Copper ionized from salts occurs in natural waters only in trace amounts up to 0.05 mg/L. Higher levels would probably indicate pollution.
The chloride, nitrate and sulfate of divalent copper are highly soluble in water, but the carbonate, hydroxide, oxide and sulfide are not. Therefore, cupric ions introduced into natural waters at a pH of 7 or above will quickly precipitate as the hydroxide or as basic copper carbonate.
As a result, copper ions are not likely to be found in natural waters or in ground water. Copper is found in traces in all plant and animal life and is believed to be essential for nutrition. The physiological function of copper appears to be involved in the metabolism of iron for the utilization of iron by blood forming organs.
The toxicity of copper to aquatic organisms varies significantly, not only with the species, but also with the physical and chemical characteristics of the water such as its temperature, hardness, turbidity and carbon dioxide content.
In hard water, the toxicity of copper salts is reduced by precipitation of copper carbonate or other insoluble compounds. Copper concentrations as low as 0.1 to .5 mg/L have been reported toxic to bacteria and other microorganisms.
Copper has a tendency to act synergistically with several other elements or compounds. For instance, copper acts synergistically with chlorine together to increase the toxicity to fish. The sulfates of copper and zinc and of copper and cadmium are synergistic also in their toxic effect on fish.
Synergism has been noted between copper and mercury and between copper and chloro-organic compounds. Experiments with rainbow trout in soft and hard waters showed synergism at higher concentrations in soft water although the threshold concentrations for the mixture of copper and zinc was about the same that would be expected on the assumption that there was no synergism.
In hard water, no synergism between copper and zinc was evident.
Lead is found in some natural waters in solution as much as 0.4 to 0.8 mg/L where mountain limestone and galena are found.
Lead is not among the metals considered essential to the nutrition of animals or human beings. Lead may enter the body through food, air and tobacco smoke as well as from water or other beverages. Consequently, the total intake of lead must be considered when setting toxic limits.
The bacterial decomposition of organic matter is inhibited by 0.1 to 0.5 mg/L of lead. The toxic concentrations of lead for aerobic bacteria are reported to be 1.0 mg/L.
The effects of small concentrations of heavy metals, particularly lead upon fish, have been studied. Such studies indicate that in water containing lead salts, a film of coagulated mucus forms first over the gills then over the whole body of the fish, probably as a result of a reaction between lead and an organic constituent of mucus. The death of the fish is caused by suffocation due to this obstructive layer.
In soft water, lead may be very toxic. In hard water, equivalent concentrations of lead are less toxic.
Calcium in concentration of 50 mg/L has destroyed the toxic effect of I mg/L of lead. The water Pollution Research Board (74) in England conducted extensive experiments to determine the effects of lead salts on rainbow trout in hard and soft waters. In water of the lowest hardness used, 14 mg/L calcium carbonate, all of the lead added as lead nitrate remained in solution and produced a curvilinear relationship of lead concentration vs. time of survival.
A similar curve was obtained for water with total hardness of 27 mg/L as calcium carbonate, although some precipitate of PbHCO3 occurred with lead concentrations greater than 8.0 mg/L. In solutions with a total hardness of 53 mg/L as calcium carbonate, the maximum concentration of lead remaining in solution was approximately 1.6 mg/L and the median period of survival of the trout exceeded 2 days even at lead dosages in excess of 20 mg/L. It seems probable therefore that the precipitated lead carbonate is not effective as a lethal agent. Further evidence that insoluble lead is not toxic to fish is evidenced by lead oxide.
Additionally, the water Pollution Board has shown that the toxicity of lead toward rainbow trout increases with a reduction of the dissolved oxygen concentration of the water.
The following table shows factors by which the threshold concentration of lead must be multiplied to determine the concentrations of equal toxicity at lower dissolved oxygen tensions.
Dissolved Oxygen % Saturation Reduction Factor