Environmental monitoring needs to be based on a quality assurance of the analytical steps. A broad number of steps have to be considered in environmental analytical chemistry, but sampling and sample-handling could be the most important if the data have to be created by different laboratories in a large geographical area. The lecture will present some examples of local and regional monitoring programmes where the quality assessment of sampling and sample-handling is the key problem.

It is also very important to be able to differentiate between systematic and random errors. In an environmental monitoring programme, systematic errors can be accepted if well identified and under control but random errors have to be totally excluded because they introduce a lot of hidden bias.

The parameters of a reliable data are its "applicability" given by the sensitivity and the resolution and its "reliability" given by the accuracy and the precision. Applicability is determined by the knowledge and the experience of the scientists and the quality of the equipment. Concerning the reliability, exactitude is obtained working with standard material and precision is assessed while implementing intercalibration exercises. In the case of a monitoring programme, precision can be considered as the critical parameter; it is assessed by the repeatability and the reproducibility the measurement.

The example of the large network implemented in Latin America, named RAQAL, will be presented. It has environmental laboratories from 13 countries: Cuba, Mexico, Guatemala, El Salvador, Honduras, Nicaragua, Costa Rica, Panama, Colombia, Brazil, Uruguay, Chile and Peru. RAQAL is not only dedicated to quality assessment, but it also organizes regular meetings where the members can exchange their experiences and invite internationally recognized scientists and it is implementing sub-continental monitoring programmes. The development of such a dynamic in East Asia will be proposed.