Everall, NC

In continuous-flow toxicity tests on brown trout, the 96 h LCeo for zinc was substantially reduced in artificial soft water (1.07, 2.31,1.41,0.60,0.05, and 0.22 mg Znl ) compared with mains hard water (2.02, 3.20, 2.69, 0.64, 1,00 and 0.46 mg Zn 1) at nominal pH values of 4,5,6,7,8 and 9 respectively. The reduced zinc toxicity in hard water was attributed to an ameliorative effect by calcium at high hardness. pH influenced metal toxicity in the pH range 5-7 with increased toxicity of dissolved zinc correlated with rising pH and the highest toxicities of zinc were recorded in the pH range 8 - 9 in the presence of metal complexes. With acute exposure to zinc over the pH range 4-9, fish survival was dependent upon the deleterious effects of the metal on branchial respiratory and ionoregulatory mechanisms. 

  

In radioisotopic studies, fish were exposed in hard and soft water to 0. 05 mg Zn 1 with 10 jaCi added and zinc influx and efflux was monitored over 48 h. In both hard and soft water an initial fast uptake component over some 0 - 5 h was followed by a second slower component of 5 - 48 h. In hard water both the fast and slow influx rates of total zinc (52 and 1.2 μg h kg) were significantly less (P ( 0.01) than the corresponding fluxes in soft water (121 and 2.3 μg h kg ) . Tissue zinc concentrations reflected both the uptake and excretion rates of the metal in hard and soft water fish. 

  

The ameliorative effects of water hardness appear to act by reducing zinc uptake in high calcium waters due to reduced branchial surface permeability and by enhancing excretion. In contrast pH modifies zinc toxicity by altering the chemical form of the metal

The effects of water hardness and pH upon toxoicity of zinc to the brown trout Salmo trutta L

Abstract

Similar works

Full text

Available Versions

Nottingham Trent Institutional Repository (IRep)