Publication

Summary

As part of the control with industrial effluents, the Norwegian Environment Agency and the Secretary of County Governor for the Environment have instructed a series of industrial companies to periodically report the composition of their effluents. The companies have to fulfil certain analytical quality requirements. This may be achieved by participating in interlaboratory comparison exercises (SLP). In accordance with an agreement between NIVA and the Norwegian Environment Agency, NIVA organises two exercises yearly. The samples distributed represent industrial effluent water. The interlaboratory comparison exercises cover the most common analytical variables included in the Norwegian Environment Agency’s control programme for industrial effluents; pH, suspended matter (dry substance and its residue on ignition), chemical oxygen demand, biochemical oxygen demand, total organic carbon, total phosphorus, total nitrogen, aluminium, lead, iron, cadmium, cobalt, copper, chromium, manganese, nickel, zinc, antimony and arsenic. All samples are synthetic and stable. Each set of samples includes four samples, grouped in two concentration levels. The “true” values of the substance in the samples are most often set as the calculated values. The limits of acceptance are most often set to ±10% and ±15% for the “high” and “low” concentration levels respectively, while ±0.2 pH units is always used as the limit of acceptance for the pH measurement (table 1). The Youden method for statistical handling of the data is employed, and the results are presented graphically in Youden plots (figure 1-42). Each participant’s pair of results is represented as a point in the diagrams. Each laboratory’s location in the diagram gives information regarding the kind and magnitude of the error. A circle showing the limit of acceptance is given in the plots. Exercise number 55, named 1655, was organised in September - December 2016 with 59 participants. The "true" values were distributed to all participants on December 1st 2016, to allow laboratories with deviating values the opportunity to start their troubleshooting as soon as possible. Many of the analyses were conducted following the Norwegian Standard (NS) or other documented methods (table B1). For the determination of total phosphorus and total nitrogen, some laboratories employed simplified methods. Employing more sophisticated methods would probably, especially for phosphorus, increase the quality of the analyses. 86 % of the results in exercise 1655 were acceptable, which is comparable to results from the previous exercises (table 1). The practice of continuous quality assurance [Hovind 2006 et. al] is a prerequisite to be able to evaluate methods and routines. Standard reference materials (SRMs) are recommended for controlling the results and methods, but in lack of SRMs, samples from previous exercises may be used.