As stated earlier, the survey of the Irish Sea required analysis of 8,000 fish samples over a period of 15 months, so it was highly desirable to use a relatively simple digestion procedure
involving one reagent, and the simplest possible glassware. Extensive analysis of biological samples at Liverpool University indicated that simple digestion by nitric acid was adequate, without the prolonged refluxing and volume reduction practised by other workers using just nitric acid, (Ministry of Agriculture, Food and Fisheries – MAFF internal method).This method, described in Table 1 and now in routine use, has been tested by spiking samples with mercury and by inter-laboratory cross-calibration studies. A long sequence of quality control, reference tissue analyses was used to confirm its reliability (see Table 4).