NYC-WTC_000195194

NYC 9/11 Public Portal Document

1.3 Development of Clearance Criteria for Lead

At the time the study was initiated, COPC benchmarks were established for all contaminants except lead. Initially, the clearance criterion used for lead was 0.1 ng/m\ which was based on an estimated national background concentration. Risk-based clearance criteria for lead in indoor air provide a means to evaluate the effectiveness of the WTC residential cleaning program. Information on background concentrations of lead in indoor air also informs attainment of cleanup objectives. Background information has been obtained from historical information on ambient air lead concentrations in urban environments, and will be further refined with data from a site­ specific background study being conducted as part of the WTC Dust Cleanup Program.

iiii Table Ltf Primary Clearance Criteria Used to Determine Reoccupancy®

Gffmpound Seitied Dust 0-0009 S/cc Polycyclic Aromatic Hydrocarbons (PAH) : 0.2 gg/m^ -300 gg/m^ Dioxin/Furan 0.001 ngZm’ Lead 1 gg/ht’ 4, 25gg/tf (micro vacuum comparison value 25 pg/tf) Fibrous Glass (Man-made Vitreous Fibers)______ lOS/L Alpha-quartz (0.001 mg/m^ - 0.004 mg/m' based on 0,004 nig,6n N/A: analytical methods)

EPA’s risk assessment methodology for lead has been advanced through use of a biokinetic modef that incorporates a biomarker of exposure/effect (blood lead) and multimedia exposure modeling. Through use of this model EPA identifies a goal of reducing environmental lead exposure so that 95 percent of childhood blood lead levels are below 10 pg/dl This goal is accomplished when the airborne lead concentration is set at 1 gg/m^, and input values for all other sources of environmental lead exposure (e.g., water, soil, dust, diet) are set at background concentrations.

® U.S. Environmental Protection Agency. (September, 2002). World Trade Center Indoor Air Assessment: Selecting Contaminants of Concern and Setting Health-Based Benchmarks. Values have been excerpted from tliis draft report.

’U.S. Environmental Protection Agency. (February, 1994). Guidance Manualfor the Integrated Exposure Uptake Biokinetic Mode! for Lead in Children. (OSWER EPA/540/R/93/081). 6

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