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 matter (DOM) (8 mg C/L as dissolved organic carbon (DOC)) protected against the acute respiratory and ionoregulatory effects of 0.2 µM Cd and 0.8 µM Cu on rainbow trout (Oncorhynchus mykiss). The protection afforded by low natural DOC was the same as that afforded by similar or higher concentrations of commercial DOC. Trout exposed to the metals alone experienced large decreases in arterial PO2, increases in arterial PCO2, increases in blood lactate, decreases in plasma concentrations of Cl, and developed pronounced haemoconcentration. There were no deleterious effects of 31 mg C/L commercial DOC on any measured aspect of trout physiology except for an increase in plasma Cl, which was probably due to elevated aqueous Cl concentrations associated 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 simulated well the accumulation of Cd and the lack of Cu accumulation by trout gills in the presence of DOM.