EPA interim final report on WTC background study, April 2003

NYC 9/11 Public Portal Document

factor that compromises the comparison of results to the WTC Background Study is that the average lead load (13.5 pg/tf) on floors is reported as a median rather than mean value. Lastly, the measurements were performed by multiple sampling procedures, including wipe sampling and both high/low flow vacuum techniques.

The study by Gallicchio et al. (2002) focused on a comparison of methods (wipe, questionnaire, and visual inspection) to assess household lead levels. An advantage is that its targeted community (i.e., “old and urban”) is much like New York City. However, the Study selected low socio-economic status (SES) households (i.e., Medicaid recipients) - which due to less available resources for building maintenance may result in a positive bias. Also, like the Lanphear Study, lead loadings (12 pg/tf and 5 pg/ft^ for non-carpeted floors and carpeted floors, respectively) were reported as median rather than mean values.

The most appropriate comparison to the WTC background Study can be made with the Housing and Urban Development (HUD 2001) survey on lead in housing. Table 7-4 provides the distribution of lead loading by wipe sampling methodology in U.S. housing for uncarpeted floors. This data is broken down by census region and building age. In the Northeast, there is a greater than five-fold increase in lead load in pre-1939 versus post-1939 housing. Excluding the pre-1939 housing (mean 24.0 pg/ft^), the weighted mean lead load for 1940 - 1998 housing stock is 3.45 pg/ft^. The results from the HUD evaluation are consistent with the results of lead load obtained in the WTC Background Study residential units for uncarpeted floors (i.e., mean = 1.82 pg/tf and 95% UCL = 2.96 pg/ft^). This comparison benefits from both studies reporting results in the same metric (i.e., arithmetic means) for the same surfaces (uncarpeted floors) by the same methodology (wipe sampling). A limited disadvantage of the comparison is the gross characterization of housing by geographic location (e.g.. Northeast) in the HUD survey and the exclusion of pre-1939 housing stock.

7.2.7 Comparison of Dioxin Concentration in Settled Dust The WTC Background Study reported in a mean dioxin concentration of 0.644 ng/m^ (95% UCL = 0.693 ng/m^) for 80 wipe samples. Results were reported for dioxin toxicity equivalents (TEQs). The literature search identified no studies that reported surface loading (mass per unit area) of dioxin in settled dust in residential dwellings. The study by Christmaim et al. (1989) reported concentrations (mass per mass or pg/kg) of various dioxin congeners (see Section 7.1.7). Converting these results into dioxin TEQs yields a value of 1.34 pg/kg (or ng/g). Multiplying by an average dust load of 500 mg/m^ or 0.5 g/m^ results in an estimated dioxin TEQ load of 0.67 ng/m^ (1.34 ng/g x 0.5 g/m^).

The dioxin TEQ load of 0.67 ng/m^ that was estimated from the Christmaim Study is consistent with the mean concentration obtained from the WTC Background Study. However, the comparison has a number of limitations. The Christmaim Study reported dioxin results in units of concentration (mass per mass), thus necessitating a conversion to the metric (mass per area) used in the WTC WORLD TRADE CENTER BACKGROUND STUDY 37

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