UV induzierte toxische Effekte von gelösten Huminstoffen auf Süßwasserorganismen

在淡水中，溶解有机碳（DOC）的显色性UV/ vis吸收化合物主要以腐殖质（HS）为代表。通过吸收太阳辐射，HS就像防晒霜一样，保护水生生物免受有害的紫外线辐射。这种光吸收的一个后果是HS的光解降解，导致低分子物质的释放，这些物质可能作为异养细菌的潜在营养物质。同时产生瞬时活性氧（ROS），可被水或HS分子本身淬灭。一些研究指出，紫外线照射对腐殖质水体中的水生生物产生不利影响，提示ROS引起光毒性作用。我们想在异养细菌、藻类和水蚤的暴露实验中研究HS的光毒性潜能。潜在的光毒性将与光致净ros相关，并将通过电子顺磁共振（EPR）、自旋阱和激光光谱方法进行量化。此外，对于水蚤，利用自旋标签，用epr层析成像研究HS与光激发之间的直接相互作用。该项目的目的是弄清楚在什么条件下和在什么营养水平上，HS的光毒性可能对生态系统的结构有贡献。EPR层析成像方法将首次适用于淡水生物。

In freshwater, the chromophoric UV/VIS-absorbing compounds of dissolved organic carbon (DOC) are mostly represented by humic substances (HS). By absorption of solar radiation, HS act like sun screens and protect aquatic organisms against harmful UV radiation. One consequence of this light absorption is the photolytical degradation of HS leading to the release of low molecular substances which may serve as potential nutrients for heterotrophic bacteria. At the same time, transient reactive oxygen species (ROS) are generated, which can be quenched by water or HS molecules itself. Some studies point to UV irradiation induced adverse effects on aquatic organisms in humic water, suggesting phototoxic effects caused by ROS. We want to investigate the phototoxic potential of HS in exposure experiments with heterotrophic bacteria, algae, and daphnids. The potential phototoxicity will be correlated with the photoinduced net-ROS, which will be quantified by electron paramagnetic resonance (EPR) using spin traps and laser spectroscopic methods. Furthermore, with daphnids the direct interaction between HS and light excitation shall be studied by EPR-tomography using spinlabels. The aim of this project is to figure out under which conditions and at which trophic level phototoxicity of HS may contribute to the structure of the ecosystem. EPR tomographic methods will be adapted to freshwater organisms for the first time.