The toxicity of zinc to the brown trout Salmo trutta L.: modification by external calcium and magnesium

Simmons, JF, 1989. The toxicity of zinc to the brown trout Salmo trutta L.: modification by external calcium and magnesium. PhD, Nottingham Trent University.

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Abstract

The toxicity of zinc, an important pollutant of aquatic ecosystems, was investigated to provide information concerning the mechanisms of toxicity and the modification of toxicity by external calcium and magnesium.

The acute toxicity of zinc was considerably lower in hard than in soft water. Increases in external calcium concentration resulted in progressive reductions of toxicity. The composition of the acclimation medium before zinc exposure had little influence on toxicity. Toxicity was governed mainly by the composition of the exposure medium.

Radioisotope studies at a sublethal zinc concentration demonstrated that both external calcium and magnesium reduced zinc influx. External calcium was of major importance and exerted greatest effect at a concentration of 0.15 mM. Acclimation medium composition had less influence than exposure medium composition in modifying zinc influx. Most zinc was accumulated by the gills, plasma, kidney and liver. The influence of external divalent ion concentration on zinc influx was reflected in radiozinc appearance in these tissues.

Hypocalcaemia in fish exposed to zinc at the lowest external calcium concentration suggested a disruption of calcium balance. This disruption was investigated using radiocalcium. Acclimation to low external calcium stimulated calcium influx. Apparent saturation of the uptake mechanism was taken as evidence for active calcium transport. External zinc caused a strong dose-dependent inhibition of calcium influx. This persisted immediately after the removal of zinc but had ceased after a further 48 h. Calcium efflux was unaffected by zinc.

External lanthanum inhibited both calcium and zinc influx suggesting a common apical membrane uptake route for these two metals.

The results are reviewed and a model proposed whereby external zinc is considered to inhibit calcium influx by blocking calcium transport across the basolateral membrane. The possibility of other heavy metals, in particular cadmium, exerting their sublethal toxic action through similar means is also discussed.

Item Type:	Thesis
Creators:	Simmons, J.F.
Date:	1989
ISBN:	9781369314014
Identifiers:	Number Type PQ10183120 Other
Rights:	This copy of the thesis has been supplied on condition that anyone who consults it is understood to recognise that its copyright rests with the author and that no quotation from the thesis and no information derived from it may be published without the author's prior written consent.
Divisions:	Schools > School of Science and Technology
Record created by:	Jeremy Silvester
Date Added:	18 Sep 2020 07:50
Last Modified:	19 Jul 2023 10:25
URI:	https://irep.ntu.ac.uk/id/eprint/40783

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