 97.5th percentile BLL of children aged 1 to 5 years from the most recent National Health and Nutrition Examination Survey (NHANES) results (ACCLPP, 2012). In deriving the 5 ug/dL BLL reference value, the ACCLPP indicated that CDC should also update the reference value based on blood lead results collected every 4 years as a part of the NHANES testing. The CDC agreed with these recommendations (CDC, 2012).
Because CDC indicates that it will provide this information to a wide variety of “federal, state, and local government agencies and nongovernment organizations interested in lead-poisoning prevention”, we believe that this will particularly affect soil lead cleanups in areas that may involve exposures in children. Also, it is likely that the 5 ug/dL reference value will also be used in assessing lead exposures for women of childbearing age and thus could also affect soil cleanup concentrations for workers.
As a preliminary indicator of the impact of using 5 ug/dL as the target blood lead level for developing residential soil action levels for lead, the remedial level for lead in soil is lowered from approximately 400 mg/kg to 150 mg/kg when default assumptions are used in the USEPA child lead exposure model (Integrated Exposure/Uptake Biokinetic model).
In summary, the CDC acceptance of ACCLPP recommendations for a lower reference value for blood lead (5 ug/dL) will likely be the basis for lower regulatory limits for lead in soil, dust, and other environmental media. We believe that it is a matter of time before USEPA and the States accept these recommendations and implement them as part of their cleanup programs.
References
ACCLPP 2012. Low Level Lead Exposure Harms Children: A Renewed Call for Primary Prevention. Advisory Committee on Childhood Lead Poisoning Prevention. Centers for
Disease Control and Prevention. January 4, 2012; available at http://www.cdc.gov/nceh/lead/ACCLPP/Final_Document_030712.pdf Accessed May 18, 2012
CDC 2012. CDC Response to Advisory Committee on Childhood Lead Poisoning Prevention Recommendations in “Low Level Lead Exposure Harms Children: A Renewed Call of Primary Prevention”; available at http://www.cdc.gov/nceh/lead/ACCLPP/CDC_Response_Lead_Exposure_Recs.pdf
