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Hedenborg, Amanda, 2016. Zinc tolerance of freshwater diatoms isolated from sites with zinc pollution; and pH effect on zinc toxicity. First cycle, G2E. Uppsala: SLU, Dept. of Aquatic Sciences and Assessment



The aim with this study was to observe the zinc (Zn), tolerance for different strains isolated from sites with Zn pollution and to observe if lower pH decreases the Zn toxicity. Another aim was to see if malformations could be an indicator for Zn pollution.

Zn is found naturally in the bedrock, sediment and waterbodies. Mining is one activity which had led to high values of Zn > 60 mg Zn l⁻¹ in some areas in Sweden. Today diatoms are used as indicators for organic pollution, the amount of nutrients and also for the pH condition. Due to problem with high values of metals, the diatom indicator has been developed further to also involve detection of metal pollution. Zn can affect diatoms growth rate, photosynthesis, cell division as well as their silica transport and thereby leading to malformed diatoms. In this study Zn toxicity was observed as decrease in number of cells, degree of malformations and as a decrease in the photosystem II efficiency.

The hypotheses for the study are the following: the tested strains isolated from polluted sites would have higher tolerance to Zn than diatoms isolated from non- polluted sites, Zn would be less toxic in pH 5 compared to pH 7 and malformations could indicate Zn pollution. The observed results confirmed the hypothesis regarding the tested strains having higher tolerance towards Zn than diatoms from non- polluted sites, by the approximated EC ₅₀ values of 0,91; 1,35 and 2,27 mg Zn l⁻¹ respectively. However, the observed results for the hypothesis regarding the lower pH decreasing the Zn toxicity, were contradictory. The hypothesis was verified by higher EC ₅₀ values for the cell growth and fluorescence in pH 5 than in pH 7 for the short term experiments. Whereas the hypothesis was rejected by a higher degree of malformation in pH 5 than in pH 7 and by a higher cell growth in pH 7 than in pH 5 in the long term experiment. The different results regarding the pH effect on Zn toxicity might be explained by the different exposure times, probably the low pH is causing more stress to the cells pre-grown in pH 7 than it relieves the Zn toxicity. The long term experiment displayed significant more malformations in the higher Zn concentrations in comparison to the controls under both pH 5 and 7, and verified that malformations could detect high Zn concentrations and indicate Zn pollution.

Main title:Zinc tolerance of freshwater diatoms isolated from sites with zinc pollution; and pH effect on zinc toxicity
Authors:Hedenborg, Amanda
Supervisor:Kahlert, Maria and Goncalves, Sara
Examiner:Fölster, Jens
Volume/Sequential designation:UNSPECIFIED
Year of Publication:2016
Level and depth descriptor:First cycle, G2E
Student's programme affiliation:NK001 Biology and Environmental Science - Bachelor's Programme, 180.0hp
Supervising department:(NL, NJ) > Dept. of Aquatic Sciences and Assessment
Keywords:freshwater diatoms, indicator for metal pollution, zinc pollution, pH, malformations
Permanent URL:
Subject. Use of subject categories until 2023-04-30.:Aquatic ecology
Water resources and management
Additional Information:Errata (added 2016-11-18) Page 3 Abstract. Old text: the approximated EC ₅₀ values of 0,91; 1,35 and 2,27 μg Zn l⁻¹. New text: the approximated EC ₅₀ values of 0,91; 1,35 and 2,27 mg Zn l⁻¹.
Deposited On:08 Jul 2016 07:53
Metadata Last Modified:18 Nov 2016 14:24

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