The interactions of water hardness and pH with the acute toxicity of zinc to the brown trout, Salmo trutta L.

Abstract

Exposure of brown trout, Safmo frurfa, to zinc under continuous flow conditions over 96 h showed that both water hardness and pH exert major influences on the toxicity of the metal. 96-h LC50 values for total zinc ranged from cO.14mg I-' in alkaline soft water (PH 8; lOmg I-' as CaCO,) to 3.20 mg I-' in acidic hard water @H 5; 204 mg I-' as CaCOJ. A variable reduction in zinc toxicity in hard water compared with soft water over the pH range 4 9 was attributed to high external calcium. Zinc toxicity was positively correlated with decreasing acidity over the pH range 5-7, the metal being most toxic at pH 8-9 where metal complexes predominate. Below pH 5 metal toxicity also increased, irrespective of hardness. Water hardness and pH interacted with zinc toxicity in a complex manner, apparently dependent on physical and chemical transformations of the metal, and as changes in uptake, detoxification and excretion by the fish.

Assessment of the exposure of two fish species to metals pollution in the Ogun river catchments, Ketu, Lagos, Nigeria

“…Of concern however, is the role played by Ca (generally regarded as essential) in the bioavailability of metals. The toxicity and bioavailability of Cd and Zn are known to decrease as water hardness increases (Sanders et al 1999;Everall et al 1989). This hardness effect is thought to result from the competition of Cd and Zn with Ca and Mg ions for binding sites (van Aardt and Booysen 2004; Sanders et al 1999).…”

Concentrations of zinc in Barbus marequensis from the lower Olifants River, Mpumalanga, South Africa

“…Chronic sub-lethal zinc concentrations can also delay or inhibit the growth, sexual maturity and reproduction of the fish (Pierson, 1981;Brungs, 1969). Sublethal effects on fish due to zinc exposure have been shown to occur over the range of approximately 30-200 pg 1-l Zn (Brungs, 1969;Eaton, 1973), while the 96-hour LC50 value can range from less than 0.14 mg 1-t Zn (Everall et al, 1989) to 41 mg 1-l Zn (Pickering & Henderson, 1966), depending on the fish species and the physio-chemical characteristics (for example: water hardness, pH, temperature) of the water (Wang, 1987).…”

Growth, biochemical variables, and zinc bioaccumulation in Nile tilapia, Oreochromis niloticus (L.) as affected by water-born zinc toxicity and exposure period

“…Zinc is one of the most common contaminants in aquatic systems and is associated with urban runoff, soil erosion, industrial discharges, pharmaceuticals, pesticides and a variety of other activities and sources (Schmitt 2004;Bowen et al 2006). The danger of Zn is aggravated by its almost indefinite persistence in the environment because it cannot be destroyed biologically and is only transformed from one oxidation state or organic complex to another (Everall et al 1989).…”