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 must fulfil certain analytical quality requirements. This may be achieved by participating in interlaboratory comparison exercises (SLP). 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 are 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 anonymously and as a point in the diagrams. Each laboratory’s location in the diagram gives information regarding the type and magnitude of the error. A circle showing the limit of acceptance is given in the plots. Exercise number 57, named 1757, was organised in September - December 2017 with 57 participants, of whom 56 reported results. The "true" values were distributed to all participants on December 8th 2017, to allow laboratories with deviating values the opportunity to start their troubleshooting as soon as possible. 83 % of the results in exercise 1757 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.