Fox, P.R., Puschner, B., and Ebel, J.G. (2008). Assessment of Acute Injuries, Exposure to Environmental Toxins, and Five-Year Health Surveillance of New York Police Department Working Dogs Following the September 11, 2001, World Trade Center Terrorist Attack. (Abstract only.) Journal of the American Veterinary Association. 233(1):48-59.
The authors studied the long-term health effects of 27 dogs that helped with relief efforts at the World Trade Center site after the 9/11 terrorist attack. They found that while nearly 63% suffered health disorders in the first week, "only mild and infrequent health conditions" occurred in the five-year period.