Determining Detection Limits for Environmental Analyses

In March 2003, the U.S. Environmental Protection Agency (EPA) proposed revisions for the method detection limit (MDL) procedure in 40 CFR Part 136 Appendix B1. Although the MDL procedure was established for determining the sensitivity of analytical test methods under EPA's Clean Water Act (CWA), the procedure has become the de facto industry standard for determining detection capability for environmental test methods. EPA's re-assessment of the existing MDL procedure and the proposed revisions that resulted from the evaluation were performed “pursuant to a settlement agreement with the Alliance of Automobile Manufacturers, et al.” The lawsuit challenged the validity of the “the general procedures used to establish the method detection limit.” Unfortunately, as stated by, the American Council of Independent Laboratories (ACIL), “The proposed approach is fundamentally an extension of the previous application and remains a poor method to determine a laboratory's method sensitivity”2. Some salient problems with the existing as well as the proposed MDL procedure are discussed below: