The Environmental Protection Agency failed to consistently disclose health risks, including possible cancer risks, to research study participants who were exposed to dangerous pollutants, an agency watchdog report has found. An E.P.A. inspector general’s report released Wednesday said that when the agency exposed 81 people to soot and diesel exhaust emissions in studies in 2010 and 2011, the risks were not always consistently represented and did not include information on cancer risks associated with long-term exposure. The E.P.A. said risks associated with cancer in the study, which only briefly exposed participants to the pollutants, were so minimal that they were not included on consent forms obtained from the subjects.