ENVIRONMENTAL SCIENTIFIC EVALUATIION OF PHOTOCHEMICAL REACTIONS IN NATURAL WATER

光化学反应是水体中溶解性有机物（DOM）的自然去除过程。然而，作为DOM主要组成部分的腐殖物质（HS）的光降解机理及其对有机污染物光降解的影响却知之甚少。我们在琵琶湖和流入的河流中进行了实地观察，并进行了实验室实验，以澄清以下几点;（a）光化学反应对琵琶湖中HS分布的影响，（B）壬基酚和其他污染物的光降解，（c）农药在湖中的光降解和分布，（d）废水处理厂流出物中DOM的光降解，（e）光反应和DOM对铁在湖泊中分布的影响。(1)HS的光化学降解导致其在琵琶湖表层水的浓度低于深层。(2)HS的荧光团对光降解的敏感性高于发色团，碳键的光降解发生较晚。这些降解反应进行的一级反应动力学与反应速率常数范围从0.01到0.04。(3)壬基酚和磷酸酯类化合物在水中易发生光降解，且受HS的影响。(4)抗光反应的农药可以长时间存活，因此全年都可以在琵琶湖水中检测到。(5)污水处理厂排出的污水中的HS会发出强烈的荧光。它们很容易被光降解，显示了光反应可应用于高等级废水处理的可能性。(6)重金属如铁与DOM形成复合物，这可能对光化学变化敏感。

Aquatic photochemical reactions caused by sunlight are important as a natural removal process for dissolved organic matter (DOM) in water. Little is known, however, about photo-degradation mechanism of humic substances (HS), a major constituent of DOM, and its influence on the photo-degradation of organic pollutants. We conducted field observations in Lake Biwa and inflowing rivers and made laboratory experiments to clarify following points;(a)contribution of photochemical reactions to the distribution of HS in Lake Biwa,(b)photo-degradation of nonyl phenols and other pollutants, (c) photo-degradation and distribution of pesticides in the lake, (d) photo-degradation of DOM in effluent from the waste-water treatment plants, and (e) influence of photo-reactions and DOM on the distribution of iron in the lake.Throughout the present study, we obtained following results.(1) Photochemical degradation of HS results in their lower concentrations at the surface water layer in Lake Biwa as compared to deeper layers.(2) The fluorophore of HS is of higher sensitivity to photo-degradation than chromophore, and photo-degradation of carbon bond take places later. These degradation reactions proceed in the first-order reaction kinetics with reaction rate constants ranging from 0.01 to 0.04.(3) Nonyl phenols and phosphate-esters in water are easily degradable on photo-reaction which is influenced by HS.(4) The pesticides being resistant to photo-reaction can survive for long time, and they are thus detected in Lake Biwa water throughout the whole year.(5) HS in the effluent from waste-water treatment plants emits strong fluorescence. They are easily photo-degraded, showing a possibility that photoreactions can be applicable to high-grade treatment of waste water.(6) Heavy metals like iron form complexes with DOM, which can be susceptible to the photochemical alteration.