All chemical treatments were in the ultra clean laboratory, and all reagents are high purity grade. Total
metal concentrations in the sediments are measured using established method. Briefly, a mass of 40 mg of
dry sample is weighted and dissolved into 10 mL Teflon bombs. About 2 mL concentrated HNO3+0.2 mL
concentrated H2O2 are added to samples and is left on a hot plate for one day. This step is to remove
organic materials from sediment samples. The samples are then taken to dryness at 120 °C. The residue is
dissolved in 1 mL HNO3+1 mL HF of sample. After 30 min ultrasonic procedure, the samples are taken
into sealed bomb and are placed in an oven at 190 °C for 48 h. This procedure resulted in clear solutions
for sediment sample. After evaporation at 120°C, samples are dissolved in 1% HNO3. Inductively
coupled plasma-mass spectrometry