In 2005, Health Canada's Pest Management Regulatory Agency (PMRA) and the U.S. Environmental Protection Agency's Office of Pesticide Programs (EPA-OPP) jointly released a spreadsheet to calculate statistically-based legal limits for pesticide residues, referred to as maximum residue levels (MRLs) in Canada or tolerances in the U.S.. The North American Free Trade Agreement (NAFTA) MRL Working Group developed this spreadsheet to better coordinate the pesticide regulatory framework among NAFTA partners with the goal of minimizing trade barriers of pesticide-treated commodities between the United States and Canada.
In addition to the NAFTA MRL spreadsheet, referred to as the "NAFTA MRL Calculator", the NAFTA MRL Working Group also released an accompanying guidance document containing instructions for using the spreadsheet, and a "white paper" that provided additional technical and explanatory material for the guidance document. A slightly modified version of the NAFTA MRL Calculator was released in 2008.
In 2008, the Organisation for Economic Co-operation and Development (OECD) formed an analogous Working Group with a similar goal of developing a statistically-based method for calculating MRLs using a spreadsheet, which would assist in coordinating the pesticide regulatory framework among OECD partners. The members of this OECD MRL Working Group include some of the same individuals from the NAFTA MRL Work Group, but also representatives from other international agencies responsible for regulating pesticides and other stakeholder OECD members.
In November 2010, the OECD MRL Working Group finalized its MRL calculator, user guide, and supporting "white paper". The Working Group on Pesticides (WGP) officially approved the MRL spreadsheet and supporting documents, and in March 2010 they became available for download from the OECD website.
Both Health Canada-PMRA and EPA-OPP agree that the OECD MRL Calculator provides statistically robust and scientifically-defensible MRLs. As of April 1, 2011, Canada and the United States joined the other OECD member countries in their use of the OECD MRL Calculator to calculate pesticide MRLs. The OECD MRL Calculator will replace and supersede the NAFTA MRL Calculator. The OECD MRL Calculator and supporting documents also are available for download from the EPA Pesticides website.