Effect of overlying water pH, dissolved oxygen and temperature on heavy metal release from river sediments under laboratory conditions

The heavy metal release experiments were conducted in the laboratory to examine the effects of 3 factors - pH, dissolved oxygen (DO), and temperature on the metal release from sediments taken from the Huangpu River. The metal concentrations in the dry sediments ranged from 0.030 to 0.296 mg g^-1 for Cr, 0.021 to 0.097 mg g^-1 for Ni, 0.014 to 0.219 mg g^-1 for Cu, 0.035 mg to 0.521 mg g^-1 for Zn, 0.0002 to 0.001 mg g^-1 for Cd and 0.023 to 0.089 mg g^-1 for Pb. Most of the metals found in the sediments were in the form of residual fraction, the exchangeable fraction consisted of only a small portion of total metals. The average dissolved metal concentrations in the overlying water during the 13-day period under different conditions were ranging from 0.82 to 1.93 μg L^-1 for Cr, 1.08 to 4.19 μg L^-1 for Ni, 40.79 to 82.28 μg L^-1 for Cu, 20.30 to 29.96 μg L-1 for Zn, 1.57 to 4.07 μg L^-1 for Cd, and 22.26 to 75.50 μg L^-1 for Pb, respectively. Statistical interpretation of the data indicated that pH (7, 8, 9), dissolved oxygen DO (1.0 and 5.0 mg L^-1) and temperature (4, 16, 25°C) had no significant effects on the heavy metal release under the studied conditions. Cu and Pb had the highest release flux, while Cd, Pb and Cu had higher mobility. The main factors controlling the metals release might be the inherent characters of metals and sediments.