Chapter 3
Photochemical Processes in the Euphotic Zone of
Sea Water: Progress and Problems
E. Pelizzetti . P. Calza
3.1
Introduction
There has been an increasing interest in the photochemical processes that occur in
the surface waters of the oceans and other natural waters. The sunlight aquatic environment, which includes the euphotic zone, aerosols, the surface microlayer and the
sediment-water interface in shallow areas, is a likely site for photochemical transformations of dissolved and particulate non-living matter, both organic and inorganic
(Zafiriou et al. 1984). The most obvious evidence of photoreaction in aquatic environments is the widespread presence of phytoplankton and other light-dependent underwater plants, and much effort has been directed towards the mathematical description of photosynthesis by freshwater as well as marine phytoplankton.
In addition to being naturally significant, the zone of surface waters is used as the
receptacle for many liquid, solid and airborne wastes. This surface layer is also essential for recreation, transportation, material exchanges, and biology; these processes
are more intense in this area than they are in deeper waters. A significant number of
experimental studies recently have appeared that provide some efforts to understand
the processes occurring, the substrates involved, their reaction rates, products and
associated effects on the environment.
Considerably less attention has been paid to possible environmental significance
of photoreactions of xenobiotics in water. As interest in transformation of xenobiotics
in the environment has increased in recent years, so have efforts to quantitatively describe the dynamics of such transformations. The chemical structures of the chemical pollutants present in the water are often very different from those of natural substances and it may take therefore considerable periods of time to degrade these structures by biological pathways. Thus, even when part of the solar energy will be stored
in biological systems present in aquatic environment, this energy will not be readily
available for the breakdown of man -made pollutants. Although there are cases in which
a clear distinction between biological breakdown and abiotic degradation cannot be
made, there are cases where both these degradation types are complementary. Early
studies (Leighton 1961; Howard 1975) paved the way for a quantitative understanding
of photochemical smog formation and other atmospheric photoreactions.
Recent studies of the dynamics of photoreactions in water have demonstrated that
adsorption of sunlight by xenobiotics can energize transformations that are surprisingly rapid. Direct photolysis half-lives of minutes or seconds have been observed in
water for xenobiotics having a wide variety of molecular structures, such as nitrosamines, polycyclic aromatic compounds, various chlorinated organic compounds and
metal complexes (Zepp 1980). Evidence has also begun to emerge that the natural com-
Photochemical Processes in the Euphotic Zone of
Sea Water: Progress and Problems
E. Pelizzetti . P. Calza
3.1
Introduction
There has been an increasing interest in the photochemical processes that occur in
the surface waters of the oceans and other natural waters. The sunlight aquatic environment, which includes the euphotic zone, aerosols, the surface microlayer and the
sediment-water interface in shallow areas, is a likely site for photochemical transformations of dissolved and particulate non-living matter, both organic and inorganic
(Zafiriou et al. 1984). The most obvious evidence of photoreaction in aquatic environments is the widespread presence of phytoplankton and other light-dependent underwater plants, and much effort has been directed towards the mathematical description of photosynthesis by freshwater as well as marine phytoplankton.
In addition to being naturally significant, the zone of surface waters is used as the
receptacle for many liquid, solid and airborne wastes. This surface layer is also essential for recreation, transportation, material exchanges, and biology; these processes
are more intense in this area than they are in deeper waters. A significant number of
experimental studies recently have appeared that provide some efforts to understand
the processes occurring, the substrates involved, their reaction rates, products and
associated effects on the environment.
Considerably less attention has been paid to possible environmental significance
of photoreactions of xenobiotics in water. As interest in transformation of xenobiotics
in the environment has increased in recent years, so have efforts to quantitatively describe the dynamics of such transformations. The chemical structures of the chemical pollutants present in the water are often very different from those of natural substances and it may take therefore considerable periods of time to degrade these structures by biological pathways. Thus, even when part of the solar energy will be stored
in biological systems present in aquatic environment, this energy will not be readily
available for the breakdown of man -made pollutants. Although there are cases in which
a clear distinction between biological breakdown and abiotic degradation cannot be
made, there are cases where both these degradation types are complementary. Early
studies (Leighton 1961; Howard 1975) paved the way for a quantitative understanding
of photochemical smog formation and other atmospheric photoreactions.
Recent studies of the dynamics of photoreactions in water have demonstrated that
adsorption of sunlight by xenobiotics can energize transformations that are surprisingly rapid. Direct photolysis half-lives of minutes or seconds have been observed in
water for xenobiotics having a wide variety of molecular structures, such as nitrosamines, polycyclic aromatic compounds, various chlorinated organic compounds and
metal complexes (Zepp 1980). Evidence has also begun to emerge that the natural com-