Office of Research and Development
U.S. Environmental Protection Agency
October 2005

Executive Summary (For the complete 114-page report, click here)

This report summarizes an independent peer review of the U.S. Environmental Protection Agency’s (EPA’s) “Final Report on the World Trade Center (WTC) Dust Screening Study” (EPA 2005a). In this study, EPA developed an analytical method to screen bulk dust samples for mineral slag wool, particles consistent with concrete compositions, and gypsum (EPA 2005b). The study included a method validation component, in which spiked background dust samples with varying levels of WTC dust were prepared and then eight laboratories measured concentrations of candidate WTC signatures in spiked and non-spiked samples. Based on the data collected during this study, EPA proposed slag wool as a signature constituent of WTC dust.

Six expert peer reviewers with various affiliations and from relevant scientific disciplines were asked to provide an independent peer review of the WTC Dust Screening Study. The peer reviewers prepared preliminary written comments on the study and further discussed these comments during a 4-hour conference call on October 4, 2005. The peer review of the WTC Dust Screening Study focused on nine charge questions, which asked the peer reviewers to comment on EPA’s proposed analytical method, data analysis and interpretation, and selection of slag wool as a signature for WTC dusts.

Following are the peer reviewers’ main findings, organized by topic. The remainder of this report documents the discussions among the reviewers that led up to these findings.

• Proposed Analytical Method. The peer reviewers had concerns about laboratories’ abilities to implement the proposed analytical method consistently or correctly, given that three out of the eight laboratories selected to participate in the method validation study failed to produce data of acceptable quality. Even after representatives from the eight laboratories “attended a 2-day session during which the method was further developed and discussed” and “all laboratory participants held weekly conference calls as the analytical program was proceeding to discuss general issues with the protocol” (EPA 2005a), data had to be massaged to differentiate WTC dust from background dust. The peer reviewers recommended several improvements to the proposed analytical method and recommended that EPA establish strict criteria for identifying and enabling “qualifying laboratories,” should EPA decide to move forward with slag wool as a WTC signature. Refer to the summary statements in Sections 3 and 5 of this report for the peer reviewers’ specific recommendations for improving and implementing the proposed analytical method.
  
  
• Data Analysis and Interpretation. The peer reviewers were skeptical that EPA’s evaluation and interpretation of the study data were performed fairly. Peer reviewers pointed to several non-standard steps taken to enhance the study’s ability to distinguish WTC dust from background dust and noted that these steps could be interpreted as attempts to prove the method’s success rather than to objectively evaluate its real-world potential for fingerprinting WTC dust. The peer reviewers’ two most notable concerns were:

  o The reported difference in slag wool levels for impacted and non-impacted locations was based on statistical analyses that excluded certain results from background samples but did not exclude results from spiked samples. The background results and spiked sample results were statistically indistinguishable when the entire data set was considered.

  o The study authors disqualified three out of the eight original selected laboratories during the screening study. There was no follow-up investigation to determine why these selected laboratories, presumably following the proposed method, failed to differentiate background dusts from WTC dusts. [After the peer review conference call, one peer reviewer noted that a possibility exists that the three laboratories were wrongly disqualified due to errors in an equation used to calculate the numbers of slag wool fibers per gram of dust. Section 4.2 describes this further.]

  Refer to Section 4 of this report for more detailed information on the peer reviewers’ comments regarding data analysis and interpretation.

• Selection of a WTC Signature. The peer reviewers supported EPA’s conclusion that gypsum and elements consistent with concrete do not meet the WTC signature selection criteria. Regarding slag wool, the peer reviewers agreed that, from the data provided, EPA has not made the case that its proposed analytical method can reliably discriminate background dust from dust contaminated with WTC residue. Thus, the proposed method has not demonstrated the utility of slag wool as a successful signature constituent. This finding was based on critical reservations, stated above, regarding the proposed analytical method and the data analysis and interpretation. Section 2 of this report further summarizes the peer reviewers’ discussions on this topic.
  
  
• General Considerations and Alternate Approaches. At the end of their conference call, the peer reviewers offered several recommendations to EPA for identifying a WTC signature. The reviewers classified some of these recommendations as modifications to the proposed analytical method, such as reconsidering the utility of polarized light microscopy (PLM), using fiber dimensions (in addition to fiber counts) to “fingerprint” dusts, and implementing a tiered sampling approach that would use slag wool as a screening marker for the potential presence of WTC dust followed by transmission electron microscopy (TEM) analysis of chrysotile asbestos as a confirmatory marker. The reviewers acknowledged that further evaluation would be necessary to assess the utility of these and other suggested modifications. The peer reviewers classified their remaining recommendations as entirely new approaches that could only be investigated through new research projects. Section 5 of this report lists all of the general considerations and alternate approaches the peer reviewers discussed during the conference call.

The remainder of this report presents additional information on the independent peer review of the WTC Dust Screening Study: Section 1 presents a detailed account of the peer review process; Sections 2 to 5 summarize how peer reviewers responded to the nine charge questions during the peer review conference call; and Appendix B includes copies of the peer reviewers’ preliminary written comments.

(For the complete 114-page report, click here)