Copper accumulation on gills of fathead minnows: Influence of water hardness, complexation and pH of the gill micro‐environment

Abstract

Water pH in the gill micro‐environment of adult fathead minnows (Pimephales promelas Rafinesque) was measured by means of opercular catheters and latex masks. Synthetic soft water of pH <5.7 was rendered more basic as it passed over the gills and water of pH >5.7 was made more acidic, so that pH of the gill micro‐environment stayed at approximately 5.4 to 5.9 over the inspired pH range 4.8 to 6.3. Copper would therefore be >99% Cu2+ at the gills. To measure Cu accumulation on gills, the target organ for Cu toxicity, adult fathead minnows were exposed for 2 to 3 h to 16 μg/L Cu in synthetic soft water (Ca2+ and Na+ approximately 50 μeq/L) at pH 4.8 and 6.3. Gill Cu concentrations were about 1.7 μg Cu/g wet tissue for the inspired pH 4.8 and 6.3 exposures. Added Ca2+ of 2,100 or 4,000 μeq/L reduced gill Cu accumulation during exposures at pH 4.8 but not at pH 6.3. EDTA eliminated Cu deposition at both pH 4.8 and pH 6.3 when equimolar with Cu, but reduced Cu deposition (by 50%) when half equimolar only in the pH 4.8 exposures. These results can be explained by Ca2+ and H+ competition with Cu for gill binding sites and by complexation of Cu by EDTA. Added CaCO3 did not reduce gill Cu, although both competition by Ca2+ and complexation by CO2−3 were expected. Water chemistry calculations suggested that because little CO2−3 is available at pH < 7, CO2−3 from CaCO3 is less likely to affect Cu deposition on fish gills than is Ca2+ from CaCO3.

The Bioavailability and Toxicity of Aluminum in Aquatic Environments

“…Mechanisms of the respiratory effects of Al have been slower to be elucidated, and consensus has not necessarily been reached. Playle and Wood (1989a), Lin and Randall (1990), and Playle et al (1992) showed that soft, acidic water (~pH<6) is made more basic as it passes over the gills of rainbow trout and fathead minnows (Pimephales promelas), primarily due to NH 3 release at the gills. Conversely, basic water is made more acidic as it passes over the gills, due to CO 2 release at the gills ( Figure 8A).…”

Interactions between copper and cadmium modify metal organ distribution in mature tilapia, Oreochromis mossambicus

“…Exposure to low Cd concentrations resulted in an unexpectedly high increase in metal concentration in the gills. However, the free available ionic metal concentration is not necessarily equivalent to the total water metal concentration to which the gill is exposed (Playle et al, 1992), since: (i) the pH at the gill surface is lower than the water, due to local release of carbon dioxide, and this facilitates the release of metal ions from complexes (Cusimano et al, 1986), and (ii) the amount of mucus on the gill surface increases during metal exposure (Handy and Eddy, 1991), which may contribute to higher metal concentrations at the gill surface (Reid and McDonald, 1991). Both phenomena might be relatively more important at low-water metal concentrations.…”

Measuring the bioavailable/toxic concentration of copper in natural water by using anodic stripping voltammetry and Vibrio-qinghaiensis sp.Nov.-Q67 bioassay

“…water hardness), and does not explain the competition of experimental metal ion with other cations. 7 Building on that concept, forming biotic-ligand model (BLM), a recently surface-interaction model of metal binding to fish gill simultaneously incorporates relative of metal speciation with its toxicity and competition between experimental metal ion and other cations. 8,9 Thus, adopting BLM could help predict acute toxicity of Cu to fish on a mechanistic basis and in various conditions of water hardness.…”