Evidence regarding carcinogenic exposures

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The collapse of the World Trade Center produced a dense dust and smoke cloud containing gypsum from wallboard, plastics, cement, fibrous glass, asbestos insulation, metals, and volatile and semi-volatile organic compounds and other products of high-temperature combustion from burning jet fuel, heating oil, transformer oil and gasoline ^14,15. Individuals caught in the dust cloud on 9/11 and working on or near the site in the days immediately following the attack experienced intense acute exposures to a mixture of substances whose concentration and composition was not measured and will never be fully known. However, it is known that the dust was highly alkaline, due to pulverized cement and other construction materials, and contained numerous particles, fibers and glass shards, resulting in acute eye, nose and throat irritation, leading rapidly to what came to be known as WTC cough. Smoke from fires that persisted into December 2011 contained polycyclic aromatic hydrocarbons, metals, organic chemicals and many other known or potential carcinogens. Heavy equipment and trucks contributed diesel emissions, and there was repeated resuspension of sediment and dust during the subsequent 10-month demolition and cleanup process. Although levels of airborne contaminants were not measured in the first four days, the high prevalence of acute and chronic respiratory conditions in rescue, recovery, clean-up and restoration workers provides evidence for significant exposure levels and toxicity ¹⁶. Although some of the dust and smoke was carried away into higher levels of the atmosphere, significant amounts settled in surrounding streets, residences and office buildings. Dusts entered buildings through broken windows, open windows, and air intakes, and many residents returned to homes that were highly contaminated and/or not adequately remediated. Area residents and workers exposed to WTC dust have also been affected by chronic respiratory diseases, including newly diagnosed asthma and asthma exacerbation ¹⁷.

Members of the STAC and individuals providing public comments have noted that exposures resulting from collapse of the World Trade Center were unlike any other exposures in intensity and variety in history. We believe that to be the case, both because of the enormous forces that pulverized the buildings and their contents and the combustion products generated by the high-temperature fires. Compounding the uniqueness of the exposures is the absence of any data on air contaminant levels or the composition of the dust and fumes in the first four days after the attack, and the presence of multiple and complex exposures. However, while acknowledging these unknown and unknowable factors, we believe that it is possible to make some judgments about the potential increased risks of developing some cancers based on the substances known to have been present. This information can be gleaned from a variety of sources, including peer-reviewed literature, government reports and unpublished reports from private laboratories and contractors.

Based on these reports, the committee believes that both responder populations and area residents and workers had potential for significant exposures to toxic and carcinogenic components of WTC dust and smoke. Factors that influence the intensity of exposures among individuals engaged in rescue, recovery, demolition, debris cleanup and/or other related services include the time and date of arrival at the WTC site and other areas where WTC materials were transported or stored, total days and hours worked, specific jobs performed, breathing rates, work locations, particularly work in areas of smoldering fires, and availability and use of personal protective equipment and other controls. Especially in the early period of rescue and recovery, many individuals worked long shifts without adequate respiratory protection and in clothing saturated with dust from the debris, likely experiencing significant exposures through inhalation, ingestion, and skin absorption. Although these exposures may be considered relatively brief compared to longer exposures typically associated with occupational cancer, many individuals had high-intensity exposures, especially in the early weeks, and many continued to work in the area for weeks and months. Numerous animal studies provide evidence that brief exposures to carcinogens can cause cancer. Evaluation of the Single-Exposure Carcinogen Database containing 5576 studies involving 800 chemicals from 2000 articles showed that in 4271 of the studies, a single dose of an agent administered by multiple routes of exposure caused tumors to develop in many different animal models. In addition to PAHs, many of the tested chemicals are environmentally relevant and are on various pollutant lists, including the IARC and NTP lists. In support of the relevance of the single-exposure carcinogen concept to human cancer, Calabrese and Blain¹⁸ identified published occupational studies on benzene, beryllium, aromatic amines including benzidine, and arsenic in which exposures for less than a year were implicated as the causal factor in the development of cancer. In addition, studies of second or higher order tumors among cancer survivors have shown that both radiation therapy and some forms of chemotherapy increase risk for subsequent cancers, often with shorter latency periods than observed for lower-dose, longer-duration occupational and environmental exposures ¹⁹.  Recent in vivo and in vitro studies using biomarkers of gene expression are consistent with potential increased cancer risks following relatively brief exposures to carcinogenic agents. The results of these studies indicate that the multistep process of chemical carcinogenesis can begin following exposures that range in duration from 1 to 90 days. In addition, some of the chemicals, dusts, fibers, metals and other materials with long half-lives may be retained in the lung and other body compartments for long periods after an environmental exposure.

Exposures among community residents and those working and attending school in the area also have the potential to be significant, although in many ways they may be even more difficult to categorize than those of responders. Some individuals returned within days of the disaster to grossly dust-contaminated homes that they cleaned themselves; others returned to homes with less visible contamination that were later found to contain high levels of asbestos and other toxic substances. Many government offices are housed in buildings below Canal Street, and many workers were required to return before any decontamination or cleaning took place and without personal protective equipment. Others worked, attended school or lived near sites where debris was transported or transferred in processes that continued to generate dusts. Still others volunteered in support activities near the site as well as residing in the community. Residential, office and school building exposures have the potential to be of longer duration than those among workers at the site if the buildings and occupied spaces were not properly remediated. Longer, lower-level exposures may be a particular issue for individuals with preexisting asthma and allergies and those who are already sensitized to dust contaminants such as nickel and hexavalent chromium. Children in contaminated homes, daycare settings and schools have greater exposure potential than adults due to crawling on floors, hand-to-mouth activities and higher respiratory rates, and may also be more susceptible to mutagens and carcinogens due to growth and rapid cell turnover.

In discussing the potential that exposures to WTC dust and smoke may cause cancer, the committee focused on classes of exposure known to be present in substantial quantities in WTC dust and smoke which also have substantial evidence regarding cancer in animals and humans. These include asbestos, polycyclic aromatic hydrocarbons (PAH’s), polychlorinated biphenyls, dioxins and furans, metals and volatile and semi volatile organic compounds (VOC’s).  In addition, we considered some contaminants present in lower quantities due to potential toxicity and/or biological persistence (polychlorinated biphenyls, dioxins and furans).