Chemical persistence is the most central property with respect to Sweden’s environmental goal of a contaminant-free environment. If we release persistent chemicals to the environment, future generations will have difficulty achieving this goal. Hence it is very important that we evaluate chemical persistence well. Currently chemical regulations recommend laboratory simulation tests to evaluate persistence (e.g., OECD 309 for water). However, we are lacking evidence that laboratory test results can be extrapolated to the environment. As noted in a recent review of persistence assessment “The relationship between chemical behaviour in laboratory tests and in the environment is often unclear”. Bluntly expressed, the tools that we are using may not be good predictors of environmental persistence. In this project we will exploit a novel benchmarking method to measure persistence in lakes. We will combine this method with cutting edge analytical techniques for sensitive multi-target analysis to quantify the persistence of a wide range of existing chemicals in a reference lake. We will measure the persistence of the same chemicals using the OECD 309 laboratory simulation test. Comparing the two datasets will allow us to calibrate OECD 309 against the persistence in the reference lake, showing whether lab-to-field extrapolation of persistence is possible.