These would be certain to affect the quality of transferred water. The current water quality conditions in several major rivers are as follows. At present the water quality of the Chang Jiang is good. The water has a pH value of 7.0 to 8.5 and a total hardness of 4 to 9 degrees. Just 3.7 per cent of those drawn in the low flow period have this high a BOD5 content.
Some pollution does appear in the river, however, after it flows through certain cities.
An analysis of 2,700 samples taken during the low flow period reveals the highest determining percentage for phenol, 22.5 per cent. Nevertheless, only 6.3 per cent of water samples have a phenol content reaching or exceeding the state's standards for surface water. Since it has a large and swift flow, the Chang Jiang has a very strong capacity for diluting and purifying pollutants. The speed of self-purification is especially marked for phenol compounds, which are volatile and easily decomposed. Heavy metal trace elements are adsorbed onto suspended matter or enter into sediment.