Marine Chemistry, 37 (1992) 239-255 239 Elsevier Science Publishers B.V., Amsterdam Determination of dissolved nucleic acids in seawater by the fluorescence dye, ethidium bromide Seiji Sakano and Akiyoshi Kamatani 1 Tokyo Universityof Fisheries, Konan 4, Minato-ku, Tokyo 108, Japan (Received 7 February 1991; revision accepted 30 August 1991 ) ABSTRACT Sakano, S. and Kamatani, A., 1992. Determination of dissolved nucleic acids in seawater by the flu- orescence dye, ethidium bromide. Mar. Chem., 37: 239-255. A new method for the determination of dissolved double-stranded deoxyribonucleic acid (DNA) and ribonucleicacid (RNA) in seawater was developed, evaluated and used to study the fates of these nucleic acids in marine ecosystems. These nucleic acids, which were pre-concentrated on a hydroxy- apatite column, were determined fluorometrically by the use of ethidium bromide dye, which binds specifically to the double-stranded polynucleotide. No dissolved organic matter coexisting in the pre- concentrated sample solution interfered in the analysis of DNA and RNA. Column recoveries of DNA and RNA in a sample volume of up to 11 were 93% and 97%, respectively, and 90% of both at 51. The detection limits of DNA and RNA concentrated from a 5 1sample by this fluorometric method were 0.6 and 1.1/tg 1-1, respectively. The concentration of dissolved nucleic acids in the waters from Tokyo Bay and Sagami Bay showed great variation in space and time. DNA ranged from 1 to 32 #g 1-1, and RNA from below the detection limit to 34/tg 1- I. The total amount of phosphorus in nucleic acids was an important fraction (12.9 + 8.2%) of the dissolved organic phosphorus (DOP) and showed a good correlation with DOP. INTRODUCTION Phosphorus is an essential element in the structure of nucleic acids, phos- pholipids and ATP (adenosine triphosphate), and it has an active role in many life processes such as protein synthesis, genetic coding, photosynthesis, nitro- gen fixation and innumerable other metabolic pathways. Most of the organic phosphorus compounds in living tissues are readily excreted and mineralized, but a portion is metabolized and eliminated as extracellular materials; this fraction remains in seawater as dissolved organic phosphorus (DOP). The DOP content varies from below the detection limit (0.5 #g 1-1 ) to 52/tg 1-1; IAuthor to whom correspondence should be addressed. 0304-4203/92/$05.00 © 1992 Elsevier Science Publishers B.V. All rights reserved.