Natural and commercial dissolved organic matter protects against the physiological effects of a combined cadmium and copper exposure on rainbow trout(Oncorhynchus mykiss)

Environmentally realistic concentrations of a natural dissolved organic mat ter (DOM) (8 mg C/L as dissolved organic carbon (DOC)) protected against th e acute respiratory and ionoregulatory effects of 0.2 mu M Cd and 0.8 mu M Cu on rainbow trout (Oncorhynchus mykiss). The protection afforded by low n atural DOC was the same as that afforded by similar or higher concentration s of commercial DOG. Trout exposed to the metals alone experienced large de creases in arterial Pot, increases in arterial P-CO2, increases in blood la ctate, decreases in plasma concentrations of Cl, and developed pronounced h aemoconcentration. There were no deleterious effects of 31 mg C/L commercia l DOC on any measured aspect of trout physiology except for an increase in plasma Cl, which was probably due to elevated aqueous Cl concentrations ass ociated with the DOM addition. No concentration of DOC used in the present study prevented Cd from being bound by trout gills, and some of these fish showed hypocalcemia; however, Cu was kept off the gills of trout exposed to metals plus DOM. Computer modelling using metal-gill binding constants sim ulated well the accumulation of Cd and the lack of Cu accumulation by trout gills in the presence of DOM.