Measurements must also be comparable over time so that long term impact studies provide meaningful data from which policy makers can make decisions about the regulation limits. Discrepancy between laboratories Currently, the quality of the analyses of environmental samples, such as fresh water sediments, is the subject of much discussion. Everyone realises the importance of obtaining reliable and comparable results, but achieving harmonised results is a different matter. In recent studies, a number of laboratories were given a sample on which to perform their usual measurements. The measurements that need to be performed are detailed and involve many steps.
Natural materials consist of many different chemicals, many of which are very similar.
This makes measuring the levels of PCB and PAH contamination less straightforward than one might think and there are many opportunities for errors to be made. To improve the quality of measurements, reference materials are often required. Some of these include pure calibration PCBs and PAHs which laboratories can use to check the accuracy of the technique they are using to perform the final detection step. Reference materials that are similar to the actual samples being tested are also required. These are required to test that laboratories are performing all steps of the measurement method correctly.