Epsilon Archive for Student Projects

Abstract

The current index, IPS, developed for benthic diatoms and used for assigning the ecological status of streams in Sweden reflects on levels of nutrients and organic pollution. Metals are not considered in the index, which leads to the risk that metal contaminated streams can be assigned a high ecological status based on this index. Thus, an index that take into consideration the impact of metals in streams should be developed. In order to develop such an index, knowledge about if factors such as temperature and phosphorus affects metal toxicity to benthic diatoms could be useful. The aim of this study was to investigate if temperature and phosphorus affects the toxicity of Zn to benthic diatoms. Several laboratory experiments were performed with diatoms isolated from Swedish streams. The hypothesis was that temperatures above 20 °C would elevate toxic effects caused by Zn, which was partly confirmed. High temperatures (30-32 °C) caused a decrease in number of cells and in the maximum efficiency of the photosystem II in the highest concentration of Zn tested. The values of the approximate EC50 for each temperature and the amount of fluorescence per cells did however not show that temperature impact the toxicity of Zn. Thus, conclusively not all parameters investigated declared that temperature impacts the toxicity of Zn, but since some of them did, it cannot be said that temperature does not impact the toxicity of Zn. The hypothesis for the impact of phosphorus on Zn toxicity was that a higher concentration of phosphorus would increase tolerance to Zn and consequently lower concentrations of phosphorus was thought to increase the toxicity of Zn. The phosphorus effects were partly in-line with the hypothesis. The highest concentration of phosphorus tested caused a decrease in toxicity, detected as a higher median value of EC50 and as a higher amount of fluorescence in the highest concentration of Zn for most strains in one experiment. However, the lower amount of phosphorus only increased the toxicity, detected as a lower amount of fluorescence, in the highest concentration of Zn tested in two of the strains in one experiment. The results regarding the impact of phosphorus on Zn toxicity was not consistent in the experiments performed. However this study indicated that phosphorus and temperature could impact the toxicity of Zn. Therefore, in order to develop an index that reflect on the levels of metals more studies should be done to establish if temperature and phosphorus in fact impact the toxicity of Zn.