Characterization of UV-absorbing organic matter in Lake Biwa using high-performance liquid chromatography/mass spectrometry

Dissolved organic matter (DOM) is a major portion of organic matter in the aquatic environment and operationally defined as the organic materials that pass through a filter with pore size 0.1-0.7 f.!m. DOM has various important roles in the environment. lt is one of the important carbon reservoirs in the global carbon cycle (HEDGES 1992), a main energy source of aquatic heterotrophic bacteria (AZAM et al. 1983), and it controls the attenuation of ultraviolet radiation in water (WILLIAMSON & ZAGARESE 1994). Recently, the solar ultraviolet radiation reaching the earth's surface has increased due to anthropogenic diminishing of the ozone layer in the stratosphere (FARMAN et al. 1985). Solar ultraviolet radiation has harmful effects not only on terrestrial plants and animals but also on aquatic organisms (HoDOKI & WATANABE 1998). Recent studies have suggested that UV-B radiation (280-320 nm) alters the balance between the biological processes producing organic materials and chemical and microbial processes degrading them (ZEPP et al. 1998). Observations in aquatic ecosystems have shown that, in stratified waters, exposure of solar UV radiation promotes net decreases of chromophoric dissolved organic matter (CDOM) and results in increases o f UV-B penetration into the water colurnn (HADER et al. 1998). The distribution and characteristics of UV absorbing organic matter such as CDOM in aquatic environments must be known to understand its influence on the aquatic ecosystems; however, information about the chemical structure or origin of it is limited. In this study, our aim was to characterize UV-absorbing organic matter in Lake Biwa using high-performance liquid chromatography (HPLC) with reverse phase octadecy silica column and investigate the mass distribution ofthe separated organic molecules using electrospray ionization mass spectrometry (ESI-MS).