A debate of more than five years could stretch even longer with Wednesday’s call for a health study on the proposed Keystone XL oil pipeline from Canada.

Two Democratic senators – Barbara Boxer of California and Sheldon Whitehouse of Rhode Island – urged Secretary of State John Kerry to examine higher rates of cancer and other illness reported in places impacted by the “tar sands” oil from northern Alberta.

Their letter to Kerry sought to further delay the project that has support from Republicans, some Democrats, the oil industry and labor unions. A Pew Research Center poll in September showed 65% of respondents favored