A Critical Assessment of Studies on the Carcinogenic Potential of Diesel Exhaust

International Truck and Engine Corporation, Warrenville, Illinois 60555, USA.
Critical Reviews in Toxicology (Impact Factor: 5.1). 11/2006; 36(9):727-76. DOI: 10.1080/10408440600908821
Source: PubMed


After decades of research involving numerous epidemiologic studies and extensive investigations in laboratory animals, a causal relationship between diesel exhaust (DE) exposure and lung cancer has not been conclusively demonstrated. Epidemiologic studies of the transportation industry (trucking, busing, and railroad) show a small elevation in lung cancer incidence (relative risks [RRs] generally below 1.5), but a dose response for DE is lacking. The studies are also limited by a lack of quantitative concurrent exposure data and inadequate or lack of controls for potential confounders, particularly tobacco smoking. Furthermore, prior to dieselization, similar elevations in lung cancer incidence have been reported for truck drivers, and in-cab diesel particulate matter (DPM) exposures of truck drivers were comparable to ambient highway exposures. Taken together, these findings suggest that an unidentified occupational agent or lifestyle factor might be responsible for the low elevations in lung cancer reported in the transportation studies. In contrast, underground miners, many of whom experience the highest occupational DPM exposures, generally do not show elevations in lung cancer. Laboratory studies must be interpreted with caution with respect to predicting the carcinogenic potential of DE in humans. Tumors observed in rats following lifetime chronic inhalation of very high levels of DPM may be attributed to species-specific overload mechanisms that lack relevance to humans. Increased tumor incidence was not observed in other species (hamsters or mice) exposed to DPM at very high levels or in rats exposed at lower levels (</=2000 mug/m3). Although DPM contains mutagens, mutagenicity studies in which cells were exposed to concentrated extracts of DPM also have limited application to human risk assessment, because such extracts can be obtained from DPM only by using strong organic solvents, agitation, and heat. Most studies have shown that whole DPM itself is not mutagenic because the adsorbed organic compounds are minimally bioavailable in aqueous-based fluids. In the past two decades, dramatic changes in diesel engine technology (e.g., low-sulfur fuel and exhaust after-treatment) have resulted in >99% reduction in DPM and other quantitative and qualitative changes in the chemical and physical characteristics of diesel exhaust. Thus, the current database, which is focused almost entirely on the potential health effects of traditional diesel exhaust (TDE), has only limited utility in assessing the potential health risks of new-technology diesel exhaust (NTDE). To overcome some of the limitations of the historical epidemiologic database on TDE and to gain further insights into the potential health effects of NTDE, new studies are underway and more studies are planned.

Download full-text


Available from: Thomas Slavin, May 16, 2014
  • Source
    • "We found decreased CC16 and lung function in workers handling nanomaterials in this follow-up study. Cardiovascular injury combined with pulmonary injury were detected in this follow-up study, and health effects induced by engineered nanoparticles in animal inhalation studies also included cardiovascular effects (Borm et al., 2006; Hesterberg et al., 2006, 2009, 2010; Hubbs et al., 2011; Oberdörster et al., 2005; Stern & McNeil, 2008). Human experimental inhalation studies found that ultrafine particles or diesel exhaust particles induced cardiovascular damage. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Abstract The aim of this study was to identify the health hazards and possible exposure surveillance markers of workers exposed to nanoparticles during manufacturing and application in comparison to a group of unexposed workers. For this longitudinal study, we recruited 158 nanomaterial-handling workers and 104 non-exposed workers from 14 manufacturing plants in Taiwan (baseline). Among them, 124 nanomaterial-handling workers and 77 unexposed workers were monitored 6 months later. We investigated pulmonary and cardiovascular disease markers, inflammation and oxidative stress markers, antioxidant enzymes and genotoxicity markers. Antioxidant enzymes (superoxide dismutase, glutathione peroxidase) and cardiovascular markers (vascular cell adhesion molecule, paraoxonase) were significantly associated with nanomaterial-handling during the 6-month follow-up period. In addition, the small airway damage marker (Clara cell protein 16) and lung function test parameters were also significantly associated with handling nanomaterials. The study markers and lung function tests are possible markers that could be useful for surveillance of nanomaterial-handling workers.
    Full-text · Article · Dec 2013 · Nanotoxicology
  • Source
    • "Polycyclic aromatic hydrocarbons (PAHs) among the urban air toxics are of global concern due to their multiple effects on human population. Attention is more importantly on PAHs bound to PM 2.5 and ultrafine fraction of the airborne particulates that are reportedly known for their higher health risk [1] [2]. About 80% of particulate matter in urban environment belongs to the size class of fine (PM 2.5) and ultrafine (PM 0.1) particles [3]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Coimbatore is one of the fast growing industrial cities of Southern India with an urban population of 1.9 million. This study attempts to evaluate the trends of airborne fine particulates (PM 2.5) and polyaromatic hydrocarbons (PAH) on them. The PM 2.5 mass was collected in polytetra fluoroethylene filters using fine particulate sampler at monthly intervals during March 2009 to February 2010. PAHs were extracted from PM 2.5 and estimated by high-performance liquid chromatography. It is alarming to note that PM 2.5 values ranged between 27.85 and 165.75 μg/m(3) and exceeded the air quality standards in many sampling events. The sum of 9 PAHs bound to PM 2.5 in a single sampling event ranged from 4.1 to 1632.3 ng/m(3). PAH diagnostic ratios and principal component analysis results revealed vehicular emissions and diesel-powered generators as predominant sources of PAH in Coimbatore.
    Full-text · Article · Apr 2012 · The Scientific World Journal
  • Source
    • "Ward et al. (2010) noted the role of epidemiological evidence in potentially upgrading the IARC classification of diesel exhaust and some 19 other agents. Multiple reviewers (Mauderly and Garshick, 2009; HEI, 1995, 1999, 2002; Hesterberg et al., 2006, 2012b; Gamble, 2010; Gamble et al., 2012) have reviewed and commented on the strengths and weaknesses of the various epidemiological studies. The HEI report made specific note of the absence of a well-accepted marker of exposure to diesel exhaust, what we now call TDE. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Diesel engines, a special type of internal combustion engine, use heat of compression, rather than electric spark, to ignite hydrocarbon fuels injected into the combustion chamber. Diesel engines have high thermal efficiency and thus, high fuel efficiency. They are widely used in commerce prompting continuous improvement in diesel engines and fuels. Concern for health effects from exposure to diesel exhaust arose in the mid-1900s and stimulated development of emissions regulations and research to improve the technology and characterize potential health hazards. This included epidemiological, controlled human exposure, laboratory animal and mechanistic studies to evaluate potential hazards of whole diesel exhaust. The International Agency for Research on Cancer (1989) classified whole diesel exhaust as - "probably carcinogenic to humans". This classification stimulated even more stringent regulations for particulate matter that required further technological developments. These included improved engine control, improved fuel injection system, enhanced exhaust cooling, use of ultra low sulfur fuel, wall-flow high-efficiency exhaust particulate filters, exhaust catalysts, and crankcase ventilation filtration. The composition of New Technology Diesel Exhaust (NTDE) is qualitatively different and the concentrations of particulate constituents are more than 90% lower than for Traditional Diesel Exhaust (TDE). We recommend that future reviews of carcinogenic hazards of diesel exhaust evaluate NTDE separately from TDE.
    Full-text · Article · Apr 2012 · Regulatory Toxicology and Pharmacology
Show more