Potash mining effluents induce moderate effects on histopathological and physiological endpoints of adult zebrafish (Danio rerio)

• Published in: The Science of the total environment 2019-12, Vol.694, p.133471, Article 133471
• Main Authors: Irob, Katja, Wagler, Marit, Baberschke, Nora, Meinelt, Thomas, Kloas, Werner
• Format: Article
• Language: English
• Subjects: Animals; Complex Mixtures - toxicity; Freshwater fish; Ion imbalances; Osmoregulatory stress; Potash mining effluents; Secondary river salinisation; Toxicity Tests; Water Pollutants, Chemical - toxicity; Zebrafish - physiology
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2019.07.277

Stress in fish can be caused by a variety of factors and has the potential to evoke stress responses leading to a reduction of physical condition and of health. The river Werra (Germany) presents a severe case of secondary salinisation caused by potash mining activities. The model organism Danio rerio was exposed to different ion-concentrations depicting current (HT) and future (LT) threshold values of the Werra, as well as to solutions with single-exceeding ions (Mg2+ + K+ (KMg), Mg2+ (Mg) and K+ (K)). After a six-week exposure period, cortisol levels, growth and weight were measured, gills and gonads were histologically analysed and mRNA expression of follicle stimulating hormone (FSH), luteinising hormone (LH), growth hormone (GH) and prolactin (PRL) were determined. Cortisol was still elevated in fish in the HT and K group, indicating moderate stress. However, gills revealed structural changes in zebrafish in all exposure groups, size of oocytes differed in the LT and K group, male FSH mRNA levels were elevated in the HT and LT group whereas PRL mRNA levels were lower in HT and LT for both, male and female fish. These results suggest that ion-stress induces moderate effects on a variety of biological parameters that mainly serve to adapt to elevated ion concentrations. For these reasons current and even future thresholds should be reconsidered, including thresholds for total as well as single ion concentrations. Future research looking at the effects on local fish species is needed, along with regular and long-term monitoring of environmental conditions, species abundance and diversity. [Display omitted] •Cortisol levels of HT (current threshold) + K (high K+ conc.) still elevated after six weeks → chronic ion-stress•Structural changes of the gill as a protective response mechanism → osmoregulatory stress•Oocytes in LT (future thresholds) were bigger in size and more mature → stress inhibited release of eggs•Prolactin mRNA levels were decreased in HT + LT → adaption to high ion conditions