Histopathologic, Histochemical and Dissolved Oxygen Tolerance Studies on the Minnow (Phoxinus Phoxinus), in Acute and Subacute Heavy Metal Toxicity

Abstract

Using the minnow (Phoxinus phoxinus) as a test animal experiments were conducted to investigate the toxicity of copper, lead, nickel and zinc. The emphasis of the investigation was upon subacute (chronic) toxicity although experiments were performed to assess the relative acute toxicity of the four metals. In acute toxicity the metals could be arranged thus: Cu > Zn> Pb> Ni, in order of decreasing toxicity (5.1). Fish were found to react more slowly to lethal concentrations of copper than of the other metals (5.2). Acutely toxic concentrations of the metals were considered to kill the fish by direct non-specific gill damage resulting in tissue hypoxia (7) and large amounts of the metals were always detectable in the gills (8). Normally acutely toxic concentrations of the metals were found to be non-toxic when tested in sewage effluents (6). Fish were exposed to subacute concentrations of the metals for periods in excess of a hundred days. Histopathologic studies revealed little or no gill damage but the internal organs were affected especially after copper exposures (9). Histochemical and analytical studies revealed a continued uptake and storage of copper in the internal organs (10,12). Lead and nickel were accumulated to a lesser extent. Zinc was also detected in the fish but there was no continued accumulation. Enzyme histochemical studies revealed some changes in the enzyme activity in the internal organs of exposed fish (13). The subacute toxic effect of all metals tested was reduced when they were present in sewage effluents (11). Survival rates at low oxygen levels in the presence of subacute concentrations of the metals were similar to those for control fish above 2 mg/1. oxygen, but below this more fish died (14.1). Exposure to subacute concentrations of zinc and copper for fifty days reduced the ability of fish to survive at low oxygen levels (14.2).