In this case report, we describe seven previously healthy WTC responders who developed lung disease after sustaining heavy first- and second-day exposures to WTC dust and debris. We summarize our findings as follows: a) CNT were found in some WTC-exposed patients with persistent lung disease with confirmation by positive controls and in the WTC dust. This finding was present in responders with extensive interstitial/parenchymal abnormalities (three of four patients) and in one of two patients with small airway disease, but not in the patient with nonnecrotizing granulomas. b) We found a higher amount of aluminum silicate and magnesium silicate in all four patients with diffuse interstitial/parenchymal abnormalities compared with those with small airway disease and granuloma. Chrysotile asbestos fibers were also found in four of seven patients in quantities modestly higher than background levels of asbestos in the New York City population. In interpreting these findings, however, it should be noted that mineralogic analysis of the lungs can be biased because of sampling variability within the lung itself.

The seven biopsies revealed multiple, partly repeating and mixed histologic patterns. a) Small airways disease was present in almost all cases at different levels of severity, and we highlight patients D and F, in whom it was the main finding. Radiologically, these two patients presented with a mosaic pattern indicative of air trapping similar to that previously described in 25 WTC responders (Mendelson et al. 2007). Small airways disease is a condition that pathologically can be controversial and includes bronchiolitis (Fenton et al. 2007; Niewoehner et al. 1974; Wright et al. 1992). It may well be the most frequent injury pattern in exposed patients with severe respiratory impairment. b) Interstitial disease was present in four cases (Patients A, B, C, and E), characterized by a generally bronchiolocentric pattern of interstitial inflammation and fibrosis of variable severity. The lungs of these patients contained large amounts of silicates, and three of them showed nanotubes. The peripheral alveolar remodeling and fibrosis could variably be characterized as honeycombing, UIP- or NSIP-like, had some fibroblastic foci, or even resembled hypersensitivity pneumonitis (which was ruled out by pertinent serologies in all cases). Patient E even showed small numbers of poorly organized granulomas in one of the lobes and a mediastinal lymph node. The number of interstitial lymphocytes was variable, and some evidence of bronchiolitis was generally present. The bronchiolocentric characteristics seem consistent with an inhalation-related etiology. c) We had only one patient with the principal diagnosis of granulomatous disease (Patient G), although Patient E also revealed some small scattered granulomas. In the intervening years, this patient has developed evidence of interstitial disease, in the form of a miliary pattern of minute nodules, but no signs of sarcoidosis, including a negative Kveim test. Mineralogic studies may reflect sampling heterogeneity. Granulomatous disease has been previously described after WTC exposure (Izbicki et al. 2007; Safirstein et al. 2003).

Determination of the epidemiology of interstitial lung diseases and exact incidence rates remains challenging. Although several studies investigating incidence rates in interstitial lung disease have been conducted, uncertainty exists because of their reliance on databases and diagnoses codes (Coultas et al. 1994; Gribbin et al. 2006; Raghu et al. 2006). Difficulties because of changes in disease definitions and histopathologic classifications have further complicated the issue, as well as differences in epidemiologic design of studies, limited large-scale epidemiologic data for specific types of interstitial lung disease, and registration bias (Demedts et al. 2001).

We have not sought to describe the incidence of interstitial disease in the WTC MMTP patients. The sudden onset of six biopsies of our cases in January 2007 and the unexpected end of such cases, in October of the same year, is likely a reflection of the availability of federal funding for comprehensive treatment for WTC responders, which only first became available in the MMTP in November 2006. Patients may have sought care outside of the MMTP in earlier years, and some patients might have been too ill to visit the MMTP. Given these limitations, these cases are not an accurate representation of the time of onset. Whether they are an accurate representation of the total burden in this cohort remains to be seen, but it is unlikely, given the fact that physicians, including pulmonologists, have different criteria with regard to ordering diagnostic tests such as CT scans, diffusion measurements, and VATS biopsies.

Electron microscopic mineralogic analysis revealed CNT in WTC responders with extensive interstitial/parenchymal abnormalities (three of four patients) and in one of two patients with small airway disease, but not in the patient with nonnecrotizing granulomas. Nanomaterials such as CNT have many potential applications in electronics, computer, and aerospace industries because of their desirable electrical, mechanical, and thermal properties (Lam et al. 2004). CNT are hydrophobic carbon cylinders with a diameter of a few to 200 nm and variable length depending on their degree of aggregation (Florito et al. 2006; Li et al. 2007; Mercer et al. 2008; Murr et al. 2005; Shvedova et al. 2008a; Tian et al. 2006). There are single-walled carbon nanotubes (SWCNT), consisting of one such cylinder, and multiwalled carbon nanotubes (MWCNT), composed of cylinders concentrically stacked and in the form of ropes with a common long axis. They can either be commercially synthesized or can develop spontaneously over flames and high temperatures in the presence of carbon and a metal catalyst.

CNT of commercial origin, common now, would not have been present in substantial numbers in the WTC complex before the disaster in 2001. However, the high temperatures generated during the WTC disaster as a result of the combustion of fuel in the presence of carbon and metals would have been sufficient to locally generate large numbers of CNT. This scenario could have caused the generation of CNT that we have noted in the dust samples and in the lung biopsy specimens.

Experimental studies, both in vitro and in animals, show the potential toxicity of some types of CNT (Florito et al. 2006; Li et al. 2007; Mercer et al. 2008; Murr et al. 2005; Shvedova et al. 2008a, 2008b; Tian et al. 2006). They are believed to be proinflammatory, fibrosing, and capable of inducing granulomas when inhaled in mouse models (Mercer et al. 2008). Shvedova et al. (2008b) observed that inhalation of SWCNT resulted in a 4-fold increase in fibrosis, along with collagen deposition, in the peribronchial and interstitial areas in the lungs of mice when compared with exposure by aspiration of SWCNT. CNT introduced into the abdominal cavity of mice can cause asbestos-like pathogenicity (Poland et al. 2008). Very recently, the Berkeley group has shown that oxidative stress can be induced by zero-valent iron (Fe) nanoparticles and Fe(II) in human bronchial epithelial cells (Keenan el al. 2009), which may contribute to the chain reaction of oxidative damages.

There is evidence that CNT may contribute to granuloma formation, although this may depend on the type of CNT present. In a study by Lam et al. (2004), granuloma formation and interstitial inflammation was observed in four of nine mice who were administered a high dose (0.5 mg) of CNT compared with mice administered a low dose (0.1 mg) of CNT. Similar findings were also observed in a study conducted by Muller et al. (2005), where granulomas, completely or partially blocking the bronchial lumen, were observed in the bronchi of rats 60 days after intratracheal instillation of MWCNT. Additionally, ground MWCNT, administered to rats via intratracheal instillation, were better dispersed in the parenchyma and also produced granulomas in the interstitial tissue (Muller et al. 2005). Shvedova et al. (2005) showed that epitheloid granulomas, which were rapid, progressive, and dose dependent, were observed at sites where SWCNT aggregates were deposited after pharyngeal aspiration of SWCNT in mice. Furthermore, diffuse interstitial fibrosis with alveolar thickening was also observed in areas distant from the site where SWCNT aggregates were deposited (Shvedova et al. 2005). In most of these studies, carbon black particles used as reference particles did not produce any granulomas (Lam et al. 2004; Muller et al. 2005; Shvedova et al. 2005). However, CNT were not found in Patient G who had granulomas, perhaps because of inadequate sampling of the tissue. Mediastinal granulomas were described in prior studies by other WTC-exposed individuals (Izbicki et al. 2007).

Aluminum and magnesium silicates were present in six of seven patients in higher amounts than normally seen in construction workers. Although these may be related to construction material, some of them were in an unusual platy configuration rarely found in our COC from construction workers. Markedly higher levels (> 100,000/g) of aluminum silicate and magnesium silicate were found in Patients C–F.

The etiology of the conditions described in WTC responders cannot be fully elucidated, because our analysis does not include toxic soluble gases. In this case report we identified the presence of unexpected CNT, silicates, and other elements, but it remains unclear whether any of these compounds may have caused the lung pathology. The combination of compounds may have increased the likelihood that individuals would develop pulmonary impairment. Further surveillance of individuals with these exposures should provide us with additional answers.

The finding of carbon nanotubes in four of seven WTC patients in concentrations ranging from 11,000/g to 230,000/g of wet weight and in four of seven dust samples collected from the WTC site, although unique and important, cannot be construed as evidence for WTC exposure. Likewise, their absence should not be used as evidence of lack of exposure. A retrospective check of specimens in unrelated asbestos cases evaluated over the past 20 years was negative for CNT. Recently, however, small numbers of CNT have been identified in control specimens from the tri-state area (New York, New Jersey, Connecticut) at minimal concentrations (Gordon R, unpublished data). These might originate in the combustion engines of automobiles (Lam et al. 2006).

The predominant finding of interstitial lung disease on pathology and presence of similar materials in most of the mineralogic samples including CNT and platy silicates suggests that WTC exposure may have contributed to the development of lung disease. Furthermore, there is consistency of the histologic patterns with those seen in inhalation-related injury. The frequency of small airways disease described in epidemiologic studies of WTC responders and the slow and relatively mild progression and long survival of the patients, which now appear to be exceeding survival of some with idiopathic interstitial lung disease, suggest that exposures at the WTC site might have caused these findings. Further follow-up of WTC-exposed individuals is critical to determine the overall health effects related to WTC exposure.