Costs of chronic waterborne zinc exposure and the consequences of zinc acclimation on the gill/zinc interactions of rainbow trout in hard and soft water

• Published in: Environmental toxicology and chemistry 1999-05, Vol.18 (5), p.1014-1025
• Main Authors: Alsop, D.H, McGeer, J.C, McDonald, D.G, Wood, C.M
• Format: Article
• Language: English
• Subjects: Acclimation; Acute/chronic toxicity; Agnatha. Pisces; animal health; Animal, plant and microbial ecology; Applied ecology; aquatic organisms; Biological and medical sciences; Ecotoxicology, biological effects of pollution; Effects of pollution and side effects of pesticides on vertebrates; environmental degradation; Freshwater; Fundamental and applied biological sciences. Psychology; Gill metal-binding model; Oncorhynchus mykiss; pollution; Rainbow trout; veterinary medicine; waste management; Zinc
• ISSN: 0730-7268; 1552-8618
• DOI: 10.1002/etc.5620180529

Juvenile rainbow trout were exposed to zinc in both moderately hard water (hardness = 120 mg CaCO(3)/L, pH = 8.0, Zn = 150 micrograms/L or 450 micrograms/L) and soft water (hardness = 20 mg CaCO(3)/L, pH = 7.2, Zn = 50 micrograms/L or 120 micrograms/L) for 30 d. Only the 450 micrograms/L zinc-exposed fish experienced significant mortality (24% in the first 2 d). Zinc exposure caused no effect on growth rate, but growth affected tissue zinc levels. Whole body zinc levels were elevated, but gills and liver showed no consistent increases relative to controls over the 30 d. Therefore, tissue zinc residues were not a good indicator of chronic zinc exposure. After the 30-d exposure, physiological function tests were performed. Zinc was 5.4 times more toxic in soft water (control 96 h LC50s in hard and soft water were 869 micrograms/L and 162 micrograms/L, respectively). All zinc-exposed trout had acclimated to the metal, as seen by an increase in the LC50 of 2.2 to 3.9 times over that seen in control fish. Physiological costs related to acclimation appeared to be few. Zinc exposure had no effect on whole body Ca(2+) or Na(+) levels, on resting or routine metabolic rates, or on fixed velocity sprint performance. However, critical swimming speed (U(Crit)) was significantly reduced in zinc-exposed fish, an effect that persisted in zinc-free water. Using radioisotopic techniques to distinguish new zinc incorporation, the gills were found to possess two zinc pools: a fast turnover pool (T(1/2) = 3-4 h) and a slow turnover pool (T(1/2)) = days to months). The fast pool was much larger in soft water than in hard water, but at most it accounted for < 3.5% of the zinc content of the gills. The size of the slow pool was unknown, but its loading rate was faster in soft water. Chronic zinc exposure was found to increase the size of the fast pool and to increase the loading rate of the slow pool.