*2.5. Quality Control*

All reagents used in the analysis were guaranteed reagents, and freshly prepared deionized water was used in the analysis and to rinse all the sampling instruments. Detection limits of FAAS for Cu was 0.0045 mg/L. To guarantee the data accuracy, a blank sample was set and all the samples were determined in triplicate. Average values of these three tests were applied in the present study. Offshore marine sediment (GBW07314) was used as the reference material in the analysis. The recovery rates of heavy metals were above 90%.
