The study found that exposures lasting one, three, and in some cases up to twelve months had effects on only a few of the many health markers tested; exposures will continue for the lifetime of the rats.

The few effects that were reported for the rats were mild hyperplasia (cell proliferation) in the lungs and slightly reduced lung function, and were most consistent with exposure to nitrogen oxides in the engine exhaust, which are being further reduced under 2010 US EPA standards now in effect.

These results are expected to play an important role in upcoming risk reviews by international and US agencies of older and new technology diesel engines, including a review of the carcinogenicity of diesel exhaust in June, 2012 by the International Agency for Research on Cancer (IARC) in Lyon, France.

We will be communicating these results to IARC, the US National Toxicology Program, and US EPA in order to ensure that the significant improvements in emissions and effects for these new diesel technologies are considered and compared with the data on older engines when those agencies reach their conclusions.

—Dan Greenbaum, President of HEI

The study—HEI Research Report 166: Advanced Collaborative Emissions Study (ACES) Subchronic Exposure Results: Biologic Responses in Rats and Mice and Assessment of Genotoxicity—was conducted by Drs. Jacob D. McDonald of the Lovelace Respiratory Research Institute, Albuquerque, New Mexico; Jeffrey C. Bemis of Litron Laboratories, Rochester, New York, and Lance M. Hallberg of the University of Texas Medical Branch, Galveston, and their colleagues. Their work was overseen by independent experts on the HEI ACES Oversight Committee, and its comprehensive description of all findings was then subjected to peer review by a separate expert ACES Review Panel who had had no part in the conduct of the study.

Part 1 of the report describes the core inhalation study by Drs. Jake McDonald and Joe Mauderly, with results on general organ toxicity, lung histopathology, pulmonary function, and markers of inflammation and oxidative stress in blood and lung lavage fluid. Parts 2 and 3 describe studies by Drs. Jeffrey Bemis and Lance Hallberg assessing genotoxic endpoints in the exposed rodents.

In their Commentary on the study the review panel concluded:

Overall...these results indicate that rats exposed to one of three levels of DE from a 2007-compliant engine for up to 12 months, for 16 hours per day, 5 days a week, and using a strenuous operating cycle that was more realistic than cycles used in previous studies, show few exposure-related effects.

The effects that were observed were limited to the respiratory tract, were mild, and were consistent with previous findings in lungs after long-term exposure to NO₂—a major component of the exposure atmosphere. Rats will continue to be exposed for at least 24 months in this study, possibly longer, depending on their survival rates. McDonald and colleagues will submit a future report with complete results from the 12- and 24- month exposures, which will provide a further comprehensive review of the cancer and non-cancer effects of long-term exposure to DE emitted by a 2007-compliant engine.

The panel did note some limitations to the interpretation of the study: the study design did not include a simultaneous comparison with emissions from an older engine built before the 2007 regulations. Noting that including such a “positive control” would have increased the complexity and cost of the study very substantially and would have been logistically impossible, the panel nonetheless thought that a side-by-side evaluation of emissions from an older engine could have enhanced the study.

The panel also identified some other limitations to the study—the lack of some positive assay controls (to identify that an assay was sensitive enough to detect changes) and the use of certain statistical approaches (combining sexes and performing a trend analysis rather than conducting a standard three-way ANOVA). In addition, the panel thought that the histopathology data could have been expanded by more detailed quantitative measures.

ACES is a comprehensive effort, supported by a wide range of public and private entities (The US Department of Energy, US Environmental Protection Agency, California Air Resources Board, Engine Manufacturers Association, American Petroleum Institute, and manufacturers of emission control equipment) and conducted under the independent oversight of HEI and the Coordinating Research Council (an Atlanta-based non-profit specializing in emissions characterization).

The overall goals of ACES are 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.

ACES was conceived in 2005, and has 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. A report from this phase found substantial reductions in particulate matter and other pollutants in the emissions from 2007 engines.

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

• Phase 3: Health effects assessment in rodents using one selected 2007-compliant heavy-duty diesel engine system—i.e., the basis of the new report. 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).

In the health studies, rats will continue to be exposed for their lifetime. Results and Commentary on another ancillary study, assessing the effects of subchronic exposure to diesel exhaust on vascular markers, will be published during the fall of 2012. The final results from the animal bioassay and all the ancillary studies will be published at the end of the program, when the animals have been exposed to diesel exhaust for 24 or 30 months. The final results and commentary are expected to be published near the end of 2013 or in early 2014.

Resources

• Advanced Collaborative Emissions Study (ACES). 2012. Advanced Collaborative Emissions Study (ACES) Subchronic Exposure Results: Biologic Responses in Rats and Mice and Assessment of Genotoxicity. Research Report 166. Health Effects Institute, Boston, MA.