*2.2. Artificial Fresh Water and Sediment Incubation*

In order to simulate the river environment, artificial freshwater prepared based on the formula provided by USEPA [28] was used in this system, instead of using purified or deionized water. To prepare 20 L of synthetic, moderately hard, reconstituted fresh water, the reagent grade chemicals as follows were used: 1.20 g MgSO4, 1.92 g NaHCO3, 0.080 g KCl, and 1.06 g CaSO4.

The metal incubation concentrations of artificial sediment and reagent grade chemicals were determined with reference to the survey report of Taiwan in 2012 [23] on main rivers with contaminated sediment. The sediment was designed to consist of 400 mg kg−<sup>1</sup> Ni, 400 mg kg−<sup>1</sup> Cr, 1000 mg kg−<sup>1</sup> Cu, 1000 mg kg−<sup>1</sup> Zn, and 50 mg kg−<sup>1</sup> Hg by adding Ni(NO3)2·6H2O, Cr(NO3)3·9H2O, Cu(NO3)2·3H2O, Zn(NO3)2·6H2O, and HgCl2. The sediment (2000 g) was placed in a 3 L glass bottle, filled with artificial freshwater, mixed thoroughly, sealed tightly, and put aside for incubation. The time of incubation lasted up to 60 days.
