The engine was run on a unique and strenuous operating cycle that represented more closely the behavior of modern engines than operating cycles used in older long-term studies of TDE. The emissions were characterized before they reached the animal exposure chambers as well as inside the chambers; in this way, the investigators could assess how the presence of the animals affected the composition of the exposure atmospheres.

In their extensive analysis of the physical and chemical composition of the emissions, McDonald and colleagues found that the most abundant pollutants were carbon dioxide, carbon monoxide, NO, and NO₂. Concentrations of engine-generated PM were very low (<11 μg/m³) at all exposure levels (in the ultrafine range of 20–40 nm in diameter), as were concentrations of sulfur dioxide and semivolatile and volatile organic species. These findings confirm that the concentrations of components of NTDE differ strikingly from those of older engines, in which the concentrations of PM, as well as volatile and PM-associated organic species, are much higher.

—ACES report

In contrast to previous health studies of TDE, the ACES study found that lifetime exposure did not induce tumors or pre-cancerous changes in the lung and did not increase tumors related to NTDE in any other tissue.

A few mild changes were seen in the lungs, consistent with long-term exposure to NO₂, a component of NTDE that has been further substantially reduced in 2010- and later model year engines compliant with US EPA rules.

The ACES results are expected to play an important role in future risk reviews of diesel engines by international and US agencies.

We are already seeing a transition in America’s roads with over 30% of the trucks and buses in use today meeting these new standards and the trend is growing in Europe as well. These results confirm the great strides that government and industry have made to reduce diesel risk—and argue for even greater efforts to accelerate the replacement of older diesel engines.

—Dan Greenbaum, President of HEI

The complete study—HEI Research Report 184: Advanced Collaborative Emissions Study (ACES): Lifetime Cancer and Non-Cancer Assessment in Rats Exposed to New-Technology Diesel Exhaust—comprises four studies conducted as Phase 3B of the multi-part Advanced Collaborative Emissions Study (ACES) program (see below) as well as a review of the work. HEI’s evaluation of the four studies was conducted by a specially convened ACES Review Panel.

The core study was led by Dr. Jacob McDonald, of Lovelace Respiratory Research Institute (LRRI) in Albuquerque, New Mexico, where the exposures were carried out. Other ancillary studies were led by Dr. Jeffrey Bemis, of Litron Laboratories, Rochester, New York; Dr. Lance Hallberg, of the University of Texas Medical Branch, Galveston, Texas; and Dr. Daniel Conklin, of the University of Louisville, Louisville, Kentucky. These ancillary studies evaluated endpoints not examined in the core study.

Their work was overseen by independent experts on the HEI ACES Oversight Committee. A separate Pathology Working Group independently reviewed the biological findings, and the investigators’ comprehensive description of all findings was then subjected to intensive peer review by an expert ACES Review Panel, the members of which had had no part in the conduct of the study.

In their Commentary on the study the Review Panel concluded:

Overall, these results indicate that rats exposed to one of three levels of NTDE from a 2007-compliant engine for up to 30 months, for 16 hours per day, 5 days a week, with use of a strenuous operating cycle that more accurately reflected the real-world operation of a modern engine than cycles used in previous studies, showed few NTDE-exposure-related biologic effects. In contrast to the findings in rats chronically exposed to TDE, there was no induction of tumors or pre-neoplastic changes in the lung and no increase in tumors that were considered to be related to NTDE in any other tissue. The effects that were observed with NTDE were limited to the respiratory tract and were mild and generally seen at only the highest exposure level. These histologic changes in the lungs were consistent with previous findings in rats after long-term exposure to NO₂—a major component of the exposure atmosphere which is being substantially further reduced in 2010-compliant engines.

—ACES Review Panel

ACES background. The Health Effects Institute and the Coordinating Research Council (CRC; a nonprofit organization that directs engineering and environmental studies on the interaction between automotive or other mobility equipment and petroleum products) developed the Advanced Collaborative Emissions Study (ACES) to characterize the emissions and assess the safety of new advanced heavy-duty engine systems and fuels.

Conceived in 2005, ACES consisted of three phases:

• Phase 1: Extensive emissions characterization of four production-ready heavy heavy-duty diesel (HHDD; i.e., gross vehicle weight higher than 33,000 lb) engines equipped with control systems designed to meet the 2007 standards for reduced PM. This phase was conducted at the Southwest Research Institute (SwRI) in 2007 and 2008 and was the basis for selecting one HHDD engine/control system for health testing in Phase 3.

• Phase 2: Extensive emissions characterization of a group of diesel engine and control systems intended for production that met the stringent 2010 standards (including more advanced NO_x controls). This phase was conducted at SwRI in 2012.

• Phase 3: Health effects assessment in rodents using the selected 2007-compliant heavy-duty diesel engine system among the four tested in Phase 1. This phase started in 2008 with the installation of a specially designed emissions-generation and animal-exposure facility at the Lovelace Respiratory Research Institute (LRRI) and was conducted in two parts.

  Phase 3A included setting up the engine, characterizing the engine performance and emissions to make sure it was operating as intended, and generating and characterizing the exposure atmospheres in the animal inhalation chambers at three dilution levels. Phase 3B included a 90-day inhalation study in mice and a lifetime inhalation study in rats with health measurements at several time points.

The overall goals of ACES were to test the emissions of new-technology diesel engines to determine not only whether they are achieving the expected substantial reductions in emissions and health effects, but also whether the new control technologies (that include particle filters and ultra-low-sulfur diesel fuel) are resulting in unintended increases in some components of the emissions. Earlier ACES reports (available at ) found substantial reductions in particulate matter and other pollutants in the emissions from both 2007 and 2010 engines.

These results are impressive for what they can mean for reducing exposure in the US and Europe, but also for the promise they hold in the developing countries of Asia and elsewhere in the world. Countries like China are already moving toward implementing the ultra-low sulfur diesel fuel that is required for these new cleaner technologies.

—Bob O’Keefe, Vice President of HEI and Chair of Clean Air Asia

HEI has funded more than 330 research projects in North America, Europe, Asia, and Latin America, the results of which have informed decisions regarding carbon monoxide, air toxics, nitrogen oxides, diesel exhaust, ozone, particulate matter, and other pollutants. These results have appeared in more than 260 comprehensive reports published by HEI, as well as more than 1,000 articles in the peer-reviewed literature.

HEI sponsors do not participate in the selection, oversight or review of HEI science, and HEI’s reports do not necessarily represent their views.

Resources

• Advanced Collaborative Emissions Study (ACES). 2015. Advanced Collaborative Emissions Study (ACES): Lifetime Cancer and Non-Cancer Assessment in Rats Exposed to New-Technology Diesel Exhaust. Research Report 184. Boston, MA:Health Effects Institute.