Determination of total copper and free cupric ion in river waters originating from an old copper mine

We attempted to distinguish the "free" cupric ion from the total copper in river waters originating from an old copper mine because the toxicity is generally attributed to the aquocomplexed free cupric ion. The total concentration of copper in the sample solutions was determined by atomic absorption spectrometry; the free cupric ion was analyzed with a copper ion-selective electrode. About 200 samples of river water around the copper mine were analyzed from November of 1993 to December of 1994. The concentration of free cupric ion at most stations is less than 1 ppm except for that near the H-8 point, where leaching water from the mine slag was led to a rock reservoir (30 cm in diameter and 1 m high) and the stored water overflowed from the reservoir. The leaching water stored in the reservoir had the highest concentration of the free cupric ion, averaging of 9.5 ppm. Fishes inhabit only the upper valley of the river and do not move into the lower valley. Fishes can not move to the downstream because of contaminating copper around the inner valley.