Differences in Accumulation Pattern of Organochlorine Compounds in Masu Salmon between Fluvial and Sea-Run Forms
Mayuko Oka, Takaomi Arai, and Nobuyuki Miyazaki
Masu salmon Oncorhynchus masou masou select one of two life histories after a year of life in the river: the sea-run form or the fluvial form (Kubo 1980). Since the masu salmon is semelparous, the sea-run form returns to the river for spawning after a year of life in the ocean. Marine organisms, such as masu salmon, that feed at higher trophic levels will have higher concentrations of organic pollutants due to bioaccumulation. Many of the masu salmon carcasses will be left on the river bottom after their spawning migration. Recently, these contaminated carcasses were of concern in transferring contaminants to the river sediments (Ewald et al. 1998; Krümmel et al. 2003), as well as transporting marine-origin nutrients. Pollution of the river sediments from masu salmon carcasses may lead to serious secondary pollution to the other organisms in the river. We determined the accumulation of organochlorine compounds in muscle and liver tissue of fluvial and sea-run masu salmon to understand the differences in contaminant accumulation between the two types of life styles. We also examined the possible source of their pollution.
Thirteen samples of fluvial masu salmon were collected by fishing from the Kogawa and Kumano rivers, located in Iwate Prefecture, northern Japan, and 10 samples of the sea-run masu salmon were collected by fixed fishing net from Otsuchi Bay in Iwate Prefecture. The pollutants analyzed were hexachlorocyclohexane, hexachlorobiphenyl (HCB), dieldrin, chlordane, DDT (dichlorodiphenyltrichloroethane), heptachlor, and mirex. Each 5-g sample was homogenized and extracted with 1:1 hexane–acetone solvent using the accelerated solvent extractor Dionex ASE 200. Cleanup preparation was done with gel permeation chromatography, Florisil column chromatography, and silica-gel column chromatography. Identification and quantification were done by gas chromatography- negative chemical ionization mass spectrometry (Agilent 5973N).