Health effects research and regulation of diesel exhaust: an historical overview focused on lung cancer risk

Abstract

The mutagenicity of organic solvent extracts from diesel exhaust particulate (DEP), first noted more than 55 years ago, initiated an avalanche of diesel exhaust (DE) health effects research that now totals more than 6000 published studies. Despite an extensive body of results, scientific debate continues regarding the nature of the lung cancer risk posed by inhalation of occupational and environmental DE, with much of the debate focused on DEP. Decades of scientific scrutiny and increasingly stringent regulation have resulted in major advances in diesel engine technologies. The changed particulate matter (PM) emissions in “New Technology Diesel Exhaust (NTDE)” from today's modern low-emission, advanced-technology on-road heavy-duty diesel engines now resemble the PM emissions in contemporary gasoline engine exhaust (GEE) and compressed natural gas engine exhaust more than those in the “traditional diesel exhaust” (TDE) characteristic of older diesel engines. Even with the continued publication of epidemiologic analyses of TDE-exposed populations, this database remains characterized by findings of small increased lung cancer risks and inconsistent evidence of exposure-response trends, both within occupational cohorts and across occupational groups considered to have markedly different exposures (e.g. truckers versus railroad shopworkers versus underground miners). The recently published National Institute for Occupational Safety and Health (NIOSH)-National Cancer Institute (NCI) epidemiologic studies of miners provide some of the strongest findings to date regarding a DE-lung cancer association, but some inconsistent exposure-response findings and possible effects of bias and exposure misclassification raise questions regarding their interpretation. Laboratory animal studies are negative for lung tumors in all species, except for rats under lifetime TDE-exposure conditions with durations and concentrations that lead to'lung overload."The species specificity of the rat lung response to overload, and its occurrence with other particle types, is now well-understood. It is thus generally accepted that the rat bioassay for inhaled particles under conditions of lung overload is not predictive of human lung cancer hazard. Overall, despite an abundance of epidemiologic and experimental data, there remain questions as to whether TDE exposure causes increased lung cancers in humans. An abundance of emissions characterization data, as well as preliminary toxicological data, support NTDE as being toxicologically distinct from TDE. Currently, neither epidemiologic data nor animal bioassay data yet exist that directly bear on NTDE carcinogenic potential. A chronic bioassay of NTDE currently in progress will provide data on whether NTDE poses a carcinogenic hazard, but based on the significant reductions in PM mass emissions and the major changes in PM composition, it has been hypothesized that NTDE has a low carcinogenic potential. When the International Agency for Research on Cancer (IARC) reevaluates DE (along with GEE and ni...

Laccase oxidation and removal of toxicants released during combustion processes

“…More than 5000 different compounds including heterogeneous mixtures of gases, uncondensed vapors and particulate matter containing many different aromatic amines, carbonyls, phenolics, polycyclic aromatic hydrocarbons (PAHs), nitroaromatics, nitroheterocyclics, inorganics, organics, volatile hydrocarbons, metals, aldehydes, ketones, etc. have been identified during combustion processes (Hesterberg et al, 2012;Prasad andBella, 2010 Zhang andTao, 2009;Ravindra et al, 2008;Venkatachari et al, 2007;Donaldson et al, 2005). Common human pathological effects of these toxicants include direct oxidation of biomolecules, generation of free radicals, induction of the inflammatory response system (Kampa and Castanas, 2008) and interference with signaling pathways (Valko et al, 2006;Hesterberg et al, 2012).…”

Exposure to diesel exhaust fumes in the context of exposure to ultrafine particles

“…The diversity of these products is huge, and their estimated number may be as high as several thousand different chemical compounds occurring as gas or in the form of solid particles. The basic gaseous components of exhaust fumes emitted by compression-ignition (diesel) engines are: carbon oxides, nitrogen and its compounds, oxygen, steam, sulfur IJOMEH 2016;29(4) 669 cancer [1,6,13]. In 2012, the International Agency for Research on Cancer (IARC) classified diesel exhaust fumes as carcinogenic to humans (group 1 of IARC classification).…”

The occurrence of polycyclic aromatic hydrocarbons and their derivatives and the proinflammatory potential of fractionated extracts of diesel exhaust and wood smoke particles

“…[5] For both DEPs and WSPs, variations in the organic fraction composition have been reported, depending on the fuel type and combustion conditions. [6,7] Several studies have indicated that the organic fraction of combustion PM is responsible for the toxicological effects. [8][9][10][11][12][13][14][15] We recently compared the potency of native DEPs, their corresponding methanol extracts and residual particles to induce expression of multiple pro-inflammatory linked genes in human bronchial epithelial cells.…”