US EPA 1999: United States Environmental Protection Agency. Method 1668, Revision A: Chlorinated Biphenyl Congeners in Water, Soil, Sediment, and Tissue by HRGC/HRMS, United States Environmental Protection Agency, Office of Water, EPA No. EPA-821-R-00-002, December 1999. [Accessed 2012 November 7]. Available from: http://nepis.epa.gov