ENVIRONMENTAL SCIENTIFIC EVALUATIION OF PHOTOCHEMICAL REACTIONS IN NATURAL WATER

太阳光引起的水生光化学反应是水中溶解有机物(DOM)的一种自然去除过程。然而，关于DOM的主要成分腐殖质(HS)的光降解机理及其对有机污染物光降解的影响，人们知之甚少。我们在琵琶湖和入湖河流进行了实地观察，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HS分布的贡献，(B)壬基酚和其他污染物的光降解，(C)湖中农药的光降解和分布，(D)废水处理厂废水中DOM的光降解，以及(E)光反应和DOM对湖中铁分布的影响。结果表明：(1)琵琶湖表层水体中HS的光化学降解导致其浓度低于表层。(2)HS的荧光基团对光降解的敏感度高于发色团，碳键的光降解发生的时间较晚。这些降解反应符合一级反应动力学，反应速率常数在0.01~0.04之间。(3)水中的壬基酚和磷酸酯在光反应中很容易降解，受HS的影响。(4)耐受光反应的农药能长期存活，全年都能在琵琶湖水中检测到它们。(5)污水处理厂出水中的HS发出强烈的荧光。它们很容易被光降解，表明光反应有可能应用于废水的高级处理。(6)铁等重金属与DOM形成络合物，容易发生光化学变化。

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.