Relationship between Growth of Marbled Flounder (Pleuronectes yokohamae) and Cs Concentration in Their Muscle Determined by ICP-MS

Abstract

For the purpose of marine environmental radioactivity monitoring, stable Cs and 137Cs concentrations were obtained from 214 marbled flounder (Pleuronectes yokohamae) samples collected from off the coast of Ibaraki prefecture in Japan in 2005 and 2006. Prior to the investigation, an analytical method for the determination of Cs in muscle of marbled flounder samples by inductively coupled plasma mass spectrometry (ICP-MS) was seriously considered from the view point of sample preparation (wet way) to a Cs measurement. Since major problems in determining Cs by the ICP-MS is the interference of matrix materials and molecular ions on Cs peak area (m/z 133), a known amount of In (m/z 115) was added to the sample solutions as an internal standard. To check the accuracy of the determination, duplication analysis and standard reference materials were used. Analytical results of Cs in muscles samples by ICP-MS agreed well with duplicated samples, and standard reference materials. The standard length and body weight were obtained from a total of 214 flounder samples. The stable Cs, stable K and 137Cs concentrations in muscle were determined by ICP-MS, flame photometry and radiochemical analysis, respectively. The mean standard length correlates closely with the mean body weight. The stable Cs concentration was in proportion to the body weight, also, the 137Cs concentration correlated closely with the stable Cs concentration in muscle. On the other hand, a stable K concentration was found to be uniform, and unrelated with 137Cs and stable Cs concentrations. The specific activities, the ratio of 137Cs/stable Cs in muscle, was found to be 5.5∼6.7 with an average of 6.2±0.35 (SD) among five different size groups of the standard length of marbled flounder samples. From these results, ICP-MS provided useful tools for the determination of a trace amount of Cs in muscle samples, combined with wet way pretreatment techniques. In addition, marbled flounder proved to be a useful species for comparing the radioactivity of fishes in coastal seas around Japan with each other in the environmental radioactivity monitoring program.